Flux-driven Josephson parametric amplifiers: Hysteretic flux response and nondegenerate gain measurements

  1. Stefan Pogorzalek,
  2. Kirill G. Fedorov,
  3. Ling Zhong,
  4. Jan Goetz,
  5. Friedrich Wulschner,
  6. Michael Fischer,
  7. Peter Eder,
  8. Edwar Xie,
  9. Kunihiro Inomata,
  10. Tsuyoshi Yamamoto,
  11. Yasunobu Nakamura,
  12. Achim Marx,
  13. Frank Deppe,
  14. and Rudolf Gross
Josephson parametric amplifiers (JPA) have become key devices in quantum science and technology with superconducting circuits. In particular, they can be utilized as quantum-limited
amplifiers or as a source of squeezed microwave fields. Here, we report on the detailed measurements of five flux-driven JPAs, three of them exhibiting a hysteretic dependence of the resonant frequency versus the applied magnetic flux. We model the measured characteristics by numerical simulations based on the two-dimensional potential landscape of the dc superconducting quantum interference devices (dc-SQUID), which provide the JPA nonlinearity, for a finite screening parameter βL>0 and demonstrate excellent agreement between the numerical results and the experimental data. Furthermore, we study the nondegenerate response of different JPAs and accurately describe the experimental results with our theory.

Multi-photon sideband transitions in an ultrastrongly-coupled circuit quantum electrodynamics system

  1. Zhen Chen,
  2. Yimin Wang,
  3. Tiefu Li,
  4. Lin Tian,
  5. Yueyin Qiu,
  6. Kunihiro Inomata,
  7. Fumiki Yoshihara,
  8. Siyuan Han,
  9. Franco Nori,
  10. J. S. Tsai,
  11. and J. Q. You
Ultrastrong coupling in circuit quantum electrodynamics systems not only provides a platform to study the quantum Rabi model, but it can also facilitate the implementation of quantum
logic operations via high-lying resonator states. In this regime, quantum manifolds with different excitation numbers are intrinsically connected via the counter-rotating interactions, which can result in multi-photon processes. Recent experiments have demonstrated ultrastrong coupling in superconducting qubits electromagnetically coupled to superconducting resonators. Here we report the experimental observation of multiphoton sideband transitions of a superconducting flux qubit coupled to a coplanar waveguide resonator in the ultrastrong coupling regime. With a coupling strength reaching about 10% of the fundamental frequency of the resonator, we obtain clear signatures of higher-order red-sideband transitions and the first-order blue-sideband transition in a transmission spectroscopic measurement. This study advances the understanding of driven ultrastrongly-coupled systems.

Single microwave-photon detector using an artificial Λ-type three-level system

  1. Kunihiro Inomata,
  2. Zhirong Lin,
  3. Kazuki Koshino,
  4. William D. Oliver,
  5. Jaw-Shen Tsai,
  6. Tsuyoshi Yamamoto,
  7. and Yasunobu Nakamura
Single photon detection is a requisite technique in quantum-optics experiments in both the optical and the microwave domains. However, the energy of microwave quanta are four to five
orders of magnitude less than their optical counterpart, making the efficient detection of single microwave photons extremely challenging. Here, we demonstrate the detection of a single microwave photon propagating through a waveguide. The detector is implemented with an „impedance-matched“ artificial Λ system comprising the dressed states of a driven superconducting qubit coupled to a microwave resonator. We attain a single-photon detection efficiency of 0.66±0.06 with a reset time of ∼400~ns. This detector can be exploited for various applications in quantum sensing, quantum communication and quantum information processing.

Dressed-state engineering for continuous detection of itinerant microwave photons

  1. Kazuki Koshino,
  2. Zhirong Lin,
  3. Kunihiro Inomata,
  4. Tsuyoshi Yamamoto,
  5. and Yasunobu Nakamura
We propose a scheme for continuous detection of itinerant microwave photons in circuit quantum electrodynamics. In the proposed device, a superconducting qubit is coupled dispersively
to two resonators: one is used to form an impedance-matched Λ system that deterministically captures incoming photons, and the other is used for continuous monitoring of the event. The present scheme enables efficient photon detection: for realistic system parameters, the detection efficiency reaches 0.9 with a bandwidth of about ten megahertz.

Theory of microwave single-photon detection using an impedance-matched Λ system

  1. Kazuki Koshino,
  2. Kunihiro Inomata,
  3. Zhirong Lin,
  4. Yasunobu Nakamura,
  5. and Tsuyoshi Yamamoto
By properly driving a qubit-resonator system in the strong dispersive regime, we implement an „impedance-matched“ Λ system in the dressed states, where a resonant single
photon deterministically induces a Raman transition and excites the qubit. Combining this effect and a fast dispersive readout of the qubit, we realize a detector of itinerant microwave photons. We theoretically analyze the single-photon response of the Λ system and evaluate its performance as a detector. We achieve a high detection efficiency close to unity without relying on precise temporal control of the input pulse shape and under a conservative estimate of the system parameters. The detector can also be reset quickly by applying microwave pulses, which allows a short dead time and a high repetition rate.