S. Dattagupta

Indian Institute of Science Education and Research Kolkata, Kolkata, Bengal, India

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Publications (124)231.26 Total impact

  • Prasenjit Das, Manas K. Roy, Sanjay Puri, Sushanta Dattagupta
    EPL (Europhysics Letters) 12/2013; 104(6). · 2.26 Impact Factor
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    ABSTRACT: The coupling of a mesoscopic system with its environment usually causes total decoherence: at long times the reduced density matrix of the system evolves in time to a limit which is independent of its initial value, losing all the quantum information stored in its initial state. Under special circumstances, a subspace of the system's Hilbert space remains coherent, or "decoherence free", and the reduced density matrix approaches a non-trivial limit which contains information on its initial quantum state, despite the coupling to the environment. This situation is called "partial decoherence". Here we find the conditions for partial decoherence for a mesoscopic system (with $N$ quantum states) which is coupled to an environment. When the Hamiltonian of the system commutes with the total Hamiltonian, one has "adiabatic decoherence", which yields N-1 time-independent combinations of the reduced density matrix elements. In the presence of a magnetic flux, one can measure circulating currents around loops in the system even at long times, and use them to retrieve information on the initial state. For N=2, we demonstrate that partial decoherence can happen only under adiabatic decoherence conditions. However, for $N>2$ we find partial decoherence even when the Hamiltonian of the system does not commute with the total Hamiltonian, and we obtain the general conditions for such non-adiabatic partial decoherence. For an electron moving on a ring, with $N>2$ single-level quantum dots, non-adiabatic partial decoherence can arise only when the total flux through the ring vanishes (or equals an integer number of flux quanta), and therefore there is no asymptotic circulating current.
    Physica Scripta Volume T. 05/2012;
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    Manas Kumar Roy, Sushanta Dattagupta
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    ABSTRACT: An effort based on the kinetic model allowed by Landau-Ginzburg-Devonshire theory is presented here. The formation of vortex, antivortex states in ferroelectric films are reported and theoretically explained. Phase transition in toroidal moment is observed. Vortex-antivortex-vortex (V-AV-V) triplet is generated by applying inhomogeneous transverse static localized fields in x-y plane. A specific boundary condition is used to keep the spirit of vortex state i.e. the net polarization across the boundary is always zero. %This is neither a periodic nor an open circuit electric boundary condition.
    06/2011;
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    Subhasis Sinha, Sushanta Dattagupta
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    ABSTRACT: We consider a prototypical system of an infinite range transverse field Ising model coupled to a bosonic bath. By integrating out the bosonic degrees, an effective anisotropic Heisenberg model is obtained for the spin system. The phase diagram of the latter is calculated as a function of coupling to the heat bath and the transverse magnetic field. Collective excitations at low temeratures are assessed within a spin-wave like analysis that exhibits a vanishing energy gap at the quantum critical point. We also consider another limit where the system reduces to a generalized spin-boson model of two interacting spins. By increasing the coupling strength with the heat bath, the two-spin wavefunction changes from an entangled state to a factorized state of two spins which are aligned along the transverse field. We also discuss the possible realization and application of the model to different physical systems.
    Physics of Condensed Matter 04/2011; · 1.28 Impact Factor
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    Ebad Kamil, Sushanta Dattagupta
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    ABSTRACT: The qubit (or a system of two quantum dots) has become a standard paradigm for studying quantum information processes. Our focus is Decoherence due to interaction of the qubit with its environment, leading to noise. We consider quantum noise generated by a dissipative quantum bath. A detailed comparative study with the results for a classical noise source such as generated by a telegraph process, enables us to set limits on the applicability of this process vis a vis its quantum counterpart, as well as lend handle on the parameters that can be tuned for analyzing decoherence. Both Ohmic and non-Ohmic dissipations are treated and appropriate limits are analyzed for facilitating comparison with the telegraph process.
    Pramana 03/2011; · 0.56 Impact Factor
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    ABSTRACT: The time evolution of a qubit, consisting of two single-level quantum dots, is studied in the presence of telegraph noise. The dots are connected by two tunneling paths, with an Aharonov-Bohm flux enclosed between them. Under special symmetry conditions, which can be achieved by tuning gate voltages, there develops partial decoherence: at long times, the off-diagonal element of the reduced density matrix (in the basis of the two dot states) approaches a non-zero value, generating a circulating current around the loop. The flux dependence of this current contains full information on the initial quantum state of the qubit, even at infinite time. Small deviations from this symmetry yield a very slow exponential decay towards the fully-decoherent limit. However, the amplitudes of this decay also contain the full information on the initial qubit state, measurable either via the current or via the occupations of the qubit dots.
    Physical review. B, Condensed matter 09/2010; 82. · 3.66 Impact Factor
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    Manas Kumar Roy, Jaita Paul, Sushanta Dattagupta
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    ABSTRACT: We employ the Ginzburg–Landau–Devonshire free energy theory to construct a set of time-dependent ordinary differential equations in order to model the interaction dynamics of the tip of an atomic force microscope (AFM) with the surface of a ferroelectric thin film. Using this method we obtain (i) domain profile and (ii) domain nucleation which starts under the AFM tip. Since ferroelectrics are piezoelectric, the electromechanical coupling considered in our equations causes polarization to oscillate with the same frequency with which the AFM tip vibrates.
    Journal of Applied Physics 09/2010; 108(6):064102-064102-8. · 2.21 Impact Factor
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    ABSTRACT: Growing colonies of bacteria on the surface of thin agar plates exhibit fractal patterns as a result of nonlinear response to environmental conditions, such as nutrients, solidity of the agar medium and temperature. Here, we examine the effect of glucose on pattern formation by growing colonies of Bacillus thuringiensis isolate KPWP1. We also present the theoretical modeling of the colony growth of KPWP1 and the associated spatio-temporal patterns. Our experimental results are in excellent agreement with simulations based on a reaction-diffusion model that describes diffusion-limited aggregation and branching, in which individual cells move actively in the periphery, but become immotile in the inner regions of the growing colony. We obtain the Hausdorff fractal dimension of the colony patterns: D(H.Expt)=1.1969 and D(H, R.D.=)1.1965, for experiment and reaction-diffusion model, respectively. Results of our experiments and modeling clearly show how glucose at higher concentration can prove to be inhibitory for motility of growing colonies of B. thuringiensis cells on semisolid support and be responsible for changes in the growth pattern.
    Journal of Theoretical Biology 08/2010; 265(3):389-95. · 2.35 Impact Factor
  • Manas K. Roy, Jaita Paul, Sushanta Dattagupta
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    ABSTRACT: In this article we consider the nonlinear dynamics of domain growth and dynamics under the influence of an external electric field and an intrinsic pinning field due to disorder. The theoretical framework is based on a finite time-difference method as applied to a time-dependent Ginzburg–Landau–Devonshire equation. The domain growth is seen to be of fractal nature, the fractal dimension of which is in good agreement with experiments. When it comes to dynamics we compute the areal velocity of the domain growth as a function of the applied field and find different regions of the nonlinearities that are also in qualitative agreement with experiments.
    Journal of Applied Physics 08/2010; · 2.21 Impact Factor
  • Malay Bandyopadhyay, Sushanta Dattagupta
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    ABSTRACT: In this Brief Report we show how the low-temperature thermodynamics of the dissipative motion of an electron in a magnetic field is sensitive to the nature of the spectral density function, J(omega), of the quantum heat bath. In all cases of couplings considered here the free energy and the entropy of the cyclotron motion of the electron fall off to zero as power law in conformity with the third law of thermodynamics. The power of the power law however depends on the nature of J(omega). We also separately discuss the influence of confinement.
    Physical Review E 04/2010; 81(4 Pt 1):042102. · 2.31 Impact Factor
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    S Dattagupta, Jishad Kumar, S Sinha, P A Sreeram
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    ABSTRACT: We present a detailed study of the quantum dissipative dynamics of a charged particle in a magnetic field. Our focus of attention is the effect of dissipation on the low- and high-temperature behaviors of the specific heat at constant volume. After providing a brief overview of two distinct approaches to the statistical mechanics of dissipative quantum systems, viz., the ensemble approach of Gibbs and the quantum Brownian motion approach due to Einstein, we present exact analyses of the specific heat. While the low-temperature expressions for the specific heat, based on the two approaches, are in conformity with power-law temperature dependence, predicted by the third law of thermodynamics, and the high-temperature expressions are in agreement with the classical equipartition theorem, there are surprising differences between the dependencies of the specific heat on different parameters in the theory, when calculations are done from these two distinct methods. In particular, we find puzzling influences of boundary confinement and the bath-induced spectral cutoff frequency. Further, when it comes to the issue of approach to equilibrium, based on the Einstein method, the way the asymptotic limit (t-->infinity) is taken seems to assume significance.
    Physical Review E 03/2010; 81(3 Pt 1):031136. · 2.31 Impact Factor
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    Manas Kumar Roy, Shamik Sarkar, Sushanta Dattagupta
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    ABSTRACT: A Landau-like theory of phase transition and its time-dependent generalization are shown to be sufficient for describing the formation and kinetics of 180°, 90°, and vortex (toroidal) domains in ferroelectric thin films. The theory relies only on the choice of boundary conditions and does not require at the outset the presence of either anisotropy or strain fields. An ingredient in the calculational scheme is the incorporation of finite element methods in the kinetic equations for the ferroelectric order parameter.
    Applied Physics Letters 12/2009; · 3.52 Impact Factor
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    Amnon Aharony, Ora Entin-Wohlman, Sushanta Dattagupta
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    ABSTRACT: A qubit (containing two quantum states, 1 and 2), is coupled to a control register (state 3), which is subject to telegraph noise. We study the time evolution of the density matrix $\rho$ of an electron which starts in some coherent state on the qubit. At infinite time, $\rho$ usually approaches the fully decoherent state, with $\rho^{}_{nm}=\delta^{}_{nm}/3$. However, when the Hamiltonian is symmetric under $1\leftrightarrow 2$, the element $\rho^{}_{12}$ approaches a non-zero real value, implying a partial coherence of the asymptotic state. The asymptotic density matrix depends only on ${\rm Re}[\rho^{}_{12}(t=0)]$. In several cases, the information stored on the qubit is protected from the noise. Comment: 4 pages, 2 figures
    08/2009;
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    Malay Bandyopadhyay, Sushanta Dattagupta
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    ABSTRACT: In this work, low temperature thermodynamic behaviour in the context of dissipative diamagnetism with anomalous coupling is analyzed. We find that finite dissipation substitutes the zero-coupling result of exponential decay of entropy by a power law behaviour at low temperature. For Ohmic bath, entropy vanishes linearly with temperature, $T$, in conformity with Nernst's theorem. It is also shown that entropy decays faster in the presence of anomalous coupling than that of the usual coordinate-coordinate coupling. It is observed that velocity-velocity coupling is the most advantageous coupling scheme to ensure the third law of thermodynamics. It is also revealed that different thermodynamic functions are independent of magnetic field at very low temperature for various coupling schemes discussed in this work.
    04/2009;
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    Jishad Kumar, P A Sreeram, Sushanta Dattagupta
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    ABSTRACT: We revisit here the effect of quantum dissipation on the much studied problem of Landau diamagnetism and analyze the results in the light of the third law of thermodynamics. The case of an additional parabolic potential is separately assessed. We find that dissipation arising from strong coupling of the system to its environment qualitatively alters the low-temperature thermodynamic attributes such as the entropy and the specific heat.
    Physical Review E 03/2009; 79(2 Pt 1):021130. · 2.31 Impact Factor
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    ABSTRACT: We report results of dc-magnetization, ac-susceptibility and magnetoresistance measurements on crystalline metallic-perovskite compounds GdPd3BxC1-x (x=0.25, 0.50, 0.75 and 1.00) and the parent cubic compound GdPd3. The interest in these materials stems from the observation of negative temperature coefficient of resistance and negative thermal expansion in some of the members of this series. In the present study, we show that by substitution of non-magnetic elements, boron and carbon, the nature of the magnetic interaction can be varied from dominating ferromagnetic to antiferromagnetic and finally to a canted magnetic structure without altering the crystal symmetry of the compounds. The variation of magnetic interaction by modifying the lattice parameter resembles Ruderman-Kittel-Kasuya-Yosida (RKKY) oscillations.
    Journal of Magnetism and Magnetic Materials 01/2009; 321(15):2311-2317. · 2.00 Impact Factor
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    ABSTRACT: Resistivity measurements and temperature-dependent X-ray structural analyses are reported for the crystalline compounds GdPd3BxC1- x. We show that a controlled tuning of the temperature coefficient of resistance (TCR) can be done by modifying the structural parameters and chemical environment of the compounds. We have achieved the result of negative TCR in an ordered, non-Kondo crystalline compound. Electronic-structure calculations have been carried out to elucidate some of our observations.
    EPL (Europhysics Letters) 11/2008; 84(4):47007. · 2.26 Impact Factor
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    ABSTRACT: We have observed negative thermal expansion (NTE) in a metallic, polycrystalline, and structurally ordered cubic compound GdPd3B0.25C0.75. Our analysis suggest that the NTE observed in this compound does not stems from valence or magnetic instability of lattice ions, which is in general the case of metallic compounds exhibiting such an anomaly. We propose a possible alternative mechanism, namely, the transverse vibrations at low temperatures arising from site anisotropy, that induce the lattice contraction thereby resulting in isotropic NTE. The observed NTE also reflects its effect on the electrical transport properties of this compounds.
    Applied Physics Letters 07/2008; 92(26):261913-261913-3. · 3.52 Impact Factor
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    ABSTRACT: Results of DC-magnetic measurements and Eu-Mössbauer spectroscopy studies are discussed for intermetallic pervoskite compounds Ce0.5Eu0.5Pd3Bx (x = 0.0, 0.5 and 1.0). Results indicate that the valence state of Eu in the compounds is vulnerable to the boron insertion at the body center position of the lattice and in that their magnetic properties change drastically.
    04/2008;
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    Malay Bandyopadhyay, Sushanta Dattagupta
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    ABSTRACT: This review deals with the dynamics of quantum systems that are subject to high frequency external perturbations. Though the problem may look hopelessly time-dependent, and poised on the extreme opposite side of adiabaticity, there exists a ‘Kapitza Window’ over which the dynamics can be treated in terms of effective time-independent Hamiltonians. The consequent results are important in the context of atomic traps as well as quantum optic properties of atoms in intense and high-frequency electromagnetic fields.
    Pramana 03/2008; 70(3):381-398. · 0.56 Impact Factor

Publication Stats

705 Citations
231.26 Total Impact Points

Institutions

  • 2007–2011
    • Indian Institute of Science Education and Research Kolkata
      Kolkata, Bengal, India
    • University of Vienna
      • Faculty of Physics
      Vienna, Vienna, Austria
  • 2010
    • Tata Institute of Fundamental Research
      • Department of Theoretical Physics
      Mumbai, State of Maharashtra, India
  • 2002–2008
    • Jawaharlal Nehru Centre for Advanced Scientific Research
      Bengalūru, Karnātaka, India
  • 1970–2008
    • S.N. Bose National Centre for Basic Sciences
      Kolkata, Bengal, India
  • 1998
    • University of Cambridge
      • Department of Earth Sciences
      Cambridge, England, United Kingdom
  • 1991–1998
    • Jawaharlal Nehru University
      • School of Physical Sciences
      New Delhi, NCT, India
  • 1996
    • Khalsa College
      Punjai Puliyampatti, Tamil Nādu, India
  • 1981–1987
    • University of Hyderabad
      • School of Physics
      Hyderābād, State of Andhra Pradesh, India
    • Indian Institute of Technology Madras
      Chennai, Tamil Nādu, India
  • 1976
    • University of Alberta
      • Theoretical Physics Institute
      Edmonton, Alberta, Canada
  • 1975–1976
    • Carnegie Mellon University
      • Department of Physics
      Pittsburgh, PA, United States
  • 1974
    • St. John's University
      New York City, New York, United States