Stationary Entangled Radiation from Micromechanical Motion

TL;DR

This paper demonstrates the stationary emission of path-entangled microwave radiation from a silicon nanostring mechanical oscillator, revealing non-classical correlations and quantum discord, advancing hybrid quantum technology.

Contribution

It reports the first observation of stationary entangled microwave radiation from a mechanical oscillator, showing non-classical correlations without direct measurement of the oscillator's state.

Findings

Squeezing of joint field operators by 3.40 dB below vacuum level.

Correlations up to 50 photons/s/Hz observed.

Robust quantum discord despite microwave noise.

Abstract

Mechanical systems facilitate the development of a new generation of hybrid quantum technology comprising electrical, optical, atomic and acoustic degrees of freedom. Entanglement is the essential resource that defines this new paradigm of quantum enabled devices. Continuous variable (CV) entangled fields, known as Einstein-Podolsky-Rosen (EPR) states, are spatially separated two-mode squeezed states that can be used to implement quantum teleportation and quantum communication. In the optical domain, EPR states are typically generated using nondegenerate optical amplifiers and at microwave frequencies Josephson circuits can serve as a nonlinear medium. It is an outstanding goal to deterministically generate and distribute entangled states with a mechanical oscillator. Here we observe stationary emission of path-entangled microwave radiation from a parametrically driven 30 micrometer long silicon nanostring oscillator, squeezing the joint field operators of two thermal modes by 3.40(37) dB below the vacuum level. This mechanical system correlates up to 50 photons/s/Hz giving rise to a quantum discord that is robust with respect to microwave noise. Such generalized quantum correlations of separable states are important for quantum enhanced detection and provide direct evidence for the non-classical nature of the mechanical oscillator without directly measuring its state. This noninvasive measurement scheme allows to infer information about otherwise inaccessible objects with potential implications in sensing, open system dynamics and fundamental tests of quantum gravity. In the near future, similar on-chip devices can be used to entangle subsystems on vastly different energy scales such as microwave and optical photons.