783 research outputs found
Strong parity effect of particle number in the interference fringes of Bose-Einstein condensates released from a double-well potential
We study the parity effect of the particle number in the interference fringes
of a Bose-Einstein condensate released from a double-well potential. For a
coherently splitting condensate in the double-well potential, with a decoupled
two-mode Bose-Hubbard model, there is well-known phase diffusion because of
interatomic interactions. After a specific holding time of the double-well
potential, the phase diffusion will make the interference patterns in the
density distribution depend strongly on the parity of the total particle number
by further overlapping two condensates. This parity effect originates from the
quantized relative phase about the total particle number. The experimental
scheme to observe this "even-odd" effect of the particle number is discussed.Comment: 5 pages, 2 figure
Wave function of string and membrane and spacetime geometry
A first-quantized string (and membrane) theory is developed here by using a
general wave function of the string (and membrane), analogously to the
first-quantized quantum theory of a point particle. From the general wave
function of the string (and membrane), the properties of the string (and
membrane) such as its relation to Bosons, Fermions and spacetime are
investigated. The string and membrane wave functions are found to be very
useful and we can deduce Klein-Gordon equation, Dirac equation and the
fundamental property of the spacetime from this new starting point.Comment: Revtex, 7 pages, [email protected]
Anomalous fermion bunching in density-density correlation
We consider theoretically density-density correlation of identical Fermi
system by including the finite resolution of a detector and delta-function term
omitted in the ordinary method. We find an anomalous fermion bunching effect,
which is a quantum effect having no classical analogue. This anomalous fermion
bunching is studied for ultracold Fermi gases released from a three-dimensional
optical lattices. It is found that this anomalous fermion bunching is supported
by a recent experiment (T. Rom et al Nature 444, 733 (2006)).Comment: RevTex, 4 page
Density-density correlation and interference mechanism for two initially independent Bose-Einstein condensates
In an exciting experiment by MIT's group (Science 275, 637 (1997)), clear
interference fringes were observed for two initially independent Bose
condensates in dilute gas. Presently, there are two different theories
(measurement-induced interference theory and interaction-induced interference
theory) which can both explain MIT's experimental results. Based on our
interaction-induced interference theory, we consider the evolution of the
density-density correlation after the releasing of a double-well potential
trapping two independent Bose condensates. Based on the interaction-induced
interference theory, we find that the interference fringes in the
density-density correlation exhibit a behavior of emergence and disappearance
with the development of time. We find essential difference for the
density-density correlation based on interaction-induced interference theory
and measurement-induced interference theory, and thus we suggest the
density-density correlation to experimentally reveal further the interference
mechanism for two initially independent Bose condensates.Comment: See also cond-mat/0612132 (or New Journal of Physics 8, 245 (2006)
Interference effect of critical ultra-cold atomic Bose gases
For ultra-cold atomic gases close to the critical temperature, there is a
divergent correlation behavior within the critical regime. This divergent
correlation behavior is the cornerstone of the universal behavior within the
critical regime, e.g. the universal critical exponent for the same class with
very different physical systems. It is still quite challenging to observe this
divergent correlation behavior in experiments with ultra-cold atomic gases.
Here we consider theoretically the interference effect of the critical atomic
Bose gas by a Kapitza-Dirac scattering. We find that the Kapitza-Dirac
scattering has the merit of enhancing the interference effect in the
observation of the correlation behavior. This provides a potential method to
study the critical behavior of ultra-cold Bose gases. A simple rule is found by
numerical simulations to get the critical exponent and correlation amplitude
ratio from the interference fringes after the Kapitza-Dirac scattering.Comment: 17pages, 4 figure
Density expectation value of two independent interacting Bose-Einstein condensates
After removing the double-well potential trapping two initially independent
Bose condensates, the density expectation value is calculated when both the
exchange symmetry of identical bosons and interatomic interaction are
considered. After the overlapping, it is shown that there is a nonzero
interference term in the density expectation value. This nonzero interference
term physically arises from the exchange symmetry of identical bosons and
interatomic interaction which make two initially independent condensates become
coherent after the overlapping. It is found that the calculated density
expectation value with this model agrees with the interference pattern observed
in the experiment by Andrews et al (Science 275, 637 (1997)).Comment: 4 pages, 2 figures. We consider in the present work a quite
challenging problem. Any comments are welcom
Dimers of ultracold two-component Fermi gases on magnetic-field Feshbach resonance
At the location of a magnetic-field Feshbach resonance, a mixture gas of
fermionic atoms and dimers of fermionic atom pairs is investigated in the
unitarity limit where the absolute value of the scattering length is much
larger than the mean distance between atoms. The dynamic equilibrium of the
mixture gases is characterized by the minimum of the Gibbs free energy. For the
fermionic atoms and dimers with divergent scattering length, it is found that
the fraction of the dimers based on a very simple theory agrees with the high
fraction of zero-momentum molecules observed in a recent experiment (M. W.
Zwierlein et al, Phys. Rev. Lett. 92, 120403 (2004)). The dimeric gas can be
also used to interpret the frequency of the radial breathing mode observed in
the experiment by J. Kinast et al (Phys. Rev. Lett. 92, 150402 (2004)).Comment: RevTex, 4 page
Josephson effect and quantum merging of two Bose superfluids
We consider the Josephson effect when two independent Bose superfluids are
weakly connected. In the presence of interparticle interaction and based on the
calculations of the one-particle density matrix of the whole system, we find
that the one-particle density matrix can be factorized which satisfies the
general criterion of Bose superfluid proposed by Penrose and Onsager. By
introducing an effective order parameter for the whole system, our researches
show that there is Josephson effect for two independent Bose superfluids.Comment: 9 pages, 4 figures. two typos in Eqs. (19) and (22) are corrected in
this versio
Condensate fraction of molecules for a spin mixture of ultracold fermionic atoms
The condensate fraction of molecules for ultracold Fermi gases is
investigated for the magnetic field below the Feshbach resonant magnetic field.
Assuming that there is no loss of particles and energy during the adiabatic
magnetic-field sweep, a simple theory is used to interpret the measured
condensate fraction in the experiments by JILA group (Phys. Rev. Lett. 92,
040403 (2004)) and MIT group (Phys. Rev. Lett. 92, 120403 (2004)). Our theory
shows that the condensate fraction of molecules is dependent on the initial
condition of the system and especially on the process of the magnetic-field
sweep.Comment: 4 pages, RevTex, 2 figs, E-mail: [email protected] A revised
version according to the comments and suggestions of the referee
Matter wave interference of dilute Bose gases in the critical regime
Ultra-cold atomic gases provide new chance to study the universal critical
behavior of phase transition. We study theoretically the matter wave
interference for ultra-cold Bose gases in the critical regime. We demonstrate
that the interference in the momentum distribution can be used to extract the
correlation in the Bose gas. A simple relation between the interference
visibility and the correlation length is found and used to interpret the
pioneering experiment about the critical behavior of dilute Bose gases [Science
{\bf 315}, 1556 (2007)]. Our theory paves the way to experimentally study
various types of ultra-cold atomic gases with the means of matter wave
interference.Comment: Accepted by Chin. Phys.
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