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arXiv:quant-ph/0108078 · Physical Review A

Geometric phases of mesoscopic spin in Bose-Einstein condensates

Ivette Fuentes, Jiannis K. Pachos, Sougato Bose, Vlatko Vedral, Seok Jin Choi

Published Aug 5, 2002• 46 citations
arXivHTMLPDF

Abstract

We propose a possible scheme for generating spin-J geometric phases using a coupled two-mode Bose-Einstein condensate (BEC). First we show how to observe the standard Berry phase using Raman coupling between two hyperfine states of the BEC. We find that the presence of intrinsic interatomic collisions creates degeneracy in energy that allows implementation of the non-Abelian geometric phases as well. The evolutions produced can be used to produce interference between different atomic species with high numbers of atoms or to fine control the difference in atoms between the two species. Finally, we show that errors in the standard Berry phase due to elastic collisions may be corrected by controlling inelastic collisions between atoms.

DOI
10.1103/physreva.66.022102

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We propose a possible scheme for generating spin-J geometric phases using a coupled two-mode Bose-Einstein condensate (BEC). First we show how to observe the standard Berry phase using Raman coupling between two hyperfine states of the BEC. We find that the presence of intrinsic interatomic collisions creates degeneracy in energy that allows implementation of the non-Abelian geometric phases as well. The evolutions produced can be used to produce interference between different atomic species with high numbers of atoms or to fine control the difference in atoms between the two species. Finally, we show that errors in the standard Berry phase due to elastic collisions may be corrected by controlling inelastic collisions between atoms.
In terms of exact solutions of the time-dependent Schr\"odinger equation for an effective giant spin modeled from a coupled two-mode Bose-Einstein condensate (BEC) with adiabatic and cyclic time-varying Raman coupling between two hyperfine states of the BEC, we obtain analytic time-evolution formulas of the population imbalance and relative phase between two components with various initial states, especially the SU(2) coherent state. We find the Berry phase depending on the number parity of atoms, and particle number dependence of the collapse revival of population-imbalance oscillation. It is shown that self-trapping and phase locking can be achieved from initial SU(2) coherent states with proper parameters.
We propose a method of entangling two spinor Bose-Einstein condensates using a geometric phase gate. The scheme relies upon only the ac Stark shift and a common controllable optical mode coupled to the spins. Our scheme allows for the creation of an SzSz{S}^{z}{S}^{z}SzSz-type interaction where Sz{S}^{z}Sz is the total spin. The geometric phase gate can be executed in times of the order of $2\ensuremath{\pi}\ensuremath{\hbar}/G$, where GGG is the magnitude of the Stark shift. In contrast to related schemes which relied on a fourth-order interaction to produce entanglement, this is a second-order interaction in the number of atomic transitions. Closed expressions for the entangling phase are derived and the effects of decoherence due to cavity decay, spontaneous emission, and incomplete de-entangling of the light to the Bose-Einstein condensates are analyzed.
Squeezed states play a key role in diverse frontiers of quantum physics. Geometrically squeezed states, a squeezed state in the orbital phase space of rotating Bose-Einstein condensates (BEC), have been conventionally generated by anisotropic trapping potentials. In this work, we propose a different route to generate geometric squeezing via spin-orbit coupling (SOC) in a pseudospin-1/2 BEC. We show that the SOC enables effective two-phonon transitions within the lowest Landau level via virtual spin-flip processes, leading to exponential squeezing dynamics in both spin components. Furthermore, by applying a π/2π/2π/2 spin rotation, the two spin channels can be coherently coupled to produce two-mode geometric squeezing. We also investigate the influence of interatomic interactions on squeezing performance and identify parameters where robust squeezing can be achieved. Our work provides a viable pathway to realize and manipulate geometric squeezing in spinor quantum gases.
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Abstract Perspective methods of quantum metrology are highly suitable for designing new types of gyroscopes. Matter waves-based gyroscopic schemes have already been implemented in optical setups. In the nearing future, it might be possible to implement them with macroscopic coherent structures of atomic Bose-Einstein condensates (BECs). This work considers a ring-shaped BEC configuration interrupted by a localized potential “defect.” It is shown that variation of the shape of this “defect” generates atomic geometric phase. In a pair of such configurations opposite geometric phases may be obtained, with their difference equal to zero in absence of rotation. This difference can be revealed by observing interference of the atoms from different configurations. Calculation of resulting geometric phases is carried out for a model “defect” in a ring of 0.5 cm diameter detecting Earth’s diurnal rotation.
We describe the behavior of two coupled Bose-Einstein condensates in time-dependent (TD) trap potentials and TD Rabi (or tunneling) frequency using the two-mode approach. Starting from Bloch states, we succeed in obtaining analytical solutions for the TD Schr\"odinger equation and present a detailed analysis of the relative and geometric phases acquired by the wave function of the condensates, as well as their population imbalance. We also establish a connection between the geometric phases and constants of motion which characterize the dynamic of the system. Besides analyzing the affects of temporality on condensates that differ by hyperfine degrees of freedom (internal Josephson effect), we also do present a brief discussion of a one-species condensate in a double-well potential (external Josephson effect).