• A M Jayannavar

      Articles written in Resonance – Journal of Science Education

    • Second Law, Landauer's Principle and Autonomous Information Machine

      Shubashis Rana A M Jayannavar

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      Second law of thermodynamics can be apparently violated insystems whose dynamics depend on information acquired bymeasurement. However, when one considers measurementand erasure together with the system, it saves the second law.We consider the simple example of an information machine,where information is used as a resource to increase the machine’s performance. The system is connected to two baths, awork source, and a moving tape which is used as an informationreservoir. The performance of the device is autonomous.The system acts as an engine, erasure or refrigerator. Evencombination of any two is possible. All these possibilities areallowed by the generalized second law.

    • Emerging Trends in Topological Insulators and Topological Superconductors

      A M Jayannavar Arijit Saha

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      Topological insulators are new class of materials which arecharacterized by a bulk band gap like ordinary band insulatorsbut have protected conducting states on their edgesor surfaces. These states emerge due to the combination ofspin-orbit coupling and time reversal symmetry. Also, thesestates are insensitive to scattering by non-magnetic impurities.A two-dimensional topological insulator has one dimensionaledge states in which the spin-momentum locking ofthe electrons give rise to quantum spin Hall effect. A threedimensionaltopological insulator supports novel spin-polarized2D Dirac fermions on its surface. These topological insulatormaterials have been theoretically predicted and experimentallyobserved in a variety of 2D and 3D systems, includingHgTe quantum wells, BiSb alloys, and Bi2Te3, Bi2Se3 crystals.Moreover, proximity induced superconductivity in these systemscan lead to a state that supports zero energy Majoranafermions, and the phase is known as topological superconductors.In this article, the basic idea of topological insulatorsand topological superconductors are presented alongwith their experimental development.

    • Fluctuation Theorems of Work and Entropy in Hamiltonian Systems

      A M Jayannavar Sourabh Lahiri

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      Fluctuation theorems are a group of exact relations that remain valid irrespective of how far the system has been driven away from equilibrium. Other than having practical applications, like determination of equilibrium free energy change from nonequilibrium processes, they help in our understandiing of the second law and the emergence of irreversibility from time-reversible equations of motion at microscopic level. A vast number of such theorems have been proposed in literature, ranging from Hamiltonian to stochastic systems, from systems in steady state to those in transient regime, and for both open and closed quantum systems. In this article, we discuss about a few such relations, when the system evolves under Hamiltonian dynamics.

    • How Long Does a Quantum Particle or Wave Stay in a Given Region of Space?

      S Anantha Ramakrishna A M Jayannavar

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      The delay time associated with a scattering process is one ofthe most important dynamical aspects in quantum mechanics.A commonmeasure of this is theWigner delay time basedon the group velocity description of a wave packet, which mayeasily indicate superluminal or even negative times of interactionthat are unacceptable. Many other measures such asdwell times have been proposed, but also suffer from seriousdeficiencies, particularly for evanescent waves. One importantway of realising timescales that are causally connected tothe spatial region of interest relies on utilising the dynamicalevolution of extra degrees of freedom, called quantum clocks,such as the precession of the spin of an electron in an appliedmagnetic field or the coherent decay or growth of light in anabsorptive or amplifying medium placed within the region ofinterest. Here we provide a review the several approaches developedto answer the basic question “how much time doesa quantum particle (or wave) spend in a specified region ofspace?” While a unique answer still evades us, importantprogress has been made in understanding the timescales andobtaining positive definite times of interaction by noting thatall such clocks are affected by spurious scattering concomitantwith the very clock potentials, however, weak they be,and by eliminating the spurious scattering.

    • Maxwell’s Demon, Szilard Engine and Landauer Principle

      P S Pal A M Jayannavar

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      The second law of thermodynamics is probabilistic in nature. Its formulation requires that the state of a system be described by a probability distribution. A natural question, thereby, arises as to whether a prior knowledge about the state of the system affects the second law. This question has nowbeen nurtured for over a century, and it was incepted by C Maxwell through his famous thought experiment wherein comes the idea of Maxwell’s demon. The next important step in this direction was provided by L Szilard, who demonstrated a theoretical model for an information engine incorporating Maxwell’s demon. The final step that led to the inter-linkage of information theory and thermodynamics was through Landauer’s principle of information erasure that established thefact that information is physical. Here, we will present an overview of these three major works that laid the foundations of information thermodynamics.

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