Electromagnetically induced transparency is an effect observed in atomic systems, originating from quantum interference, in which electromagnetic transitions to and from a certain quantum state become suppressed. This dark state is also characterized by a quantum phase, relative to other states, which theoretically should stop evolving, but remain phase coherent, during transparency. We test th...

We study an extended Hubbard model in the limit of infinite dimensions and its zero dimensional counterpart, a generalized asymmetric Anderson model. In the impurity model we find three kinds of mixed valence states: a) the usual strong coupling state in which a resonance forms at the Fermi level; b) a weak coupling state in which neither the impurity spin nor the impurity charge degrees of fre...

It is shown that coherent spin motion of electron–hole pairs localized in band gap states of silicon can influence charge carrier recombination. Based on this effect, a readout concept for silicon based solid–state spin–quantum computers as proposed by Kane is suggested. The P quantum bit (qbit) is connected via hyperfine coupling to the spin of the localized donor electron. When a second local...

we study the coherent spin-polarized transport through a zigzag-edge graphene flake (zgf), using hubbard model in the nearest neighbor approximation within the framework of the green function’s technique and landauer formalism. the system considered consists of electrode/ (zgf)/electrode, in which the electrodes are chosen to be armchair nanoribbons. the study was performed for two types of ele...

We simulate the effect of special excitation pulses on a cold gas of atoms. First, a rotary echo sequence is used to examine the coherent nature of a frozen Rydberg gas. If collective excitation and de-excitation is present with little or no source of dephasing, after these pulses the system should be returned to a state with few excitations, and a strong echo signal should occur. We investigat...

The core of a ferromagnetic vortex domain creates a strong, localized magnetic field, which can be manipulated on nanosecond timescales, providing a platform for addressing and controlling individual nitrogen-vacancy centre spins in diamond at room temperature, with nanometre-scale resolution. Here, we show that the ferromagnetic vortex can be driven into proximity with a nitrogen-vacancy defec...

We construct coherent states of the massless and massive representations of the Poincaré group. They are parameterised by points on the classical state space of spinning particles. Their properties are explored, with special emphasis on the geometrical structures on the state space.