7 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
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
The neutron and its role in cosmology and particle physics
Experiments with cold and ultracold neutrons have reached a level of
precision such that problems far beyond the scale of the present Standard Model
of particle physics become accessible to experimental investigation. Due to the
close links between particle physics and cosmology, these studies also permit a
deep look into the very first instances of our universe. First addressed in
this article, both in theory and experiment, is the problem of baryogenesis ...
The question how baryogenesis could have happened is open to experimental
tests, and it turns out that this problem can be curbed by the very stringent
limits on an electric dipole moment of the neutron, a quantity that also has
deep implications for particle physics. Then we discuss the recent spectacular
observation of neutron quantization in the earth's gravitational field and of
resonance transitions between such gravitational energy states. These
measurements, together with new evaluations of neutron scattering data, set new
constraints on deviations from Newton's gravitational law at the picometer
scale. Such deviations are predicted in modern theories with extra-dimensions
that propose unification of the Planck scale with the scale of the Standard
Model ... Another main topic is the weak-interaction parameters in various
fields of physics and astrophysics that must all be derived from measured
neutron decay data. Up to now, about 10 different neutron decay observables
have been measured, much more than needed in the electroweak Standard Model.
This allows various precise tests for new physics beyond the Standard Model,
competing with or surpassing similar tests at high-energy. The review ends with
a discussion of neutron and nuclear data required in the synthesis of the
elements during the "first three minutes" and later on in stellar
nucleosynthesis.Comment: 91 pages, 30 figures, accepted by Reviews of Modern Physic