RQC Seminar

140th RQC Seminar

• Speaker

  Prof. IoChun Hoi
  ( Department of Physics, City University of Hong Kong )

• Date

  4:00 p.m.-5:00 p.m., August 20, 2024 (Tuesday)

• Venue

  Onsite( Wako Main Research 3F 345-347 Seminar Room/ 研究本館3階 セミナー室(345-347) C01）

• Title

  Waveguide quantum electrodynamics with superconducting artificial atom and spin ensembles

• Inquiries

  rqc_info[at]ml.riken.jp

Abstract
In this talk, I will address recent advances in waveguide quantum electrodynamics with superconducting artificial atom and spin ensembles.
In the first set of experiments, we investigate the amplification of a microwave probe signal by a superconducting artificial atom, a transmon, positioned at the end of a semi-infinite transmission line, under a strong pump field. The end of the transmission line acts as a mirror for microwave fields. Due to the weak anharmonicity of the artificial atom, the strong pump field creates multi-photon excitations among the dressed states. Transitions between these dressed states, Rabi sidebands, give rise to either amplification or attenuation of the weak probe. We obtain a maximum power amplification of 1.402, higher than in any previous experiment with a single artificial atom. Additionally, we achieve near-quantum-limited added noise (0.157 quanta; the quantum limit is 0.143 quanta for this level of amplification, due to quantum coherence between Rabi sidebands, leading to constructive interference between emitted photons.
In the second set of experiments, we investigate microwave interference from a spin ensemble and its mirror image in a one-dimensional (1D) waveguide. Away from a mirror, the resonance frequency of the Kittel mode (KM) inside a ferrimagnetic spin ensemble has a sinusoidal frequency shift as the normalized distance increases compared to the setup without the mirror. This shift is attributed to the interaction of the KM with its own image. Meanwhile, its radiative decay rate shows a cosine squared oscillation. We also observe the critical coupling condition that enables perfect adsorption of the input photons. By placing the KM near the node of resonance field, the lifetime is more than eight times than near the antinode.