Quadrature readout and generation of squeezed states of a harmonic oscillator using a qubit-based indirect measurement
Abstract
We present a protocol for measuring the quadrature of a harmonic oscillator (HO). The HO is coupled to a qubit, with an interaction modulated by the qubit control and effectively proportional to the HO quadrature I. Repeated measurement of the qubit leads to gradually increasing information on the quadrature I, leading to squeezing. We derive an analytical formula for the quadrature variance, ( I)2 = 1/(1+4φ2 s), with φ the product of interaction strength and interaction time and s the number of repetitions of the measurement. We discuss the robustness of this scheme against decoherence. We find that this protocol could lead to significant squeezing in a realistic setup formed of a superconducting flux qubit used to measure an electrical or mechanical resonator.