Department of Physics

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Now showing 1 - 9 of 9
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    Thermodynamics of multiple Maxwell demons
    (Springer, 2022-08) Dutta, Sandipan
    In many assembly line processes like metabolic and signaling networks in biological systems, the products of the first enzyme are the reactant for the next enzyme in the network. Working of multiple machines leads to efficient utilization of resources. Motivated by this, we investigate if multiple Maxwell demons lead to more efficient information processing. We study the phase space of multiple demons acting on an information tape based on the model of Mandal and Jarzynski [1, 2]. Their model is analytically solvable and the phase space of the device has three regions: engine, where work is delivered by writing information to the tape, erasure, where work is performed on the device to erase information on the tape, and dud, when work is performed and, at the same time, the information is written to the tape. For identical demons, we find that the erasure region increases at the expense of the dud region, while the information engine region does not change appreciably. The efficiency of the multiple demon device increases with the number of demons in the device and saturates to the equilibrium (maximum) efficiency even at short cycle times for very large numbers of demons. By investigating a device with non-identical demons acting on a tape, we identify the demon parameters that control the different regions of the phase space. Our model is well suited to study information processing in assembly line systems.
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    Finite Temperature Quantum Effects in Many-Body Systems by Classical Methods
    (Elsevier, 2016) Dutta, Sandipan
    A recent description of an exact map for the equilibrium structure and thermodynamics of a quantum system onto a corresponding classical system is summarized. Approximate implementations are constructed by pinning exact limits (ideal gas, weak coupling) and illustrated by calculation of pair correlations for the uniform electron gas and shell structure for harmonically confined charges. A wide range of temperatures and densities are addressed in each case. For the electron gas, comparisons are made to recent path integral Monte Carlo simulations showing good agreement. Finally, the relevance for orbital-free density functional theory for conditions of warm, dense matter is discussed briefly.
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    Colossal Power Extraction from Active Cyclic Brownian Information Engines
    (ACS, 2022-07) Dutta, Sandipan
    Brownian information engines can extract work from thermal fluctuations by utilizing information. To date, the studies on Brownian information engines consider the system in a thermal bath; however, many processes in nature occur in a nonequilibrium setting, such as the suspensions of self-propelled microorganisms or cellular environments called an active bath. Here, we introduce an archetypal model for a Maxwell-demon type cyclic Brownian information engine operating in a Gaussian correlated active bath capable of extracting more work than its thermal counterpart. We obtain a general integral fluctuation theorem for the active engine that includes additional mutual information gained from the active bath with a unique effective temperature. This effective description modifies the generalized second law and provides a new upper bound for the extracted work. Unlike the passive information engine operating in a thermal bath, the active information engine extracts colossal power that peaks at the finite cycle period. Our study provides fundamental insights into the design and functioning of synthetic and biological submicrometer motors in active baths under measurement and feedback control.
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    Classical Representation of a Quantum System at Equilibrium
    (Wiley, 2012-01) Dutta, Sandipan
    A quantum system at equilibrium is represented by a corresponding classical system, chosen to reproduce the thermodynamic and structural properties. The objective is to develop a means for exploiting strong coupling classical methods (e.g., MD, integral equations, DFT) to describe quantum systems. The classical system has an effective temperature, local chemical potential, and pair interaction that are defined by requiring equivalence of the grand potential and its functional derivatives with respect to the external and pair potentials for the classical and quantum systems. Practical inversion of this mapping for the classical properties is effected via the hypernetted chain approximation, leading to representations as functionals of the quantum pair correlation function. As an illustration, the parameters of the classical system are determined approximately such that ideal gas and weak coupling RPA limits are preserved
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    Reaching and violating thermodynamic uncertainty bounds in information engines
    (APS, 2020-09) Dutta, Sandipan
    Thermodynamic uncertainty relations (TURs) set fundamental bounds on the fluctuation and dissipation of stochastic systems. Here, we examine these bounds, in experiment and theory, by exploring the entire phase space of a cyclic information engine operating in a nonequilibrium steady state. Close to its maximal efficiency, we find that the engine violates the original TUR. This experimental demonstration of TUR violation agrees with recently proposed softer bounds: The engine satisfies two generalized TUR bounds derived from the detailed fluctuation theorem with feedback control and another bound linking fluctuation and dissipation to mutual information and Renyi divergence. We examine how the interplay of work fluctuation and dissipation shapes the information conversion efficiency of the engine, and find that dissipation is minimal at a finite noise level, where the original TUR is violated.
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    Classical representation of a quantum system at equilibrium: Theory
    (APS, 2013-03) Dutta, Sandipan
    A quantum system at equilibrium is represented by a corresponding classical system, chosen to reproduce thermodynamic and structural properties. The motivation is to allow application of classical strong-coupling theories and molecular dynamics simulation to quantum systems at strong coupling. The correspondence is made at the level of the grand-canonical ensembles for the two systems. An effective temperature, local chemical potential, and pair potential are introduced to define the corresponding classical system. These are determined formally by requiring the equivalence of the grand potentials and their functional derivatives. Practical inversions of these formal definitions are indicated via the integral equations for densities and pair correlation functions of classical liquid theory. Application to the ideal Fermi gas is demonstrated, and the weak-coupling form for the pair potential is given. In a companion paper two applications are described: the thermodynamics and structure of uniform jellium over a range of temperatures and densities and the shell structure of harmonically bound charges.
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    Classical representation of a quantum system at equilibrium: Applications
    (APS, 2013-03) Dutta, Sandipan
    In the preceding paper, the structure and thermodynamics of a given quantum system was represented by a corresponding classical system having an effective temperature, local chemical potential, and pair potential. Here, that formal correspondence is implemented approximately for applications to two quantum systems. The first is the electron gas (jellium) over a range of temperatures and densities. The second is an investigation of quantum effects on shell structure for charges confined by a harmonic potential.
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    Efficiency fluctuations and noise induced refrigerator-to-heater transition in information engines
    (Springer Nature, 2020-02) Dutta, Sandipan
    Understanding noisy information engines is a fundamental problem of non-equilibrium physics, particularly in biomolecular systems agitated by thermal and active fluctuations in the cell. By the generalized second law of thermodynamics, the efficiency of these engines is bounded by the mutual information passing through their noisy feedback loop. Yet, direct measurement of the interplay between mutual information and energy has so far been elusive. To allow such examination, we explore here the entire phase-space of a noisy colloidal information engine, and study efficiency fluctuations due to the stochasticity of the mutual information and extracted work. We find that the average efficiency is maximal for non-zero noise level, at which the distribution of efficiency switches from bimodal to unimodal, and the stochastic efficiency often exceeds unity. We identify a line of anomalous, noise-driven equilibrium states that defines a refrigerator-to-heater transition, and test the generalized integral fluctuation theorem for continuous engines.
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    Evolution of electronic and vibrational properties of M@Xn (M = Ag, Au, X = Ge, Si, n = 10, 12, 14) clusters: a density functional modeling
    (Springer, 2018-03) Bandyopadhyay, Debashis
    Evolution of electronic and vibrational properties of M@Xn (M = Ag, Au, X = Ge, Si, n = 10, 12, 14) nanoclusters is investigated by using first-principle density functional theory (DFT)-based calculations with effective core potentials. To explain the thermodynamic and chemical stability of the ground state cluster in each size, variation of different thermodynamic and chemical parameters, like, binding energy (BE), HOMO–LUMO gap (ΔE), vertical ionization potential (VIP) and vertical electron affinity (VEA) was studied with the variation of the size of the clusters for emphasizing the differences and similarities in the clusters. It is found that Au doping in Ge and Si cages prefers endohedral position, whereas Ag prefers to take the position at the surface of the cages. In addition, IR and Raman spectra of the clusters are also studied to understand the vibrational nature of the stable clusters. At the end, present theoretical results are compared with existing experimental data. Theoretical knowledge of the thermodynamic, chemical and vibrational properties of these specific ground state structures is important for understanding its potential application in the field of optoelectronic science.