K. Inomata

Squeezing with a flux-driven Josephson parametric amplifier

  1. L. Zhong,
  2. E. P. Menzel,
  3. R. Di Candia,
  4. P. Eder,
  5. M. Ihmig,
  6. A. Baust,
  7. M. Haeberlein,
  8. E. Hoffmann,
  9. K. Inomata,
  10. T. Yamamoto,
  11. Y. Nakamura,
  12. E. Solano,
  13. F. Deppe,
  14. A. Marx,
  15. and R. Gross
Josephson parametric amplifiers (JPA) are promising devices for applications in circuit quantum electrodynamics (QED) and for studies on propagating quantum microwaves because of their
good noise performance. In this work, we present a systematic characterization of a flux-driven JPA at millikelvin temperatures. In particular, we study in detail its squeezing properties by two different detection techniques. With the homodyne setup, we observe squeezing of vacuum fluctuations by superposing signal and idler bands. For a quantitative analysis we apply dual-path cross-correlation techniques to reconstruct the Wigner functions of various squeezed vacuum and thermal states. At 10 dB signal gain, we find 4.9+-0.2 dB squeezing below vacuum. In addition, we discuss the physics behind squeezed coherent microwave fields. Finally, we analyze the JPA noise temperature in the degenerate mode and find a value smaller than the standard quantum limit for phase-insensitive amplifiers.
arxiv pdf

Observation of three-state dressed states in circuit quantum electrodynamics

  1. K. Koshino,
  2. H. Terai,
  3. K. Inomata,
  4. T. Yamamoto,
  5. W. Qiu,
  6. Z. Wang,
  7. and Y. Nakamura
We have investigated the microwave response of a transmon qubit coupled directly to a transmission line. In a transmon qubit, owing to its weak anharmonicity, a single driving field
may generate dressed states involving more than two bare states. We confirmed the formation of three-state dressed states by observing all of the six associated Rabi sidebands, which appear as either amplification or attenuation of the probe field. The experimental results are reproduced with good precision by a theoretical model incorporating the radiative coupling between the qubit and the microwave.
arxiv pdf

Path Entanglement of Continuous-Variable Quantum Microwaves

  1. E. P. Menzel,
  2. R. Di Candia,
  3. F. Deppe,
  4. P. Eder,
  5. L. Zhong,
  6. M. Ihmig,
  7. M. Haeberlein,
  8. A. Baust,
  9. E. Hoffmann,
  10. D. Ballester,
  11. K. Inomata,
  12. T. Yamamoto,
  13. Y. Nakamura,
  14. E. Solano,
  15. A. Marx,
  16. and R. Gross
Path entanglement constitutes an essential resource in quantum information and communication protocols. Here, we demonstrate frequency-degenerate entanglement between continuous-variable
quantum microwaves propagating along two spatially separated paths. We combine a squeezed and a vacuum state using a microwave beam splitter. Via correlation measurements, we detect and quantify the path entanglement contained in the beam splitter output state. Our experiments open the avenue to quantum teleportation, quantum communication, or quantum radar with continuous variables at microwave frequencies.
arxiv pdf

Large Dispersive Shift of Cavity Resonance Induced by a Superconducting Flux Qubit in the Straddling Regime

  1. K. Inomata,
  2. T. Yamamoto,
  3. P.-M. Billangeon,
  4. Y. Nakamura,
  5. and J. S. Tsai
We demonstrate enhancement of the dispersive frequency shift in a coplanar waveguide resonator induced by a capacitively-coupled superconducting flux qubit in the straddling regime.
The magnitude of the observed shift, 80 MHz for the qubit-resonator detuning of 5 GHz, is quantitatively explained by the generalized Jaynes-Cummings model which takes into account the contribution of the qubit higher energy levels. By applying the enhanced dispersive shift to the qubit readout, we achieved 90% contrast of the Rabi oscillations which is mainly limited by the energy relaxation of the qubit.
arxiv pdf