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FROM CAVITY OPTOMECHANICS TO THE DICKE QUANTUM PHASE TRANSITION Ferdinand Brennecke Department of Physics, ETH Zürich, Switzerland Coupling the collective motion of ultracold gases to high-Q optical resonators provides an approach towards unexplored regimes in cavity optomechanics [1, 2]. In these mesoscopic systems, the ground state of the mechanical oscillator is naturally prepared by the initial cooling of the atomic gas. In our experiment, a Bose-Einstein condensate of about 10 5 alkali atoms is coupled dispersively to the single-mode field of an ultrahigh-finesse optical cavity. A collective density oscillation of the condensate serves as a mechanical element which couples to the cavity field intensity. We observe optical bistability already below the single-photon level and a strong backaction dynamics, in quantitative agreement with a cavity optomechanical model. The experiment reaches the strong coupling regime of cavity optomechanics, where already single mechanical excitations have a significant effect on the cavity field. In a different setting of the experiment exploiting the mechanical effects of light on quantum gases, we recently observed a non-equilibrium version of the Dicke quantum phase transition [3, 4, 5]. A far-detuned pump field aligned perpendicular to the cavity axis induces a dipole-like interaction between the cavity field and a collective density wave. Above a critical pump strength the atoms self-organize on a checkerboard structure, which is associated with a spontaneously broken symmetry. The cavity decay channel allows us to extract valuable in-situ information about the system like its phase diagram, the appearance of spontaneous symmetry breaking, and the vanishing excitation gap close to the critical point. Our observations are quantitatively described by the Dicke model. References: [1] K. W. Murch, K.L. Moore, S. Gupta, D. M. Stamper-Kurn, Nature Physics 4, 561 (2008) [2] F. Brennecke, S. Ritter, T. Donner, T. Esslinger, Science 322, 235 (2008) [ [3] K. Baumann, C. Guerlin, F. Brennecke, T. Esslinger, Nature 464, 1301 (2010) [4] R. H. Dicke, Phys.Rev 93(1), 99 (1954) [5] K. Hepp, E.H. Lieb, Annals of Physics 76(2), 360 (1973) 10
LINEAR AND QUADRATIC OPTOMECHANICS WITH AN ARRAY OF ULTRACOLD ATOMIC ENSEMBLES Daniel Brooks UC Berkeley Atomic ensembles have a number of advantages as optomechanical oscillators . They can be cooled to their motional ground state using atomic cooling techniques, have very low thermal coupling to the surrounding environment, and can be probed in the single-photon strong coupling regime. We present an experiment using an integrated atom-chip/cavity device operated with atoms initialized in their motional ground state. Strong magnetic-field gradients from the atom chip allow us to prepare atomic ensembles centered on locations that are primarily either linearly or quadratically coupled to the cavity field. In addition, we can alter the light-atom coupling strength of neighboring atomic ensembles in a 1D array by using a magnetic resonance technique to address the atomic spin. We also present ongoing studies of the linear optomechanical gain of the atom-cavity device driven by near shot-noise fluctuations of the light. 11
Page 1 and 2: Table of Contents WORKSHOP SCHEDULE
Page 3 and 4: Schedule MONDAY, FEBRUARY 7 Phillip
Page 5 and 6: JAMIL ABO-SHAEER PARTICIPANTS Darpa
Page 7 and 8: MONIKA SCHLEIER-SMITH SWATI SINGH P
Page 9: TOWARDS QUANTUM SUPERPOSITIONS OF A
Page 13 and 14: OPTOMECHANICS OF A QUANTUM DEGENERA
Page 15 and 16: NONLINEAR OPTOMECHANICS: QUADRATIC
Page 17 and 18: THE PHOTON BLOCKADE EFFECT IN OPTOM
Page 19 and 20: OPTOMECHANICAL MATTER-WAVE INTERFER
Page 21 and 22: CAVITY OPTOMECHANICS: BEYOND THE GR
Page 23 and 24: CIRCUIT CAVITY ELECTROMECHANICS IN
Page 25 and 26: RADIATION PRESSURE AND QUANTUM NOIS
Page 27 and 28: ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !

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