PhD thesis in English

we discuss in some detail the experimental realization of a BEC.1.2.2 Experimental realizationAs already mentioned, it was a pursuit of the clear physical realization of a veryfundamental concept of a BEC that triggered an enormous amount of the experimentaleffort starting in the eighties of the last century. Although today BECsof different atoms are readily produced in laboratories worldwide, the creation ofquantum degenerate atomic gases took many years during which many experimentaltechniques at the forefront of technology were developed. In this subsection we givea basic description of today’s typical experimental setup with a very brief historicaloverview. The main reference we rely on is Ref. [21].Already in the early experimental phase of the quest for nanokelvin temperatures,possibility of storing atoms in any type of a vessel was ruled out. Instead, a properconfiguration of magnetic, optical or combined magneto-optical potential is used asan external confining potential, usually called a trap. Atoms are trapped around thepotential minimum due to interaction of their induced magnetic or electric dipolemoments with external field. In most cases, harmonic potentialV (⃗r) = 1 2 M(ω2 xx 2 + ω 2 yy 2 + ω 2 zz 2 ) , (1.19)is a reasonable approximation of the external trap potential. Different trap configurationshave been experimentally realized: for instance, highly elongated traps(which can be considered as effectively one dimensional), or pancake shaped traps(effectively two-dimensional regime). Beside this common type of a harmonic confinement,periodic external potentials (optical lattices) are widely used in nowadaysexperiments. We will mainly consider an axially-symmetric harmonic trap potential,with the radial trap frequency ω x = ω y = ω. The usual form of the potential isV (⃗r) = 1 2 Mω2 (ρ 2 + λ 2 z z2 ) , (1.20)where we introduce the trap aspect ratio λ z = ω z /ω. Typical values of the trapfrequencies are of the order of 2π × (10 − 100)Hz, with a typical length scale of theorder of several microns.The initial attempts to realize a BEC, focused on the spin-polarized hydrogen.The hydrogen was singled out among other atom types since it remains in the9