Quantum efficiency, purity and stability of a tunable, narrowband microwave single-photon source

Yong Lu*, Andreas Bengtsson, Jonathan J. Burnett, Baladitya Suri, Sankar Raman Sathyamoorthy, Hampus Renberg Nilsson, Marco Scigliuzzo, Jonas Bylander, Göran Johansson, Per Delsing*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


We demonstrate an on-demand source of microwave single photons with 71–99% intrinsic quantum efficiency. The source is narrowband (300 kHz) and tuneable over a 600 MHz range around 5.2 GHz. Such a device is an important element in numerous quantum technologies and applications. The device consists of a superconducting transmon qubit coupled to the open end of a transmission line. A π-pulse excites the qubit, which subsequently rapidly emits a single photon into the transmission line. A cancellation pulse then suppresses the reflected π-pulse by 33.5 dB, resulting in 0.005 photons leaking into the photon emission channel. We verify strong antibunching of the emitted photon field and determine its Wigner function. Non-radiative decay and 1/f flux noise both affect the quantum efficiency. We also study the device stability over time and identify uncorrelated discrete jumps of the pure dephasing rate at different qubit frequencies on a time scale of hours, which we attribute to independent two-level system defects in the device dielectrics, dispersively coupled to the qubit. Our single-photon source with only one input port is more compact and scalable compared to standard implementations.

Original languageEnglish
Article number140
Journalnpj Quantum Information
Issue number1
StatePublished - Dec 2021
Externally publishedYes


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