ABOVE BARRIER TRANSMISSION OF BOSE-EINSTEIN CONDENSATES IN GROSS- PITAEVSKII APPROXIMATION Moscow, H.A. Ishkhanyan, V.P. Krainov

Outline Introduction Reflection from the step potential The rectangular barrier Rosen-Morse Potential Double delta barrier A different approach  Rosen-Morse Potential  Rectangular barrier Conclusion, future directions

Temperature T=Tcritical Potential Well

The Gross-Pitaevskii equation Stationary

Outline Introduction Reflection from the step potential The rectangular barrier Rosen-Morse Potential Double delta barrier A different approach  Rosen-Morse Potential  Rectangular barrier Conclusion, future directions

1. Reflection from the step potential An atom moves slowly oppositely to the focused laser beam Resonant laser presents an one-dimensional potential barrier Hartree approximation. Resonant impulse р p ph p ph - р Atom laser Fig. 1. Resonant light as a potential barrier for the atom. For real optical laser frequency and mass of atom the kinetic energy is of the order of frequency of transition to the first excited state

1.1 The step potential From the matching conditions one obtains (Linear case)

1.2 The step potential The stationary Gross-Pitaevskii equation In the left region we do not have such a simple solution, so we use the multiscale analysis Considering only linear terms with respect to a

Zero interation First interation The whole solution

When  increases, the role of nonlinearity diminishes Oppositely, for repulsive nonlinearity transmission through barrier begins not when µ = V, but for the definite energy µ0> V.

An example The probability density The phase of wave function H.A. Ishkhanyan and V.P. Krainov, Laser Physics 19(8), 1729 (2009)

Outline Introduction Reflection from the step potential The rectangular barrier Rosen-Morse Potential Double delta barrier A different approach  Rosen-Morse Potential  Rectangular barrier Conclusion, future directions

An example The probability density The phase of wave function H.A. Ishkhanyan and V.P. Krainov, Laser Physics 19(8), 1729 (2009)

2.1 Rectangular barrier When For example

Outline Introduction Reflection from the step potential The rectangular barrier Rosen-Morse Potential Double delta barrier A different approach  Rosen-Morse Potential  Rectangular barrier Conclusion, future directions

The Gross-Pitaevskii equation The Problem Time-independent GPE The case of the first resonance H.A. Ishkhanyan and V.P. Krainov, 'Resonance reflection by the one- dimensional Rosen-Morse potential well in the Gross-Pitaevskii problem', JETP 136(4), 1 (2009). With the boundary conditions

Rosen-Morse potential Example The reflection coefficient is zero

Outline Introduction Reflection from the step potential The rectangular barrier Rosen-Morse Potential Double delta barrier A different approach  Rosen-Morse Potential  Rectangular barrier Conclusion, future directions

Double-Delta potential

H.A. Ishkhanyan and V.P. Krainov, Phys. Rev. A (2009) H.A. Ishkhanyan and V.P. Krainov, JETP 136(4), 1 (2009) H.A. Ishkhanyan and V.P. Krainov, Laser Physics 19(8), 1729 (2009) V.P. Kraynov and H.A. Ishkhanyan, “Resonant reflection of Bose- Einstein condensate by a double barrier within the Gross-Pitaevskii equation”, xxx Physica Scripta (2010) (in press)

A different approach

The Gross-Pitaevskii equation The Problem Time-independent GPE The case of the first resonance H.A. Ishkhanyan and V.P. Krainov, 'Resonance reflection by the one- dimensional Rosen-Morse potential well in the Gross-Pitaevskii problem', JETP 136(4), 1 (2009). With the boundary conditions

The solution A bit of mathematics We have a quasi-linear eigenvalue problem for the potential depth that we formulate in the following operator form where

Reflectionless transmission g=0 Reflectionless transmission if the condition is satisfied The corresponding transmission resonances are then achieved for As it is immediately seen, reflectionless transmission in the linear case is possible only for potential wells ! The linear part is the hypergeometric equation,where

Since the solution to the linear problem is known, it is straightforward to apply the Rayleigh-Schrödinger perturbation theory Then one obtains The derived formula is highly accurate if and it provides a rather good approximation up to Reflectionless transmission g≠0

The dependence of on Fig. 1. The nonlinear shift of the resonance position vs. the wave vector. Resonance position shift is approximately equidistant For each fixed the separation between the curves is approximately equidistant! is shown in Fig. 1. Remarkably simple structure In this case may be positive – barriers!

Note that for an integer n the function is a polynomial in z. Hence, the integral can be analytically calculated for any given order n A remarkable observation is that the formula for the first resonance, interestingly, turns out to be exact! Calculation of the integral

Outline Introduction Reflection from the step potential The rectangular barrier Rosen-Morse Potential Double delta barrier A different approach  Rosen-Morse Potential  Rectangular barrier Conclusion, future directions

Rectangular barrier Transmission resonances in the linear case The shift The final result for the nonlinear resonance position reads The immediate observation is that for the rectangular barrier the nonlinear shift of the resonance position is approximately constant!,where An assymetric potential

Results, Conclusions Reflection coefficients of Bose-Einstein condensates from four potentials are obtained. In some cases the exact analytical solutions are obtained. For the higher order resonances the onlinear shift of the resonance potential depth is determined within a modified Rayleigh-Schrödinger theory. Resonance position shift is approximately equidistant in the case of R-M potential and constant for the rectangular barrier.

Future Directions... Other potentials, other governing equations (e.g., assymetric potential), …Other types of nonlinearities (e.g., saturation nonlinearity ) … Stability of the resonances

H.A. Ishkhanyan and V.P. Krainov, 'Resonance reflection by the one- dimensional Rosen-Morse potential well in the Gross-Pitaevskii problem', JETP 136(4), 1 (2009). H.A. Ishkhanyan and V.P. Krainov, 'Multiple-scale analysis for resonance reflection by a one-dimensional rectangular barrier in the Gross-Pitaevskii problem', PRA 80, (2009). H.A. Ishkhanyan and V.P. Krainov, 'Above-Barrier Reflection of Cold Atoms by Resonant Laser Light within the Gross-Pitaevskii Approximation', Laser Physics 19(8), 1729 (2009). Publications Some parts of the problem are already published H.A. Ishkhanyan, V.P. Krainov, and A.M. Ishkhanyan, Transmission resonances in above-barrier reflection of ultra-cold atoms by the Rosen- Morse potential ', J. Phys. B 43, , J. Phys. B 43, (2010). And in a "World Scientific" publishing’s book entitled “ Modern Problems of Optics and Photonics”.

And some more are in press H.A. Ishkhanyan, V.P. Krainov “Higher order transmission resonances in above-barrier reflection of ultra-cold atoms”, European Physical Journal D, xxx (2010)(in press) H.A. Ishkhanyan “Higher order above-barrier resonance transmission of cold atoms in the Gross-Pitaevskii approximation”, Proc. of Intl. Advanced Research Workshop MPOP-2009, Yerevan, Armenia, xxx (2010) (in press). V.P. Kraynov and H.A. Ishkhanyan “The reflection coefficient of Bose-Einstein condensate by a double delta barrier within the Gross-Pitaevskii equation”, xxx Laser Physics (2010) (submitted)

Hayk Ishkhanyan

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