Homodyne measurement with a Schrödinger cat state as a local oscillator

Abstract

Homodyne measurements are a widely used quantum measurement. Using a coherent state of large amplitude as the local oscillator, it can be shown that the quantum homodyne measurement limits to a field quadrature measurement. In this work, we give an example of a general idea: injecting non-classical states as a local oscillator can led to non-classical measurements. Specifically we consider injecting a superposition of coherent states, a Schrödinger cat state, as a local oscillator. We derive the Kraus operators and the positive operator-valued measure (POVM) in this situation and show the POVM is a reflection symmetric quadrature measurement when the coherent state amplitudes are large.

Two-photon driven Kerr quantum oscillator with multiple spectral degeneracies

“…The bit-flip errors, which correspond to a transition from one coherent state to the other, are suppressed exponentially with their phase space separation, while the phase-flip errors only increase linearly [13]. This tunable noise bias leads to important reductions of hardware overhead for quantum error correction [14][15][16]. The recent proposal of bias-preserving gates [17,18] has paved the way towards hardware-efficient fault-tolerant and universal quantum processors based on such qubits [19][20][21].…”