Quantum materials

IQC Colloquium featuring Francesco Di Colandrea

Takudzwa Chipo Valerie Mudzongo — Thu, 30 Jan 2025 17:50:32 +0000

IQC Colloquium featuring Francesco Di Colandrea Takudzwa Chipo… Thu, 01/30/2025 - 12:50

Large-scale quantum walks via complex polarization transformations

Francesco Di Colandrea | University of Naples Federico II

Optical losses are the main barrier to photonic simulations of large-scale quantum dynamics. In fact, within the standard approach, the complexity of the setup increases with the extension of the simulated evolution in time. In the case of discrete-time quantum walks, experimental realizations have typically been limited to a few tens of steps, involving at most a hundred modes.

By focusing on different protocols of discrete-time quantum walks, we experimentally demonstrate a photonic circuit technology that compresses multiple time steps into only three liquid-crystal metasurfaces. Exploiting spin-orbit effects, these metasurfaces enable the simultaneous activation of several hundred optical modes from a single localized input, allowing for a precise and efficient reproduction of the target dynamics. Acting as waveplates with artificially patterned optic-axis orientations, the metasurfaces implement space-dependent polarization transformations that mix circularly polarized optical modes carrying quantized units of transverse momentum.

The performance of our circuit is validated for walker dynamics spanning both one-dimensional [1] and two-dimensional [2] lattices, up to 320 and 20 time steps, respectively. The experimental results certify that our setup can process a huge number of modes while maintaining a high level of coherence. In principle, the metasurfaces can be designed for an arbitrarily large walk extension and number of connected modes, by keeping optical losses constant. Our platform thus paves the way to the simulation of extreme quantum dynamics in the multi-photon regime.

[1] F. Di Colandrea, A. Babazadeh, A. Dauphin, P. Massignan, L. Marrucci, F. Cardano, “Ultra-long quantum walks via spin-orbit photonics”, Optica, 10(3), 2023

[2] M. G. Ammendola, F. Di Colandrea, L. Marrucci, F. Cardano, “Large-scale spin-orbit photonic circuits in two dimensions”, arXiv:2406.08652

Biography

Francesco Di Colandrea is a researcher at the University of Naples Federico II and a visiting scientist at the University of Ottawa. His research focuses on the manipulation of structured light for quantum simulations, particularly in the study of topological physics and open quantum systems. His work also extends to quantum communications and the application of machine-learning techniques in optical experiments.

Location

QNC 0101

IQC Student Summer Conference

Takudzwa Chipo Valerie Mudzongo — Thu, 03 Jul 2025 18:25:32 +0000

IQC Student Summer Conference Takudzwa Chipo… Thu, 07/03/2025 - 14:25

On Wednesday, July 23, 2025 the Institute for Quantum Computing (IQC) will host the IQC Student Summer Conference.

This is a student-organized event that brings together students at IQC to share their research in a friendly setting. The conference aims to foster connections across different quantum research areas and provide a supportive environment for early-career researchers. All IQC members and guests are welcome to attend.

Organizers

Alec Gow, Devin Blankespoor, Jiayue Yang, Jingwen Zhu, Maria Rosa Preciado Rivas, Mikka Stasiuk, Parinaz Rafati, Sebastian Parsons-Hall, Vyom Patel and Ziyuan Yang from the Institute for Quantum Computing (IQC).

Location

The IQC Student Summer Conference will be hosted in the Mike & Ophelia Lazaridis Quantum-Nano Centre (QNC) Room 0101.

Toronto Ultracold Atom Network (TUCAN) meeting 2025

Takudzwa Chipo Valerie Mudzongo — Tue, 29 Apr 2025 16:47:11 +0000

Toronto Ultracold Atom Network (TUCAN) meeting 2025 Takudzwa Chipo… Tue, 04/29/2025 - 12:47

On Wednesday, May 7, 2025 the Institute for Quantum Computing will host the Toronto Ultracold Atom Network (TUCAN) meeting.

The one-day meeting aims to both share knowledge and strengthen ties between local ultracold atom groups. The day will consist of talks and posters on topics including trapped ions, optical lattices, Bose-Einstein condensates and optical techniques for atomic state manipulation.

Organizers

Rajibul Islam, Alan Jamison, Katie McDonnell, Collin Epstein, and Akimasa Ihara from the Institute for Quantum Computing (IQC).

Location

TUCAN will be hosted in the Mike & Ophelia Lazaridis Quantum-Nano Centre (QNC) Room 0101.

Schedule

Time	Agenda	Speaker	Research group
0930 - 1100	Arrival, coffee and refreshments
1000 - 1010	Welcome
1010 - 1030	High-dimensional qudit quantum computing with trapped 137Ba+ ions	Nicholas Zutt	Trapped Ion Quantum Control Lab
1030 - 1050	Progress towards a barium-133 trapped ion quantum processor	Ali Khatia	Laboratory for Quantum Information with Trapped Ions (QITI)
1050 - 1110	A cryogenic single-ion Sr+ clock	Takahiro Tow	Vutha group
1110 - 1130	Humpty-Dumpty is three-dimensional	Jim Martin	Martin group
1130 - 1230	Lunch - St. Jerome's
1230 - 1250	Magneto-optical trapping of neutral atoms with light-induced effective magnetic fields	Nicholas Sullivan	Braverman group
1250 - 1310	Dynamical instability as a PT-symmetry breaking phase transition in a rotating Bose-Einstein condensate	Denise Kamp	O'Dell group
1310 - 1330	Feedback Control Systems for the Stabilization of Traps in Large Rydberg Atom Arrays	Soroush Khoubyarian	Quantum Simulation Group
1330 - 1350	Coffee break and networking
1350 - 1410	Dimer-associated contact of a unitary Fermi gas	Kevin Xie	Thywissen Lab
1410 - 1430	Metasurface-based cavities for quantum optical applications with atomic ensembles	Anya Houk	Nano-Photonics and Quantum Optics Laboratory
1430 - 1600	Poster session: All attendees are welcome to bring posters. The poster display boards are 5ft wide by 4 ft high. Fixtures for mounting the posters to the boards will be provided.
1600 - 1645	Lab tours

Abstracts

Nicholas Sullivan

Magneto-optical trapping of neutral atoms with light-induced effective magnetic fields

We introduce a novel method for producing ensembles of cold neutral atoms without the use of magnetic fields. The proposed laser cooling and trapping method is similar to the typical magneto-optical trap (MOT), but replaces the quadrupole magnetic field with an asymmetrical arrangement of additional laser beams that produce a fictitious magnetic field through state-dependent light shifts. This effective field induces a spatial dependence on the scattering force of the optical molasses beams, taking the place of the real magnetic field in a MOT. We show that this “opto-optical trap” can be applied to commonly trapped atomic species and discuss the unique advantages and potential applications of this approach to laser trapping of atoms.

Braverman group

Takahiro Tow

A cryogenic single-ion Sr+ clock

Single-ion clocks are among the most accurate devices ever constructed. However, even the best clocks -- such as the Sr+ clock operated by the National Research Council of Canada -- are limited by systematic errors caused by blackbody radiation and background-gas collisions. To mitigate these two problems, we have designed and built a Sr+ clock that operates at 4 K: cryogenic operation suppresses both blackbody radiation and collisional shifts by many orders of magnitude. I will discuss the rationale for developing this device, present some unique aspects of its design, and discuss our efforts to characterize its performance.

Vutha group

Jim Martin

Humpty-Dumpty is three-dimensional

Matter-wave Interferometry using Stern-Gerlach based beam-splitters has been described by Schwinger and co-workers [1] as a task as difficult as putting Humpty-Dumpty back together again! Nonetheless, such a Stern-Gerlach Interferometer (SGI) has recently been demonstrated [2].

As shown by Comparat [3], simple models in one spatial dimension are insufficient to analyze SGIs, due to the three-dimensional nature of magnetic fields. I will discuss these effects on SGI using Rydberg atoms with electric field gradients, and the surprising prediction that many superficially similar SGI protocols are significantly different, with only some protocols demonstrating robust visibility in experimentally relevant regimes, and others infeasible.

Work done in collaboration with Danny Meng and Darren Chan.

[1] B.-G. Englert, J. Schwinger, and M. O. Scully, “Is spin coherence like Humpty-Dumpty? I. Simplified treatment”, en, Foundations of Physics 18, 1045–1056 (1988).

[2] Y. Margalit, O. Dobkowski, Z. Zhou, O. Amit, Y. Japha, S. Moukouri, D. Rohrlich, A. Mazumdar, S. Bose, C. Henkel, and R. Folman, “Realization of a complete Stern-Gerlach interferometer: Toward a test of quantum gravity”, Science Advances 7, Publisher: American Association for the Advancement of Science, eabg2879 (2021).

[3] D. Comparat, “Limitations for field-enhanced atom interferometry”, Physical Review A 101, Publisher: American Physical Society, 023606 (2020). "

Martin group

Soroush Khoubyarian

Feedback Control Systems for the Stabilization of Traps in Large Rydberg Atom Arrays

Quantum processors have the potential to perform computations beyond the capabilities of classical processors. Realizing this potential would enable innovative applications in materials science, computational chemistry, and quantum many-body physics. Among the various platforms under development, Rydberg atom array quantum processors stand out for their scalability and controllability.

However, a critical challenge is generating large arrays of optical traps that are uniform in space and stable in time. Here, we introduce a closed-loop feedback system to create large, homogeneous arrays of optical traps whose power is stabilized in real time. The system tracks the power of more than a thousand traps on a camera, continuously updating polychromatic RF tones actuating a pair of acousto-optic deflectors. This enables the simultaneous optimization of processes such as trapping, cooling, and imaging of single neutral atoms in all traps.

We demonstrate a reduction in shot-to-shot fluctuations in loading efficiency and an increase in relative stability when performing adiabatic ramp-down experiments. This system can readily be deployed to implement atom-selective quantum gates across a large field of view and reduce atom loss during atom displacement.

Quantum Simulation Group

Anya Houk

Metasurface-based cavities for quantum optical applications with atomic ensembles

Nano-Photonics and Quantum Optics Laboratory

Atomic ensembles coupled with cavity quantum electrodynamics (QED) offer a promising platform for quantum computing and networking, though with large challenges in implementation and scalability. We explore the use of metasurfaces and photonic crystals, sub-wavelegth nanostructues used to engineer optical wavefronts, to build exotic cavities for enhaced light-matter interaction. We present novel dichroic cavity designs and implementations tailored for free-space and fiber-integrated configurations.

Ali Khatai

Progress towards a barium-133 trapped ion quantum processor

We present our recent progress in developing a barium based trapped ion quantum processor using a microfabricated surface trap with 94 controllable DC electrode channels. Barium ions are among the most promising qubit candidates due to their long-lived quantum states and visible-wavelength optical transitions, allowing the use of commercial optics and waveguide-based modulators for individual qubit control.

Our trap is centrally mounted in the vacuum chamber, departing from conventional flange-mounted designs to maximize optical access while maintaining ultra-high vacuum conditions (3×10⁻¹¹ mbar). We highlight two major technical challenges: building a custom in-vacuum wire harness with 100 electrical connections to the trap, and implementing a multi-species barium atomic source that includes both radioactive barium-133 salt and rapidly oxidizing barium metal, each requiring specialized preparation and installation methods.

Laboratory for Quantum Information with Trapped Ions (QITI)

Nicholas Zutt

High-Dimensional Qudit Quantum Computing with Trapped 137Ba+ Ions

Authors: Nicholas CF Zutt, Gaurav A Tathed, Pei Jiang Low, Crystal Senko

The angular momentum eigenstates of the unpaired electron in trapped 137Ba+ ions offer a promising pathway toward high-fidelity qudit (d > 2) encoding. Due to the nonzero nuclear spin (I = 3/2), the 6S1/2 and 5D5/2 manifolds contain, respectively, 8 and 24 non-degenerate levels at intermediate magnetic fields (∼ few Gauss). Leveraging recent developments in state preparation techniques for trapped ion quantum computing, we demonstrate high-fidelity (> 99.5%) state preparation and measurement results over 25 basis states, the maximal measurable qudit encoding across the 6S1/2 and 5D5/2 manifolds in 137Ba+.

We demonstrate coherent control over this enlarged Hilbert space by performing Ramsey-type coherence probing measurements (generating many-state superpositions and probing phase-sensitive population recovery) and benchmark the scaling of decohering effects with increasing qudit dimension. We discuss the largest contributors to error in our system and the steps needed to maintain highdimensional coherence (as measured via the contrast of Ramsey-type measurements) in this qudit implementation.

Finally, we implement two-qubit algorithms (BernsteinVazirani and Grover’s search) on this single trapped ion qudit. This work establishes the feasibility of using trapped ions for large-qudit (d > 10) quantum computation, which is a promising alternative approach to expanding the Hilbert space in trapped ion quantum computing.

This research was supported in part by the Natural Sciences and Engineering Research Council of Canada (NSERC) and Canada Research Chairs.

Trapped Ion Quantum Control Lab

Kevin Xie

Dimer-association contact of a unitary Fermi gas

Interaction shifts of spectroscopic lines are a nuisance for atomic clocks, but also a signature of two-body correlations. We prepare a unitary Fermi gas of potassium-40, where atom-atom correlations manifest in the radiofrequency (rf) transfer spectra between internal states. In certain cases, the complete spectrum has a negative total clock shift, in seeming disagreement with the well studied positive high-frequency tail governed by the contact parameter.

We report that the “missing link” is a relatively deeply bound ac dimer. With a highly concentrated spectral weight, rf pulses on microsecond timescales can produce significant dimer-association rates, while Fourier broadening does not convolve the bare atomic resonance. We calibrate a Fourier-width-dominated dimer lineshape and observe that the integrated spectral weight and clock shift are directly proportional to correlations in the initial state extracted from the usual high- frequency tail.

The results are compared both to an analytic model with finite effective range and to a coupled-channels calculation. Our measurements inform the complete rf spectra of a unitary Fermi gas and provide a new tool for rapid observation of pair correlation dynamics.

Thywissen Lab

Denise Kamp

Dynamical instability as a PT-symmetry breaking phase transition in a rotating Bose-Einstein condensate

We study a dilute gas of bosons in a rotating toroidal trap, focusing on a two-mode regime with a non-rotating mode and a rotating mode corresponding to a singly charged vortex. The system undergoes a symmetry-breaking transition as the ratio of interactions to disorder potential is varied, spontaneously selecting one mode, demonstrating macroscopic quantum self-trapping. The symmetry breaking is associated with dynamical instabilities driven by complex eigenvalues that can occur in a theoretical treatment as the Bogoliubov Hamiltonian is non-Hermitian, essentially because a U(1) symmetry is broken by choosing a phase for the BEC. A special feature of non-Hermitian quantum theory is that PT-symmetry replaces self-adjointness and we explore the connection between dynamical instability and PT-symmetry breaking phase transitions in this system.

O'Dell group

IQC Student seminar featuring Zach Merino

Takudzwa Chipo Valerie Mudzongo — Fri, 21 Mar 2025 16:05:58 +0000

IQC Student seminar featuring Zach Merino Takudzwa Chipo… Fri, 03/21/2025 - 12:05

Simulating spin qubits in silicon quantum dots

Zach Merino

Spin qubits in semiconductor quantum dots are a promising platform for scalable fault-tolerant quantum computing. However, the fabrication and control of such large-scale quantum processors present significant engineering challenges, including precise device geometry design and optimal tuning of spin and charge states.

To address these challenges, we develop a simulation tool that accelerates quantum device design iteration prior to fabrication. By leveraging three-dimensional Poisson simulations, we extract electrostatic potential landscapes of isolated quantum dots to compute spin and Hubbard Hamiltonian effective parameters, enabling efficient modeling of linear quantum dot arrays.

Precise spin qubit control requires a detailed mapping between experimental parameters—such as electrode voltages and radio-frequency magnetic fields—and effective qubit properties, including the electronic g-factor, exchange energy, and chemical potential. This mapping enables the application of various optimal qubit control strategies, such as GRAPE or in-house-developed reverse engineering techniques for time-ordered Hamiltonians. This lightweight simulation framework facilitates the design of experimental voltage pulses needed to control Hamiltonian parameters, ensuring that simulated results align with experimental expectations.

These results serve as figures of merit for device characterization and the implementation of single- and two-qubit gate operations forming a universal gate set. Such operations are essential for constructing entangled states within a node-based quantum network and performing surface code error correction protocols.

Location

QNC 1201

World Quantum Day – Quantum Shorts: Encore

Takudzwa Chipo Valerie Mudzongo — Thu, 20 Mar 2025 12:42:00 +0000

World Quantum Day – Quantum Shorts: Encore Takudzwa Chipo… Thu, 03/20/2025 - 08:42

Celebrate World Quantum Day with an IQC film experience!

As part of the International Year of Quantum, join us for a special screening of the Quantum Shorts Film Festival winners!

These short films bring quantum to life through imaginative storytelling—both narrative and abstract. As part of the screening curated panel of experts will provide additional insights and local context, connection quantum to the ��ݮ��Ƶ story in an engaging discussion.

Join us after for light refreshments and networking, where you can connect with fellow quantum enthusiasts.

Meet the panel

Christine Muschik | Panelist - faculty member, IQC
Kayleigh Platz | Moderator - director of communications and strategic initiatives, IQC
Fiona Thompson | Panelist - science outreach officer, IQC

Stay tuned as we’ll be adding more industry and academic speakers to this exciting discussion.

Location

Apollo Cinema
141 Ontario St N
Kitchener, ON, CA N2H 4Y5

Register

Faculty of Science presents: Science in the City - Quantum

Takudzwa Chipo Valerie Mudzongo — Thu, 13 Feb 2025 16:07:59 +0000

Faculty of Science presents: Science in the City - Quantum Takudzwa Chipo… Thu, 02/13/2025 - 11:07

The 2025 International Year of Quantum recognizes 100 years since the development of quantum mechanics. Researchers at the University of ��ݮ��Ƶ are at the forefront of quantum innovation, pushing the boundaries of discovery and positioning ��ݮ��Ƶ as a global leader in quantum research. Join us to celebrate the Year of Quantum by engaging with leading experts who share what’s next in quantum science!

The event is free. Light snacks and beverages will be available for purchase.

Meet the speakers

Jonathan Baugh(Chemistry)
Kazi Rajibul Islam(Physics & Astronomy)
Adam Wei Tsen(Chemistry)

IQC Colloquium featuring Machiel Blok

Takudzwa Chipo Valerie Mudzongo — Mon, 25 Nov 2024 16:56:30 +0000

IQC Colloquium featuring Machiel Blok Takudzwa Chipo… Mon, 11/25/2024 - 11:56

Beyond Binary Quantum Information in Superconducting Circuits: Taking the Transmon for a Spin

Machiel Blok | University of Rochester

Encoding quantum information in the many-level systems provides a resource efficient path towards quantum computing-, and simulation. Here I will discuss ongoing work in our lab at the University of Rochester to explore excited states in superconducting circuits. We demonstrate preparation and readout of Fock states of up to eleven microwave photons in a transmon circuit[1].

Furthermore, we illustrate how we can efficiently control this high-dimensional system using spin-displacement operations that correspond to rotations of large-angular moment spins[2]. In the long term, we anticipate this new approach to controlling higher-level quantum information to yield benefits for bosonic quantum error correction and qu-dit simulation.

[1] Systematic Study of High Ej/Ec transmon qudits up to d=12 Z. Wang et al arXiv:2407.17407 (2024)

[2] Multi-frequency control and measurement of a spin-7/2 system encoded in a transmon qudit E. Chamion et al arXiv:2405.15857 (2024)

Location

QNC 0101

IQC Student seminar featuring Tales Rick Perche

Takudzwa Chipo Valerie Mudzongo — Wed, 13 Nov 2024 16:54:37 +0000

IQC Student seminar featuring Tales Rick Perche Takudzwa Chipo… Wed, 11/13/2024 - 11:54

A description of the spin-spin interaction from Quantum Electrodynamics

by Tales Rick Perche

When implementing entangling operations in two quantum systems, it is usual to consider interactions prescribed by Hamiltonians that directly couple the different systems (e.g. the J-coupling). On the other hand, a fundamental description of these systems using quantum field theory is entirely local, which forbids coupling disjoint systems directly.

In this talk we will discuss how a fully quantum field theoretic treatment of electrons in atoms gives rise to the spin-spin interaction, focusing on the assumptions necessary to reach the effective J-coupling model and the corrections that arise in this more detailed description.

Location

QNC 1201

IQC Colloquium featuring Paul Barclay

Takudzwa Chipo Valerie Mudzongo — Tue, 22 Oct 2024 20:19:08 +0000

IQC Colloquium featuring Paul Barclay Takudzwa Chipo… Tue, 10/22/2024 - 16:19

Spin, photons and phonons: diamond nanophotonics

by Paul Barclay | University of Calgary

Defects in diamond are a promising platform for quantum information processing and sensing. Recently, the potential for coupling electron spins in these systems using mechanical resonators has attracted significant attention. Phonons in engineered nanomechanical devices, which exhibit exceptionally long coherence times in state-of-the-art demonstrations, can be coupled to a wide variety of physical systems.

Furthermore, when nanomechanical resonators are integrated within an optical cavity—realising a cavity optomechanical device—it is possible to optically control their mechanical motion. We have recently shown that cavity optomechanical devices in diamond allow spin-phonon driving. The resulting spin-photon interface is “universal”: it is independent from the optical properties of the spin system.

In this talk we discuss these results, as well as recent discoveries in nonlinear optics related to the microscopic properties of diamond defects.

Location

QNC 0101

Quantum Innovators 2024

Takudzwa Chipo Valerie Mudzongo — Tue, 08 Oct 2024 18:59:30 +0000

Quantum Innovators 2024 Takudzwa Chipo… Tue, 10/08/2024 - 14:59

Quantum Innovators is a five-day workshop offered by the Institute for Quantum Computing (IQC) since 2012 bringing the most promising postdoctoral fellows in quantum information science and technology together.

Quantum Innovators 2024 will take place from Monday November 11 to Friday November 15. Monday to Wednesday will focus on computer science, mathematics, and theory, while Wednesday to Friday will focus on science and engineering. Invited participants may elect to attend either stream or both.

Location

Quantum Innovators will take place on-campus at the University of ��ݮ��Ƶ in ��ݮ��Ƶ, Ontario, Canada, at both the Quantum-Nano Centre (QNC) and the Research Advancement Centre (RAC).

How to attend

Talks at Quantum Innovators are invitation only.

These workshops held at IQC, University of ��ݮ��Ƶ, are partly funded by the Canada First Research Excellence Fund (CFREF) as part of the Transformative Quantum Technologies research initiative.

Event recap

Earlier this month, IQC hosted postdoctoral fellows in quantum information science and technology from around the world at the Quantum Innovators (QI) 2024 workshop.

Schedule

Monday, November 11 – QNC 0101

Time	Agenda
08:45	Registration and coffee
09:15	Introductory remarks Norbert Lütkenhaus, Executive Director, Institute for Quantum Computing
09:30	Shraddha Singh, Yale Towards non-abelian quantum signal processing: efficient control of hybrid continuous-and discrete-variable architectures
10:15	Coffee break, QNC 0101
10:35	Uma Girish, Columbia University Trade-offs between entanglement and communication
11:20	Allen Liu, MIT High-temperature Gibbs states are unentangled and efficiently preparable
12:05	Lunch, St. Jerome’s Cafeteria
13:05	Quynh The Nguyen, Harvard Quantum fault tolerance with constant-space and logarithmic-time overheads
13:50	Harold Nieuwboer, University of Copenhagen Entanglement polytopes in action
14:35	Coffee break, QNC 0101
15:05	Alexander Poremba, MIT The learning stabilizers with noise problem
15:50	Esther Cruz Rico, Max-Planck-Institute for Quantum Optics Filter algorithm for dynamical properties of many-body systems at finite energies
16:35	End of day

Tuesday, November 12 – QNC 0101

Time	Agenda
08:45	Registration and coffee
09:15	Thomas Schuster, California Institute of Technology Random unitaries in extremely low depth
10:00	Coffee break, QNC 0101
10:20	Thiago Bergamaschi, UC Berkeley Quantum computational advantage with constant-temperature Gibbs sampling
11:05	Yuxin Wang, University of Maryland Exponential entanglement advantage in sensing correlated noise
12:00	Lunch, St. Jerome’s Cafeteria
13:00	Yunchao Liu, UC Berkeley Learning shallow quantum circuits and quantum states prepared by shallow circuits in polynomial time
13:45	Kewen Wu, UC Berkeley Quantum state preparation with optimal T-count
14:30	Coffee break, QNC 0101
15:00	Luke Schaeffer, Institute for Quantum Computing
15:45	Jiaqing Jiang, California Institute of Technology Quantum metropolis sampling via weak measurement
16:35	End of day
18:30	Conference banquet #1 The Bauer Kitchen, 187 King St S, ��ݮ��Ƶ ON For invited speakers only

Wednesday, November 13 – QNC 0101

Time	Agenda
08:30	Registration and coffee
09:00	Introductory remarks Norbert Lütkenhaus, Executive Director, Institute for Quantum Computing
09:15	Ariadna Soro, Chalmers University of Technology Giant atoms in 1D and 2D structured environments
10:00	Sebastian Zur, CWI Amsterdam and QuSoft (Multidimensional) Quantum walks and electrical networks
10:45	Coffee break, QNC 0101
11:00	Panel discussion Academics careers in quantum information science
11:45	Group photo
12:00	Lunch, St. Jerome’s Cafeteria
13:00	QNC Lab tours
14:00	Coffee break, QNC 0101
14:20	Madelyn Cain, Harvard Low-overhead fault tolerance for transversal quantum algorithms
15:05	Benjamin Brock, Yale Quantum error correction of qudits beyond break-even
16:00	Poster session and community reception, QNC second-floor kitchen
18:00	End of day

Confirmed posters from IQC members

Matteo Pennacchietti, Oscillating Photonic Bell State from a Semiconductor Quantum Dot for Quantum Key Distribution
Forouzan Forouharmanesh, TBD
Paul Godin, QEYSSat: Space Quantum Key Distribution
Alexander Frei, TBD
Matthew Duschenes, Channel Expressivity Measures and their Operational Meaning
María Rosa Preciado-Rivas, Quantum control of permittivities
Avantika Agarwal, Oracle Separations for Quantum-Classical Polynomial Hierarchy
Anastasiia Mashko, Towards Realizing Single-Spin Excitation Transport in Rydberg Chains
Sascha Zakaib-Bernier, Implementing the Möbius decoder using Coxeter groups
Daniel Tay, Nanoscale imaging with force-detected NMR
Sanchit Srivastava, Contextuality and chaos
Zach Merino, Simulated control of spin qubits in MOSFET quantum dot linear arrays
Peixue Wu, Average gate complexity from quantum optimal transport
Bohdan Khromets, Quantum optimal control in the presence of 1/f ɑ noise using fractional calculus: voltage-controlled exchange operations on semiconductor spin qubits
Stephane Vinet, TBD
Devashish Tupkary, de Finetti reductions with applications in Quantum Key Distribution
Shlok Nahar, Imperfect detectors for adversarial tasks with applications to quantum key distribution

Thursday, November 14 – RAC 2009

Time	Agenda
08:30	Registration and coffee
09:10	Gurudev Dutt, University of Pittsburgh Nansocale electron paramagnetic resonance and quantum opto-mechanics with diamond spin qubits
10:10	Coffee break, RAC 2009
10:30	Behrooz Semnani, Institute for Quantum Computing TBD
11:15	Xueyue (Sherry) Zhang, Columbia University and UC Berkeley T centers in silicon: an emerging platform as a spin-photon interface
12:00	Lunch, RAC 2009
13:00	Eric I. Rosenthal, Stanford The tin-vacancy center in diamond: understanding this emerging qubit and its application to quantum networks
13:45	Nana Shumiya, Princeton Disentangling and eliminating loss sources in tantalum superconducting circuits
14:30	Coffee break
15:00	RAC Lab tours
16:30	End of day
18:30	Conference banquet #2 Proof Kitchen & Lounge, in the Delta hotel For invited speakers only

Friday, November 15 – QNC 0101

Time	Agenda
08:45	Coffee, QNC 0101
09:10	Michał Parniak, University of Warsaw Quantum sensing with Rydberg atoms: from applications to fundamentals
10:10	Coffee break, QNC 0101
10:30	Alexander McDonald, Université de Sherbrooke Measurement-induced transmon ionization
11:15	Sophie Hermans, Caltech Quantum networks using single rare‐earth ions
12:00	Lunch, St. Jerome’s Cafeteria
13:00	Shankari Rajagopal, Stanford Dynamical engineering of Rydberg atom systems for quantum-enhanced sensing, simulation, and optimization
13:45	Jameson O'Reilly, University of Oregon Doing more with the same: using metastable states of trapped ions
14:30	Bradley Hauer, Institute for Quantum Computing Quantum optomechanics with millimeter-wave circuits
15:15	End of conference; coffee in QNC second-floor kitchen

Invited speakers

Computer Science and Mathematics

Thiago Bergamaschi, UC Berkeley
Uma Girish, Columbia University
Jiaqing Jiang, California Institute of Technology
Allen Liu, MIT
Yunchao Liu, UC Berkeley
Quynh The Nguyen, Harvard
Harold Nieuwboer, University of Copenhagen
Alexander Poremba, MIT
Esther Cruz Rico, Max-Planck-Institute for Quantum Optics
Thomas Schuster, California Institute of Technology
Shraddha Singh, Yale
Yuxin Wang, University of Maryland
Kewen Wu, UC Berkeley
Sebastian Zur, CWI Amsterdam and QuSoft
Luke Schaeffer, Institute for Quantum Computing

Speaker abstracts and biographies

Thiago Bergamaschi, UC Berkeley

Quantum computational advantage with constant-temperature Gibbs sampling

A quantum system coupled to a bath at some fixed, finite temperature converges to its Gibbs state. This thermalization process defines a natural, physically-motivated model of quantum computation. However, whether quantum computational advantage can be achieved within this realistic physical setup has remained open, due to the challenge of finding systems that thermalize quickly, but are classically intractable. Here we consider sampling from the measurement outcome distribution of quantum Gibbs states at constant temperatures, and prove that this task demonstrates quantum computational advantage. We design a family of commuting local Hamiltonians (parent Hamiltonians of shallow quantum circuits) and prove that they rapidly converge to their Gibbs states under the standard physical model of thermalization (as a continuous-time quantum Markov chain). On the other hand, we show that no polynomial time classical algorithm can sample from the measurement outcome distribution by reducing to the classical hardness of sampling from noiseless shallow quantum circuits. The key step in the reduction is constructing a fault-tolerance scheme for shallow IQP circuits against input noise.

Based on joint work with Yunchao Liu and Chi-Fang Chen.

Thiago is a fourth year PhD student in Computer Science at UC Berkeley, advised by Umesh Vazirani. Previously, he obtained undergraduate degrees in Physics and EECS at MIT, where he was advised by Aram Harrow and Virginia Vassilevska Williams. His current research interests lie in quantum information theory, and quantum error-correction in particular.

Uma Girish, Columbia University

Trade-offs between entanglement and communication

We study the power of entanglement in communication complexity. We consider classical communication models that are equipped with a limited number of qubits of entanglement, i.e., models where Alice and Bob share entanglement and can exchange classical messages that depend on measurement outcomes of their shared state. We demonstrate in a number of settings that reducing the entanglement even by a small factor can exponentially increase the classical communication complexity. Among several results, we show that for every k >= 1:

Quantum simultaneous protocols with O(k^5 log^3 N) qubits of entanglement can exponentially outperform classical two-way protocols with O(k) qubits of entanglement. This improves the state-of-the-art separations between quantum and classical communication complexity.
Classical simultaneous protocols with O(k log N) qubits of entanglement can exponentially outperform quantum simultaneous protocols with O(k) qubits of entanglement.

This is based on a joint work with Srinivasan Arunachalam.

I am a postdoctoral research scientist at Columbia University hosted by Henry Yuen. I obtained a PhD at Princeton University, where I was extremely fortunate to be advised by Ran Raz. Previously, I obtained an M.Sc. and B.Sc. from Chennai Mathematical Institute. I'm broadly interested in quantum computing and analysis of Boolean functions. I'm especially interested in provable exponential speedups of quantum over classical, eliminating intermediate measurements and parallel repetition.

Jiaqing Jiang, California Institute of Technology

Quantum metropolis sampling via weak measurement

Gibbs sampling is a crucial computational technique used in physics, statistics, and many other scientific fields. For classical Hamiltonians, the most commonly used Gibbs sampler is the Metropolis algorithm, known for having the Gibbs state as its unique fixed point. For quantum Hamiltonians, designing provably correct Gibbs samplers has been more challenging. [TOV+11] introduced a novel method that uses quantum phase estimation (QPE) and the Marriot-Watrous rewinding technique to mimic the classical Metropolis algorithm for quantum Hamiltonians. The analysis of their algorithm relies upon the use of a boosted and shift-invariant version of QPE which may not exist [CKBG23]. Recent efforts to design quantum Gibbs samplers take a very different approach and are based on simulating Davies generators [CKBG23,CKG23,RWW23,DLL24]. Currently, these are the only provably correct Gibbs samplers for quantum Hamiltonians.

We revisit the inspiration for the Metropolis-style algorithm of [TOV+11] and incorporate weak measurement to design a conceptually simple and provably correct quantum Gibbs sampler, with the Gibbs state as its approximate unique fixed point. Our method uses a Boosted QPE which takes the median of multiple runs of QPE, but we do not require the shift-invariant property. In addition, we do not use the Marriott-Watrous rewinding technique which simplifies the algorithm significantly.

Jiaqing Jiang is a PhD student in Computer Science at Caltech, supervised by Thomas Vidick, Urmila Mahadev and John Preskill. She is broadly interested in quantum information, especially in quantum algorithm and complexity for quantum many-body systems, like problems related to preparing ground state or Gibbs states.

Allen Liu, MIT

High-temperature Gibbs states are unentangled and efficiently preparable

We show that thermal states of local Hamiltonians are separable above a constant temperature. Specifically, for a local Hamiltonian $H$ on a graph with constant degree, its Gibbs state at inverse temperature $\beta$, denoted by $\rho =e^{-\beta H}/ \tr(e^{-\beta H})$, is a classical distribution over product states for all $\beta < 1/c$, where $c$ is a constant. This proof of sudden death of thermal entanglement resolves the fundamental question of whether many-body systems can exhibit entanglement at high temperature. Moreover, we show that we can efficiently sample from the distribution over product states. In particular, we can prepare a state $\eps$-close to $\rho$ in trace distance with a depth-one quantum circuit and $\poly(n, \log 1/\eps)$ classical overhead.

I am currently a graduate student in EECS at MIT where I am in my fifth year, working under the wonderful supervision of Ankur Moitra. I also completed my undergraduate degree (in mathematics) at MIT. I am generally interested in machine learning theory, focusing on developing algorithms with provable guarantees for fundamental learning tasks. Recently, I have been especially interested in connections to statistical and algorithmic problems arising in quantum information.

Yunchao Liu, UC Berkeley

Learning shallow quantum circuits and quantum states prepared by shallow circuits in polynomial time

In this talk we give polynomial time algorithms for the following two problems: (1) Given access to an unknown constant depth quantum circuit U on a finite-dimensional lattice, learn a constant depth circuit that approximates U to small diamond distance, and (2) Given copies of an unknown quantum state |ψ>=U|0^n> that is prepared by an unknown constant depth circuit U on a finite-dimensional lattice, learn a constant depth circuit that prepares |ψ>. These algorithms extend to the case when the depth of U is polylog(n)

Yunchao Liu is a HQI Postdoctoral Fellow at Harvard University, hosted by Anurag Anshu and Sitan Chen. He got his PhD in Computer Science from UC Berkeley, advised by Umesh Vazirani. His research interests are in quantum information, computation, and complexity theory. Recently, he has been working on establishing theoretical foundations for achieving quantum computational advantage on NISQ and early fault tolerant devices.

Quynh The Nguyen, Harvard

Quantum fault tolerance with constant-space and logarithmic-time overheads

In a model of fault-tolerant quantum computation (FTQC) with quick and noiseless polylog-time classical auxiliary computation, we construct a quantum fault tolerance protocol with constant-space overhead and logarithmic-time overhead (up to sub-polylog factors). This significantly improves over the previous state-of-the-art due to Yamasaki and Koashi who achieved constant-space and quasipolylog-time overhead. Our construction is obtained by using constant-rate quantum locally testable codes (qLTC) of appropriately chosen block size and developing new fault-tolerant gadgets on qLTCs and qLDPC codes.

In particular, we obtain the following new technical results: 1) a magic state distillation protocol with almost-constant spacetime overhead, 2) an efficient single-shot decoder for quantum codes based on cubical complexes, 3) a state preparation scheme for qLTC with almost-constant spacetime overhead. To our knowledge, this scheme gives the lowest overhead to date in the considered model of FTQC, which we conjecture is optimal up to sub-polylog factors.

Quynh is a PhD student at Harvard, advised by Anurag Anshu. He has been working on quantum complexity theory, fault-tolerant computation, and quantum algorithms.

Harold Nieuwboer, University of Copenhagen

Entanglement polytopes in action

Entanglement polytopes are an object associated with quantum states, and capture the possible joint one-body spectra obtainable under SLOCC transformations. I will survey some recent developments on practical determination of properties of entanglement polytopes, in particular rigorous algorithms for determining them, as well as applications of newly computed ones.

I’m broadly interested in algorithmic approaches to fundamental mathematical questions in geometric invariant theory, representation theory, and quantum information theory. In particular I have worked on classical and quantum algorithms for scaling problems, which amounts to testing membership in moment polytopes. Examples include matrix scaling, operator scaling and tensor scaling. These can be recast as optimization problems with a lot of geometric or algebraic structure, such as (geodesic) convexity or having many symmetries. These problems have further connections to functional analysis, quantum many-body physics, machine learning, statistics, and numerical linear algebra.

Alexander Poremba, MIT

The Learning Stabilizers with Noise problem

Random codes have good error correcting properties, and yet they are notoriously hard to decode in practice. Despite many decades of extensive study, the fastest known algorithms still run in exponential time. The Learning Parity with Noise (LPN) problem, which can be seen as the task of decoding a random linear code in the presence of noise, has thus emerged as a prominent hardness assumption with numerous applications in both cryptography and learning theory. While random quantum codes---typically in the form of stabilizer codes---are also known to give rise to good quantum error correcting codes, their decoding complexity is far less understood.

In this work, we introduce a natural quantum analogue of LPN which we call the Learning Stabilizers with Noise (LSN) problem. This can be seen as the task of decoding a random stabilizer code in the presence of local depolarizing noise. We give both polynomial-time and exponential-time quantum algorithms for solving LSN in various depolarizing noise regimes, ranging from extremely low noise, to low constant noise rates, and even in a high constant noise regime. We then go on to provide concrete evidence for the average-case hardness of our learning task. First, we show that LSN includes LPN as a special case, which suggests that it is at least as hard as its classical counterpart. In addition, we prove a worst-case to average-case reduction for variants of LSN, and we identify a natural barrier for extending our results further.

Next, we ask: what is the computational complexity of solving LSN? Because the task features quantum inputs, its complexity cannot be characterized by traditional complexity classes. Instead, we show that the LSN problem lies in a recently introduced (distributional and oracle) unitary synthesis class. Finally, we identify several applications of our LSN assumption, ranging from the existence of quantum bit commitment schemes to the computational limitations of learning from quantum data.

Joint work with Yihui Quek (MIT) and Peter Shor (MIT).

I am a postdoctoral researcher at MIT, hosted by both Vinod Vaikuntanathan and Peter Shor. I am affiliated with the Computer Science & Artificial Intelligence Laboratory (CSAIL) and the Department of Mathematics. I received my PhD from Caltech, where I was fortunate to have been advised by Thomas Vidick. My research lies at the intersection of quantum computation and cryptography. Recently, I've been especially interested in quantum pseudorandomness and how to obtain quantum advantage in cryptography.

Esther Cruz Rico, Max-Planck-Institute for Quantum Optics

Filter algorithm for dynamical properties of many-body systems at finite energies

The study of quantum many-body systems at finite temperatures and energies is a central yet challenging problem in condensed matter physics. Classical methods are very limited, especially when it comes to the study of dynamics. However, quantum computers may allow us to probe highly correlated systems that have remained intractable in this context.

Studying the dynamics of correlated systems reveals essential properties of the underlying system. Time-dependent correlators and spectral functions, for example, provide information about the behavior of the system under perturbations, as well as about the spectral properties of the Hamiltonian, and can be used to detect phase transitions. Several works (e.g.[1]) have proposed quantum algorithms to compute response functions. These rely on the ability to perform time evolution and calculate quantities like the Loschmidt echo through variations of the Hadamard test. However, these approaches typically assume access to equilibrium states, such as thermal states or eigenstates, which are usually difficult to prepare in practice and involve a considerable overhead in the quantum resources.

On the other hand, filter algorithms [2] have been recently introduced to compute quantities on states within a small energy window, approximating microcanonical expectation values. Unlike other approaches such as phase estimation, these algorithms do not prepare an eigenstate approximation. Instead, they recover the microcanonical expectation value through classical post-processing. The only requirement is the ability to implement time evolution on simple-to-prepare states and to compute quantities similar to those used in response functions.

In this work, we show how filter techniques can be combined to compute response functions on the diagonal, thermal and microcanonical ensembles. Crucially, the quantum resources needed by the filter algorithm are the same as those required by response functions. This allows to integrate the state preparation within the algorithm itself, reducing the quantum complexity at the expense of classical post-processing.

To showcase this quantum algorithm, we study Gaussian fermionic systems that exhibit localization transitions as a function of Hamiltonian parameters or energy. Filtering states across the spectrum, these phase transitions can be detected by specific response functions. Although these are toy models, they offer valuable insights into the performance of the algorithm on interacting systems.

[1] Kökcü, E., Labib, H.A., Freericks, J.K. et al. A linear response framework for quantum simulation of bosonic and fermionic correlation functions. Nat Commun 15, 3881 (2024).
[2] Lu, S., Bañuls, M.C., Cirac, J.I. Algorithms for quantum simulation at finite energies. PRX Quantum 2,020321 (2021).

Esther Cruz is PhD student at the Max-Planck Institute of Quantum Optics in Munich, supervised by Ignacio Cirac. She is interested in quantum algorithms, quantum state preparation and verification of quantum computation. She obtained a B.Sc. degree in Physics and in Mathematics at Universidad Complutense of Madrid, and a Msc. degree in Physics at the Ludwig-Maximilian University in Munich.

Thomas Schuster, California Institute of Technology

Random unitaries in extremely low depth

Random unitaries form the backbone of numerous components of quantum technologies, and serve as indispensable toy models for complex processes in quantum many-body physics. In all of these applications, a crucial consideration is in what circuit depth a random unitary can be generated. I will present recent work, in which we show that local quantum circuits can form random unitaries in exponentially lower circuit depths than previously thought. We prove that random quantum circuits on any geometry, including a 1D line, can form approximate unitary designs over n qubits in log n depth. In a similar manner, we construct pseudorandom unitaries (PRUs) in 1D circuits in poly log n depth, and in all-to-all-connected circuits in poly log log n depth. These shallow quantum circuits have low complexity and create only short-range entanglement, yet are indistinguishable from unitaries with exponential complexity. Applications of our results include proving that classical shadows with 1D log-depth Clifford circuits are as powerful as those with deep circuits, demonstrating superpolynomial quantum advantage in learning low-complexity physical systems, and establishing quantum hardness for recognizing phases of matter with topological order.

Based on joint work with Jonas Haferkamp and Hsin-Yuan Huang.

Thomas Schuster is a Sherman Fairchild Postdoctoral Scholar at the California Institute for Technology, working at the intersection of many-body physics and quantum information science. He received his Ph.D. in Physics from UC Berkeley in December 2022, working with Norman Y. Yao.

Shraddha Singh, Yale

Towards non-abelian quantum signal processing: Efficient control of hybrid continuous-and discrete-variable architectures

Quantum signal processing (QSP) is a technique for transforming a unitary operation parameterized by a variable `x' into a unitary parameterized by a polynomial function f(x). This technique underlies many important quantum algorithms and is a descendant of composite pulse techniques developed in NMR spectroscopy which were designed to make spin rotations robust against experimental fluctuations in the value of the classical control parameter `x'.

In this talk, we will extend the concept of quantum signal processing to the case of multiple control parameters x, p,... which are themselves non-commuting quantum operators–namely the positions and momenta of quantum harmonic oscillators.

We introduce Gaussian-Controlled-Rotation (GCR), a composite pulse sequence leveraging non-commuting quantum control variables, demonstrating comparable performance with traditional QSP pulses such as BB1 but with a sixfold reduction in circuit depth. The non-commutativity of the control parameters implies that they unavoidably suffer intrinsic quantum fluctuations. Still, the richer commutator algebra also significantly enhances the power of QSP and reduces circuit depths. Our framework enables deterministic entangling and disentangling of continuous-variable (CV) and discrete-variable (DV) systems, essential for fast oscillator control and bosonic error correction.

We will illustrate the power of non-abelian QSP with applications to deterministic schemes of non-Gaussian CV state preparation and control, with a special focus on the bosonic GKP encoding. The versatility of our framework bridges the gap between theoretically ideal infinitely-squeezed GKP states and experimentally realistic finitely-squeezed GKP states, significantly enhancing the fidelity of practical GKP gate operations.

Shraddha Singh's research focus lies on bosonic error correction and magic state factories with a focus on reducing the resource overhead of fault-tolerant quantum computing. Shraddha grew up in India. She pursued an integrated BS-MS program at the University of Mumbai-Department of Atomic Energy, Centre for Excellence in Basic Sciences. For her master's thesis, in 2018, she worked for the quantum internet team of Elham Kashefi, at Sorbonne University, and founded Quantum Protocol Zoo, an online repository of quantum network protocols. Currently, she is a graduate student at Yale University, jointly advised by Steven M. Girvin and Shruti Puri.

Yuxin Wang, University of Maryland

Exponential entanglement advantage in sensing correlated noise

Quantum sensing is one of the most promising applications of near-term quantum systems. In this talk, I will introduce a new form of exponential entanglement advantage in the context of sensing correlated noise. Specifically, we focus on the problem of estimating parameters associated with Lindblad dephasing dynamics and show that entanglement can lead to an exponential enhancement in the sensitivity (as quantified via quantum Fisher information of the sensor state), for estimating a small parameter characterizing the deviation of system Lindbladian from a class of maximally correlated dephasing dynamics.

This result stands in stark contrast to previously studied scenarios of sensing uncorrelated dephasing noise, where one can prove that entanglement does not lead to an advantage in the signal-to-noise ratio. Our work thus opens a novel pathway towards achieving entanglement-based sensing advantage, which may find applications in characterizing decoherence dynamics of current quantum devices. Further, our approach provides a potential quantum-enhanced probe of many-body correlated phases by measuring noise generated by a sensing target. We also discuss the realization of our protocol using near-term quantum hardware.

Yuxin is a Hartree Postdoctoral Fellow at the Joint Center for Quantum Information and Computer Science. She completed her PhD in the group of Aashish Clerk at the University of Chicago. During her PhD, Yuxin worked on topics including reservoir engineering, quantum noise spectroscopy, non-reciprocal interactions, and non-Hermitian dynamics. She also closely collaborated with experimentalists to implement some of her theoretical work using different physical systems such as solid-state spin defects and superconducting circuits. Her current research focuses on the theory of noise and dissipation in quantum systems and their implications for quantum information processing applications.

Kewen Wu, UC Berkeley

Quantum state preparation with optimal T-count

How many T gates are needed to approximate an arbitrary eps-qubit quantum state to within a given precision eps? Improving prior work of Low, Kliuchnikov, and Schaeffer, we show that the optimal asymptotic scaling is sqrt{2^n * log(1/eps)} + log(1/eps) if we allow ancilla qubits. We also show that this is the optimal T-count for implementing an arbitrary diagonal n-qubit unitary to within error eps. We describe applications in which a tensor product of many single-qubit unitaries can be synthesized in parallel for the price of one.

Kewen Wu is a fifth-year graduate student, advised by Avishay Tal, at the theory group of UC Berkeley. He received Bachelor's degree in Computer Sciences and Mathematics from Peking University.
He is broadly interested in theoretical computer sciences and related fields, with recent focuses on provable quantum advantages and the analysis of Boolean functions.

Sebastian Zur, CWI Amsterdam

(Multidimensional) quantum walks and electrical networks

The relationship between random walks and electrical networks has played an important role in classical computer science. In the quantum setting, this connection becomes even more explicit. In this talk, we explore how this relationship enables the design of quantum algorithms—specifically, discrete quantum walks—whose construction and complexity can be derived directly from electrical network theory. We will also delve into how extending these algorithms through the multidimensional quantum walk framework unlocks exponential speedups and give rise to a generalized definition of electrical networks.

I am Sebastian Zur, and I am currently finishing up my PhD at CWI and QuSoft, under the supervision of prof. Stacey Jeffery. My primary research interest is the query, time, and/or space complexity theory of quantum algorithms. On the one hand I study the limitations of these algorithms, by studying lower bound techniques to conclude that certain problems are ``hard'' for any possible quantum algorithm with regards to the aforementioned measures. On the other hand, I study their power, by constructing explicit quantum algorithms inspired by the classical design paradigms of random walks and electrical networks.

Luke Schaeffer, Institute for Quantum Computing

Talk title, abstract and bio to be updated

Science and Engineering

Benjamin Brock, Yale
Madelyn Cain, Harvard
Gurudev Dutt, University of Pittsburgh
Sophie Hermans, Caltech
Alexander McDonald, Université de Sherbrooke
Jameson O'Reilly, University of Oregon
Michał Parniak, University of Warsaw
Shankari Rajagopal, Stanford
Eric I. Rosenthal, Stanford
Nana Shumiya, Princeton
Ariadna Soro, Chalmers University of Technology
Xueyue (Sherry) Zhang, Columbia University and UC Berkeley
Behrooz Semnani, Institute for Quantum Computing
Bradley Hauer, Institute for Quantum Computing

Speaker abstracts and biographies

Benjamin Brock, Yale

Quantum error correction of qudits beyond break-even

Hilbert space dimension is a key resource for quantum information processing. A large Hilbert space is not only an essential requirement for quantum error correction, but it can also be advantageous for realizing gates and algorithms more efficiently. There has thus been considerable experimental effort in recent years to develop quantum computing platforms using qudits (d-dimensional quantum systems with d>2) as the fundamental unit of quantum information.

Just as with qubits, quantum error correction of these qudits will be necessary in the long run, but to date error correction of logical qudits has not been demonstrated experimentally. Here we report the experimental realization of an error-corrected logical qutrit (d=3) and ququart (d=4) by employing the Gottesman-Kitaev-Preskill (GKP) bosonic code. Using a reinforcement learning agent, we optimize the GKP qutrit (ququart) as a ternary (quaternary) quantum memory and achieve beyond break-even error correction with a gain of 1.82 +/- 0.03 (1.87 +/- 0.03). This work represents a new way of leveraging the large Hilbert space of a harmonic oscillator for hardware-efficient quantum error correction.

Benjamin Brock is a postdoctoral researcher in Prof. Michel Devoret’s lab at Yale University. His experimental research focuses on new strategies for bosonic quantum error correction with superconducting circuits. He received his PhD in Physics from Dartmouth College in 2021 for his work on the cavity-embedded Cooper pair transistor: an ultrasensitive electrometer that can operate at the single-photon level.

Madelyn Cain, Harvard

Low-overhead fault tolerance for transversal quantum algorithms

We will discuss experimental and theoretical progress towards large-scale error-corrected quantum computation. First, we report recent advances in quantum information processing using dynamically reconfigurable arrays of neutral atoms. Using this logical processor with various types of error-correcting codes, we demonstrate that we can improve logical two-qubit gates by increasing code distance, create logical GHZ states, and perform computationally complex quantum simulation of information scrambling.

In performing such circuits, we observe that the performance can be substantially improved by accounting for error propagation during transversal logical entangling gates and decoding the logical qubits jointly. We find that by using this correlated decoding technique and correctly handling feedforward operations, the number of noisy syndrome extraction rounds in universal quantum computation can be reduced from O(d) to O(1), where d is the code distance. These techniques result in new theories of fault-tolerance and in practical reductions to the cost of large-scale computation by over an order of magnitude.

Maddie Cain is a 6th year PhD student in theoretical physics working in Professor Mikhail Lukin’s group at Harvard University. Her research explores the theory of quantum information processing, including topics spanning quantum algorithms and quantum error correction. She is interested in developing resource-efficient, fault-tolerant compilations of useful quantum algorithms, with a focus on reducing the overhead of error correction in hardware. She closely collaborates with experimentalists in the Lukin group developing neutral atom arrays.

Gurudev Dutt, University of Pittsburgh

Nansocale electron paramagnetic resonance and quantum opto-mechanics with diamond spin qubits

Single spins associated with nitrogen-vacancy (NV) defects in diamond have emerged as a promising and versatile experimental platform for quantum information processing. They can be used as nodes in optically connected quantum networks, as sensors for magnetic imaging with sub-micron resolution, for detecting and engineering quantum states of nano-mechanical oscillators, and even as probes in biological systems. Our group has demonstrated improvements to dynamic range and sensitivity of magnetometry using phase estimation algorithms, and carried out electron paramagnetic resonance detection and spectroscopy of single Cu ions on the diamond surface. I will also discuss a unique system in our lab where we magnetically trap and laser cool diamond microcrystals under high-vacuum room-temperature conditions for the first time, and discuss the path forward to observing quantum superpositions of macroscopically separated motional states.

Gurudev Dutt is an Associate Professor in the Department of Physics and Astronomy at University of Pittsburgh. He received his Ph.D. in Physics and M. S. in Elect. Engr. from University of Michigan in 2004. Subsequently he was a Research Associate at Harvard University till 2009. PI Dutt has won numerous awards including the Alfred P. Sloan Research Fellow, Kavli Fellow of the National Academy of Sciences, NSF CAREER, and DOE Early Career awards. His areas of expertise include quantum information, solid-state quantum optics, and microwave and optical spectroscopy of solid-state materials and semiconductor nanostructures.

Sophie Hermans, Caltech

Quantum networks using single rare‐earth ions

A future quantum internet will enable fundamentally new applications such as secure communication, distributed quantum computing, and quantum-enhanced metrology and sensing [1]. Recently, a rudimentary quantum network hosting multiple nodes has been demonstrated [2]. However, challenges in scaling up this network motivate the further development of different qubit platforms, such as trapped ions and atoms, and solid-state emitters.

Qubits based on single rare-earth ions (REIs) are promising candidates; they exhibit good qubit and optical properties due to their internal atomic structure. Auxiliary qubits are offered in the form of nuclear spins present in the host material. In the Faraon lab, we have recently established distributed entanglement of two and subsequently three qubits, across two nodes [3].

In this seminar, I will discuss ongoing projects: extending the auxiliary qubit control and understanding the noise processes limiting the REI qubit coherence. Additionally, I will outline the future research directions for my lab in Delft: exploring different host materials, developing robust and scalable nanofabrication methods for more elaborate REI-based devices, and investigating two-REI-qubit interactions.

[1 ] S. Wehner, D. Elkouss, and R. Hanson, “Quantum internet: A vision for the road ahead,” Science, vol. 362, no. 6412 (2018)
[2] M. Pompili, S. L. N. Hermans, S. Baier, et al., “Realization of a multinode quantum network of remote solid-state qubits,” Science, vol. 372, no. 6539, pp. 259–264 (2021)
[3] A. Ruskuc, C.-J. Wu, E. Green, S. L. N. Hermans, J. Choi, and A. Faraon, “Scalable Multipartite Entanglement of Remote Rare-earth Ion Qubits,” arXiv:2402.16224 (2024)

Dr. Sophie Hermans is an incoming Assistant Professor/Group leader at the research institute QuTech, at the Delft University of Technology in the Netherlands. Starting in May 2025, her research team will focus on rare-earth ions doped in host materials for quantum networking applications.
Hermans is a postdoctoral scholar in the group of Prof. Faraon at the California Institute of Technology (Caltech). She works on utilizing single ytterbium ions doped in host crystals for quantum networks and quantum sensing purposes.
Before moving to the United States, Hermans received her PhD degree (with distinction) at the Delft University of Technology in the Netherlands. In the team of Prof. Hanson, she developed the world’s first multi-node quantum network, based on nitrogen-vacancy centers in diamond. Additionally, she worked on quantum frequency conversion of single photons from the visible to the telecom regime.
Hermans was elected one of the Faces of Science by the Dutch Royal Academy of Science and serves as an ambassador of science through outreach and science communication. Upon joining Caltech, she was awarded the AWS Quantum Fellowship. In 2024, Hermans received the Delft Technology Fellowship to support the start of her research program.

Alexander McDonald, Université de Sherbrooke

Measurement-induced transmon ionization

Dispersive readout - which consists of encoding a qubit’s state in the phase of light interaction with the qubit - is the de facto method for measuring qubits in circuit quantum electrodynamics. Despite the high measurement fidelity that can now be reached, this technique is plagued by a loss of its quantum nondemolotion (QND) character and a decrease in fidelity with increased measurement strength. Although this is a widely-observed phenomena, there is no clear parameter dependence for the onset of non-QNDness in experiments. Understanding the nature of this phenomena to eventually implement mitigation strategies is a necessary step in the quest to build a superconducting circuit-based fault-tolerant quantum computer.

In this talk, I will elucidate the nature of this dynamical process, which we refer to as transmon ionization. We develop a comprehensive framework which provides a unified physical picture of the origin of transmon ionization. This framework consists of three complementary levels of descriptions: a fully quantized transmon-resonator model, a semiclassical model where the resonator is treated as a classical drive on the transmon, and a fully classical model. Crucially, all three approaches lead to similar predictions. This framework identifies the multiphoton resonances responsible for transmon ionization. It also allows to efficiently compute numerical estimates of the photon number threshold for ionization, which are in remarkable agreement with recent experimental results.

Alexander is a postdoc at the Université de Sherbrooke's Institut Quantique in the group of Alexandre Blais. His research involves understanding the limitations and improving the performance of readout in superconducting quantum bits. Before returning to his native Canada, he obtained a PhD from the University of Chicago under the supervision of Aash Clerk. There, he studied quantum non-reciprocity and non-Hermitian quantum physics. Alexander also holds a Master's from McGill and a Bachelor's from the University of Ottawa.

Jameson O'Reilly, University of Oregon

Doing more with the same: using metastable states of trapped ions

Today’s most advanced ion trap quantum computers have at most one qubit per ion, each defined within the ground state manifold. Additional non-qubit ions provide sympathetic cooling to keep the computational ions cold enough to perform many rounds of high-fidelity coherent operations. Typically, the two subsets of ions must be different species to prevent cooling light from disturbing the computation. To bypass this added system complexity, we can instead promote our computational ions to a long-lived excited state that is isolated from the ground-state cooling transitions. This promotion also enables new features including erasure conversion and projective state preparation.

We will discuss two recent efforts to develop this architecture: entangling gates between metastable qubits and sympathetic cooling of a metastable ion by a ground-state ion. Finally, we will take advantage of the larger metastable manifold to explore high-fidelity qudit control.

Jameson is a postdoctoral scholar at the University of Oregon, where he works with David Allcock and Dave Wineland. He received his PhD from Duke University and his MSc from the University of Maryland, College Park, both of which were supervised by Chris Monroe. During this time, he worked on quantum networking with trapped ions, helping to demonstrate the best photon-mediated entanglement rate and fidelity to-date on this platform.

Michał Parniak, University of Warsaw

Quantum sensing with Rydberg atoms: from applications to fundamentals

Rydberg atoms can interact strongly with each other, which is the basis for their applications in quantum computing and simulation. The very same property allows them to also act as exceptional sensors. In my talk I will describe our story of developing new microwave and mm-wave sensors based on Rydberg atoms. In particular, I will describe two unconventional approaches we have undertaken.

First, in a hot atom system we employ a complex loop of transitions to achieve sensing via transduction, which has allowed us to receive thermal radiation. In the most recent experiment, with the goal to reach more fundamental limits than available in hot-atom systems, we tried to use a cold-atom system along with the most-standard Ramsey-sequence protocol to combine optimized signal collection with photon-counting detection. Here, we have observed atomic interaction effects which suggest a collective gain can be achieved in the understanding of quantum metrology, even though the interaction caused collective dephasing.

Overall, the exploration of Rydberg sensing stems from the simple observation of exceptional sensitivity to microwaves, but rapidly leads to both fascinating applications for example in space technologies, as well as interesting fundamental metrological questions.

Dr Michał Parniak is a group leader in the Centre for Quantum Optical Technologies QOT and assistant professor at Optics Division, Institute of Experimental Physics, Faculty of Physics. His research interests cover a range of topics in quantum optics, such as single photon detection, optical quantum information processing and communication, atomic ensembles, nonlinear optics and quantum optomechanics. Within QOT he develops experimental implementations of quantum protocols designed by the theory groups and maintains close experimental collaboration with prof. Wojciech Wasilewski (QOT) and prof. Eugene Polzik (Niels Bohr Institute, University of Copenhagen). His most significant scientific achievements include demonstrating superresolution in imaging using two-photon interference, demonstrating the record-breaking quantum memory in terms of its capacity, and demonstration of the first entanglement of macroscopic spin and mechanical systems. In most recent times his team explores fundamentals as well as applications of Rydberg atom sensors and microwave and THz radiation, with applications in space technologies.

Shankari Rajagopal, Stanford

Dynamical engineering of Rydberg atom systems for quantum-enhanced sensing, simulation, and optimization

Quantum sensors hold promise for improved sensing of time, electromagnetic fields, and forces; however, the inherent probabilistic nature of quantum mechanics introduces uncertainty that can limit sensor precision. We can hope to overcome this uncertainty by engineering entanglement to create correlated behavior in atomic systems. Unfortunately, in practice, introducing and controlling these correlations is limited by the local nature of interactions on many promising sensing platforms, including optical tweezer clocks and solid-state magnetometers.

In this talk, I will discuss how we can use temporal control over local Rydberg interactions to extend interaction coherence times and minimize atomic loss in an array of atomic ensembles. With these improvements, we generate metrologically useful entanglement across several spatially separated ensembles in parallel. This work demonstrates the power of dynamical control to enhance and expand our understanding of entanglement in atomic systems. I will also discuss future prospects in quantum sensing, simulation, and optimization on a new experiment utilizing a Rydberg atom array in an optical cavity.

Shankari Rajagopal is an atomic physics experimentalist interested in driven systems, measurement, and interactive quantum dynamics. Over the past five years, she has been a postdoctoral research scholar and Stanford Science Fellow at Stanford University in the group of Monika Schleier-Smith, working on improved coherence and uses of dressed Rydberg interactions in atomic tweezer arrays. She completed her graduate studies in 2019 at the University of California Santa Barbara in the lab of David Weld, studying non-equilibrium dynamics with Bose-Einstein condensates in lattices. Shankari is particularly interested in applications of driven quantum systems and measurement feedback to quantum simulation, optimization, and metrology. Starting in January 2025, she will be an assistant professor at the University of Michigan Department of Physics.

Eric I. Rosenthal, Stanford

The tin-vacancy center in diamond: understanding this emerging qubit and its application to quantum networks

The negatively charged tin-vacancy (SnV) center in diamond is a desirable spin/photon interface for use in quantum networking. In particular, the SnV has bright emission, reduced sensitivity to electrical noise, and long spin coherence at elevated temperature. Here, we develop the SnV as a spin qubit including demonstrations of both high-fidelity spin control, and, single-shot spin readout. In the process, we gain understanding of the SnV including study of its Hamiltonian, and, noise affecting its spin and optical properties.

Finally, we use an SnV spin as a tool to study weak quantum measurement in solid-state atomic systems. These results pave the way for SnV spins to be used as a building block for future quantum technologies including quantum networking, sensing, and information processing.

Eric I. Rosenthal is an IC Postdoctoral Scholar from the Vuckovic group at Stanford University. Previously, Eric completed his B.A. in physics at the University of Pennsylvania, and his Ph.D. in physics in Konrad Lehnert’s group at JILA and the University of Colorado, Boulder. After undergraduate research spanning from carbon nanotubes to photonic crystals in deep sea fish skin, Eric was passionate about a career in scientific research and became excited about quantum physics. Eric came to Konrad Lehnert’s group at JILA, the University of Colorado, Boulder, where his research focused on technology related to superconducting qubits – a promising platform for building scalable quantum computers. Specifically, Eric was interested in how to better measure superconducting qubits, which lead to developing superconducting integrated circuits including fast, high-bandwidth switches, circulators, and parametric amplifier technology to be used in conjunction with qubit readout. His Ph.D. culminated with a chip-scale detector for superconducting qubit measurement that had favorable performance compared to conventional approaches. For a postdoc, Eric remained passionate about quantum science but wanted to expand his knowledge and especially, to learn optical measurement techniques. This led him to Jelena Vuckovic’s group at Stanford to study semiconductor spin centers. Specifically, Eric’s postdoc research has focused on the tin-vacancy center in diamond, a promising platform for scaling quantum networks. Eric developed understanding of this qubit including novel demonstrations of coherent microwave spin control and single-shot readout, and subsequent scientific exploration of this center’s spin properties. This work enables use of the tin-vacancy qubit for the next generation of quantum networks. In the future, Eric is interested in developing hybrid quantum technology involving both superconducting and solid-state systems. These platforms have complementing strengths: fast operations for superconducting qubits, and long spin lifetimes and an optical interface for solid-state spin qubits. How to best overcome the materials-related challenges of combining these systems is an open and fascinating question. While engaged in research, Eric will continue his deep commitment to teaching and mentorship spanning from outreach activities, working with undergraduate students, and mentoring Ph.D. students and postdocs. Eric hopes to do this as the future P.I. of a research laboratory.

Nana Shumiya, Princeton

Disentangling and eliminating loss sources in tantalum superconducting circuits

The field of quantum computing has seen an explosion in research efforts and interest in both academia and industry within recent years. While there are several candidate platforms for quantum computing, superconducting circuits are one of the most promising platforms due to their scalability, design flexibility and stableness to the environment. However, single qubit coherence remains a major limiting factor in building scalable processors based on superconducting qubits. Recently, tantalum-based superconducting qubits have been discovered to enable long lifetimes and coherence times because of their chemical robustness and well-behaved surface oxide.

In this talk, I will first talk about our recent work to characterize the dominant sources of loss in state-of-the-art tantalum superconducting circuits. Using systematic measurements of tantalum resonators, we find the dominant source of loss at qubit operating conditions is from two-level systems (TLSs) present at material interfaces and surfaces, including TLSs residing in the amorphous native oxide layer.

In the second part, I will discuss our strategy for avoiding oxide formation by encapsulating the tantalum with noble metals that do not form native oxide. Microwave loss measurements of superconducting resonators reveal that the noble metal is proximitized, with a superconducting gap over 80% of the bare tantalum at thicknesses where the oxide is fully suppressed, suggesting it as a promising strategy for eliminating surface oxide TLS loss in superconducting qubits.

Nana is a PQI postdoctoral research fellow at Princeton University. She graduated with a B.A. in Physics from University of California, Berkeley and M.S. and Ph.D. in Physics from Princeton University. During her Ph.D., she used scanning tunneling microscopy with vector magnetic fields to study various quantum topological material systems with Prof. M. Zahid Hasan. In her current study, she works with Prof. Nathalie de Leon and Prof. Andrew Houck on exploring material systems to improve coherence of superconducting qubits.

Ariadna Soro, Chalmers University of Technology

Giant atoms in 1D and 2D structured environments

Giant atoms are quantum emitters that can couple to light at several discrete points, which may be spaced wavelengths apart. They receive the name ""giant"" because they break the dipole approximation, i.e., the assumption that atoms are ""small"" compared to the wavelength of the light they interact with. Among their many remarkable properties, giant atoms have the ability to interact through a common bath without decohering, which is promising for applications in quantum computing and quantum simulation.

In this talk, I will focus on how giant atoms behave when coupled to 1D and 2D structured environments. These environments have an energy spectrum characterized by finite bands and band gaps, which affect atomic dynamics beyond the Markovian regime. In particular, I will show how giant atoms can avoid decoherence, and how their dynamics compare to that of small atoms and continuous waveguides.

I am a PhD student in Anton Frisk Kockum’s group, at Chalmers University of Technology in Sweden. My research is in quantum optics with giant atoms, and I study how these quantum emitters behave when coupled to unconventional environments. In particular, I focus on how giant atoms interact with other emitters through the environment and how they can avoid decoherence. At a broader level, I am interested in harnessing giant-atom interactions for applications in quantum simulation and quantum computing. Before my PhD, I got a double BSc in physics and mathematics at the Autonomous University of Barcelona (Spain), and a MSc in engineering physics at KTH Royal Institute of Technology (Sweden).

Xueyue (Sherry) Zhang, Columbia University and UC Berkeley

T centers in silicon: an emerging platform as a spin-photon interface

Silicon is notably the most advanced platform for scalable integrated photonics and electronics. In the realm of quantum science, silicon is also known to be a high-quality host material for solid-state spins. However, an efficient spin-photon interface within silicon is still under development. In this talk, I will present an integrated photonics platform with color centers in silicon operating at the telecom O-band. Specifically, we focus on T centers – a type of carbon-hydrogen defect – featuring long electron and nuclear spin coherence times. For an efficient photonic interface, we incorporate T centers into photonic crystal cavities (PCCs) and achieve a tenfold lifetime reduction due to Purcell enhancement.

Furthermore, using a novel architecture of PCC arrays coupled to a bus waveguide, we perform wavelength-multiplexed emission from T centers in different cavities. We also probe signatures of waveguide-mediated interactions between cavities based on T center emissions.

Lastly, I will discuss our progress in coherent microwave spin control and optical readout for waveguide-integrated individual T centers. These advances represent the first steps towards building a scalable quantum network based on silicon photonics.

Xueyue (Sherry) Zhang will be an Assistant Professor in the Department of Applied Physics and Applied Mathematics at Columbia University starting in January 2025. She earned her B.Eng. from Tsinghua University in 2017 and her Ph.D. in Applied Physics from Caltech in 2023. Dr. Zhang then joined UC Berkeley as a Miller Postdoctoral Fellow in EECS and Physics. Dr. Zhang's research interests include superconducting circuits, quantum many-body simulations, and color centers in silicon. Her work has earned her several awards, including the Miller Research Fellowship, the Boeing Quantum Creator Prize, and the Rising Star in Physics Award in 2023.

Behrooz Semnani, Institute for Quantum Computing

Talk title, abstract and bio to be updated

Bradley Hauer, Institute for Quantum Computing

Talk title, abstract and bio to be updated

Quantum materials

IQC Colloquium featuring Francesco Di Colandrea

Large-scale quantum walks via complex polarization transformations

Biography

Location

IQC Student Summer Conference

Organizers

Location

Toronto Ultracold Atom Network (TUCAN) meeting 2025

Organizers

Location

Schedule

Abstracts

Nicholas Sullivan

Magneto-optical trapping of neutral atoms with light-induced effective magnetic fields

Takahiro Tow

A cryogenic single-ion Sr+ clock

Jim Martin

Humpty-Dumpty is three-dimensional

Soroush Khoubyarian

Feedback Control Systems for the Stabilization of Traps in Large Rydberg Atom Arrays

Anya Houk

Metasurface-based cavities for quantum optical applications with atomic ensembles

Ali Khatai

Progress towards a barium-133 trapped ion quantum processor

Nicholas Zutt

High-Dimensional Qudit Quantum Computing with Trapped 137Ba+ Ions

Kevin Xie

Dimer-association contact of a unitary Fermi gas

Denise Kamp

Dynamical instability as a PT-symmetry breaking phase transition in a rotating Bose-Einstein condensate

IQC Student seminar featuring Zach Merino

Simulating spin qubits in silicon quantum dots

Location

World Quantum Day – Quantum Shorts: Encore

Meet the panel

Location

Register

Faculty of Science presents: Science in the City - Quantum

Meet the speakers

IQC Colloquium featuring Machiel Blok

Beyond Binary Quantum Information in Superconducting Circuits: Taking the Transmon for a Spin

Location

IQC Student seminar featuring Tales Rick Perche

A description of the spin-spin interaction from Quantum Electrodynamics

Location

IQC Colloquium featuring Paul Barclay

Spin, photons and phonons: diamond nanophotonics

Location

Quantum Innovators 2024

Location

How to attend

Event recap

IQC community welcomes rising stars of quantum information science and technology

Schedule

Monday, November 11 – QNC 0101

Tuesday, November 12 – QNC 0101

Wednesday, November 13 – QNC 0101

Confirmed posters from IQC members

Thursday, November 14 – RAC 2009

Friday, November 15 – QNC 0101

Invited speakers

Computer Science and Mathematics

Speaker abstracts and biographies

Thiago Bergamaschi, UC Berkeley

Quantum computational advantage with constant-temperature Gibbs sampling

Uma Girish, Columbia University

Trade-offs between entanglement and communication

Jiaqing Jiang, California Institute of Technology

Quantum metropolis sampling via weak measurement

Allen Liu, MIT

High-temperature Gibbs states are unentangled and efficiently preparable

Yunchao Liu, UC Berkeley

Learning shallow quantum circuits and quantum states prepared by shallow circuits in polynomial time

Quynh The Nguyen, Harvard

Quantum fault tolerance with constant-space and logarithmic-time overheads

Harold Nieuwboer, University of Copenhagen

Entanglement polytopes in action

Alexander Poremba, MIT

The Learning Stabilizers with Noise problem