Micromechanical oscillator ground-state cooling via resonant intracavity optical gain or absorption

Abstract

We predict ground state cooling of a micro-mechanical oscillator, i.e. a vibrating end-mirror of an optical cavity, by resonant coupling of mirror vibrations to a narrow internal optical transition of an ensemble of two level systems. The particles represented by a collective mesoscopic spin model implement, together with the cavity, an efficient, frequency tailorable zero temperature loss channel which can be turned to a gain channel of pump. As opposed to the case of resolved-sideband cavity cooling requiring a small cavity linewidth, one can work here with low finesses and very small cavity volumes to enhance the light mirror and light atom coupling. The tailored loss and gain channels provide for efficient removal of vibrational quanta and suppress reheating. In a simple physical picture of sideband cooling, the atoms shape the cavity profile to enhance/inhibit scattering into higher/lower energy sidebands. The method should be applicable to other cavity based cooling schemes for atomic and molecular gases as for molecular ensembles coupled to stripline cavities.Cavity cooling of micro-mechanical oscillators has seen tremendous experimental progress [1,2,3,4,5,6,7,8] in the past few years, also stimulated by theoretical analysis showing that the quantum ground state of such oscillators is achievable [9,10,11]. In essence, through cavity mediated interaction the mechanical vibrations at kHz-MHz frequencies are converted to strongly damped sidebands of light modes at optical frequencies, that contain essentially no thermal excitations (thermal photons). Standard sideband cooling is effective only when the linewidth of the optical resonator κ is smaller than the mirror vibration frequency ω m and one has a sufficient optomechanical coupling. For a given mirror reflectance a small enough κ can be reached using longer cavities, but strong optomechanical coupling then requires a very large intracavity field and input power.Here we propose the alternative use of atomic, molecular or solid state electronic transitions as extremely localized narrow bandwidth oscillators, for the cooling process. These are coupled to the vibrational modes via a cavity light mode. Strong mirror-light and light-atom coupling can be achieved while still maintaining a narrow and tailorable resonance behavior. As the simplest generic example we will consider ensembles of two-level atoms with a narrow transition suitably detuned from the cavity resonance. At optical frequencies thermal excitations of the atoms can be neglected and the atoms constitute an effective zero temperature reservoir, where energy and entropy can be dissipated efficiently. Note that using optical resonances to cool solids has already been shown successful in optical fibers [12].Cavity assisted sideband cooling is based on unequal scattering of pump photons into higher/lower energy (antiStokes/Stokes) photons; the cavity modifies the density of optical modes around the laser frequency such that a higher density at the anti-Stokes frequency leads to a higher scattering...

Single-Polariton Optomechanics

“…The coupling of an optomechanical cavity to an atom motion [9] or to collective excitations of an ensemble of atoms [10] was also discussed, resulting in the physical situation of two linearly coupled harmonic oscillators. In that case the anharmonic internal structure of a single atom and its corresponding nonlinear dynamics, a key feature of cavity and circuit QED, is absent.…”

Ground-state cooling of a dispersively coupled optomechanical system in the unresolved sideband regime via a dissipatively coupled oscillator

“…Thus, a solution to the difficult problem of cooling the dispersively coupled oscillator is provided. Note that this approach is not the first reported technique of this kind; however, the existing schemes for ground-state cooling in the unresolved sideband, such as cooling with optomechanically induced transparency (OMIT) [33,34], coupled-cavity configurations [35,36], atom-optomechanical hybrid systems [37][38][39][40][41][42][43][44], and the recently proposed scheme using quantum non-demolition interactions [45], require multiple driving lasers, multiple optical modes, high-quality cavities, and ground-state atom ensembles. Compared with those methods, our proposal offers a simpler option for cases in which dissipative coupling is accessible.…”

Single-atom cavity QED and optomicromechanics

“…Most generally the interaction is mediated by a light field that couples the mechanical resonator via the radiation pressure effect to either internal levels of the atoms [13][14][15], or to their motional degrees of freedom [16], which can result, e.g., in cooling of the mechanical resonator via a bath of atoms [17]. Also a direct coupling has been proposed where a magnetic tip mounted on a cantilever provides a Zeeman coupling to the atomic spin of the Bose-Einstein-condensed [18] or ultracold [19] atoms.…”