| CPC G06N 10/70 (2022.01) | 26 Claims |
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1. An apparatus for performing a logical n-qubit Greenberger-Horne-Zeilinger (GHZ) measurement on n≥3 logical qubits, the apparatus comprising:
an optical circuit comprising:
an interferometer configured to:
receive, as a plurality of input optical modes, the n logical qubits;
interfere the n logical qubits; and
output the interfered n logical qubits as output optical modes; and
a detector arrangement comprising a plurality of photon detectors to measure a photon occupation of each of the output optical modes; and
control logic coupled to the detector arrangement;
wherein each logical qubit of the n logical qubits comprises a first Calderbank-Shor-Steane-encoded (CSS-encoded) qubit;
wherein at least (n−2) of the n logical qubits further comprise a second CSS-encoded qubit, the first and second CSS-encoded qubits together comprising a repetition-encoded qubit;
wherein each CSS-encoded qubit comprises a plurality of dual-rail encoded photonic qubits, each dual-rail encoded photonic qubit encoded as probability amplitudes corresponding to the photon occupation of two orthogonal optical modes;
wherein interfering the n logical qubits comprises interfering a CSS-encoded qubit of the jth logical qubit with a CSS-encoded qubit of the (j+1)th logical qubit, for all j between 1 and n−1;
wherein interfering a first CSS-encoded qubit with a second CSS-encoded qubit comprises interfering optical modes of each dual-rail encoded photonic qubit of the first CSS-encoded qubit with optical modes of a corresponding dual-rail encoded photonic qubit of the second CSS-encoded qubit; and
wherein the control logic is configured to:
receive an indication from the detector arrangement whether a dual-rail Bell state measurement (DR-BSM) has been performed on each interfered pair of dual-rail encoded photonic qubits; and
determine, from the indication, that a logical n-qubit GHZ measurement has been performed on the n logical qubits.
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