EGAS41 - Swansea University

41 st EGAS CP 116 Gdańsk 2009
Collisions of ultracold polar molecules in microwave traps
A.V. Avdeenkov
National Institute for Theoretical Physics, Stellenbosch Institute of Advanced Study, Private
BagX1, Matieland, 7602, South Africa
E-mail: avdeenkov@sun.ac.za
The collisions between linear polar molecules, trapped in a microwave field with a circular
polarization, are theoretically analyzed. The microwave trap suggested by DeMille[1]
seems to be rather advantageous in comparison with other traps. Here we have demonstrated
that the microwave trap can provide the successful evaporative cooling for polar
molecules not only in their absolute ground state but also in almost any strong-field seeking
states and the collision losses should not be of much concern to them[2]. But the
state in which molecules can be safely loaded and trapped depends on the frequency of
the AC-field.
In this work we are studying the collisional dynamics of linear polar molecules in the
1 Σ and 2 Π states. For 1 Σ state molecules the collisional dynamics is mostly controlled
by two ratios ν/B and x = µ 0 E 0 /hB (ν is the microwave frequency, B is the molecular
rotational constant, µ 0 is the dipole moment, and E 0 is the electric field strength). The
AC- Stark splitting is characterized by |J, M, n > states, where M is the projection of
rotation spin J and n is the deviation of the photon number. We are mostly interested in
the lowest energy strong-field-seeking state of the ground vibrational state, |JM >= |00 >
and found rather large inelastic cross sections for molecules even in this state. But we
found that the nature of this inelasticity is simply the ”undressing” of molecules by one
photon each and should not cause the loss of molecules from the trap. From the loading
with molecules point of view we suggested that it is ”safer” to load |J = 0, M = 0 >
molecules at ν/B < 2, |J = 1, M = −1 > at around ν/B = 3 , |J = 2, M = −2 > at
around ν/B = 5 and so on and it would be better to have the parameter x < 1 which
makes the regions of strong mixing smaller. But x must not be too small in order to
keep the depth of the trap practical. We are considering the collisional dynamics of 2 Π
state like OH molecules[3] and discussing that now ratios ν/∆ and x = µ 0 E 0 /∆ ( ∆ is Λ-
doubling splitting) play as controlling parameters.
References
[1] D. DeMille, D.R. Glenn, J. Petricka, Eur. Phys. J. D 31, 375 (2004)
[2] A.V. Avdeenkov, New J. Phys. 11 (2009) (accepted for publication)
[3] A.V. Avdeenkov, J.L. Bohn, Phys. Rev. A, 66, 052718 (2002)
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