116 research outputs found
Distilling momentum-space entanglement in Luttinger liquids at finite temperature
While much is known about the entanglement characteristics of ground states,
the properties of reduced thermal density matrices have received significantly
less attention. Here we investigate the entanglement content of reduced thermal
density matrices for momentum-space bipartitioning in Luttinger liquids using
analytical and numerical methods. The low lying part of its spectrum contains
an "entanglement gap", which persists up to temperatures comparable to the
level spacing. With increasing temperature, the low energy modes acquire
dispersion and resemble to those in the physical Hamiltonian with an enhanced
effective temperature. The momentum-space entanglement is carried by high
energy modes (compared to temperature), featuring a completely flat spectrum.
The von-Neumann entropy increases with temperature with a universal Sommerfeld
coefficient. The momentum-space entanglement Hamiltonian turns out to be as
universal as the physical Hamiltonian.Comment: 6 pages, 2 figure
Robust engineering of maximally entangled states by identical particle interferometry
We propose a procedure for the robust preparation of maximally entangled
states of identical fermionic qubits, studying the role played by particle
statistics in the process. The protocol exploits externally activated noisy
channels to reset the system to a known state. The subsequent interference
effects generated at a beam splitter result in a mixture of maximally entangled
Bell states and NOON states. We also discuss how every maximally entangled
state of two fermionic qubits distributed over two spatial modes can be
obtained from one another by fermionic passive optical transformations. Using a
pseudospin-insensitive, non-absorbing, parity check detector, the proposed
technique is thus shown to deterministically prepare any arbitrary maximally
entangled state of two identical fermions. These results extend recent findings
related to bosonic qubits. Finally, we analyze the performance of the protocol
for both bosons and fermions when the externally activated noisy channels are
not used and the two qubits undergo standard types of noise. The results supply
further insights towards viable strategies for noise-protected entanglement
exploitable in quantum-enhanced technologies.Comment: 9 pages, 6 figure
Bound entanglement in the XY model
We study the multi-spin entanglement for the 1D anisotropic XY model
concentrating on the simplest case of three-spin entanglement. As compared to
the pairwise entanglement, three-party quantum correlations have a longer range
and they are more robust on increasing the temperature.
We find regions of the phase diagram of the system where bound entanglement
occurs, both at zero and finite temperature. Bound entanglement in the ground
state can be obtained by tuning the magnetic field. Thermal bound entanglement
emerges naturally due to the effect of temperature on the free ground state
entanglement.Comment: 7 pages, 3 figures; some typos corrected, references adde
Entanglement crossover close to a quantum critical point
We discuss the thermal entanglement close to a quantum phase transition by
analyzing the concurrence for one dimensional models in the quantum Ising
universality class. We demonstrate that the entanglement sensitivity to thermal
and to quantum fluctuations obeys universal --scaling behaviour. We
show that the entanglement, together with its criticality, exhibits a peculiar
universal crossover behaviour.Comment: 12 pages; 5 figures (eps). References added; to be published in
Europhysics Letter
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