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

• Main Authors: Lu, Yong, Bengtsson, Andreas, Burnett, Jonathan J, Suri, Baladitya, Sathyamoorthy, Sankar Raman, Nilsson, Hampus Renberg, Scigliuzzo, Marco, Bylander, Jonas, Johansson, Göran, Delsing, Per
• Format: Journal Article
• Language: English
• Published: 24-05-2021
• Subjects: Physics - Quantum Physics
• DOI: 10.48550/arxiv.2105.11234

npj Quantum Information 7, 140 (2021) We demonstrate an on-demand source of microwave single photons with 71--99\%
intrinsic quantum efficiency. The source is narrowband (300\unite{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 $\pi$-pulse excites the qubit, which subsequently rapidly emits a
single photon into the transmission line. A cancellation pulse then suppresses
the reflected $\pi$-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.