Numerical modeling of collisional dynamics of Sr in an optical dipole trap

Spin-polarized metastable atoms of ultracold ytterbium are trapped at high density and their inelastic collisional properties are measured. We reveal that in collisions of Yb( 3 P 2 ) with Yb( 1 S 0 ) there is relatively weak inelastic loss, but with a significant spin dependence consistent with Zeeman sublevel changes as being the dominant decay process. This is in strong contrast to our observations of Yb( 3 P 2 )-Yb( 3 P 2 ) collisional losses, which are, at low field, much more rapid and have essentially no spin dependence. Our results give a guideline to using the 3 P 2 states in many possible applications.

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“…In a large-η approximation, f can be approximated to a simple analytic equation [36]. In the present condition, β in /β varies from 0.87 to 0.93.…”

Section: Resultsmentioning

confidence: 96%

Spin-dependent collision of ultracold metastable atoms

et al. 2012

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“…We create condensates with about 7000 atoms, size σ 0 = 0.8 µm, and peak density n 0 = 1 × 10 15 cm −3 . About 10% of the trapped atoms are in the condensate and this represents about 95% of the critical number for collapse with the background scattering length of 88 Sr for our ODT, which is close to spherically symmetric with the geometric mean of the trap oscillation frequency ω = 2π ×(60±5) Hz [41]. The 689 nm OFR laser beam is tuned near the photoassociative transition to the second least bound vibrational level on the 1 S 0 + 3 P 1 molecular potential, which has the binding energy of h × 24 MHz [42].…”

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confidence: 87%

Controlling Condensate Collapse and Expansion with an Optical Feshbach Resonance

et al. 2013

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We demonstrate control of the collapse and expansion of an 88 Sr Bose-Einstein condensate using an optical Feshbach resonance (OFR) near the 1 S0-3 P1 intercombination transition at 689 nm. Significant changes in dynamics are caused by modifications of scattering length by up to ±10 a bg , where the background scattering length of 88 Sr is a bg = −2 a0 (1 a0 = 0.053 nm). Changes in scattering length are monitored through changes in the size of the condensate after a time-of-flight measurement. Because the background scattering length is close to zero, blue detuning of the OFR laser with respect to a photoassociative resonance leads to increased interaction energy and a faster condensate expansion, while red detuning triggers a collapse of the condensate. The results are modeled with the time-dependent non-linear Gross-Pitaevskii equation.The ability to tune interactions in ultracold atomic gases makes these systems ideal for exploring many-body physics [1] and has enabled some of the most important recent advances in atomic physics, such as investigation of the Bose-Einstein condensate (BEC)-Bardeen-CooperSchrieffer crossover regime [1] and creation of quantum degenerate molecules [2,3]. Magnetic Feshbach resonances [4], which are the standard tool for changing atomic interactions, have proven incredibly powerful, but they are also limited because the methods for creating magnetic fields preclude high-frequency spatial and temporal modulation. Also, in atoms with non-degenerate ground states, such as alkaline-earth-metal atoms, magnetic Feshbach resonances do not exist.These limitations can be overcome by using an optical Feshbach resonance (OFR), which tunes interatomic interactions by coupling a colliding atom pair to a bound molecular level of an excited state potential with a laser tuned near a photoassociative resonance [5]. Optical Feshbach resonances may open new avenues of research in nonlinear matter waves [6][7][8] and quantum fluids [9][10][11], and could be very valuable for experiments with fermionic alkaline-earth atoms [12,13] Early experiments on OFRs [22-24] used strong dipoleallowed transitions in alkali-metal atoms to alter atomic collision properties, but substantial change in the atomatom scattering length was accompanied by rapid atom losses. Tuning of interactions in alkali-metal atoms, but with smaller atom loss, was recently obtained with a magnetic Feshbach resonance using an AC Stark shift of the closed channel to modify the position of the resonance [25,26]. Recently, a multiple-laser optical method was proposed for wider modulation of the interaction strength near a magnetic Feshbach resonance [27]. Unfortunately, none of these hybrid variations are feasible for atoms lacking magnetic Feshbach resonances.Ciurylo et al. [28,29] predicted that an OFR induced by a laser tuned near a weakly allowed transition should tune the scattering length with significantly less induced losses. This can be done with divalent atoms, such as strontium and ytterbium, by exciting near an intercombinatio...

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“…Crucially, unlike in 1-body loss dominated systems, the inverted scaling of R with density means maintaining a large N leads to loweredω, reduced collision rates and longer evaporation timescales. Numerical modeling of evaporative cooling in an ODT [22,23] can help optimize γ, but the challenges of large number and speed remain.…”

Section: Introductionmentioning

confidence: 99%

Rapid cooling to quantum degeneracy in dynamically shaped atom traps

et al. 2016

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We report on a general method for the rapid production of quantum degenerate gases. Using 174 Yb, we achieve an experimental cycle time as low as (1.6 − 1.8) s for the production of BoseEinstein condensates (BECs) of (0.5−1)×10 5 atoms. While laser cooling to 30 µK proceeds in a standard way, evaporative cooling is highly optimized by performing it in an optical trap that is dynamically shaped by utilizing the time-averaged potential of a single laser beam moving rapidly in one dimension. We also produce large (> 10 6 ) atom number BECs and successfully model the evaporation dynamics over more than three orders of magnitude in phase space density. Our method provides a simple and general approach to solving the problem of long production times of quantum degenerate gases.

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Numerical modeling of collisional dynamics of Sr in an optical dipole trap

Cited by 15 publications

References 42 publications

Spin-dependent collision of ultracold metastable atoms

Spin-dependent collision of ultracold metastable atoms

Controlling Condensate Collapse and Expansion with an Optical Feshbach Resonance

Rapid cooling to quantum degeneracy in dynamically shaped atom traps

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