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Degeneracy-preserving quantum non-demolition measurement of parity-type observables for cat-qubits

Joachim Cohen 1 W. Clarke Smith 2 Michel H. Devoret 2 Mazyar Mirrahimi 1, 2 
1 QUANTIC - QUANTum Information Circuits
ENS-PSL - École normale supérieure - Paris, UPMC - Université Pierre et Marie Curie - Paris 6, Mines Paris - PSL (École nationale supérieure des mines de Paris), Inria de Paris
Abstract : A central requirement for any quantum error correction scheme is the ability to perform quantum non-demolition measurements of an error syndrome, corresponding to a special symmetry property of the encoding scheme. It is in particular important that such a measurement does not introduce extra error mechanisms, not included in the error model of the correction scheme. In this letter, we ensure such a robustness by designing an interaction with a measurement device that preserves the degeneracy of the measured observable. More precisely, we propose a scheme to perform continuous and quantum non-demolition measurement of photon-number parity in a microwave cavity. This corresponds to the error syndrome in a class of error correcting codes called the cat-codes, which have recently proven to be efficient and versatile for quantum information processing. In our design, we exploit the strongly nonlinear Hamiltonian of a high-impedance Josephson circuit, coupling a high-Q cavity storage cavity mode to a low-Q readout one. By driving the readout resonator at its resonance, the phase of the reflected/transmitted signal carries directly exploitable information on parity-type observables for encoded cat-qubits of the high-Q mode.
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Submitted on : Tuesday, January 17, 2017 - 10:27:32 AM
Last modification on : Friday, November 18, 2022 - 9:26:29 AM

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Joachim Cohen, W. Clarke Smith, Michel H. Devoret, Mazyar Mirrahimi. Degeneracy-preserving quantum non-demolition measurement of parity-type observables for cat-qubits. Physical Review Letters, 2017, ⟨10.1103/PhysRevLett.119.060503⟩. ⟨hal-01437156⟩



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