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Title: Coherent control of ultracold collisions with chirped light: Direction matters

Abstract

We demonstrate the ability to coherently control ultracold atomic Rb collisions using frequency-chirped light on the nanosecond time scale. For certain center frequencies of the chirp, the rate of inelastic trap-loss collisions induced by negatively chirped light is dramatically suppressed compared to the case of a positive chirp. We attribute this to a fundamental asymmetry in the system: an excited wave packet moves inward on the attractive molecular potential. For a positive chirp, the resonance condition moves outward in time, while for a negative chirp, it moves inward, in the same direction as the excited wave packet; this allows multiple interactions between the wave packet and the light, enabling the wave packet to be returned coherently to the ground state. Classical and quantum calculations support this interpretation.

Authors:
; ; ;  [1]; ;  [2]
  1. Department of Physics, University of Connecticut, Storrs, Connecticut 06269 (United States)
  2. Department of Physical Chemistry and the Fritz Haber Research Center for Molecular Dynamics, The Hebrew University, 91094, Jerusalem (Israel)
Publication Date:
OSTI Identifier:
20982441
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. A; Journal Volume: 75; Journal Issue: 5; Other Information: DOI: 10.1103/PhysRevA.75.051401; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; ASYMMETRY; COMPUTER CALCULATIONS; GROUND STATES; INTERACTIONS; LASER RADIATION; LOSSES; PHOTON-ATOM COLLISIONS; POTENTIALS; PULSES; RESONANCE; RUBIDIUM; TEMPERATURE RANGE 0000-0013 K; TRAPS; WAVE PACKETS

Citation Formats

Wright, M. J., Pechkis, J. A., Carini, J. L., Gould, P. L., Kallush, S., and Kosloff, R.. Coherent control of ultracold collisions with chirped light: Direction matters. United States: N. p., 2007. Web. doi:10.1103/PHYSREVA.75.051401.
Wright, M. J., Pechkis, J. A., Carini, J. L., Gould, P. L., Kallush, S., & Kosloff, R.. Coherent control of ultracold collisions with chirped light: Direction matters. United States. doi:10.1103/PHYSREVA.75.051401.
Wright, M. J., Pechkis, J. A., Carini, J. L., Gould, P. L., Kallush, S., and Kosloff, R.. Tue . "Coherent control of ultracold collisions with chirped light: Direction matters". United States. doi:10.1103/PHYSREVA.75.051401.
@article{osti_20982441,
title = {Coherent control of ultracold collisions with chirped light: Direction matters},
author = {Wright, M. J. and Pechkis, J. A. and Carini, J. L. and Gould, P. L. and Kallush, S. and Kosloff, R.},
abstractNote = {We demonstrate the ability to coherently control ultracold atomic Rb collisions using frequency-chirped light on the nanosecond time scale. For certain center frequencies of the chirp, the rate of inelastic trap-loss collisions induced by negatively chirped light is dramatically suppressed compared to the case of a positive chirp. We attribute this to a fundamental asymmetry in the system: an excited wave packet moves inward on the attractive molecular potential. For a positive chirp, the resonance condition moves outward in time, while for a negative chirp, it moves inward, in the same direction as the excited wave packet; this allows multiple interactions between the wave packet and the light, enabling the wave packet to be returned coherently to the ground state. Classical and quantum calculations support this interpretation.},
doi = {10.1103/PHYSREVA.75.051401},
journal = {Physical Review. A},
number = 5,
volume = 75,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}
  • We present results on coherent control of ultracold trap-loss collisions using 40-ns pulses of nonlinearly frequency-chirped light. The chirps, either positive or negative, sweep {approx}1 GHz in 100 ns and are centered at various detunings below the D{sub 2} line of {sup 85}Rb. At each center detuning, we compare the collisional rate constant {beta} for chirps that are linear in time, concave-down, and concave-up. For positive chirps, we find that {beta} generally depends very little on the shape of the chirp. For negative chirps, however, we find that {beta} can be enhanced by up to 50(20)% for the case ofmore » the concave-down shape. This occurs at detunings where the evolution of the wave packet is expected to be coherent. An enhancement at these detunings is also seen in quantum-mechanical simulations of the collisional process.« less
  • We report on ultracold atomic collision experiments utilizing frequency-chirped laser light. A rapid chirp below the atomic resonance results in adiabatic excitation to an attractive molecular potential over a wide range of internuclear separation. This leads to a transient inelastic collision rate which is large compared to that obtained with fixed-frequency excitation. The combination of high efficiency and temporal control demonstrates the benefit of applying the techniques of coherent control to the ultracold domain.
  • We have studied the effects of chirped femtosecond laser pulses on the formation of ultracold molecules in a Rb magneto-optical trap. We have found that application of chirped femtosecond pulses suppressed the formation of {sup 85}Rb{sub 2} and {sup 87}Rb{sub 2} a {sup 3}{sigma}{sub u}{sup +} molecules in contrast to comparable nonchirped pulses, cw illumination, and background formation rates. Variation of the amount of chirp indicated that this suppression is coherent in nature, suggesting that coherent control is likely to be useful for manipulating the dynamics of ultracold quantum molecular gases.
  • A selective excitation technique based on light interference is proposed to control quantum systems by frequency-chirped laser fields. Interference of two identical, delayed and phase-shifted pulses is used to modulate the laser spectrum and project it onto the time domain. By adjusting the delay and phase shift, selected transitions can be brought into the 'holes' of the spectrum and thus remain nonexcited. The possibility to selectively manipulate or even 'shut down' resonant transitions, making the medium transparent to the field, is shown for the Rb atom.
  • We present a scheme of population transfer between two metastable (ground) states of the {lambda} atom without considerable excitation of the atom using single frequency-chirped laser pulses. The physics of the process is generation of the 'trapped' superposition of the ground states by the laser pulse at sufficiently high laser peak intensity. The main conditions for realization of this regime are the following: The width of the transform-limited laser pulse envelope frequency spectrum (without chirp) must be smaller and the peak Rabi frequency of the pulse must be larger than the frequency interval between the two ground states of themore » {lambda} atom. During the frequency chirp, the laser pulse must first come into resonance with the transition from the initially occupied ground state to the excited state and after that with the transition between the excited and second initially empty ground states. In the case when the envelope frequency spectrum width (without chirp) of the pulse exceeds the frequency interval between the two ground states, we show a possibility of controllable generation of superposition of the ground states with a controllable excitation of the {lambda} atom.« less