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

  1. Yong Lu,
  2. Andreas Bengtsson,
  3. Jonathan J. Burnett,
  4. Baladitya Suri,
  5. Sankar Raman Sathyamoorthy,
  6. Hampus Renberg Nilsson,
  7. Marco Scigliuzzo,
  8. Jonas Bylander,
  9. Göran Johansson,
  10. and Per Delsing
We demonstrate an on-demand source of microwave single photons with 71–99% intrinsic quantum efficiency. The source is narrowband (300unite{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.

Resonant and off-resonant microwave signal manipulations in coupled superconducting resonators

  1. Mathieu Pierre,
  2. Sankar Raman Sathyamoorthy,
  3. Ida-Maria Svensson,
  4. Göran Johansson,
  5. and Per Delsing
We present an experimental demonstration as well as a theoretical model of an integrated circuit designed for the manipulation of a microwave field down to the single-photon level.
The device is made of a superconducting resonator coupled to a transmission line via a second frequency-tunable resonator. The tunable resonator can be used as a tunable coupler between the fixed resonator and the transmission line. Moreover, the manipulation of the microwave field between the two resonators is possible. In particular, we demonstrate the swapping of the field from one resonator to the other by pulsing the frequency detuning between the two resonators. The behavior of the system, which determines how the device can be operated, is analyzed as a function of one key parameter of the system, the damping ratio of the coupled resonators. We show a good agreement between experiments and simulations, realized by solving a set of coupled differential equations.

Simple, robust and on-demand generation of single and correlated photons

  1. Sankar Raman Sathyamoorthy,
  2. Andreas Bengtsson,
  3. Per Delsing,
  4. and Göran Johansson
We propose two different setups to generate single photons on demand using an atom in front of a mirror, along with either a beam-splitter or a tunable coupling. We show that photon
generation efficiency ~ 99% is straightforward to achieve. The proposed schemes are simple and easily tunable in frequency. The operation is relatively insensitive to dephasing and can be easily extended to generate correlated pairs of photons. They can also in principle be used to generate any photonic qubit in arbitrary wave-packets, making them very attractive for quantum communication applications.

Detecting itinerant single microwave photons

  1. Sankar Raman Sathyamoorthy,
  2. Thomas M. Stace,
  3. and Göran Johansson
Single photon detectors are fundamental tools of investigation in quantum optics and play a central role in measurement theory and quantum informatics. Photodetectors based on different
technologies exist at optical frequencies and much effort is currently being spent on pushing their efficiencies to meet the demands coming from the quantum computing and quantum communication proposals. In the microwave regime however, a single photon detector has remained elusive although several theoretical proposals have been put forth. In this article, we review these recent proposals, especially focusing on non-destructive detectors of propagating microwave photons. These detection schemes using superconducting artificial atoms can reach detection efficiencies of 90\% with existing technologies and are ripe for experimental investigations.