64 research outputs found
Splitting of doubly quantized vortices in dilute Bose-Einstein condensates
We investigate the dynamics of doubly charged vortices generated in dilute
Bose-Einstein condensates by using the topological phase imprinting technique.
We find splitting times of such vortices and show that thermal atoms are
responsible for their decay.Comment: 1 page, 1 figur
Rate limit for photoassociation of a Bose-Einstein condensate
We simulate numerically the photodissociation of molecules into noncondensate
atom pairs that accompanies photoassociation of an atomic Bose-Einstein
condensate into a molecular condensate. Such rogue photodissociation sets a
limit on the achievable rate of photoassociation. Given the atom density \rho
and mass m, the limit is approximately 6\hbar\rho^{2/3}/m. At low temperatures
this is a more stringent restriction than the unitary limit of scattering
theory.Comment: 5 pgs, 18 refs., 3 figs., submitted to Phys. Rev. Let
Noncanonical quantum optics
Modification of the right-hand-side of canonical commutation relations (CCR)
naturally occurs if one considers a harmonic oscillator with indefinite
frequency. Quantization of electromagnetic field by means of such a non-CCR
algebra naturally removes the infinite energy of vacuum but still results in a
theory which is very similar to quantum electrodynamics. An analysis of
perturbation theory shows that the non-canonical theory has an automatically
built-in cut-off but requires charge/mass renormalization already at the
nonrelativistic level. A simple rule allowing to compare perturbative
predictions of canonical and non-canonical theories is given. The notion of a
unique vacuum state is replaced by a set of different vacua. Multi-photon
states are defined in the standard way but depend on the choice of vacuum.
Making a simplified choice of the vacuum state we estimate corrections to
atomic lifetimes, probabilities of multiphoton spontaneous and stimulated
emission, and the Planck law. The results are practically identical to the
standard ones. Two different candidates for a free-field Hamiltonian are
compared.Comment: Completely rewritten version of quant-ph/0002003v2. There are
overlaps between the papers, but sections on perturbative calculations show
the same problem from different sides, therefore quant-ph/0002003v2 is not
replace
Probing the classical field approximation - thermodynamics and decaying vortices
We review our version of the classical field approximation to the dynamics of
a finite temperature Bose gas. In the case of a periodic box potential, we
investigate the role of the high momentum cut-off, essential in the method. In
particular, we show that the cut-off going to infinity limit decribes the
particle number going to infinity with the scattering length going to zero. In
this weak interaction limit, the relative population of the condensate tends to
unity. We also show that the cross-over energy, at which the probability
distribution of the condensate occupation changes its character, grows with a
growing scattering length. In the more physical case of the condensate in the
harmonic trap we investigate the dissipative dynamics of a vortex. We compare
the decay time and the velocities of the vortex with the available analytic
estimates.Comment: 7 pages, 8 eps figures, submitted to J. Optics B for the proceedings
of the "Atom Optics and Interferometry" Lunteren 2002 worksho
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