arXiv subjects

M. Rohith

Publications and source records attributed to M. Rohith.

10 recordsLinked to original sources

arXiv2026

Tomogram-based quantifiers of nonclassicality dynamics in Kerr and cubic media

The reliable quantification of nonclassicality in quantum states under realistic decoherence remains a central challenge in advancing quantum technologies. Conventional quantifiers such as Wigner negativity, Mandel's $Q$-parameter, nonclassical depth, etc., are often experimentally intractable, non-unique, or insensitive to key quantum signatures. We demonstrate that tomogram-based measures, the homodyne nonclassical area and sum tomographic entropy, offer a robust, experimentally accessible alternative for quantifying nonclassicality dynamics, as they can be directly obtained from optical tomograms via balanced homodyne detection, avoiding density matrix reconstruction and ensuring feasibility. We study coherent, photon-added coherent, and even coherent states evolving in Kerr and cubic nonlinear systems, with environmental effects modelled using the Lindblad master equation under amplitude and phase damping. The homodyne nonclassical area, which quantifies the excess quadrature variance beyond that of a coherent state, tracks both the onset and decay of nonclassicality, clearly identifying fractional revivals, wave packet splitting, and macroscopic superpositions. We find that amplitude damping drives a rapid monotonic decay toward the vacuum, while phase damping allows partial revival features to survive longer. Complementing this, the sum tomographic entropy derived from conjugate-quadrature tomograms captures higher-order fractional revivals and phase-space interference through persistent entropy minima under weak damping. Our results establish homodyne-based quantifiers as powerful, real-time, and experimentally viable tools for tracking nonclassical dynamics in nonlinear optical media, offering a compelling alternative to conventional, experimentally challenging measures.

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arXiv2025

Characterizing quantum synchronization in the van der Pol oscillator via tomogram and photon correlation

Scalable methods for detecting and quantifying the nonclassical nature of a quantum state in noisy environments are challenging due to a complex relationship between noise and quantum coherence. In particular, identifying experimentally accessible signatures of synchronization in such regimes remains an open problem. By leveraging promising experimental implementation, we underpin what possible direct measures of nonclassicality are available. This work outlines accessing quantum synchronization (QS) in the steady state of a driven quantum van der Pol oscillator (vdPo) using two distinct figures of merit: (i) the nonclassical area $\delta$ and (ii) the second-order correlation function $g^{(2)}(0)$, both of which are viable in experimental architectures. The nonclassical area quantifier based on homodyne tomography allows us to assess the nonclassical nature of the vdPo state directly from the tomogram without requiring full state reconstruction or Wigner function negativity. Within a well-defined parameter regime of drive strength and detuning, both $\delta$ and $g^{(2)}(0)$ exhibit pronounced signatures of synchronization that complements the phase coherence between the drive and the vdPo. We derive an analytical expression for the steady state density matrix and the corresponding tomogram of the system, valid for arbitrary strengths of the harmonic drive. Analysis of the quantum tomogram uncovers clear phase locking behaviour, enabling the identification of the synchronization region (Arnold tongue) directly in terms of $g^{(2)}(0)$ and $\delta$. Furthermore, the behaviour of $g^{(2)}(0)$ provides a statistical perspective that reinforces the tomographic signatures of QS. By analyzing the interplay between the aforementioned metrics, our findings indicate a scalable and experimentally relevant framework for characterizing QS in the driven vdPo.

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arXiv2024

Wave packet dynamics of entangled q-deformed states

This paper explores the wave packet dynamics of a math-type q- deformed field interacting with atoms in a Kerr-type nonlinear medium. The primary focus is on the generation and dynamics of entanglement using the q- deformed field, with the quantification of entanglement accomplished through the von Neumann entropy. Two distinct initial q-deformed states, the q-deformed Fock state, and the q-deformed coherent state, are investigated. The entanglement dynamics reveal characteristics of periodic, quasi-periodic, and chaotic behavior. Non-deformed initial states display wave packet near revivals and fractional revivals in entanglement dynamics while introducing q-deformation eliminates these features. The q-deformation significantly influences wave packet revivals and fractional revivals, with even a slight introduction causing their disappearance. For large values of q, the entanglement dynamics exhibit a chaotic nature. In the case of a beam splitter-type interaction applied to the initial deformed Fock state, an optimal deformation parameter q is identified, leading to maximum entanglement exceeding the non-deformed scenario.

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arXiv2020

Nonlinear dynamics of superpostion of wavepackets

We study nonlinear dynamics of superposition of quantum wavepackets in various systems such as Kerr medium, Morse oscillator and bosonic Josephson junction. The prime reason behind this study is to find out how the superposition of states influence the dynamics of quantum systems. We consider the superposition states which are potential candidates for quantum computing and quantum communication and so it is most necessary that we study the dynamics for their proper understanding and usage. Methods in nonlinear time series analysis such as first return time distribution, recurrence plot and Lyapunov exponent are used for the qualification and quantification of dynamics. We found that there is a vast change in the dynamics of quantum systems when we consider the superposition of wave packets. These changes are observed in various kinds of dynamics such as periodic, quasi-periodic, ergodic, and chaotic dynamics.

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arXiv2018

Homodyne nonclassical area as a nonclassicality indicator

We propose a legitimate and easily computable nonclassicality indicator for the states of electromagnetic fields based on the standard deviation in the measurement of the homodyne rotated quadrature operator. The proposed nonclassicality indicator is the nonclassical area projected by the optical tomogram of the quantum state of light on the optical tomographic plane. If the nonclassical area projected by the optical tomogram of a quantum state is greater than zero, the state is nonclassical, and the area is zero for the pure classical state. It is also noted that the nonclassical area of a quantum state increases with an increase in the strength of nonclassicality inducing operations on the state such as squeezing, photon addition, etc. We have tested the validity of the nonclassical area measure by calculating the same for certain well-known nonclassical states and found that essential features of the nonclassicality shown by the states are captured in the nonclassical area. We have also shown that the nonclassical area is robust against environment-induced decoherence of the states. Nonclassical area projected by the optical tomogram of a quantum state of light is experimentally tractable using the balanced homodyne detection of the quadrature operator of the field, avoiding the reconstruction of the density matrix or the quasiprobability distribution of the state.

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arXiv2016

An investigation of nonclassical properties of light using an optical tomogram

By analyzing the optical tomogram of a linear superposition of coherent states, we show that distinctive signatures of the macroscopic superposition states are displayed directly in the optical tomograms of the states. We also study the effect of decoherence on the optical tomograms of the macroscopic superposition states. Since the wave packet fractional revivals are associated with the generation of macroscopic superposition states, these signatures help in visualizing the revivals and fractional revivals occurring in a nonlinear medium directly in the optical tomogram of the time-evolved state. We found that the optical tomogram of the time-evolved state at the instants of fractional revivals show structures with sinusoidal strands. Using a class of initial superposed wave packets evolving in the Kerr-like medium, we further show that the condition for the occurrence of fractional revival phenomenon depends on the number of wave packets composing the initial superposition state. In the case of a two-mode electromagnetic field, we investigate the entanglement of the state directly using the optical tomogram. We have shown that the signatures of entanglement can be observed directly in the single-mode optical tomogram of the state without reconstructing the density matrix of the system. We also analyze the effect of decoherence on the optical tomograms of the entangled states. Further, we examine the optical tomograms of the entangled states generated using a beam splitter with a Kerr medium placed into one of its input modes. We have found the signatures of entanglement in the optical tomogram for the entangled states generated at the instants of two- and three-subpacket fractional revival times.

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arXiv2015

Visualizing revivals and fractional revivals in a Kerr medium using optical tomogram

We theoretically study the optical tomography of the time evolved states generated by the evolution of different kinds of initial wave packets in a Kerr medium. Exact analytical expression for the optical tomogram of the quantum state at any instant during the evolution of a generic initial wave packet is derived in terms of Hermite polynomials. Time evolution of the optical tomogram is discussed for three kinds of initial states: a coherent state, an $m$-photon-added coherent state, and even and odd coherent states. We show the manifestation of revival and fractional revivals in the optical tomograms of the time evolved states. We find that the optical tomogram of the time evolved state at the instants of fractional revivals shows structures with sinusoidal strands. The number of sinusoidal strands in the optical tomogram of the time evolved state at $l$-sub-packet fractional revivals is $l$ times the number of sinusoidal strands present in the optical tomogram of the initial state. We have also investigated the effect of decoherence on the optical tomograms of the states at the instants of fractional revivals for the initial states considered above. We consider amplitude decay and phase damping models of decoherence, and show the direct manifestations of decoherence in the optical tomogram.

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arXiv2015

Signatures of entanglement in an optical tomogram

We theoretically study the optical tomography of maximally entangled states generated at the output modes of a beam splitter. We consider even and odd coherent states in one of the input modes and vacuum state in the other input mode of the beam splitter. We have shown that the signatures of entanglement can be observed directly in the optical tomogram of the state, without reconstructing the density matrix of the system. Two distinct types of optical tomograms are observed in any one of the output modes of the beam splitter based on the quadrature measurement in the other output mode if the output modes are entangled. The different features shown by the optical tomograms are verified by investigating the photon number statistics of the corresponding state.

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arXiv2014

Entanglement dynamics of quantum states in a beam splitter

We theoretically study the dynamics of entangled states created in a beam splitter with a nonlinear Kerr medium placed into one input arm. Entanglement dynamics of initial classical and nonclassical states are studied and compared. Signatures of revival and fractional revival phenomena exhibited during the time evolution of states in the Kerr medium are captured in the entangled states produced by the beam splitter. Maximum entanglement is obtained at the instants of collapses of wave packets in the medium. Our analysis shows increase in entanglement with increase in the degree of nonclassicality of the initial states considered. We show that the states generated at the output of the beam splitter using initial nonclassical states are more robust against decoherence, due to photon absorption by an environment, than those formed by an initial classical state.

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arXiv2013

Fractional revivals of superposed coherent states

We study the dynamics of superposed wave packets in a specific nonlinear Hamiltonian which models the wave packet propagation in Kerr-like media and the dynamics of Bose-Einstein condensates. We show the dependence of initial wave packet superposition on fractional revival times using analysis based on the expectation values, R\'{e}nyi entropy and Wigner function. We also show how the selective identification of fractional revivals using moments of appropriate observables depends on the number of wave packets present in the initial state.

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