Ours is a research group in the Department of Physical Sciences of IISER Kolkata, which works on open quantum systems, quantum dynamics, and quantum information.
Rangeet Bhattacharyya completed his doctoral studies on experimental magnetic resonance techniques under the tutelage of Anil Kumar from the Physics department of the Indian Institute of Science, Bangalore, India (2005). Later, he gained experience in solid-state magnetic resonance techniques with Lucio Frydman of Weizmann Institute of Science, Isreal, and in the spectroscopy of energy materials with Clare P Grey, FRS, Stony Brook University, NY, USA. He also worked briefly on quantum rotors with Malcolm Levitt at Southampton University, UK.
Since 2010, he is a faculty member in the Department of Physical Sciences, in the Indian Institute of Science Education and Research Kolkata. His present research interests lie in the area of driven-dissipative quantum systems. He works on the developments of quantum master equations and applications of the master equations in quantum optics and in quantum information processing. He also studies the aggregation dynamics of polymers in solutions using magnetic resonance techniques.
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?"
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.
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.
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.
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.
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.
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.
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.
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.
Research Scholar, Physics (joined August 2020)
Gourab is working on the information transfer along a noisy quantum channel. In particular,
he investigates the optimal speed of information propagation along a 1D ising chain, analyzed using
a
Masters student, Physics (joined August 2020).
Yeshma is working the intermediate-timescale thermalization problem with the help of our
Department of Biophysics, Bose Institute, P-1/12 C.I.T. Scheme VII-M, Kolkata - 700054, India
Ipsita worked on the solvent relaxation of polymer solutions and used
the method 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 T_{2} in the presence of field noise.
Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot -- 7610001, Israel
Arnab worked on the construction of Quantum Master Equations in the presence
of thermal fluctuations. He also used 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.
Masters student, DPS, IISER Kolkata (Completed July 2020)
Abhinaba did a project on the applications of a
Masters student, DPS, IISER Kolkata (Completed July 2020)
Srishti worked on the connection between the NMR and the weak measurements.
Masters student, Physics (Completed August 2021).
Amlan worked on the modeling of spin noise using a modified form of the quantum master equation.