arXiv subjects

N. K. Sharma

Publications and source records attributed to N. K. Sharma.

28 records · Page 2Linked to original sources

arXiv2005

Dynamics of tripartite entanglement

Maximally entangled states are of utmost importance to quantum communication, dense coding, and quantum teleportation. With a trapped ion placed inside a high finesse optical cavity, interacting with field of an external laser and quantized cavity field, a scheme to generate a maximally entangled three qubit GHZ state, is proposed. The dynamics of tripartite entanglement is investigated, using negativity as an entanglement measure and linear entropy as a measure of mixedness of a state. It is found that (a) the number of modes available to the subsystem determines the maximum entanglement of a subsystem, b) at entanglement maxima and minima, linear entropy and negativity uniquely determine the nature of state, but the two measures do not induce the same ordering of states, and c) for a special choice of system parameters maximally entangled tripartite two mode GHZ state is generated. The scheme presented for GHZ state generation is a single step process and is reduction free. PACS: 03.67.-a, 42.50.-p, 03.67.Dd

quant-ph↗

arXiv2004

Intrinsic decoherence effects on tripartite GHZ state generation using a trapped ion coupled to an optical cavity

We analyse the effects of intrinsic decoherence on the probability of generating a tripartite GHZ state using a cool trapped ion coupled to a single mode of the cavity field and interacting with a resonant laser field. Milburn equation is solved for this tripartite system to obtain the time evolution of density matrix as a function of cavity-ion coupling, laser-ion coupling, and the size of unitary time step relative to the time scale determined by system parameters. Starting with the system prepared initially in a separable state, density matrix is used to calculate the probability of tripartite GHZ state generation using coupling strengths reported in a recent experiment.

quant-ph↗

arXiv2002

Bounds on the W-Boson Electric Dipole Moment -Revisited

Keeping in view the suggestion of Barr and Marciano [7] that the cut of procedure involves a good deal of uncertainity in the prediction of E.D.M. of W - boson, we have re-examined the earlier calculation by Marciano and Queijeiro [2] by replacing the Cut-off regularization process by BPHZ regularization[8]. This works in a clean and unambiguous manner without involving any approximation. We also examine apparently inapplicable approximations like using m(f) = m(f')in [2]. The bounds on lambda(w) and d(w) are significantly changed in all cases as compared with those reported in [2]. The necessary caution that is to be excercised while using approximations is explicitly pointed out. PACS number (s): 13.40. Em

hep-ph↗

arXiv2002

Schrödinger cat state of trapped ions in harmonic and anharmonic oscillator traps

We examine the time evolution of a two level ion interacting with a light field in harmonic oscillator trap and in a trap with anharmonicities. The anharmonicities of the trap are quantified in terms of the deformation parameter $τ$ characterizing the q-analog of the harmonic oscillator trap. Initially the ion is prepared in a Schrödinger cat state. The entanglement of the center of mass motional states and the internal degrees of freedom of the ion results in characteristic collapse and revival pattern. We calculate numerically the population inversion I(t), quasi-probabilities $Q(t),$ and partial mutual quantum entropy S(P), for the system as a function of time. Interestingly, small deformations of the trap enhance the contrast between population inversion collapse and revival peaks as compared to the zero deformation case. For β=3 and $4,(% β$ determines the average number of trap quanta linked to center of mass motion) the best collapse and revival sequence is obtained for τ=0.0047 and τ=0.004 respectively. For large values of τdecoherence sets in accompanied by loss of amplitude of population inversion and for τ\sim 0.1 the collapse and revival phenomenon disappear. Each collapse or revival of population inversion is characterized by a peak in S(P) versus t plot. During the transition from collapse to revival and vice-versa we have minimum mutual entropy value that is S(P)=0. Successive revival peaks show a lowering of the local maximum point indicating a dissipative irreversible change in the ionic state. Improved definition of collapse and revival pattern as the anharminicity of the trapping potential increases is also reflected in the Quasi- probability versus t plots.

quant-ph↗

arXiv2001

Quantum mutual entropy for two-level ion in a q-analog trap

Quantum mutual entropy is used as a measure of information content of ionic state due to ion-laser interaction in a q-analog trap. The initial state of the system is a Schrodinger cat state. It is found that the partial mutual entropy is a good measure of the entanglement and purity of the ionic state at $t>0$.

quant-ph↗

arXiv2000

Quantum Group SU_{q}(2) and Pairing in Nuclei

A scheme for treating the pairing of nucleons in terms of generators of Quantum Group SU_{q}(2) is presented. The possible applications to nucleon pairs in a single orbit, multishell case, pairing vibrations and superconducting nuclei are discussed. The formalism for performing BCS calculations with q-deformed nucleon pairs is constructed and the role played by deformation parameter q analyzed in the context of nucleons in a single orbit and for Sn Isotopes.

nucl-th↗

arXiv2000

The BCS theory of q-deformed nucleon pairs - qBCS

We construct a coherent state of q-deformed zero coupled nucleon pairs distributed in several single-particle orbits. Using a variational approach, the set of equations of qBCS theory, to be solved self consistently for occupation probabilities, gap parameter Delta, and the chemical potential lambda, is obtained. Results for valence nucleons in nuclear degenerate sdg major shell show that the strongly coupled zero angular momentum nucleon pairs can be substituted by weakly coupled q-deformed zero angular momentum nucleon pairs. A study of Sn isotopes reveals a well defined universe of (G, q) values, for which qBCS converges. While the qBCS and BCS show similar results for Gap parameter Delta in Sn isotopes, the ground state energies are lower in qBCS. The pairing correlations in N nucleon system, increase with increasing q (for q real).

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arXiv1999

Reply on `comment on our paper `Single two-level ion in an anharmonic-oscillator trap: Time evolution of the Q function and population inversion ''

We show here that the model Hamiltonian used in our paper for ion vibrating in a q-analog harmonic oscillator trap and interacting with a classical single-mode light field is indeed obtained by replacing the usual bosonic creation and annihilation operators of the harmonic trap model by their q-deformed counterparts. The approximations made in our paper amount to using for the ion-laser interaction in a q-analog harmonic oscillator trap, the operator $F_{q}=exp{-(|ε|^2}/2)}exp{iεA^{\dagger}}exp{iεA}$, which is analogous to the corresponding operator for ion in a harmonic oscillator trap that is $F=exp{-(|ε|^2 /2)}exp{iεa^{\dagger }}exp{iεa}$. In our article we do not claim to have diagonalized the operator, $F_q = exp{i ε(A^{\dagger}+A)}$, for which the basis states |g,m> and |e,m> are not analytic vectors.

quant-ph↗

arXiv1995

Atom in a $q$-Analog Harmonic Oscillator Trap

We study the population inversion and Q-function of a two-level atom, interacting with single-mode laser light field, in a $q$-analog harmonic oscillator trap for increasing $q$. For $τ=.003(q=e^τ)$ the collapses and revivals of population inversion become well defined facilitating experimental observation but for large $τ\sim 0.1$ the time dependence of population inversion is completely wiped out.

quant-ph↗

arXiv1994

q-deformed pairing-vibrations

Boson creation operators constructed from linear combinations of q- deformed zero coupled nucleon pair operators acting on the nucleus (A,0), are used to derive pp-RPA equations. The solutions of these equations are the pairing vibrations in (A${\underline{+}}$2) nuclei. For the $0^+_1$ and $0^+_2$ states of the nucleus $^{208}$Pb, the variations of relative energies and transfer cross-sections for populating these states via (t,p) reaction, with deformation parameter $τ$ have been analysed. For $τ=0.405$ the experimental excitation energy of 4.87MeV and the ratio $\frac{σ(0^+_2) }{σ(0^+_1)}=0.45$ are well reproduced. The critical value of pairing interaction strength for which phase transition takes place, is seen to be lower for deformed zero-coupled nucleon pair condensate with $τ$ real, supporting our earlier conclusion that the real deformation simulates the two-body residual interaction. For $τ$ purely imaginary a stronger pairing interaction is required to bring about the phase transition. The effect of imaginary deformation is akin to that of an antipairing type repulsive interaction. Using deformed zero coupled quasi-particle pairs, a deformed version of Quasi-boson approximation for $0^+$ states in superconducting nuclei is developed. For the test model of 20 particles in two shells, the results of q-deformed boson and quasi-boson approximations have been compared with exact results. It is found that the deformation effectively takes into account the anharmonicities and may be taken as a quantitative measure of the correlations not being accounted for in a certain approximate treatment.

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