55
55
Sep 23, 2013
09/13
by
B. Pasquiou; E. Marechal; L. Vernac; O. Gorceix; B. Laburthe-Tolra
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We study thermodynamic properties of a gas of spin 3 52Cr atoms across Bose Einstein condensation. Magnetization is free, due to dipole-dipole interactions (DDIs). We show that the critical temperature for condensation is lowered at extremely low magnetic fields, when the spin degree of freedom is thermally activated. The depolarized gas condenses in only one spin component, unless the magnetic field is set below a critical value, below which a non ferromagnetic phase is favored. Finally we...
Source: http://arxiv.org/abs/1110.0786v1
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59
Sep 20, 2013
09/13
by
G. Bismut; B. Laburthe-Tolra; E. Marechal; P. Pedri; O. Gorceix; L. Vernac
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eye 59
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We measure the excitation spectrum of a dipolar Chromium Bose Einstein Condensate with Raman-Bragg spectroscopy. The energy spectrum depends on the orientation of the dipoles with respect to the excitation momentum, demonstrating an anisotropy which originates from the dipole-dipole interactions between the atoms. We compare our results with the Bogoliubov theory based on the local density approximation, and, at large excitation wavelengths, with numerical simulations of the time dependent...
Source: http://arxiv.org/abs/1205.6305v1
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58
Sep 17, 2013
09/13
by
E. Marechal; B. Laburthe-Tolra; L. Vernac; J. -C. Keller; O. Gorceix
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eye 58
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We report on a new type of magnetic lens that focuses atomic clouds using a static inhomogeneous magnetic field in combination with a radio-frequency field. The experimental study is performed with a cloud of cold cesium atoms. The rf field adiabatically deforms the magnetic potential of a coil and therefore changes its focusing properties. The focal length can be tuned precisely by changing the rf frequency value. Depending on the rf antenna position relative to the DC magnetic profile, the...
Source: http://arxiv.org/abs/0711.4667v2
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6.0
Jun 30, 2018
06/18
by
B. Naylor; A. Reigue; E. Maréchal; O. Gorceix; B. Laburthe-Tolra; L. Vernac
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We report on the production of a degenerate Fermi gas of 53Cr atoms, polarized in the state F=9/2, m_F=-9/2, by sympathetic cooling with bosonic S=3, m_S=-3 52Cr atoms. We load in an optical dipole trap 3.10^4 53Cr atoms with 10^6 52Cr atoms. Despite this initial small number of fermionic atoms, we reach a final temperature of T=0.6 T_f (Fermi temperature), with up to 10^3 53Cr atoms. This surprisingly efficient evaporation stems from an inter-isotope scattering length |a_{BF}| = (85+/- 10)...
Topics: Quantum Gases, Condensed Matter
Source: http://arxiv.org/abs/1411.4634
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54
Sep 21, 2013
09/13
by
D. Comparat; A. Fioretti; G. Stern; E. Dimova; B. Laburthe Tolra; P. Pillet
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eye 54
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We suggest different simple schemes to efficiently load and evaporate a ''dimple'' crossed dipolar trap. The collisional processes between atoms which are trapped in a reservoir load in a non adiabatic way the dimple. The reservoir trap can be provided either by a dark SPOT Magneto Optical Trap, the (aberrated) laser beam itself or by a quadrupolar or quadratic magnetic trap. Optimal parameters for the dimple are derived from thermodynamical equations and from loading time, including possible...
Source: http://arxiv.org/abs/quant-ph/0602010v1
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49
Sep 22, 2013
09/13
by
Q. Beaufils; A. Crubellier; T. Zanon; B. Laburthe-Tolra; E. Marechal; L. Vernac; O. Gorceix
texts
eye 49
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We develop a theoretical model to describe the radio-frequency (rf) induced coupling of a pair of colliding atoms to a Feshbach molecule when a magnetic field arbitrarily far from the Feshbach resonance is modulated in time. We use the dressed atom picture, and show that the coupling strength in presence of rf is equal to the Feshbach coupling strength multiplied by the square of a Bessel function. The argument of this function is equal to the ratio of the atomic rf Rabi frequency to the rf...
Source: http://arxiv.org/abs/0812.4355v1
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77
Sep 22, 2013
09/13
by
Q. Beaufils; A. Crubellier; T. Zanon; B. Laburthe-Tolra; E. Marechal; L. Vernac; O. Gorceix
texts
eye 77
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We analyse a narrow Feshbach resonance with ultra-cold chromium atoms colliding in d-wave. The resonance is made possible by dipole-dipole interactions, which couple an incoming $l=2$ collision channel with a bound molecular state with $l=0$. We find that three-body losses associated to this resonance increase with temperature, and that the loss feature width as a function of magnetic field also increases linearly with temperature. The analysis of our experimental data shows that the Feshbach...
Source: http://arxiv.org/abs/0811.4282v1
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51
Sep 21, 2013
09/13
by
J. H. Huckans; I. B. Spielman; B. Laburthe Tolra; W. D. Phillips; J. V. Porto
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eye 51
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We experimentally investigate diffraction of a Rb-87 Bose-Einstein condensate from a 1D optical lattice. We use a range of lattice periods and timescales, including those beyond the Raman-Nath limit. We compare the results to quantum mechanical and classical simulations, with quantitative and qualitative agreement, respectively. The classical simulation predicts that the envelope of the time-evolving diffraction pattern is shaped by caustics: singularities in the phase space density of...
Source: http://arxiv.org/abs/0901.1386v1
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42
Sep 22, 2013
09/13
by
G. Bismut; B. Pasquiou; D. Ciampini; B. Laburthe-Tolra; E. Marechal; L. Vernac; O. Gorceix
texts
eye 42
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We report on a strategy to maximize the number of chromium atoms transferred from a magneto-optical trap into an optical trap through accumulation in metastable states via strong optical pumping. We analyse how the number of atoms in a chromium Bose Einstein condensate can be raised by a proper handling of the metastable state populations. Four laser diodes have been implemented to address the four levels that are populated during the MOT phase. The individual importance of each state is...
Source: http://arxiv.org/abs/1004.3642v1
51
51
Jul 19, 2013
07/13
by
G. Bismut; B. Pasquiou; E. Maréchal; P. Pedri; L. Vernac; O. Gorceix; B. Laburthe-Tolra
texts
eye 51
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We have measured the effect of dipole-dipole interactions on the frequency of a collective mode of a Bose-Einstein condensate. At relatively large numbers of atoms, the experimental measurements are in good agreement with zero temperature theoretical predictions based on the Thomas Fermi approach. Experimental results obtained for the dipolar shift of a collective mode show a larger dependency to both the trap geometry and the atom number than the ones obtained when measuring the modification...
Source: http://arxiv.org/abs/1005.2493v1
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49
Sep 19, 2013
09/13
by
B. Pasquiou; G. Bismut; E. Maréchal; P. Pedri; L. Vernac; O. Gorceix; B. Laburthe-Tolra
texts
eye 49
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We observe interband transitions mediated by the dipole-dipole interaction for an array of 1D quantum gases of chromium atoms, trapped in a 2D optical lattice. Interband transitions occur when dipolar relaxation releases an energy which matches or overcomes the lattice band gap. We analyze the role of tunneling in higher lattice bands on this process. We compare the experimental dipolar relaxation rate with a calculation based on a multiple Fermi Golden Rule approach, when the lattice sites are...
Source: http://arxiv.org/abs/1010.3241v2
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30
Sep 23, 2013
09/13
by
A. de Paz; A. Chotia; E. Marechal; P. Pedri; L. Vernac; O. Gorceix; B. Laburthe-Tolra
texts
eye 30
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We study dipolar relaxation of a chromium BEC loaded into a 3D optical lattice. We observe dipolar relaxation resonances when the magnetic energy released during the inelastic collision matches an excitation towards higher energy bands. A spectroscopy of these resonances for two orientations of the magnetic field provides a 3D band spectroscopy of the lattice. The narrowest resonance is registered for the lowest excitation energy. Its line-shape is sensitive to the on-site interaction energy....
Source: http://arxiv.org/abs/1212.5469v1
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48
Sep 22, 2013
09/13
by
R. Chicireanu; A. Pouderous; R. Barbe; B. Laburthe-Tolra; E. Marechal; L. Vernac; J. -C. Keller; O. Gorceix
texts
eye 48
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We report on magneto-optical trapping of fermionic 53Cr atoms. A Zeeman-slowed atomic beam provides loading rates up to 3 10^6 /s. We present systematic characterization of the magneto-optical trap (MOT). We obtain up to 5 10^5 atoms in the steady state MOT. The atoms radiatively decay from the excited P state into metastable D states, and, due to the large dipolar magnetic moment of chromium atoms in these states, they can remain magnetically trapped in the quadrupole field gradient of the...
Source: http://arxiv.org/abs/quant-ph/0603028v1
62
62
Sep 18, 2013
09/13
by
R. Chicireanu; Q. Beaufils; A. Pouderous; B. Laburthe-Tolra; E. Marechal; L. Vernac; J. -C. Keller; O. Gorceix
texts
eye 62
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We report the fast accumulation of a large number of metastable 52Cr atoms in a mixed trap, formed by the superposition of a strongly confining optical trap and a quadrupolar magnetic trap. The steady state is reached after about 400 ms, providing a cloud of more than one million metastable atoms at a temperature of about 100 microK, with a peak density of 10^{18} atoms.m^{-3}. We have optimized the loading procedure, and measured the light shift of the 5D4 state by analyzing how the trapped...
Source: http://arxiv.org/abs/0705.1479v1
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39
Sep 21, 2013
09/13
by
Q. Beaufils; T. Zanon; R. Chicireanu; B. Laburthe-Tolra; E. Marechal; L. Vernac; J. -C. Keller; O. Gorceix
texts
eye 39
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We study the effect of strong radio-frequency (rf) fields on a chromium Bose-Einstein condensate (BEC), in a regime where the rf frequency is much larger than the Larmor frequency. We use the modification of the Land\'{e} factor by the rf field to bring all Zeeman states to degeneracy, despite the presence of a static magnetic field of up to 100 mG. This is demonstrated by analyzing the trajectories of the atoms under the influence of dressed magnetic potentials in the strong field regime. We...
Source: http://arxiv.org/abs/0808.3931v2
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42
Sep 21, 2013
09/13
by
Q. Beaufils; R. Chicireanu; T. Zanon; B. Laburthe-Tolra; E. Marechal; L. Vernac; J. -C. Keller; O. Gorceix
texts
eye 42
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We report on the production of ^52Cr Bose Einstein Condensates (BEC) with an all-optical method. We first load 5.10^6 metastable chromium atoms in a 1D far-off-resonance optical trap (FORT) from a Magneto Optical Trap (MOT), by combining the use of Radio Frequency (RF) frequency sweeps and depumping towards the ^5S_2 state. The atoms are then pumped to the absolute ground state, and transferred into a crossed FORT in which they are evaporated. The fast loading of the 1D FORT (35 ms 1/e time),...
Source: http://arxiv.org/abs/0712.3521v2
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54
Sep 23, 2013
09/13
by
B. Laburthe Tolra; K. M. O'Hara; J. H. Huckans; W. D. Phillips; S. L. Rolston; J. V. Porto
texts
eye 54
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We investigate correlation properties of a one-dimensional interacting Bose gas by loading a magnetically trapped 87-Rb Bose-Einstein condensate into a deep two-dimensional optical lattice. We measure the three-body recombination rate for both the BEC in the magnetic trap and the BEC loaded into the optical lattice. The recombination rate coefficient is a factor of seven smaller in the lattice, which we interpret as a reduction in the local three-body correlation function in the 1D case. This...
Source: http://arxiv.org/abs/cond-mat/0312003v1
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48
Sep 20, 2013
09/13
by
B. Pasquiou; G. Bismut; Q. Beaufils; A. Crubellier; E. Maréchal; P. Pedri; L. Vernac; O. Gorceix; B. Laburthe-Tolra
texts
eye 48
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We study dipolar relaxation in both ultra-cold thermal and Bose-condensed chromium atom gases. We show three different ways to control dipolar relaxation, making use of either a static magnetic field, an oscillatory magnetic field, or an optical lattice to reduce the dimensionality of the gas from 3D to 2D. Although dipolar relaxation generally increases as a function of a static magnetic field intensity, we find a range of non-zero magnetic field intensities where dipolar relaxation is...
Source: http://arxiv.org/abs/1002.0222v1
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68
Jun 30, 2018
06/18
by
A. de Paz; B. Naylor; J. Huckans A. Carrance; O. Gorceix; E. Marechal; P. Pedri; B. Laburthe-Tolra; L. Vernac
texts
eye 68
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We experimentally study the spin dynamics of mesoscopic ensembles of ultracold magnetic spin-3 atoms located in two separated wells of an optical dipole trap. We use a radio-frequency sweep to selectively flip the spin of the atoms in one of the wells, which produces two separated spin domains of opposite polarization. We observe that these engineered spin domains are metastable with respect to the long-range magnetic dipolar interactions between the two ensembles. The absence of inter-cloud...
Topics: Physics, Quantum Gases, Atomic Physics, Quantum Physics, Condensed Matter
Source: http://arxiv.org/abs/1407.8130
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68
Sep 20, 2013
09/13
by
R. Chicireanu; Q. Beaufils; A. Pouderous; B. Laburthe-Tolra; E. Marechal; J. V. Porto; L. Vernac; J. C. Keller; O. Gorceix
texts
eye 68
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We experimentally and theoretically study the continuous accumulation of cold atoms from a magneto-optical trap (MOT) into a finite depth trap, consisting in a magnetic quadrupole trap dressed by a radiofrequency (RF) field. Chromium atoms (52 isotope) in a MOT are continuously optically pumped by the MOT lasers to metastable dark states. In presence of a RF field, the temperature of the metastable atoms that remain magnetically trapped can be as low as 25 microK, with a density of 10^17...
Source: http://arxiv.org/abs/physics/0612133v1
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50
Sep 17, 2013
09/13
by
Q. Beaufils; R. Chicireanu; A. Pouderous; W. de Souza Melo; B. Laburthe-Tolra; E. Maréchal; L. Vernac; J. C. Keller; O. Gorceix
texts
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We introduce a novel type of time-averaged trap, in which the internal state of the atoms is rapidly modulated to modify magnetic trapping potentials. In our experiment, fast radiofrequency (rf) linear sweeps flip the spin of atoms at a fast rate, which averages out magnetic forces. We use this procedure to optimize the accumulation of metastable chomium atoms into an optical dipole trap from a magneto-optical trap. The potential experienced by the metastable atoms is identical to the bare...
Source: http://arxiv.org/abs/0711.0663v1
