117 research outputs found
Coherent chemical kinetics as quantum walks II: Radical-pair reactions in Arabidopsis thaliana
We apply the quantum-walk approach recently proposed in
arXiv:quant-ph-1506.04213 to a radical-pair reaction where realistic estimates
for the intermediate transition rates are available. The well-known average
hitting time from quantum walks can be adopted as a measure of how quickly the
reaction occurs and we calculate this for varying degrees of dephasing in the
radical pair. The time for the radical pair to react to a product is found to
be independent of the amount of dephasing introduced, even in the limit of no
dephasing where the transient population dynamics exhibit strong coherent
oscillations. This can be seen to arise from the existence of a rate-limiting
step in the reaction and we argue that in such examples, a purely classical
model based on rate equations can be used for estimating the timescale of the
reaction but not necessarily its population dynamics
Using Explainability for Constrained Matrix Factorization
Explainable Model Black Box (opaque) predictors such as Deep learning and Matrix Factorization are accurate, ... but lack interpretability and ability to give explanations. White Box models such as rules and decision trees are interpretable (explainable), ... but lack accuracy
Logical independence and quantum randomness
We propose a link between logical independence and quantum physics. We
demonstrate that quantum systems in the eigenstates of Pauli group operators
are capable of encoding mathematical axioms and show that Pauli group quantum
measurements are capable of revealing whether or not a given proposition is
logically dependent on the axiomatic system. Whenever a mathematical
proposition is logically independent of the axioms encoded in the measured
state, the measurement associated with the proposition gives random outcomes.
This allows for an experimental test of logical independence. Conversely, it
also allows for an explanation of the probabilities of random outcomes observed
in Pauli group measurements from logical independence without invoking quantum
theory. The axiomatic systems we study can be completed and are therefore not
subject to Goedel's incompleteness theorem.Comment: 9 pages, 4 figures, published version plus additional experimental
appendi
Bell inequality with an arbitrary number of settings and its applications
Based on a geometrical argument introduced by Zukowski, a new multisetting
Bell inequality is derived, for the scenario in which many parties make
measurements on two-level systems. This generalizes and unifies some previous
results. Moreover, a necessary and sufficient condition for the violation of
this inequality is presented. It turns out that the class of non-separable
states which do not admit local realistic description is extended when compared
to the two-setting inequalities. However, supporting the conjecture of Peres,
quantum states with positive partial transposes with respect to all subsystems
do not violate the inequality. Additionally, we follow a general link between
Bell inequalities and communication complexity problems, and present a quantum
protocol linked with the inequality, which outperforms the best classical
protocol.Comment: 8 pages, To appear in Phys. Rev.
Nonclassical trajectories in head-on collisions
Rutherford scattering is usually described by treating the projectile either
classically or as quantum mechanical plane waves. Here we treat them as wave
packets and study their head-on collisions with the stationary target nuclei.
We simulate the quantum dynamics of this one-dimensional system and study
deviations of the average quantum solution from the classical one. These
deviations are traced back to the convexity properties of Coulomb potential.
Finally, we sketch how these theoretical findings could be tested in
experiments looking for the onset of nuclear reactions.Comment: 16 pages, 8 figure
Information complementarity in quantum physics
We demonstrate that the concept of information offers a more complete
description of complementarity than the traditional approach based on
observables. We present the first experimental test of information
complementarity for two-qubit pure states, achieving close agreement with
theory; We also explore the distribution of information in a comprehensive
range of mixed states. Our results highlight the strange and subtle properties
of even the simplest quantum systems: for example, entanglement can be
increased by reducing correlations between two subsystems.Comment: 6 pages, 7 figures (including supplementary material
Local Realism of Macroscopic Correlations
We show that for macroscopic measurements which cannot reveal full
information about microscopic states of the system, the monogamy of Bell
inequality violations present in quantum mechanics implies that practically all
correlations between macroscopic measurements can be described by local
realistic models. Our results hold for sharp measurement and arbitrary closed
quantum systems.Comment: 9 pages incl. one Appendix, 2 figure
Correlation tensor criteria for genuine multiqubit entanglement
We present a development of a geometric approach to entanglement indicators.
The method is applied to detect genuine multiqubit entanglement. The criteria
are given in form of non-linear conditions imposed on correlation tensors. Thus
they involve directly observable quantities, and in some cases require only few
specific measurements to find multiqubit entanglement. The non-linearity of
each of the criteria allows detection of entanglement in wide classes of
states. In contrast to entanglement witnesses, which in the space of Hermitian
operators define a hyperplane, the new conditions define a geometric figure
encapsulating the non-fully entangled states within it.Comment: 8 pages, 1 figure, journal versio
Experimental test of nonlocal realistic theories without the rotational symmetry assumption
We analyze the class of nonlocal realistic theories that was originally
considered by Leggett [Found. Phys. 33, 1469 (2003)] and tested by us in a
recent experiment [Nature (London) 446, 871 (2007)]. We derive an
incompatibility theorem that works for finite numbers of polarizer settings and
that does not require the previously assumed rotational symmetry of the
two-particle correlation functions. The experimentally measured case involves
seven different measurement settings. Using polarization-entangled photon
pairs, we exclude this broader class of nonlocal realistic models by
experimentally violating a new Leggett-type inequality by 80 standard
deviations.Comment: Published versio
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