One of the pivotal questions in the physics of high-temperature superconductors is whether the low-energy dynamics of the charge carriers is mediated by bosons with an ultra fast characteristic timescale detected using ultrafast optical spectroscopy. This extremely fast timescale is in agreement with numerical calculations based on the t–J model in which the relaxation of the photo-excited charges is achieved via inelastic scattering with short-range antiferromagnetic excitations.
COBISS.SI-ID: 2794596
In integrable many-particle systems, it is widely believed that the stationary state reached at late times after a quantum quench can be described by a generalized Gibbs ensemble (GGE) constructed from their extensive number of conserved charges. A crucial issue is then to identify a complete set of these charges, enabling the GGE to provide exact steady state predictions. Here we solve this long-standing problem for the case of the spin-1/2 Heisenberg chain by explicitly constructing a GGE which uniquely fixes the macrostate describing the stationary behaviour after a general quantum quench. A crucial ingredient in our method, which readily generalizes to other integrable models, are recently discovered quasi-local charges. As a test, we reproduce the exact post-quench steady state of the Neel quench problem obtained previously by means of the Quench Action method.
COBISS.SI-ID: 2857572
We have developed an approach for the systematic study of the creation of collective knowledge via logically conditioned interactions between users on the Internet, each of which possesses a limited expertise. We have shown that the emerging user groups, associated with the transmission of knowledge, can be characterized as a collective state of the physical processes of two scales.
COBISS.SI-ID: 28758567
We geometrically characterize one-qubit dissipators of a Lindblad type. An efficient parametrization in terms of 6 linear parameters opens the way to various optimizations with local dissipation. As an example, we study maximal steady-state singlet fraction that can be achieved with an arbitrary local dissipation and two qubit Hamiltonian. We show that this singlet fraction has a discontinuity as one moves from unital to non-unital dissipators and demonstrate that the largest possible singlet fraction is approximately 0.654. This means that for systems with a sufficiently entangled ground state there is a fundamental quantum limit to the lowest attainable energy. With local dissipation one is unable to cool the system below some limiting non-zero temperature.
COBISS.SI-ID: 2828388
In a joint theoretical and experimental work, we investigated the quasi-condensation of strongly interacting bosons at finite momenta in a far-from-equilibrium case. Usually, long-range order in quantum many-body systems is associated with equilibrium situations. In our work, in contrast, a long-lived phase order emerges spontaneously in non-equilibrium. To this end, we prepared an inhomogeneous initial state consisting of one-dimensional Mott insulators in the center of otherwise empty one-dimensional chains in an optical lattice. After suddenly quenching the trapping potential to zero, we observed the onset of coherence in spontaneously forming quasi-condensates in the lattice. Remarkably, the emerging phase order differs from the ground-state order and is characterized by peaks at finite momenta +/- Pi/2 in the momentum distribution function.
COBISS.SI-ID: 29076007