2,650 research outputs found
The role of entanglement in dynamical evolution
Entanglement or entanglement generating interactions permit to achieve the
maximum allowed speed in the dynamical evolution of a composite system, when
the energy resources are distributed among subsystems. The cases of
pre-existing entanglement and of entanglement-building interactions are
separately addressed. The role of classical correlations is also discussed.Comment: 5 pages, 1 figure. Revised versio
Limits to clock synchronization induced by completely dephasing communication channels
Clock synchronization procedures are analyzed in the presence of imperfect
communications. In this context we show that there are physical limitations
which prevent one from synchronizing distant clocks when the intervening medium
is completely dephasing, as in the case of a rapidly varying dispersive medium.Comment: 6 Pages. Revised version as published in PR
Bosonic Memory Channels
We discuss a Bosonic channel model with memory effects. It relies on a
multi-mode squeezed (entangled) environment's state. The case of lossy Bosonic
channels is analyzed in detail. We show that in the absence of input energy
constraints the memory channels are equivalent to their memoryless
counterparts. In the case of input energy constraint we provide lower and upper
bounds for the memory channel capacity.Comment: 6 pages, 2 figure
Quantum cryptographic ranging
We present a system to measure the distance between two parties that allows
only trusted people to access the result. The security of the protocol is
guaranteed by the complementarity principle in quantum mechanics. The protocol
can be realized with available technology, at least as a proof of principle
experiment.Comment: 2 pages, 1 figure. Contribution to the proceedings of the IV edition
of the Garda Lake Workshop "Mysteries, Puzzles and Paradoxes in Quantum
Mechanics
Theory of integer quantum Hall polaritons in graphene
We present a theory of the cavity quantum electrodynamics of the graphene
cyclotron resonance. By employing a canonical transformation, we derive an
effective Hamiltonian for the system comprised of two neighboring Landau levels
dressed by the cavity electromagnetic field (integer quantum Hall polaritons).
This generalized Dicke Hamiltonian, which contains terms that are quadratic in
the electromagnetic field and respects gauge invariance, is then used to
calculate thermodynamic properties of the quantum Hall polariton system.
Finally, we demonstrate that the generalized Dicke description fails when the
graphene sheet is heavily doped, i.e. when the Landau level spectrum of 2D
massless Dirac fermions is approximately harmonic. In this case we `integrate
out' the Landau levels in valence band and obtain an effective Hamiltonian for
the entire stack of Landau levels in conduction band, as dressed by strong
light-matter interactions.Comment: 20 pages, 7 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
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
Clock synchronization with dispersion cancellation
The dispersion cancellation feature of pulses which are entangled in
frequency is employed to synchronize clocks of distant parties. The proposed
protocol is insensitive to the pulse distortion caused by transit through a
dispersive medium. Since there is cancellation to all orders, also the effects
of slowly fluctuating dispersive media are compensated. The experimental setup
can be realized with currently available technology, at least for a proof of
principle.Comment: 4 pages, 3 figure
Photon losses depending on polarization mixedness
We introduce a quantum channel describing photon losses depending on the
degree of polarization mixedness. This can be regarded as a model of quantum
channel with correlated errors between discrete and continuous degrees of
freedom. We consider classical information over a continuous alphabet encoded
on weak coherent states as well as classical information over a discrete
alphabet encoded on single photons using dual rail representation. In both
cases we study the one-shot capacity of the channel and its behaviour in terms
of correlation between losses and polarization mixedness
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