Oscillator state reconstruction via tunable qubit coupling in Markovian environments

TL;DR

This paper presents a method using a tunable qubit to fully reconstruct the quantum state of a harmonic oscillator in Markovian environments, effectively filtering decoherence effects and enabling state estimation and superposition preparation.

Contribution

It introduces a novel approach for quantum state reconstruction of oscillators via tunable qubit coupling, applicable even under decoherence, with potential for nanomechanical systems.

Findings

Full quantum state reconstruction is achievable despite decoherence.

The method allows estimation of low order quadrature moments.

Superposition states of the oscillator can be prepared using the framework.

Abstract

We show that a parametrically coupled qubit can be used to fully reconstruct the quantum state of a harmonic oscillator, even when both systems are subject to decoherence. By controlling the coupling strength of the qubit over time, the characteristic function of the oscillator at any phase space point can be directly measured by combining the expectation values of two Pauli operators. The effect of decoherence can be filtered out from the measured data, provided a sufficient number of experimental runs is performed. In situations where full state reconstruction is not practical or not necessary, the method can still be used to estimate low order moments of the mechanical quadratures. We also show that in the same framework it is possible to prepare superposition states of the oscillator. The model is very general but particularly appropriate for nanomechanical systems.