Transmon Architecture for Emission and Detection of Single Microwave Photons

TL;DR

This paper introduces a compact superconducting transmon circuit capable of emitting and detecting single microwave photons, demonstrating high efficiency and potential for quantum communication and information processing.

Contribution

The development of a dual-function transmon emitter/detector with high efficiency and a novel microwave photon detection scheme, advancing quantum communication interfaces.

Findings

Detected 60% of emitted photons with a 95% efficiency at the input of the detector.

Achieved photon emission and detection processes each within approximately 2 microseconds.

Demonstrated the use of the double transmon coupler as a tunable link in quantum circuits.

Abstract

We develop a compact transmon emitter/detector (TED) superconducting circuit and demonstrate its dual functionality as a single-photon source and detector. In our setup, photons emitted by a source TED are transmitted via a meter-long coaxial cable, routed through a circulator, and captured by a measurement TED. Both TED modules operate with nominally identical parameters, highlighting the flexibility of this novel architecture. Furthermore, we introduce an efficient microwave photon detection scheme tailored to the TED. Using this setup, we detect 60% of the emitted Fock state photons and infer a 95% detection efficiency at the input of the measurement TED, which we calibrate against coherent state measurements. The reset and photon emission/detection processes each require approximately $2\,\mu s$, yielding a minimum protocol duration of $4\,\mu s$ as constrained by our chosen TED parameters. Ultimately, the TED demonstrates a new use case for the recently developed double transmon coupler (DTC): a compact, drop-in, tunable, and transition-selective link between a coherent data transmon and a waveguide. Circuits like the TED will play a vital role in quantum information processing by facilitating unconditional fast reset, enabling microwave photon metrology, and serving as nascent quantum communication interfaces (QCIs). QCIs mediate entanglement distribution between quantum processing units (QPUs) within a cryostat or interface with microwave-to-optical transducers for long-range quantum networking.