Quantum transduction of superconducting qubit in electro-optomechanical and electro-optomagnonical system

  1. Roson Nongthombam,
  2. Pooja Kumari Gupta,
  3. and Amarendra K. Sarma
We study the quantum transduction of a superconducting qubit to an optical photon in electro-optomechanical and electro-optomagnonical systems. The electro-optomechanical system comprises
a flux-tunable transmon qubit coupled to a suspended mechanical beam, which then couples to an optical cavity. Similarly, in an electro-optomagnonical system, a flux-tunable transmon qubit is coupled to an optical whispering gallery mode via a magnon excitation in a YIG ferromagnetic sphere. In both systems, the transduction process is done in sequence. In the first sequence, the qubit states are encoded in coherent excitations of phonon/magnon modes through the phonon/magnon-qubit interaction, which is non-demolition in the qubit part. We then measure the phonon/magnon excitations, which reveal the qubit states, by counting the average number of photons in the optical cavities. The measurement of the phonon/magnon excitations can be performed at a regular intervals of time.

Synchronization of a superconducting qubit to an optical field mediated by a mechanical resonator

  1. Roson Nongthombam,
  2. Sampreet Kalita,
  3. and Amarendra K. Sarma
We study the synchronization of a superconducting qubit to an external optical field via a mechanical resonator in a hybrid optoelectromechanical system. The quantum trajectory method
is employed to investigate synchronization. The bistability in one of the qubit polarization vectors, where the qubit rotates about the polarization vector, is observed for a single quantum trajectory run. The rotation in one of the stable states is synced with the external optical drive. When the number of trajectories is significantly increased, the qubit no longer displays bistability. However, synchronization with less quantum fluctuations is still observed. The scheme could be used to transfer the phase of the microwave qubit’s rotation to a long-lived optical photon through synchronization, which may find applications in long-distance quantum communication. Also, this hybrid system can be used to study quantum synchronization.