31 research outputs found
Entanglement in spin-one Heisenberg chains
By using the concept of negativity, we study entanglement in spin-one
Heisenberg chains. Both the bilinear chain and the bilinear-biquadratic chain
are considered. Due to the SU(2) symmetry, the negativity can be determined by
two correlators, which greatly facilitate the study of entanglement properties.
Analytical results of negativity are obtained in the bilinear model up to four
spins and the two-spin bilinear-biquadratic model, and numerical results of
negativity are presented. We determine the threshold temperature before which
the thermal state is doomed to be entangled.Comment: 7 pages and 4 figure
Swapping and permutation operators as entanglement witnesses for quantum Heisenberg spin- systems
Using the SU() representation of the group theory, we derive the general
form of the spin swapping operator for the quantum Heisenberg spin- systems.
We further prove that such a spin swapping operator is equal to the spin
singlet pairing operator under the partial transposition. For SU(2) invariant
states, it is shown that the expectation value of the spin swapping operator
and its generalizations, the permutations, can be used as an entanglement
witness, especially, for the formulation of observable conditions of
entanglement.Comment: 8 pages, no figures, accepted by Journal of Physics A: Mathematical
and Genera
Entanglement Entropy dynamics in Heisenberg chains
By means of the time-dependent density matrix renormalization group algorithm
we study the zero-temperature dynamics of the Von Neumann entropy of a block of
spins in a Heisenberg chain after a sudden quench in the anisotropy parameter.
In the absence of any disorder the block entropy increases linearly with time
and then saturates. We analyze the velocity of propagation of the entanglement
as a function of the initial and final anisotropies and compare, wherever
possible, our results with those obtained by means of Conformal Field Theory.
In the disordered case we find a slower (logarithmic) evolution which may
signals the onset of entanglement localization.Comment: 15 pages, 9 figure
Selective Detection of Dopamine Combining Multilayers of Conducting Polymers with Gold Nanoparticles
Conditional displacement interaction in transversal direction from the quantum Rabi model
Implementation of Geometric Quantum Gates on MicrowaveâDriven Semiconductor Charge Qubits
Evolution of entanglement entropy in one-dimensional systems
We study the unitary time evolution of the entropy of entanglement of a one-dimensional system between the degrees of freedom in an interval of length l and its complement, starting from a pure state which is not an eigenstate of the Hamiltonian. We use path integral methods of quantum field theory as well as explicit computations for the transverse Ising spin chain. In both cases, there is a maximum speed v of propagation of signals. In general the entanglement entropy increases linearly with time t up to t = l/2v, after which it saturates at a value proportional to l, the coefficient depending on the initial state. This behaviour may be understood as a consequence of causality
Nanosized Materials in Amperometric Sensors
The use of nanosized materials nowadays constitutes one of the most diffused approach to modify electrode surface when aiming at obtaining efficient amperometric sensors; quite spontaneously, this trend has also involved the field of environmental monitoring. The chapter aims at discussing the properties of nanosized materials, the most widespread strategies for their deposition on the electrode surface as well as the main advantages and limitations of their use in electroanalysis. Metal and carbon nanostructures, and the relevant composite materials, are particularly discussed