The New Lab (BEC II)




 

Daniel Miller, Claudiu Stan, Widagdo "Junior" Setiawan, Jit Kee Chin, Yingmei Liu, Kaiwen Xu


Recent Work



Coherent Molecule Optics



A number of groups have produced diatomic molecules by sweeping through a Feschbach resonance. In short, the free atomic state and a weakly bound molecular state are tuned to degeneracy with a strong external magnetic field. Starting with a sodium BEC, we use this technique to prepare an ultra-cold sample of Na_2 molecules. Bragg diffraction is used as a spectroscopic technique and to manipulate the sample, yielding a molecular interference pattern and matter-wave sum frequency generation (SFG).


Bragg Scattering of (a) atoms and (b) molecules. Note that the molecules recoil with half the velocity of the atoms, due to their doubled mass. Kapitza-Dirac scattering of (c) atoms and (d) molecules. Sum Frequency Generation of a matter wave. (a) Atoms were intially prepared in momentum states 0 and 1. (b) By sweeping through a Feshbach resonance, atoms combine to form molecules with momenta 0,1 and 2. Momentum state 1 is the sum frequency of the two atomic matter waves. The "nonlinear medium" is provided by the atomic interactions.


Phys. Rev. Lett. 94, 040405 (2005)



Thermal Interference

Bragg diffraction is used to prepare two coherent "copies" of a thermal atomic cloud, which interfere in ballistic expansion, analogous to a Young's Double Slit experiment. While high contrast interference is often associated with BEC, we show that a trapped cloud of any temperature can exhibit high contrast interference.
(a) Schematic depiction of the Bragg sequence. The first pulse at t=0 creates a superposition of staionary and moving clouds. After the two have separated a distance "d", a second pulse mixes them again, yielding two pairs of clouds (one moving, one stationary). (b-d) In expansion, fringe contrast emerges, and approaches unity for longer expansion times. Contrast is observed to be enhanced when long velocity selective Bragg pulses are used. The velocity selectivity is obvious in this (a) absorption image and (b) cross section of an expanded cloud.


pre-print cond-mat/0412672

The Future



We have recently added a dual-species oven to our machine, and are looking forward to new and interesting work with fermionic Lithium-6.

Away with the old oven. Alligning the slowing light with the differential pumping tube.
Our beautiful new oven.