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arXiv:0907.1126

Strong parity effect of particle number in the interference fringes of Bose-Einstein condensates released from a double-well potential

Hongwei Xiong, Shujuan Liu

Published Jul 7, 2009• 0 citations
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Abstract

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.

DOI
10.48550/arxiv.0907.1126

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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.
The interference pattern of two Bose—Einstein condensates released from a double-well potential for different holding times is theoretically investigated using a decoupled two-mode Bose—Hubbard model. For two coherently separated condensates, the interference displays a periodic behavior, which is closely related to the atomic interaction. A remarkable parity effect is found in the interference patterns. For certain holding times, the even/odd total number of atoms would result in different interference fringes. The influences of different initial conditions on the evolution of interference and the observation of parity effects are discussed.
Abstract We investigate the dynamical evolution and atom number parity effect of bosonic condensates in a double-well potential within the two-mode Bose–Hubbard model (BHM), following a quench from the Josephson to the Fock regime. We demonstrate the different behaviors of systems with even and odd numbers of atoms on a mesoscopic scale by calculating the correlation function  ( t ) , visibility α , number fluctuation  and entanglement entropy S . In contrast to the full collapse and revival of quantum correlations for systems with even numbers of atoms, we find that the correlations for systems with odd numbers will not collapse thoroughly, predicting a nonvanishing interference pattern. We relate this phenomenon to the parity effect of the energy spectrum, explain the effect in the pseudo-angular-momentum representation of the BHM Hamiltonian and suggest its confirmation in experiments.
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. The density expectation value and evolution equations are obtained based on both the first-quantization and second-quantization methods. When the interatomic interaction is considered carefully, after the overlapping of two initially independent condensates, it is shown that there is a nonzero interference term in the density expectation value. It is found that the calculated density expectation value with this model agrees with the interference pattern observed in the experiment by Andrews (Science 275, 637 (1997)). The nonzero interference term in the density expectation value physically arises from the exchange symmetry of identical bosons and interatomic interaction which make two initially independent condensates become coherent after the overlapping. For two initially independent condensates, our researches show that there is an interaction-induced coherence process.
We study the dynamics of Bose-Einstein condensates in symmetric double-well potentials following a sudden change of the potential from the Mott-insulator to the superfluid regime. We introduce a continuum approximation that maps that problem onto the wave-packet dynamics of a particle in an anharmonic effective potential. For repulsive two-body interactions the visibility of interference fringes that result from the superposition of the two condensates following a stage of ballistic expansion exhibits a collapse of coherent oscillations onto a background value whose magnitude depends on the amount of squeezing of the initial state. Strong attractive interactions are found to stabilize the relative number dynamics. We visualize the dynamics of the system in phase space using a quasiprobability distribution that allows for an intuitive interpretation of the various types of dynamics.
Quantum superpositions of macroscopically distinguishable states having distinct phases can be created with a Bose-Einstein condensate trapped in a periodic potential. The experimental signature is contained in the phase distribution of the interference patterns obtained after releasing the traps. Moreover, in the double-well case, this distribution exhibits a dramatic dependence on the parity of the total number of atoms. We finally show that, for single-well occupations up to a few hundred atoms, the macroscopic quantum superposition can be robust enough against decoherence to be experimentally revealable within current technology.
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)).