115 research outputs found
Photon exchange and entanglement formation during the transmission through a rectangular quantum barrier
When a quantum particle traverses a rectangular potential created by a
quantum field both photon exchange and entanglement between particle and field
take place. We present analytic results for the transition amplitudes of any
possible photon exchange processes for an incoming plane wave and initial Fock,
thermal and coherent field states. We show that for coherent field states the
entanglement correlates the particle's position to the photon number in the
field instead of the particle's energy as usual. Besides entanglement
formation, remarkable differences to the classical field treatment also appear
with respect to the symmetry between photon emission and absorption, resonance
effects and if the field initially occupies the vacuum state.Comment: 6 pages (double column), 6 figure
Invasions of isotopes and of neobiota
We report on invasions with low diffusivity: one in materials science and one in ecology. What is interesting in materials science is to describe diffusivities in order to model technological important materials. In ecology on the other hand predictions into the future appear the most challenging issue
Engineering of triply entangled states in a single-neutron system
We implemented a triply entangled Greenberger-Horne-Zeilinger(GHZ)-like state
and coherently manipulated the spin, path, and energy degrees of freedom in a
single neutron system. The GHZ-like state was analyzed with an inequality
derived by Mermin: we determined the four expectation values and finally
obtained M = 2.558 +/- 0.004 > 2, which exhibits a clear violation of the
noncontextual assumption and confirms quantum contextuality.Comment: 4 pages, 2figure
Energy entanglement in neutron interferometry
Entanglement between degrees of freedom, namely between the spin, path and
(total) energy degrees of freedom, for single neutrons is exploited. We
implemented a triply entangled Greenberger-Horne-Zeilinger(GHZ)-like state and
coherently manipulated relative phases of two-level quantum subsystems. An
inequality derived by Mermin was applied to analyze the generated GHZ-like
state: we determined the four expectation values and finally obtained M=2.558
+/- 0.004 which is clearly above the threshold of 2. This demonstrates the
violation of a Mermin-like inequality for triply entangled GHZ-like state in a
single-particle system, which, in turn, exhibits a clear inconsistency between
noncontextual assumptions and quantum mechanics and confirms quantum
contextuality.Comment: 4 pages, 3 figure
Kochen-Specker theorem studied with neutron interferometer
The Kochen-Specker theorem theoretically shows evidence of the
incompatibility of noncontextual hidden variable theories with quantum
mechanics. Quantum contextuality is a more general concept than quantum
non-locality which is quite well tested in experiments by using Bell
inequalities. Within neutron interferometry we performed an experimental test
of the Kochen-Specker theorem with an inequality, which identifies quantum
contextuality, by using spin-path entanglement in a single neutron system. Here
entanglement is achieved not between different particles, but between degrees
of freedom, i.e., between spin and path degree of freedom. Appropriate
combinations of the spin analysis and the position of the phase shifter allow
an experimental verification of the violation of an inequality of the
Kochen-Specker theorem. The observed value of (2.291 +/- 0.008), which is above
the threshold of 1, clearly shows that quantum mechanical predictions cannot be
reproduced by noncontextual hidden variable theories.Comment: 5 pages, 3 figure
New Aspects of Geometric Phases in Experiments with polarized Neutrons
Geometric phase phenomena in single neutrons have been observed in
polarimeter and interferometer experiments. Interacting with static and time
dependent magnetic fields, the state vectors acquire a geometric phase tied to
the evolution within spin subspace. In a polarimeter experiment the
non-additivity of quantum phases for mixed spin input states is observed. In a
Si perfect-crystal interferometer experiment appearance of geometric phases,
induced by interaction with an oscillating magnetic field, is verified. The
total system is characterized by an entangled state, consisting of neutron and
radiation fields, governed by a Jaynes-Cummings Hamiltonian. In addition, the
influence of the geometric phase on a Bell measurement, expressed by the
Clauser-Horne-Shimony-Holt (CHSH) inequality, is studied. It is demonstrated
that the effect of geometric phase can be balanced by an appropriate change of
Bell angles.Comment: 17 pages, 9 figure
Geometric Phase in Entangled Systems: A Single-Neutron Interferometer Experiment
The influence of the geometric phase on a Bell measurement, as proposed by
Bertlmann et al. in [Phys. Rev. A 69, 032112 (2004)], and expressed by the
Clauser-Horne-Shimony-Holt (CHSH) inequality, has been observed for a spin-path
entangled neutron state in an interferometric setup. It is experimentally
demonstrated that the effect of geometric phase can be balanced by a change in
Bell angles. The geometric phase is acquired during a time dependent
interaction with two radio-frequency (rf) fields. Two schemes, polar and
azimuthal adjustment of the Bell angles, are realized and analyzed in detail.
The former scheme, yields a sinusoidal oscillation of the correlation function
S, dependent on the geometric phase, such that it varies in the range between 2
and 2\sqrt{2} and, therefore, always exceeds the boundary value 2 between
quantum mechanic and noncontextual theories. The latter scheme results in a
constant, maximal violation of the Bell-like-CHSH inequality, where S remains
2\sqrt2 for all settings of the geometric phase.Comment: 10 pages 9 figure
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