Bosons

Robert Roth

The structure of trapped binary mixtures of bosonic and fermionic atoms at zero temperature is studied using a modified Gross-Pitaevskii equation for the bosons which self-consistently includes the mean-field interaction generated by the fermionic cloud. The density of the fermionic component is described within the Thomas-Fermi approximation. The influence of the boson-boson and the boson-fermion s-wave interaction on the density profiles and the stability of the mixture is investigated systematically. Critical particle numbers for the mean-field collapse caused either by attractive boson-boson or by attractive boson-fermion interactions and for the onset of spatial component separation are discussed. It is shown that the interplay between the boson-boson and the boson-fermion interaction generates a rich and complex phase diagram. Finally, the specific properties and prospects of the boson-fermion mixtures available in present experiments are addressed.

Franz Schwabl

Thomas Brougham, Stephen Mark Barnett, Igor Jex

We investigate multi-boson interference. A Hamiltonian is presented that treats pairs of bosons as a single composite boson. This Hamiltonian allows two pairs of bosons to interact as if they were two single composite bosons. We show that this leads to the composite bosons exhibiting novel interference effects, such as Hong–Ou–Mandel interference. We then investigate generalisations of the formalism to the case of interference between two general composite bosons. Finally, we show how one can realise interference between composite bosons in the two-atom Dicke model.

Franz Schwabl

Richard Giovanni Avella, Ramón Rafael Rey González, K. M. Fonseca-Romero

The sequential to correlated-tunneling transition of two identical bosons confined in a symmetrical double well potential is studied using a time-dependent variational formalism. Increasing the strength of the short-range boson-boson interaction, the probability of finding both bosons in the same well allow to identify three regimes. For small values of the boson- boson coupling constante, this probability display beatings. Then, the probability of finding both bosons in the same well becomes quasi-periodical in time, for almost all values of the coupling constant; however, there is a zero-measure set, which contains an infinity of points, for which this probability is time-periodic. Finally, for larger values of the coupling constant, this probability changes periodically. Based on the dynamics of the probability of finding one boson on each well and increasing the boson-boson interaction, we find that tunnelling changes from a regime where one boson tunnels after the other to a regime in which they tunnel together.