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Chinese Physics B

Tunneling between double wells of atom in crossed electromagnetic fields

Shen Li, Lei Wang, Yang Hai-Feng, Xiaojun Liu, Hongping Liu

Published Dec 1, 2009• 1 citation
Publisher

Abstract

The tunneling between double wells of atom in crossed electromagnetic fields is investigated by a one-dimensional Hamiltonian model. The crossed fields induced outer well is apart from the nuclear origin and it is very difficult to access by means of spectroscopy but it will be possible if there exists the tunneling of the electron between the outer well and the Coulomb potential predominated well at the nuclear origin. A one-dimensional quantum calculation with B-spline basis has been performed for hydrogen atom in crossed fields accessible in our laboratory, at B = 0.8 T and F = −220 V·cm −1 . The calculation shows that the wavefunctions of some excited states close to the Stark saddle point in the outer well extend over to the Coulomb potential well, making it possible to penetrate the quantum information of the outer well. However, the tunneling rate is very small and the spectral measurement of the transitions from the ground state should be of a high resolution and high sensitivity.

DOI
10.1088/1674-1056/18/12/027

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The tunneling between double wells of atom in crossed electromagnetic fields is investigated by a one-dimensional Hamiltonian model. The crossed fields induced outer well is apart from the nuclear origin and it is very difficult to access by means of spectroscopy but it will be possible if there exists the tunneling of the electron between the outer well and the Coulomb potential predominated well at the nuclear origin. A one-dimensional quantum calculation with B-spline basis has been performed for hydrogen atom in crossed fields accessible in our laboratory, at B = 0.8 T and F = −220 V·cm −1 . The calculation shows that the wavefunctions of some excited states close to the Stark saddle point in the outer well extend over to the Coulomb potential well, making it possible to penetrate the quantum information of the outer well. However, the tunneling rate is very small and the spectral measurement of the transitions from the ground state should be of a high resolution and high sensitivity.
The pseudoseparation of the center of mass and relative motion of a hydrogen atom in crossed electric and magnetic fields led to a theoretical prediction of highly extended states localized in the outer potential well. These states correspond to an almost macroscopic separation between a proton and an electron, and give rise to giant dipole moments. In the present work we describe a simple, experimentally feasible, scheme for the preparation of a hydrogen atom in a superposition of such states. The preparation scheme is based on a two-step switching on of an external electric field, in the course of which the relative motion is trapped in the outer well. On the basis of classical simulations we suggest the experimental parameters at which trapping is achieved extremely efficiently.
The movement of a proton which moves in a one-dimensional effective double-minimum potential V(x) and can pass by means of the tunnel effect from one well into the other was investigated. The lingering times of the proton in the potential wells (a) and (b) were calculated for more than 150 potential models as functions of the height Vmax of the potential barrier separating the two wells, the energy difference ΔV, and separation d of the minima. In the determination of the lingering times, it was assumed that the proton at time t = 0 is to be found with certainty in one of the wells and can be represented by means of a statistical operator related to the eigenstates of a one-well Hamiltonian H(a)orH(b), respectively. The times determined on this basis were compared with those which result with a quasiclassical method from the classical frequency of oscillation of a particle in a well and from the penetration coefficient of the potential barrier. The deviation between the values determined with both methods is largest if an eigenvalue of H(a) becomes approximately equal to an eigenvalue of H(b). For the potential model V(x) a polynomial of fourth degree in the position coordinate x was chosen. The eigenfunctions of H(a)andH(b) as well as those of the effective Hamiltonian H corresponding to V(x) were represented as linear combinations of eigenfunctions of the harmonic oscillator with angular frequency ω. ω was chosen so that the mean square deviations of the approximated eigenvalues of H became as small as possible for the states of lowest energy.
Electromagnetically induced transparency is an important tool for controlling light propagation and nonlinear wave mixing in atomic gases with potential applications ranging from quantum computing to table top tests of general relativity.Here we consider electromagnetically induced transparency in an atomic Bose-Einstein condensate trapped in a double well potential.One well is prepared as in standard electromagnetically induced transparency with a weak probe laser and control laser in a Λ configuration while tunneling between the wells provides a coherent coupling between identical electronic states in the two wells leading to the formation of spatially delocalized inter-well dressed states.The macroscopic inter-well coherence of the Bose-Einstein condensate wave function qualitatively modifies the normal electromagnetically induced transparency linear susceptibility and leads to the formation of additional absorption resonances and larger dispersion than electromagnetically induced transparency.We show that these new resonances can be interpreted in terms of the inter-well dressed states and the formation of a novel type of dark state involving the control laser and the inter-well tunneling.
We study the tunnelling of a two-level atom in a double well potential while the atom is coupled to a single electromagnetic field mode of a cavity. The coupling between internal and external degrees of freedom, due to the mechanical effect on the atom from photon emission into the cavity mode, can dramatically change the tunnelling behaviour. We predict that in general the tunnelling process becomes quasiperiodic. In a certain regime of parameters a collapse and revival of the tunnelling occurs. Accessing the internal degrees of freedom of the atom with a laser allows us to coherently manipulate the atom position, and in particular to prepare the atom in one of the two wells.
Abstract Previous results for nuclear fluxes during coherent tunnelling of molecules with symmetric double well potentials are extended to fluxes in asymmetric double well potentials. The theory is derived using the two-state approximation (TSA). The symmetric system serves as a reference. As an example, we consider the one-dimensional model of the tunnelling inversion of oriented ammonia, with semiclassical dipole coupling to an electric field. The tunnelling splitting increases with the dipole coupling by a factor The tunnelling time decreases by The nuclear density appears as the sum of two parts: The tunnelling part decreases as times the density of the symmetric reference, whereas the non-tunnelling part is the initial density times Likewise, the nuclear flux decreases by with essentially the same shape as for the symmetric reference, with maximum value at the potential barrier. Coherent nuclear tunnellings starting from the upper or lower wells of the asymmetric potential are equivalent. The results are universal, in the frame of the TSA, hence they allow straightforward extrapolations from one system to others. This is demonstrated by the prediction of isotope effects for five isotopomers of ammonia.
The possibility of the electron oscillations in a two-well potential is investigated in the article. The Hamiltonian of the system is calculated taking into account the formulas of the James-Cummings model. The unitary dynamics is carried out using a general solution of the Schrodinger equation. The conditions for the parameters of the problem under which the oscillation takes place are shown. These conditions for the exact formulation are discrete. However, it is valuable to find out at what parameters of the problem there occur approximate oscillations, at which an incomplete transition of a particle from one well to another is observed. In the standard manuals on the quantum theory of a single particle, the Hamiltonian was considered from the very beginning without photons, so it was assumed that complete oscillations always take place. This approximate consideration corresponds to reality only with a high potential between the wells. If the potential is low, the wells actually merge into one well, so that the spectrum and eigenvalues of the Hamiltonian become similar to the spectrum and eigenvalues of a one-dimensional potential – a radically different case. Such a discrepancy occurs due to ignoring the interaction of the electron with the electromagnetic field. If such an interaction is taken into account we get the dynamics described by the Jaynes-Cummings Hamiltonian. At a low potential, the energy gap between the ground and excited energy states of the electron grows. Since the probability of photon emission is proportional to this value, the interaction with the field cannot be ignored.