All-optical production and transport of a large $^{6}\mathrm{Li}$ quantum gas in a crossed optical dipole trap

All-optical production and transport of a large ${}^{6}{Li}$ quantum gas in a crossed optical dipole trap

Ch. Gross, H. C. J. Gan, and K. Dieckmann

Phys. Rev. A 93, 053424 – Published 26 May 2016

Abstract

We report on an efficient production scheme for a large quantum degenerate sample of fermionic lithium. The approach is based on our previous work on narrow-line $2 S_{1 / 2} \to 3 P_{3 / 2}$ laser cooling resulting in a high phase-space density of up to $3 \times 10^{- 4}$ . This allows utilizing a large-volume crossed optical dipole trap with a total power of $45 W$ , leading to high loading efficiency and $8 \times 10^{6}$ trapped atoms. The same optical trapping configuration is used for rapid adiabatic transport over a distance of $25 cm$ in $0.9 s$ , and subsequent evaporative cooling. With optimized evaporation we achieve a degenerate Fermi gas with $1.7 \times 10^{6}$ atoms at a temperature of $60 nK$ , corresponding to $T / T_{F} = 0.16 (2)$ . Furthermore, the performance is demonstrated by evaporation near a broad Feshbach resonance creating a molecular Bose-Einstein condensate of $3 \times 10^{5}$ lithium dimers.

Received 24 April 2016

DOI:https://doi.org/10.1103/PhysRevA.93.053424

Physics Subject Headings (PhySH)

Atom & ion cooling Atom & ion trapping & guiding Bose-Einstein condensates Fermi gases

Atomic, Molecular & Optical

Authors & Affiliations

Ch. Gross¹, H. C. J. Gan¹, and K. Dieckmann^1,2,*

¹Centre for Quantum Technologies (CQT), 3 Science Drive 2, Singapore 117543
²Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542

^*phydk@nus.edu.sg

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Vol. 93, Iss. 5 — May 2016

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Figure 1
Schematic overview of our $^{6} Li$ apparatus. The atoms are loaded from a Zeeman-slowed atomic beam into a MOT on the $D_{2}$ transition. The atomic cloud is further cooled and compressed on the narrow UV transition and then transferred into a crossed ODT comprised of two laser beams focused by a single lens. Subsequently, the atomic cloud is transported from the MOT chamber into an attached fused silica cell by moving the lens with an air-bearing stage. A magnetic bias field is applied to access a Feshbach resonance for efficient evaporation of the atomic cloud into the quantum degenerate regime.
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Figure 2
(a) Total number of atoms $N$ in the ODT after plain evaporation as a function of the laser detuning with respect to the UV cooling transition for different axial magnetic field gradients of the MOT. The highest atom number is achieved with a detuning of $δ ≃ - 3.2 Γ_{3 P}$ at a gradient of $15.8 G / cm$ . An increase of the magnetic field gradient beyond this value does not further improve the atom number. (b) Atom number vs duration of continued UV cooling after the ODT is ramped up to full power. The initial increase in atom number demonstrates the effectiveness of UV cooling in the presence of the 1070-nm trapping light, while the decrease at longer overlap durations is attributed to density-dependent losses (see text). The error bars account for the statistical uncertainty.
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Figure 3
(a) Total number of atoms $N$ (blue squares) and temperature $T$ (red filled circles) at various points during forced evaporative cooling performed at $330 G$ . $P$ is the optical power per beam of the ODT at which the evaporation ramp was halted. The dashed line corresponds to $0.1 U_{0} / k_{B}$ , which is in close agreement with the measured temperature of the atomic cloud, indicating an approximately constant truncation $η$ parameter throughout the evaporation. (b) $T / T_{F}$ vs $N$ for the same measurement. The error shown in (b) includes, in addition to the statistical error of 10 repetitions for each point, a systematic uncertainty of $10 %$ in the measured quantities.
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Figure 4
Density distribution and individually normalized horizontal central profiles of the $^{6} {Li}_{2}$ cloud. Forced evaporative cooling is performed at 770 G to a final optical power of (a),(d) 100 mW, (b),(e) 45 mW, and (c),(f) 35 mW per beam of the ODT. The optical density (OD) of the cloud is recorded after a TOF of 6 ms at a magnetic field of 690 G. Each central profile (blue filled circles) is normalized to unity and the bimodal fitting function (dashed line) consists of a parabolic curve added to a Gaussian. The Gaussian component (solid line) illustrates the bimodal character of the density distribution.
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Physical Review A

covering atomic, molecular, and optical physics and quantum information

All-optical production and transport of a large ${}^{6}{Li}$ quantum gas in a crossed optical dipole trap

Ch. Gross, H. C. J. Gan, and K. Dieckmann

Phys. Rev. A 93, 053424 – Published 26 May 2016

Abstract

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Physical Review A

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All-optical production and transport of a large Li6 quantum gas in a crossed optical dipole trap

Ch. Gross, H. C. J. Gan, and K. Dieckmann

Phys. Rev. A 93, 053424 – Published 26 May 2016

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All-optical production and transport of a large ${}^{6}{Li}$ quantum gas in a crossed optical dipole trap