Steven T. Flammia
YOU?
Author Swipe
View article: Ansatz-Free Hamiltonian Learning with Heisenberg-Limited Scaling
Ansatz-Free Hamiltonian Learning with Heisenberg-Limited Scaling Open
Learning the unknown interactions that govern a quantum system is crucial for quantum information processing, device benchmarking, and quantum sensing. The problem, known as Hamiltonian learning, is well understood under the assumption tha…
View article: Ansatz-free Hamiltonian learning with Heisenberg-limited scaling
Ansatz-free Hamiltonian learning with Heisenberg-limited scaling Open
Learning the unknown interactions that govern a quantum system is crucial for quantum information processing, device benchmarking, and quantum sensing. The problem, known as Hamiltonian learning, is well understood under the assumption tha…
View article: Fault-tolerant quantum memory using low-depth random circuit codes
Fault-tolerant quantum memory using low-depth random circuit codes Open
Low-depth random circuit codes possess many desirable properties for quantum error correction but have so far only been analyzed in the code capacity setting where it is assumed that encoding gates and syndrome measurements are noiseless. …
View article: A Constructive Approach to Zauner's Conjecture via the Stark Conjectures
A Constructive Approach to Zauner's Conjecture via the Stark Conjectures Open
We propose a construction of $d^2$ complex equiangular lines in $\mathbb{C}^d$, also known as SICPOVMs, conjectured by Zauner to exist for all d. The construction gives a putatively complete list of SICs with Weyl-Heisenberg symmetry in al…
View article: Learning $k$-body Hamiltonians via compressed sensing
Learning $k$-body Hamiltonians via compressed sensing Open
We study the problem of learning a $k$-body Hamiltonian with $M$ unknown Pauli terms that are not necessarily geometrically local. We propose a protocol that learns the Hamiltonian to precision $ε$ with total evolution time ${\mathcal{O}}(…
View article: Efficient self-consistent learning of gate set Pauli noise
Efficient self-consistent learning of gate set Pauli noise Open
Understanding quantum noise is an essential step towards building practical quantum information processing systems. Pauli noise is a useful model that has been widely applied in quantum benchmarking, error mitigation, and error correction.…
View article: Quantum chi-squared tomography and mutual information testing
Quantum chi-squared tomography and mutual information testing Open
For quantum state tomography on rank- dimension- states, we show that copies suffice for accuracy with respect to (Bures) -divergence, and copies suffice for accuracy with respect to quantum relative entropy. The best previous bound wa…
View article: Demonstrating a Long-Coherence Dual-Rail Erasure Qubit Using Tunable Transmons
Demonstrating a Long-Coherence Dual-Rail Erasure Qubit Using Tunable Transmons Open
Quantum error correction with erasure qubits promises significant advantages over standard error correction due to favorable thresholds for erasure errors. To realize this advantage in practice requires a qubit for which nearly all errors …
View article: Clifford-Deformed Surface Codes
Clifford-Deformed Surface Codes Open
Various realizations of Kitaev’s surface code perform surprisingly well for biased Pauli noise. Attracted by these potential gains, we study the performance of Clifford-deformed surface codes (CDSCs) obtained from the surface code by the a…
View article: Fault-Tolerant Quantum Memory using Low-Depth Random Circuit Codes
Fault-Tolerant Quantum Memory using Low-Depth Random Circuit Codes Open
Low-depth random circuit codes possess many desirable properties for quantum error correction but have so far only been analyzed in the code capacity setting where it is assumed that encoding gates and syndrome measurements are noiseless. …
View article: Learning Correlated Noise in a 39-Qubit Quantum Processor
Learning Correlated Noise in a 39-Qubit Quantum Processor Open
Building error-corrected quantum computers relies crucially on measuring and modeling noise on candidate devices. In particular, optimal error correction requires knowing the noise that occurs in the device as it executes the circuits requ…
View article: Improved Decoding of Circuit Noise and Fragile Boundaries of Tailored Surface Codes
Improved Decoding of Circuit Noise and Fragile Boundaries of Tailored Surface Codes Open
Realizing the full potential of quantum computation requires quantum error correction (QEC), with most recent breakthrough demonstrations of QEC using the surface code. QEC codes use multiple noisy physical qubits to encode information in …
View article: Quantum chi-squared tomography and mutual information testing
Quantum chi-squared tomography and mutual information testing Open
For quantum state tomography on rank-$r$ dimension-$d$ states, we show that $\widetilde{O}(r^{.5}d^{1.5}/ε) \leq \widetilde{O}(d^2/ε)$ copies suffice for accuracy~$ε$ with respect to (Bures) $χ^2$-divergence, and $\widetilde{O}(rd/ε)$ copi…
View article: Learning correlated noise in a 39-qubit quantum processor
Learning correlated noise in a 39-qubit quantum processor Open
Building error-corrected quantum computers relies crucially on measuring and modeling noise on candidate devices. In particular, optimal error correction requires knowing the noise that occurs in the device as it executes the circuits requ…
View article: Tailored XZZX codes for biased noise
Tailored XZZX codes for biased noise Open
Quantum error correction (QEC) for generic errors is challenging due to the demanding threshold and resource requirements. Interestingly, when physical noise is biased, we can tailor our QEC schemes to the noise to improve performance. Her…
View article: Free-Fermion Subsystem Codes
Free-Fermion Subsystem Codes Open
We consider quantum error-correcting subsystem codes whose gauge generators realize a translation-invariant, free-fermion-solvable spin model. In this setting, errors are suppressed by a Hamiltonian whose terms are the gauge generators of …
View article: Foundations for learning from noisy quantum experiments
Foundations for learning from noisy quantum experiments Open
Understanding what can be learned from experiments is central to scientific progress. In this work, we use a learning-theoretic perspective to study the task of learning physical operations in a quantum machine when all operations (state p…
View article: Tailored XZZX codes for biased noise
Tailored XZZX codes for biased noise Open
Quantum error correction (QEC) for generic errors is challenging due to the demanding threshold and resource requirements. Interestingly, when physical noise is biased, we can tailor our QEC schemes to the noise to improve performance. Her…
View article: The randomized measurement toolbox
The randomized measurement toolbox Open
Increasingly sophisticated programmable quantum simulators and quantum computers are opening unprecedented opportunities for exploring and exploiting the properties of highly entangled complex quantum systems. The complexity of large quant…
View article: Improved decoding of circuit noise and fragile boundaries of tailored surface codes
Improved decoding of circuit noise and fragile boundaries of tailored surface codes Open
Realizing the full potential of quantum computation requires quantum error correction (QEC), with most recent breakthrough demonstrations of QEC using the surface code. QEC codes use multiple noisy physical qubits to encode information in …
View article: Building a Fault-Tolerant Quantum Computer Using Concatenated Cat Codes
Building a Fault-Tolerant Quantum Computer Using Concatenated Cat Codes Open
We present a comprehensive architectural analysis for a proposed fault-tolerant quantum computer based on cat codes concatenated with outer quantum error-correcting codes. For the physical hardware, we propose a system of acoustic resonato…
View article: Clifford-deformed Surface Codes
Clifford-deformed Surface Codes Open
Various realizations of Kitaev's surface code perform surprisingly well for biased Pauli noise. Attracted by these potential gains, we study the performance of Clifford-deformed surface codes (CDSCs) obtained from the surface code by apply…
View article: Free-Fermion Subsystem Codes
Free-Fermion Subsystem Codes Open
We consider quantum error-correcting subsystem codes whose gauge generators realize a translation-invariant, free-fermion-solvable spin model. In this setting, errors are suppressed by a Hamiltonian whose terms are the gauge generators of …
View article: Averaged Circuit Eigenvalue Sampling
Averaged Circuit Eigenvalue Sampling Open
We introduce ACES, a method for scalable noise metrology of quantum circuits that stands for Averaged Circuit Eigenvalue Sampling. It simultaneously estimates the individual error rates of all the gates in collections of quantum circuits, …
View article: Quantum Coding with Low-Depth Random Circuits
Quantum Coding with Low-Depth Random Circuits Open
Random quantum circuits have played a central role in establishing the computational advantages of near-term quantum computers over their conventional counterparts. Here, we use ensembles of low-depth random circuits with local connectivit…
View article: Pauli error estimation via Population Recovery
Pauli error estimation via Population Recovery Open
Motivated by estimation of quantum noise models, we study the problem of learning a Pauli channel, or more generally the Pauli error rates of an arbitrary channel. By employing a novel reduction to the "Population Recovery" problem, we giv…
View article: Pauli Error Estimation via Population Recovery
Pauli Error Estimation via Population Recovery Open
Motivated by estimation of quantum noise models, we study the problem of learning a Pauli channel, or more generally the Pauli error rates of an arbitrary channel. By employing a novel reduction to the "Population Recovery" problem, we giv…
View article: The XZZX surface code
The XZZX surface code Open
We show that a variant of the surface code—the XZZX code—offers remarkable performance for fault-tolerant quantum computation. The error threshold of this code matches what can be achieved with random codes (hashing) for every single-qubit …
View article: Unboxing Quantum Black Box Models: Learning Non-Markovian Dynamics
Unboxing Quantum Black Box Models: Learning Non-Markovian Dynamics Open
Characterizing the memory properties of the environment has become critical for the high-fidelity control of qubits and other advanced quantum systems. However, current non-Markovian tomography techniques are either limited to discrete sup…
View article: Fault-Tolerant Thresholds for the Surface Code in Excess of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mn>5</mml:mn><mml:mo>%</mml:mo></mml:math> Under Biased Noise
Fault-Tolerant Thresholds for the Surface Code in Excess of Under Biased Noise Open
Noise in quantum computing is countered with quantum error correction. Achieving optimal performance will require tailoring codes and decoding algorithms to account for features of realistic noise, such as the common situation where the no…