Accumulation of chromium metastable atoms into an optical trap

Chicireanu, Radu; Beaufils, Quentin; Pouderous, A.; Laburthe‐Tolra, B.; Maréchal, É.; Vernac, L.; Keller, J.; Gorceix, O.

doi:10.1140/epjd/e2007-00245-y

Cited by 13 publications

(17 citation statements)

References 16 publications

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“…The optimum detuning is slightly shifted from δ = 2π × 47.3 MHz = 9.4Γ (with Γ = 2π × 5.029 MHz) to δ = 2π × 42.7 MHz = 8.5Γ when the trap is turned on, which is attributed to the fact that the ground and excited states do not undergo the same AC Stark shift at 1075 nm. Such a differential light shift is confirmed by numerical estimates [35], and by the observation that, during the MOT stage, atoms in the ODT region undergo stronger fluorescence than away from the ODT, despite the fact that only a negligible fraction of 7 S 3 atoms are trapped in the ODT.…”

Section: Gray Molasses Optimizationsupporting

confidence: 52%

Cooling all external degrees of freedom of optically trapped chromium atoms using gray molasses

et al. 2019

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We report on a scheme to cool and compress trapped clouds of highly magnetic 52 Cr atoms. This scheme combines sequences of gray molasses, which freeze the velocity distribution, and free evolutions in the (close to) harmonic trap, which periodically exchange the spatial and velocity degrees of freedom. Taken together, the successive gray molasses pulses cool all external degrees of freedom, which leads to an increase of the phase-space density (P.S.D.) by a factor of ≈ 250, allowing to reach a high final P.S.D. of ≈ 1.7 −3 . These experiments are performed within an optical dipole trap, in which gray molasses work equally well as in free space. The obtained samples are then an ideal starting point for the evaporation stage aiming at the quantum regime.

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Section: Gray Molasses Optimizationsupporting

confidence: 52%

Cooling all external degrees of freedom of optically trapped chromium atoms using gray molasses

et al. 2019

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“…The slightly smaller values extracted from the experiments can be due to additional systematic effects in the measurements. For comparison, we note that at 1064 nm, κ 0 for ground-state Er is slightly larger than the one for Dy, which was predicted to be around κ th 0,Dy = 1.1 % [15], and larger than the one of Cr atoms, which was calcu- lated to be κ th 0,Cr = 0.5 % (at 1075 nm) [23] but was then measured to be significantly lower [22]. In Cr experiments, the tensorial contribution to the total light shift was then enhanced by using near-resonant light.…”

Section: A Measurement Of the Ground-state Polarizabilitymentioning

confidence: 99%

“…This term gives rise to a light shift, which is quadratic in the angular-momentum projection quantum number, m J , and provides an additional tool for optical spin manipulation, as recently studied in ultracold Dy experiments [21]. The anisotropy in the polarizability has been observed not only in atoms with large orbital-momentum quantum number but also in large-spin atomic system, such as cromium (Cr), [22,23] and molecular systems [24][25][26][27]. This paper reports on the measurement of the dynamical polarizability in ultracold Er atoms in both the ground state and one excited state for trapping-relevant wavelengths.…”

Section: Introductionmentioning

confidence: 99%

Anisotropic polarizability of erbium atoms

et al. 2018

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We report on the determination of the dynamical polarizability of ultracold erbium atoms in the ground and in one excited state at three different wavelengths, which are particularly relevant for optical trapping. Our study combines experimental measurements of the light shift and theoretical calculations. In particular, our experimental approach allows us to isolate the different contributions to the polarizability, namely the isotropic scalar and anisotropic tensor part. For the latter contribution, we observe a clear dependence of the atomic polarizability on the angle between the laser-field-polarization axis and the quantization axis, set by the external magnetic field. Such an angle-dependence is particularly pronounced in the excited-state polarizability. We compare our experimental findings with the theoretical values, based on semi-empirical electronic-structure calculations and we observe a very good overall agreement. Our results pave the way to exploit the anisotropy of the tensor polarizability for spin-selective preparation and manipulation.

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“…When atoms decay into these D states in the low field seeking substates, they remain trapped due to the strong confinement of the IR laser along two transverse directions, and to the magnetic gradient created by the MOT coils along the IR beam propagation axis. We reported in [16] how we could obtain about one million metastable atoms in this continuous FORT loading procedure. However encouraging, this result turned out to be insufficient to reach quantum degeneracy: we obtained a final phase space density in the 5.10 −4 range after evaporation in a crossed FORT.…”

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confidence: 99%

All-optical production of chromium Bose-Einstein condensates

et al. 2008

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We report on the production of 52 Cr 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 5 S2 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), and the use of relatively fast evaporative ramps allow us to obtain in 20 s about 15000 atoms in an almost pure condensate.PACS numbers: 03.75. Hh , The study of the degenerate quantum phases of chromium is especially appealing for two main reasons. First, the atomic magnetic moment of 6 µ B (Bohr magneton) leads to large anisotropic long range dipole-dipole interactions, which are non negligible compared to the contact interaction [1], and can even become the dominant interaction close to a Feshbach resonance [2]. In this regime, the stability and excitation properties of dipolar BECs are completely modified by dipole-dipole interactions [3]. In addition, the large S = 3 spin in the ground state makes Cr a unique element for spinor physics [4]. Second, the existence of a fermionic isotope ( 53 Cr, 10 % natural abundance) opens the way to obtain a degenerate dipolar Fermi sea, and to study the interesting stability properties of a dipolar boson-fermion mixture [5].The historic [6] and still conventional way to produce quantum degenerate gases is evaporation inside a magnetic trap (MT). An other possibility, demonstrated first for Rb [7], is to evaporatively cool in an optical trap created by a far red detuned laser. These traps offer an interesting experimental alternative as the highly confining MTs required to evaporate efficiently demand either large currents, or the use of integrated structures [8]. For some atoms, the winning strategy to obtain condensation has been to use a FORT, either because of high inelastic collision rates (for Cs [9] and Cr [10],[11]), or because of the absence of a permanent magnetic moment (for Yb [12]). In the first case optically pumping the atoms to the lowest energy Zeeman substate suppresses all twobody inelastic collisions at low temperature, but these high field seeking states cannot be trapped magnetically: the use of optical traps is necessary. The evaporation is then performed in a crossed FORT with a standard procedure, for which the evaporation dynamics is well understood [13].However, efficiently loading a FORT is not straightforward in general and especially for Cr. In particular in our experiment, a direct loading of a Cr optical trap in the ground 7 S 3 state from a MOT leads to small number of atoms, presumably because of a high light assisted inelastic collision rate [14,15]. The loading procedure used to obtain the first Cr BEC [11] was to accumulate the atoms in metastable D states inside a MT, before transferring them first into an elongated Ioffe Pritchard MT, and then in ...

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Accumulation of chromium metastable atoms into an optical trap

Cited by 13 publications

References 16 publications

Cooling all external degrees of freedom of optically trapped chromium atoms using gray molasses

Cooling all external degrees of freedom of optically trapped chromium atoms using gray molasses

Anisotropic polarizability of erbium atoms

All-optical production of chromium Bose-Einstein condensates

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