Bulletin of the American Physical Society
43rd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 57, Number 5
Monday–Friday, June 4–8, 2012; Orange County, California
Session C2: Advances in Laser Cooling |
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Chair: Russell Hart, Rice University Room: Grand Ballroom GF |
Tuesday, June 5, 2012 2:00PM - 2:12PM |
C2.00001: Low-temperature, high-density magneto-optical trapping of potassium using the open 4S $\rightarrow$ 5P transition at 405\,nm David McKay, Dylan Jervis, Dan Fine, John Simpson-Porco, Graham Edge, Joseph Thywissen We report [1] the laser cooling and trapping of neutral potassium on an open transition. Fermionic $^{40}$K is captured using a magneto-optical trap (MOT) on the closed $\mathrm{4S_{1/2}} \rightarrow \mathrm{4P_{3/2}} $ transition at 767\,nm and then transferred, with unit efficiency, to a MOT on the open $\mathrm{4S_{1/2}} \rightarrow \mathrm{5P_{3/2} }$ transition at 405\,nm. Because the $\mathrm{5P_{3/2} }$ state has a smaller line width than the $\mathrm{4P_{3/2}}$ state, the Doppler limit is reduced. We observe temperatures as low as 63(6)\,$\mu$K, the coldest potassium MOT reported to date. The density of trapped atoms also increases, due to reduced temperature and reduced expulsive light forces. We measure a two-body loss coefficient of $\beta = 2 \times 10^{-10}$\,cm$^3\,$s$^{-1}$, and estimate an upper bound of $8 \times 10^{-18}$\,cm$^2$ for the ionization cross section of the 5P state at 405\,nm. The combined temperature and density improvement in the 405\,nm MOT is a twenty-fold increase in phase space density over our 767\,nm MOT, showing enhanced pre-cooling for quantum gas experiments. A qualitatively similar enhancement is observed in a 405\,nm MOT of bosonic $^{41}$K. \\[4pt] [1] Physical Review A, 84, 063420 (2011) [Preview Abstract] |
Tuesday, June 5, 2012 2:12PM - 2:24PM |
C2.00002: Direct laser cooling of yttrium monoxide Matthew Hummon, Mark Yeo, Benjamin Stuhl, Yong Xia, Jun Ye Using a laser system consisting of only three lasers, one for the main cooling transition and two for vibrational repumping, we create a quasi-closed optical cycling transition for the molecule yttrium monoxide (YO) capable of scattering more than one thousand photons. Using this laser system in conjunction with a cryogenic buffer-gas-cooled source we characterize the photon scattering rate by observation of deflection of the YO molecular beam. Additionally, we observe transverse Doppler laser cooling of the YO molecular beam. [Preview Abstract] |
Tuesday, June 5, 2012 2:24PM - 2:36PM |
C2.00003: Trapped atom number in millimeter-scale magneto-optical traps Gregory W. Hoth, Elizabeth A. Donley, John Kitching For compact cold-atom instruments, it is desirable to trap a large number of atoms in a small volume to maximize the signal-to-noise ratio. In MOTs with beam diameters of a centimeter or larger, the slowing force is roughly constant versus velocity and the trapped atom number scales as $d^4$. For millimeter-scale MOTs formed from pyramidal reflectors, a $d^6$ dependence has been observed [Pollack et al., Opt. Express {\bf{17}}, 14109 (2009)]. A $d^6$ scaling is expected for small MOTs, where the slowing force is proportional to the atom velocity. For a 1 mm diameter MOT, a $d^6$ scaling results in 10 atoms, and the difference between a $d^4$ and a $d^6$ dependence corresponds to a factor of 1000 in atom number and a factor of 30 in the signal-to-noise ratio. We have observed $>10^4$ atoms in 1 mm diameter MOTs, consistent with a $d^4$ dependence. We are currently performing measurements for sub-mm MOTs to determine where the $d^4$ to $d^6$ crossover occurs in our system. We are also exploring MOTs based on linear polarization, which can potentially produce stronger slowing forces due to stimulated emission [Emile et al., Europhys. Lett. {\bf{20}}, 687 (1992)]. It may be possible to trap more atoms in small volumes with this method, since high intensities can be easily achieved. [Preview Abstract] |
Tuesday, June 5, 2012 2:36PM - 2:48PM |
C2.00004: All-Optical Production of a Lithium Quantum Gas Using Narrow-Line Laser Cooling Tsung-Lin Yang, Pedro M. Duarte, Russell A. Hart, Randall G. Hulet We have used the narrow $2S_{1/2}\rightarrow 3P_{3/2}$ transition in the ultraviolet (UV) to laser cool and magneto-optically trap (MOT) $^6$Li atoms.\footnote{P. M. Duarte et al., Phys. Rev. A \textbf{84}, 061406 (2011).} Laser cooling of lithium is usually performed on the $2S_{1/2}\rightarrow 3P_{3/2}$ (D2) transition, and temperatures of $\sim$300 $\mu$K are typically achieved. The linewidth of the UV transition is seven times narrower than the D2 line, resulting in lower laser cooling temperatures. We demonstrate that a MOT operating on the UV transition reaches temperatures as low as 59 $\mu$K. Furthermore, we find that the light shift of the UV transition in an optical dipole trap at 1070 nm is small and blue-shifted\footnote{M. Safronova, Personal Communication.}, facilitating efficient loading from the UV MOT. After loading from the UV MOT, $6 \times 10^6$ atoms with peak density $n_0=2.7\times 10^{13} \,{cm}^{-3}$ remain at $T=60\,\mu{K}$, which corresponds to $T/T_{F}\approx2.7$. Evaporative cooling of a two spin-state mixture of $^6$Li in the optical trap produces a quantum degenerate Fermi gas with $3 \times 10^{6}$ atoms in only 5~s. [Preview Abstract] |
Tuesday, June 5, 2012 2:48PM - 3:00PM |
C2.00005: ABSTRACT WITHDRAWN |
Tuesday, June 5, 2012 3:00PM - 3:12PM |
C2.00006: Two Level Atom in Bichromatic Field: Von Neumann Entropy and Laser Cooling Robinjeet Singh, Petr Anisimov, Kim Barnabas, Harold Metcalf, Hwang Lee, Jonathan Dowling We present the analysis of entropy flow during the two-level atomic interaction with a bichromatic field in the absence of spontaneous emission. Jaynes Cummings approach was used to develop the numerical model describing the system. The two mode field was detuned from atomic transition. Our calculation for flow characterizes improvement in Carnot's efficiency for laser cooling. This suggests efficient cooling of atom over a wide range of temperature and thus may give a whole new dimension to the field of laser cooling. [Preview Abstract] |
Tuesday, June 5, 2012 3:12PM - 3:24PM |
C2.00007: Sisyphus Cooling of Polyatomic Molecules Martin Zeppenfeld, Barbara G.U. Englert, Rosa Gloeckner, Alexander Prehn, Gerhard Rempe The long-range dipole-dipole interactions between polar molecules and their rich internal structure offer a multitude of experimentally unexplored possibilities for fundamental investigations at ultracold temperatures, ranging from many body physics to quantum information processing. Towards this end, a general approach to cool molecular ensembles akin to laser cooling for alkali atoms has been a much sought-after goal. In this talk, we present the experimental realization of opto-electrical cooling,\footnote{M. Zeppenfeld {\it et al.}, Phys. Rev. A {\bf 80}, 041401 (2009)} a general Sisyphus-type cooling scheme for polar molecules. As a first result, an ensemble of $10^6$ methyl-fluoride molecules has been cooled by more than a factor of 4 to 77mK, resulting in an increase in phase-space density by a factor of 7. The scheme proceeds in an electric trap, and requires only a single infrared laser with additional RF and microwave fields. The cooling cycle depends on generic properties of polar molecules and can thus be extended to a wide range of molecule species. Ongoing improvements in our trap design will allow cooling to sub-mK temperatures and beyond, opening wide-ranging opportunities for fundamental studies with polyatomic molecules at ultracold temperatures. [Preview Abstract] |
Tuesday, June 5, 2012 3:24PM - 3:36PM |
C2.00008: The Construction and Properties of an AC-MOT Melissa Anholm, H. Norton, R.M.A. Anderson, O. Theriault, J. Donohue, J.A. Behr Magneto-Optical Traps (MOTs) have long been used to produce samples of cold trapped neutral atoms, which can be used in the measurement of a variety of physical quantities and theories. Until recently, one limitation of this type of trap was the necessity for the presence of a relatively large magnetic field which would decay only slowly after the trapping mechanism was turned off. This residual magnetic field is expected to partially destroy any atomic polarization induced, for example, by optical pumping. As a result, the precision of any physical measurement which requires polarization is limited. We will discuss the construction of our version of a newer type of MOT, the AC-MOT (originally developed by Harvey and Murray, PRL 101, 173201 (2008)), which is designed specifically so as to minimize residual magnetic fields. We have found that our AC-MOT has lifetimes and cloud sizes similar to those we measured in our DC-MOT. We intend to use a trap similar to this in upcoming nuclear beta decay parity-violation measurements. [Preview Abstract] |
Tuesday, June 5, 2012 3:36PM - 3:48PM |
C2.00009: Verifying the Reif model of MOT loading:Trap depth and density dependence James Booth, Magnus Haw, Nathan Evetts, Will Gunton, Janelle Van Dongen, Kirk Madison We have studied the loading of rubidium atoms into a magneto-optical trap (MOT) with the aim of verifying a long-standing conjecture referred to as the Reif model. This model predicts that the loading rate should be proportional to the escape velocity of atoms from the trap to the fourth power, or equivalently, to the trap depth squared, and is directly proportional to the background rubidium atom density. The first prediction was confirmed by comparing the MOT loading rates to trap depths deduced from optical excitation of trapped atoms to a repulsive molecular potential. The rubidium density dependence was demonstrated by comparing the elastic collision-induced loss rate of atoms from a magnetic trap (MT) and the loading rate of a MOT: since the MT loss rate is proportional to the background density, the linear correlation to the MOT loading rate verified the Reif model. As a consequence of these findings, i) we have shown that the loading rates of different MOTs can be used as a convenient measure of their relative trap depths, and ii) we have experimentally determined the relationship between the capture and escape velocities in the MOTs studied (ranging in depth from 0.5 K to 1.8 K) to be v$_{c}$ = 1.29(0.12)v$_{e}$. [Preview Abstract] |
Tuesday, June 5, 2012 3:48PM - 4:00PM |
C2.00010: Cooling of particle ensembles with cooperative effects Guin-Dar Lin, Susanne Yelin Superradiance is known as speed-up of decay of an excited particle, essentially due to presence of near particles. Such cooperative effects can facilitate the cooling efficiency for certain particles who's transition coupling strength is usually very weak so that the normal laser cooling cannot directly apply. We investigate the possibility and scenarios where this superradiance-assisted cooling can be put into practice. [Preview Abstract] |
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