A Bose-Einstein condensate was produced in a vapor of rubidium-87 atoms that was confined by magnetic fields and evaporatively cooled. The condensate fraction first appeared near a temperature of 170 nanokelvin and a number density of 2.5 x 10 12 per cubic centimeter and could be preserved for more than 15 seconds. Three primary signatures of Bose-Einstein condensation were seen. (i) On top of a broad thermal velocity distribution, a narrow peak appeared that was centered at zero velocity. (ii) The fraction of the atoms that were in this low-velocity peak increased abruptly as the sample temperature was lowered. (iii) The peak exhibited a nonthermal, anisotropic velocity distribution expected of the minimum-energy quantum state of the magnetic trap in contrast to the isotropic, thermal velocity distribution observed in the broad uncondensed fraction.

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Observation of Bose-Einstein Condensation in a Dilute Atomic Vapor

1. Introduction 2. Theoretical foundations 3. Propagation and focusing of optical fields 4. Spatial resolution and position accuracy 5. Nanoscale optical microscopy 6. Near-field optical probes 7. Probe-sample distance control 8. Light emission and optical interaction in nanoscale environments 9. Quantum emitters 10. Dipole emission near planar interfaces 11. Photonic crystals and resonators 12. Surface plasmons 13. Forces in confined fields 14. Fluctuation-induced phenomena 15. Theoretical methods in nano-optics Appendices Index.

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Principles of nano-optics

Optical trapping and manipulation of viruses and bacteria by laser radiation pressure were demonstrated with single-beam gradient traps. Individual tobacco mosaic viruses and dense oriented arrays of viruses were trapped in aqueous solution with no apparent damage using approximately 120 milliwatts of argon laser power. Trapping and manipulation of single live motile bacteria and Escherichia coli bacteria were also demonstrated in a high-resolution microscope at powers of a few milliwatts.

https://science.sciencemag.org/content/sci/235/4795/1517.full.pdf

Optical Trapping and Manipulation of Viruses and Bacteria

Forces of a single-beam gradient laser trap on a dielectric sphere in the ray optics regime.

The techniques of optical trapping and manipulation of neutral particles by lasers provide unique means to control the dynamics of small particles. These new experimental methods have played a revolutionary role in areas of the physical and biological sciences. This paper reviews the early developments in the field leading to the demonstration of cooling and trapping of neutral atoms in atomic physics and to the first use of optical tweezers traps in biology. Some further major achievements of these rapidly developing methods also are considered.

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Optical trapping and manipulation of neutral particles using lasers

We report the confinement and cooling of an optically dense cloud of neutral sodium atoms by radiation pressure. The trapping and damping forces were provided by three retroreflected laser beams propagating along orthogonal axes, with a weak magnetic field used to distinguish between the beams. We have trapped as many as ${10}^{7}$ atoms for 2 min at densities exceeding ${10}^{11}$ atoms ${\mathrm{cm}}^{\ensuremath{-}3}$. The trap was \ensuremath{\simeq}0.4 K deep and the atoms, once trapped, were cooled to less than a millikelvin and compacted into a region less than 0.5 mm in diameter.

Trapping of neutral sodium atoms with radiation pressure

We report the first observation of optically trapped atoms Sodium atoms cooled below ${10}^{\ensuremath{-}3}$ K in "optical molasses" are captured by a dipole-force optical trap created by a single, strongly focused, Gaussian laser beam tuned several hundred gigahertz below the ${D}_{1}$ resonance transition We estimate that about 500 atoms are confined in a volume of about ${10}^{3}$ \ensuremath{\mu}${\mathrm{m}}^{3}$ at a density of ${10}^{11}$-${10}^{12}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ Trap lifetimes are limited by background pressure to several seconds The observed trapping behavior is in good quantitative agreement with theoretical expectations

https://link.aps.org/pdf/10.1103/PhysRevLett.57.314

Experimental observation of optically trapped atoms.

The scattering force due to resonance radiation pressure was first detected by Frisch in 1933.[1] Later, Ashkin[2] pointed out that laser light can exert a substantial force suitable for the optical manipulation of atoms, and numerous proposals to cool and trap neutral atoms with laser light.[3] Atoms in an atomic beam have been stopped by light,[4] in which the final velocity spread corresponds to a temperature of 50−100 mK. We report here the confinement and cooling of atoms with laser light, in which the atoms are localized in a 0.2 cm volume for a time in excess of 0.1 second and cooled to a temperature of T = 2.4 × 10−4K.[5]

https://link.aps.org/pdf/10.1103/PhysRevLett.55.48

Three-dimensional viscous confinement and cooling of atoms by resonance radiation pressure

We have observed that two-body collisions between cold sodium atoms confined within a magnetic-molasses optical trap lead to significant atomic-density-dependent trap losses. Such losses set an upper limit to the product of atomic density and confinement time that can be achieved in such a trap.

Atomic-density-dependent losses in an optical trap

We describe observations of atoms trapped in magnetic molasses made by using a simplified apparatus that is loaded by a continuous uncooled source of atoms. We also measured the cross section for collisions in which trapped sodium atoms are ejected from the trap by thermal sodium atoms and estimate that the cross section is 30 times larger than for collisions with other background thermal atoms.

Alex E. Cable

Papers

Trapping of neutral sodium atoms with radiation pressure

Experimental observation of optically trapped atoms.

Three-dimensional viscous confinement and cooling of atoms by resonance radiation pressure

Atomic-density-dependent losses in an optical trap

Observations of sodium atoms in a magnetic molasses trap loaded by a continuous uncooled source.