Abstract

Experiments in many fields of quantum physics require well-defined quantum states and well-defined interactions. For example, the basic ingredient of the quantum computer is a well-defined qubit - a two-state quantum system. Real quantum systems, however, possess many states and special care is needed to isolate just two of them. In real and artificial atoms this is usually done with polarized laser light, carefully aligned with the quantization axis. However, unwanted transition channels may still be present, which reduce the fidelity of the operations. For example, when an ultracold atomic ensemble held in an optical dipole trap is addressed by right circularly polarized light, many atoms often “see” an admixture of σ+ and σ− light (i.e., elliptical polarization [1]) since not all of them are exactly in the focus of the laser fields. Unwanted transitions may be present also due to imperfect polarization or alignment, off-resonant couplings, perturbing excitations in molecules and solids, etc.

© 2013 IEEE