Generation and efficient measurement of single photons from fixed frequency superconducting qubits

TL;DR

This paper presents a method for generating and efficiently measuring single microwave photons from a fixed-frequency superconducting qubit-cavity system, analyzing detection inefficiencies and backaction effects.

Contribution

It introduces a protocol for on-demand microwave photon generation using a fixed-frequency qubit-cavity system and characterizes the impact of JPA gain on detection efficiency and backaction.

Findings

Maximum single photon component $ ho_{11} = 0.36$ at 29 dB JPA gain

Detection efficiency and backaction increase with JPA gain

Backaction induces cavity photon number fluctuations modeled as a thermal distribution

Abstract

We demonstrate and evaluate an on-demand source of single itinerant microwave photons. Photons are generated using a highly coherent, fixed-frequency qubit-cavity system, and a protocol where the microwave control field is far detuned from the photon emission frequency. By using a Josephson parametric amplifier (JPA), we perform efficient single-quadrature detection of the state emerging from the cavity. We characterize the imperfections of the photon generation and detection, including detection inefficiency and state infidelity caused by measurement backaction over a range of JPA gains from 17 to 33 dB. We observe that both detection efficiency and undesirable backaction increase with JPA gain. We find that the density matrix has its maximum single photon component $\rho_{11} = 0.36 \pm 0.01$ at 29 dB JPA gain. At this gain, backaction of the JPA creates cavity photon number fluctuations that we model as a thermal distribution with an average photon number $\bar{n} = 0.041 \pm 0.003$.