Simultaneous magneto-optical trapping of bosonic and fermionic chromium atoms

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

doi:10.1103/physreva.73.053406

Cited by 49 publications

(80 citation statements)

References 29 publications

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“…Chromium atoms are heated to 1500 C, decelerated in a Zeeman slower, and captured in a MOT whose magnetic field gradient is 18 G/cm in the vertical direction, and 9 G/cm in the other two directions. Compared to reference [6], the MOT laser beam 1/e 2 radius is reduced to 3 mm. Here, we specifically study the accumulation of 52 Cr atoms in the 5 D 4 state, in presence of a RF field.…”

Section: Continuous Accumulation In a Rf-dressed Magnetic Trapmentioning

confidence: 86%

“…Our experimental setup was described in a previous paper [6]. Chromium atoms are heated to 1500 C, decelerated in a Zeeman slower, and captured in a MOT whose magnetic field gradient is 18 G/cm in the vertical direction, and 9 G/cm in the other two directions.…”

Section: Continuous Accumulation In a Rf-dressed Magnetic Trapmentioning

confidence: 99%

“…As in [2] and [6], chromium atoms in the 7 S 3 ground state are captured in a MOT, and depumped to dark metastable states 5 D 4,3 . We observe different regimes as a function of the RF frequency.…”

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Accumulation and thermalization of cold atoms in a finite-depth magnetic trap

et al. 2007

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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 Cr) 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 µK, with a density of 10 17 atoms.m −3 , resulting in an increase of the phase-space density, still limited to 7.10 −6 by inelastic collisions. To investigate the thermalization issues in the truncated trap, we measure the free evaporation rate in the RF-truncated magnetic trap, and deduce the average elastic cross section for atoms in the 5 D4 metastable states, σ el = 7.0 × 10 −16 m 2 . We finally discuss the possibilities for using this scheme of continuous accumulation and RF evaporation to rapidly reach high phase-space densities from a MOT.PACS numbers: 32.80. Pj, 47.45.Ab, 32.80.Cy Magneto-optical trapping is one of the greatest recent advances in atomic and molecular physics, opening many new areas in physics, including the study of Bose-Einstein condensation in dilute systems. One of the advantages of a magneto-optical trap (MOT), is that cooling and trapping are simultaneous. However, inherent limitations of the cooling mechanism, for example light-assisted collisions or multiple scattering of light, limit typical phasespace densities to 10 −7 when strong fluorescence lines are involved in the cooling transition [1]. To reach higher phase-space densities, it is usually necessary to use sequential operations, such as cooling in molasses, loading in conservative traps, and forced evaporation, which greatly limits the rate at which a Bose-Einstein condensates (BEC) can be produced.New possibilities arise for atoms whose electronic level structure includes metastable dark states (such as Sr, Er, Yb, or Cr). Spontaneous emission from the excited state of the cooling transition depumps atoms into a dark metastable state, which can be trapped, either optically, or magnetically. This provides an interesting means to continuously accumulate atoms in a magnetic trap [2], or for a continuous loading of an optical or magnetic waveguide. Cold metastable atoms are directly produced inside the waveguide or the trap, which reduces heating associated with the sequential loading from a MOT. This may have promising applications in the prospect of continuously producing a coherent beam of atoms, by performing forced evaporation as the atoms propagate along a waveguide [3].In this paper, we study the accumulation of metastable chromium atoms in a magnetic trap (MT), dressed by a radiofrequency (RF) field (see Fig 1) . We observe different regimes as a function of the RF frequency. When the RF frequency is small, atoms in internal states adiabatically connected to high field seeking states at small magnetic fields are accumulated in a (3D) W-shaped potential. When the RF ...

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Section: Continuous Accumulation In a Rf-dressed Magnetic Trapmentioning

confidence: 86%

Section: Continuous Accumulation In a Rf-dressed Magnetic Trapmentioning

confidence: 99%

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Accumulation and thermalization of cold atoms in a finite-depth magnetic trap

et al. 2007

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“…The trapping lasers needed to obtain a 53 Cr MOT using the 7 S 3 → 7 P 4 transition at 425 nm were reported in [17]. They are generated from a dedicated laser system producing 800 mW of 425 nm light.…”

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confidence: 99%

“…In our experiment, the Zeeman Slower beam used to slow down 53 Cr substantially reduces the 52 Cr MOT atom number [17]. Therefore, we do not load the two isotopes at the same time in the ODT.…”

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Chromium dipolar Fermi sea

et al. 2015

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We report on the production of a degenerate Fermi gas of 53 Cr atoms, polarized in the state F=9/2, mF = −9/2, by sympathetic cooling with bosonic S=3, mS = −3 52 Cr atoms. We load in an optical dipole trap 3 ×10 4 53 Cr atoms with 10 6 52 Cr 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 53 Cr atoms. This surprisingly efficient evaporation stems from an inter-isotope scattering length |aBF | = 85(±10) aB (Bohr radius) which is small enough to reduce evaporative losses of the fermionic isotope, but large enough to insure thermalization.PACS numbers: 03.75. Ss , 37.10.De, 67.85.Pq There has recently been tremendous activity on dipolar quantum gases. This is due to the fact that in dipolar gases the particles interact through long-range and anisotropic dipole-dipole interactions (DDIs), which drastically changes the nature of many-body ground and excited states. [15,16], due to anisotropic short range interactions. As this density promises to be even higher in the context of spinor gases where more than one spin state is populated, study of magnetism might be difficult with these atoms. For this reason, chromium, with a combination of relatively strong dipole-dipole long-range anisotropic interactions and simple isotropic short range interactions, remains a unique atom for the study of the unconventional spinor properties of dipolar quantum degenerate Fermi gases.Despite its interest, producing a dipolar Fermi gas of chromium atoms has been elusive for many years, as it represents a real experimental challenge. The main reason is the small number of 53 Cr atoms that can be captured in a magneto-optical trap (MOT), at most typically 10 5 , due to relatively small natural abundance, the complex hyperfine structure, and, most importantly, the very large light-assisted loss rate in a MOT [17]. In this paper, we describe and demonstrate a way to produce quantum gases of fermionic 53 Cr atoms.Our scheme consists in loading a mixture of mostabundant 52 Cr atoms and minority 53 Cr atoms in the same far-detuned optical dipole trap (ODT), and in performing forced evaporative cooling. Evaporative losses are smaller for 53 Cr atoms than for 52 Cr atoms, which results in very efficient evaporative cooling characterized by a gain of typically four orders of magnitude in phasespace density for one order of magnitude of atom losses. As a consequence, although only 3 × 10 4 53 Cr atoms are loaded in the dipole trap at 60 µK before evaporation, degenerate Fermi gases of up to 10 3 atoms can be produced in less than 15 s. We analyze our evaporation scheme and are able to point out the decisive role played by the numerical value of the inter-isotope scattering length, which is smaller than the bosonic scattering length. We measure this quantity, and compare it with theoretical predictions based on mass scaling [18].Fermi statistics leads to vanishing s-wave collisions due to Van der Walls interactions at low temperatures for polarize...

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Optimized loading of an optical dipole trap for the production of chromium BECs

et al. 2010

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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 specified. To stabilize two of our laser diode, we have developed a simple ultrastable passive reference cavity whose long term stability is better than 1 MHz.

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Simultaneous magneto-optical trapping of bosonic and fermionic chromium atoms

Cited by 49 publications

References 29 publications

Accumulation and thermalization of cold atoms in a finite-depth magnetic trap

Accumulation and thermalization of cold atoms in a finite-depth magnetic trap

Chromium dipolar Fermi sea

Optimized loading of an optical dipole trap for the production of chromium BECs

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