11,967 research outputs found
A deeper insight into quantum state transfer from an information flux viewpoint
We use the recently introduced concept of information flux in a many-body
register in order to give an alternative viewpoint on quantum state transfer in
linear chains of many spins.Comment: 6 pages, 3 figures, RevTeX
Bypassing state initialization in Hamiltonian tomography on spin-chains
We provide an extensive discussion on a scheme for Hamiltonian tomography of
a spin-chain model that does not require state initialization [Phys. Rev. Lett.
102, 187203 (2009)]. The method has spurred the attention of the physics
community interested in indirect acquisition of information on the dynamics of
quantum many-body systems and represents a genuine instance of a
control-limited quantum protocol.Comment: 7 pages, 2 figures, RevTeX
Nested entangled states for distributed quantum channels
We find a coupling-strength configuration for a linear chain of N spins which
gives rise to simultaneous multiple Bell states. We suggest a way such an
interesting entanglement pattern can be used in order to distribute maximally
entangled channels to remote locations and generate multipartite entanglement
with a minimum-control approach. Our proposal thus provides a way to achieve
the core resources in distributed information processing. The schemes we
describe can be efficiently tested in chains of coupled cavities interacting
with three-level atoms.Comment: 4 pages, 2 figures, RevTeX
Alternate two-dimensional quantum walk with a single-qubit coin
We have recently proposed a two-dimensional quantum walk where the
requirement of a higher dimensionality of the coin space is substituted with
the alternance of the directions in which the walker can move [C. Di Franco, M.
Mc Gettrick, and Th. Busch, Phys. Rev. Lett. {\bf 106}, 080502 (2011)]. For a
particular initial state of the coin, this walk is able to perfectly reproduce
the spatial probability distribution of the non-localized case of the Grover
walk. Here, we present a more detailed proof of this equivalence. We also
extend the analysis to other initial states, in order to provide a more
complete picture of our walk. We show that this scheme outperforms the Grover
walk in the generation of - spatial entanglement for any initial
condition, with the maximum entanglement obtained in the case of the particular
aforementioned state. Finally, the equivalence is generalized to wider classes
of quantum walks and a limit theorem for the alternate walk in this context is
presented.Comment: 9 pages, 9 figures, RevTeX
Bypassing state initialisation in perfect state transfer protocols on spin-chains
Although a complete picture of the full evolution of complex quantum systems
would certainly be the most desirable goal, for particular Quantum Information
Processing schemes such an analysis is not necessary. When quantum correlations
between only specific elements of a many-body system are required for the
performance of a protocol, a more distinguished and specialised investigation
is helpful. Here, we provide a striking example with the achievement of perfect
state transfer in a spin chain without state initialisation, whose realisation
has been shown to be possible in virtue of the correlations set between the
first and last spin of the transmission-chain.Comment: 8 pages, 2 figures, RevTeX
Quantum state transfer via temporal kicking of information
We propose a strategy for perfect state transfer in spin chains based on the
use of an unmodulated coupling Hamiltonian whose coefficients are explicitly
time dependent. We show that, if specific and non-demanding conditions are
satisfied by the temporal behavior of the coupling strengths, our model allows
perfect state transfer. The paradigma put forward by our proposal holds the
promises to set an alternative standard to the use of clever encoding and
coupling-strength engineering for perfect state transfer.Comment: 7 pages, 7 figures, RevTeX
Patterns of variability in early life traits of a Mediterranean coastal fish
Spawning dates and pelagic larval duration (PLD) are early life traits (ELT) crucial for understanding life cycles, properly assessing patterns of connectivity and gathering indications about patchiness or homogeneity of larval pools. Considering that little attention has been paid to spatial variability in these traits, we investigated variability of ELT from the analysis of otolith microstructure in the common two-banded sea bream Diplodus vulgaris. In the southwestern Adriatic Sea, along ~200 km of coast (∼1° in latitude, 41.2° to 40.2°N), variability of ELT was assessed at multiple spatial scales. Overall, PLD (ranging from 25 to 61 d) and spawning dates (October 2009 to February 2010) showed significant variability at small scales (i.e. <6 km), but not at larger scales. These outcomes suggest patchiness of the larval pool at small spatial scales. Multiple causal processes underlying the observed variability are discussed, along with the need to properly consider spatial variability in ELT, for example when delineating patterns of connectivity. Copyright © 2013 Inter-Research
Measurement-induced generation of spatial entanglement in a two-dimensional quantum walk with single-qubit coin
One of the proposals for the exploitation of two-dimensional quantum walks
has been the efficient generation of entanglement. Unfortunately, the
technological effort required for the experimental realization of standard
two-dimensional quantum walks is significantly demanding. In this respect, an
alternative scheme with less challenging conditions has been recently studied,
particularly in terms of spatial-entanglement generation [C. Di Franco, M. Mc
Gettrick, and Th. Busch, Phys. Rev. Lett. 106, 080502 (2011)]. Here, we extend
the investigation to a scenario where a measurement is performed on the coin
degree of freedom after the evolution, allowing a further comparison with the
standard two-dimensional Grover walk.Comment: 9 pages, 4 figures, RevTeX
Information-flux approach to multiple-spin dynamics
We introduce and formalize the concept of information flux in a many-body
register as the influence that the dynamics of a specific element receive from
any other element of the register. By quantifying the information flux in a
protocol, we can design the most appropriate initial state of the system and,
noticeably, the distribution of coupling strengths among the parts of the
register itself. The intuitive nature of this tool and its flexibility, which
allow for easily manageable numerical approaches when analytic expressions are
not straightforward, are greatly useful in interacting many-body systems such
as quantum spin chains. We illustrate the use of this concept in quantum
cloning and quantum state transfer and we also sketch its extension to
non-unitary dynamics.Comment: 7 pages, 4 figures, RevTeX
NonClassicality Criteria in Multiport Interferometry
Interference lies at the heart of the behavior of classical and quantum
light. It is thus crucial to understand the boundaries between which
interference patterns can be explained by a classical electromagnetic
description of light and which, on the other hand, can only be understood with
a proper quantum mechanical approach. While the case of two-mode interference
has received a lot of attention, the multimode case has not yet been fully
explored. Here we study a general scenario of intensity interferometry: we
derive a bound on the average correlations between pairs of output intensities
for the classical wavelike model of light, and we show how it can be violated
in a quantum framework. As a consequence, this violation acts as a
nonclassicality witness, able to detect the presence of sources with
sub-Poissonian photon-number statistics. We also develop a criterion that can
certify the impossibility of dividing a given interferometer into two
independent subblocks.Comment: 5 + 3 pages, published versio
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