50 research outputs found
Bipartite entanglement of quantum states in a pair basis
The unambiguous detection and quantification of entanglement is a hot topic
of scientific research, though it is limited to low dimensions or specific
classes of states. Here we identify an additional class of quantum states, for
which bipartite entanglement measures can be efficiently computed, providing
new rigorous results. Such states are written in arbitrary
dimensions, where each basis state in the subsystem A is paired with only one
state in B. This new class, that we refer to as pair basis states, is
remarkably relevant in many physical situations, including quantum optics. We
find that negativity is a necessary and sufficient measure of entanglement for
mixtures of states written in the same pair basis. We also provide analytical
expressions for a tight lower-bound estimation of the entanglement of
formation, a central quantity in quantum information.Comment: 8 pages, 10 figure
Solvable 2D superconductors with l-wave pairing
We analyze a family of two-dimensional BCS Hamiltonians with general l-wave
pairing interactions, classifying the models in this family that are
Bethe-ansatz solvable in the finite-size regime. We show that these solutions
are characterized by nontrivial winding numbers, associated with topological
phases, in some part of the corresponding phase diagrams. By means of a
comparative study, we demonstrate benefits and limitations of the mean-field
approximation, which is the standard approach in the limit of a large number of
particles. The mean-field analysis also allows to extend part of the results
beyond integrability, clarifying the peculiarities associable with the
integrability itself.Comment: 9 pages, 1 figur
Hidden XY structure of the bond-charge Hubbard model
The repulsive one-dimensional Hubbard model with bond-charge interaction
(HBC) in the superconducting regime is mapped onto the spin-1/2 XY model with
transverse field. We calculate correlations and phase boundaries, realizing an
excellent agreement with numerical results. The critical line for the
superconducting transition is shown to coincide with the analytical
factorization line identifying the commensurate-incommensurate transition in
the XY model.Comment: 4 pages, 3 figure
Brane parity orders in the insulating state of Hubbard ladders
The Mott insulating state of the Hubbard model at half-filling could be
depicted as a spin liquid of singly occupied sites with holon-doublon quantum
fluctuations localized in pairs. In one dimension the behavior is captured by a
finite value of the charge parity string correlator, which fails to remain
finite when generalized to higher dimensions. We recover a definition of parity
brane correlator which may remain nonvanishing in presence of interchain
coupling, by assigning an appropriate fractional phase to the parity breaking
fluctuations. In case of Hubbard ladders at half-filling, we find that the
charge parity brane is non-zero at any repulsive value of interaction. The spin
parity brane instead becomes nonvanishing in the even-leg case, in
correspondence to the onset of the spin gapped D-Mott phase, which is absent in
the odd-leg case. The behavior of the parity correlators is also analyzed by
means of a numerical DMRG analysis of the one- and two-leg ladder.Comment: Main article: 5 pages, 1 figure. Supplementary information: 4 pages,
8 figure
Non-local order parameters for the 1D Hubbard model
We characterize the Mott insulator and Luther-Emery phases of the 1D Hubbard
model through correlators that measure the parity of spin and charge strings
along the chain. These non-local quantities order in the corresponding gapped
phases and vanish at the critical point . The Mott insulator consists of
bound doublon-holon pairs, which in the Luther-Emery phase turn into electron
pairs with opposite spins, both unbinding at . The behavior of the parity
correlators can be captured by an effective free spinless fermion model.Comment: 4 pages; 3 figure
Entanglement Generation and Dynamics for a Bose-Hubbard model in a Double-Well Potential
The study of entanglement between bosonic systems is of primary importance
for establishing feasible resources needed for implementing quantum information
protocols, both in their interacting atomic or photonic realizations. Atomic
systems are particularly efficient in the production of large amounts of
entanglement, providing higher information density than conventional qubit
entangled states. Such increased quantum resources pave the way to novel
fundamental tests of nature and efficient applications in quantum information,
metrology and sensing. We consider a basic setup made up of two parties A and
B, each one populated by a single level bosonic variable. The bosons are
interacting and can hop between A and B, thus describing a two-site
Bose-Hubbard Hamiltonian. We consider the generation of quantum states in
several situations that cover the majority of physical realizations: ground
state, finite temperature, unitary dynamics, dissipation through dephasing and
loss of particles. The system is analyzed through truncated exact
diagonalization, as a function of the microscopic parameters. The non
separability of the obtained quantum states is estimated by means of the
negativity, which has recently been proven to be a suitable measure of
entanglement. Finally, we calculate lower bounds of the entanglement of
formation, an indicator that quantifies the minimal amount of entanglement
resources needed to build up such states.Comment: 17 pages, 9 figure
How hidden orders generate gaps in one-dimensional fermionic systems
We demonstrate that hidden long range order is always present in the gapped phases of interacting fermionic systems on one dimensional lattices. It is captured by correlation functions of appropriate nonlocal charge and/or spin operators, which remain asymptotically finite. The corresponding microscopic orders are classified. The results are confirmed by DMRG numerical simulation of the phase diagram of the extended Hubbard model, and of a Haldane insulator phas
Hidden magnetism in periodically modulated one dimensional dipolar fermions
The experimental realization of time-dependent ultracold lattice systems has paved the way towards the implementation of new Hubbard-like Hamiltonians. We show that in a one-dimensional two-components lattice dipolar Fermi gas the competition between long range repulsion and correlated hopping induced by periodically modulated on-site interaction allows for the formation of hidden magnetic phases, with degenerate protected edge modes. The magnetism, characterized solely by string-like nonlocal order parameters, manifests in the charge and/or in the spin degrees of freedom. Such behavior is enlighten by employing Luttinger liquid theory and numerical methods. The range of parameters for which hidden magnetism is present can be reached by means of the currently available experimental setups and probes