Mechanical Squeezed-Fock Qubit: Towards Quantum Weak-Force Sensing

TL;DR

This paper introduces a novel mechanical squeezed-Fock qubit using squeezed phonon states in a nonlinear oscillator, significantly enhancing weak-force sensing capabilities and coherence properties.

Contribution

It proposes a new type of mechanical qubit based on squeezed Fock states with exponentially increased anharmonicity for improved quantum sensing.

Findings

Squeezed Fock states become eigenstates under two-phonon driving.

Energy spectrum exhibits exponentially enhanced and tunable anharmonicity.

Mechanical squeezed-Fock qubit sensitivity exceeds traditional qubits by at least ten times.

Abstract

Mechanical qubits offer unique advantages over other qubit platforms, primarily in terms of coherence time and possibilities for enhanced sensing applications, but their potential is constrained by the inherently weak nonlinearities and small anharmonicity of nanomechanical resonators. We propose to overcome this shortcoming by using squeezed Fock states of phonons in a parametrically driven nonlinear mechanical oscillator. We find that, under two-phonon driving, squeezed Fock states become eigenstates of a Kerr-nonlinear mechanical oscillator, featuring an energy spectrum with exponentially enhanced and tunable anharmonicity, such that the transitions to higher energy states are exponentially suppressed. This enables us to encode the mechanical qubit within the ground and first excited squeezed Fock states of the driven mechanical oscillator. This kind of mechanical qubit is termed mechanical squeezed-Fock qubit. We also show that our mechanical qubit can serve as a quantum sensor for weak forces, with its resulting sensitivity increased by at least one order of magnitude over that of traditional mechanical qubits. The proposed mechanical squeezed-Fock qubit provides a powerful quantum phonon platform for quantum sensing and information processing.