Phonon blockade in a nanomechanical resonator resonantly coupled to a qubit

TL;DR

This paper investigates phonon blockade phenomena in a nanomechanical resonator coupled to a qubit, revealing two mechanisms for blockade, their fragility to thermal effects, and methods to enhance phonon antibunching through external driving fields.

Contribution

It identifies two distinct mechanisms for phonon blockade in a NAMR-qubit system and proposes a scheme to enhance phonon antibunching using external drives.

Findings

Two mechanisms for phonon blockade: anharmonicity and destructive interference.

Phonon blockade is fragile at higher thermal occupations.

External driving fields can synchronize blockade mechanisms.

Abstract

We study phonon statistics in a nanomechanical resonator (NAMR) which is resonantly coupled to a qubit. We find that there are two different mechanisms for phonon blockade in such a resonantly coupled NAMR-qubit system. One is due to the strong anharmonicity of the NAMR-qubit system with large coupling strength; the other one is due to the destructive interference between different paths for two-phonon excitation in the NAMR-qubit system with a moderate coupling strength. We find that the phonon blockade is fragile towards thermal mode occupations and can only be observed for NAMR being at ultracold effective temperature. In order to enlarge the mean phonon number for strong phonon antibunching with a moderate NAMR-qubit coupling strength, we assume that two external driving fields are applied to the NAMR and qubit, respectively. In this case, we find that the phonon blockades under two mechanisms can appear at the same frequency regime by optimizing the strength ratio and phase difference of the two external driving fields.