Matter-wave interferometry with phase fluctuating Bose-Einstein condensates

Elongated Bose-Einstein condensates (BECs) exhibit strong spatial phase fluctuations even well below the BEC transition temperature. We demonstrate that atom interferometers using such condensates are robust against phase fluctuations; i.e., the relative phase of the split condensate is reproducible despite axial phase fluctuations. However, larger phase fluctuations limit the coherence time, especially in the presence of some asymmetries in the two wells of the interferometer.     

Strong correlation effects in 2D Bose-Einstein condensed dipolar excitons

By doing quantum Monte Carlo ab initio simulations we show that dipolar excitons, which are now under experimental study, actually are strongly correlated systems. Strong correlations manifest in significant deviations of excitation spectra from the Bogoliubov one, large Bose condensate depletion, short-range order in the pair correlation function, and peak(s) in the structure factor.     

Atom interferometry with a weakly interacting Bose-Einstein condensate

We demonstrate the operation of an atom interferometer based on a weakly interacting Bose-Einstein condensate. We strongly reduce the interaction induced decoherence that usually limits interferometers based on trapped condensates by tuning the s-wave scattering length almost to zero via a magnetic Feshbach resonance. We employ a 39K condensate trapped in an optical lattice, where Bloch oscillations are forced by gravity. The fine-tuning of the scattering length down to 0.1 a_(0) and the micrometric sizes of the atomic sample make our system a very promising candidate for measuring forces with high spatial resolution. Our technique can be in principle extended to other measurement schemes opening new possibilities in the field of trapped atom interferometry.     

Atom interferometry with Bose-Einstein condensates in a double-well potential

A trapped-atom interferometer was demonstrated using gaseous Bose-Einstein condensates coherently split by deforming an optical single-well potential into a double-well potential. The relative phase between the two condensates was determined from the spatial phase of the matter wave interference pattern formed upon releasing the condensates from the separated potential wells. Coherent phase evolution was observed for condensates held separated by 13 microm for up to 5 ms and was controlled by applying ac Stark shift potentials to either of the two separated condensates.     

Improved description of Bose-Einstein correlation function

The L3 data on Bose–Einstein correlations of equally charged pion pairs produced in hadronic Z decays are analyzed in terms of various parametrizations. Preliminary results are presented here.     

Low-coherence interferometry by intensity correlation

‘Low-coherence interferometry’ is an old technique which has had a wide development recently, and is based on the fact that interference with a path difference much longer that the coherence length gives rise to a ‘channeled spectrum’, which can be detected either by a dispersive spectroscope or by a second interferometer with a variable delay. We have tested an alternative way to detect path differences in this kind of interferometry, by analyzing the output intensity fluctuation correlations by a radiofrequency spectrum analyzer, and Fourier transforming the data. This method is suitable for very long path differences. The experiments have been performed with different lengths of single-mode fibre, in Mach–Zehnder and Fabry–Pérot configurations. Received: 30 March 2000 / Revised version: 17 Juli 2000 / Published online: 20 September 2000     

The correlation strength in pion interferometry

Distortions of single-boson spectra and their influence on two-particle correlations are studied. In a simplified simulation the importance of these effects especially in the case of small source sizes is investigated. The apparent correlation strength may be strongly altered, thereby making the interpretation of such a measurement even more difficult.     

The correlation strength in pion interferometry

The role of the parameter in pion interferometry, thecorrelation strength, is investigated. The relations between the extracted values for and the radii are emphasized and illustrated by a compilation of published data. It is shown that radii from interferometry measurements can often not be interpreted independently from . The validity of quantitative radius estimates based on the freeze-out picture is discussed. From pion interferometry data at target rapidity in 200A GeV¹⁶O+Au collisions an effective rescattering cross section for soft pions of 11 mb is extracted.     

Contrast interferometry using Bose-Einstein condensates to measure h/m and alpha

The kinetic energy of an atom recoiling due to absorption of a photon was measured as a frequency, using an interferometric technique called "contrast interferometry." Optical standing wave pulses were used to create a symmetric three-path interferometer with a Bose-Einstein condensate. Its recoil phase, measurable with a single shot, varies quadratically with additional recoils and is insensitive to errors from vibrations and ac Stark shifts. We have measured the photon recoil frequency of sodium to 7 ppm precision, using a simple realization of this scheme. Plausible extensions should yield sufficient precision to attain a ppb-level determination of h/m and the fine structure constant alpha.     

Interaction effects on atomic laboratory trapped Bose-Einstein condensates

We discuss the effect of inter-atoms interactions on the condensation temperature T _c of an atomic laboratory trapped Bose-Einstein condensate. We show that, in the mean-field Hartree-Fock and semiclassical approximations, interactions produce a shift Δ T _c /T _c ⁰ ≈ b ₁(a/λ _{T c} ) + b ₂(a/λ _{T c} )² + ψ[a / λ _{T c} ] with a the s-wave scattering length, λ _T the thermal wavelength and ψ[a / λ _{T c} ] a non-analytic function such that ψ[0] = ψ′[0] = ψ′′[0] = 0 and |ψ′′′[0]| = ∞. Therefore, with no more assumptions than Hartree-Fock and semiclassical approximations, interaction effecs are perturbative to second order in a / λ _{T c} and the expected non-perturbativity of physical quantities at critical temperature appears only to third order. We compare this finding with different results by other authors, which are based on more than the Hartree-Fock and semiclassical approximations. Moreover, we obtain an analytical estimation for b ₂ ? 18.8 which improves a previous numerical result. We also discuss how the discrepancy between b ₂ and the empirical value of b ₂ = 46 ± 5 may be explained with no need to resort to beyond-mean field effects.     

Double-image encryption based on joint transform correlation and phase-shifting interferometry

An image encryption method combining the joint transform correlator (JTC) architecture with phaseshifting interferometry to realize double random-phase encoding is proposed. The encrypted field and the decrypting key are registered as holograms by phase-shifting interferometry. This method can encrypt two images simultaneously to improve the encryption efficiency of the methods based on JTC architecture, and eliminate the system alignment constraint of the methods based on Mach-Zehnder interferometer (MZI)architecture. Its feasibility and validity are verified by computer simulations. Moreover, image encryption and decryption can be achieved at high speed optically or digitally. The encrypted data are suitable for Internet transmission.     

自由膨胀准二维玻色-爱因斯坦凝聚中的密度-密度关联

利用Madelung变换, 考虑密度和相位涨落, 给出了准二维玻色-爱因斯坦凝聚体的有效拉格朗日密度函数和波函数量子涨落的算符化表示, 计算了凝聚体在去除约束势场自由膨胀时两点之间的密度-密度关联函数, 结果表明在长波极限下, 两点之间的密度关联函数正比于波数k, 而在短波极限下, 密度关联函数趋近于一个常数. 关键词： 玻色-爱因斯坦凝聚 量子涨落 密度关联     

On the Bose-Einstein correlation in inelastic collisions of nuclei

The Bose-Einstein correlation function for two pions of same charge produced in a high energy nucleus-nucleus collision is computed in the framework of the reggeon theory. We obtain a coherence parameter λ=1 and a transverse radius of the sourceR _T close to the radius of the smaller of the colliding nuclei.

     

Nonlocal quantum effects with Bose-Einstein condensates

We study theoretically the properties of two Bose-Einstein condensates in different spin states, represented by a double Fock state. Individual measurements of the spins of the particles are performed in transverse directions, giving access to the relative phase of the condensates. Initially, this phase is completely undefined, and the first measurements provide random results. But a fixed value of this phase rapidly emerges under the effect of the successive quantum measurements, giving rise to a quasiclassical situation where all spins have parallel transverse orientations. If the number of measurements reaches its maximum (the number of particles), quantum effects show up again, giving rise to violations of Bell type inequalities. The violation of Bell-Clauser-Horne-Shimony-Holt inequalities with an arbitrarily large number of spins may be comparable (or even equal) to that obtained with two spins.     

Spin correlation and discrete symmetry in spinor Bose-Einstein condensates

We study spin correlations in Bose-Einstein condensates of spin 1 bosons with scatterings dominated by a total spin equal 2 channel. We show that the low energy spin dynamics in the system can be mapped into an o(n) nonlinear sigma model. n = 3 at the zero magnetic field limit and n = 2 in the presence of weak magnetic fields. In an ordered phase, the ground state has a discrete Z2 symmetry and is degenerate under the group [U(1)xS(n-1)]/Z(2). We explore consequences of the discrete symmetry and propose some measurements to probe it.