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Klimov PV, Bengtsson A, Quintana C, Bourassa A, Hong S, Dunsworth A, Satzinger KJ, Livingston WP, Sivak V, Niu MY, Andersen TI, Zhang Y, Chik D, Chen Z, Neill C, Erickson C, Grajales Dau A, Megrant A, Roushan P, Korotkov AN, Kelly J, Smelyanskiy V, Chen Y, Neven H. Optimizing quantum gates towards the scale of logical qubits. Nat Commun 2024; 15:2442. [PMID: 38499541 PMCID: PMC10948820 DOI: 10.1038/s41467-024-46623-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2023] [Accepted: 03/04/2024] [Indexed: 03/20/2024] Open
Abstract
A foundational assumption of quantum error correction theory is that quantum gates can be scaled to large processors without exceeding the error-threshold for fault tolerance. Two major challenges that could become fundamental roadblocks are manufacturing high-performance quantum hardware and engineering a control system that can reach its performance limits. The control challenge of scaling quantum gates from small to large processors without degrading performance often maps to non-convex, high-constraint, and time-dynamic control optimization over an exponentially expanding configuration space. Here we report on a control optimization strategy that can scalably overcome the complexity of such problems. We demonstrate it by choreographing the frequency trajectories of 68 frequency-tunable superconducting qubits to execute single- and two-qubit gates while mitigating computational errors. When combined with a comprehensive model of physical errors across our processor, the strategy suppresses physical error rates by ~3.7× compared with the case of no optimization. Furthermore, it is projected to achieve a similar performance advantage on a distance-23 surface code logical qubit with 1057 physical qubits. Our control optimization strategy solves a generic scaling challenge in a way that can be adapted to a variety of quantum operations, algorithms, and computing architectures.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | - Alexander N Korotkov
- Google AI, Mountain View, CA, USA
- Department of Electrical and Computer Engineering, University of California, Riverside, CA, USA
| | | | | | - Yu Chen
- Google AI, Mountain View, CA, USA
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Livingston WP, Blok MS, Flurin E, Dressel J, Jordan AN, Siddiqi I. Experimental demonstration of continuous quantum error correction. Nat Commun 2022; 13:2307. [PMID: 35484135 DOI: 10.1038/s41467-022-29906-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Accepted: 04/06/2022] [Indexed: 11/09/2022] Open
Abstract
The storage and processing of quantum information are susceptible to external noise, resulting in computational errors. A powerful method to suppress these effects is quantum error correction. Typically, quantum error correction is executed in discrete rounds, using entangling gates and projective measurement on ancillary qubits to complete each round of error correction. Here we use direct parity measurements to implement a continuous quantum bit-flip correction code in a resource-efficient manner, eliminating entangling gates, ancillary qubits, and their associated errors. An FPGA controller actively corrects errors as they are detected, achieving an average bit-flip detection efficiency of up to 91%. Furthermore, the protocol increases the relaxation time of the protected logical qubit by a factor of 2.7 over the relaxation times of the bare comprising qubits. Our results showcase resource-efficient stabilizer measurements in a multi-qubit architecture and demonstrate how continuous error correction codes can address challenges in realizing a fault-tolerant system.
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Affiliation(s)
- William P Livingston
- Department of Physics, University of California, Berkeley, CA, 94720, USA. .,Center for Quantum Coherent Science, University of California, Berkeley, CA, 94720, USA.
| | - Machiel S Blok
- Department of Physics, University of California, Berkeley, CA, 94720, USA.,Center for Quantum Coherent Science, University of California, Berkeley, CA, 94720, USA.,Department of Physics and Astronomy, University of Rochester, Rochester, NY, 14627, USA
| | - Emmanuel Flurin
- Université Paris-Saclay, CEA, CNRS, SPEC, 91191, Gif-sur-Yvette Cedex, France
| | - Justin Dressel
- Institute for Quantum Studies, Chapman University, Orange, CA, 92866, USA.,Schmid College of Science and Technology, Chapman University, Orange, CA, 92866, USA
| | - Andrew N Jordan
- Department of Physics and Astronomy, University of Rochester, Rochester, NY, 14627, USA.,Institute for Quantum Studies, Chapman University, Orange, CA, 92866, USA
| | - Irfan Siddiqi
- Department of Physics, University of California, Berkeley, CA, 94720, USA.,Center for Quantum Coherent Science, University of California, Berkeley, CA, 94720, USA
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