arXiv subjects

S. Dumitru

Publications and source records attributed to S. Dumitru.

11 recordsLinked to original sources

arXiv2008

On the measurements regarding random observables

Both classical and respectively quantum observables can be modeled as somewhat similar examples of random variables. In such a model the associated measurements preserve the values spectrum of an observable but change the corresponding probabilistic weights (probability density or respectively the wave function). Such a model ensures theoretical estimations for predicted errors specific to the mean values as well as to the fluctuations of both types of observables. The model stands out of ourdays prevalent opinion that measurement theories must be depicted in entirely different manners in the classical respectively quantum cases.

cond-mat.stat-mech↗

arXiv2008

First order phase transitions in nanoscopic systems

The problem of first order phase transitions in nanoscopic systems is investigated in the framework of Hill's nanothermodynamics. We obtain the equilibrium conditions and a generalized version of the Clapeyron-Clausius equation for a nanoscopic system which contains two phases. Our study is exemplified for the case when one of the phases consists of an ideal gas.

cond-mat.stat-mech↗

arXiv2006

A possible general approach regarding the conformability of angular observables with mathematical rules of quantum mechanics

The conformability of angular observales (angular momentum and azimuthal angle) with the mathematical rules of quantum mechanics is a question which still rouses debates. It is valued negatively within the existing approaches which are restricted by two amendable presumptions. If the respective presumptions are removed one can obtain a general approach in which the mentioned question is valued positively.

quant-ph↗

arXiv2005

On the uncertainty relations and quantum measurements: conventionalities, shortcomings, reconsiderations

Unsolved controversies about uncertainty relations and quantum measurements still persists nowadays. They originate around the shortcomings regarding the conventional interpretation of uncertainty relations. Here we show that the respective shortcomings disclose veridic and unavoidable facts which require the abandonment of the mentioned interpretation. So the primitive uncertainty relations appear as being either thought fictions or fluctuations formulae. Subsequently we reveal that the conventional approaches of quantum measurements are grounded on incorrect premises. We propose a new approach in which : (i) the quantum observables are considered as generalized stochastic variables, (ii) the view is focused only on the pre-existent state of the measured system, without any interest for the collapse of the respective state, (iii) a measurement is described as an input-output transformation which modify the probability density and current but preserve the expressions of the operators. The measuring uncertainties are evaluated as changes in the probabilistic estimators of observables. Related to different observables we do not find reasons of principle neither for uncertainties-connections nor for measuring compatibility/incompatibility.

quant-ph↗

arXiv2005

On the number-phase problem

The known approaches of number-phase problem (for a quantum oscillator) are mutually contradictory. All of them are subsequent in respect with the Robertson-Schrödinger uncertainty relation (RSUR). In oposition here it is proposed a new approacch aimed to be aboriginal as regard RSRUR. From the new perspective the Dirac's operators for vibrational number and phase appear as correct mathematical tools while the alluded problem receives a natural solution. PACS codes: 03.65.-w, 03.65.Ca, 03.65.Fd, 03.65.Ta Keywords: quantum oscillator, number and phase, uncertainty relations.

quant-ph↗

arXiv2003

On the uncertainty relations for angular observables and beyond them

For angular observables pairs (angular momentum-angle and number-phase) the adequate reference element of normality is not the Robertson-Schrödinger uncertainty relation but a Schwarz formula regarding the quantum fluctuations. Beyond such a fact the traditional interpretation of the uncertainty relations appears as an unjustified doctrine.

quant-ph↗

arXiv2003

On the quantum measurements from a reconsidered perspective

For theoretical approach of quantum measurements it is proposed a set of reconsidered conjectures. The proposed approach implies linear functional transformations for probability density and current but preserves the expressions for operators of observables. The measuring uncertainties appear as changes in the probabilistic estimators of observables.

quant-ph↗

arXiv2002

On a subject of diverse improvisations: The uncertainty relations on a circle

The disputed question of uncertainty relations (UR) on a circle is regarded as a particular element of a more general problem which refers to the quantum description of angular observables $L_z$ and $ϕ$. The improvised $L_z-ϕ$ UR are found to be affected by unsourmontable shortcomings. Also in contradiction with a largely accepted belief it is proved that the usual procedures of quantum mechanics are accurately applicable for the $L_z-ϕ$ pair. The applicability regards both the known circular motions and the less known non-circular rotational motions. The presented facts contribute as arguments to the following indubitable conclusions: (i) the traditional interpretation of UR must be denied as an incorrect doctrine, (ii) for a natural physical consideration of the the $L_z-ϕ$ pair the results from the usual quantum mechanics are sufficient while the improvised $L_z-ϕ$ UR must be rejected as senseless formulas and (iii) the descriptions of quantum measurements have to be done in a framework which is distinct and additional in respect with the usual quantum mechanics.

quant-ph↗

arXiv2002

A possible new approach of quantum measurements

It is proposed a possible new approach of quantum measurements (QMS), disconnected of the traditional interpretation of uncertainty relations and independent of any appeal to the strange idea of collapse (reduction) of wave functions. The new approach regards QMS as a statistical samplings (but not as simple detection acts) and their description as a distinct task, independent of actual procedures of quantum mechanics. A QMS is described by means of transformations of probability density and probability current, from intrinsic into recorded readings. The quantum observables appear as random variables, described by usual operators and valuable through probabilistic numerical parameters (mean values, correlations and standard deviations). The values of the respective parameters are not the same in the two mentioned readings. Then the measurement uncertainties (errors) are described by means of the changes in the alluded values. The new QMS approach is illustrated through an one-dimensional example.

quant-ph↗

arXiv2002

Higher order correlations for fluctuations in the presence of fields

The higher order moments of the fluctuations for the thermodynamical systems in the presence of fields are investigated in the framework of a theoretical method. The metod uses a generalized statistical ensemble consonant with the adequate expression for the generalized internal energy. The applications refer to the case of a system in magnetoquasistatic field. In the case of linear magnetic media one finds that for the description of the magnetic induction fluctuations the Gaussian approximation is good enough. For nonlinear media the coresponding fluctuations are non-Gaussian, they having a non-null asymmetry. Aditionally the respective fluctuations have characteristics of leptokurtic, mesokurtic and platykurtic type, depending of the value of the magnetic field strength comparatively with a scaling factor of the magnetization curve.

cond-mat.stat-mech↗

arXiv2000

Fluctuations in the presence of fields -Phenomenological Gaussian approximation and a new class of thermodynamic inequalities-

The work approaches the study of the fluctuations for the thermodynamic systems in the presence of the fields. The approach is of phenomenological nature and developed in a Gaussian approximation. The study is exemplified on the cases of a magnetizable continuum in a magnetoquasistatic field, as well as for the so called discrete systems. In the last case one finds that the fluctuations estimators depends both on the intrinsic properties of the system and on the characteristics of the environment. Following some earlier ideas of one of the authors we present a new class of thermodynamic inequalities for the systems investigated in this paper. In the case of two variables the mentioned inequalities are nothing but non-quantum analogues of the well known quantum Heisenberg (''uncertainty'') relations. Also the obtained fluctuations estimators support the idea that the Boltzmann's constant k has the signification of a generic indicator of stochasticity for thermodynamic systems. Pacs number(s): 05.20.-y, 05.40.-a, 05.70.-a, 41.20.Gz

cond-mat.stat-mech↗