Coupling electromagnetic waves in a cavity and mechanical vibrations via the radiation pressure of the photons is a promising platform for investigations of quantum mechanical propertiesof motion of macroscopic bodies and thereby the limits of quantum mechanics [3,4]. A drawback is that the effect of one photon tends to be tiny, and hence one of the pressing challenges is to substantially increase the interaction strength towards the scale of the cavity damping rate. A novel scenario is to introduce into the setup a quantum two-level system (qubit), which, besides strengthening the coupling, allows for rich physics via strongly enhanced nonlinearities [5-8]. Addressing these issues, here we present a design of cavity optomechanics in the microwave frequency regime involving a Josephson junction qubit. We demonstrate boosting of the radiation pressure interaction energy by six orders of magnitude, allowing to approach the strong coupling regime, where a single quantum of vibrations shifts the cavity frequency by more than its linewidth. We observe nonlinear phenomena at single-photon energies, such as an enhanced damping due to the two-level system. This work opens up nonlinear cavity optomechanics as a plausible tool for the study of quantum properties of motion.
Hybrid quantum systems with inherently distinct degrees of freedom play a key
role in many physical phenomena. A strong coupling can make the constituents
loose their individual characterand form entangled states. The properties of
these collective excitations, such as polaritons of light and phonons in
semiconductors, can combine the benefits of each subsystem. In the emerging
field of quantum information control, a promising direction is provided by the
combination between long-lived atomic states and the accessible electrical
degrees of freedom in superconducting cavities and qubits. Here we demonstrate
the possibility to integrate circuit cavity quantum electrodynamics with
phonons. Besides coupling to a microwave cavity, our superconducting transmon
qubit interacts with a resonant phonon mode in a micromechanical resonator,
allowing the combination of long lifetime, strong tunable coupling, and ease of
access. We measure the phonon Stark shift, as well as the splitting of the
transmon qubit spectral line into motional sidebands representing transitions
between electromechanical polaritons formed by phonons and the qubit. In the
time domain, we observe coherent sideband Rabi oscillations between the qubit
states and phonons. This advance may allow for storage of quantum information
in long-lived phonon states, and for investigations of strongly coupled quantum
systems near the classical limit.
Superconducting circuits with Josephson junctions are promising candidates
for developing future quantum technologies. Of particular interest is to use
these circuits to study effectsthat typically occur in complex
condensed-matter systems. Here, we employ a superconducting quantum bit
(qubit), a transmon, to carry out an analog simulation of motional averaging, a
phenomenon initially observed in nuclear magnetic resonance (NMR) spectroscopy.
To realize this effect, the flux bias of the transmon is modulated by a
controllable pseudo-random telegraph noise, resulting in stochastic jumping of
the energy separation between two discrete values. When the jumping is faster
than a dynamical threshold set by the frequency displacement of the levels, the
two separated spectral lines merge into a single narrow-width,
motional-averaged line. With sinusoidal modulation a complex pattern of
additional sidebands is observed. We demonstrate experimentally that the
modulated system remains quantum coherent, with modified transition
frequencies, Rabi couplings, and dephasing rates. These results represent the
first steps towards more advanced quantum simulations using artificial atoms.