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.

/pdf/optical-trapping-and-manipulation-of-neutral-particles-using-4qf0uymz6l.pdf

Optical trapping and manipulation of neutral particles using lasers

The development of wave optics for light brought many new insights into our understanding of physics, driven by fundamental experiments like the ones by Young, Fizeau, Michelson-Morley and others. Quantum mechanics, and especially the de Broglie’s postulate relating the momentum p of a particle to the wave vector k of an matter wave: k = 2 λ = p/ℏ, suggested that wave optical experiments should be also possible with massive particles (see table 1), and over the last 40 years electron and neutron interferometers have demonstrated many fundamental aspects of quantum mechanics [1].

/pdf/optics-and-interferometry-with-atoms-and-molecules-1vnuwajb51.pdf

Optics and interferometry with atoms and molecules

Quantum phase engineering is demonstrated with two techniques that allow the spatial phase distribution of a Bose-Einstein condensate (BEC) to be written and read out. A quantum state was designed and produced by optically imprinting a phase pattern onto a BEC of sodium atoms, and matter-wave interferometry with spatially resolved imaging was used to analyze the resultant phase distribution. An appropriate phase imprint created solitons, the first experimental realization of this nonlinear phenomenon in a BEC. The subsequent evolution of these excitations was investigated both experimentally and theoretically.

https://science.sciencemag.org/content/sci/287/5450/97.full.pdf

Generating solitons by phase engineering of a bose-einstein condensate

In the developing frog visual system, topographic refinement of the retinotectal projection depends on electrical activity. In vivo whole-cell recording from developing Xenopus tectal neurons shows that convergent retinotectal synapses undergo activity-dependent cooperation and competition following correlated pre- and postsynaptic spiking within a narrow time window. Synaptic inputs activated repetitively within 20 ms before spiking of the tectal neuron become potentiated, whereas subthreshold inputs activated within 20 ms after spiking become depressed. Thus both the initial synaptic strength and the temporal order of activation are critical for heterosynaptic interactions among convergent synaptic inputs during activity-dependent refinement of developing neural networks.

A critical window for cooperation and competition among developing retinotectal synapses

Reviews the history of optical trapping and manipulation of small-neutral particles, from the time of its origin in 1970 up to the present. As we shall see, the unique characteristics of this technique are having a major impact on the many subfields of physics, chemistry, and biology where small particles play a role.

History of optical trapping and manipulation of small-neutral particle, atoms, and molecules

We report the first observation of Bragg scattering of sodium atoms from a standing light wave. We also present a theory which quantitatively predicts the amplitude of the various Bragg orders as a function of the light's detuning and power, and the interaction time. The analog of the Pendello$uml---sung effect, previously observed in Bragg scattering of neutrons from crystals, is predicted and qualitatively observed for first-order Bragg scattering of atoms from a standing light wave.

Bragg scattering of atoms from a standing light wave.

The diffraction of sodium atoms from a standing wave of near-resonant light is studied as a function of the atomic velocity component along the k vector of the wave. A simple theory is presented which quantitatively predicts the observed diffraction patterns and the decrease of the rms momentum transfer to the atoms with increasing velocity. This decrease results from the dephasing between the two counterpropagating traveling waves due to the first-order Doppler shift. In addition, these measurements have resolved the previous discrepancy between theory and experiment concerning the overall momentum transferred by a standing wave.

Diffraction of atoms moving through a standing light wave

This paper presents experiments concerning momentum transfer to atoms by a standing light wave in the absence of spontaneous decay. This momentum transfer, which occurs in discrete units of 2 ħ k along the k-vector of the standing light wave, can be viewed as absorption/stimulated emission of photon pairs from the counterpropagating traveling waves which make up the standing light wave. In a dual sense, this phenomenon can also be viewed as diffraction of an atomic de Broglie wave from the periodic intensity grating of the standing light wave. In addition, we address how the inherent Heisenberg uncertainty between the focussed waist of the standing light wave and the angular spread of the k-vectors of photons traveling through this waist affects momentum transfer to the atoms by the light. For large widths of the standing light wave, the reduction of the uncertainty in the direction of the photons results in resonances for the momentum transfer only for discrete values of atomic momentum along the k-vector of the standing light wave which satisfy the Bragg condition. We present experimental data which display the Pendellosung effect for Bragg scattering of atomic de Broglie waves from a standing light wave. Finally, we discuss the possibility of exploiting these phenomena to build an atomic interferometer, one that interferes atomic de Broglie waves.

Andrew H. Miklich

Papers

Bragg scattering of atoms from a standing light wave.

Diffraction of atoms moving through a standing light wave

Diffraction of atoms from a standing light wave