Optical lattice

An optical grating (English technical term optical lattice ) referred to in quantum optics, a spatially periodic structure of laser radiation, can be caught in the atoms or molecules.

Operation

The structure of the optical grating is formed by interference of laser light. It comes with a suitable choice of the laser parameters to the standing wave that induces a periodic potential due to the Stark shift for atoms. The underlying principle is the same as that of the optical tweezers: the laser light is induced in each of the atoms of an electric dipole moment, its interaction with the light results in a force on the atom. Depending on the sign of the detuning of the laser light with respect to the atomic transition frequency, the atoms in the nodes ( intensity minima ) and antinodes (intensity maxima ) are drawn to the standing wave. The exact geometry of the potential generated thereby depending on the arrangement of the laser beams and the resulting complexity of the interference pattern.

Band structure

The periodic potential change the dispersion relation for the movement of atoms according to the Bloch theorem. The result is a band structure similar to the band structure of electrons in crystals. With the geometry of the interference pattern can be, in principle, this band structure tailoring. In contrast to solid-state systems, it is also possible in optical lattices, the potential depth and thus the band structure dynamically ( ie, while the atoms in it to sit) to change.

Consequences of the band structure

If there is a sufficiently strong interaction between the atoms, the band structure allows the formation of dark ( hole-like ) and light ( particle-like ) solitons, since the interaction from exactly the dispersion can compensate. On an external force, such as gravity, the atoms react in the optical lattice with Bloch oscillations, which can be measured in these systems extremely accurate.

Observation

Most of the atoms are not observed in the optical lattice, but after switching off the light potential and a certain flight time. The absorption of the atoms of the illuminating laser beam is recorded on a CCD camera. The methodology is similar to the detection of Bose-Einstein condensates. In this way, you can generally measure the quasi-momentum distribution, but not directly the spatial distribution of the atoms. In particular it is difficult to observe individual grid locations, since these are only a half wavelength of light away from each other in the extreme case. Therefore, it has to fight for optical observation of single lattice sites with the diffraction limit of optical resolution. In 2008, however, several research groups have succeeded in imaging single lattice sites in an optical lattice, and - in some cases in real time and with a detection sensitivity sufficient to detect single atoms - to track their movement. In addition, a method has been developed which is related to the scanning electron microscopy, and single atoms prove by ionization of an electron beam which can be focused much sharper.

Application

Are all sinks a three-dimensional optical lattice filled, can produce artificial crystals of light. These have the advantage that it is absolutely perfect crystals without defects, their parameters by the laser light used are easily changeable in addition, compared with the known from solid state physics systems. They can therefore be used as model systems for problems in solid-state physics and are regarded as promising candidates for the realization of a quantum computer.

Atoms in optical lattices are furthermore in addition trapped ions as promising candidates for the realization of even more precise atomic clocks, so-called lattice clocks.