Large flux-mediated coupling in hybrid electromechanical system with a transmon qubit

Mechanical resonators coupled to superconducting qubits are interesting platforms for quantum science and technology, but controlling them in quantum regime remains a challenge. The authors realize a hybrid device consisting of a superconducting transmon qubit and a mechanical resonator coupled using the magnetic-flux with the overall ability to increase the coupling strength and hence their control. Control over the quantum states of a massive oscillator is important for several technological applications and to test the fundamental limits of quantum mechanics. Addition of an internal degree of freedom to the oscillator could be a valuable resource for such control. Recently, hybrid electromechanical systems using superconducting qubits, based on electric-charge mediated coupling, have been quite successful. Here, we show a hybrid device, consisting of a superconducting transmon qubit and a mechanical resonator coupled using the magnetic-flux. The coupling stems from the quantum-interference of the superconducting phase across the tunnel junctions. We demonstrate a vacuum electromechanical coupling rate up to 4 kHz by making the transmon qubit resonant with the readout cavity. Consequently, thermal-motion of the mechanical resonator is detected by driving the hybridized-mode with mean-occupancy well below one photon. By tuning qubit away from the cavity, electromechanical coupling can be enhanced to 40 kHz. In this limit, a small coherent drive on the mechanical resonator results in the splitting of qubit spectrum, and we observe interference signature arising from the Landau-Zener-Stuckelberg effect. With improvements in qubit coherence, this system offers a platform to realize rich interactions and could potentially provide full control over the quantum motional states.

Automated summary

Researchers have demonstrated a hybrid device incorporating a superconducting transmon qubit and a mechanical resonator coupled using magnetic-flux. They showed a high vacuum electromechanical coupling rate and the enhancement of electromechanical coupling by tuning the qubit position, while observing specific interference features.