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R. R. Puri

Publications and source records attributed to R. R. Puri.

8 recordsLinked to original sources
arXiv2014

Quasiprobability Based Criterion for Classicality and Separability of States of Spin-1/2 Particles

A sufficient condition for a quantum state of a system of spin-1/2 particles (spin-1/2s) to admit a local hidden variable (LHV) description i.e. to be classical is the separability of the density matrix characterizing its state, but not all classical states are separable. This leads one to infer that separability and classicality are two different concepts. These concepts are examined here in the framework of a criterion for identifying classicality of a system of spin-1/2s based on the concept of joint quasiprobability (JQP) for the eigevalues of spin components. The said criterion identifies a state as classical if a suitably defined JQP of the eigenvalues of spin components in suitably chosen three or two orthogonal directions is non-negative. In agreement with other approaches, the JQP based criterion leads to the result that all non-factorizable pure states of two spin-1/2s are non-classical. Furthermore, the validity of the criterion is confirmed by comparing its predictions with those arrived at by other methods when applied to several mixed states of two spin-1/2s and the Werner like state of three spin-1/2s (G.Toth and A.Acin,Phys.Rev. A74, 030306(R) (2006)). The JQP based approach, formulated as it is along the lines of the P-function approach for identifying classical states of the electromagnetic field, offers a unified approach for systems of arbitrary number of spin-1/2s and the possibility of linking classicality with the nature of the measurement process.

quant-ph↗
arXiv2014

Local Hidden Variable Theoretic Measure of Quantumness of Mutual Information

Entanglement, a manifestation of quantumness of correlations between the observables of the subsystems of a composite system, and the quantumness of their mutual information are widely studied characteristics of a system of spin-1/2 particles. The concept of quantumness of correlations between the observables of a system is based on incommensurability of the correlations with the predictions of some local hidden variable (LHV) theory. However, the concept of quantumness of mutual information does not invoke the LHV theory explicitly. In this paper, by invoking explicitly the local hidden variable theory, a measure of quantumness of mutual information, $Q_{LHV}$, for a system of two spin-1/2 particles is proposed. It is based on finding the difference between the quantum and classical mutual informations in which the classical mutual information corresponds to the joint probability of the eigenvalues of the spins each along a specified direction. The proposed measure circumvents the need of optimization when the Bloch vector of each spin is non-zero; the optimization is needed but can be performed analytically exactly when the Bloch vector of each spin vanishes and is simplified when the Bloch vector of only one of the spins is zero. In essence, the proposed measure is identical with the measurement induced disturbance when the Bloch vector of each of the spins is non-zero. However, whereas the measurement induced disturbance is non-unique when the Bloch vector of one or both the spins is zero, the proposed measure even then determines the quantumness of mutual information unambiguously. The $Q_{LHV}$ is identical with the symmetric discord if the Bloch vector of each spin vanishes. It is same as the quantum discord if the Bloch vector of only one spin is zero and if the state in question possesses certain additional properties.

quant-ph↗
arXiv2005

Power loss in open cavity diodes and a modified Child Langmuir Law

Diodes used in most high power devices are inherently open. It is shown that under such circumstances, there is a loss of electromagnetic radiation leading to a lower critical current as compared to closed diodes. The power loss can be incorporated in the standard Child-Langmuir framework by introducing an effective potential. The modified Child-Langmuir law can be used to predict the maximum power loss for a given plate separation and potential difference as well as the maximum transmitted current for this power loss. The effectiveness of the theory is tested numerically.

physics.plasm-ph↗
arXiv2004

Generalization of Child-Langmuir Law for Non-Zero Injection Velocities in a Planar Diode

The Child-Langmuir law relates the voltage applied across a planar diode to the saturation value J_CL of current density that can be transmitted through it in case the injection velocity of electrons into the diode is zero. The Child-Langmuir current density J_CL is, at the same time, (i) the maximum current density that can be transmitted through a planar diode, (ii) the current density below which the flow is steady and unidirectional in the long time limit and (iii) the average transmitted current density for {\em any} value of injected current density above J_CL. Existing generalizations of Child-Langmuir law to non-zero velocities of injection are based on the characteristics (i) and (ii) of J_CL. This paper generalizes the law to non-zero velocities of injection based on the characteristic (iii) by deriving an analytical expression for the saturation value of current density. The analytical expression for the saturation current density is found to be well supported by numerical computations. A reason behind preferring the saturation property of the Child-Langmuir current density as the basis for its generalization is the importance of that property in numerical simulations of high current diode devices.

physics.plasm-ph↗
arXiv2004

Absence of saturation for finite injected currents in axially symmetric cavity diode

The Child-Langmuir law is investigated numerically using a fully electromagnetic particle-in-cell code for a closed axially symmetric diode. It is found that the average current transmitted to the anode increases with the injected current even after the formation of virtual cathode in both the non-relativistic and relativistic cases. The increase is found to be a power law. In other words, the time averaged fraction $f$ of electrons reaching the anode varies with the input current as, $f\sim J_{\rm IN}^{-β}$ where $β< 1$. In contrast, for an infinite parallel plate diode, $f \sim J_{\rm IN}^{-1}$. The possibility of asymptotic saturation is also discussed.

physics.plasm-ph↗
arXiv2000

A Critique on `Quantum No-Deleting Principle'

The argument used, in a recent letter to Nature (Nature 130 vol 404, 2000) to arrive at the `quantum-no-deleting principle' is erroneous. It is pointed out here that there may not be anything like such a principle. In any case, the claims made in the letter are beyond its working premise.

quant-ph↗
arXiv1999

Stroboscopic theory of atomic statistics in the micromaser

We study the statistics of the atoms emerging from the cavity of a micromaser in a dynamical, discrete-time `stroboscopic' description which takes into account the measurements made, in general, with imperfect efficiencies, on the states of the outcoming atoms. Inverted atoms enter stochastically, in general, with a binomial distribution in discrete time; but we also consider the continuous-time limit of this input statistics which is Poissonian. We envisage two alternative experimental procedures: one of these is to consider a fixed number N of atoms pumped into the cavity and subsequently leaving it to undergo state detection; the other is to consider input of the excited atoms and their subsequent detection and collection in a fixed time t. We consider, in particular, the steady state behaviors achieved in the two limits, N -> infinity and t -> infinity, as well as the approaches to these two limits. Although these limits are the same for the state of the cavity field, they are not the same, in general, for the observable outcoming atom statistics. We evaluate, in particular, Mandel's Q-parameters $Q_{e}$ $(Q_{g})$ for outcoming atoms detected in their excited states (ground states), for both N -> infinity and t -> infinity, as functions of $N_{ex} = RT_{c}$: R is the mean rate of entry for the incoming atoms and $T_c$ is the cavity damping time. The behavior of these atomic Q-parameters is compared with that parameter for the cavity field.

quant-ph↗