R. Yamazaki

Information-to-work conversion by Maxwell’s demon in a superconducting circuit-QED system

  1. Y. Masuyama,
  2. K. Funo,
  3. Y. Murashita,
  4. A. Noguchi,
  5. S. Kono,
  6. Y. Tabuchi,
  7. R. Yamazaki,
  8. M. Ueda,
  9. and Y. Nakamura
The gedanken experiment of Maxwell’s demon has led to the studies concerning the foundations of thermodynamics and statistical mechanics. The demon measures fluctuations of a
system’s observable and converts the information gain into work via feedback control. Recent developments have elucidated the relationship between the acquired information and the entropy production and generalized the second law of thermodynamics and the fluctuation theorems. Here we extend the scope to a system subject to quantum fluctuations by exploiting techniques in superconducting circuit quantum electrodynamics. We implement Maxwell’s demon equipped with coherent control and quantum nondemolition projective measurements on a superconducting qubit, where we verify the generalized integral fluctuation theorems and demonstrate the information-to-work conversion. This reveals the potential of superconducting circuits as a versatile platform for investigating quantum information thermodynamics under feedback control, which is closely linked to quantum error correction for computation and metrology.
arxiv pdf

Nonclassical photon number distribution in a superconducting cavity under a squeezed drive

  1. S. Kono,
  2. Y. Masuyama,
  3. T. Ishikawa,
  4. Y. Tabuchi,
  5. R. Yamazaki,
  6. K. Usami,
  7. K. Koshino,
  8. and Y. Nakamura
A superconducting qubit in the strong dispersive regime of a circuit quantum electrodynamics system is a powerful probe for microwave photons in a cavity mode. In this regime, a qubit
spectrum is split into multiple peaks, with each peak corresponding to an individual photon number in the cavity (discrete ac Stark shift). Here, we measure the qubit spectrum in the cavity that is driven continuously with a squeezed vacuum field generated by a Josephson parametric amplifier. By fitting the qubit spectrum with a model which takes into account the finite qubit excitation power, the photon number distribution, which is dissimilar from the apparent peak area ratio in the spectrum, is determined. The photon number distribution shows the even-odd photon number oscillation and quantitatively fulfills Klyshko’s criterion for the nonclassicality.
arxiv pdf