Chiral coupling between a ferromagnetic magnon to a superconducting qubit

  1. Ya-long Ren,
  2. Sheng-li Ma,
  3. and Fu-li Li
Chiral coupling at the single-quantum level promises to be a remarkable potential for quantum information processing. Here we propose to achieve a chiral interaction between a magnon
mode in a ferromagnetic sphere and a superconducting qubit mediated by a one-dimensional coupled-cavity array. When the qubit is coupled to two lattice sites of the array and each one is encoded with a tunable phase, we can acquire a directional qubit-magnon interaction via the quantum interference effect. This work opens up a new route to construct chiral devices, which are expected to become a building block in quantum magnonic networks.

Two-color electromagnetically induced transparency via modulated coupling between a mechanical resonator and a qubit

  1. Xin Wang,
  2. Adam Miranowicz,
  3. Hong-Rong Li,
  4. Fu-Li Li,
  5. and Franco Nori
We discuss level splitting and sideband transitions induced by a modulated coupling between a superconducting quantum circuit and a nanomechanical resonator. First, we show how to achieve
an unconventional time-dependent longitudinal coupling between a flux (transmon) qubit and the resonator. Considering a sinusoidal modulation of the coupling strength, we find that a first-order sideband transition can be split into two. Moreover, under the driving of a red-detuned field, we discuss the optical response of the qubit for a resonant probe field. We show that level splitting induced by modulating this longitudinal coupling can enable two-color electromagnetically induced transparency (EIT), in addition to single-color EIT. In contrast to standard predictions of two-color EIT in atomic systems, we apply here only a single drive (control) field. The monochromatic modulation of the coupling strength is equivalent to employing two eigenfrequency-tunable mechanical resonators. Both drive-probe detuning for single-color EIT and the distance between transparent windows for two-color EIT, can be adjusted by tuning the modulation frequency of the coupling.

Quantum microwave-optical interface with nitrogen-vacancy centers in diamond

  1. Bo Li,
  2. Peng-Bo Li,
  3. Yuan Zhou,
  4. Sheng-Li Ma,
  5. and Fu-Li Li
We propose an efficient scheme for a coherent quantum interface between microwave and optical photons using nitrogen-vacancy (NV) centers in diamond. In this setup, an NV center ensemble
is simultaneously coupled to an optical and a microwave cavity. We show that, by using the collective spin excitation modes as an intermediary, quantum states can be transferred between the microwave cavity and the optical cavity through either a double-swap scheme or a dark-state protocol. This hybrid quantum interface may provide interesting applications in single microwave photon detections or quantum information processing.

Tunable electromagnetically induced transparency with a coupled superconducting system

  1. Xin Wang,
  2. Hong-rong Li,
  3. Wen-xiao Liu,
  4. and Fu-li Li
Electromagnetically induced transparency (EIT) has usually been demonstrated by using three-level atomic systems. In this paper, we theoretically proposed an efficient method to realize
EIT in microwave regime through a coupled system consisting of a flux qubit and a superconducting LC resonator with relatively high quality factor. In the present composed system, the working levels are the dressed states of a two-level flux qubit and the resonators with a probe pump field. There exits a second order coherent transfer between the dressed states. By comparing the results with those in the conventional atomic system we have revealed the physical origin of the EIT phenomenon in this composed system. Since the whole system is artificial and tunable, our scheme may have potential applications in various domains.

Engineering two-mode entangled states between two superconducting resonators by dissipation

  1. Peng-Bo Li,
  2. Shao-Yan Gao,
  3. and Fu-Li Li
We present an experimental feasible scheme to synthesize two-mode continuous-variable entangled states of two superconducting resonators that are interconnected by two gap-tunable superconducting
qubits. We show that, with each artificial atom suitably driven by a bichromatic microwave field to induce sidebands in the qubit-resonator coupling, the stationary state of the photon fields in the two resonators can be cooled and steered into a two-mode squeezed vacuum state via a dissipative quantum dynamical process, while the superconducting qubits remain in their ground states. In this scheme the qubit decay plays a positive role and can help drive the system to the target state, which thus converts a detrimental source of noise into a resource.