Optical lattice 3800688 215134728 2008-05-26T21:29:48Z Barticus88 1396480 [[Conductor]]→[[Electrical conductor]] in the holy name of [[WP:DPL|WikiProject Disambiguation]] using [[WP:POP|Popups]] [[Image:OptLat.jpg|right|Simulation of an optical lattice potential]]An '''optical lattice''' is formed by the [[interference]] of counterpropagating [[laser]] beams, which creates a periodic (in space) [[intensity (physics)|intensity]] pattern. The resulting periodic [[Scalar potential|potential]] can then be used to trap neutral [[atom]]s via the [[Stark shift]]. Atoms are cooled and congregated in the potential minima. The resulting system of trapped atoms resembles a [[crystal]] in the sense that the atoms are in a periodical potential. <ref>[http://physicsworld.com/cws/article/print/19273 Quantum gases in optical lattices]</ref> Because of [[quantum tunneling]], atoms can move in the optical lattice even if the well depth of the lattice is higher than the energy of the atoms, which is similar to the electrons in a [[Electrical conductor|conductor]]. However, there will be a [[superfluid-Mott insulator transition]]<ref> M. Greiner, O. Mandel, T. Esslinger, T. W. Hansch, and I. Bloch, "Quantum phase transition from a superfluid to a Mott insulator in a gas of ultracold atoms," Nature 415, 39-44 (2002). </ref> if the interaction energy between the atoms becomes larger than the hopping energy when the well depth is very large. In the [[Mott insulator]] phase, atoms will be trapped in the potential minima and can not move freely, which is similar to the electrons in an insulator. Atoms in an optical lattice provide an ideal quantum system where all parameters can be controlled. Thus they can be used to study effects that are difficult to observe in real crystals. They are also promising candidates for [[quantum information]] processing.<ref> G. K. Brennen, C. M. Caves, P. S. Jessen, and I. H. Deutsch, "Quantum logic gates in optical lattices," Phys. Rev. Lett. 82, 1060-1063 (1999). </ref> There are two important parameters of an optical lattice: the [[well depth]] and the [[periodicity]]. The well depth of the optical lattice can be tuned in [[real time]] by changing the power of the laser, which is normally controlled by an AOM ([[acousto-optic modulator]]). The [[periodicity]] of the optical lattice can be tuned by changing the [[wavelength]] of the laser or by changing the relative angle between the two laser beams. The real-time control of the periodicity of the lattice is still a challenging task. Because the wavelength of the laser can not be varied over a large range in real time, the periodicity of the lattice is normally controlled by the relative angle between the laser beams.<ref>L. Fallani, C. Fort, J. E. Lye, and M. Inguscio, "Bose-Einstein condensate in an optical lattice with tunable spacing: transport and static properties," Opt. Express 13, 4303-4313 (2005) </ref> However, it is difficult to keep the lattice stable while changing the relative angles, since the interference is sensitive to the relative [[phase]] between the laser beams. Recently, a novel method of real-time control of the lattice periodicity was demonstrated<ref>T. C. Li, H. Kelkar, D. Medellin, and M. G. Raizen, "Real-time control of the periodicity of a standing wave: an optical accordion," Opt. Express, 16, 5465-5470 (2008). </ref>, in which the center fringe moved less than 2.7 microns while the lattice periodicity was changed from 0.96 microns to 11.2 microns. Whether this method can keep atoms (or other particles) trapped while changing the lattice periodicity remains to be tested experimentally. Such [[accordion]] lattices are useful for controlling untracold atoms in optical lattices, where small spacing is essential for quantum tunneling, and large spacing enables single-site [[manipulation]] and spatially resolved [[detection]]. Besides of trapping cold atoms, optical lattices have been widely used in creating [[grating]]s and [[photonic crystal]]s. They are also useful for sorting microscopic particles<ref>M. P. MacDonald, G. C. Spalding, and K. Dholakia, "Microfluidic sorting in an optical lattice," Nature 426, 421-424 (2003). </ref>, and may be useful for assembling [[cell array]]s. ==References== <references/> == External links == * [http://cold-atoms.physics.lsa.umich.edu/projects/lattice/latticeindex.html More about optical lattices] * [http://www.optical-lattice.com Introduction to optical lattices] {{Quantum computing}} {{optics-stub}} {{atomic-physics-stub}} {{quantum-stub}} [[Category:Quantum optics]] [[Category:Atomic physics]] [[de:Optisches Gitter (Atomphysik)]]