Radiation-pressure self-cooling of a micromirror in a cryogenic environment (original) (raw)

Self-cooling of a micromirror by radiation pressure

Nature, 2006

Cooling of mechanical resonators is currently a popular topic in many fields of physics including ultra-high precision measurements 1 , detection of gravitational waves 2,3 and the study of the transition between classical and quantum behaviour of a mechanical system 4-6 . Here we report the observation of self-cooling of a micromirror by radiation pressure inside a high-finesse optical cavity. In essence, changes in intensity in a detuned cavity, as caused by the thermal vibration of the mirror, provide the mechanism for entropy flow from the mirror's oscillatory motion to the low-entropy cavity field 2 . The crucial coupling between radiation and mechanical motion was made possible by producing freestanding micromirrors of low mass (m < 400 ng), high reflectance (more than 99.6%) and high mechanical quality (Q < 10,000). We observe cooling of the mechanical oscillator by a factor of more than 30; that is, from room temperature to below 10 K. In addition to purely photothermal effects 7 we identify radiation pressure as a relevant mechanism responsible for the cooling. In contrast with earlier experiments, our technique does not need any active feedback 8-10 . We expect that improvements of our method will permit cooling ratios beyond 1,000 and will thus possibly enable cooling all the way down to the quantum mechanical ground state of the micromirror.

Radiation pressure excitation and cooling of a cryogenic MEMS-cavity

CLEO/Europe - EQEC 2009 - European Conference on Lasers and Electro-Optics and the European Quantum Electronics Conference, 2009

We describe an experiment achieving radiation pressure excitation and cooling of a mechanical mode in a cryogenic Fabry-Perot cavity with a micro-mechanical oscillator (MEMS) as end mirror.

Optical cooling of a micromirror of wavelength size

Applied Physics Letters, 2007

The authors report on the passive optical cooling of the Brownian motion of a cantilever suspended micromirror. They show that laser cooling is possible for a mirror of size in the range of the diffraction limit ͑at = 1.3 m͒. This represents the tiniest mirror optically cooled so far, with a mass of 11.3 pg, more than four orders of magnitude lighter than current mirrors used in cavity cooling. The reciprocal effect of cooling is also investigated and opens the way to the optical excitation of megahertz vibrational modes under continuous wave laser illumination.

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

Physical Review A, 2009

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.

Simultaneous cooling and entanglement of mechanical modes of a micromirror in an optical cavity

New Journal of Physics, 2008

Laser cooling of a mechanical mode of a resonator by the radiation pressure of a detuned optical cavity mode has been recently demonstrated by various groups in different experimental configurations. Here we consider the effect of a second mechanical mode with a close, but different resonance frequency. We show that the nearby mechanical resonance is simultaneously cooled by the cavity field, provided that the difference between the two mechanical frequencies is not too small. When this frequency difference becomes smaller than the effective mechanical damping of the secondary mode, the two cooling processes interfere destructively and cavity cooling is suppressed in the limit of identical mechanical frequencies. We show that also the entanglement properties of the steady state of the tripartite system crucially depend upon on the difference between the two mechanical frequencies. If the latter is larger than the effective damping of the second mechanical mode, the state shows fully tripartite entanglement and each mechanical mode is entangled with the cavity mode. If instead the frequency difference is smaller, the steady state is a two-mode biseparable state, inseparable only when one splits the cavity mode from the two mechanical modes. In this latter case, the entanglement of each mechanical mode with the cavity mode is extremely fragile with respect to temperature.

Resolved-sideband cooling of a micromechanical oscillator

Nature Physics, 2008

Micro-and nanoscale opto-mechanical systems-based on cantilevers , micro-cavities or macroscopic mirrors -provide radiation pressure coupling of optical and mechanical degree of freedom and are actively pursued for their ability to explore quantum mechanical phenomena of macroscopic objects . Many of these investigations require preparation of the mechanical system in or close to its quantum ground state. In the past decades, remarkable progress in ground state cooling has been achieved for trapped ions and atoms confined in optical lattices , enabling the preparation of non-classical states of motion and Schrödinger cat states . Imperative to this progress has been the technique of resolved sideband cooling , which allows overcoming the inherent temperature limit of Doppler cooling and necessitates a harmonic trapping frequency which exceeds the atomic species' transition rate. The recent advent of cavity back-action cooling [20] of mechanical oscillators by radiation pressure has followed a similar path with Doppler-type cooling being demonstrated [1, 2, 4, 5, 21], but lacking inherently the ability to attain ground state cooling as recently predicted . Here we demonstrate for the first time resolved sideband cooling of a mechanical oscillator. By pumping the first lower sideband of an optical microcavity , whose decay rate is more than twenty times smaller than the eigen-frequency of the associated mechanical oscillator, cooling rates above 1.5 MHz are attained, exceeding the achievable rates in atomic species . Direct spectroscopy of the motional sidebands reveals 40-fold suppression of motional increasing processes, which could enable attaining final phonon occupancies well below unity (< 0.03). Elemental demonstration of resolved sideband cooling as reported here, should find widespread use in opto-mechanical cooling experiments and represents a key step to attain ground state cooling of macroscopic mechanical oscillators . Equally important, this regime allows realization of motion measurement with an accuracy exceeding the standard quantum limit by two mode pumping [25] and could thereby allow preparation of non-classical states of motion.

Optomechanical sideband cooling of a micromechanical oscillator close to the quantum ground state

Phys Rev a, 2011

Cooling a mesoscopic mechanical oscillator to its quantum ground state is elementary for the preparation and control of low entropy quantum states of large scale objects. Here, we pre-cool a 70-MHz micromechanical silica oscillator to an occupancy below 200 quanta by thermalizing it with a 600-mK cold 3 He gas. Two-level system induced damping via structural defect states is shown to be strongly reduced, and simultaneously serves as novel thermometry method to independently quantify excess heating due to a cooling laser. We demonstrate that dynamical backaction sideband cooling can reduce the average occupancy to 9 ± 1 quanta, implying that the mechanical oscillator can be found (10 ± 1)% of the time in its quantum ground state.

Radiation-Pressure Cooling of a Micro-Mechanical Oscillator Using Dynamical Backaction

Conference on Coherence and Quantum Optics, 2007

Cooling of a 58 MHz micromechanical resonator from room temperature to 11 K is demonstrated using cavity enhanced radiation pressure. Detuned pumping of an optical resonance allows enhancement of the blueshifted motional sideband (caused by the oscillator's Brownian motion) with respect to the redshifted sideband leading to cooling of the mechanical oscillator mode. The reported cooling mechanism is a manifestation of the effect of radiation pressure induced dynamical backaction. These results constitute an important step towards achieving ground state cooling of a mechanical oscillator.