29,041 research outputs found
Signifying quantum benchmarks for qubit teleportation and secure communication using Einstein-Podolsky-Rosen steering inequalities
The demonstration of quantum teleportation of a photonic qubit from Alice to
Bob usually relies on data conditioned on detection at Bob's location. I show
that Bohm's Einstein-Podolsky-Rosen (EPR) paradox can be used to verify that
the quantum benchmark for qubit teleportation has been reached, without
postselection. This is possible for scenarios insensitive to losses at the
generation station, and with efficiencies of for the
teleportation process. The benchmark is obtained, if it is shown that Bob can
{}"steer" Alice's record of the qubit as stored by Charlie. EPR steering
inequalities involving measurement settings can also be used to confirm
quantum teleportation, for efficiencies , if one assumes trusted
detectors for Charlie and Alice. Using proofs of monogamy, I show that
two-setting EPR steering inequalities can signify secure teleportation of the
qubit state.Comment: 10 pages, 1 Figur
Einstein-Podolsky-Rosen paradox and quantum steering in pulsed optomechanics
We describe how to generate an Einstein-Podolsky-Rosen (EPR) paradox between
a mesoscopic mechanical oscillator and an optical pulse. We find two types of
paradox, defined by whether it is the oscillator or the pulse that shows the
effect Schrodinger called "steering". Only the oscillator paradox addresses the
question of mesoscopic local reality for a massive system. In that case, EPR's
"elements of reality" are defined for the oscillator, and it is these elements
of reality that are falsified (if quantum mechanics is complete). For this sort
of paradox, we show that a thermal barrier exists, meaning that a threshold
level of pulse-oscillator interaction is required for a given thermal
occupation n_0 of the oscillator. We find there is no equivalent thermal
barrier for the entanglement of the pulse with the oscillator, nor for the EPR
paradox that addresses the local reality of the optical system. Finally, we
examine the possibility of an EPR paradox between two entangled oscillators.
Our work highlights the asymmetrical effect of thermal noise on quantum
nonlocality.Comment: 9 pages, 7 figure
Scattering of low-energy electrons and positrons by atomic beryllium: Ramsauer-Townsend effect
Total cross sections for the scattering of low-energy electrons and positrons
by atomic beryllium in the energy range below the first inelastic thresholds
are calculated. A Ramsauer-Townsend minimum is seen in the electron scattering
cross sections, while no such effect is found in the case of positron
scattering. A minimum total cross section of 0.016 a.u. at 0.0029 eV is
observed for the electron case. In the limit of zero energy, the cross sections
yield a scattering length of -0.61 a.u. for electron and +13.8 a.u. for
positron scattering
Criteria for generalized macroscopic and mesoscopic quantum coherence
We consider macroscopic, mesoscopic and "S-scopic" quantum superpositions of
eigenstates of an observable, and develop some signatures for their existence.
We define the extent, or size of a superposition, with respect to an
observable \hat{x}, as being the range of outcomes of \hat{x} predicted by that
superposition. Such superpositions are referred to as generalized -scopic
superpositions to distinguish them from the extreme superpositions that
superpose only the two states that have a difference in their prediction
for the observable. We also consider generalized -scopic superpositions of
coherent states. We explore the constraints that are placed on the statistics
if we suppose a system to be described by mixtures of superpositions that are
restricted in size. In this way we arrive at experimental criteria that are
sufficient to deduce the existence of a generalized -scopic superposition.
The signatures developed are useful where one is able to demonstrate a degree
of squeezing. We also discuss how the signatures enable a new type of
Einstein-Podolsky-Rosen gedanken experiment.Comment: 15 pages, accepted for publication in Phys. Rev.
- …