T. Yamaji

Theoretical study of reflection spectroscopy for superconducting quantum parametrons

  1. S. Masuda,
  2. A. Yamaguchi,
  3. T. Yamaji,
  4. T. Yamamoto,
  5. T. Ishikawa,
  6. Y. Matsuzaki,
  7. and S. Kawabata
Superconducting parametrons in the single-photon Kerr regime, also called KPOs, have been attracting increasing attention in terms of their applications to quantum annealing and universal
quantum computation. It is of practical importance to obtain information of superconducting parametrons operating under an oscillating pump field. Spectroscopy can provide information of a superconducting parametron under examination, such as energy level structure and occupation of energy levels, and also useful information for calibration of the pump field. We theoretically study the reflection spectroscopy of superconducting parametrons, and develop a method to obtain the reflection coefficient. We present formulae of the reflection coefficient, the nominal external and the internal decay rates, and examine the obtained spectra.
arxiv pdf

Spectroscopic observation of crossover from classical Duffing oscillator to Kerr parametric oscillator

  1. T. Yamaji,
  2. S. Kagami,
  3. A. Yamaguchi,
  4. T. Satoh,
  5. K. Koshino,
  6. H. Goto,
  7. Z. R. Lin,
  8. Y. Nakamura,
  9. and T. Yamamoto
We study microwave response of a Josephson parametric oscillator consisting of a superconducting transmission-line resonator with an embedded dc-SQUID. The dc-SQUID allows to control
the magnitude of a Kerr nonlinearity over the ranges where it is smaller or larger than the photon loss rate. Spectroscopy measurements reveal the change of the microwave response from a classical Duffing oscillator to a Kerr parametric oscillator in a single device. In the single-photon Kerr regime, we observe parametric oscillations with a well-defined phase of either 0 or π, whose probability can be controlled by an externally injected signal.
arxiv pdf