Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session C34: Experimental Results for Small Quantum CodesLive
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Sponsoring Units: DQI Chair: Natalie Brown, Honeywell |
Monday, March 15, 2021 3:00PM - 3:12PM Live |
C34.00001: A Device for Realizing Error Correction with a Distance-3 Surface Code using Superconducting Circuits Christian Kraglund Andersen, Ants Remm, Stefania Lazar, Sebastian Krinner, Nathan Lacroix, Christoph Hellings, Agustin Di Paolo, Francois Swiadek, Graham J. Norris, Johannes Hermann, Mihai Gabureac, Alexandre Blais, Christopher Eichler, Andreas Wallraff Quantum error correction is a key challenge in the field of quantum computing and a next milestone to be passed is to demonstrate the correction of bit- and phase-flip errors on a logical qubit. A promising approach to quantum error correction is the surface code, where physical qubits are arranged into a 2D grid. For a distance-3 code, the smallest distance that can correct single-qubit bit- and phase-flip errors, the surface code uses 9 data qubits for encoding the logical state and 8 ancilla qubits for performing measurements of the error syndromes. In this talk, we discuss the design and realization of a 17 qubit superconducting quantum device used to implement the distance-3 surface code. We characterized the device performance of the elementary operations needed to implement quantum error correction, including single and two-qubit gates, qubit readout and weight-2 and weight-4 stabilizer measurements. |
Monday, March 15, 2021 3:12PM - 3:24PM Live |
C34.00002: Quantum Error Correction Using a Distance Three Surface Code with Superconducting Qubits. Ants Remm, Christian Kraglund Andersen, Stefania Lazar, Sebastian Krinner, Nathan Lacroix, Christoph Hellings, Agustin Di Paolo, Francois Swiadek, Graham J. Norris, Johannes Hermann, Mihai Gabureac, Alexandre Blais, Christopher Eichler, Andreas Wallraff Quantum error correction (QEC) is essential for executing large-scale quantum algorithms with high fidelity. A promising approach to QEC is based on the surface code, as it requires only local connectivity and has a high error threshold. In this talk, we present our progress towards the operation of a distance d=3 surface code consisting of 17 superconducting qubits. We verify the performance of the subsystems of the device by preparing logical states on four d=2 subsets of the full code using error detection [C. K. Andersen et al., Nat. Phys. 16, 875–880 (2020)]. We can then characterize the performance of the d=3 surface code by measuring the logical operator expectation values after one or several error correction cycles. We compare the logical states obtained when postselecting on no detected errors to the states from a minimum weight perfect matching error decoder that identifies and corrects for errors based on the syndrome measurements. |
Monday, March 15, 2021 3:24PM - 3:36PM Live |
C34.00003: Continuous Error Correction with Parity Measurements William Livingston, Machiel S Blok, Juan Atalaya, Razieh Mohseninia, Andrew N Jordan, Justin G. Dressel, Irfan Siddiqi In a multi-qubit system, performing continuous measurements of joint properties such as parity allows us to study the collapse dynamics of multipartite states. Simultaneous parity measurements in a three-qubit system also act as continuous stabilizer detection for a quantum error correction code, allowing us to observe a single qubit flip in real time. The parity of two superconducting transmons may be directly measured without qubit ancilla by coupling them to a single readout resonator, using identical dispersive coupling chis much larger than the resonator bandwidth kappa. Using a chip with three qubits and connecting each of two pairs to a parity readout resonator, we implement the two parity measurements needed to perform the conventional three-qubit bit-flip code. We control the qubits from a field programmable gate array board which also continuously monitors the parity, allowing for low latency correction pulses to be applied when a qubit flip occurs. Using this method, we extend the lifetime of an excited logical state past the lifetime of an excited bare qubit. |
Monday, March 15, 2021 3:36PM - 3:48PM Live |
C34.00004: Exponential suppression of bit or phase flip errors using repetition codes on superconducting qubits (Part I) Sabrina Hong Practical applications using quantum computers will require error rates below 1e-10, but state-of-the-art hardware features physical error rates near 1e-3. Quantum error correction theoretically promises to bridge this divide by combining physical qubits into logical qubits, and exponentially reducing error rates according to the number of physical qubits used. In this work, we run distance 3-11 repetition codes and distance 2 surface codes in the Sycamore superconducting qubit architecture. Using repetition codes, we demonstrate exponential suppression of bit or phase errors with 100x reduction in error rate from d=3 to d=11, even after 50 rounds of measurement. We also show that our device is well described by a simple depolarizing error model, allowing us to project the performance of larger codes. The exponential suppression of error and validation of theoretical assumptions about the behavior of errors provides further evidence that surface codes with superconducting qubits are a viable path towards a fault tolerant quantum computer. |
Monday, March 15, 2021 3:48PM - 4:00PM Live |
C34.00005: Exponential suppression of bit or phase flip errors using repetition codes on superconducting qubits (Part II) Zijun Chen Practical applications using quantum computers will require error rates below 1e-10, but state-of-the-art hardware features physical error rates near 1e-3. Quantum error correction theoretically promises to bridge this divide by combining physical qubits into logical qubits, and exponentially reducing error rates according to the number of physical qubits used. In this work, we run distance 3-11 repetition codes and distance 2 surface codes in the Sycamore superconducting qubit architecture. Using repetition codes, we demonstrate exponential suppression of bit or phase errors with 100x reduction in error rate from d=3 to d=11, even after 50 rounds of measurement. We also show that our device is well described by a simple depolarizing error model, allowing us to project the performance of larger codes. The exponential suppression of error and validation of theoretical assumptions about the behavior of errors provides further evidence that surface codes with superconducting qubits are a viable path towards a fault tolerant quantum computer. |
Monday, March 15, 2021 4:00PM - 4:12PM Live |
C34.00006: Exponential suppression of bit or phase flip errors using repetition codes on superconducting qubits (Part III) Kevin Satzinger
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Monday, March 15, 2021 4:12PM - 4:24PM Live |
C34.00007: Operating a logical-qubit size system of superconducting qubits with a heavy-hexagon layout Maika Takita, Antonio Corcoles, Ken Inoue, Scott Lekuch, Andrew Cross, Muyuan Li, John A Smolin, Guanyu Zhu, Jerry Chow, Jay M Gambetta Recent experimental progress in quantum computing, in different platforms, has enabled the possibility to realize and operate quantum systems of large enough size to support logical qubit encoding and quantum error correction operations. In the field of superconducting qubits in particular, a very interesting topology is the heavy-hexagon. This topology leads to a lower degree connectivity than other popular low-degree parity-check codes, which helps with crosstalk, with little increase in logical error rate. In this talk, we present experiments on small distance logical qubit size systems with the heavy-hexagon topology. We accompany the data with noisy simulations and explore current main hurdles towards full fault-tolerant operation of a logical qubit. |
Monday, March 15, 2021 4:24PM - 4:36PM Live |
C34.00008: Error correction of a logical grid state qubit by dissipative pumping Brennan de Neeve, Thanh Long Nguyen, Tanja Behrle, Jonathan P Home Stabilization of encoded logical qubits using quantum error correction is key to the realization of reliable quantum computers. GKP states are a powerful encoding for oscillators, which allow small displacement errors to be corrected. I will present theory and implementation of a dissipative map designed for physically realistic finite GKP codes which performs quantum error correction of a logical qubit implemented in the motion of a single trapped ion. The correction cycle involves mapping the finite GKP code stabilizer information onto an internal electronic state ancilla qubit, and then applying coherent feedback and ancilla repumping. We demonstrate the extension of logical coherence using both square and hexagonal GKP codes, achieving an increase in logical lifetime of a factor of three. The simple dissipative map used for the correction can be viewed as a type of reservoir engineering, which pumps into the highly non-classical GKP qubit manifold. These techniques open new possibilities for quantum state control alongside their application to scaling quantum computing. |
Monday, March 15, 2021 4:36PM - 4:48PM Live |
C34.00009: Creation, verification, and scalability of decoherence-free subspaces and noiseless subsystems on superconducting qubits Gregory Quiroz, Bibek Pokharel, Yifan Sun, Joseph Boen, Lina Tewala, Vinay Tripathi, Matthew Kowalsky, Devon Williams, Jun-Yi Zhang, Paraj Titum, Lian-Ao Wu, Kevin Schultz, Daniel Lidar Decoherence-free subspaces/noiseless subsystems (DFS/NS) preserve quantum information by identifying subspaces/subsystems of the Hilbert space that remain unaffected by decoherence. Identifying DFS/NS codes under collective decoherence is well-understood, and the resultant codes support scalable and universal quantum computation. While most experimental systems, including superconducting qubit-based devices, do not decohere collectively, it is possible to engineer the conditions for collective decoherence using dynamical decoupling (DD) sequences. We report on the creation and verification of DD assisted DFS/NS codes on quantum processors provided by the IBM Quantum Experience. We compare the performance of a DFS/NS encoded qubit with its unprotected counterpart. We show that qubit lifetime can be improved substantially using DD assisted DFS/NS codes. Furthermore, we exploit gate set tomography to characterize logical error channels and estimate logical gate error rates for the DFS/NS encoding. When combined with an analysis of qubit lifetimes for multiple simultaneously encoded qubits, we obtain a comprehensive picture of DFS/NS feasibility and scalability on near-term quantum processors. |
Monday, March 15, 2021 4:48PM - 5:00PM Live |
C34.00010: Protecting a Bosonic Qubit with Autonomous Quantum Error Correction I - Parity Recovery by Selective Photon Addition Shruti Shirol, Jeffrey Gertler, Brian Baker, Juliang Li, Jens Koch, Chen Wang To make a universal quantum computer, we need an effective method for combining short-lived physical qubits into redundant encodings where quantum error correction (QEC) is possible. Existing demonstrations of QEC, based on active error syndrome measurements and adaptive recovery operations, are susceptible to additional errors and are hardware intensive. Using reservoir engineering, we construct a dissipative operator, acting on a multiphoton bosonic qubit, that corrects the dominant error of the system: single photon loss. This operator, Parity Recovery by Selective Photon Addition (PReSPA), which stabilizes the even-number fock state manifold, can be used for autonomous quantum error correction (AQEC). In Part I, we show the experimental implementation of PReSPA in a conventional 3d cQED architecture. Notably, it is realized with only time-independent CW drives and without active feedback protocols. We characterize the ability of PReSPA to coherently protect multiphoton states against single photon loss. |
Monday, March 15, 2021 5:00PM - 5:12PM Live |
C34.00011: Protecting a Bosonic Qubit with Autonomous Quantum Error Correction II - AQEC Results Jeffrey Gertler, Brian Baker, Juliang Li, Shruti Shirol, Jens Koch, Chen Wang To make a universal quantum computer, we need an effective method for combining short-lived physical qubits into redundant encodings where quantum error correction (QEC) is possible. Existing demonstrations of QEC, based on active error syndrome measurements and adaptive recovery operations, are susceptible to additional errors and are hardware intensive. Using reservoir engineering, we construct a dissipative operator, acting on a multiphoton bosonic qubit, that corrects the dominant error of the system: single photon loss. This operator, Parity Recovery by Selective Photon Addition (PReSPA), which stabilizes the even-number fock state manifold, can be used for autonomous quantum error correction (AQEC). In Part 2 we demonstrate the ability of PReSPA to extend the logical lifetime of a truncated 4-component cat (T4C) code. The protection against single photon loss boosts the process fidelity decay time of this encoding by greater than a factor of 2. We identify the limiting factors of this AQEC encoding and discuss the potential of the scheme. |
Monday, March 15, 2021 5:12PM - 5:24PM Live |
C34.00012: Experimental implementation of pair-cat code with superconducting microwave circuits (1/2) Akshay Koottandavida, Ioannis Tsioutsios, Shantanu O Mundhada, Luigi Frunzio, Michel Devoret Stabilized quantum manifolds of a bosonic system can encode error-protected qubits. In particular, a logical qubit encoded in a single-mode manifold spanned by cat states is exponentially protected against phase-flip errors. However, in existing experimental implementations with microwave superconducting circuits, detecting and fully correcting photon-loss errors is challenging without turning off the dissipative stabilization process. On the other hand, a phase-flip error protected logical qubit can be encoded in a stabilized manifold spanned by pair-cat states, which are superpositions of two-mode states called Barut-Girardello/pair-coherent states. Advantageously, photon loss errors in either mode can be detected by monitoring the photon-number difference between them, without stopping manifold stabilization. |
Monday, March 15, 2021 5:24PM - 5:36PM Live |
C34.00013: Experimental implementation of pair-cat code with superconducting microwave circuits (2/2) Ioannis Tsioutsios, Akshay Koottandavida, Shantanu O Mundhada, Luigi Frunzio, Michel Devoret Stabilized quantum manifolds of a bosonic system can encode error-protected qubits. In particular, a logical qubit encoded in a single-mode manifold spanned by cat states is exponentially protected against phase-flip errors. However, in existing experimental implementations with microwave superconducting circuits, detecting and fully correcting photon-loss errors is challenging without turning off the dissipative stabilization process. On the other hand, a phase-flip error protected logical qubit can be encoded in a stabilized manifold spanned by pair-cat states, which are superpositions of two-mode states called Barut-Girardello/pair-coherent states. Advantageously, photon loss errors in either mode can be detected by monitoring the photon-number difference between them, without stopping manifold stabilization. |
Monday, March 15, 2021 5:36PM - 5:48PM Live |
C34.00014: Realistic numerical simulation of a distance-3 surface code implemented on a superconducting chip Agustin Di Paolo, Christian Kraglund Andersen, Ants Remm, Stefania Lazar, Sebastian Krinner, Nathan Lacroix, Christoph Hellings, Francois Swiadek, Graham J. Norris, Johannes Hermann, Mihai Gabureac, Christopher Eichler, Andreas Wallraff, Alexandre Blais The surface code is an appealing candidate for quantum error correction because of its relatively high threshold and the locality of the interactions needed to perform syndrome measurements. In this talk, we study the performance of small surface codes implemented on transmon-based superconducting processors with realistic time-domain numerical simulations. More precisely, we investigate the memory fidelity of a near-term implementation of a distance-3 surface code by characterizing the logical error channel as a function of device parameters. Our analysis focuses on the interplay between the effects of decoherence and spurious cross-Kerr interactions on the error rate of the logical qubit. |
Monday, March 15, 2021 5:48PM - 6:00PM On Demand |
C34.00015: Use Alibaba Cloud Quantum Development Platform to Simulate Quantum Error Correction Performance Cupjin Huang, Xiaotong Ni, Fang Zhang, Michael Newman, Dawei Ding, Xun Gao, Tenghui Wang, Hui-Hai Zhao, Feng Wu, Gengyan Zhang, Chunqing Deng, Hsiang-Sheng Ku, Jianxin Chen, Yaoyun Shi Although significant progresses have been made in the direction of simulating large-scale quantum circuits in the past few years, simulating the behavior of a small quantum chip accurately to aid the system design is still challenging. In this talk, we report our result on simulating a distance-3 logical qubit encoded in the 17-qubit surface code using experimental noise parameters for transmon qubits in a planar circuit QED architecture. By using Alibaba Cloud Quantum Development Platform, we are able to evaluate the quantum error correction performance with different noise parameters and code implementations. Our simulation also features crosstalk induced by ZZ-interactions, which has never done before due to high computation cost. |
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