Venue: AB2-103; Time: 15:30 hrs
Speaker:
Prof. Anki Reddy Katha
Indian Institute Of Technology, Tirupati
Granular matter is ubiquitous in nature and industry and encompasses a wide range of systems composed of macroscopic particles. Despite their apparent simplicity, granular materials exhibit rich and often counterintuitive behavior when subjected to external forcing. Understanding these phenomena presents fundamental challenges in nonequilibrium physics and has important implications for engineering applications. In this seminar, I will discuss several physical phenomena investigated in driven granular systems. These include activated processes in granular media; nucleation and growth in sheared granular sphere packings; attractive and repulsive interactions between moving intruders; lift forces (Magnus effect) on translating and rotating disks; the rising and sinking dynamics of horizontally oscillating bodies; granular flow in silos; and the Brazil-nut effect. Through these examples, I will highlight how collective particle interactions, fluctuations, and external forcing give rise to emergent macroscopic behavior in granular systems.
Past Seminars
Speaker:
Dr. K. S. Vasu
Newcastle University, UK.
Unlike water flowing through a garden hose, the physics of fluid motion through nanometre-sized pores remains poorly understood. Key challenges include understanding liquid friction at solid interfaces, mechanisms of molecular separation, and controlling ionic transport under extreme confinement.
In this talk, I will begin with a brief overview of our research activities at Newcastle University, focusing on nanofluidics and optical sensing. I will then share my research journey, highlighting the transition from electrical to molecular transport, and my work on graphene-based membranes. Following this, I will discuss our investigations into ion transport in carbon nanoconduits and flow through nanoscale channels. Finally, I will present our collaborative research with IMEC on liquid-based memory devices for next-generation data storage.
Throughout the presentation, I will emphasize how our research drives innovation in water, energy, and advanced technologies, addressing critical scientific and societal challenges.
Speaker:
Dr. Parthajit Mohapatra
Indian Institute Of Technology, Tirupati
This talk focuses on an information-theoretic journey from bits to quantum information, highlighting the challenges and fundamental differences that arise in moving from the classical to the quantum world. It will shed light on how quantum information can be quantified, compressed, and communicated, and on the fundamental limits governing these tasks. It will conclude with my perspective on information processing over quantum networks and emerging research directions in quantum network information theory.
Speaker:
Dr. Ananya Lahiri
Indian Institute Of Technology, Tirupati
Malliavin calculus, often described as a stochastic calculus of variations, provides a differential structure for functionals of Gaussian noise. Its Malliavin derivative and Skorokhod integral form an adjoint pair, paralleling gradient–divergence structures in classical variational calculus. Through Wiener chaos decomposition, Gaussian functionals can be identified with symmetric Fock space. Under this correspondence, Malliavin differentiation and Skorokhod integration resemble annihilation and creation operators of quantum probability. The talk highlights this structural bridge from Wiener space to Fock space and from classical stochastic variation to quantum stochastic calculus.
Speaker:
Prof. B. Harihara Venkataraman
Birla Institute of Technology and Science - Pilani, Hyderabad
Layered ferroelectric materials, strontium bismuth tantalate (SrBi2Ta2O9, SBT) and bismuth titanate (Bi4Ti3O12, BIT) have been recognized for their wide-ranging applications due to their functionalities in actuators, data storage, and photovoltaic devices. However, owing to the volatility of bismuth oxide and the complex kinetics of phase formation, achieving the desirable properties of these layered ferroelectric compounds has been challenging. Recent research has revealed that substituting suitable ions into the perovskite block of the crystal lattice of these technologically renewed materials effectively enhances their physical properties, thereby improving performance, especially in capacitor and memory-based storage devices. Keeping this view in mind, polycrystalline, textured pure and rare-earth (Sm3+)-ion-doped SBT and BIT ceramics were synthesized using a cost-effective, low-temperature molten-salt flux route and characterized by X-ray diffraction to determine their crystal structures. FESEM analysis revealed a plate-like morphology for both the pure and doped SBT and BIT ceramics. Interestingly, the Bi3.85Sm0.15Ti3O12 composition showed a maximum dielectric constant of 165 and a low dielectric loss (0.16) at 100 kHz. Furthermore, the preferential orientation influenced the ferroelectric hysteresis behaviour of the rare-earth-doped BIT ceramics, associated with an energy storage efficiency of ~63%. In addition, incorporating SrTiO3 perovskites and biopolymers (cellulose) into composite materials fulfilled the requirements for embedded capacitors in integrated electronic devices. These composite films also exhibited promising results in removing toxic chromium (VI) from industrial effluents. In this talk, I will highlight the promising aspects of perovskite and layered ferroelectric materials and our investigations of their physical properties in ceramic and composite forms to enable their exploitation for the aforementioned applications.
Speaker:
Prof. Mishkatul Bhattacharya
Rochester Institute of Technology, Rochester, NY, USA.
The Josephson effect presents a fundamental example of macroscopic quantum coherence as well as a crucial enabler for metrology (e.g., voltage standard), sensing (e.g., superconducting quantum interference device), and quantum information processing (Josephson qubits). Recently, there has been a major renewal of interest in the effect, following its observation in Bose, Fermi, and dipolar atomic condensates, in exciton-polariton condensates, and in momentum space. We present theoretically a nondestructive, in situ, and real time protocol for observing the ac and dc Josephson effects including integer (recently observed in cold atoms) and fractional (hitherto unobserved in cold atoms) Shapiro steps, using a ring condensate coupled to an optical cavity. Our results have implications for the fields of atomtronics, sensing, metrology, and quantum information processing.
Speaker:
Dr. Arnab Sen
Max-Born Institute, Berlin
Understanding photochemical processes in molecules remains a fundamental challenge, as they involve coupled electronic–nuclear dynamics that often extend beyond the validity of the Born–Oppenheimer approximation (BOA). In such situations, molecular potential energy surfaces can become degenerate, particularly in the vicinity of conical intersections (CIs). These intersections act as ultrafast funnels for radiationless transitions and play a central role in numerous photochemical processes in nature. Notable examples include the cis–trans isomerization of the retinal chromophore in rhodopsin, the remarkable photostability of UV-excited DNA and RNA nucleobases, and the ring-opening reaction leading to the formation of pre-vitamin D₃. Real-time observation of coupled electronic–nuclear dynamics is therefore essential for achieving predictive control over photochemical reactivity in areas such as biological systems, atmospheric chemistry, photocatalysis, and solar energy conversion. The earliest stages of photoinduced processes occur on ultrashort timescales, ranging from a few to several hundred femtoseconds, and involve vibronically coupled electronic–nuclear wavepackets. Experimentally capturing these dynamics remains highly challenging, as it requires both ultrafast temporal resolution and sensitivity to electronic coherence and nuclear rearrangement.
Advances in ultrafast laser technology and pump–probe spectroscopy—particularly following the pioneering work of Ahmed Zewail, later recognized with the Nobel Prize in Chemistry—have enabled direct observation of molecular dynamics on their intrinsic femtosecond timescales. While many time-resolved techniques primarily probe either nuclear motion (e.g., vibrational spectroscopy and diffraction) or electronic dynamics (e.g., attosecond streaking), most photochemical processes are governed by strongly coupled electronic and nuclear motion. Capturing this interplay therefore requires techniques that are simultaneously sensitive to both degrees of freedom. In this context, time-resolved photoelectron spectroscopy (TRPES) and time-resolved X-ray absorption spectroscopy (TRXAS) have emerged as powerful tools for probing coupled electronic–nuclear wavepacket dynamics.
In this talk, the speaker will focus on TRPES, in which tuneable, few-femtosecond vacuum-ultraviolet (VUV) pulses generated via resonant dispersive wave (RDW) emission in gas-filled hollow-core fibers are used to probe the early-time dynamics of photoexcited ethylene and its deuterated isotopologue. This approach enables the direct observation of a previously unrecognized mechanism governing the initial stages of ethylene’s ultrafast excited-state dynamics. In particular, a strong nonadiabatic coupling between the initially populated π π* state and the σ π* state drives rapid torsional motion in VUV-excited ethylene, resulting in substantial population transfer between these states within less than 10 fs. Also, the speaker will present their recent work using TRXAS, in which ultrashort X-ray pulses generated from a table-top high-harmonic-generation source are employed to investigate the ultrafast structural rearrangement of nitromethane following strong-field ionization. These measurements are the first of their kind, to identify the transient intermediate involved in the nitro–nitrite rearrangement.
Speaker:
Dr. Sai Chaitanya
Indiana University, USA
Our current best-fit cosmological model explains structure formation primarily through adiabatic fluctuations. Complementary and orthogonal to these are isocurvature fluctuations. Primordial isocurvature is undetected on CMB scales and often treated as a constrained nuisance within LambdaCDM, but it can also act as a structured degree of freedom with real impact on cosmological inference. In this talk I will present an isocurvature-forward program: we study CDM/axion isocurvature sourced by a new "hyperbolic geometry" mechanism with scale-dependent (often blue-tilted) spectra, construct data-ready templates, and quantify their impact within standard analyses. I will highlight an application where a subdominant CDM component carrying isocurvature compensates the power suppression from dominant warm dark matter, reopening parameter space and allowing WDM masses as low as 300 eV (about an order of magnitude below typical current WDM mass bounds). I will briefly discuss extensions to ultra-light axion (fuzzy) dark matter, and conclude with comments on unexplored degeneracies between isocurvature contributions and neutrino-mass inference.