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All-Optical BEC
CO2 laser dipole traps
We create a
Bose-Einstein condensate (BEC) in an optical dipole trap, a
technique that was pioneered in our group.
Our atom trap is formed from a focused CO2. The wavelength
of this laser is λ=10.6μm, which is ∼ 14 times longer than the longest
wavelength transitions
in Rb. The atomic light-shift induced by such a laser is independent of
Zeeman sub-states and is also attractive for all relevant states.
A CO2 laser trap is desirable for the following reasons:
- Very low photon scattering rates, meaning negligable trap
heating.
- Traps all spin states.
- Fast and accurate control of trap depth
- Many geometries easily available; single focus, crossed
dipole, n-D lattices.
Routes to BEC
Evaporation to BEC in an optical trap is very fast; in our experiments
only ∼ 2s of evaporation is required to reach a BEC. We have developed
a number of different aproaches to BEC in a CO2 trap. The
details are outlined in this table:
Of specific interest are the crossed dipole trap, a 1-D lattice, and
the compressed, single focus trap.:
- Crossed dipole trap
- Large loading volume
- Very high trap frequencies
- Geometry used for first observation of BEC
- 1-D lattice
- Can create between 1 and 4 independent BECs
simultaneously
- Creates small BECs, which is important for coherent
spinor BEC studies
- Compressed single focus trap
- Loads very large number of atoms from MOT
- Comressing trap during evaporation maintains high
rapping frequencies
- Creates large BECs; ∼ 300,000 atoms
For initial loading we have a large trap volume,
allowing the capture of > 107 atoms.
During evaporation the trap is compressed
maintaining a high trapping frequency and high densities while lowering
the trapping potential.
A BEC of atoms with spin degrees of freedom offers an entirely new form
of coherent matter with complex internal quantum structures. While most
current experiments employ magnetic trapping techniques in which the
spin degree of freedom is fixed, an optical dipole trap allows all
Zeeman components to be trapped, liberating the spin degree of freedom.
A spinor Bose-Einstein condensate displays richer physics than a
one-component BEC because it is a system of weakly coupled superfluids.
Due to spin-dependent interactions phenomena such as coherent spin
mixing, spin domain formation, and spin squeezing can be observed.
Our results include
- Observation of F = 1, 87Rb spinor in first
all-optical BEC
- First observation of coherent spin mixing
- Determination of ferromagnetic nature of ground state of F
= 1, 87Rb spinor
- Observation of coherent spin dynamics at high B fields,
analagous to the internal AC Josephson effect
- Coherent control of spinor dynamics
- Observation of miscibility of different mF
states
- Observation of spin waves
- Observation of spin domains
Michael Chapman, group leader
Paul Griffin, post doc
Eva Bookjans, grad student
Chris Hamley, gard student
for further information:
michael.chapman - at - physics.gatech.edu
paul.griffin - at - physics.gatech.edu
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