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A defining signature of classical systems is “in principle measurability” without disturbance: a feature manifestly violated by quantum systems. We describe a multi-interferometer experimental setup that can, in principle, reveal the nonclassicality of a spatial superposition-sourced gravitational field if an irreducible disturbance is caused by a...

We theoretically formulate and experimentally demonstrate a secure scheme for semi-device-independent quantum random number generation by utilizing Leggett-Garg inequality violations, within a loophole-free photonic architecture. The quantification of the generated randomness is rigorously estimated by analytical as well as numerical approaches, bo...

We focus on characterising entanglement of high-dimensional bipartite states using various statistical correlators for two-qudit mixed states. The salient results obtained are as follows: (a) A scheme for determining the entanglement measure given by negativity is explored by analytically relating it to the widely used statistical correlators, viz....

A comprehensive treatment of the quantification of randomness certified device-independently by using the Hardy and Cabello-Liang-Li (CLL) nonlocality relations is provided in the two parties – two measurements per party – two outcomes per measurement (2-2-2) scenario. For the Hardy nonlocality, it is revealed that for a given amount of nonlocality...

The search for empirical schemes to evidence the nonclassicality of large masses is a central quest of current research. However, practical schemes to witness the irreducible quantumness of an arbitrarily large mass are still lacking. To this end, we incorporate crucial modifications to the standard tools for probing the quantum violation of the pi...

An open challenge in physics is to expand the frontiers of the validity of quantum mechanics by evidencing nonclassicality of the center of mass state of a macroscopic object. Yet another equally important task is to evidence the essential nonclassicality of the interactions which act between macroscopic objects. Here we introduce a new tool to mee...

It has recently been argued that among the various suggested measures of tripartite entanglement, the two particular measures, viz. the Concurrence Fill and the Genuine Multipartite Concurrence are the only 'genuine' tripartite entanglement measures based on certain suitably specified criteria. In this context, we show that these two genuine tripar...

The quantum superposition principle implies that a particle entering an interferometer evolves by simultaneously taking both arms. If a non-destructive, minimally-disturbing interaction coupling a particle property to a pointer is implemented on each arm while maintaining the path superposition, quantum theory predicts that, for a fixed state measu...

A defining signature of classical systems is their noninvasive measurability: a feature manifestly violated by quantum systems. We show that this can be used to test the non-classicality of the gravitational field (curvature) generated by a source in quantum superposition. To this end, we describe a multi-interferometer experimental setup that can,...

Distinct from Bell's approach, Wigner derived a form of local realist (LR) inequality which is quantum-mechanically violated for a bipartite maximally entangled state. Subsequently, this approach was generalized to obtain a multipartite LR inequality. However, the violation of such a generalized Wigner inequality does not guarantee nonlocality betw...

Search for empirically implementable schemes that can evidence the nonclassicality of large masses is a quest currently attracting considerable research. Motivated by this, we investigate the quantum violation of the pivotal classical notion of macrorealism (MR) for arbitrary masses in a harmonic potential. To this end, we use two standard tools fo...

How best one can recycle a given quantum resource, mitigating the various difficulties involved in its preparation and preservation, is of considerable importance for ensuring efficient applications in quantum technology. Here, we demonstrate quantitatively the resource-theoretic advantage of reusing a single copy of a two-qubit entangled state tow...

Evidencing the quantum nature of gravity through the entanglement of two masses has recently been proposed. Proposals using qubits to witness this entanglement can afford to bring two masses close enough so that the complete 1/r interaction is at play (as opposed to its second-order Taylor expansion), and micron-sized masses separated by 10-100 mic...

Distinct from Bell's approach, Wigner had derived a form of local realist (LR) inequality which is quantum mechanically violated for a bipartite maximally entangled state. Subsequently, this approach was generalized to obtain a multipartite LR inequality. However, the violation of such generalised Wigner's inequality does not signify what has been...

The quantum superposition principle implies that a particle entering an interferometer evolves by simultaneously taking both arms. If a non-destructive, minimally-disturbing interaction coupling a particle property to a pointer is implemented on each arm while maintaining the path superposition, quantum theory predicts that, for a fixed state measu...

We focus on characterizing entanglement of high dimensional bipartite states using various statistical correlators for two-qudit mixed states. The salient results obtained are as follows: (a) A scheme for determining the entanglement measure given by Negativity is explored by analytically relating it to the widely used statistical correlators viz....

How best one can recycle a given quantum resource, mitigating the various difficulties involved in its preparation and preservation, is of considerable importance for ensuring efficient applications in quantum technology. Here we demonstrate quantitatively the resource theoretic advantage of reusing the single copy of a two-qubit entangled state to...

An open challenge in physics is to expand the frontiers of the validity of quantum mechanics by evidencing nonclassicality of the centre of mass state of a macroscopic object. Yet another equally important task is to evidence the essential nonclassicality of the interactions which act between macroscopic objects. Here we introduce a new tool to mee...

We show unambiguous violations of different macrorealist inequalities, like the LGI and the WLGI using a heralded, single-photon based experimental setup comprising one Mach-Zehnder interferometer followed by a displaced Sagnac one. The negative result measurements (NRM) are implemented in order to validate the presumption of non-invasive measurabi...

We explore the relationship between randomness and nonlocality based on arguments which demonstrate nonlocality without requiring Bell-type inequalities, such as using Hardy relations and its variant like Cabello-Liang (CL) relations. We first clarify the way these relations enable certification of Genuine Randomness (GR) based on the No-signalling...

In a very recent work [arXiv:2004.07451], Kim et al claimed to have made the first genuine experimental observation of the Quantum Cheshire Cat effect. We dispute this claim on the ground that the setup employed is not adequate for making the weak measurements that define this interferometric effect. Half of the necessary weak values are not observ...

A scheme for characterizing entanglement using the statistical measure of correlation given by the Pearson correlation coefficient (PCC) was recently suggested that has remained unexplored beyond the qubit case. Towards the application of this scheme for the high-dimensional states, a key step has been taken in a very recent work by experimentally...

Random access code (RAC) is a strategy to access remote data even if one has limited information about it. We derive here the conditions for the optimal performance of two most basic RAC protocols implemented using two-qubit states. The conditions derived are valid for any set of decoding operations. This allows a meaningful comparison between quan...

Given a non-maximally entangled state, an operationally significant question is to quantitatively assess as to what extent the state is away from the maximally entangled state, which is of importance in evaluating the efficacy of the state for its various uses as a resource. It is this question which is examined in this paper for two-qubit pure ent...

We investigate quantum violation of macrorealism for multilevel spin systems under the condition of coars-ening of measurement times-i.e., when measurement times have experimental indeterminacy. This is studied together with the effect of coarsening of measurement outcomes for which individual outcomes cannot be unam-biguously discriminated. In our...

A scheme for characterizing entanglement using the statistical measure of correlation given by the Pearson correlation coefficient (PCC) was recently suggested that has remained unexplored beyond the qubit case. Towards the application of this scheme for the high dimensional states, a key step has been taken in a very recent work by experimentally...

Given a non-maximally entangled state, an operationally significant question is to quantitatively assess as to what extent the state is away from the maximally entangled state, which is of importance in evaluating the efficacy of the state for its various uses as a resource. It is this question which is examined in this paper for two-qubit pure ent...

Given a non-maximally entangled state, an operationally significant question is to quantitatively assess as to what extent the state is away from the maximally entangled state, which is of importance in evaluating the efficacy of the state for its various uses as a resource. It is this question which is examined in this paper for two-qubit pure ent...

In recent years, exploration of the possible use of separable states as a resource to achieve quantum information processing (QIP) tasks has been gaining increasing significance. In this context, a particularly important demonstration has been that nonvanishing discord is the necessary condition for separable states to be used as a resource for rem...

The present work is motivated by the question what aspect of correlation entailed by the two-qubit state serves as the appropriate quantitative resource for steering. To this end, considering Bell-diagonal states, suitable measures of simultaneous correlations in two and three complementary (mutually unbiased) bases are identified as the relevant r...

In recent years, exploring the possible use of separable states as resource for achieving quantum information processing(QIP) tasks has been gaining increasing significance. In this context, a particularly important demonstration has been that non-vanishing discord is the necessary condition for the separable states to be used as resource for remot...

Can the most “classical-like” of all quantum states, namely the Schrödinger coherent state of a harmonic oscillator, exhibit nonclassical behavior? We find that for an oscillating object initially in a coherent state, merely by observing at various instants which spatial region the object is in, the Leggett-Garg inequality (LGI) can be violated thr...

A hitherto unnoticed feature of quantum steering is demonstrated, namely that, while entanglement is necessary for steering, higher degree of entanglement does not necessarily imply higher degree of quantum steering. This leads to the question as to what aspect of correlation entailed by the quantum state serves as the appropriate quantitative reso...

Generalized quantum measurements with two outcomes are fully characterized by two real parameters, dubbed as sharpness parameter and biasedness parameter and they can be linked with different aspects of the experimental setup. It is known that sharpness parameter characterizes precision of the measurements and decreasing sharpness parameter of the...

We consider quantum steering by non-Gaussian entangled states. The Reid steering criterion based on the Heisenberg uncertainty relation fails to detect steerability for many categories of such states. Here, we derive a tighter steering criterion using the Robertson-Schr\"{o}dinger uncertainty relation. We show that our steering condition is able to...

We consider quantum steering by non-Gaussian entangled states. The Reid steering criterion based on the Heisenberg uncertainty relation fails to detect steerability for many categories of such states. Here, we derive a tighter steering criterion using the Robertson-Schr\"{o}dinger uncertainty relation. We show that our steering condition is able to...

Distinct from the type of local realist inequality (known as the Collins–Gisin–Linden–Massar–Popescu or CGLMP inequality) usually used for bipartite qutrit systems, we formulate a new set of local realist inequalities for bipartite qutrits by generalizing Wigner’s argument that was originally formulated for the bipartite qubit singlet state. This t...

Generalised quantum measurements with two outcomes are fully characterised by two real parameters, dubbed as sharpness parameter and biasedness parameter and they can be linked with different aspects of the experimental setup. It is known that precision of measurements, characterised by the sharpness parameter of the measurements, reduces the possi...

Prima facie, there are good reasons to answer in the negative the question posed in the title: the Bennett–Brassard 1984 (BB84) protocol is provably secure subject to the assumption of trusted devices, while the Leggett–Garg-type inequality (LGI) does not seem to be readily adaptable to the device independent (DI) or semi-DI scenario. Nevertheless,...

For multilevel spin systems, robustness of the quantum mechanical (QM) violation of macrorealism (MR) with respect to coarse grained measurements is investigated using three different necessary conditions of MR, namely, the Leggett-Garg inequality (LGI), Wigner's form of the Leggett-Garg inequality (WLGI) and the condition of no-signalling in time...

The hitherto unexplored nonlocality of quantum correlations in the information transfer protocol of remote state preparation (RSP) is investigated in terms of a unified nonlocality argument formulated for teleportation as well as for two distinct RSP schemes. The argument differs only in the respective types of local measurements used in each scena...

Distinct from the type of local realist inequality (known as the Collins-Gisin-Linden-Massar-Popescu or CGLMP inequality) usually used for bipartite qutrit systems, we formulate a new set of local realist inequalities for bipartite qutrits by generalizing Wigner's argument that was originally formulated for the bipartite qubit singlet state. This t...

We address the recently posed question as to whether the nonlocality of a single member of an entangled pair of spin 1 / 2 particles can be shared among multiple observers on the other wing who act sequentially and independently of each other. We first show that the optimality condition for the trade-off between information gain and disturbance in...

We address the recently posed question as to whether the nonlocality of a single member of an entangled pair of spin $1/2$ particles can be shared among multiple observers on the other wing who act sequentially and independently of each other [1]. We first show that the optimality condition for the trade-off between information gain and disturbance...

For multilevel spin systems, robustness of the quantum mechanical (QM) violation of macrorealism (MR) with respect to coarse grained measurements is investigated using three different necessary conditions of MR, namely, the Leggett-Garg inequality (LGI), Wigner's form of the Leggett-Garg inequality (WLGI) and the condition of no-signalling in time...

Experimental test of dualism in the entangled state of two identical particles using the modification of a Bell-state apparatus.

In the weak measurement (WM) scenario involving weak interaction and postselection by projective measurement, the empirical significance of weak values is manifested in terms of shifts in the measurement pointer's mean position and mean momentum. In this context, a general quantitative treatment is presented in this paper by taking into account the...

We study the effect of quantum statistics on the arrival time distribution of quantum particles computed through the probability current density. It is shown that symmetrization or asymmetrization of the wave function affects the arrival time distribution for even freely propagating particles. In order to investigate the effect of statistics on the...

Temporal steering and violation of the Leggett-Garg inequality are two different ways of probing the violation of macro-realistic assumptions in quantum mechanics. It is shown here that under unitary evolution and projective measurements the two types of temporal correlations lead to similar results. However, their inequivalence may be exhibited...

The Leggett-Garg inequality (LGI), based on the notions of realism and noninvasive measurability, is applied in the context of a linear harmonic oscillator. It is found that merely through observing at various instants which region of the potential well, the oscillating quantum object is in, the LGI can be violated without taking recourse to any an...

We explore the use of the resource of intra-particle entanglement for secure quantum key distribution in the device-independent scenario. By virtue of the local nature of such entanglement, Bell tests must be implemented locally, which leads to a natural decoupling of device errors from channel errors. We consider a side-channel attack on the sende...

We show how a property of dualism, which can exist in the entanglement of identical particles, can be tested in the usual photonic Bell measurement apparatus with minor modifications. Two different sets of coincidence measurements on the same experimental setup consisting of a Hong-Ou-Mandel interferometer demonstrate how the same two-photon state...

Using Wigner's form of local realist inequality, its temporal version for a single two-level system involving two-time joint probabilities is derived as a novel form of the Leggett-Garg inequality (LGI). The robustness of its quantum mechanical (QM) violation against unsharpness of measurement is investigated. It is found that there exists a range...

We explore the use of the resource of intra-particle entanglement for secure quantum key distribution in the device-independent scenario. By virtue of the local nature of such entanglement, Bell tests must be implemented locally, which leads to a natural decoupling of device errors from channel errors. We consider a side channel attack on the sende...

Wigner's argument inferring Bell-type inequality for the EPR-Bohm entangled state is generalized here for any N-partite state. This is based on assuming for the relevant dichotomic observables the existence of the overall joint probability distributions, satisfying the locality condition, that would yield the measurable marginal probabilities. For...

The hybrid Unsteady Reynolds-Averaged Navier–Stokes (URANS)/Large Eddy Simulation (LES) methodology was used to investigate the flow dynamics and associated gap vortex structure in compound rectangular channels for isothermal flows. The specific form of the hybrid URANS/LES approach that was used is the Strelets (2001) version of the Shear Stress T...

The Bell-type (spatial), Kochen-Specker (contextuality) or Leggett-Garg (temporal) inequalities are based on classically plausible but otherwise quite distinct assumptions. For any of these inequalities, satisfaction is equivalent to a joint probability distribution for all observables in the experiment. This implies a joint distribution for all pa...

Nonlocality is generally deemed necessary to ensure security of quantum key distribution (QKD) in the device-independent (DI) scenario. We show that some progress can be made towards DI-QKD without invoking nonlocality, via violation of the Leggett-Garg inequality (LGI) by using temporal correlations of a single qubit, which is a novel application...

In this article, after briefly providing the pertinent historical background, the underlying motivation and essence of Bohr’s idea of wave-particle complementarity are explained. To what extent the Bohrian notion of complementarity is relevant in the modern context is discussed. Bohr’s belief in the generality of the complementarity framework is al...

The Leggett-Garg inequality (LGI) as a temporal analogue of Bell's inequality, derived using the notion of realism, is applied in a hitherto unexplored context involving the weak interaction induced two-state oscillations of decaying neutral kaons and neutrinos. The maximum violation of LGI obtained from the quantum mechanical results is significan...

We provide a careful analysis of the proper significance of Riahi's comment in light of our paper (2009 J. Phys. A: Math. Theor. 42 165302). We point out a fundamental difference between the quantum–classical correspondence scheme considered in our paper and that used in Riahi's comment.

We point out an earlier unnoticed implication of quantum indistinguishability, namely, a property which we call `dualism' that characterizes the entanglement of two identical particles (say, two ions of the same species) -- a feature which is absent in the entanglement of two non-identical particles (say, two ions of different species). A crucial a...

We point out an earlier unnoticed implication of quantum indistinguishability, namely, a property which we call “dualism” that characterizes the entanglement of two identical particles (say, two ions of the same species)—a feature which is absent in the entanglement of two nonidentical particles (say, two ions of different species). A crucial appli...

For a spin-polarized plane wave passing through a spin-rotator containing uniform magnetic field, we provide a detailed analysis for solving the appropriate Schrödinger equation. A modified expression for spin precession is obtained which reduces to the standard Larmor precession relation when kinetic energy is very large compared to the spin-magne...

Predictive power of the no-signalling condition (NSC) is demonstrated in a testable situation involving a non-ideal Stern-Gerlach (SG) device in one of the two wings of the EPR-Bohm entangled pairs. In this wing, for two types of measurement in the other wing, we consider the spin state of a selected set of particles that are confined to a particul...

An analytical treatment of a propagating wavepacket incident on a transient barrier reveals an effect in which, for a particular time interval, the time-varying transmission probability exceeds that for the free propagation of the wavepacket. We show that this effect can be interpreted semiclassically. This effect is quantified and it is shown that...

We study quantum teleportation with the resource of non-orthogonal qubit states. We first extend the standard teleportation protocol to the case of such states. We investigate how the loss of teleportation fidelity resulting for the use of non-orthogonal states compares to a similar loss of fidelity when noisy or non-maximally entangled states as u...

The state-independent quantum violation of non-contextual realist models has been demonstrated both theoretically and experimentally for any two-qubit state using suitable choices of nine product observables and six different measurement setups. In this paper, for the separable states, a considerable simplification of such a demonstration is achiev...

A setup that entails nonuniqueness in the quantum prediction of the arrival/transit time distribution is analysed using the Bohmian model, implying the plausibility of two distinct calculational schemes having empirically distinguishable predictions. One of them agrees with the results obtained from the probability current density based approach th...

The weak equivalence principle of gravity is examined at the quantum level in two ways. First, the position detection probabilities of particles described by a non-Gaussian wave-packet projected upwards against gravity around the classical turning point and also around the point of initial projection are calculated. These probabilities exhibit mass...

A scheme is formulated for testing nonlocality of single photons by considering the state of a single photon that could be located within one of two spatially separated cavities. The outcomes of four experiments on this state involving the resonant interactions of two-level atoms with these cavities and a couple of other auxiliary ones is shown to...

In this paper, we describe how it is possible to verify the quantum statistics of identical particles prepared in distinguishable internal states without ever bringing these particles to the same internal state. Examples are given for two, three and four identical particles prepared in two, three or four distinct states, respectively. We show that...

Scitation is the online home of leading journals and conference proceedings from AIP Publishing and AIP Member Societies

In recent times, there is an upsurge of interest in demonstrating the quantum contextuality. In this proceedings, we explore the two different forms of arguments that have been used for showing the contextual character of quantum mechanics. First line of study concerns the violations of the noncontextual realist models by quantum mechanics, where s...

Based on a scheme that produces pure entanglement between the spin and the path variables of a single spin-1∕2 particle (qubit) using a beam-splitter and a spin flipper, we formulate a procedure for transferring this intraparticle hybrid entanglement to an interparticle pure entanglement between the spin variables of two other spatially separated s...

Leggett-type nonlocal realist inequalities that have been derived to date are all contingent upon suitable geometrical constraints to be strictly satisfied by the spatial arrangement of the relevant measurement settings. This undesirable restriction is removed in the present work by deriving appropriate forms of nonlocal realist inequalities, one o...

We propose the use of intra-particle entanglement to enhance the security of a practical implementation of the Bennett-Brassard-1984 (BB84) quantum key distribution scheme. Intra-particle entanglement is an attractive resource since it can be easily generated using only linear optics. Security is studied under a simple model of incoherent attack fo...

In this work, we present a quantum key distribution scheme which exploits quantum mechanical violation of non-contextuality for checking the security of the protocol. In this scheme the sender encodes the key using path-spin intraparticle entanglement of a single particle. The receiver decodes the information using a combination of beam splitters a...

An analytical treatment of a propagating wave packet incident on a transient barrier reveals a counterintuitive quantum mechanical effect in which, for a particular time interval, the time-varying transmission probability {\it exceeds} (`superarrival') that for the free propagation of the wave packet. It is found that the speed with which the infor...

The present article focuses on studying the extent to which the nonuniqueness that is inherent in the standard quantum mechanical calculation of arrival/transit time distribution can be exploited to enable an empirical scrutiny of any causal trajectory model such as the Bohmian scheme. For this purpose, we consider the example of spin-1/2 neutral p...

A scheme is formulated for testing nonlocality of single photons by considering the state of a single photon that could be located within one of two spatially separated cavities. The outcomes of four experiments on this state involving the resonant interactions of two-level atoms with these cavities and a couple of other auxiliary ones is shown to...

Using measurements pertaining to a suitable Mach-Zehnder(MZ) type setup, a curious quantum mechanical effect of contextuality between the path and the polarization degrees of freedom of a polarized photon is demonstrated, without using any notion of realism or hidden variables - an effect that holds good for the product as well as the entangled sta...

In this reply, we point out that the claim by De Zela (2010) [2] is unjustified because the setup he discusses is not equivalent to the setup analysed in our paper (Pan and Home (2009) [1]). Hence his subsequent argument claiming the reproducibility of our demonstrated quantum effect of path-spin contextuality by the Kochen–Specker realist model is...

In this reply, we point out that the claim by De Zela[2] is unjustified because the setup he discusses is \emph{not} equivalent to the setup analysed in our paper[1]. Hence his subsequent argument claiming the reproducibility of our demonstrated quantum effect of path-spin contextuality by the Kochen-Specker realist model is \emph{not} relevant.

The path-spin entangled state of a single spin-1/2 particle is considered which is generated by using a beam-spitter and a spin-flipper. Using this hybrid entanglement at the level of a single particle as a resource, we formulate a protocol for transferring of the state of an unknown qubit to a distant location. Our scheme is implemented by a seque...

Based on a scheme that produces an entanglement between the spin and the path variables of a single spin-1/2 particle (qubit) using a beam-splitter and a spin-flipper, we formulate a procedure for transferring this intraparticle hybrid entanglement to an interparticle entanglement between the spin variables of two other spatially separated spin-1/2...

For spin-1/2 particles, using a suitable Mach-Zehnder-type setup with a spin-flipper, we argue that it is a direct consequence of the quantum mechanical treatment that an experimentally verifiable \textit{subensemble} mean of the measured values of an arbitrarily chosen spin variable exhibits dependence on the choice of a comeasurable `path' observ...

An unsteady Reynolds Averaged Navier–Stokes (URANS) based turbulence model, the Spalart–Allmaras (SA) model, was used to investigate the flow pulsation phenomena in compound rectangular channels for isothermal flows. The studied geometry was composed of two rectangular sub-channels connected by a gap, on which experiments were conducted by Meyer an...

Recently, a striking experimental demonstration [G. Kirchmair \emph{et al.}, Nature, \textbf{460}, 494(2009)] of the state-independent quantum mechanical violation of non-contextual realist models has been reported for any two-qubit state using suitable choices of \emph{nine} product observables and \emph{six} different measurement setups. In this...

The classical limit problem of quantum mechanics is revisited on the basis of a scheme that enables a quantitative study of the way the quantum-classical agreement emerges while going through the intermediate mass range between the microscopic and the macroscopic domains. As a specific application of such a scheme, we investigate the classical limi...

By sending a classical two-level system, one can transfer information about only \emph{two} distinguishable outcomes. Here we show that in quantum mechanics, using both the spin and path degrees of freedom of a spin-1/2 particle, and a Mach-Zehnder type interferometric arrangement with two suitable Stern-Gerlach detectors, it is possible to transfe...

On the basis of a variant of the EPR-Bohm example, we show that the no-signaling condition can be employed as a useful tool for deriving a constraint on a suitably defined measure of the `nonidealness' of a Stern-Gerlach(SG) setup. In this demonstration, a key ingredient is provided by the characteristics of the exact solution of the time-dependent...

This work discusses simulations using the detached eddy simulation based (DES) turbulence model to investigate turbulent channel flows. Applicability of Strelets' (2001) version of the DES model was tested for a fully developed turbulent channel flow problem in a rectangular duct. The unsteady Navier-Stokes equations were solved numerically at Reyn...

Einstein's Struggles with Quantum Theory: A Reappraisal by Dipankar Home and Andrew Whitaker provides a detailed account of Albert Einstein's thinking in regard to quantum physics. Until recently, most of Einstein's views on quantum physics were dismissed and even ridiculed; some critics even suggested that Einstein was not able to grasp the comple...

The logical foundations of Bell's inequality are reexamined. We argue that the form of the reality condition that underpins Bell's inequality comes from the requirement of solving the quantum measurement problem. Hence any violation of Bell's inequality necessarily implies nonlocality because of the measurement problem. The differences in the impli...