In order to confine any object, it is necessary to exchange kinetic for potential energy in the trapping field, and in neutral atom traps, the potential energy must be stored as internal atomic energy. Thus practical traps for ground-state neutral atoms are necessarily very shallow compared with thermal energy because the energy level shifts that result from conveniently sized fields are typically considerably smaller than k B T , even for T = 1 K. Neutral atom trapping therefore depends on substantial cooling of a thermal atomic sample, and is often connected with the cooling process. In most practical cases, atoms are loaded from magneto-optical traps, where they have been efficiently accumulated and cooled to mK temperatures (see Sec. 20.3), or from optical molasses, where they have been optically cooled to μK temperatures (see Sec. 19.4). The small depth of typical neutral atom traps dictates stringent vacuum requirements, because an atom cannot remain trapped after a collision with a thermal energy background gas molecule. Since these atoms are vulnerable targets for thermal energy background gas, the mean free time between collisions must exceed the desired trapping time. The cross-section for destructive collisions is quite large because even a gentle collision (i.e. large impact parameter) can impart enough energy to eject an atom from a trap. At pressure P sufficiently low to be of practical interest, the trapping time is ~(10 -8 / P ) s, where P is in torr. This chapter begins with a discussion of ordinary, single-center traps, but also considers arrays of traps. Such “optical lattices” are playing an increasingly important role in research in atomic physics, so discussion of their properties is an appropriate part of the education of a student of the subject. Dipole force optical traps Single-beam optical traps for two-level atoms The simplest imaginable optical trap consists of a single, strongly focused Gaussian laser beam (see Fig. 20.1) [214, 215] whose intensity at the focus varies transversely with r as where is the beam waist size. Such a trap has a well-studied and important macroscopic classical analog in a phenomenon called optical tweezers (see App. 1.C) [216–218].In order to confine any object, it is necessary to exchange kinetic for potential energy in the trapping field, and in neutral atom traps, the potential energy must be stored as internal atomic energy. Thus practical traps for ground-state neutral atoms are necessarily very shallow compared with thermal energy because the energy level shifts that result from conveniently sized fields are typically considerably smaller than k B T , even for T = 1 K. Neutral atom trapping therefore depends on substantial cooling of a thermal atomic sample, and is often connected with the cooling process. In most practical cases, atoms are loaded from magneto-optical traps, where they have been efficiently accumulated and cooled to mK temperatures (see Sec. 20.3), or from optical molasses, where they have been optically cooled to μK temperatures (see Sec. 19.4). The small depth of typical neutral atom traps dictates stringent vacuum requirements, because an atom cannot remain trapped after a collision with a thermal energy background gas molecule. Since these atoms are vulnerable targets for thermal energy background gas, the mean free time between collisions must exceed the desired trapping time. The cross-section for destructive collisions is quite large because even a gentle collision (i.e. large impact parameter) can impart enough energy to eject an atom from a trap. At pressure P sufficiently low to be of practical interest, the trapping time is ~(10 -8 / P ) s, where P is in torr. This chapter begins with a discussion of ordinary, single-center traps, but also considers arrays of traps. Such “optical lattices” are playing an increasingly important role in research in atomic physics, so discussion of their properties is an appropriate part of the education of a student of the subject. Dipole force optical traps Single-beam optical traps for two-level atoms The simplest imaginable optical trap consists of a single, strongly focused Gaussian laser beam (see Fig. 20.1) [214, 215] whose intensity at the focus varies transversely with r as where is the beam waist size. Such a trap has a well-studied and important macroscopic classical analog in a phenomenon called optical tweezers (see App. 1.C) [216–218].

Cambridge University Press eBooksDec 31, 20150 citations

Optical Dipole Traps for Neutral Atoms

Rudolf Grimm, Matthias Weidemüller, Yuri B. Ovchinnikov

Advances in atomic, molecular, and optical physicsJan 1, 20001,549 citations

Dissipative pure-optical trap for laser cooling and trapping of neutral atoms

Прудников Олег Николаевич, R. Ya. Ilenkov, A. V. Taichenachev +2 more

We show the possibility of implementing a deep dissipative optical lattice for neutral atoms with a macroscopic period. The depth of the lattice can reach magnitudes comparable to the depth of the magneto-optical traps (MOT), while the presence of dissipative friction forces allows for trapping and cooling of atoms. The area of localization of trapped atoms reaches sub-millimeter size, and the number of atoms is comparable to the number trapped in MOT. As an example, we study lithium atoms for which the macroscopic period of the lattice $Λ=1.5$ cm. Such deep optical lattices with a macroscopic period open up possibility for developing effective methods for cooling and trapping neutral atoms without use of magnetic field as an alternative to MOT. This is important for developing compact systems based on cold atoms.We show the possibility of implementing a deep dissipative optical lattice for neutral atoms with a macroscopic period. The depth of the lattice can reach magnitudes comparable to the depth of the magneto-optical traps (MOT), while the presence of dissipative friction forces allows for trapping and cooling of atoms. The area of localization of trapped atoms reaches sub-millimeter size, and the number of atoms is comparable to the number trapped in MOT. As an example, we study lithium atoms for which the macroscopic period of the lattice $Λ=1.5$ cm. Such deep optical lattices with a macroscopic period open up possibility for developing effective methods for cooling and trapping neutral atoms without use of magnetic field as an alternative to MOT. This is important for developing compact systems based on cold atoms.

arXiv:2306.13294Jun 23, 20230 citations

Laser Beam Focus Forms Optical Trap for Neutral Atoms

Bertram M. Schwarzschild

The first color photographs ever to grace the pages of Physical Review Letters show us the fluorescent glow from some 500 sodium atoms caught in the first successfully demonstrated optical trap for neutral atoms. The 21 July Letter by Steven Chu, John Bjorkholm, Arthur Ashkin and Alex Cable at Bell Labs, reports that this tiny “optical dipole” trap, formed at the focus of a single laser beam, was able to hold onto an ultracold, high-density accumulation of atoms for several seconds and manipulate them in space. In recent days the group has been able to hold a much larger collection of sodium atoms for a fraction of a minute with a newer optical-trap design.The first color photographs ever to grace the pages of Physical Review Letters show us the fluorescent glow from some 500 sodium atoms caught in the first successfully demonstrated optical trap for neutral atoms. The 21 July Letter by Steven Chu, John Bjorkholm, Arthur Ashkin and Alex Cable at Bell Labs, reports that this tiny “optical dipole” trap, formed at the focus of a single laser beam, was able to hold onto an ultracold, high-density accumulation of atoms for several seconds and manipulate them in space. In recent days the group has been able to hold a much larger collection of sodium atoms for a fraction of a minute with a newer optical-trap design.

Physics TodaySep 1, 19862 citations

Λ=1.5

cm. Such deep optical lattices with a macroscopic period open up possibility for developing effective methods for cooling and trapping neutral atoms without use of magnetic field as an alternative to MOT. This is important for developing compact systems based on cold atoms.