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Physical Review A

Interferometer within a molecule

B. M. Garraway, Stig Stenholm

Published Aug 1, 1992• 27 citations
Publisher

Abstract

We show how interferometry can be carried out within a molecule. The method can be used to test semiclassical quantum mechanics and to map out Born-Oppenheimer energy surfaces. The interference occurs between molecular wave packets that travel through different molecular states. Packet splitting and recombination is carried out at laser-induced level crossings. We have compared the exact quantum-mechanical behavior (calculated numerically on a Cray computer) with a pseudoclassical method.

DOI
10.1103/physreva.46.1413

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We show how interferometry can be carried out within a molecule. The method can be used to test semiclassical quantum mechanics and to map out Born-Oppenheimer energy surfaces. The interference occurs between molecular wave packets that travel through different molecular states. Packet splitting and recombination is carried out at laser-induced level crossings. We have compared the exact quantum-mechanical behavior (calculated numerically on a Cray computer) with a pseudoclassical method.
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Mixed adiabatic and diabatic passages through avoided crossings in the Stark map of cesium Rydberg atoms are employed as beam splitters and recombiners in an atom-interferometric measurement of energy-level splittings. We subject cold cesium atoms to laser-excitation, electric-field, and detection sequences that constitute an (internal-state) atom interferometer. The adiabatic state transformation in the interferometer's beam splitters enables the spectroscopy of states that are, due to selection rules, inaccessible to direct laser-spectroscopic observation. For the read-out of the interferometer we utilize state-dependent collisions, which selectively remove atoms of one kind from the detected signal. We investigate the dependence of the interferometric signal on timing and field parameters, and find good agreement with quantum simulations of the interferometer. Fourier analysis of the interferometric signals yield coherence frequencies that agree with corresponding energy-level differences in calculated Stark maps.
An experiment is described which is an analog of Young's double-slit interferometer using an atomic electron instead of light. Two phase-coherent laser pulses are used to excite a single electron into a state of the form of a pair of Rydberg wave packets that are initially on opposite sides of the orbit. The two wave packets propagate and spread until they completely overlap, then a third phase-coherent laser pulse probes the resulting fringe pattern. The relative phase of the two wave packets is varied so that the interference produces a single localized electron wave packet on one side of the orbit or the other.
We investigate the quantum dynamics of ultra-long-range trilobite molecules exposed to homogeneous electric fields. A trilobite molecule consists of a Rydberg atom and a ground-state atom, which is trapped at large internuclear distances in an oscillatory potential due to scattering of the Rydberg electron off the ground-state atom. Within the Born-Oppenheimer approximation, we derive an analytic expression for the two-dimensional adiabatic electronic potential energy surface in weak electric fields valid up to 500 V/m. This is used to unravel the molecular quantum dynamics employing the multiconfigurational time-dependent Hartree method. Quenches of the electric field are performed to trigger the wave-packet dynamics including the case of field inversion. Depending on the initial wave packet, we observe radial intrawell and interwell oscillations as well as angular oscillations and rotations of the respective one-body probability densities. Opportunities to control the molecular configuration are identified, a specific example being the possibility to superimpose different molecular bond lengths by a series of periodic quenches of the electric field.