Quantum squeezing in a nonlinear mechanical oscillator

TL;DR

This paper demonstrates ground state squeezing and non-Gaussian state preparation in a GHz mechanical resonator coupled to a superconducting qubit, advancing quantum information processing and sensing capabilities.

Contribution

It introduces a method to generate mechanical squeezing and tunable nonlinearities in a GHz resonator via qubit coupling, enabling non-Gaussian state engineering.

Findings

Ground state squeezing of a GHz mechanical resonator achieved.

Preparation of non-Gaussian quantum states with Wigner negativities.

Tunable nonlinearity inherited from qubit-resonator coupling.

Abstract

Mechanical degrees of freedom are natural candidates for continuous-variable quantum information processing and bosonic quantum simulations. These applications, however, require the engineering of squeezing and nonlinearities in the quantum regime. Here we demonstrate ground state squeezing of a gigahertz-frequency mechanical resonator coupled to a superconducting qubit. This is achieved by parametrically driving the qubit, which results in an effective two-phonon drive. In addition, we show that the resonator mode inherits a nonlinearity from the off-resonant coupling with the qubit, which can be tuned by controlling the detuning. We thus realize a mechanical squeezed Kerr oscillator, where we demonstrate the preparation of non-Gaussian quantum states of motion with Wigner function negativities and high quantum Fisher information. This shows that our results also have applications in quantum metrology and sensing.