SPIN LAB

Ours is a research group in the Department of Physical Sciences of IISER Kolkata, which focusses on fundamentals of quantum dynamics. We also work on applications of NMR on polymers.


Principal Investigator

Dr. Rangeet Bhattacharyya

After completing his PhD from IISc, Bangalore, India on methodological developments in liquid NMR (with Anil Kumar), he gained experience in method developments in solid state NMR (with Lucio Frydman in Weizmann Institute of Science, Rehovot, israel). Later, he worked on applications of in-situ NMR methods in Lithium ion batteries (with Clare P Grey in Stony Brook University, USA) and briefly on quantum rotors (with Malcolm Levitt in Southampton University). He is a faculty member of the Department of Physical Sciences in IISER Kolkata since August 2010.

Presently, his main research interests lie in the dynamics of quantum systems coupled to a reservoir undergoing thermal fluctuations. A parallel line of active research is to apply NMR relaxation techniques to study morphological changes in polymer in solutions.

Positions

  • Associate Professor, Indian Institute of Science Education and Research Kolkata, India (2016 - present)
  • Assistant Professor, Indian Institute of Science Education and Research Kolkata, India (2010 - 2016)
  • Postdoctoral Fellowship, Southampton University, Southampton, UK (2009-2010)
  • Postdoctoral Fellowship, State University of New York Stony Brook, Stony Brook, USA (2008-2009)
  • Postdoctoral Fellowship, Weizmann Institute of Science, Rehovot, Israel (2005-2007)
  • PhD, Indian Institute of Science, Bengaluru, India (2000-2005)

Awards and Honors

  • Laura Marinelli Award, 50th Rocky Mountain conference on solid state NMR, USA (2008)
  • Fellowship, Feinberg Graduate School, Weizmann Institute of Science, Israel (2006-2007)
  • Reva G Stone fellowship (Feinberg Graduate School), Weizmann Institute of Science, Israel (2005-2006)
  • University Gold medal, Jadavpur University, Kolkata, India (1997).


Research areas

Quantum dynamics

We investigate the time evolution of quantum systems in the contact of a thermal reservoir which are undergoing thermal fluctuations. A thermal reservoir consists of a large number of degrees of freedom and is in equilibrium at a given temperature. It is expected that the reservoir undergoes fluctuations which has no long-term deleterious effect on the equilibrium. If a quantum system is in contact with the bath, then one may visualize the problem as: the system and the bath together are part of one single Hilbert space; only a subset of this Hilber space (the bath part) experiences thermal fluctuations. The question that we strive to answer is "How does these fluctuations affect the dynamics of the quantum system?"

Quantum Master Equation

To answer the above question, we begin by creating a finite propagator which takes into account a finite evolution due to the fluctuations (or many instances thereof) and a comparatively weak evolution (and hence linearlizable) under system Hamiltonians (drive on the system and spin-bath coupling). A coarse-grained approach results in a quantum master equation (QME) which has a exponential regulator from the fluctuations for all second order system processes. We show that this regulator is also present in the second order drive terms and hence we obtain a drive-induced dissipation term. We have also verified this term experimentally. The Kramer-Kronig pair of this term (at an appropriate limit) explains the well-known Bloch-Siegert and light shift.

Drive-induced dissipation

The drive-induced dissipation is known for many years and are usually attributed to the cross terms between the drive and the spin-bath coupling. Our result differs from this traditional view, in the sense that, drive-induced dissipation would have at least a part which does not strictly depend on spin-bath coupling. Our lab is pioneer in discovering such effects and we aim to generalize our theoretical framework to better estimate this novel effect.

Spin-boson systems

A natural choice of application of these QME is spin-boson systems i.e. a single Two Level System (TLS) coupled to a bosonic bath; the former being subjected to a coherent drive. We aim to better explain the vast volume of experimental reports on drive-induced dissipation (and shifts) with our newly formulated QME.

Quantum Information

We are also interested and are presently investigating the protocols of the quantum information processing using strong drive (and hence induced dissipation). It is expected that the drive-induced dissipation would result in less-efficient computation. We aim to quantify the loss and the remedial actions for realistic quantum information processing.

Applications of NMR (relaxation and polymers)

The chemists of our lab are actively involved in designing novel techniques based on solvent relaxation. We have shown that monitoring solvent relaxation can provide ways to monitor morphological changes in polymers (pH-sensitive or thermotropic). We have developed techniques by which one can monitor the fractional changes in the solvent-polymer Hydrogen bonds across LCST for the thermotropic polymers.


Lab members

  • Ipsita Chakraborty

    Research Scholar, Chemistry (Thesis submitted)
    Ipsita works on the solvent relaxation of polymer solutions and uses these to monitor morphological changes of pH and/or thermotropic polymers. She has also worked on checking the utility of Uhrig's dynamic decoupling sequences for efficient measurement of T2 in the presence of field noise.

  • Arnab Chakrabarti

    Research Scholar, Physics (expected to submit in 2018)
    Arnab works on the construction of Quantum Master Equations in the presence of thermal fluctuations. He also uses NMR experiments to validate the theoretical predictions, notably drive-induced dissipation. He has also worked on the efficiency of decoupling sequences in the presence of 1D Brownian motion.

  • Saptarshi Saha

    Research Scholar, Physics (joined August 2017)
    Saptarshi works on the construction of a generalized propagator to better predict the drive-induced dissipation and the journey to equilibrium. He also works on the extension of the QME to higher orders of the drive and the system-bath coupling.

  • Arpan Chatterjee

    Research Scholar, Physics (joined August 2017)
    Arpan works on the complete dynamics of two level systems coupled to bosonic bath undergoing stochastic thermal fluctuations. He also investigates the origin and the modelling of the thermal fluctuations in a bosonic bath using a first principle approach.

  • Nilanjana Chanda

    Research Scholar, Physics (joined January 2018)
    Nilanjana works on the problem of the quantum information processing in the presence of dissipations. In particular, she investigates the efficiencies of quantum algorithms as affected by drive-induced dissipation.

  • Swagata Mandal

    Research Scholar, Chemistry (joined August 2018, as a joint studet under RB and Prof. Priyadarshi De)
    Swagata focusses on monitoring UCST of thermotropic polymers in acquous solution using solvent relaxation as a tool; she also works on designing and synthesis of novel polymers.

  • Amlan Datta

    The distinguished student visitor.
    After completing his summer project in the lab, Amlan is learning the basics of quantum dynamics while he attends his other mundane duties such as going to regular classes for his course work.

Selected publications

Complete list of publications


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