Bixuan Fan

Non-absorbing high-efficiency counter for itinerant microwave photons

  1. Bixuan Fan,
  2. Göran Johansson,
  3. Joshua Combes,
  4. G. J. Milburn,
  5. and Thomas M. Stace
Detecting an itinerant microwave photon with high efficiency is an outstanding problem in microwave photonics and its applications. We present a scheme to detect an itinerant microwave
photon in a transmission line via the nonlinearity provided by a transmon in a driven microwave resonator. By performing continuous measurements on the output field of the resonator we theoretically achieve an over-unity signal-to-noise (SNR) for a single shot measurement and 84% distinguishability between zero and one microwave photon with a single transmon and 90% distinguishability with two cascaded transmons. We also show how the measurement diminishes coherence in the photon number basis thereby illustrating a fundamental principle of quantum measurement: the higher the measurement efficiency, the greater is the decoherence.
arxiv pdf

Breakdown of the cross-Kerr scheme for Photon Counting

  1. Bixuan Fan,
  2. Anton F. Kockum,
  3. Joshua Combes,
  4. Göran Johansson,
  5. Io-chun Hoi,
  6. Christopher Wilson,
  7. Per Delsing,
  8. G. J. Milburn,
  9. and Thomas M. Stace
We show, in the context of single photon detection, that an atomic three-level model for a transmon in a transmission line does not support the predictions of the nonlinear polarisability
model known as the cross-Kerr effect. We show that the induced displacement of a probe in the presence or absence of a single photon in the signal field, cannot be resolved above the quantum noise in the probe. This strongly suggests that cross-Kerr media are not suitable for photon counting or related single photon applications. Our results are presented in the context of a transmon in a one dimensional microwave waveguide, but the conclusions also apply to optical systems.
arxiv pdf