Fast and Ultrasensitive Electrometer Operating at the Single-Photon Level

TL;DR

This paper presents a cavity-embedded Cooper pair transistor (cCPT) that achieves fast, ultrasensitive charge detection at the single-photon level, with sensitivities close to the quantum limit, enabling new possibilities in quantum optomechanics.

Contribution

The work demonstrates for the first time a cCPT device operating at the single-photon level with near-quantum-limited sensitivity, surpassing traditional charge detectors in speed and sensitivity.

Findings

Achieved charge sensitivity of 14 μe/√Hz at 1 MHz bandwidth

Operates with only 16 attowatts of power, at the single-photon level

Sensitivity within a factor of 5 of the quantum limit

Abstract

We demonstrate fast and ultrasensitive charge detection with a cavity-embedded Cooper pair transistor (cCPT) via dispersive readout of its Josephson inductance. We report a minimum charge sensitivity of $14$ $\mu e/\sqrt{\mathrm{Hz}}$ with a detection bandwidth on the order of $1$ MHz using $16$ attowatts of power, corresponding to the single-photon level of the cavity. In addition, our measured sensitivities are within a factor of $5$ of the quantum limit for this device. The single-photon-level sensitivity of the cCPT is comparable to that of the rf-SET, which typically operates using picowatts of power corresponding to hundreds of thousands of photons in its tank circuit. Our results support the feasibility of using the cCPT to mediate an optomechanical interaction that reaches the single-photon strong coupling regime.