2,738 research outputs found
Electronic correlations stabilize the antiferromagnetic Mott state in CsC
CsC in the A15 structure is an antiferromagnet at ambient pressure
in contrast with other superconducting trivalent fullerides. Superconductivity
is recovered under pressure and reaches the highest critical temperature of the
family. Comparing density-functional calculations with generalized gradient
approximation to the hybrid functional HSE, which includes a suitable component
of exchange, we establish that the antiferromagnetic state of CsC is
not due to a Slater mechanism, and it is stabilized by electron correlation.
HSE also reproduces the pressure-driven metalization. Our findings corroborate
previous analyses suggesting that the properties of this compound can be
understood as the result of the interplay between electron correlations and
Jahn-Teller electron-phonon interaction.Comment: 4 pages, 3 figure
Electronic Hong-Ou-Mandel interferometer for multi-mode entanglement detection
We show that multi-mode entanglement of electrons in a mesoscopic conductor
can be detected by a measurement of the zero-frequency current correlations in
an electronic Hong-Ou-Mandel interferometer. By this mean, one can further
establish a lower bound to the entanglement of formation of two-electron input
states. Our results extend the work of Burkard and Loss [Phys. Rev. Lett. 91,
087903 (2003)] to many channels and provide a way to test the existence of
entangled states involving both orbital and spin degrees of freedom.Comment: 6 pages. Revised version. Ref. adde
An Analysis of Information Assurance Relating to the Department of Defense Radio Frequency Identification (RFID) Passive Network
The mandates for suppliers to commence Radio Frequency Identification tagging set by Wal-Mart and the Department of Defense is changing this long-time rumored technology into reality. Despite the many conveniences to automate and improve asset tracking this technology offers, consumer groups have obstinately opposed this adoption due to the perceived weaknesses in security and privacy of the network. While the heated debate between consumers and retailers continues, little to no research has addressed the implications of security on the Department of Defense Radio Frequency Identification network. This thesis utilized a historical analysis of Radio Frequency Identification literature to determine whether the current network design causes any serious security concerns adversaries could exploit. The research concluded that at the present level of implementation, there is little cause for concern over the security of the network, but as the network grows to its full deployment, more evaluation and monitoring of security issues will require further consideration
Heat flux dynamics in dissipative cascaded systems
We study the dynamics of heat flux in the thermalization process of a pair of
identical quantum system that interact dissipatively with a reservoir in a {\it
cascaded} fashion. Despite the open dynamics of the bipartite system S is
globally Lindbladian, one of the subsystems "sees" the reservoir in a state
modified by the interaction with the other subsystem and hence it undergoes a
non-Markovian dynamics. As a consequence, the heat flow exhibits a
non-exponential time behaviour which can greatly deviate from the case where
each party is independently coupled to the reservoir. We investigate both
thermal and correlated initial states of and show that the presence of
correlations at the beginning can considerably affect the heat flux rate. We
carry out our study in two paradigmatic cases -- a pair of harmonic oscillators
with a reservoir of bosonic modes and two qubits with a reservoir of fermionic
modes -- and compare the corresponding behaviours. In the case of qubits and
for initial thermal states, we find that the trace distance discord is at any
time interpretable as the correlated contribution to the total heat flux.Comment: Final accepted versio
Information transmission through lossy bosonic memory channels
We study the information transmission through a quantum channel, defined over
a continuous alphabet and losing its energy en route, in presence of correlated
noise among different channel uses. We then show that entangled inputs improve
the rate of transmission of such a channel.Comment: 6 pages revtex, 2 eps figure
The time as an emergent property of quantum mechanics, a synthetic description of a first experimental approach
The "problem of time" in present physics substantially consists in the fact
that a straightforward quantization of the general relativistic evolution
equation and constraints generates for the Universe wave function the
Wheeler-De Witt equation, which describes a static Universe. Page and Wootters
considered the fact that there exist states of a system composed by entangled
subsystems that are stationary, but one can interpret the component subsystems
as evolving: this leads them to suppose that the global state of the universe
can be envisaged as one of this static entangled state, whereas the state of
the subsystems can evolve. Here we synthetically present an experiment, based
on PDC polarization entangled photons, that allows showing with a practical
example a situation where this idea works, i.e. a subsystem of an entangled
state works as a "clock" of another subsystem
First-principles study of the interaction and charge transfer between graphene and metals
Measuring the transport of electrons through a graphene sheet necessarily
involves contacting it with metal electrodes. We study the adsorption of
graphene on metal substrates using first-principles calculations at the level
of density functional theory. The bonding of graphene to Al, Ag, Cu, Au and
Pt(111) surfaces is so weak that its unique "ultrarelativistic" electronic
structure is preserved. The interaction does, however, lead to a charge
transfer that shifts the Fermi level by up to 0.5 eV with respect to the
conical points. The crossover from p-type to n-type doping occurs for a metal
with a work function ~5.4 eV, a value much larger than the work function of
free-standing graphene, 4.5 eV. We develop a simple analytical model that
describes the Fermi level shift in graphene in terms of the metal substrate
work function. Graphene interacts with and binds more strongly to Co, Ni, Pd
and Ti. This chemisorption involves hybridization between graphene -states
and metal d-states that opens a band gap in graphene. The graphene work
function is as a result reduced considerably. In a current-in-plane device
geometry this should lead to n-type doping of graphene.Comment: 12 pages, 9 figure
Cavity QED of Strongly Correlated Electron Systems: A No-go Theorem for Photon Condensation
In spite of decades of work it has remained unclear whether or not
superradiant quantum phases, referred to here as photon condensates, can occur
in equilibrium. In this Letter, we first show that when a non-relativistic
quantum many-body system is coupled to a cavity field, gauge invariance forbids
photon condensation. We then present a microscopic theory of the cavity quantum
electrodynamics of an extended Falicov-Kimball model, showing that, in
agreement with the general theorem, its insulating ferroelectric and exciton
condensate phases are not altered by the cavity and do not support photon
condensation.Comment: Reference list updated and minor typos correcte
Non-Linear Beam Splitter in Bose-Einstein Condensate Interferometers
A beam splitter is an important component of an atomic/optical Mach-Zehnder
interferometer. Here we study a Bose Einstein Condensate beam splitter,
realized with a double well potential of tunable height. We analyze how the
sensitivity of a Mach Zehnder interferometer is degraded by the non-linear
particle-particle interaction during the splitting dynamics. We distinguish
three regimes, Rabi, Josephson and Fock, and associate to them a different
scaling of the phase sensitivity with the total number of particles.Comment: draft, 19 pages, 10 figure
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