We report the experimental achievement of 87Rb Bose-Einstein condensation in a magnetic trap with microwave and radio frequency (RF) induced evaporation. Evaporative cooling is realized by using 6.8 GHz microwave radiation driving the 87Rb atoms to transit from the ground-state hyperfine state |F = 2,mF =2> to |F = 1,mF = 1>. Compared with RF-induced evaporation, 87Rb atoms are hardly to achieve pure condensate by microwave evaporation cooling due to the effect of atoms in the |F = 1,mF = 1> state being pumped back into the trapping |F = 2,mF = 1> state.We report the experimental achievement of 87Rb Bose-Einstein condensation in a magnetic trap with microwave and radio frequency (RF) induced evaporation. Evaporative cooling is realized by using 6.8 GHz microwave radiation driving the 87Rb atoms to transit from the ground-state hyperfine state |F = 2,mF =2> to |F = 1,mF = 1>. Compared with RF-induced evaporation, 87Rb atoms are hardly to achieve pure condensate by microwave evaporation cooling due to the effect of atoms in the |F = 1,mF = 1> state being pumped back into the trapping |F = 2,mF = 1> state.

Chinese Optics LettersJan 1, 20104 citations

Experimental investigation of evaporative cooling mixture of bosonic 87 Rb and fermionic 40 K atoms with microwave and radio frequency radiation

Pengjun Wang, Dezhi Xiong, Zhengkun Fu +1 more

We investigate sympathetic cooling fermions 40 K by evaporatively cooling bosonic 87 Rb atoms in a magnetic trap with microwave and radio frequency induced evaporations in detail. The mixture of bosonic and fermionic atoms is prepared in their polarized spin states | F = 9/2, m F = 9/2〉 for 40 K and | F = 2, m F = 2〉 for 87 Rb, which is trapped in Quadrupole—Ioffe—Configuration trap. Comparing microwave with radio frequency evaporatively cooling bosonic 87 Rb atoms with sympathetically cooling Fermi gas 40 K, we find that the presence of rubidium atoms in the |2, 1〉 Zeeman states, which are generated in the evaporative process, gives rise to a significant loss of 40 K due to inelastic collisions. Thus, the rubidium atoms populated in the |2, 1〉 Zeeman states should be removed in order to effectively perform sympathetically cooling 40 K with the evaporatively cooled 87 Rb atoms.We investigate sympathetic cooling fermions 40 K by evaporatively cooling bosonic 87 Rb atoms in a magnetic trap with microwave and radio frequency induced evaporations in detail. The mixture of bosonic and fermionic atoms is prepared in their polarized spin states | F = 9/2, m F = 9/2〉 for 40 K and | F = 2, m F = 2〉 for 87 Rb, which is trapped in Quadrupole—Ioffe—Configuration trap. Comparing microwave with radio frequency evaporatively cooling bosonic 87 Rb atoms with sympathetically cooling Fermi gas 40 K, we find that the presence of rubidium atoms in the |2, 1〉 Zeeman states, which are generated in the evaporative process, gives rise to a significant loss of 40 K due to inelastic collisions. Thus, the rubidium atoms populated in the |2, 1〉 Zeeman states should be removed in order to effectively perform sympathetically cooling 40 K with the evaporatively cooled 87 Rb atoms.

Chinese Physics BJan 1, 20115 citations

Interrupted evaporative cooling of 87Rb atoms trapped in a high magnetic field

Bruno Desruelle, Vincent Boyer, Stuart G. Murdoch +4 more

Radio-frequency-induced evaporative cooling of ${}^{87}\mathrm{Rb}$ atoms in the $F=2,$ $m=2$ ground state in a magnetic trap with a high bias field is found to be hampered, and eventually interrupted, by the presence of nonlinear Zeeman shifts. An experiment studying evaporation at a fixed adjustable rf frequency was used to illustrate this effect. These nonlinear shifts prevent us from reaching quantum degeneracy in the $F=2,$ $m=2$ ground state; however, evaporation in the $F=1,$ $m=\ensuremath{-}1$ ground state is not adversely affected, and we can produce a Bose-Einstein condensate (BEC). Our analysis shows that this effect can play a role in many BEC experiments.Radio-frequency-induced evaporative cooling of ${}^{87}\mathrm{Rb}$ atoms in the $F=2,$ $m=2$ ground state in a magnetic trap with a high bias field is found to be hampered, and eventually interrupted, by the presence of nonlinear Zeeman shifts. An experiment studying evaporation at a fixed adjustable rf frequency was used to illustrate this effect. These nonlinear shifts prevent us from reaching quantum degeneracy in the $F=2,$ $m=2$ ground state; however, evaporation in the $F=1,$ $m=\ensuremath{-}1$ ground state is not adversely affected, and we can produce a Bose-Einstein condensate (BEC). Our analysis shows that this effect can play a role in many BEC experiments.

Physical Review ASep 1, 199926 citations

Production of87Rb Bose—Einstein condensates in a hybrid trap

Yafan Duan, Bo-Nan Jiang, Jian-Fang Sun +3 more

We report a rapid evaporative cooling method using a hybrid trap which is composed of a quadrupole magnetic trap and a one-beam optical dipole trap. It contains two kinds of evaporative coolings to reach the quantum degeneracy: initial radio-frequency (RF) enforced evaporative cooling in the quadrupole magnetic trap and further runaway evaporative cooling in the optical dipole trap. The hybrid trap does not require a very high power laser such as that in the traditional pure optical trap, but still has a deep trap depth and a large trap volume, and has better optical access than the normal magnetic trap like the quadrupole-Ioffe-configuration (QUIC) cloverleaf trap. A high trap frequency can be easily realized in the hybrid trap to enhance the elastic collision rate and shorten the evaporative cooling time. In our experiment, pure Bose—Einstein condensates (BECs) with about 1 × 10 5 atoms can be realized in 6 s evaporative cooling in the optical dipole trap.We report a rapid evaporative cooling method using a hybrid trap which is composed of a quadrupole magnetic trap and a one-beam optical dipole trap. It contains two kinds of evaporative coolings to reach the quantum degeneracy: initial radio-frequency (RF) enforced evaporative cooling in the quadrupole magnetic trap and further runaway evaporative cooling in the optical dipole trap. The hybrid trap does not require a very high power laser such as that in the traditional pure optical trap, but still has a deep trap depth and a large trap volume, and has better optical access than the normal magnetic trap like the quadrupole-Ioffe-configuration (QUIC) cloverleaf trap. A high trap frequency can be easily realized in the hybrid trap to enhance the elastic collision rate and shorten the evaporative cooling time. In our experiment, pure Bose—Einstein condensates (BECs) with about 1 × 10 5 atoms can be realized in 6 s evaporative cooling in the optical dipole trap.

Chinese Physics BMay 1, 20134 citations

在光学偶极力阱中87Rb原子玻色-爱因斯坦凝聚的实现

Dezhi Xiong, Pengjun Wang, Zhengkun Fu +2 more

We create a Bose-Einstein condensate (BEC) of 87 Rb atoms by runaway evaporative cooling in an optical trap.Two crossed infrared laser beams with a wavelength of 1064 nm are used to form an optical dipole trap.After precooling the atom samples in a quadrupole-Ioffe configuration (QUIC) trap under 1.5 µK by radio-frequency (RF) evaporative cooling, the samples are transferred into the center of the glass cell, then loaded into the optical dipole trap with 800 ms.The pure condensate with up to 1.5×10 5 atoms is obtained over 1.17 s by lowering the power of the trap beams.We create a Bose-Einstein condensate (BEC) of 87 Rb atoms by runaway evaporative cooling in an optical trap.Two crossed infrared laser beams with a wavelength of 1064 nm are used to form an optical dipole trap.After precooling the atom samples in a quadrupole-Ioffe configuration (QUIC) trap under 1.5 µK by radio-frequency (RF) evaporative cooling, the samples are transferred into the center of the glass cell, then loaded into the optical dipole trap with 800 ms.The pure condensate with up to 1.5×10 5 atoms is obtained over 1.17 s by lowering the power of the trap beams.

Chinese Optics LettersJan 1, 201019 citations

Dynamics of evaporative cooling and growth of a Bose-Einstein condensate

Makoto Yamashita

The dynamics of evaporative cooling of magnetically trapped 87 Rb atoms is studied on the basis of the quantum kinetic theory of a Bose gas. The theoretical optimization of the cooling trajectory clarifies that the acceleration of evaporative cooling around the transition point of Bose-Einstein condensation is very effective against serious three-body recombination loss. The number of condensed atoms is expected to be largely enhanced by the optimization as compared with the typical value produced by the conventional evaporative cooling, where the frequency of the radio-frequency magnetic field is swept exponentially. Next, we precisely examine how the growth of a condensate depends on the experimental parameters of evaporative cooling in this inefficient exponential-sweep cooling. We find that, due to large nonlinear three-body loss, the number of condensed atoms finally becomes insensitive to the initial number of trapped atoms, the initial temperature, and the bias field of a magnetic trap. This result opens up the experimental possibility that the final number of condensed atoms can be well stabilized against the shot-to-shot fluctuations of experimental conditions in evaporative cooling.The dynamics of evaporative cooling of magnetically trapped 87 Rb atoms is studied on the basis of the quantum kinetic theory of a Bose gas. The theoretical optimization of the cooling trajectory clarifies that the acceleration of evaporative cooling around the transition point of Bose-Einstein condensation is very effective against serious three-body recombination loss. The number of condensed atoms is expected to be largely enhanced by the optimization as compared with the typical value produced by the conventional evaporative cooling, where the frequency of the radio-frequency magnetic field is swept exponentially. Next, we precisely examine how the growth of a condensate depends on the experimental parameters of evaporative cooling in this inefficient exponential-sweep cooling. We find that, due to large nonlinear three-body loss, the number of condensed atoms finally becomes insensitive to the initial number of trapped atoms, the initial temperature, and the bias field of a magnetic trap. This result opens up the experimental possibility that the final number of condensed atoms can be well stabilized against the shot-to-shot fluctuations of experimental conditions in evaporative cooling.

Laser PhysicsJan 1, 20040 citations

Radio-frequency-induced evaporative cooling of

{}^{87}\mathrm{Rb}

atoms in the

F=2,

m=2

ground state in a magnetic trap with a high bias field is found to be hampered, and eventually interrupted, by the presence of nonlinear Zeeman shifts. An experiment studying evaporation at a fixed adjustable rf frequency was used to illustrate this effect. These nonlinear shifts prevent us from reaching quantum degeneracy in the

F=2,

m=2

ground state; however, evaporation in the

F=1,

$m=\ensuremath{-}1$ ground state is not adversely affected, and we can produce a Bose-Einstein condensate (BEC). Our analysis shows that this effect can play a role in many BEC experiments.