Fock-state bosonic code


Qudit-into-oscillator code whose protection against amplitude damping (i.e., photon loss) stems from the use of disjoint sets of Fock states for the construction of each code basis state. The simplest example is the dual-rail code, which has codewords consisting of single Fock states \(|10\rangle\) and \(|01\rangle\). This code can detect a single loss error since a loss operator in either mode maps one of the codewords to a different Fock state \(|00\rangle\). More involved codewords consist of several well-separated Fock states such that multiple loss events can be detected and corrected.


Code distance \(d\) is the minimum distance (assuming some metric) between any two labels of Fock states corresponding to different code basis states. For a single mode, \(d\) is the minimum absolute value of the difference between any two Fock-state labels; such codes can detect up to \(d-1\) loss events. Multimode distances can be defined analogously; see, e.g., Chuang-Leung-Yamamoto codes.




  • Binary code — Fock-state code distance is a natural extension of Hamming distance between binary strings.
  • Qubit code — Fock-state code whose codewords are finite superpositions of Fock states with maximum occupation \(N\) can be mapped into a qubit code with \(n\geq\log_2 N\) by performing a binary expansion of the Fock-state labels \(n\) and treating each binary digit as an index for a qubit state. Pauli operators for the constituent qubits can be expressed in terms of bosonic raising and lowering operators [1]. However, noise models for the two code families induce different notions of locality and thus qualitatively different physical interpretations [2].
  • Fusion-based quantum computing (FBQC) code — While FBQC is a general framework, an intended application to linear-optical quantum computing will likely utilize small Fock-state bosonic codes such as the dual-rail code.


Victor V. Albert, private communication, 2016
Steven M. Girvin, “Introduction to Quantum Error Correction and Fault Tolerance”. 2111.08894
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“Fock-state bosonic code”, The Error Correction Zoo (V. V. Albert & P. Faist, eds.), 2022.
@incollection{eczoo_fock_state, title={Fock-state bosonic code}, booktitle={The Error Correction Zoo}, year={2022}, editor={Albert, Victor V. and Faist, Philippe}, url={} }
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“Fock-state bosonic code”, The Error Correction Zoo (V. V. Albert & P. Faist, eds.), 2022.