Soliton molecule formation from two dipolar Bose-Einstein condensate bright solitons

Bose-Einstein condensate (BEC) is a state of matter composed of a gas of bosonic atoms attained at very low temperatures near 0 K. Many peculiar things happen in BEC superfluid matter with zero viscosity. The superfluidity in BEC was first detected experimentally in liquid helium near 0 K in 1930s by London brothers. BEC was predicted by Bose and Einstein in 1924 and was observed experimentally in 1996 in purest form in a controlled fashion.

Among many peculiar properties of BEC is the ability of BEC to form bright solitons when the atomic interaction is attractive. Bright solitons are robust objects whch move long distances without deformation. In frontal collision in one dimension two such BEC solitons pass through each other without deformation. The experimental set up uses a strong magnetic trap in transverse directions to confine the BEC, so that a quasi-one-dimensional configuration is achieved where the BEC can move freely in the axial direction. In such a set up, if the atomic interaction is attractive, a droplet of BEC of a small number of atoms form a bright soliton.

However, many bosonic atoms have (electric or magnetic) dipole moment, which changes the above scenario dramatically. Because of peculiar properties of dipolar interaction, strange things can happen. In the cigar-shaped quasi-one dimensional configuration of the bright soliton, the dipolar interaction leads to attraction, as many dipoles placed on a linear chain attract each other. Consequently, a cigar-shaped dipolar BEC could be attractive even for a finite repulsive atomic interaction. We have studied the dynamics of bright solitons formed in cigar-shaped dipolar BEC with repulsive atomic interactions.

If two bright solitons collide frontally with a large relative velocity, they move towards each other and pass through each other unchanged. However, if two such solitons are placed side-by-side, they move towards each other slowly due to atomic interaction and form a soliton molecule -- a bound state of two solitons -- and never come out as individual solitons.

We used the solution of the mean-field Gross-Pitaevskii equation for this theoretical investigation using two cigar-shaped bright solitons, each of 1000 Cromium atoms, with a permanent dipole moment and with a repulsive atomic interaction (atomic scattering length of +0.5 nm) . Two BEC bright solitons placed side-by side with an initial distance of about 50 microns slowly move towards each other and combine to form a soliton molecule and oscillate for ever without allowing the individual solitons to come out.

Authors: L. E. Young-S., P. Muruganandam, and S. K. Adhikari

Category:

Science & Technology

Tags:

• Vortex
• Soliton
• Elastic
• Collision
• Dipolar
• Bose-Einstein
• condensate
• adhikari
• muruganandam
• young-s
• superfluid
• superfluidity
• nonlinear
• numerical
• simulation
• Gross-Pitaevskii
• equation
• bright
• dark
• dynamics
• rotation
• rotating
• supercold
• atoms
• low
• ultralow
• temperature
• phase
• transition

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