Collisional Properties of Ultracold K-Rb Mixtures (original) (raw)
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Prospects for Mixed-Isotope Bose-Einstein Condensates in Rubidium
Physical Review Letters, 1998
We calculate binary collision parameters for mixtures of ultracold gases of 85 Rb and 87 Rb atoms. We predict a large positive triplet scattering length for mixed-isotope collisions, which implies that a stable mixed-isotope double condensate can be formed by sympathetic evaporative cooling. Moreover, collisions between 85 Rb and 87 Rb atoms in the lowest hyperfine manifold exhibit magnetic-fieldinduced Feshbach resonances which should allow partial control of the interaction between condensates. These considerations make Rb an ideal system for the study of interpenetrating bosonic superfluids.
Dual-species Bose-Einstein condensate of K41 and Rb87 in a hybrid trap
Physical Review A
We report on the production of a 41 K-87 Rb dual-species Bose-Einstein condensate in a hybrid trap, consisting of a magnetic quadrupole and an optical dipole potential. After loading both atomic species in the trap, we cool down 87 Rb first by magnetic and then by optical evaporation, while 41 K is sympathetically cooled by elastic collisions with 87 Rb. We eventually produce two-component condensates with more than 10 5 atoms and tunable species population imbalance. We observe the immiscibility of the quantum mixture by measuring the density profile of each species after releasing them from the trap.
Journal of Research of the National Institute of Standards and Technology, 1996
We present quantum scattering calculations for the collisional relaxation rate coefficient of spin-polarized 87 Rb(f = 2,m = 2) atoms, which determines the loss rate of cold Rb atoms from a magnetic trap. Unlike the lighter alkali atoms, spin-polarized 87 Rb atoms can undergo dipolar relaxation due to both the normal spin-spin dipole interaction and a second-order spinorbit interaction with distant electronic states of the dimer. We present ab initio calculations for the second-order spin-orbit terms for both Rb2 and Cs2. The corrections lead to a reduction in the relaxation rate for 87 Rb. Our primary concern is to analyze the sensitivity of the 87 Rb trap loss to the uncertainties in the ground state molecular potentials. Since the scattering length for the a 3 ⌺ + u state is already known, the major uncertainties are associated with the X 1 ⌺ + g potential. After testing the effect of systematically modifying the short-range form of the molecular potentials over a reasonable range, and introducing our best estimate of the second-order spin-orbit interaction, we estimate that in the low temperature limit the rate coefficient for loss of Rb atoms from the f = 2,m = 2 state is between 0.4 ϫ 10 Ϫ15 cm 3 /s and 2.4 ϫ 10 Ϫ15 cm 3 /s (where this number counts two atoms lost per collision). In a pure condensate the rate coefficient would be reduced by 1/2.
Resonant Magnetic Field Control of Elastic Scattering in Cold ^{85}Rb
Physical Review Letters, 1998
A magnetic field dependent Feshbach resonance has been observed in the elastic scattering collision rate between atoms in the F = 2, M = −2 state of 85 Rb. Changing the magnetic field by several Gauss caused the collision rate to vary by a factor of 10 4 , and the sign of the scattering length could be reversed. The resonance peak is at 155.2(4) G and its width is 11.6(5) G. From these results we extract much improved values for the three quantities that characterize the interaction potential: the van der Waals coefficient C6, the singlet scattering length aS, and the triplet scattering length aT .
Collisional properties of sympathetically cooled ^{39}K
Physical Review A, 2007
We report the experimental evidence of the sympathetic cooling of 39 K with 87 Rb down to 1 µK, obtained in a novel tight confining magnetic trap. This allowed us to perform the first direct measurement of the elastic cross section of 39 K below 50 µK. The result obtained for the triplet scattering length, aT = −51(7) Bohr radii, agrees with previous results derived from photoassociation spectra and from Feshbach spectroscopy of 40 K.
Feshbach spectroscopy of a K-Rb atomic mixture
Physical Review A, 2006
We perform extensive magnetic Feshbach spectroscopy of an ultracold mixture of fermionic 40K and bosonic 87Rb atoms. The magnetic-field locations of 14 interspecies resonances is used to construct a quantum collision model able to predict accurate collisional parameters for all K-Rb isotopic pairs. In particular we determine the interspecies s-wave singlet and triplet scattering lengths for the 40K-87Rb mixture as -111 +/- 5 Bohr and -215 +/- 10 Bohr respectively. We also predict accurate scattering lengths and position of Feshbach resonances for the other K-Rb isotopic pairs. We discuss the consequences of our results for current and future experiments with ultracold K-Rb mixtures.
Cooling of Sr to high phase-space density by laser and sympathetic cooling in isotopic mixtures
Physical Review A, 2006
Based on an experimental study of two-body and three-body collisions in ultracold strontium samples, a novel optical-sympathetic cooling method in isotopic mixtures is demonstrated. Without evaporative cooling, a phase-space density of 6 × 10 −2 is obtained with a high spatial density that should allow to overcome the difficulties encountered so far to reach quantum degeneracy for Sr atoms. PACS numbers: 32.80.Pj, 34.50.-s, 05.30.Jp, 32.80.-t.
Bose-Einstein Condensation of Strontium
Physical Review Letters, 2009
We report on the attainment of Bose-Einstein condensation with ultracold strontium atoms. We use the 84 Sr isotope, which has a low natural abundance but offers excellent scattering properties for evaporative cooling. Accumulation in a metastable state using a magnetic-trap, narrowline cooling, and straightforward evaporative cooling in an optical trap lead to pure condensates containing 1.5 × 10 5 atoms. This puts 84 Sr in a prime position for future experiments on quantum-degenerate gases involving atomic two-electron systems.
Tunable dual-species Bose-Einstein condensates ofK39andRb87
Physical Review A, 2015
We present the production of dual-species Bose-Einstein condensates of 39 K and 87 Rb. Preparation of both species in the |F = 1, mF = −1 state enabled us to exploit a total of three Feshbach resonances which allows for simultaneous Feshbach tuning of the 39 K intraspecies and the 39 K-87 Rb interspecies scattering length. Thus dual-species Bose-Einstein condensates were produced by sympathetic cooling of 39 K with 87 Rb. A dark spontaneous force optical trap was used for 87 Rb, to reduce the losses in 39 K due to light-assisted collisions in the optical trapping phase, which can be of benefit for other dual-species experiments. The tunability of the scattering length was used to perform precision spectroscopy of the interspecies Feshbach resonance located at 117.56(2) G and to determine the width of the resonance to 1.21(5) G by rethermalization measurements. The transition region from miscible to immiscible dual-species condensates was investigated and the interspecies background scattering length was determined to 28.5 a0 using an empirical model. This paves the way for dual-species experiments with 39 K and 87 Rb BECs ranging from molecular physics to precision metrology.