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Bulletin of the American Physical Society

Coherent momentum transfer in helium by adiabatic passage

John Lawall, Mara Goff Prentiss

Published May 1, 1993• 0 citations
OpenAlex

Abstract

We have demonstrated a coherent beam splitter for metastable helium based on adiabatic passage. Light from a homemade LNA laser at 1.083 {mu} is used to excite the {sup 3}S{sub 1}-{sup 3}P{sub 0} transition in a highly collimated beam of metastable helium. The atoms are first optically pumped into the m=0 and m=-1 sublevels. These sublevels are two independent {open_quotes}dark{close_quotes} states from which no further absorption is possible. Population is transferred adiabatically from the m = -1 level to the m =+1 level by means of two partially overlapping laser beams. As well as absorbing 2{h_bar} of angular momentum from the radiation field, the atoms initially in the m = -1 sublevel acquire 2{h_bar}k of linear momentum via an absorption/stimulated emission process. The process can be repeated back to m = -1, and we have demonstrated 4{h_bar}k and 6{h_bar}k coherent momentum transfer using successive interactions regions. The population initially in the m = 0 sublevel is undeflected by the light.

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We have demonstrated a novel beam splitter for atoms. The J=1 to J=0 system in metastable helium has two independent ``dark'' states which are radiatively stable. By preparing atoms in the two ``dark'' states of the ${2}^{3}$${\mathit{S}}_{1}$ level and passing them through a sequence of partially overlapping laser beams tuned to the ${2}^{3}$${\mathit{S}}_{1\mathrm{\ensuremath{-}}}$${2}^{2}$${\mathit{P}}_{0}$ transition, we cause the atoms in one ``dark'' state to be deflected by integral multiples of 2\ensuremath{\Elzxh}k, while the atoms in the other ``dark'' state are undeflected. The excited ${2}^{3}$${\mathit{P}}_{0}$ state is not populated, so the process is unaffected by spontaneous emission. We have observed up to 90% coherent momentum transfer with 4\ensuremath{\Elzxh}k deflection. We conclude by describing how one might construct an atom interferometer based on these ``dark state'' beam splitters.

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Optical Forces from Periodic Adiabatic Rapid Passage Sequences on Metastable Helium Atoms

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Over the past 30 years, optical manipulation of neutral atoms has been primarily performed with a monochromatic laser beam. The simplest tool for the control of atomic motion is the radiative force exerted by a monochromatic laser on a twolevel atom. The radiative force arises from absorption followed by spontaneous emission, and its magnitude is limited by the atom's excited state lifetime. The coherent momentum exchanges between light elds and atoms can be exploited to produce long-range optical forces much greater than the radiative force through the use of absorption-stimulated emission processes. Adiabatic Rapid Passage (ARP) is a long-existing method to invert the population of a two-level nuclear spin system. Its extension to the optical domain necessitates a frequency chirped light pulse to interact with a two-level atom via the dipole interaction. I will first present a numerical study of the properties of optical forces on moving atoms derived from purely stimulated processes produced by multiple ARP sequences. This will be followed by experimental observations of long-range ARP forces much larger than the radiative force in metastable helium. Sequences of properly timed laser pulses may be used for rapid deceleration of neutral atomic (or molecular) beams. | 171 pages

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Stimulated hyper-Raman adiabatic passage. III. Experiment

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We report the experimental realization of coherent population transfer from the $2{}^{3}S$ state to $2{}^{3}P$ fine-structure levels of helium, using the technique of hyper-Raman adiabatic passage, in which the pump-laser coupling involves a two-photon transition. We discuss the dependence of population transfer upon pump and Stokes detunings, and show that by suitably setting the detunings one can transfer population efficiently as either a two-step process to final states or as a single-step two-photon transition to an intermediate state. We use an adiabatic-state picture to interpret these experimental results. Since the optimum detuning depends on the pump laser intensity the transfer efficiency is compromised by the variation of the intensity across the spatial profile of the laser beam. Our experimental data agree well with numerical simulation based on density-matrix equations, including all 15 magnetic sublevels.

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Coherent population transfer in multilevel systems with magnetic sublevels. III. Experimental results

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The technique of stimulated Raman adiabatic passage (STIRAP) has become an established procedure for producing complete population inversion in atoms or molecules via application of Stokes and pump pulses in a counterintuitive sequence. Previously we reported on numerical and analytical investigations showing some of the additional and important phenomena that arise when some of the levels involved have nonzero angular momentum, the field polarization directions have no simplifying symmetries, and Zeeman splitting lifts the magnetic sublevel degeneracy. Here we verify our theoretical findings using the metastable neon system: $^{3}$${\mathit{P}}_{0}$${\mathrm{?}}^{3}$${\mathit{P}}_{1}$${\mathrm{?}}^{3}$${\mathit{P}}_{2}$ with the corresponding angular momentum sequence J=0?J=1?J=2. In particular, we demonstrate that it is possible to transfer all population from the single initial state to any single selectable final magnetic sublevel M. Selectivity can be achieved either by choosing special laser polarization angles or, for fixed polarizations, by tuning the two lasers into two-photon resonance between the initial and desired final state. The complete control of magnetic sublevel population enabled by this procedure extends the customary experimental methods for producing oriented or aligned beams of atoms. In addition, we demonstrate very clearly the previous prediction that population transfer may fail for certain sets of parameters (detunings, Rabi frequencies, and polarization angles). \textcopyright{} 1996 The American Physical Society.

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We investigate the coherent population transfer and associated effects for a three level atomic system, with the third level being a Rydberg state. The scheme adopted here is the stimulated Raman adiabatic passage (STIRAP). An atomic beam of metastable helium is orthogonally crossing two laser beams in a tunable dc electric field. The ir laser of 790 - 830 nm connects the triplet 3P state to the Rydberg states (n = 12 - 50) and the uv laser of 389 nm connects the metastable triplet 2S state to the triplet 3P state. A third laser of 1083 nm driving 2S-2P transition is applied downstream, providing a strong bichromatic force on the atoms remaining in the 2S state to deflect them, establishing the absolute count of Rydberg atoms. Rydberg atoms can be ionized by background thermal radiations at room temperature and it is observed in this experiment. This fact actually enables precise measurement, especially spectroscopy, of Rydberg atoms by simply looking at the ions, which are easy to detect. It is also confirmed that background thermal radiation could significantly redistribute the population between neighboring Rydberg states. The 2S, 3P and the final Rydberg states all have magnetic sub-levels, hence the linkage pattern of the excitation has non-trivial crossings, if the polarizations of the two lasers are not parallel to each other. Those phase differences in different excitation paths induced by the laser polarizations can lead to interference which would determine the excitation probability and the polarization of the excited atom. Theoretical calculations predict interesting interference patterns as a function of laser polarizations and Rabi frequencies. Those interference structures have been experimentally observed. Transverse velocity distribution in the atomic beam turns out to be a limiting factor in the efficiency of production of Rydberg atoms. The transverse velocity of an atom can not only induce one-photon detuning but also two-photon detuning, which could effectively reduce the STIRAP process efficiency. By adding a laser to make Doppler molasses in the transverse direction, we can heat or cool the atomic beam transversely and verify this effect. | 190 pages

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P. Marte, P. Zoller, J. L. Hall

We study atomic-beam deflection by adiabatic passage between Zeeman ground levels via Raman transitions induced by counterpropagating ${\mathrm{\ensuremath{\sigma}}}^{\ifmmode\pm\else\textpm\fi{}}$-polarized lasers. We show that complete population transfer between the ground states can be achieved, which corresponds to the scattering of the atomic wave packet into a single final momentum state by absorption and induced emission of laser photons. Although the lasers can be resonant, the excited state(s) are never populated during the adiabatic transfer, which suppresses the effects of spontaneous emission and preserves the coherence of the atomic wave function. This scheme has attractive features as a beam splitter and mirror for atomic interferometry.

Physical Review A•Oct 1, 1991•254 citations
We have demonstrated a coherent beam splitter for metastable helium based on adiabatic passage. Light from a homemade LNA laser at 1.083 {mu} is used to excite the {sup 3}S{sub 1}-{sup 3}P{sub 0} transition in a highly collimated beam of metastable helium. The atoms are first optically pumped into the m=0 and m=-1 sublevels. These sublevels are two independent {open_quotes}dark{close_quotes} states from which no further absorption is possible. Population is transferred adiabatically from the m = -1 level to the m =+1 level by means of two partially overlapping laser beams. As well as absorbing 2{h_bar} of angular momentum from the radiation field, the atoms initially in the m = -1 sublevel acquire 2{h_bar}k of linear momentum via an absorption/stimulated emission process. The process can be repeated back to m = -1, and we have demonstrated 4{h_bar}k and 6{h_bar}k coherent momentum transfer using successive interactions regions. The population initially in the m = 0 sublevel is undeflected by the light.
We have demonstrated a novel beam splitter for atoms. The J=1 to J=0 system in metastable helium has two independent ``dark'' states which are radiatively stable. By preparing atoms in the two ``dark'' states of the 23{2}^{3}23S1{\mathit{S}}_{1}S1​ level and passing them through a sequence of partially overlapping laser beams tuned to the 23{2}^{3}23${\mathit{S}}_{1\mathrm{\ensuremath{-}}}$22{2}^{2}22P0{\mathit{P}}_{0}P0​ transition, we cause the atoms in one ``dark'' state to be deflected by integral multiples of 2\ensuremath{\Elzxh}k, while the atoms in the other ``dark'' state are undeflected. The excited 23{2}^{3}23P0{\mathit{P}}_{0}P0​ state is not populated, so the process is unaffected by spontaneous emission. We have observed up to 90% coherent momentum transfer with 4\ensuremath{\Elzxh}k deflection. We conclude by describing how one might construct an atom interferometer based on these ``dark state'' beam splitters.
Over the past 30 years, optical manipulation of neutral atoms has been primarily performed with a monochromatic laser beam. The simplest tool for the control of atomic motion is the radiative force exerted by a monochromatic laser on a twolevel atom. The radiative force arises from absorption followed by spontaneous emission, and its magnitude is limited by the atom's excited state lifetime. The coherent momentum exchanges between light elds and atoms can be exploited to produce long-range optical forces much greater than the radiative force through the use of absorption-stimulated emission processes. Adiabatic Rapid Passage (ARP) is a long-existing method to invert the population of a two-level nuclear spin system. Its extension to the optical domain necessitates a frequency chirped light pulse to interact with a two-level atom via the dipole interaction. I will first present a numerical study of the properties of optical forces on moving atoms derived from purely stimulated processes produced by multiple ARP sequences. This will be followed by experimental observations of long-range ARP forces much larger than the radiative force in metastable helium. Sequences of properly timed laser pulses may be used for rapid deceleration of neutral atomic (or molecular) beams. | 171 pages
We report the experimental realization of coherent population transfer from the 23S2{}^{3}S23S state to 23P2{}^{3}P23P fine-structure levels of helium, using the technique of hyper-Raman adiabatic passage, in which the pump-laser coupling involves a two-photon transition. We discuss the dependence of population transfer upon pump and Stokes detunings, and show that by suitably setting the detunings one can transfer population efficiently as either a two-step process to final states or as a single-step two-photon transition to an intermediate state. We use an adiabatic-state picture to interpret these experimental results. Since the optimum detuning depends on the pump laser intensity the transfer efficiency is compromised by the variation of the intensity across the spatial profile of the laser beam. Our experimental data agree well with numerical simulation based on density-matrix equations, including all 15 magnetic sublevels.
The technique of stimulated Raman adiabatic passage (STIRAP) has become an established procedure for producing complete population inversion in atoms or molecules via application of Stokes and pump pulses in a counterintuitive sequence. Previously we reported on numerical and analytical investigations showing some of the additional and important phenomena that arise when some of the levels involved have nonzero angular momentum, the field polarization directions have no simplifying symmetries, and Zeeman splitting lifts the magnetic sublevel degeneracy. Here we verify our theoretical findings using the metastable neon system: 3^{3}3P0{\mathit{P}}_{0}P0​?3{\mathrm{?}}^{3}?3P1{\mathit{P}}_{1}P1​?3{\mathrm{?}}^{3}?3P2{\mathit{P}}_{2}P2​ with the corresponding angular momentum sequence J=0?J=1?J=2. In particular, we demonstrate that it is possible to transfer all population from the single initial state to any single selectable final magnetic sublevel M. Selectivity can be achieved either by choosing special laser polarization angles or, for fixed polarizations, by tuning the two lasers into two-photon resonance between the initial and desired final state. The complete control of magnetic sublevel population enabled by this procedure extends the customary experimental methods for producing oriented or aligned beams of atoms. In addition, we demonstrate very clearly the previous prediction that population transfer may fail for certain sets of parameters (detunings, Rabi frequencies, and polarization angles). \textcopyright{} 1996 The American Physical Society.
We investigate the coherent population transfer and associated effects for a three level atomic system, with the third level being a Rydberg state. The scheme adopted here is the stimulated Raman adiabatic passage (STIRAP). An atomic beam of metastable helium is orthogonally crossing two laser beams in a tunable dc electric field. The ir laser of 790 - 830 nm connects the triplet 3P state to the Rydberg states (n = 12 - 50) and the uv laser of 389 nm connects the metastable triplet 2S state to the triplet 3P state. A third laser of 1083 nm driving 2S-2P transition is applied downstream, providing a strong bichromatic force on the atoms remaining in the 2S state to deflect them, establishing the absolute count of Rydberg atoms. Rydberg atoms can be ionized by background thermal radiations at room temperature and it is observed in this experiment. This fact actually enables precise measurement, especially spectroscopy, of Rydberg atoms by simply looking at the ions, which are easy to detect. It is also confirmed that background thermal radiation could significantly redistribute the population between neighboring Rydberg states. The 2S, 3P and the final Rydberg states all have magnetic sub-levels, hence the linkage pattern of the excitation has non-trivial crossings, if the polarizations of the two lasers are not parallel to each other. Those phase differences in different excitation paths induced by the laser polarizations can lead to interference which would determine the excitation probability and the polarization of the excited atom. Theoretical calculations predict interesting interference patterns as a function of laser polarizations and Rabi frequencies. Those interference structures have been experimentally observed. Transverse velocity distribution in the atomic beam turns out to be a limiting factor in the efficiency of production of Rydberg atoms. The transverse velocity of an atom can not only induce one-photon detuning but also two-photon detuning, which could effectively reduce the STIRAP process efficiency. By adding a laser to make Doppler molasses in the transverse direction, we can heat or cool the atomic beam transversely and verify this effect. | 190 pages
We study atomic-beam deflection by adiabatic passage between Zeeman ground levels via Raman transitions induced by counterpropagating ${\mathrm{\ensuremath{\sigma}}}^{\ifmmode\pm\else\textpm\fi{}}$-polarized lasers. We show that complete population transfer between the ground states can be achieved, which corresponds to the scattering of the atomic wave packet into a single final momentum state by absorption and induced emission of laser photons. Although the lasers can be resonant, the excited state(s) are never populated during the adiabatic transfer, which suppresses the effects of spontaneous emission and preserves the coherence of the atomic wave function. This scheme has attractive features as a beam splitter and mirror for atomic interferometry.