40 research outputs found
Quantum-state transfer via resonant tunnelling through local field induced barriers
Efficient quantum-state transfer is achieved in a uniformly coupled spin-1/2
chain, with open boundaries, by application of local magnetic fields on the
second and last-but-one spins, respectively. These effective \textit{barriers}
induce appearance of two eigenstates, bi-localized at the edges of the chain,
which allow a high quality transfer also at relatively long distances. The same
mechanism may be used to send an entire e-bit (e.g., an entangled qubit pair)
from one to the other end of the chain
Global Quantum Correlation in the Ising model
We study quantum correlations in an isotropic Ising ring under the effects of
a transverse magnetic field. After characterizing the behavior of two-spin
quantum correlations, we extend our analysis to global properties of the ring,
using a figure of merit for quantum correlations that shows enough sensitivity
to reveal the drastic changes in the properties of the system at criticality.
This opens up the possibility to relate statistical properties of quantum
many-body systems to suitably tailored measures of quantum correlations that
capture features going far beyond standard quantum entanglement.Comment: Published in the International Journal of Quantum Information as part
of the special issue devoted to "Quantum Correlations: entanglement and
beyond
Optimal dynamics for quantum-state and entanglement transfer through homogeneous quantum wires
It is shown that effective quantum-state and entanglement transfer can be
obtained by inducing a coherent dynamics in quantum wires with homogeneous
intrawire interactions. This goal is accomplished by tuning the coupling
between the wire endpoints and the two qubits there attached, to an optimal
value. A general procedure to determine such value is devised, and scaling laws
between the optimal coupling and the length of the wire are found. The
procedure is implemented in the case of a wire consisting of a spin-1/2 XY
chain: results for the time dependence of the quantities which characterize
quantum-state and entanglement transfer are found of extremely good quality and
almost independent of the wire length. The present approach does not require
`ad hoc' engineering of the intrawire interactions nor a specific initial pulse
shaping, and can be applied to a vast class of quantum channels.Comment: 5 pages, 5 figure
Using the J1-J2 Quantum Spin Chain as an Adiabatic Quantum Data Bus
This paper investigates numerically a phenomenon which can be used to
transport a single q-bit down a J1-J2 Heisenberg spin chain using a quantum
adiabatic process. The motivation for investigating such processes comes from
the idea that this method of transport could potentially be used as a means of
sending data to various parts of a quantum computer made of artificial spins,
and that this method could take advantage of the easily prepared ground state
at the so called Majumdar-Ghosh point. We examine several annealing protocols
for this process and find similar result for all of them. The annealing process
works well up to a critical frustration threshold.Comment: 14 pages, 13 figures (2 added), revisions made to add citations and
additional discussion at request of referee
Long quantum channels for high-quality entanglement transfer
High-quality quantum-state and entanglement transfer can be achieved in an
unmodulated spin bus operating in the ballistic regime, which occurs when the
endpoint qubits A and B are coupled to the chain by an exchange interaction
comparable with the intrachain exchange. Indeed, the transition amplitude
characterizing the transfer quality exhibits a maximum for a finite optimal
value , where is the channel length. We show that
scales as for large and that it ensures a
high-quality entanglement transfer even in the limit of arbitrarily long
channels, almost independently of the channel initialization. For instance, the
average quantum-state transmission fidelity exceeds 90% for any chain length.
We emphasize that, taking the reverse point of view, should be
experimentally constrained, high-quality transfer can still be obtained by
adjusting the channel length to its optimal value.Comment: 12 pages, 9 figure
Irreversible Work and Inner Friction in Quantum Thermodynamic Processes
We discuss the thermodynamics of closed quantum systems driven out of equilibrium by a change in a control parameter and undergoing a unitary process. We compare the work actually done on the system with the one that would be performed along ideal adiabatic and isothermal transformations. The comparison with the latter leads to the introduction of irreversible work, while that with the former leads to the introduction of inner friction. We show that these two quantities can be treated on an equal footing, as both can be linked with the heat exchanged in thermalization processes and both can be expressed as relative entropies. Furthermore, we show that a specific fluctuation relation for the entropy production associated with the inner friction exists, which allows the inner friction to be written in terms of its cumulants.All the authors acknowledge support from COST MP1209 Action. F. P., G. F., and N. L. G. acknowledge insightful discussions with Michele Campisi, John Goold, and Mauro Paternostro. T. J. G. A. is supported by the European Commission, the European Social Fund, and the Region Calabria through the program POR Calabria FSE 2007-2013-Asse IV Capitale Umano-Obiettivo Operativo M2. F. G. and R. Z. acknowledge MINECO, CSIC, the EU commission, UIB and FEDER funding under Grants FIS2011-23526 (TIQS), postdoctoral JAE program (ESF) and Invited professors program.Peer reviewe
Remnants of Anderson localization in prethermalization induced by white noise
We study the nonequilibrium evolution of a one-dimensional quantum Ising chain with spatially disordered, time-dependent, transverse fields characterized by white noise correlation dynamics. We establish prethermalization in this model, showing that the quench dynamics of the on-site transverse magnetization first approaches a metastable state unaffected by noise fluctuations, and then relaxes exponentially fast toward an infinite temperature state as a result of the noise. We also consider energy transport in the model, starting from an inhomogeneous state with two domain walls which separate regions characterized by spins with opposite transverse magnetization. We observe at intermediate timescales a phenomenology akin to Anderson localization: energy remains localized within the two domain walls, until the Markovian noise destroys coherence and, accordingly, disorder-induced localization, allowing the system to relax toward the late stages of its nonequilibrium dynamics. We compare our results with the simpler case of a noisy quantum Ising chain without disorder, and we find that the prethermal plateau is a generic property of spin chains with weak noise, while the phenomenon of prethermal Anderson localization is a specific feature arising from the competition of noise and disorder in the real-time transport properties of the system
Abelian gauge potentials on cubic lattices
The study of the properties of quantum particles in a periodic potential
subject to a magnetic field is an active area of research both in physics and
mathematics; it has been and it is still deeply investigated. In this review we
discuss how to implement and describe tunable Abelian magnetic fields in a
system of ultracold atoms in optical lattices. After discussing two of the main
experimental schemes for the physical realization of synthetic gauge potentials
in ultracold set-ups, we study cubic lattice tight-binding models with
commensurate flux. We finally examine applications of gauge potentials in
one-dimensional rings.Comment: To appear on: "Advances in Quantum Mechanics: Contemporary Trends and
Open Problems", G. Dell'Antonio and A. Michelangeli eds., Springer-INdAM
series 201