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Conference on Lasers and Electro-Optics

Optical trapping of fermionic /sup 40/K atoms

W. Jastrzȩbski, David Lau, G. Roati, Giovanni Carlo Modugno, M. Inguscio

Published Aug 29, 2005• 0 citations
Publisher

Abstract

Summary form only only given. We report on trapping of /sup 40/K atoms at low temperatures and high densities in a far-detuned optical trap. The trap is a vertical standing-wave created with about 550 mW of radiation tuned 10 nm on the red of the D/sub 2/ transition, and is loaded from a sample held in a magneto optical trap (MOT) at sub-Doppler temperatures, with the help of a temporal dark-spot phase and a magnetic compression phase. We are able to trap as many as 5/spl times/10/sup 6/ atoms with a lifetime of 200 ms in the F=9/2 ground state. From the temperature of the trapped atoms, which is around 30 /spl mu/K, and the measured trap frequencies (1 kHz radial, 500 kHz axial) we estimate a density of 5/spl times/10/sup 12/ cm/sup -3/.

DOI
10.1109/iqec.2000.907805

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Summary form only only given. We report on trapping of /sup 40/K atoms at low temperatures and high densities in a far-detuned optical trap. The trap is a vertical standing-wave created with about 550 mW of radiation tuned 10 nm on the red of the D/sub 2/ transition, and is loaded from a sample held in a magneto optical trap (MOT) at sub-Doppler temperatures, with the help of a temporal dark-spot phase and a magnetic compression phase. We are able to trap as many as 5/spl times/10/sup 6/ atoms with a lifetime of 200 ms in the F=9/2 ground state. From the temperature of the trapped atoms, which is around 30 /spl mu/K, and the measured trap frequencies (1 kHz radial, 500 kHz axial) we estimate a density of 5/spl times/10/sup 12/ cm/sup -3/.
We report the laser cooling and trapping of neutral potassium on an open transition. Fermionic 40{}^{40}40K is captured using a magneto-optical trap (MOT) on the closed $4{S}_{1/2}\ensuremath{\rightarrow}4{P}_{3/2}$ transition at 767 nm and then transferred, with high efficiency, to a MOT on the open $4{S}_{1/2}\ensuremath{\rightarrow}5{P}_{3/2}$ transition at 405 nm. Because the 5P3/25{P}_{3/2}5P3/2​ state has a smaller linewidth than the 4P3/24{P}_{3/2}4P3/2​ state, the Doppler limit is reduced from 145 \ensuremath{\mu}K to 24 \ensuremath{\mu}K, and we observe temperatures as low as 63(6) $\ensuremath{\mu}$K. The density of trapped atoms also increases, due to reduced temperature and reduced expulsive light forces. We measure a two-body loss coefficient of $\ensuremath{\beta}=1.4(1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ cm3{}^{3}3/s near saturation intensity, and estimate an upper bound of $8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}18}$ cm2{}^{2}2 for the ionization cross section of the 5P5P5P 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 precooling for quantum gas experiments. A qualitatively similar enhancement is observed in a 405 nm MOT of bosonic 41{}^{41}41K.
We report on trapping of fermionic 40K{}^{40}\mathrm{K}40K atoms in a red-detuned standing-wave optical trap, loaded from a magneto-optical trap. Typically, unpolarized samples of 106{10}^{6}106 atoms are loaded at a density of ${10}^{12}{\mathrm{cm}}^{\ensuremath{-}3}$ and a temperature of $65\ensuremath{\mu}\mathrm{K},$ and trapped for more than 1 s. The optical trap appears to be the proper environment for performing collisional measurements on the cold atomic sample. In particular, we measure the spherically averaged elastic collision rate by detecting the rethermalization following an intentional parametric heating of the atoms. We also measure spherically averaged inelastic two-body collision rates for atoms in the ground hyperfine states, through detection of trap losses.
Direct observation and frequency measurement of /sup 1/S/sub 0//spl rarr//sup 3/P/sub 0 /line within an accuracy of 20 kHz is reported. The resonance frequency with an accuracy of /spl sim/ 100 kHz is reported by indirect measurement of the energy difference between /sup 1/S/sub 0/ and /sup 3/P/sub 0/ states. It is performed by successive frequency measurements of atomic transitions with higher linewidth, easier to observe: /sup 1/S/sub 0/ - /sup 3/P/sub 1/, /sup 3/P/sub 1/ - /sup 3/S/sub 1/ and /sup 3/S/sub 1/ - /sup 3/P/sub 0/ transitions. To perform direct observation of the clock transition, atoms are cooled to a temperature of /spl sim/ 2 mK in a magneto-optical trap (MOT). Although the saturation broadening of the transition is orders of magnitude smaller than the Doppler width (1.5 MHz), a detectable signal is achieved by inducing a small leak in the MOT with a laser tuned to resonance. Atoms accumulate in the metastable /sup 3/P/sub 0 /state where they escape the trap. The resonance is detected by a decrease in the MOT fluorescence signal with a contrast of 1%.
Low-temperature, high-density magneto-optical trapping of potassium using the open 4S →\rightarrow→ 5P transition at 405\,nm
We report the laser cooling and trapping of neutral potassium on an open transition. Fermionic 40K is captured using a magneto-optical trap (MOT) on the closed 4S1/2 → 4P3/2 transition at 767 nm and then transferred, with high efficiency, to a MOT on the open 4S1/2 → 5P3/2 transition at 405 nm. Because the 5P3/2 state has a smaller linewidth than the 4P3/2 state, the Doppler limit is reduced from 145 μK to 24 μK, and we observe temperatures as low as 63(6) μK. The density of trapped atoms also increases, due to reduced temperature and reduced expulsive light forces. We measure a two-body loss coefficient of β = 1.4(1) × 10−10 cm3/s near saturation intensity, and estimate an upper bound of 8 × 10−18 cm2 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 precooling for quantum gas experiments. A qualitatively similar enhancement is observed in a 405 nm MOT of bosonic 41K.
We present the properties and advantages of a new magneto-optical trap (MOT) where blue-detuned light drives "type-II" transitions that have dark ground states. Using ^{87}Rb, we reach a radiation-pressure-limited density exceeding 10^{11} cm^{-3} and a temperature below 30 μK. The phase-space density is higher than in normal atomic MOTs and a million times higher than comparable red-detuned type-II MOTs, making the blue-detuned MOT particularly attractive for molecular MOTs, which rely on type-II transitions. The loss of atoms from the trap is dominated by ultracold collisions between Rb atoms. For typical trapping conditions, we measure a loss rate of 1.8(4)×10^{-10} cm^{3} s^{-1}.
For the first time ultra-cold thulium atoms were trapped in a magnetic quadrupole trap with a small field gradient (20 Gs cm -1 ). The atoms were loaded from a cloud containing 4 × 10 5 atoms that were preliminarily cooled in a magneto-optical trap to the sub-Doppler temperature of 80 μK. As many as 4 × 10 4 atoms were trapped in the magnetic trap at the temperature of 40 μK. By the character of trap population decay the lifetime of atoms was determined (0.5 s) and an upper estimate was obtained for the rate constant of inelastic binary collisions for spin-polarised thulium atoms in the ground state (g in < 10 -11 cm 3 s -1 ).