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Pinaki Patra

Publications and source records attributed to Pinaki Patra.

At least 19 recordsLinked to original sources

On the entanglement induced by the deformation of phase-space

Most quantum gravity theories propose that the fundamental concept of space-time is mostly compatible with quantum theory in noncommutative (NC) space. In the present paper, we revisit the notion of entanglement induced by NC deformations of phase space. The positive partial transpose (PPT) criterion for separability of bipartite Gaussian states is extended to a general class of Bopp's shift. In particular, we have considered both the position-position and momentum-momentum noncommutativity, with deformation parameters $\theta$ and $\eta$, respectively. It turns out that $\theta$ and $\eta$ induce the entanglement. We have directly applied the formalism for an anisotropic two-dimensional harmonic oscillator. Peres-Horodecki separability condition leads to a constraint equation for the parameter values of the oscillator in NC space. It turns out that the bipartite Gaussian state is almost always entangled in deformed space. To implement the theoretical idea, we provide an outline for a gedankenexperiment to identify the signature of phase-space noncommutativity, i.e., quantum gravity. In particular, the gedankenexperiment is devised to test the separability of supposedly separable Gaussian states in the usual commutative space, through the covariance matrix, which is constructed via measured output photocurrents after interaction of input Gaussian states and reference states. If the experiment shows that the supposedly separable states are actually entangled, then the entanglement is created through the intermediate background noncommutative space, which is a signature of the quantum nature of gravity.

quant-ph

Information geometry and entanglement under phase-space deformation through nonsymplectic congruence transformation

The Fisher-Rao (FR) information matrix is a central object in multiparameter quantum estimation theory. The geometry of a quantum state can be envisaged through the Riemannian manifold generated by the FR-metric corresponding to the quantum state. Interestingly, any congruence transformation $GL(2n,\mathbb{R})$ in phase space leaves the FR-distance for Gaussian states invariant. In the present paper, we investigate whether this isometry affects the entanglement in the bipartite system. It turns out that the entanglement-generating congruent transformation depends upon the system and background space. To make our study relevant to physical systems, we choose Bopp's shift in phase space as an example of $GL(2n,\mathbb{R})$, so that the results can be interpreted in terms of noncommutative (NC) phase-space deformation. We provide an estimation of the measure of entangled states over separable states for bipartite Gaussian states under a Bopp's shift. Since the dynamics of free oscillators in background NC-space is mathematically equivalent to the dynamics of a charged particle under a homogeneous magnetic field, we provide an outline for a gedankenexperiment through photocurrent measurement in order to determine the effects of congruent transformation on the distinguishibility of Gaussian states.

quant-ph

Information geometry of entangled states induced by noncommutative deformation of phase space

In this paper, we revisit the notion of quantum entanglement induced by the deformation of phase-space through noncommutative space (NC) parameters. The geometric structure of the state space for Gaussian states in NC-space is illustrated through information geometry approach. We parametrize the phase-space distributions by their covariances and utilize the Fisher-Rao metric to construct the statistical manifold associated with quantum states. We describe the notion of the Robertson-Scr\"{o}dinger uncertainty principle (RSUP) and positive partial transpose (PPT) conditions for allowed quantum states and separable states, respectively, for NC-space. RSUP and PPT provide the restrictions on all allowed states and separable states, respectively. This enables us to estimate the relative volumes of set of separable states and entangled states. Numerical estimations are provided for a toy model of a bipartite Gaussian state. We restrict our study to such bipartite Gaussian states, for which the entanglement is induced by the noncommutative phase-space parameters.

quant-ph

On the entanglement of co-ordinate and momentum degrees of freedom in noncommutative space

In this paper, we investigate the quantum entanglement induced by phase-space noncommutativity. Both the position-position and momentum-momentum noncommutativity are incorporated to study the entanglement properties of coordinate and momentum degrees of freedom under the shade of oscillators in noncommutative space. Exact solutions for the systems are obtained after the model is re-expressed in terms of canonical variables, by performing a particular Bopp's shift to the noncommuting degrees of freedom. It is shown that the bipartite Gaussian state for an isotropic oscillator is always separable. To extend our study for the time-dependent system, we allow arbitrary time dependency on parameters. The time-dependent isotropic oscillator is solved with the Lewis-Riesenfeld invariant method. It turns out that even for arbitrary time-dependent scenarios, the separability property does not alter. We extend our study to the anisotropic oscillator, which provides an entangled state even for time-independent parameters. The Wigner quasi-probability distribution is constructed for a bipartite Gaussian state. The noise matrix (covariance matrix) is explicitly studied with the help of Wigner distribution. Simon's separability criterion (generalized Peres-Horodecki criterion) has been employed to find the unique function of the (mass and frequency) parameters, for which the bipartite states are separable. In particular, we show that the mere inclusion of non-commutativity of phase-space is not sufficient to generate the entanglement, rather anisotropy is important at the same footing.

quant-ph

On the $\mathcal{P}\mathcal{T}$-symmetric parametric amplifier

Parametric amplifiers are an integral part of measurements involving the conversion of propagating quantum information to mechanical motion. General time-dependent PT-symmetric parametric oscillators for unbroken parity and time reversal (PT) symmetry regimes are studied theoretically. By constructing an explicit metric operator, we have transformed the non-Hermitian PT-symmetric system to an equivalent Hermitian Hamiltonian, which enables us to utilize the available mechanism of $\mathbb{L}^2$ space. The time-dependent (TD) Schr\"{o}dinger equation for the system is solved with the Lewis-Riesenfeld (LR) phase space method. The eigenstates of the LR-invariant operator ($\hat{\mathcal{I}}$) is obtained after transforming $\hat{\mathcal{I}}$ to its diagonal symplectic equivalent form (group $Sp(2, \mathbb{R})$). Both the dynamical and geometrical phase factors associated with the eigenstates of $\hat{\mathcal{I}}$ are explicitly written. The experimental pheasibility of our result is outlined through the construction of Wigner quasiprobability distribution. Moreover, we have demostrated the time variation of the Wigner distribution for the system consisting of two spatially separated prepared ground state of the TD-parametric amplifier. With graphical illustration of time variation of Wigner distributions, we show that the phase-space entanglement remains intact even for time-dependent situation, no matter how far the particles goes, at least for the cat-state under consideration. The exact expressions for the physically relevant qualities are obtained and illustrated for a toy model.

quant-ph

Tuning the separability in noncommutative space

We study the Separability of the noncommutative (NC) space coordinate degrees of freedom with the generalized Peres-Horodecki separability criterion (Simon's condition) for a bipartite Gaussian state. Non-symplectic nature of the transformation between the usual commutative space and NC space restricts the use of Simon's condition in NCS. We transform the NCS system to an equivalent Hamiltonian in commutative space through Bopp shift, which enables the utilization of the separability criterion in NC space. For afairly general study, we consider a bilinear Hamiltonian with time-dependent (TD) parameters, along with a TD external interaction, which is linear in field modes. The system is transformed into canonical form keeping the intrinsic symplectic structure ($Sp(4,\mathbb{R})$) intact. The solution of the TD-Schr\"{o}dinger equation is obtained with the help of Lewis-Riesenfeld invariant method (LRIM). Expectation values of the observables (thus the covariance matrix ) are constructed from the states obtained from LRIM. It turns out that the existence of the NC parameters in the oscillator determines the separability of the states. In particular, for isotropic oscillators, the separability condition for the bipartite Gaussian states depends on NC parameters. Moreover, anisotropic parameter values for the oscillator affects the separability. In other words, both the deformation parameters ($\theta,\;\eta$) and parameter values of the oscillator are important for the separability of bipartite states. Thus tuning the parameter values, one can destroy or recreate the separability of states. With the help of toy models, we have demonstrated TD-NC space parameters effect on separability.

quant-ph

Generalized coherent states and uncertainty relations in $\mathcal{P}\mathcal{T}$-symmetric position dependent mass systems

In this paper, we investigate a class of PT-symmetric quantum systems with position-dependent effective mass (PDEM). We factorize the PDEM Hamiltonian using a pair of generalized annihilation and creation operators. The resulting commutation relation introduces the notion of a position-dependent effective Planck parameter, which reduces to Planck's constant in the conventional Hermitian quantum system with constant mass. These generalized ladder operators define a deformed phase space, within which we construct a generalized Gaussian state to first order in the PT-symmetry parameter. We then revisit the Heisenberg uncertainty principle for this state and demonstrate that the deformed position and momentum operators satisfy the corresponding uncertainty relation in the PT-symmetric PDEM framework. Finally, we present explicit computational results for a toy-model oscillator with position-dependent effective mass in a PT-symmetric setting. In the conclusions section, we outline a gedankenexperiment for experimental determination of $PT-symmetric parameter.

quant-ph

On the two-dimensional time-dependent anisotropic harmonic oscillator in a magnetic field

A Charged harmonic oscillator in a magnetic field, Landau problems, and an oscillator in a noncommutative space, share the same mathematical structure in their Hamiltonians. We have considered a two-dimensional anisotropic harmonic oscillator (AHO) with arbitrarily time-dependent parameters (effective mass and frequencies), placed in an arbitrarily time-dependent magnetic field. A class of quadratic invariant operators (in the sense of Lewis and Riesenfeld) have been constructed. The invariant operators ($\hat{\mathcal{I}}$) have been reduced to a simplified representative form by a linear canonical transformation (the group $Sp(4, \mathbb{R})$). An orthonormal basis of the Hilbert space consisting of the eigenvectors of $\hat{\mathcal{I}}$ is obtained. In order to obtain the solutions of the time-dependent Schr\"{o}dinger equation corresponding to the system, both the geometric and dynamical phase-factors are constructed. Peres-Horodecki Separability Criterion for the bipartite coherent states corresponding to our system has been demonstrated.

quant-ph

Entanglement in phase-space distribution for an anisotropic harmonic oscillator in noncommutative space

The bi-partite Gaussian state, corresponding to an anisotropic harmonic oscillator in a noncommutative-space, is investigated with the help of the Simon's separability condition (generalized Peres-Horodecki criterion). It turns out that, in order to exhibit the entanglement between the noncommutative co-ordinates, the parameters (mass and frequency) have to satisfy an unique constraint equation. Exact solutions for the system are obtained after diagonalizing the model, keeping the intrinsic symplectic structure intact. It is shown that, the identification of the entangled degrees of freedom is possible by studying the Wigner quasiprobability distribution in phase-space. We have shown that the co-ordinates are entangled only with the conjugate momentum corresponding to other co-ordinates.

quant-ph

Dynamics of free time-dependent effective mass

The consensus is that an object with a large mass will not manifest quantum behavior. Therefore, we expect that the quantumness of a time-dependent effective mass (TDEM) will erase after a long time when the mass profile continuously grows with time. However, the present article depicts that the Wigner quasi-probability distribution (WQD) will manifest an entanglement behavour forever for two spatially separated free TDEM. The time-dependent Schr\"{o}dinger equation for a free particle with TDEM is solved with the help of Lewis-Riesenfeld phase space invariant method. WQD for the system of two identical TDEM with quadratically increasing mass profile shows that the particles are never separated. In particular, their reminiscent is present at the origin of the phase-space forever.

quant-ph

Squeezed coherent states for gravitational well in noncommutative space

Gravitational well is a widely used system for the verification of the quantum weak equivalence principle (WEP). We have studied the quantum gravitational well (GW) under the shed of noncommutative (NC) space so that the results can be utilized for testing the validity of WEP in NC-space. To keep our study widely usable, we have considered both position-position and momentum-momentum noncommutativity. Since coherent state (CS) structure provides a natural bridging between the classical and quantum domain descriptions, the quantum domain validity of purely classical phenomena like free-fall under gravity might be verified with the help of CS. We have constructed CS with the aid of a Lewis-Riesenfeld phase space invariant operator. From the uncertainty relations deduced from the expectation values of the observables, we have shown that the solutions of the time-dependent Schr\"{o}dinger equation are squeezed-coherent states.

quant-ph

Entropy uncertainty principle for Dirac system with mass jump

Dependency on the preparation of state for the Heisenberg uncertainty principle can be removed with the help of entropy uncertainty principle. The shortness of the uncertainty principle (UP) can be overcome with the help of the concept of Shannon's information entropy (SE). In this article, we have shown that UP in terms of SE holds for a position-dependent effective mass system. We have considered the Dirac system with a mass-jump at the origin. We have proved the existence of a lower bound for a UP for this position-dependent effective mass.

quant-ph

Generalized Lewis-Riesenfeld invariance for dynamical effective mass in jammed granullar media under a potential well in non-commutative space

Consideration of the asteroid belt (Kuiper belt) as a jammed-granular media establishes a bridge between condensed matter physics and astrophysics. It opens up an experimental possibility to determine the deformation parameters for noncommutative space-time. Dynamics of the Kuiper belt can be simplified as dynamics of a dynamical effective mass for a jammed granular media under a gravitational well. Alongside, if one considers the space-time to be noncommutative, then an experimental model for the determination of the deformation parameters for noncommutative space-time can be done. The construction of eigenfunctions and invariance for this model is in general a tricky problem. We have utilized the Lewis-Riesenfeld invariant method to determine the invariance for this time-dependent quantum system. In this article, we have shown that a class of generalized time-dependent Lewis-Riesenfeld invariant operators exist for the system with dynamical effective mass in jammed granular media under a potential well in noncommutative space. To keep the discussion fairly general, we have considered both position-position and momentum-momentum noncommutativity. Since, up to a time-dependent phase-factor, the eigenfunctions of the invariant operator will satisfy the time-dependent Schr\"{o}dinger equation for the time-dependent Hamiltonian of the system, the construction of the invariant operator fairly solve the problem mathematically, the results of which can be utilized to demonstrate an experiment.

physics.gen-ph

Constraints on the choice of position dependent effective mass and external potential for the existence of Lewis-Riesenfeld invariance and quantum canonical transformation

Lewis-Riesenfeld -Ermakov's (LR) invariant method for the construction of time-dependent phase-space invariant is extended for the general quantum system with position-dependent effective mass (PDEM) Hamiltonian. It turns out that, only a specific class of PDEM and a particular class of external potentials will exhibit the LR-invariant operator in close form. Then we have determined a class of unitary time-dependent quantum canonical transformation for the concerned PDEM and external potentials so that an equivalent time-independent PDEM Hamiltonian is obtained.

quant-ph

On the position dependent effective mass Hamiltonian

Noncommutivity of position and momentum makes it difficult to formulate the unambiguous structure of the kinetic part of Hamiltonian for the position-dependent effective mass (PDEM). Various existing proposals of writing the viable kinetic part of the Hamiltonian for PDEM, conceptually lack from first principle calculation. Starting from the first principle calculation, in this article, we have advocated the proper self-adjoint form of the kinetic part of Hamiltonian for PDEM. We have proposed that ambiguity of construction of viable kinetic part for PDEM can be avoided if one takes the care from the Classical level combination of position and momentum. \\ In the quantum level, the spatial points do not appear in equivalent footing for the measure of inertia (mass). This exhibits the existence of an inertia potential. Thus the new structure of the Kinetic part differs from the existing structure of the kinetic part of Hamiltonian by providing an extra potential like contribution. This inertia potential can be absorbed with the external potential and redefine the known structure of PDEM under this effective potential. This enables us to apply the existing formalism of quantum mechanics. The coherent state structures for the newly proposed form of Hamiltonian are provided for a few simple experimentally important models.

physics.gen-ph

Self-adjoint extension for Maxwell-Chern-Simons model in long wavelength limit

In the long wavelength limit, Maxwell-Chern-Simmon model and the dynamics of a particle in a plane under an external magnetic field perpendicular to that plane are identical. The self adjoint extension of such a problem depends on the value of angular momentum quantum number $l$. In this article, we have shown that for $l\neq 0$, the operator describing the Landau level wave-function is self adjoint; whereas, for $l=0$, infinite number of self-adjoint extension by an one parameter unitary mapping is possible.

hep-th

Modified Hamiltonian formalism for Regge Teitelboim Cosmology

The Ostrogradski approach for the Hamiltonian formalism of higher derivative theory is not satisfactory because of the reason that the Lagrangian cannot be viewed as a function on the tangent bundle to coordinate manifold. In this article, we have used an alternative approach which leads directly to the Lagrangian which, being a function on the tangent manifold, gives correct equation of motion; no new coordinate variables need to be added. This approach can be directly used to the singular (in Ostrogradski sense) Lagrangian. We have used this method for the Regge Teitelboim (RT) minisuperspace cosmological model. We have obtained the Hamiltonian of the dynamical equation of the scale factor of RT model.

hep-th

Current conservation in charge conjugation parity time reversal symmetry (CPT) violating gauge-invariant nonlocal Thirring model

Charge conjugation, parity transformation and time reversal symmetry (CPT) violation and Lorentz invariance can coexist in the framework of non-local field theory. In this article we have proposed a class of Charge conjugation, parity transformation and time reversal symmetry (CPT) violating Lorentz invariant nonlocal gauge-invariant models, which can be termed as non-local Thirring models. The conserved currents in this aspect are obtained.

hep-th