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Dual-rail quantum code[13]

Description

Two-mode bosonic code encoding a logical qubit in Fock states with one excitation. The logical-zero state is represented by \(|10\rangle\), while the logical-one state is represented by \(|01\rangle\). This encoding is often realized in temporal or spatial modes, corresponding to a time-bin or frequency-bin encoding. Two different types of photon polarization can also be used.

This code is a DFS [47] with respect to phase errors [8].

Protection

This is an error-detecting code against one photon loss event; it is often used in photonic quantum devices because of its ease of realization. A single loss event can be detected because, after the loss occurs, the output state \(|00\rangle\) is orthogonal to the codespace. Recovery is not possible, so a successful run of a quantum circuit is conditioned on not losing a photon during the circuit.

For Deutsch''s problem specifically, this code protects against errors resulting in states that have the correct photon number, but in the wrong modes [9].

Encoding

Optimal control pulses [10]

Gates

General gates are performed using two-body Hamiltonian rotations [8].Bosonic gates include beamsplitters [11] and Kerr nonlinearities. Universal quantum computing can be achieved using the KLM protocol [12] with only linear optical elements and photon detectors.Dynamical-decoupling protocols [8,13].A probabilistic CZ gate via a non-linear sign-shift gate, which transforms the Fock states \( \alpha|0\rangle+\beta|1\rangle+\gamma|2\rangle\) into \(\alpha|0\rangle+\beta|1\rangle-\gamma|2\rangle \), followed by measurement [14].Error-detecting \(CCZ\) and \(cSWAP\) gates using three-level ancilla [15].

Fault Tolerance

Dual-rail qubits can be used to convert leakage and AD noise into erasure noise [16,17].

Realizations

The dual-rail code is ubiquitous in linear-optical quantum devices and is behind the KLM protocol, one of the first proposals for fault-tolerant computation. See reviews [1820] for more details.Superconducting circuit devices: Gates have been demonstrated in the Schoelkopf group at Yale University [11]. Error detection has been demonstrated in 3D cavities in the Devoret group at Yale University [10] and Amazon Web Services [21] using transmon qubits, following earlier theoretical proposals [17,22]. Logical readout in 3D cavities has been demonstrated by Quantum Circuits Inc. [23].Photonic platforms: state preparation and measurement fidelity of \(99.98\%\) in the C telecom band by PsiQuantum [24].

Cousins

  • Concatenated bosonic code— The KLM protocol, one of the first protocols for fault-tolerant quantum computation, utilizes concatenations of the dual-rail code with a stabilizer code such as the Steane code [12,25,26]. Concatenating the dual-rail code with an \([[n,k,d]]\) stabilizer code yields an \([[2n,k,d]]\) constant-excitation code [27] that protects against \(d-1\) AD errors [28]. Concatenating the outer dual-rail code with an inner single-mode bosonic code yields several gates that are independent of the inner code [29].
  • \([[7,1,3]]\) Steane code— The KLM protocol, one of the first protocols for fault-tolerant quantum computation, utilizes concatenations of the dual-rail code with a stabilizer code such as the Steane code [12,25,26].
  • Single-mode bosonic code— Concatenating the outer dual-rail code with an inner single-mode bosonic code yields several gates that are independent of the inner code [29].
  • Amplitude-damping (AD) code— Dual-rail qubits can be used to convert leakage and AD noise into erasure noise [16,17]. Concatenating the dual-rail code with an \([[n,k,d]]\) stabilizer code yields an \([[2n,k,d]]\) constant-excitation code [27] that protects against \(d-1\) AD errors [28].
  • Quantum parity code (QPC)— An \([[8,1,2]]\) QPC correcting a single AD error is equivalent to a concatenation of the \(\{|\overline{01}\rangle,|\overline{11}\rangle\}\) (constant-excitation) subcode of the \([[4,2,2]]\) code with the dual-rail code [27,30,31]. More generally, an \([[m^2,1,m]]\) QPC corrects \(m-1\) AD errors [28].
  • \([[4,2,2]]\) Four-qubit code— An \([[8,1,2]]\) QPC correcting a single AD error is equivalent to a concatenation of the \(\{|\overline{01}\rangle,|\overline{11}\rangle\}\) (constant-excitation) subcode of the \([[4,2,2]]\) code with the dual-rail code [27,30,31]. More generally, an \([[m^2,1,m]]\) QPC corrects \(m-1\) AD errors [28].
  • Cluster-state code— The KLM protocol can be combined with cluster states in various ways to yield MBQC protocols [3234]; see review [20].
  • Fusion-based quantum computing (FBQC) code— FBQC resource states are concatenated with dual-rail codes to increase loss detection.

References

[1]
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[2]
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D. Bacon, D. A. Lidar, and K. B. Whaley, “Robustness of decoherence-free subspaces for quantum computation”, Physical Review A 60, 1944 (1999) arXiv:quant-ph/9902041 DOI
[6]
D. A. Lidar, D. Bacon, J. Kempe, and K. B. Whaley, “Decoherence-free subspaces for multiple-qubit errors. I. Characterization”, Physical Review A 63, (2001) arXiv:quant-ph/9908064 DOI
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[8]
M. S. Byrd and D. A. Lidar, “Combined error correction techniques for quantum computing architectures”, Journal of Modern Optics 50, 1285 (2003) arXiv:quant-ph/0210072 DOI
[9]
I. L. Chuang and Y. Yamamoto, “Simple quantum computer”, Physical Review A 52, 3489 (1995) DOI
[10]
A. Koottandavida et al., “Erasure detection of a dual-rail qubit encoded in a double-post superconducting cavity”, (2023) arXiv:2311.04423
[11]
Y. Lu, A. Maiti, J. W. O. Garmon, S. Ganjam, Y. Zhang, J. Claes, L. Frunzio, S. M. Girvin, and R. J. Schoelkopf, “High-fidelity parametric beamsplitting with a parity-protected converter”, Nature Communications 14, (2023) DOI
[12]
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[13]
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[14]
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[15]
T. Tsunoda, J. D. Teoh, W. D. Kalfus, S. J. de Graaf, B. J. Chapman, J. C. Curtis, N. Thakur, S. M. Girvin, and R. J. Schoelkopf, “Error-detectable bosonic entangling gates with a noisy ancilla”, (2022) arXiv:2212.11196
[16]
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[17]
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[18]
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[19]
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[20]
S. Slussarenko and G. J. Pryde, “Photonic quantum information processing: A concise review”, Applied Physics Reviews 6, (2019) arXiv:1907.06331 DOI
[21]
H. Levine et al., “Demonstrating a Long-Coherence Dual-Rail Erasure Qubit Using Tunable Transmons”, Physical Review X 14, (2024) arXiv:2307.08737 DOI
[22]
J. D. Teoh et al., “Dual-rail encoding with superconducting cavities”, Proceedings of the National Academy of Sciences 120, (2023) arXiv:2212.12077 DOI
[23]
K. S. Chou et al., “Demonstrating a superconducting dual-rail cavity qubit with erasure-detected logical measurements”, (2023) arXiv:2307.03169
[24]
K. Alexander et al., “A manufacturable platform for photonic quantum computing”, (2024) arXiv:2404.17570
[25]
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[26]
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[27]
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[28]
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[29]
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[30]
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[31]
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[32]
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[33]
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[34]
D. E. Browne and T. Rudolph, “Resource-Efficient Linear Optical Quantum Computation”, Physical Review Letters 95, (2005) arXiv:quant-ph/0405157 DOI
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Zoo Code ID: dual_rail

Cite as:
“Dual-rail quantum code”, The Error Correction Zoo (V. V. Albert & P. Faist, eds.), 2024. https://errorcorrectionzoo.org/c/dual_rail
BibTeX:
@incollection{eczoo_dual_rail, title={Dual-rail quantum code}, booktitle={The Error Correction Zoo}, year={2024}, editor={Albert, Victor V. and Faist, Philippe}, url={https://errorcorrectionzoo.org/c/dual_rail} }
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“Dual-rail quantum code”, The Error Correction Zoo (V. V. Albert & P. Faist, eds.), 2024. https://errorcorrectionzoo.org/c/dual_rail

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