Session A8: Quantum Opto-Mechanics

Strong quadratic and quartic optomechanical couplings for QND measurements

We describe a new class of optomechanical couplings which occur in devices consisting of a dielectric membrane placed inside an optical cavity. These couplings arise from avoided crossings in the spectrum of such a cavity, and provide a number of new functionalities to existing optomechanical devices. We show that these crossings result in purely quadratic optomechanical coupling three orders of magnitude stronger than previously demonstrated, and that optical modes with strong quadratic couplings coexist with other modes having linear coupling. In addition, we show that it is possible to realize a purely quartic optomechanical coupling. The complex cavity spectrum, including the avoided crossings, is reproduced by a straightforward theoretical model. These results are demonstrated using a stochiometric silicon nitride membrane, which for 1064 nm laser light results in an intracavity absorption more than two orders of magnitude lower than the non-stochiometric membranes used previously. We describe the possible roles these improved couplings and decreased optical loss may play in the quantum regime of optomechanical devices.   

Interfacing Opto-mechanics with Atoms

We propose and analyze setups interfacing opto-mechanical systems with single atoms or atomic ensembles. In particular we show that strong, coherent coupling between a single trapped atom and a mechanical oscillator can be mediated via a laser-driven high-finesse cavity. In free space it is still possible to achieve a coherent coupling between a micromirror and an ensemble of atoms trapped in a standing wave field reflected thereof. Finally, in a travelling wave, pulsed scheme allows for a quantum non-demolition measurement of hybrid atomic-micromechanical Einstein-Podolsky-Rosen variables. The wave function of the massive mechanical oscillator and the collective atomic spin is thereby collapsed into an entangled EPR state. These setups provide the basic toolbox for coherent manipulation, preparation and measurement of micro- and nanomechanical oscillators via the tools of atomic physics. Beyond interfaces of optomechanics to AMO systems, I will discuss general perspectives of strong and super-strong optomechanical coupling.   

Interfacing ultracold atoms and mechanical oscillators on an atom chip

Ultracold atoms can be trapped and coherently manipulated close to a chip surface using atom chip technology. This opens the exciting possibility of studying interactions between atoms and on-chip solid-state systems such as micro- and nanostructured mechanical oscillators. One goal is to form hybrid quantum systems, in which atoms are used to read out, cool, and coherently manipulate the oscillators' state. In our work, we investigate different coupling mechanisms between ultracold atoms and mechanical oscillators. In a first experiment, we use atom-surface forces to couple the vibrations of a mechanical cantilever to the motion of a Bose-Einstein condensate in a magnetic microtrap on an atom chip. The atoms are trapped at about one micrometer distance from the cantilever surface. We make use of the coupling to read out the cantilever vibrations with the atoms and observe resonant coupling to several well-resolved mechanical modes of the condensate. In a second experiment, we investigate coupling via a 1D optical lattice that is formed by a laser beam retroreflected from a SiN membrane oscillator. The optical lattice serves as a `transfer rod' that couples vibrations of the membrane to the atoms and vice versa. We point out that the strong coupling regime can be reached in coupled atom-oscillator systems by placing both the atoms and the oscillator in a high-finesse optical cavity.   

Tunable cavity optomechanics with ultracold neutral atoms

Optomechanical systems are typically implemented in solid state, with significant environmental couplings, thermal occupation of the mechanical resonator mode, and optomechanical parameters fixed during device fabrication. Here we present a widely tunable optomechanical system, in which the mechanical resonator is the collective motion of an ensemble of ultracold neutral atoms, trapped in the ground state of a harmonic oscillator potential. The atoms can be positioned anywhere along a strongly coupled cavity optical probe field, allowing access to both linear and quadratic optomechanical couplings, with contrast in coupling as large as $80\%$. Varying the optical fields provides high-dynamic- range control of both the mechanical resonator natural frequency (over a factor of 10) and the strength of the per-photon optomechanical coupling (over a factor of more than 1000). We demonstrate highly tunable cavity shifts and optical bistability. We also discuss experiments to explore wave mixing, squeezing, and spin-opto-mechanical interactions in our system.