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Older Experimental Work in BEC III
Research in BEC III is focused on the manipulation of condensates and novel trapping geometries. Below is a bit about the most recent research that we've been doing. Theses from previous group members can be found below as well.
A trapped-atom interferometer was demonstrated using gaseous Bose-Einstein condensates coherently split by deforming an optical single-well potential into a double-well potential. The relative phase between the two condensates was determined from the spatial phase of the matter wave interference pattern formed upon releasing the condensates from the separated potential wells. Coherent phase evolution was observed for condensates held separated by 13 µm for up to 5 ms and was controlled by applying ac Stark shift potentials to either of the two separated condensates.
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| Cartoon schematic of the optical matter wave interferometer. | Typical fringe pattern and the fitting function used to obtain the phase. |
Dilute Condensates below 500 PicoKelvin
Spin-polarized gaseous Bose-Einstein condensates were confined by a combination of fravitational and magnetic forces. The partially condensed atomic vapors were adiabatically decompressed by weakening the gravito-magnetic trap to a mean frequency of 1 Hz, then evaporatively reduced in size to 2500 atoms. This lowered the peak condensate density to 5e10 atoms/cm3 and cooled the entire cloud in all three dimensions to a kinetic temperature of 450 +- 800 pK. Such spin-polarized, dilute, and ultracold gases are important for spectroscopy, metrology, and atom optics.
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| Gravito-magnetic trap for dilute condensates. | PicoKelvin condensates. The temperatures from top to bottom are 1nK, 750pK, and 450pK. |
Coreless vortices were phase imprinted in a spinor Bose-Einstein condensate. The three-component order parameter of F = 1 sodium condensates held in a Ioffe-Pritchard magnetic trap was manipulated by adiabatically reducing the magnetic bias field along the trap axis to zero. This distributed the condensate population across its three spin states and created a spin texture. Each spin state acquired a different phase winding which caused the spin components to separate radially.
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| Observation of spin texture by Stern-Gerlach separation of spin states. |
Magnetically and optically confined Bose-Einstein condensates were studied near a microfabricated surface. Condensate fragmentation observed in microfabricated magnetic traps was not observed in optical dipole traps at the same location. The measured condensate lifetime was 20 s and independent of the atom-surface separation under both magnetic and optical confinement. Radio-frequency spin-flip transitions driven by technical noise were directly observed for optically confined condensates and could limit the condensate lifetime in microfabricated magnetic traps.
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| Condensates confined optically (top) and magnetically (bottom) near a surface. |
Vortices were imprinted in a Bose-Einstein condensate using topological phases. Sodium condensates held in a Ioffe-Pritchard magnetic trap were transformed from a nonrotating state to one with quantized circulation by adiabatically inverting the magnetic bias field along the trap axis. Using surface wave spectroscopy, the axial angular momentum per particle of the vortex states was found to be consistent with 2 h or 4 h, depending on the hyperfine state of the condensate.
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| Vortices being imprinted on a condensate in the F= 1, -1 state (top) and F=2,+2 state (bottom). | Surface wave spectroscopy. |
A continuous source of Bose-Einstein condensed sodium atoms was created by periodically replenishing a condensate held in an optical dipole trap with new condensates delivered using optical tweezers. The source contained more than 1 million atoms at all times, raising the possibility of realizing a continuous atom laser.
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| Condensate atoms being transfered from the tweezers into the condensate resevoir. |
Gaseous Bose-Einstein condensates were loaded into a microfabricated magnetic trap using optical tweezers. Subsequently, the condensates were released into a magnetic waveguide and propagated 12 mm. Single-mode propagation was observed along homogeneous segments of the waveguide. Inhomogeneities in the guiding potential arose from geometric deformations of the microfabricated wires and caused strong transverse excitations. Such deformations may restrict the waveguide physics that can be explored with propagating condensates. Finer perturbations to the guiding potential fragmented the condensate when it was brought closer to the surface.
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| Schematic of microchip waveguide. | Propogation in the ground state and excited modes. |
Condensate Transport with Tweezers
We have transported gaseous Bose-Einstein condensates over distances up to 44 cm. This was accomplished by trapping the condensate in the focus of an infrared laser and translating the location of the laser focus with controlled acceleration. Condensates of order 106 atoms were moved into an auxiliary chamber and loaded into a magnetic trap formed by a Z-shaped wire. This transport technique avoids the optical and mechanical access constraints of conventional condensate experiments and creates many new scientific opportunities.
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| Vacuum chamber for condensate production (right) and the science chamber (left). | Schematic of the optical tweezers in action. |
Science Chamber Thesis Work
Christian Sanner: Diploma Thesis 2004
Momentum Interferometry and Quantum Reflection with Bose-Einstein Condensates
Andre Schirotzek: Diploma Thesis 2004
Fundamental Dynamics of Bose-Einstein Condensates: Photon Recoil and Distillation
Aaron Leanhardt: PhD Thesis 2004
Microtraps and Waveguides for Bose-Einstein Condensates
Ananth Chikkatur: PhD Thesis 2002
Colliding and Moving Bose-Einstein Condensates: Studies of
superfluidity and optical tweezers for condensate transport