Abstract
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-Stückelberg 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.
Highlights
Control over the quantum states of a massive oscillator is important for several technological applications and to test the fundamental limits of quantum mechanics
Cavity optomechanical systems, where a mechanical mode parametrically modulates the resonant frequency of an electromagnetic (EM) mode, have been very successful in controlling the motional states of massive oscillators[1]
By recording the thermomechanical motion of the resonator, we demonstrate a magnetic field tunable electromechanical coupling rate up to 4 kHz when qubit is tuned in resonance with the cavity
Summary
Control over the quantum states of a massive oscillator is important for several technological applications and to test the fundamental limits of quantum mechanics. Beyond the traditional two-mode systems, consisting of one EM and one mechanical mode, cavity optomechanical systems with an auxiliary mode provides a wide range of interactions Such systems have been used to realize nonreciprocal devices[7–9], and to demonstrate quantum entanglement between two mechanical resonators[10,11]. We engineer the device parameters such that in addition to the flux-based electromechanical coupling, one mode maintains sufficient anharmonicity to be qualified as a qubit This approach results in an electromechanical system with an internal spin-half degree of freedom. Similar to vacuum-electromechanical coupling rate’s scaling with total charge in charge-dispersion-based schemes[14–16], the coupling rate here scales linearly with the magnetic field Such an approach has the potential to reach the elusive single-photon strong coupling regime with suitable choice of materials[21]
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