Controllable coupling between a nanomechanical resonator and a coplanar-waveguide resonator via a superconducting flux qubit

TL;DR

This paper demonstrates a controllable quantum coupling between a nanomechanical resonator and a coplanar-waveguide resonator mediated by a flux qubit, enabling tunable photon transport and potential quantum routing.

Contribution

It introduces a method to achieve magnetic-field-controlled strong coupling in a hybrid quantum system involving a flux qubit, a nanomechanical resonator, and a CPW resonator.

Findings

Vacuum Rabi splitting observed in voltage-fluctuation spectrum.

Reflectance and phase shift spectra show tunable narrow spectral features.

System can function as a controllable quantum router.

Abstract

We study a tripartite quantum system consisting of a coplanar-waveguide (CPW) resonator and a nanomechanical resonator (NAMR) connected by a flux qubit, where the flux qubit has a large detuning from both resonators. By a unitray transformation and a second-order approximation, we obtain a strong and controllable (i.e., magnetic-field-dependent) effective coupling between the NAMR and the CPW resonator. Due to the strong coupling, vacuum Rabi splitting can be observed from the voltage-fluctuation spectrum of the CPW resonator. We further study the properties of single photon transport as inferred from the reflectance or equivalently the transmittance. We show that the reflectance and the corresponding phase shift spectra both exhibit doublet of narrow spectral features due to vacuum Rabi splitting. By tuning the external magnetic field, the reflectance and the phase shift can be varied from 0 to 1 and $-\pi$ to $\pi$, respectively. The results indicate that this hybrid quantum system can act as a quantum router.