A squeezed mechanical oscillator with milli-second quantum decoherence

TL;DR

This paper demonstrates a superconducting circuit optomechanical system with ultra-low quantum decoherence, enabling high-fidelity ground and squeezed states of motion, and preserving non-classical states over milliseconds, advancing quantum control of macroscopic systems.

Contribution

Introduces a novel superconducting circuit platform achieving significantly reduced quantum decoherence, facilitating high-fidelity quantum state preparation and long-lived mechanical squeezing.

Findings

Thermal decoherence rate of 20.5 Hz (T_1 = 7.7 ms)

Pure dephasing rate of 0.09 Hz

Mechanical squeezing of -2.7 dB below zero-point-fluctuation

Abstract

An enduring challenge in constructing mechanical oscillator-based hybrid quantum systems is to ensure engineered coupling to an auxiliary degree of freedom while maintaining good mechanical isolation from the environment, that is, low quantum decoherence, consisting of thermal decoherence and dephasing. Here, we overcome this challenge by introducing a superconducting circuit optomechanical platform which exhibits a low quantum decoherence while having a large optomechanical coupling, which allows us to prepare the quantum ground and squeezed states of motion with high fidelity. We directly measure a thermal decoherence rate of 20.5 Hz (corresponding to T_1 = 7.7 ms) as well as a pure dephasing rate of 0.09 Hz, resulted in a 100-fold improvement of quantum-state lifetime compared to the prior optomechanical systems. This enables us to reach to 0.07 quanta motional ground state occupation (93% fidelity) and realize mechanical squeezing of -2.7 dB below zero-point-fluctuation. Furthermore, we observe the free evolution of mechanical squeezed state, preserving its non-classical nature over milli-second timescales. Such ultra-low quantum decoherence not only increases the fidelity of quantum control and measurement of macroscopic mechanical systems, but may also benefit interfacing with qubits, and places the system in a parameter regime suitable for tests of quantum gravity. (Keywords: Quantum optomechanics, Superconducting circuit electromechanics, Quantum squeezing, Quantum memory, Quantum coherence)