Magnetic dipole trapping

The same interactions lead to the observation that the magnetisation in thin hlms changes with him thickness. In thick hlms, of ordinary dimensions, domains form and the magnetic hux is trapped in the him (Figure 12.19a). When the thickness of a him is reduced to below single domain size, the magnetic dipoles align in a parallel direchon in a... 

The hyperfine structure of the ESR spectrum is used to identify trapped radicals. This is due to the interaction of unpaired electrons with magnetic moments of the nuclei surrounding unpaired electrons localized at the radical site. Hyperfine interaction is described by two terms. One is the isotropic interaction, a, originating from the contact interaction of the wave functions of electron- and nuclear spins, and the other is the anisotropic interaction, D, originating from the magnetic dipole-dipole interaction. The total hyperfine interaction, a -f D, is therefore essentially anisotropic and can also be expressed in the form of a tensor A. As in the case of g-tensor, A can be described by three principal values. A, Aj, and A3, corresponding to the principal axes in a proper molecular coordinate system. The magnitude of the isotropic term of hyperfine interaction depends on an overlap of the wave packets of the unpaired electrons and nuclei in the case of the hyperfine interaction of an unpaired electron with a P-proton (see Fig. 2.2), McConnell s relation [Eq. (2.3)] has been derived... 

All static magnetic traps for atoms use nonuniform stationary magnetic fields. In a nonuniform magnetic field B = B(r), an atom with a permanent magnetic moment /LX has a magnetic dipole interaction energy... 

All atoms for which BEC has achieved, have a magnetic moment which is due to the vector sum of electron spin and nuclear spin. Collisions between such atoms can flip the spin and therefore the direction of the magnetic moment. This will lead to an escape of the atoms from the trap and will decrease the density of the trapped atoms. Spin flips during a collision are due either to the direct dipole-dipole interaction between the collision partners or to an indirect interaction between the nuclear spins which is mediated by the electron spins, since they are coupled through the hyperfine-interaction with the nuclear spins. 

The rdtracold molecules formed by PA are well suited to precision measurements and tests of fundamental physics because they are nearly at rest, and can readily be retained for long interrogation times in magnetic or optical traps. In tests of fundamental physics, molecules are preferred over atoms when either (1) an intrinsic dipole moment or very large polarizability is needed, or (2) a high density of states is beneficial. There is an excellent summary of molecular tests of fundamental principles in Section 15.2 of this book. 

If qubits are stored in hyperfine sublevels of the ground rovibrational electronic state the phase is relatively insensitive to local fluctuations of dc and ac electric fields, but more sensitive to magnetic field fluctuations, which should be minimized. The time scale of this minimization should be of the order of the coherence time of the trap. The states used to switch on the dipole-dipole interaction have to be long-lived to minimize decoherence from spontaneous emission. With gate operation times of <100 (jLsec and metastable excited state lifetimes of several hundred millisecond, decoherence due to spontaneous emission will be small. 

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