Universal frozen spectra after time-dependent symmetry restoring phase transitions.

For a general O(N) model, we study the time-dependent phase transition from a state with broken symmetry <φ> ≠ 0 to the symmetric phase <φ> = 0. During this non-equilibrium process, the primordial quantum (or thermal) fluctuations of the initial Goldstone modes are frozen and result in a deviation from the final ground (or thermal) state. For very slow transitions, we find that these fluctuations display a universal scaling behaviour. Their spectra are universal functions of a single parameter, which combines the initial frequency of the Goldstone modes and the sweep rate. As a result, the final two-point function [φa(r)φb(r')] is not exponentially suppressed at large distances Δr = r - r' (as it would be in the ground state) but decays polynomially in 1/|Δr|. Finally, we exemplify this universal behaviour for the transition from the super-fluid phase to the Mott state in the Bose-Hubbard model.

Strong magnetophotoelectric effect in folded graphene.

We study electronic transport in graphene under the influence of a transversal magnetic field B(r)=B(x)ez with the asymptotics B(x→±∞)=±B0, which could be realized via a folded graphene sheet in a constant magnetic field, for example. By solving the effective Dirac equation, we find robust modes with a finite energy gap which propagate along the fold-where particles and holes move in opposite directions. Exciting these particle-hole pairs with incident (optical or infrared) photons would then generate a nearly perfect charge separation and thus a strong magnetophotoelectric or magnetothermoelectric effect-even at room temperature.

Distance dependence of entanglement generation via a bosonic heat bath.

Within a generalized Caldeira-Leggett model, we analyze the conditions under which a bosonic heat bath can entangle two microscopic quantum systems at a distance r. We find that the attainable entanglement is extremely distance-sensitive. Significant entanglement can only be achieved if the systems are within a microscopic distance that is of order of the cutoff wavelength lambda of the system-bath interaction. At larger distances, the maximal entanglement is exponentially suppressed with a decay length of order lambda. We conclude that entanglement generation via a heat bath is not suitable for entangling remote objects.