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Register a new userOptomechanical self-structuring in cold atomic gases
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The rapidly developing field of optomechanics aims at the combined control of optical and mechanical (solid-state or atomic) modes. In particular, laser cooled atoms have been used to exploit optomechanical coupling for self-organization in a variety of schemes where the accessible length scales are constrained by a combination of pump modes and those associated to a second imposed axis, typically a cavity axis. Here, we consider a system with many spatial degrees of freedom around a single distinguished axis, in which two symmetries - rotations and translations in the plane orthogonal to the pump axis - are spontaneously broken. We observe the simultaneous spatial structuring of the density of a cold atomic cloud and an optical pump beam. The resulting patterns have hexagonal symmetry. The experiment demonstrates the manipulation of matter by opto-mechanical self-assembly with adjustable length scales and can be potentially extended to quantum degenerate gases.
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We design and implement an efficient high-current radio-frequency (RF) circuit, enabling fast and coherent coupling between magnetic levels in cold alkali atomic samples. It is based on a compact shape-optimized coil that maximizes the RF field coupling with the atomic magnetic dipole, and on coaxial transmission-line transformers that step up the field-generating current flowing in the coil to about 8 A for 100 W of RF power. The system is robust and versatile, as it generates a large RF field without compromising on the available optical access, and its central resonant frequency can be adjusted in situ. Our approach provides a cost-effective, reliable solution, featuring a low level of interference with surrounding electronic equipment thanks to its symmetric layout. We test the circuit performance using a maximum RF power of 80 W at a frequency around 82 MHz, which corresponds to a measured Rabi frequency $Omega_R/2pi simeq 18.5$ kHz, i.e. a $pi$-pulse duration of about 27 $mu$s, between two of the lowest states of ${}^6$Li at an offset magnetic field of 770 G. Our solution can be readily adapted to other atomic species and vacuum chamber designs, in view of increasing modularity of ultracold atom experiments.
We report on the successful extension of production of Bose-Einstein Condensate (BEC) to rare species. Despite its low natural abundance of 0.13%, $^{168}$Yb is directly evaporatively cooled down to BEC. Our successful demonstration encourages attempts to obtain quantum gases of radioactive atoms, which extends the possibility of quantum many-body physics and precision measurement. Moreover, a stable binary mixture of $^{168}$Yb BEC and $^{174}$Yb BEC is successfully formed.
We observe the shift of Rydberg levels of rubidium close to a copper surface when atomic clouds are repeatedly deposited on it. We measure transition frequencies of rubidium to S and D Rydberg states with principal quantum numbers n between 31 and 48 using the technique of electromagnetically induced transparency. The spectroscopic measurement shows a strong increase of electric fields towards the surface that evolves with the deposition of atoms. Starting with a clean surface, we measure the evolution of electrostatic fields in the range between 30 and 300 mum from the surface. We find that after the deposition of a few hundred atomic clouds, each containing ~10^6 atoms, the field of adsorbates reaches 1 V/cm for a distance of 30 mum from the surface. This evolution of the electrostatic field sets serious limitations on cavity QED experiments proposed for Rydberg atoms on atom chips.
Self-organized phases in cold atoms as a result of light-mediated interactions can be induced by coupling to internal or external degrees of the atoms. There has been growing interest in the interaction of internal spin degrees of freedom with the optomechanical dynamics of the external centre-of-mass motion. We present a model for the coupling between magnetic and optomechanical structuring in a $J=1/2 to J=3/2$ system in a single-mirror feedback scheme, being representative for a larger class of diffractively coupled systems such as longitudinally pumped cavities and counter-propagating beam schemes. For negative detunings, a linear stability analysis demonstrates that optical pumping and optomechanical driving cooperate to create magnetic ordering. However, for long-period transmission gratings the magnetic driving will strongly dominate the optomechanical driving, unless one operates very close to the existence range of the magnetic instability. At small lattice periods, in particular at wavelength-scale periods, the optomechanical driving will dominate.
A quasi-resonant laser induces a long-range attractive force within a cloud of cold atoms. We take advantage of this force to build in the laboratory a system of particles with a one-dimensional gravitational-like interaction, at a fluid level of modeling. We give experimental evidences of such an interaction in a cold Strontium gas, studying the density profile of the cloud, its size as a function of the number of atoms, and its breathing oscillations.
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