Three-qubit direct dispersive parity measurement with tunable coupling qubits

Ciani, Alessandro; DiVincenzo, David P.

doi:10.1103/physrevb.96.214511

Cited by 12 publications

(9 citation statements)

References 44 publications

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“…As such, we have ignored other sources of infidelity, particularly dephasing of the parity subspaces due to imperfect overlap of the entangled microwave fields, which is analogous to ignoring entangling gate infidelity in analyses of ancilla-based error correction. Some analysis of these types of implementation imperfections has begun in recent years [58][59][60][61], but more investigation is needed for a definitive assessment. Second, while we have presented a practical method for directly measuring the ZZ parities needed for bit-flip correction, we have not addressed how to directly measure the XX parities needed for additional phase-flip correction.…”

Section: Discussionmentioning

confidence: 99%

Always-On Quantum Error Tracking with Continuous Parity Measurements

Mohseninia

Yang

Siddiqi

et al. 2020

Quantum

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We investigate quantum error correction using continuous parity measurements to correct bit-flip errors with the three-qubit code. Continuous monitoring of errors brings the benefit of a continuous stream of information, which facilitates passive error tracking in real time. It reduces overhead from the standard gate-based approach that periodically entangles and measures additional ancilla qubits. However, the noisy analog signals from continuous parity measurements mandate more complicated signal processing to interpret syndromes accurately. We analyze the performance of several practical filtering methods for continuous error correction and demonstrate that they are viable alternatives to the standard ancilla-based approach. As an optimal filter, we discuss an unnormalized (linear) Bayesian filter, with improved computational efficiency compared to the related Wonham filter introduced by Mabuchi [New J. Phys. 11, 105044 (2009)]. We compare this optimal continuous filter to two practical variations of the simplest periodic boxcar-averaging-and-thresholding filter, targeting real-time hardware implementations with low-latency circuitry. As variations, we introduce a non-Markovian ``half-boxcar'' filter and a Markovian filter with a second adjustable threshold; these filters eliminate the dominant source of error in the boxcar filter, and compare favorably to the optimal filter. For each filter, we derive analytic results for the decay in average fidelity and verify them with numerical simulations.

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Section: Discussionmentioning

confidence: 99%

Always-On Quantum Error Tracking with Continuous Parity Measurements

Mohseninia

Yang

Siddiqi

et al. 2020

Quantum

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“…The picture changes qualitatively if entanglement is instead generated using native two-body measurements -a context for which this code is optimized [1]. Direct two-body measurements have been proposed and demonstrated experimentally in circuit QED [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31], and are expected to be the native operation in Majorana-based architectures [1,14,32]. In this setting, we observe a honeycomb code threshold between 1.5% and 2.0% -by comparison, previous work reported a surface code threshold of 0.237% in the same error model [14] (but using a less accurate union-find decoder).…”

Section: Summary Of Resultsmentioning

confidence: 99%

A Fault-Tolerant Honeycomb Memory

Gidney,

Newman,

Fowler

et al. 2021

Preprint

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Recently, Hastings & Haah introduced a quantum memory defined on the honeycomb lattice [1]. Remarkably, this honeycomb code assembles weight-six parity checks using only two-local measurements. The sparse connectivity and two-local measurements are desirable features for certain hardware, while the weight-six parity checks enable robust performance in the circuit model.In this work, we quantify the robustness of logical qubits preserved by the honeycomb code using a correlated minimum-weight perfect-matching decoder. Using Monte Carlo sampling, we estimate the honeycomb code's threshold in different error models, and project how efficiently it can reach the "teraquop regime" where trillions of quantum logical operations can be executed reliably. We perform the same estimates for the rotated surface code, and find a threshold of 0.2% − 0.3% for the honeycomb code compared to a threshold of 0.5% − 0.7% for the surface code in a controlled-not circuit model. In a circuit model with native two-body measurements, the honeycomb code achieves a threshold of 1.5% < p < 2.0%, where p is the collective error rate of the two-body measurement gate -including both measurement and correlated data depolarization error processes. With such gates at a physical error rate of 10 −3 , we project that the honeycomb code can reach the teraquop regime with only 600 physical qubits.

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“…This can to some extent already be achieved with a small atom, whose single coupling point can be at a node for some modes and at an antinode for others. However, we note that a recent theory proposal (Ciani and DiVincenzo 2017) uses a superconducting qubit with tunable coupling connected at multiple points to two resonators to cancel certain unwanted interaction terms while keeping desired interaction terms; it is shown that this would not have been possible with a small atom.…”

Section: Coupling a Giant Atom To A Cavitymentioning

confidence: 92%

Quantum Optics with Giant Atoms—the First Five Years

Kockum

2020

Mathematics for Industry

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In quantum optics, it is common to assume that atoms can be approximated as point-like compared to the wavelength of the light they interact with. However, recent advances in experiments with artificial atoms built from superconducting circuits have shown that this assumption can be violated. Instead, these artificial atoms can couple to an electromagnetic field at multiple points, which are spaced wavelength distances apart. In this chapter, we present a survey of such systems, which we call giant atoms. The main novelty of giant atoms is that the multiple coupling points give rise to interference effects that are not present in quantum optics with ordinary, small atoms. We discuss both theoretical and experimental results for single and multiple giant atoms, and show how the interference effects can be used for interesting applications. We also give an outlook for this emerging field of quantum optics.

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Three-qubit direct dispersive parity measurement with tunable coupling qubits

Cited by 12 publications

References 44 publications

Always-On Quantum Error Tracking with Continuous Parity Measurements

Always-On Quantum Error Tracking with Continuous Parity Measurements

A Fault-Tolerant Honeycomb Memory

Quantum Optics with Giant Atoms—the First Five Years

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