The descriptions of the quantum realm and the macroscopic classical world di�er signi
�cantly not only in their mathematical formulations, but also in their foundational concepts
and philosophical consequences. The assumptions of local realism, non-contextuality
and macroscopic realism (macro-realism) along with the quantum mechanical violations
of these assumptions are discussed.
A complete generalization is provided of Wigner's argument inferring quantum nonlocality,
originally restricted for the EPR-Bohm entangled state, based on assuming joint
probability distributions for all the relevant dichotomic observables. Such Generalized
Wigner Inequality (GWI) turns out to be the N-partite local realist inequality which is
violated by quantum mechanics for all pure entangled states for any N.
We then exploit the non-trivial manifestation of quantum non-locality via local contextuality
on three qubit system. Here, we propose an experimental scheme to realize this
feature by deriving a new local realist inequality. The way quantum entanglement can
be used for global contextual value assigning is discussed in a quantum pseudo-telepathy
game.
In the second part of this report, we formulate Leggett-Garg inequality (LGI) in terms
of joint probability and demonstrate its quantum mechanical violation for two state oscillation,
which is initial state dependent, unlike the case of standard LGI. It has been
shown that, the newly formulated LGI reveals robustness against unsharp measurement
for testing compatibility between macro-realism and quantum mechanics. Finally we
show that, the recently proposed No-signaling in time condition, contradicts with quantum
mechanical predictions for any degree of unsharpness in measurement.
Abstract We propose a protocol that allows to assess the precise correspondence between thought and practical experiments, a critical point for addressing experimental clumsiness in a test of macro- or micro-realism. Two-time generalized von Neumann measurements of properties <?CDATA
A?> A and <?CDATA
B?> B are shown to obey the so-called no-signaling in time condition for initial states defined as an incoherent sum of eigenstates of <?CDATA
A?> A . An experiment for witnessing the use of this type of measurements in the laboratory is then devised by proving the existence of five conditions that have to be fulfilled by any generalized von Neumann measurement. Ensuring the use of this type of measurements and then testing the no-signaling in time condition for a range of system-meter coupling strengths allows to test realism in a highly reproducible manner and to critically narrow the so-called clumsiness loophole. The resulting protocol is applicable to general (not only dichotomic) variables, and it is employed to show, both analytically for general systems and numerically for a collection of harmonic oscillators, that quantum systems made of a large number of uncorrelated particles are genuinely macrorealist, i.e., realistic with respect to all intensive properties at any time.
In recent years parametric-down-conversion photon sources have been proposed and used to test local realism via Bell-type inequalities. This study shows that this technique fails to discriminate between quantum mechanics and local realism in all those tests in which polarization correlations are measured, since dichotomic observables cannot be associated satisfactorily with the state produced in these experiments. A more adequate description of these photon sources leads to an alternative inequality for Einstein locality, which is always satisfied by quantum-mechanical predictions. The result can be extended to all the experiments in which only one-half of the emitted pairs are detected.