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Afshin Shafiee

Publications and source records attributed to Afshin Shafiee.

At least 37 records · Page 2Linked to original sources
arXiv2015

On the meaning of locality: the overlapping assumptions

We examine the locality assumption of Bell's theorem in three steps of EPRB experiment. Depending on the context, locality is embodied in the conditions of separability, local causality, factorizability, relativistic causality, and non-contextuality. We show that separability, characterized by the constraint of zero covariance, is equivalent to local causality which leads to factorizability through the measurement process. Factorizability is the conjunction of parameter independence and outcome independence. It is commonly believed that relativistic causality is equivalent to parameter independence, which is satisfied by quantum mechanics. According to our approach, however, this is unjustified due to the second step analysis of EPRB experiment, including the measurement on the first particle. We define non-contextuality based on preparation procedure and measurement process. Preparation-based non-contextuality is an independent assumption, but non-locality within the framework of a separable model can be interpreted as measurement-based contextuality. Finally, we show that any fundamental theory consistent with quantum mechanics, should refute outcome independence in its framework of description.

quant-ph↗
arXiv2014

Emergence of molecular chirality due to chiral interactions in a biological environment

We explore the interplay between tunneling process and chiral interactions in the discrimination of chiral states for an ensemble of molecules in a biological environment. Each molecule is described by an asymmetric double-well potential and the environment is modeled as a bath of harmonic oscillators. We carefully analyze different time-scales appearing in the resulting master equation at both weak- and strong-coupling limits. The corresponding results are accompanied by a set of coupled differential equations characterizing optical activity of the molecules. We show that, at the weak-coupling limit, chiral interactions prohibit the coherent racemization induced by decoherence effects and thus preserve the initial chiral state. At the strong-coupling limit, considering the memory effects of the environment, Markovian behavior is observed at long times.

q-bio.BM↗
arXiv2013

Emergence of Molecular Chirality by Vibrational Raman Scattering

In this study, we apply the monitoring master equation describing decoherence of internal states to an optically active molecule prepared in a coherent superposition of nondegenerate internal states interacting with thermal photons at low temperatures. We use vibrational Raman scattering theory up to the first chiral-sensitive contribution, i.e., the mixed electric-magnetic interaction, to obtain scattering amplitudes in terms of molecular polarizability tensors. The resulting density matrix is used to obtain elastic decoherence rates.

quant-ph↗
arXiv2012

Decoherence Effects on Superpositions of Chiral States in a Chiral Molecule

The superposition of chiral states of chiral molecules, as delocalized quantum states of a many-particle system, can be used for the experimental investigations of decoherence theory. In this regard, a great challenge is the precise quantification of the robustness of these superpositions against environmental effects. The methods so far proposed need the detailed specification of the internal states of the molecule, usually requiring heavy numerical calculations. Here, by using the linearized quantum Boltzmann equation and by borrowing ideas employed for analyzing other quantum systems, we present a general and simple approach, of large applicability, which can be used to compute the dominant contribution to the decoherence rate for the superpositions of chiral states of chiral molecules, due to environmental scattering.

cond-mat.stat-mech↗
arXiv2012

Optical Activity, Hund Paradox, and Molecular Parity Violation

We study the problem of stability of optical activity, also known as Hund paradox, in a two-dimensional approximation of a double-well potential. We discuss how the introduction of molecular parity violation breaks the symmetry of the potential. By using a dynamical approach, we show how this effect modifies the dynamics and can stabilize the chiral states for some molecules.

physics.chem-ph↗
arXiv2011

Stability of Chiral States, Role of Intermolecular Interactions and Molecular Parity Violation

We study the problem of stability of chiral states, also known as problem of chirality, within the framework of a two-dimensional approximation of a symmetric double-well potential. We show how the symmetry breaking of the potential due to the molecular parity violation can stop the tunneling in a coherent way, accordingly stabilize the chiral states. Then, we use the quantum Brownian motion within a linear Lindblad-type equation to model how the intermolecular interactions make the tunneling incoherent, thus inducing a racemization by dephasing. Finally, we investigate the normal physical conditions where the dephasing racemization does not suppress the effects of the molecular parity violation, accordingly the molecular parity violation may be observed experimentally.

physics.chem-ph↗
arXiv2011

On A New Formulation of Micro-phenomena: Basic Principles, Stationary Fields And Beyond

In a series of essays, beginning with this article, we are going to develop a new formulation of micro-phenomena based on the principles of reality and causality. The new theory provides with us a new depiction of micro-phenomena assuming an unified concept of information, matter and energy. So, we suppose that in a definite micro-physical context (including other interacting particles), each particle is enfolded by a probability field whose existence is contingent upon the existence of the particle, but it can locally affect the physical status of the particle in a context-dependent manner. The dynamics of the whole particle-field system obeys deterministic equations in a manner that when the particle is subjected to a conservative force, the field also experiences a conservative complex force which its form is determined by the dynamics of particle. So, the field is endowed with a given amount of energy, but its value is contingent upon the physical conditions the particle is subjected to. Based on the energy balance of the particle and its associated field, we argue why the field has a probabilistic objective nature. In such a way, the basic elements of this new formulation, its application for some stationary states and its nonlinear generalization for conservative systems are discussed here.

quant-ph↗
arXiv2011

Comparison between Decoherence time for a Two-state Spin 1/2 System with Its Corresponding Quantum Retrieval Period

We consider the evolution of a two-state quantum system (a spin 1/2 particle) in both the framework of standard quantum mechanics and under the decoherence regime. The former approach on this issue is the well-known quantum flipping process of a dichotomic system subjected to a time-dependent magnetic field. In the latter approach, utilizing the Spin-Boson model to describe the interaction of system with its environment, we derive the Born-Markov master equation to obtain the decoherence time. It is possible to show that under some legitimate conditions, one may find a potential conflict between the predictions of decoherence theory and the result observed in a typical quantum flipping experiment.

quant-ph↗
arXiv2009

On A New Formulation of Micro-phenomena: Quantum Paradoxes And the Measurement Problem

As a serious attempt for constructing a new foundation for describing micro-incidents from a local causal standpoint, I explained before that each micro-entity can be assumed to be composed of a probability field joined to a particle (called a particle-field or PF system) which is endowed with energy, having an objective character. In this essay, some odd quantum phenomena including the tunneling effect, the measurement problem and the EPR theorem are reexamined in detail from the standpoint of the new theory.

quant-ph↗
arXiv2008

On A New Formulation of Micro-phenomena: The Double-slit Experiment

Based on the novel view that a micro-entity could be considered as a particle associated with a field partaking of the energy of particle which are both described by deterministic causal equations of motion, we examine the success of our new theory in elucidating the underlying physics of the double-slit experiment. Here, we explain with clear details how each micro-particle scatters from one of the slits at a given time. After the scattering through one of the slits, the particle shares some of its energy with its surrounding field and a particle-field system is again formed which its motion is governed by a deterministic dynamics during its flight towards the detecting screen. The interference pattern is then explained by showing how the final location of each particle-field system at the time of reaching the detecting screen is distributed according to an angular distribution (equal to the what quantum theory predicts for the fringe effects in a two-slit experiment). The probabilistic nature of such a distribution can be explained by considering the variations of the kinetic energy of the particle-field system at different local situations.

quant-ph↗
arXiv2007

On the relationship between entropy and information

In this paper, we analyze the relationship between entropy and information in the context of the mixing process of two identical ideal gases. We will argue that entropy has a special information-based feature that is enfolded in the statistical entropy, but the second law does not include it directly. Therefore, in some given processes in thermodynamics where there is no matter and energy interaction between the system and environment, the state of the system may go towards a situation of lower probability to increase observer's information in environment. This is a kind of an information-based interaction in which the total entropy is not constrained by the second law.

quant-ph↗
arXiv2007

On The Significance of Which-Way Expositions: Propounding a New Possibility

In this article, we survey some controversial problems concerning the idea of erasing Which Way information proposed in recent years. A statistical examination of these proposals suggests that whenever the Bayesian rule is taken into account for two relevant events in two successive times, the probabilistic description of them is unavoidably time-symmetric. Consequently, it seems that they cannot fulfill the implications of a so-called delayed-choice experiment. As a possible alternative, however, we suggest a new experimental arrangement in which one can change the whole state of a given system at a proper time (without measurement) to accomplish an actual delayed-choice experiment with a time-asymmetric attribute. The peculiar features of this experiment are then discussed.

quant-ph↗
arXiv2005

A GHZ-type proof of Bell's Theorem for A Two-particle Singlet State

For the case of two spin-1/2 particles in the singlet state, we provide a GHZ-type proof of Bell's theorem by using the idea of postselected measurements. Furthermore, we show that in spite of the low efficiency of the detectors one can derive an inequality in the case of real experiments which is violated by quantum mechanics.

quant-ph↗
arXiv2005

Information and The Brukner-Zeilinger Interpretation of Quantum Mechanics: A Critical Investigation

In Brukner and Zeilinger's interpretation of quantum mechanics, information is introduced as the most fundamental notion and the finiteness of information is considered as an essential feature of quantum systems. They also define a new measure of information which is inherently different from the Shannon information and try to show that the latter is not useful in defining the information content in a quantum object. Here, we show that there are serious problems in their approach which make their efforts unsatisfactory. The finiteness of information does not explain how objective results appear in experiments and what an instantaneous change in the so-called information vector (or catalog of knowledge) really means during the measurement. On the other hand, Brukner and Zeilinger's definition of a new measure of information may lose its significance, when the spin measurement of an elementary system is treated realistically. Hence, the sum of the individual measures of information may not be a conserved value in real experiments.

quant-ph↗
arXiv2005

On The Relevance Of Fair Sampling Assumption In The Recent Bell Photonic Experiments

In the experimental verification of Bell's inequalities in real photonic experiments, it is generally believed that the so-called fair sampling assumption (which means that a small fraction of results provide a fair statistical sample) has an unavoidable role. Here, we want to show that the interpretation of these experiments could be feasible, if some different alternative assumptions other than the fair sampling were used. For this purpose, we derive an efficient Bell-type inequality which is a CHSH-type inequality in real experiments. Quantum mechanics violates our proposed inequality, independent of the detection-efficiency problems.

quant-ph↗
arXiv2004

Complete Correlation, Detection loophole and Bell's Theorem

Two new formulations of Bell's theorem are given here. First, we consider a definite set of two entangled photons with only two polarization directions, for which Bell's locality assumption is violated for the case of perfect correlation. Then, using a different approach, we prove an efficient Bell-type inequality which is violated by some quantum mechanical predictions, independent of the efficiency factors.

quant-ph↗
arXiv2002

Bell's Theorem and Chemical Potential

Chemical potential is a property which involves the effect of interaction between the components of a system, and it results from the whole system. In this paper, we argue that for two particles which have interacted via their spins and are now spatially separated, the so-called Bell's locality condition implies that the chemical potential of each particle is an individual property. Here is a point where quantum statistical mechanics and the local hidden variable theories are in conflict. Based on two distinct concepts of chemical potential, the two theories predict two different patterns for the energy levels of a system of two entangled particles. In this manner, we show how one can distinguish the non-separable features of a two-particle system.

quant-ph↗