Nonequilibrium quantum dynamics
We study open quantum systems and driven-dissipative dynamics: how quantum states evolve, lose coherence, organize collectively, and sometimes become more useful because dissipation is present—not despite it.
Our theory is built around quantum master equations. Nuclear magnetic resonance provides a versatile experimental test bed, letting us probe relaxation, driven response, collective coherence, quantum control, sensing, measurement, and nonequilibrium phases.
NMROpen systemsQuantum control
What we ask
Our central question is simple to state and difficult to answer: what genuinely new dynamics emerge when coherent driving, interactions, fluctuations, and dissipation act together?
We investigate quantum systems pushed away from equilibrium by external drives while remaining coupled to fluctuating environments. The competition creates optimal operating points, non-Bloch dynamics, drive-induced dissipation, frequency shifts, prethermal plateaus, and robust nonequilibrium phases.
We develop fluctuation-regularized master-equation methods that treat coherent driving and system interactions alongside environmental relaxation. These tools connect microscopic fluctuation timescales to experimentally observable rates and shifts.
We study state transfer, entanglement creation and storage, quantum speed limits, dynamic nuclear polarization, sensing, dynamical decoupling, and control under realistic dissipation.
Our interests include discrete time crystals, prethermalization, collective decay, measurement-induced dynamics, quantum trajectories, and the quantum-to-classical transition.
Nuclear magnetic resonance gives us precise control of spin Hamiltonians and relaxation. We use it to test theory, engineer driven dynamics, and identify effects that remain hidden in purely unitary descriptions.
Principal investigator
Professor · Department of Physical Sciences · IISER Kolkata
Rangeet trained in experimental magnetic resonance with Anil Kumar at the Indian Institute of Science, then worked with Lucio Frydman on solid-state NMR, Clare P. Grey on spectroscopy of energy materials, and Malcolm Levitt on quantum rotors. He joined IISER Kolkata in 2010.
These days he is usually found asking quantum systems what they do when driven, dissipated, measured, or otherwise denied a quiet life. When not persuading master equations to behave, he takes an active interest in coding and LaTeX, and reads books that contain rather fewer commutators.
The people doing the calculations
Six researchers, connected by a shared interest in how quantum systems behave once the idealizations are switched off.
PhD student
Gourab studies pathways selected by dissipation. His work follows the Stern–Gerlach experiment from spin–path entanglement to separated, broadened classical beams; explores relaxation-stabilized discrete time crystals demonstrated with NMR; and investigates quantum sensing and nonuniform collective dissipation, including superradiance-like spin dynamics.
PhD student
Sarfraj works on quantum control in driven open systems. He has studied microwave-controlled polarization transfer in dynamic nuclear polarization, quantum speed limits under drive-induced dissipation, and state-selective quantum pumping produced by coupling a system to a prepared quantum source and tracing over that source.
PhD student
Shubhamay studies measurement-induced discrete time-crystalline dynamics using the lab’s open-system measurement framework, related to its earlier work on the emergence of the Born rule. His broader interests include quantum measurement problems and quantum-trajectory descriptions of monitored systems.
PhD student
Debanu works on cavity quantum electrodynamics with two atoms coupled to a cavity, with or without direct interatomic coupling. He asks when driven and dissipation-assisted dynamics can create atomic entanglement, how that entanglement can be preserved, and what the results imply for quantum information processing and storage.
PhD student
Tanaya develops and applies quantum master-equation methods to relaxation and collective coherences. Her current problems include spin-locking dynamics and dynamical decoupling, with an emphasis on identifying compact descriptions of correlated dissipative evolution.
Master’s student
Debopriyo studies fluctuations in quantum thermodynamics. He is investigating heat flow between reservoirs and the thermodynamics of driven quantum systems, asking how drive and environmental fluctuations reshape energy transport and performance.
Life beyond research
A few moments from the people and occasions that make up life in Spin Lab.
Peer-reviewed journal articles · 2021–present
S. Fency and R. Bhattacharyya · Europhysics Letters 155, 55001
G. Das, S. Saha and R. Bhattacharyya · Physical Review A 113, 042216
S. Saha, Y. Ibrahim and R. Bhattacharyya · Journal of Physics A 58, 035302
G. Das and R. Bhattacharyya · Physical Review A 110, 062211
A. Chatterjee and R. Bhattacharyya · European Physical Journal D 78, 44
S. Saha and R. Bhattacharyya · European Physical Journal Special Topics 233, 1425–1441
S. Saha and R. Bhattacharyya · Physical Review A 109, 012208
S. Saha and R. Bhattacharyya · Journal of Statistical Mechanics, 023103
N. Chanda, P. Patnaik, and R. Bhattacharyya · Physical Review A 107, 063708
A. Chakrabarti and R. Bhattacharyya · Europhysics Letters 142, 55001
S. Saha and R. Bhattacharyya · Physical Review A 107, 022206
S. Saha and R. Bhattacharyya · Journal of Physics B 55, 235501
S. Saha and R. Bhattacharyya · Journal of Magnetic Resonance Open 10, 100046
N. Chanda and R. Bhattacharyya · Physical Review A 104, 022436
Past members
The group’s earlier work spans master equations, quantum measurement, nonequilibrium phases, quantum optics, NMR relaxation, entanglement, and stochastic dynamics.
NMR solvent relaxation, responsive polymers, and dynamical-decoupling measurements of transverse relaxation.
Fluctuation-regularized quantum master equations, drive-induced dissipation, and NMR tests.
Dissipative dipolar systems, prethermalization, time crystals, entanglement storage, and solid-state NMR.
Quantum optics, drive-induced dissipation, coherent population trapping, and resonance fluorescence.
Quantum gates under drive-induced dissipation and open-system models of quantum measurement.
Applications of fluctuation-regularized master equations to strongly coupled spin networks.
Connections between nuclear magnetic resonance and weak quantum measurement.
Open-system modelling of spin noise using modified quantum master equations.
Intermediate-timescale thermalization and collective dissipation in spin systems.
Landau–Zener dynamics in an open two-level system under frequency-swept driving.
Multipartite entanglement in cavity systems and its use for quantum-state storage.
Microscopic connections between fluctuation and dissipation in stochastic Langevin dynamics.
Open quantum systems
Master’s project on driven quantum Otto engines and drive-assisted enhancement of engine efficiency. Graduated June 2026.
Find us
Department of Physical Sciences
Indian Institute of Science Education and Research Kolkata
Laboratory
E-036, Research Complex
Mohanpur 741246, Nadia
West Bengal, India
Email
rangeet [at] iiserkol.ac.in
Phone
+91 33 6136 0000 · Ext. 1292