Жарық сәулелерімен атомдық құрылымның қалыптасуы

Atomic scale structure formed through the Stark shift by opposing beams of light

An optical lattice is formed by the interference of counter propagating laser beams, creating a spatially periodic polarization pattern. The resulting periodic potential may trap neutral atoms via the Stark shift. Atoms are cooled and congregate at the potential extrema (at maxima for blue detuned lattices, and minima for red detuned lattices). The resulting arrangement of trapped atoms resembles a crystal lattice and can be used for quantum simulation. Atoms trapped in the optical lattice may move due to quantum tunneling, even if the potential well depth of the lattice points exceeds the kinetic energy of the atoms, which is similar to the electrons in a conductor. However, a superfluid–Mott insulator transition may occur, 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 cannot move freely, which is similar to the electrons in an insulator. In the case of fermionic atoms, if the well depth is further increased the atoms are predicted to form an antiferromagnetic, i. e. Néel state at sufficiently low temperatures.

Trapping atoms in standing waves of light was first proposed by V. S. Letokhov in 1968.

There are two important parameters of an optical lattice: the potential well depth and the periodicity.

The potential experienced by the atoms is related to the intensity of the laser used to generate the optical lattice. The potential depth of the optical lattice can be tuned in real time by changing the power of the laser, which is normally controlled by an acousto optic modulator (AOM). The AOM is tuned to deflect a variable amount of the laser power into the optical lattice. Active power stabilization of the lattice laser can be accomplished by feedback of a photodiode signal to the AOM.

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. The wavelength of the laser cannot easily be varied over a large range in real time, and so the periodicity of the lattice is normally controlled by the relative angle between the laser beams. 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. Titanium sapphire lasers, with their large tunable range, provide a possible platform for direct tuning of wavelength in optical lattice systems. Continuous control of the periodicity of a one dimensional optical lattice while maintaining trapped atoms in situ was first demonstrated in 2005 using a single axis servo controlled galvanometer. This "accordion lattice" was able to vary the lattice periodicity from 1.30 to 9.3 μm. More recently, a different method of real time control of the lattice periodicity was demonstrated, in which the center fringe moved less than 2.7 μm while the lattice periodicity was changed from 0.96 to 11.2 μm. Keeping atoms (or other particles) trapped while changing the lattice periodicity remains to be tested more thoroughly experimentally. Such accordion lattices are useful for controlling ultracold atoms in optical lattices, where small spacing is essential for quantum tunneling, and large spacing enables single site manipulation and spatially resolved detection. Site resolved detection of the occupancy of lattice sites of both bosons and fermions within a high tunneling regime is regularly performed in quantum gas microscopes.

A basic 1D optical lattice is formed by the interference pattern of two counter propagating laser beams of the same linear polarization, most often in the far detuned regime. The trapping mechanism is via the Stark shift, where off resonant light causes shifts to an atom's internal structure. The effect of the Stark shift is to create a potential proportional to the intensity. This is the same trapping mechanism as in optical dipole traps (ODTs), with the only major difference being that the intensity of an optical lattice has a much more dramatic spatial variation than a standard ODT. and the Aubry–André model. By studying the evolution of atoms under the influence of these Hamiltonians, insight about the solutions to the Hamiltonian can be gained. This is particularly relevant to complicated Hamiltonians which are not easily solvable using theoretical or numerical techniques, such as those for strongly correlated systems.

The best atomic clocks in the world use atoms trapped in optical lattices, to obtain narrow spectral lines that are unaffected by the Doppler effect and recoil.

They are also promising candidates for quantum information processing.

Shaken optical lattices – where the phase of the lattice is modulated, causing the lattice pattern to scan back and forth – can be used to control the momentum state of the atoms trapped in the lattice. This control is exercised to split the atoms into populations of different momenta, propagate them to accumulate phase differences between the populations, and recombine them to produce an interference pattern.

Besides trapping cold atoms, optical lattices have been widely used in creating gratings and photonic crystals. They are also useful for sorting microscopic particles, and may be useful for assembling cell arrays.