Measurements of nanoresonator-qubit interactions in a hybrid quantum electromechanical system

Abstract

Experiments to probe the basic quantum properties of motional degrees of freedom of mechanical systems have developed rapidly over the last decade. One promising approach is to use hybrid electromechanical systems incorporating superconducting qubits and microwave circuitry. However, a critical challenge facing the development of these systems is to achieve strong coupling between mechanics and qubits while simultaneously reducing coupling of both the qubit and mechanical mode to the environment. Here we report measurements of a qubit-coupled mechanical resonator system consisting of an ultra-high-frequency nanoresonator and a long coherence-time superconducting transmon qubit, embedded in a superconducting coplanar waveguide cavity. It is demonstrated that the nanoresonator and transmon have commensurate energies and transmon coherence times are one order of magnitude larger than for all previously reported qubit-coupled nanoresonators. Moreover, we show that numerical simulations of this new hybrid quantum system are in good agreement with spectroscopic measurements and suggest that the nanoresonator in our device resides at low thermal occupation number, near its ground state, acting as a dissipative bath seen by the qubit. We also outline how this system could soon be developed as a platform for implementing more advanced experiments with direct relevance to quantum information processing and quantum thermodynamics, including the study of nanoresonator quantum noise properties, reservoir engineering, and nanomechanical quantum state generation and detection.

Qubit-flip-induced cavity mode squeezing in the strong dispersive regime of the quantum Rabi model

“…However, a substantial increase in squeezing over that present in the initial state can still be obtained. It is worth noting that this value of Γ corresponds to a cavity Q of about 150, which is two orders of magnitude less than Q-factors routinely achieved for microwave resonators in circuit QED293233 and similar to the value recently measured for a qubit-coupled nanomechanical resonator29.…”

“…As the qubit and cavity are far from resonance, we do not invoke the RWA to simplify the light-matter interaction; this also allows us to work with values of g/ω ranging up to ≈0.1. Although the theory presented here may describe many different types of experimental systems, the dispersive limit is particularly applicable to experiments in circuit QED1930316465 and qubit-coupled nanomechanics29, which we touch on near the end of the paper.…”

“…The original quantum Rabi model is a ubiquitous physical model capable of describing a wide variety of other physical systems, including trapped ions2627, qubit-coupled nanomechanical resonators2829, and circuit QED systems303132333435. Circuit QED architectures are particularly interesting because it is possible to reach physical regimes where the light-matter coupling strength g becomes a sizeable fraction of the transition frequency of the boson field and/or the two-level system, meaning that the RWA is no longer a valid approximation.…”

Quantum acoustics with superconducting qubits

“…propagating surface acoustic waves 15 and micromechanical resonators in both the dispersive 14,20 and resonant 13 regimes. A central goal of these experiments is to reach the regime of quantum acoustics, in which the ability to make, manipulate, and measure non-classical states of light in cavity or circuit QED becomes applicable to mechanical degrees of freedom.…”

Conversion of mechanical noise into correlated photon pairs: Dynamical Casimir effect from an incoherent mechanical drive

“…This output photon flux is remarkable since it is much higher than the detection threshold of the state-of-the-art detectors, despite the quite low quality factor Q c = ω c /κ = 40 of the cavity considered in the numerical calculations. Furthermore, also the mechanical loss rate γ corresponds to a quality factor Q m one order of magnitude lower than the values which are experimentally measured in ultrahigh-frequency mechanical resonators [78,79]. Moreover, in Fig.…”