Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session Q64: Quantum Error Correction Code Performance and ImplementationFocus
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Sponsoring Units: DQI Chair: Natalie Brown, Quantinuum Room: Room 415 |
Wednesday, March 8, 2023 3:00PM - 3:12PM |
Q64.00001: Calibrating and benchmarking a distance-5 surface code with superconducting qubits, Part 1 Zijun Chen Quantum error correction offers a path to algorithmically-relevant error rates by encoding logical qubits within many physical qubits, where increasing the number of physical qubits enhances protection against physical errors. However, introducing more qubits also increases the number of error sources, so the density of errors must be sufficiently low in order for logical performance to improve with increasing code size. In this talk, we report the measurement of logical qubit performance on distance-3 and distance-5 surface codes on a Sycamore superconducting processor, and demonstrate that our code has sufficient performance to overcome the additional errors from increasing qubit number [1]. |
Wednesday, March 8, 2023 3:12PM - 3:24PM |
Q64.00002: Calibrating and benchmarking a distance-5 surface code with superconducting qubits, Part 1 Kevin J Satzinger Quantum error correction offers a path to algorithmically-relevant error rates by encoding logical qubits within many physical qubits, where increasing the number of physical qubits enhances protection against physical errors. However, introducing more qubits also increases the number of error sources, so the density of errors must be sufficiently low in order for logical performance to improve with increasing code size. In this talk, we report the measurement of logical qubit performance on distance-3 and distance-5 surface codes on a Sycamore superconducting processor, and demonstrate that our code has sufficient performance to overcome the additional errors from increasing qubit number [1]. |
Wednesday, March 8, 2023 3:24PM - 3:36PM |
Q64.00003: Repeated stabilizer measurements in a superconducting distance-3 surface code Hany Ali, Jorge F Marques, Boris Varbanov, Matvey Finkel, Christos Zachariadis, Wouter J Vlothuizen, Marc Beekman, Nadia Haider, Barbara M Terhal, Leonardo DiCarlo We show the calibration and benchmarking of the weight-2 and weight-4 stabilizer measurements of the distance-3 surface code with a 17-transmon processor. We compare measured performance to a density matrix simulation considering various error models with input parameters extracted from experiment. We then initialize a logical state and assess the defect rates for multiple rounds of X- and Z-type stabilizer measurements. We also compare the defect error rates when running stabilizer measurements individually and simultaneously to evidence the impact of crosstalk and leakage errors. |
Wednesday, March 8, 2023 3:36PM - 4:12PM |
Q64.00004: Recent experimental demonstrations: logical memory and an error-suppressed magic state with superconducting qubits Invited Speaker: Neereja Sundaresan In the pursuit of fault-tolerant quantum computation, recent hardware progress and improvements in control electronics, have provided new capabilities for performing real-time feedback useful to quantum error correction applications. In this talk we review two recent demonstrations on superconducting qubits in a heavy-hexagon lattice. In the first, we performed several rounds of fault-tolerant syndrome measurements on a distance three logical qubit. Comparing the performance of matching and maximum likelihood decoders, we observe logical error per round as low as ∼0.04 for the matching decoder and as low as ∼0.035 for the maximum likelihood decoder – underscoring the importance of improving decoders alongside quantum experiment. Next we focus on preparation of high-fidelity magic states, a necessary component for universal fault-tolerant computation that is experimentally hampered by the large resource overhead of distilling magic states in pre-fault tolerant quantum devices. In this work, we decrease this overhead by reducing the error rate of the physical system at the initial preparation step of a distillation protocol. Drawing on key properties of an error-detecting code, we propose and demonstrate a protocol to suppress the state-preparation error of a two-qubit magic state, that we call the 'CZ state'. We highlight how this error-suppressed magic-state preparation protocol further benefits from reduced resource cost by the addition of a single classically controlled unitary operation. |
Wednesday, March 8, 2023 4:12PM - 4:24PM |
Q64.00005: Hybrid cat-transmon architecture for scalable, hardware-efficient quantum error correction Connor T Hann, Christopher Chamberland, Harald Putterman, Joseph Iverson, Arne Grimsmo, Oskar Painter, Fernando Brandao, Kyungjoo Noh Dissipative cat qubits are a promising physical platform for quantum computing, since their large noise bias can enable more hardware-efficient quantum error correction. However, implementing high-fidelity, bias-preserving gates between dissipative cats is experimentally challenging, requiring both low loss and strong engineered dissipation. To circumvent these onerous experimental requirements, we propose a scalable quantum computing architecture where dissipative cat qubits are concatenated into repetition or surface codes, and syndromes are measured using ancillary transmon qubits. The use of transmons, rather than cats, as ancillary qubits significantly eases requirements on loss and engineered dissipation, while the use of cats as data qubits means the benefits of biased noise are retained. To analyze the architecture, we propose implementations of bias-preserving cat-transmon entangling gates, benchmark their performance with master equation simulations, and feed the results into error correction simulations of repetition and surface codes (both XZZX and CSS). We find a significant increase in the error correction threshold relative to an all-cat architecture, a promising sign for near-term experimental implementations. |
Wednesday, March 8, 2023 4:24PM - 4:36PM |
Q64.00006: Performance of surface codes with imperfect erasure detection Kathleen M Chang, Shraddha Singh, Kaavya Sahay, Robert J Schoelkopf, Steven M Girvin, Shruti Puri It is known that surface codes are highly effective at correcting erasures, that is, unknown errors at known locations. With this motivation, one recent work by Wu et al. [Nat Commun 13, 4657 (2022)] tailored the noise channel of a neutral atom qubit so that the dominant decay errors in the system could be detected with η=100% efficiency. The noise channel in this system is described by erasure errors which occur at high rate and Pauli errors which occur at a low rate. In this work, we consider the situation when the erasure-conversion efficiency (η) is not 100%. We numerically analyze the performance of the surface code under this noise model, estimate the thresholds, and determine logical error scaling as a function of η. Our results are important to design near-term experiments and also identify other platforms where it may be possible to achieve good (albeit imperfect) erasure conversion. |
Wednesday, March 8, 2023 4:36PM - 4:48PM |
Q64.00007: Complete leakage removal in the surface code on superconducting qubits - Part 1 Matthew J McEwen, Kevin C Miao, Juan Atalaya, Daniel T Sank, Yu Chen Quantum error correction can suppress errors only when they are sufficiently uncorrelated. During computation, unused higher energy levels of superconducting qubits can become excited, creating leakage states that are long-lived and mobile. These states induce a large number of correlated error detections, playing an outsized role in producing logical errors. Further, the population accumulates in these states as the code is extended in time, and is a limiting factor in cutting-edge QEC experiments. Here, we study the dynamics of such leakage events in the context of the surface code error correction circuit, showing how leakage spreads in space and time. Finally, we summarize the state of the art in the impact of leakage on cutting-edge surface code experiments. |
Wednesday, March 8, 2023 4:48PM - 5:00PM |
Q64.00008: Complete leakage removal in the surface code on superconducting qubits - Part 2 Kevin C Miao, Matthew J McEwen, Juan Atalaya, Daniel T Sank, Yu Chen Removing excitations from non-computational (leakage) states is an essential challenge in achieving stable quantum error correction. We present the experimental realization of a distance-3 surface code with leakage removed on all qubits in each error correction cycle. We show that leakage populations over all qubits stabilize at 0.1%, and remain low as the code is extended in time. Furthermore, this leakage removal strategy also stabilizes the rate of detected errors and improves logical performance, resolving a major challenge for the field. Finally, when this leakage removal strategy is incorporated into a distance-21 repetition code, we minimize differences in logical performance under the influence of injected leakage errors when compared to injected Pauli errors, confirming that the correlated nature of leakage errors has been successfully mitigated. |
Wednesday, March 8, 2023 5:00PM - 5:12PM |
Q64.00009: Star Code: Experimental Demonstration of Autonomous Error Correction with Two-Qutrits (Part I Theory) Tanay Roy, Ziqian Li, David Rodriguez Perez, Eliot Kapit, David Schuster Large-scale future quantum computers will need quantum error correction (QEC) to protect fragile quantum information against decoherence. Autonomous quantum error correction (AQEC) is one hardware-efficient path that avoids feedback control and fast high-fidelity readout. The very small logical qubit (VSLQ) is one of the AQEC proposals requiring only two qutrits and two lossy resonators to protect against the single-photon loss, the dominating source of error [1]. We develop a new protocol, called the star code, that utilizes only two-photon beam-splitting and squeezing processes to preserve a logical qubit. The scheme's simplicity provides the potential for adoption in any linear two-qutrit coupler device. Our simulations indicate significant improvements in logical qubit lifetimes and suppression of dephasing noise. We discuss the design choices for the successful realization of the star code. |
Wednesday, March 8, 2023 5:12PM - 5:24PM |
Q64.00010: Star Code: Experimental Demonstration of Autonomous Error Correction with Two-Qutrits (Part II Experiment) Ziqian Li, Tanay Roy, David Rodriguez Perez, Eliot Kapit, David Schuster The implementation of the star code requires strong qutrit-qutrit (QQ) red (beam-splitting) and blue (two-photon squeezing) sideband interactions. We develop a coherence-preserving inductive coupler capable of providing individual sideband rates larger than 5 MHz while suppressing residual static cross-Kerr strength below 300 kHz. Utilizing this linear coupler for the star code scheme, we experimentally demonstrate lifetime improvements of the logical zero |L0>, logical one |L1>, and logical superposition states by factors of 3.2, 5.6, and 3.7 respectively. Among these, the lifetime of |L0> surpasses the longest coherence time in the system achieving partial-breakeven performance. To our knowledge, this is the first such realization in a transmon-based system with autonomous error correction. |
Wednesday, March 8, 2023 5:24PM - 5:36PM |
Q64.00011: Error correcting codes on near-term devices of quasi-linear and central-spin-like connectivity Regina Finsterhoelzl, Guido Burkard We evaluate the performance of small error-correcting codes which we implement on hardware platforms of very different connectivity and coherence: On a superconducting processor and on a spintronic quantum register consisting of a colour centre in diamond. Taking the hardware-specific errors and connectivity into account, we investigate the dependence of the resulting logical error rate on the platform features such as the native gates, the native connectivity, gate times and coherence times. We investigate different recovery schemes for the encoded quantum state based upon the classical information obtained by the measurement outcome. Using an error model parametrized for the given hardware, we simulate the performance and benchmark these predictions with experimental results when running the code on the superconducting processor. The results indicate that for small, low-weight parity check codes, the hexagonal, quasi-linear layout proves advantageous, yet for codes relying on controlled multi-qubit operations with high-weight stabilizers, the CSS-like connectivity and native Toffoli gate of the colour centre enables a favourable transpilation. |
Wednesday, March 8, 2023 5:36PM - 5:48PM |
Q64.00012: Scalable and robust reinforcement learning decoding of surface codes Alexandru Paler, Jerome Lenssen A key component of fault-tolerant quantum computing is error decoding. For most practical quantum computing platforms, the decoder needs to overcome severe time and space constraints. Neural network decoders for quantum error-correction codes have constant runtimes, but it is difficult to derive robustness guarantees. |
Wednesday, March 8, 2023 5:48PM - 6:00PM |
Q64.00013: Implementing leakage reduction units for quantum error correction with superconducting qubits Jorge F Marques, Hany Ali, Matvey Finkel, Hendrik M Veen, Sean van der Meer, Santiago Valles-Sanclemente, Boris Varbanov, Wouter Vlothuizen, Marc Beekman, Nadia Haider, Barbara M Terhal, Leonardo DiCarlo Leakage presents a major threat to quantum error correction with superconducting qubits. We present the realization of hardware-efficient leakage reduction units (LRU) in superconducting qubits in the context of quantum error correction. In particular, we show LRUs suitable for both ancilla and data qubits and benchmark their performance in the leakage and qubit subspaces. Finally, we assess the impact of the LRU operations on repeated stabilizer measurements in a 17-transmon device designed for the distance-3 surface code. |
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