Cyclically operated Single Microwave Photon Counter with $10^\mathrm{-22}$ $\mathrm{W/\sqrt{Hz}}$ sensitivity

TL;DR

This paper introduces a microwave photon detector with unprecedented sensitivity of 10^{-22} W/√Hz, utilizing a transmon qubit and four-wave mixing, enabling continuous, tunable, and efficient single-photon detection in the microwave domain.

Contribution

The paper presents a practical microwave photon detector based on a transmon qubit with record sensitivity and continuous operation capabilities, advancing microwave quantum optics detection technology.

Findings

Detection efficiency of 0.43 achieved.

Power sensitivity of 10^{-22} W/√Hz demonstrated.

Operates continuously with high duty cycle and tunability.

Abstract

Single photon detection played an important role in the development of quantum optics. Its implementation in the microwave domain is challenging because the photon energy is 5 orders of magnitude smaller. In recent years, significant progress has been made in developing single microwave photon detectors (SMPDs) based on superconducting quantum bits or bolometers. In this paper we present a practical SMPD based on the irreversible transfer of an incoming photon to the excited state of a transmon qubit by a four-wave mixing process. This device achieves a detection efficiency $\eta = 0.43$ and an operational dark count rate $\alpha = 85$ $\mathrm{s^{-1}}$, mainly due to the out-of-equilibrium microwave photons in the input line. The corresponding power sensitivity is $\mathcal{S} = 10^{-22}$ $\mathrm{W/\sqrt{Hz}}$, one order of magnitude lower than the state of the art. The detector operates continuously over hour timescales with a duty cycle $\eta_\mathrm{D}=0.84$, and offers frequency tunability of at least 50 MHz around 7 GHz.