Monday, November 11, 2024 8:30 am - 4:30 pm EST (GMT -05:00)
Tuesday, November 12, 2024 8:30 am - 4:30 pm EST (GMT -05:00) Wednesday, November 13, 2024 8:30 am - 4:30 pm EST (GMT -05:00) Thursday, November 14, 2024 8:30 am - 4:30 pm EST (GMT -05:00) Friday, November 15, 2024 8:30 am - 4:30 pm EST (GMT -05:00)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 Waterloo in Waterloo, 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 Waterloo, are partly funded by the Canada First Research Excellence Fund (CFREF) as part of the Transformative Quantum Technologies research initiative.
Schedule
Monday, November 11 – QNC 0101
Time | Agenda |
---|---|
08:45 | |
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 | |
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 | |
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 | |
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 | |
09:15 |
Thomas Schuster, California Institute of Technology Random unitaries in extremely low depth |
10:00 | |
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 | |
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 | |
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 |
Wednesday, November 13 – QNC 0101
Time | Agenda |
---|---|
08:30 | |
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 | |
11:00 |
Panel discussion Academics careers in quantum information science |
11:45 |
Group photo |
12:00 | |
13:00 |
QNC Lab tours |
14:00 | |
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 | |
09:10 |
Gurudev Dutt, University of Pittsburgh Nansocale electron paramagnetic resonance and quantum opto-mechanics with diamond spin qubits |
10:10 | |
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 | |
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 | |
15:00 |
RAC Lab tours |
16:30 | End of day |
18:30 |
Conference banquet #2 |
Friday, November 15 – QNC 0101
Time | Agenda |
---|---|
08:45 | |
09:10 |
Michał Parniak, University of Warsaw Quantum sensing with Rydberg atoms: from applications to fundamentals |
10:10 | |
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 | |
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 |
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.
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.
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.
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.
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)
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.
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).
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).
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.
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.
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.
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.
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.
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.
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.
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.
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)
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.
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.
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.
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.
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.
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.
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.
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.
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