Department Colloquia | Ashoka PhySoc

MONSOON 2023

Quantum Materials by Computation: Challenges & Opportunities

Prof. Tanusri Saha-Dasgupta

6/12/23

In recent times, there has been a worldwide surge of activity on Quantum materials, materials whose properties are dominated by quantum fluctuations, quantum entanglement, quantum coherence, and topological behavior. In this talk, I will discuss the contribution of computation in understanding and predicting these materials. In particular, I will discuss its application in understanding materials properties by understanding the structure-property relation, prediction of new functionalities in known materials, and predicting new materials all together.

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Prof. Tanusri Saha-Dasgupta is the Director of S. N. Bose National Centre for Basic Sciences, Kolkata and a Senior Professor in the Department of Condensed Matter Physics & Materials Science, Thematic Unit of Computational Materials Science. Her main area of work lies in the First principles of electronic structure calculation and study of magnetic, optical and electronic properties of complex materials, Realistic theory of strongly correlated electron system, Electronic structure and properties of materials at nanoscale, and Electronic structure and phase stability in disordered alloys. She was Elected Fellow of the Indian National Academy of Sciences in 2021, J.C. Bose National Fellowship in 2020, Fellow of The World Academy of Sciences in 2019 and Elected Fellow of American Physical Society, 2015. She has won "MRSI-ICSC Superconductivity & Materials Science Annual Prize" for the year 2016 and DAE Rajaramanna Prize Lecture in 2015 and many more accolades.

Closing down the observation gap on millisecond to second timescale relativistic X-ray and radio transients

Dr. Sujay Mate

29/11/23

Over the past few decades, transient astronomy has boomed with the discovery of different types of energetic transient phenomena such as Gamma-ray Bursts (GRBs), Fast Radio Burst (FRBs) and Gravitational Waves (GW) from binary systems of neutron stars and/or black holes. Most of these transients are highly relativistic events and key to understanding them is to do multi-wavelength and multi-messenger observations. The unpredictable nature of these transients (both in space and time) coupled with the relatively short duration (from few milliseconds to few tens of seconds) makes it challenging to detect and study them in detail. To overcome this challenge, it is necessary to build sensitive instruments that cover large part of the sky. In this talk I will present our efforts to build two instruments that can detect second timescale transients at high-energies (X-ray to gamma-ray) and at radio frequencies. In the first part, I will present the proposed Indian mission Daksha that aims to detect GRBs and electromagnetic counterparts of GW events. Particularly, I will focus on how Daksha can measure hard X-ray polarisation in GRBs. In the second part, I will briefly talk about the CHIME/Slow search, that involves our novel efforts to detect radio transients at seconds timescale with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) radio telescope. This parameter space is as-yet unexplored and could harbour interesting transients such as "slower" duration or extremely scattered FRBs, radio counterparts of GRBs or binary neutron star mergers, flaring stars, magnetized white dwarfs and radio emission from X-ray binaries.

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Dr. Sujay Mate is a Postdoctoral Fellow in the Department of Astronomy and Astrophysics at the Tata Institute of Fundamental Research (TIFR), Mumbai. He is interested in studying radio and high-energy transients, such as Fast Radio Bursts (FRBs), GRBs, and Electromagnetic Counterparts of Gravitational Waves (EMGW). His current research covers two aspects of transient search; one focuses on developing an algorithm to detect seconds timescale FRB-like radio transients with the CHIME telescope and the other focuses on developing instrumentation to detect GRBs and EMGW events at X/gamma-ray energies. Before joining TIFR he was at the Institut de Recherche en Astrophysique et Planétologie (IRAP), Toulouse, France, where he worked on the upcoming Chinese-French gamma-ray burst (GRB) monitor — SVOM and obtained my PhD from the Université de Toulouse III - Paul Sabatier.

Quantum Simulation using Noisy Quantum Circuits

Prof. Arijeet Pal

22/11/23

Many-body quantum systems are notoriously hard to study theoretically due to the exponential growth of their Hilbert space. It is also challenging to probe the quantum correlations in many-body states in experiments due to their sensitivity to external noise. Using synthetic quantum matter to simulate quantum systems has opened new ways of probing quantum many-body systems with unprecedented control, and of engineering phases of matter which are otherwise hard to find in nature. Noisy quantum circuits have become an important cornerstone of our understanding of far-from-equilibrium quantum many-body dynamics. In this talk I will discuss the dynamics of hybrid quantum circuits consisting of unitary gates interspersed with nonunitary projective measurements. In particular I will focus on the growth of entanglement in these engineered systems and how they lead to the simulation of localized and macroscopically entangled states of matter.

Dr. Arijeet Pal is a Professor of Physics at University College London. He obtained his PhD in Physics from Princeton University following postgraduate and undergraduate degrees from Cambridge and Delhi. He held research fellowships at Oxford and Harvard Universities. He is a condensed matter physicist and is known for his contributions to many-body localization and non-equilibrium phases of matter. His current research interests include quantum many-body phenomena at the intersection of condensed matter physics and quantum information science.

Outflows from Galaxies

Prof. Biman Nath

15/11/23

Galaxies often throw out gas in a violent manner. These powerful ‘galactic winds’ are detected in different wavebands, from radio to optical to X-rays. This phenomenon is intimately connected to a regulatory process by which stars form in galaxies. In the absence of these outflows, stars would have formed in galaxies more abundantly, which would have quickly depleted the gas reserve in the universe, and the universe would have become full of passive and dim galaxies by now. I will talk about how observations, theoretical calculations and simulations have helped us to understand the gaseous outflows, and in turn, how galaxies evolve.

Prof. Biman Nath is a professor of Astrophysics and Astronomy at Raman Research Institute (RRI), Bangalore. He has done his MS/PhD in Astronomy from the University of Maryland, and Postdoctoral work at Max Planck Institute in Bonn and in IUCAA Pune. He has been in the Raman Research Institute since 1997. He received the Indira Gandhi Award for science popularization from INSA in 2011. His current research interests involve diffuse gas in the universe (intracluster and intergalactic medium) and interaction between galaxies and diffuse gas.

Novel Effects in Laser/EM Wave Interaction with Magnetised Plasmas

Prof. Amita Das

8/11/23

Laser plasma interaction has opened up many areas of frontier research activities of fundamental and applied interest. The technological advancements ( in terms of laser power, frequency, etc.,) keep this area alive for research exploration and revelation of interesting physics and the study of its consequences. With the availability of high magnetic fields (of the order of kilo Tesla and ongoing proposals for generating Mega Teslamagnetic fields in the laboratory), a new possible direction of research seems to emerge in the near future, wherein the gyro frequency of one (or both ) of the plasma species can be made higher than the laser/Electromagnetic (EM) wave frequency. Recent Particle-in-cell simulations conducted by my group at IIT Delhi has unraveled novel mechanism of laser energy absorption, harmonic generation, and several other effects in this particular regime. An important observation made in this regard is that the plasma becomes completely transparent in strong magnetic fields when thegyrofrequency of both the plasma species becomes higher than the laser/EM wave frequency The talk will cover this magnetized laser-plasma interaction regime in detail and discuss some of these novel effects.

Prof. Amita Das is an Indian plasma physicist. She is currently a professor in the Department of Physics at the Indian Institute of Technology Delhi. Her research interests are in laser-plasma interactions, nonlinear plasmas, plasma turbulence, and the properties of strongly coupled and dusty plasma systems. She has been awarded a J.C. Bose fellowship by DST and is a Fellow of the Indian National Science Academy India in 2019. Prof. Das also received the Women Excellence Award (Scientist and Innovator) from Utkarsh Foundation India in 2015. She has been Vice President (2006-2008) and General Secretary (2004-2006) of the Plasma Science Society of India (PSSI).

Astrophysical Compact Objects in the Context of General Relativity

Prof. Patrick Das Gupta

18/10/23

In this talk, we will begin with an introduction to astrophysical compact objects (ACO) like white dwarfs, neutron stars, black holes, etc. emphasizing on the basic physics as well as on observational evidence. It will be followed by an exposition of the physical aspects of general relativity (GR). Thereafter, we will discuss how GR studies buttress ACO research and vice versa. In the final segment, we will briefly discuss the challenges posed by the supermassive black holes and the fast radio bursts.

After receiving the National Science Talent Search scholarship in 1976, Patrick Das Gupta joined B.I.T.S., Pilani, to do a 5-years integrated M.Sc. Physics. In 1981, he took admission in the Ph.D. program at the Indian Institute of Science., Bengaluru, but left for Tata Institute of Fundamental Research, Mumbai, in 1982 as a research scholar in the Theoretical Astrophysics Group. He did his PhD on the Theoretical determination of the Luminosity Function of radio galaxies in various cosmological models. Soon after submitting his Ph.D. thesis in 1988, he joined IUCAA, Pune, as a postdoctoral fellow. During 1989-90, he had short stints at the University of Wales, Cardiff (UK), as a senior research fellow as well as at the Observatoire de Paris, Meudon, to learn about gravitational wave sources and the corresponding data analysis techniques. He joined the Department of Physics and Astrophysics, University of Delhi, in 1993, and has been a full professor there since 2004. His current research interests include studies related to the confirmation of Hawking Area Theorem from the observed gravitational waves from binary black holes, proposing a unified model for Gamma Ray Bursts and Fast Radio Bursts, modelling dark energy, torsion and Chern-Simon gravity using a dynamical four-form, mechanisms to generate supermassive black holes from Bose-Einstein condensation of bosonic dark matter, baryogenesis from primordial black holes as well as measurement problem in quantum mechanics. Patrick Das Gupta was the Head of the Department of the Department of Physics & Astrophysics, Delhi University, in year 2020. He was also the elected president of IAGRG (Indian Association of General Relativity and Gravitation) from March 2020 to March 2022. He had also been active in training and leading students for the International Physics Olympiads under the aegis of Homi Bhabha Centre for Science Education, TIFR, Mumbai. He is currently a member of the Editorial Board of Resonance, a Science Education Journal that is brought out by the Indian Academy of Sciences, Bengaluru.

Engineering Floquet Topological Phases using Periodic Driving

Dr. Ranjani Seshadri

4/10/23

Topological systems driven out of equilibrium have been a popular topic of research for the last several years. A periodic drive can be used to manipulate the topological character and/or generate topologically non-trivial phases in a system which was trivial to begin with. In this talk, I am going to use one of the earliest known two-dimensional topological insulators - the Bernevig-Hughes-Zhang model - as an example to demonstrate the realization of such "Floquet topological phases" using a time-periodic perturbation. In particular, I will be discussing the effect of changing the polarization of incident light on these phases. Moreover, such perturbations are also shown to generate higher-order topological phases. Finally, I will discuss the effect of breaking the time-periodicity of the perturbation. This is motivated by advances in pump-probe techniques where ultrafast laser pulses are used to probe materials.

Dr. Ranjani Seshadri is presently working as a postdoctoral researcher at the Department of Physics, Ben-Gurion University of the Negev, Israel. She completed her B.Sc. (Hons) in Physics from St.Stephen's College in 2011 and MSc-Ph.D. in Physics in 2018 from the Indian Institute of Science, Bengaluru under the guidance of Prof. Diptiman Sen, after which she worked as a postdoctoral researcher at McGill University (2019-2020). Her area of research is theoretical condensed matter physics including the study of topological phases of matter both in equilibrium and driven out of equilibrium, several aspects of graphene, and topological aspects of unconventional superconductivity.

Step in Time: Discovery of the Gravitational Wave background using Pulsars

Prof. Dipankar Bhattacharya

27/9/23

Pulsars, by virtue of the excellent stability of their periodic signals, can be used as clocks to detect minute motions and gravitational effects in space. Using an array of pulsars distributed across the sky, members of the International Pulsar Timing Array announced on 29 June 2023 the discovery of a cosmic background of long-wavelength gravitational waves, likely originating from supermassive black holes orbiting around each other. This talk will introduce the audience to the science and technology of Pulsar Timing, describe the steps that led to this remarkable discovery, and discuss the future prospects.

Prof. Dipankar Bhattacharya is the Sunanda and Santimay Basu Chair Professor in Astrophysics at Ashoka University. Prior to joining Ashoka he was the Dean, Core Academic Programmes at the Inter-University Centre for Astronomy and Astrophysics (IUCAA). He received his Bachelors’ and Masters’ degrees in Physics from Jadavpur University, Kolkata, and his PhD from the Indian Institute of Science, Bengaluru. He carried out post-doctoral research at the University of Amsterdam and the University of California, Santa Barbara and was a member of the faculty at the Raman Research Institute, Bengaluru before moving to IUCAA. His research interests cover both theoretical astrophysics and observational astronomy, with particular emphasis on High Energy Astrophysics including compact stars, black holes and cosmic explosions. He is closely associated with the Indian space astronomy mission AstroSat and is the chair of its Science Working Group.

A Twist in the Hunt for Axion Dark Matter

Dr. Pranjal Trivedi

15/9/23

Dark Matter is an outstanding mystery at the heart of cosmology and the axion is a leading and well-motivated candidate currently being pursued intensively. In the first half of the talk I will review the evidence and properties of dark matter. A new axion particle (also wave) is motivated by the CP-problem in the strong nuclear interaction. It could also arise generically and has all the characteristics to be cold dark matter in the Universe. I will then describe key ideas at the forefront of the worldwide hunt for axion dark matter and compare laboratory experiments to astrophysical and cosmological probes of axions. In the second half I will focus on how axion dark matter produces a rotation of the linear polarization of the cosmic microwave background (CMB). This cosmological birefringence is a unique signal of parity-violating axion dark matter. Our results enable a search for the axion-photon coupling in new areas of parameter space and improve constraints by several orders, over a wide range of axion mass, up to the fuzzy dark matter scale. Recent tentative evidence of birefringence from re-analyzed Planck CMB data could be an axion signal and future CMB observations have the potential to more precisely probe the existence and properties of axion dark matter.

Dr. Pranjal Trivedi is a post-doctoral scientist at the University of Hamburg, Germany. He studied at Delhi, Cambridge, Caltech and did his Ph.D. work at IUCAA (with Prof. Kandaswamy Subramanian) and also at Johns Hopkins. His research investigates open questions in cosmology and dark matter using theory, simulations and data analysis. He has been working on how axion dark matter could be discovered using new cosmic effects, particularly with the cosmic background radiation. He is also working to understand how cosmic magnetic fields could have originated from the early Universe and uniquely altered the evolution of structures and the background radiation. He takes a keen interest in teaching physics and astrophysics. Previously, he was a permanent faculty member at the University of Delhi, Sri Venkateswara College, where he taught the range of undergraduate physics and led students on a solar eclipse expedition. At the University of Hamburg he has received several teaching prizes. He is also active in science & astronomy outreach and public engagement, collaborates with artists and has exhibited work at the intersection of physics with art.

DNA without Borders

Prof. Somendra Mohan Bhattacharjee

6/9/23

The unique thermal and topological properties of double-stranded DNA arise from the Watson-Crick base pairing, making it an exceptional interacting polymeric system. This talk will explore a few physical phenomena associated with DNA in biology, and the potential it holds for tackling physics and computation problems.

Prof. Somendra Mohan Bhattacharjee received his Ph.D. in Physics from Carnegie Mellon University, Pittsburgh, USA, B. Sc in Physics (Honours) from Presidency College, Calcutta, and M. Sc. in Physics from the University of Calcutta. After doing post-doctoral research at the University of Massachusettes, Amherst, USA, and Bell Labs, Murray Hill, he joined the Institute of Physics, Bhubaneswar as a faculty member and continued till April 2019. His research interest is in theoretical condensed matter physics and biology-inspired physics mostly related to phase transitions. The force-induced unzipping transition of DNA is one of his most important contributions. He is a fellow of the Indian National Science Academy and Indian Academy of Sciences, and a J C Bose National Fellow. He was a Regular Associate of ICTP, Trieste, Italy.

Galaxies Inside and Out — The Resolved Stellar Populations of the Milky Way, Andromeda, and Triangulum Galaxies

Prof. Puragra (Raja) GuhaThakurta

4/9/23

I will present results from our group's recent/ongoing single epoch and time domain spectroscopic, photometric, and astrometric studies of the resolved stellar populations of our Galaxy and two of its large galactic companions in the Local Group, Andromeda (M31) and Triangulum (M33). We have used a combination of Keck/DEIMOS, CFHT/MegaCam, Gaia, HST, and JWST data for the HALO7D and NGVS surveys of the Milky Way, the SPLASH survey of M31, and the TREX survey of M33. Highlights from these surveys include the discovery of the most distant RR Lyrae in the Galaxy's halo (R ~ 300 kpc), constraints on the accretion history of the Galaxy's inner halo (R ~ 25 kpc) via pencil beam studies of main sequence turnoff stars in 7-dimensional space, the discovery of a dynamically hot inner halo population in M33. and an age-velocity dispersion trend in the stellar disk of M31.

Prof Puragra (Raja) GuhaThakurta is a Professor and Department Chair of Astronomy and Astrophysics at UC Santa Cruz. He founded SIP in 2009. He and his students and postdocs have mentored many SIP interns. Prof. Raja also has a parent’s perspective: his daughter was a SIP intern. As an offshoot of SIP, Raja and his colleagues started the Creating Equity in STEAM (CrEST) umbrella of initiatives in 2020, which includes (among others): Shadow the Scientists (StS) [2020], a virtual window into researchers and research in action; and Global SPHERE Network [2017], a community of practice for researchers who engage high school students in STEAM research. He has taught astrophysics for UCSC COSMOS and algebra for Project for Inmate Education (PIE) at Santa Cruz County Jail. He teaches introductory astronomy classes at UCSC. His research topics include galaxy formation, mergers, dark matter, etc. using the Keck and Hubble telescopes. He dabbles in art in his (non-existent) free time.

Probing the Universe Using Cosmic Microwave Background Radiation

Prof. T. R. Seshadri

30/8/23

The Cosmic Microwave Background radiation was first detected in 1965. Over the years important developments have taken place, both on the theoretical as well as experimental fronts, due to which we have a much better understanding of its minute features. The four aspects of CMBR, namely the isotropic component, anisotropy, spectrum as well as polarization contain a plethora of information, which when decoded, can together reveal how different physical processes dominated at different epochs of the evolutionary history of the universe. In this talk I will highlight the origin of CMBR and discuss how its features can be used to probe the evolution, constitution and the distribution of matter in the Universe.

Prof. Seshadri is a faculty at University of Delhi since 2001. He has done his MS Physics from IIT Delhi and Ph.D. from TIFR, Bombay. He is Postdoc from Physical Research Laboratory (Ahmedabad), University of Delhi and Astronomy Centre, University of Sussex, Brighton, UK. His research interests lies in Cosmic Microwave Background Radiation, Origin of Cosmic Magnetic Field, Magnetic fled in High redshift Galaxies, and Nature of Large Scale Structures.

Exploring the Exotic Exoplanets: Are We Alone?

Prof. Sujan Sengupta

29/8/23

As soon as the Copernican theory established the fact that the Earth and the other planets are orbiting around the Sun, many scholars realized that the billions of lights in the night sky are like the Sun and they should also have planets and planetary systems similar to the Solar planets. The speculation that some of these planets must be similar to the Earth and the eternal curiosity of mankind “Is anybody out there?” culminated as a result of such a realization. The first false alarm of an exoplanet was reported by the astronomers of the Madras Observatory in 1855. Ultimately a Jupiter size planet orbiting a Sun-like star was discovered in 1995. Soon, astronomers discovered many exoplanets orbiting stars of various kinds and the diversity in the physical properties of these planets revolutionized our concept of planets. Consequently, the focus has been shifted to the quest for Earth-like habitable planets and hence the presence of extraterrestrial life. On the other hand, six decades of hectic search by astronomers has not provided any techno-signature of alien civilization. In this talk I shall describe the systematic scientific search for Earth-like planets that may show the signature of life. In this context I shall also discuss the rare astronomical and geological coincidences that enabled life on the Earth to survive and evolve.

Dr. Sujan Sengupta is a Senior Professor at the Indian Institute of Astrophysics, a premier research institute of the country in Bangalore under the Ministry of Science and Technology, Govt. of India. After completing post-graduation in Mathematics from Burdwan University, West Bengal in 1990, he joined Indian Institute of Astrophysics at Bangalore as a CSIR Research Fellow. He obtained his Ph.D. degree from the Department of Physics, Bangalore University in 1996 in Astrophysics. After a brief period of postdoctoral research at Vanderbilt University, Nashville, USA, with a NASA fellowship, he returned to India and joined the same institute as a faculty in 2002. His main research activities include theory and observation of Extra-solar planets and Exo-moons, Astrobiology Brown Dwarfs. He pioneered the polarimetric method for detection and characterization of exoplanets and brown dwarfs. Prof. Sujan Sengupta was one of the signatories along with the late Stephen Hawking, Prof. Frank Drake, Prof. Kip Thorne et al. of the Breakthrough Initiative project, established by Yuri Milner, that searches for extra-terrestrial intelligence. He is a member of the International Astronomical Union. Besides publishing several research papers in the top most international peer reviewed journals, Prof. Sengupta has also authored a popular book in English entitled “Worlds Beyond Our Own- The search for Habitable Planets” published by Springer International. He has also written a similar book in Bengali which was recently published by Ananda Publishers Private Ltd.

Colloquium posters by Sanjana Gupta

SPRING 2023

Quantum Watch Based on a Rydberg Wave Packet

Dr. Marta Berholts

11/5/23

In this talk, I will present the concept of the quantum watch that was developed during my postdoctoral project at Uppsala University in the HELIOS laser laboratory. The watch consists of a helium atom that is excited into a wave packet of Rydberg states using an ultrashort laser pulse with a wide energy bandwidth. Rydberg states are excited states in atoms that exhibit long lifetimes and have orbitals that extend micrometers away from the atomic core. By coherently exciting more than one Rydberg state, it is possible to perform quantum beat spectroscopy where the energy difference between the states results in constructive and destructive interference of the photoelectron yield. We found a remarkably rich beat structure in the time-resolved photoelectron yield when exciting multiple Rydberg states located close to He ionisation potential. Furthermore, we found an almost perfect agreement between simulations and the complex experimental signal. With this quantum watch, we show how to measure time in a different way, not by counting the clock's ticks as it is usually done, but by obtaining time fingerprints and therefore knowing the time very accurately on the femtosecond timescale without using a counter. The quantum watch has the potential to become a valuable tool in time-resolved spectroscopy. The study is recently published in Physical Review Research journal https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.4.043041.

Dr. Martha Berholts did her PhD in materials science, University of Tartu. She is currently a Research Fellow in the Department of Materials Science, Laboratory of X-ray Spectroscopy, University of Tartu.

Charge-spin Conversion and Spin-orbit Torques in Spintronic Devices

Prof. Pietro Gambardella

8/5/23

The spintronic landscape has changed dramatically over the last ten years thanks to a deeper understanding of the charge-spin conversion processes and magnetic interactions mediated by spin-orbit coupling in different classes of materials. In this talk, I will present prominent mechanisms that allow for angular momentum transfer and unusual magnetic couplings in magnetic heterostructures, which enable unprecedented control over magnetization reversal and domain wall motion in a variety of materials and devices. Illustrative examples include 3-terminal magnetic tunnel junctions, in which the combination of spin-orbit torques, spin transfer torque, and voltage control of magnetic anisotropy leads to reproducible sub-ns magnetization reversal with an extremely narrow spread of the switching time distributions. Further, we exploit the chiral coupling induced by the interfacial Dzyaloshinskii–Moriya interaction. to realize interconnected magnetic networks and domain wall racetracks that function as inverters, diodes, and reconfigurable minority logic gates, which perform logic operations with current-induced domain-wall motion. By cascading several gates we demonstrate electrical control of magnetic data and device interconnection in logic circuits. Finally, we discuss the emergence of novel material systems and discuss opportunities to fabricate scalable and energy-efficient magnetic random access memories and non-volatile logic.

Professor Gambardella and his team form an experimental research group studying magnetic materials and surface systems for applications in magnetoelectronics; this includes, for example, magnetic storage media and sensors. The main focus is on the fabrication of new materials (functional metal-organic and metal-oxide thin-film materials, nanoparticles, and nanostructures) and their characterization using complex methods such as synchrotron radiation spectroscopy, scanning probe microscopy, and electrical transport measurements.

Deciphering Cosmic Dawn: A Conquest of the Final Frontier

Dr. Hamsa Padmanabhan

3/5/23

I will begin with a broad-based introduction to some of the big open questions in cosmology, and illustrate how upcoming experiments are well-poised to help answer them, especially at the Cosmic Dawn — the birth of the first galaxies in our Universe — widely believed to be the 'final frontier' of cosmological surveys today. This period — about a hundred million years after the Big Bang — is primarily accessible due to radiation from hydrogen, the most abundant element in the Universe, which emits at a wavelength of 21 cm, in the radio band. An exquisite investigation of the Cosmic Dawn will soon become possible with an emerging technique called intensity mapping (IM), which measures the integrated 21 cm emission from all sources, using large arrays of radio telescopes. A particular advantage of IM is that it provides a tomographic, or three-dimensional picture of the Universe, unlocking significantly more information than we presently have from galaxy surveys. I will overview the latest advances in research related to the evolution of hydrogen over 12 billion years of cosmic time, involving a novel data-driven framework to interpret current and future observations. This allows us to fully utilize our present knowledge of astrophysics in order to develop cosmological forecasts from IM. Apart from offering key insights into the nature of the first galaxies, this opens up the exciting possibility of testing theories of fundamental physics from the Cosmic Dawn.

Dr Hamsa Padmanabhan is Collaboratrice Scientifique II and a principal investigator of the Swiss National Science Foundation (SNSF) Ambizione Grant at the University of Geneva, Switzerland. She was previously a CITA Fellow at the Canadian Institute for Theoretical Astrophysics, Toronto, Canada and a Tomalla post-doctoral fellow at the Institute for Particle Physics and Astrophysics, ETH Zurich, Switzerland. She graduated from IUCAA, Pune, India with a PhD in Physics in December 2015. She has a wide breadth of research expertise, ranging from theoretical investigations (in quantum field theory and relativity) to data-intensive, observation-oriented astronomy and astrophysics. The novel halo model framework developed by her is used extensively in the community to interpret cosmological observations of atomic and molecular gas and to exploit the tremendous potential of future astrophysical surveys in the radio, millimetre and optical wavelengths. These studies, in which she plays an active role — with collaborators from India, Europe, Canada and the USA — probe both fundamental physics and cosmology. She was the co-lead of the chapter on Cosmic Dawn and Reionization for the White paper on Fundamental Physics with the Square Kilometre Array (SKA), one of the biggest astrophysics projects of the coming decades, and is a member of the SKA Communications and Outreach Network (SKACON). Hamsa has received several prestigious awards and fellowships throughout her career. She was selected as a Goldman Sachs Global Leader by the Institute of International Education (IIE) and the Goldman Sachs Foundation and is one of the few in the world who has the honour of a minor planet in the solar system being named after her.

From an Impossible Dream to the Unreachable Stars: the Journey of the Neutrino

Prof. Srubabati Goswami

26/4/23

Neutrinos were proposed by Wolfgang Pauli to explain the conservation of energy principle in nuclear beta decay. This elusive electrically neutral particle was detected almost three decades later by Clyde Cowan and Frederick Reines. Since then neutrino physics has remained an active area of research, providing an indication of physics beyond our established ideas. Neutrinos also carry information from distant stars. This talk will trace the journey of the neutrino from the impossible dream of Pauli to the observation of neutrinos from unreachable stars, by the state-of-the-art ICECUBE detector at the south pole.

Prof. Srubabati Goswami did her Ph.D. at Calcutta University and is currently a Senior Professor in the Physical Research Laboratory, Ahmedabad. Her topic of research is High Energy Physics with special emphasis on neutrino physics and probing physics beyond the Standard Model. She is a member of the India-based Neutrino Observatory collaboration. She has received several awards including the Humboldt fellowship from the Alexander-von-Humboldt Foundation, the P. Sheel memorial lecture award for women scientists from NASI, the J.C. Bose National Fellowship of SERB, etc. She is an elected fellow of all three science academies of India and The World Academy of Sciences (TWAS).

Living Liquid Crystals

Prof. Varsha Banerjee

3/4/23

An amalgamate of nematic liquid crystals and active matter, referred to as living liquid crystals, is a promising self-healing material with futuristic applications for targeted delivery of information and micro-cargo. We provide a phenomenological model to study the symbiotic pattern dynamics in this contemporary system using the Toner-Tu model for active matter (AM), the Landau-de Gennes free energy for liquid crystals (LCs), and an experimentally motivated coupling term that favours co-alignment of the active and nematic components. Our extensive theoretical studies unfold two novel steady states, chimeras and solitons, with sharp regions of distinct orientational order that sweep through the coupled system in synchrony. We show that the symbiotic dynamics of the AM and LC components can be exploited to induce and manipulate order in an otherwise disordered system.

Prof. Varsha Banerjee did her PhD in “Analytic and Numerical Studies of Neural Network Models for Content Addressable Memory “ under the supervision of Professor Chandan Dasgupta, Department of Physics, Indian Institute of Science, Bangalore in 1991. She was a C.S.I.R Research Associate-ship at the School of Physical Sciences, JNU, New Delhi from 1992 to 1996. She was a D.S.T. Scientist (under the Scheme for Young Scientist) at the School of Physical Sciences, JNU, New Delhi from 1996 to 1997. In 1997, she joined IIT Delhi as a visiting faculty and then she became a lecturer there. She was also a Regular Associate at, International Centre for Theoretical Physics, Trieste, Italy from 2003 to 2010. Currently, she is a Professor of Physics at IIT Delhi. She was awarded the DST Young Scientist Project Award in 1996. She was also nominated for the Theoretical Physics Seminar Circuit from 2004 to 2006. She has received various prestigious research grants like German Academic Exchange Service and Department of Science and Technology, India (DAAD-DST), Mathematical Research Impact Centric Support (MATRICS) by SERB India, UK-India Education and Research Initiative (UKIERI), Indo-French Centre for Promotion of Advanced Scientific Research (IFCPAR/CEFIPRA).

Aspects of Classical and Quantum Computing of Quantum Many-Body Systems

Dr. Raghav Govind Jha

10/2/23

Over the past few decades, the study of quantum many-body systems on classical computers have made use of tensor network methods. We will discuss these ideas and apply them to some well-known models.We then elaborate on problems that are beyond the reach of classical computers and explain how in the next few decades, we can hope to study them using quantum computing methods.

Dr. Jha is currently a postdoctoral researcher at Jefferson Lab in Newport News, VA, USA working on topics related to quantum computing. Before starting this position, he spent three years at Perimeter Institute for Theoretical Physics in Waterloo, Canada. He completed his Ph.D. at Syracuse University in 2019.

SPRING 2024

Different Angles on Accreting Supermassive Black Holes

Prof. Prajval Shastri

14/2/24

Supermassive black holes inhabit the centres of most galaxies and appear to co-evolve with their host galaxies. While we do not yet fully understand how galaxies and their central supermassive black holes grow hand in hand, evidence suggests that such black holes play a significant role in regulating galaxy assembly. We are able to spot these black holes to the far reaches of the universe if and when they accrete matter, which is also what causes them to impact their environments out to spatial scales that are well beyond their gravitational sphere of influence. In this talk, I will discuss the understanding that has emerged from studies of the systematics of accreting supermassive black holes from across the electromagnetic spectrum, and also pointers to the way forward.

Prajval Shastri is an astrophysicist of over four decades. She investigates the physics of giant black holes that are found in the centres of distant galaxies using telescopes at multiple frequencies based on Earth as well as in space. She got her PhD from the Tata Institute of Fundamental Research and after post-doctoral research positions in the University of Texas at Austin, University of California at Berkeley and the Harvard-Smithsonian Centre for Astrophysics she was a faculty of the Indian Institute of Astrophysics, Bengaluru for 23 years. She has been a Fulbright fellow at Stanford University and Senior Fellow at the International Centre for Radio Astronomy Research, Australia. She is currently Emeritus Scientist at the Raman Research Institute. She is extremely passionate about science outreach. She believes that the cultivation of scientific thinking is for everyone, uses astrophysics as a vehicle to engage lay audiences of all ages with these questions in multiple languages, and works for the peoples science movement towards this goal. She is also deeply concerned about the inequities in the sciences and attempts to bring an intersectional lens to the endeavours to mitigate them. She is the founder and past chair of the Gender in Physics Working Group of the Indian Physics Association and past member of the Working Group for Gender Equity of the Astronomical Society of India. She is Vice-chair of the Women in Physics Working Group of the International Union of Pure and Applied Physics and Vice-Chair of the Executive Committee for the International Year of Basic Sciences for Sustainable Development. In addition to her research publications and popular articles on astrophysics, her published work includes writings on gender inequity as well as science and society.Electronics set-up with the help of MeitY, Govt. of India. He is also deeply interested in pedagogical issues of science education and sociological issues of S&T as a human activity.

Investigating Quantum Speed Limits with Superconducting Qubits

Prof. Meenakshi Singh

9/2/24

The speed at which quantum entanglement between qubits with short range interactions can be generated is limited by the Lieb-Robinson bound. Introducing longer range interactions relaxes this bound and entanglement can be generated at a faster rate. The speed limit for this has been analytically found only for a two-qubit system under the assumption of negligible single qubit gate time. We seek to demonstrate this speed limit experimentally using two superconducting transmon qubits. Moreover, we aim to measure the increase in this speed limit induced by introducing additional qubits (coupled with the first two). Since the speed up grows with additional entangled qubits, it is expected to increase as the system size increases. This has important implications for large-scale quantum computing.

Dr. Singh is an experimental physicist with research focused on quantum thermal effects and quantum computing. She graduated from the Indian Institute of Technology with an M. S. in Physics in 2006 and received a Ph. D. in Physics from the Pennsylvania State University in 2012. Her Ph. D. thesis was focused on quantum transport in nanowires. She went on to work at Sandia National Laboratories on Quantum Computing as a post-doctoral scholar. She is currently an Associate Professor in the Department of Physics at the Colorado School of Mines. At Mines, her research projects include measurements of spin-orbit coupling in novel materials and thermal effects in superconducting hybrids. She recently received the NSF CAREER award to pursue research in phonon interactions with spin qubits in silicon quantum dots.

Why Don't Astronomers Use SI Units?

Prof. Prasenjit Saha

6/2/24

Astrophysics is well-known for idiosyncratic units that have never in practice been superseded by the SI. Why is that? Do astronomers use parsecs, optical magnitudes, and so on just to annoy students, or is there actually a problem with using SI units consistently in astrophysics? This talk will argue that there actually was aproblem with the SI, but the reforms of 2019 solved it, and the new SI works very well with astrophysics.

Dr. Prasenjit Saha is a Professor in the University of Zurich since 2005. He did his bachelors from Delhi University and Master's from IIT Kanpur. He obtained his DPhil from Oxford University. His research lies in several topics within theoretical astrophysics. Prof. Saha started very theoretical, working on regular vs chaotic orbits and now has almost completed the transition to experiment: working on new instruments that apply quantum optics to astronomical imaging.

Physics of Soft & Flexible Electronics: Contours of an Emerging Revolution

Prof. Yashowanta N. Mohapatra

24/1/24

The emergence of large area flexible and stretchable electronics is all set to bring about a revolution akin to silicon revolution. I will describe the science behind this new technology and its enormous potential through examples from our work on various applications and devices that can be printed on a variety of substrates such as plastic, paper and textile. I will also in the process describe the nature of problems and physics questions that are crucial to the development of basic components of this technology such as printable diodes, displays and thin film transistors using embedded nanostructures such as carbon nanotubes (CNT), and hybrid heterostructures.

Dr. Yashowanta N. Mohapatra is currently Professor of Physics and Materials Science in Indian Institute of Technology Kanpur, India. His main interests are in Electronic and Photonic Materials, specially inorganic and organic semiconductors for novel applications. He joined IIT Kanpur in 1990 after completing doctoral degree and postdoctoral work at Indian Institute of Science Bangalore. Recently he has been deeply interested in development technologies related to the emerging area of Flexible Electronics, especially development of functional inks, devices and printing processes appropriate for large scale manufacturing of flexible electronics. Prof. Mohapatra has been the Head, Department of Physics, Materials Science Programme at IIT Kanpur, and Coordinator and founding member of Samtel Centre for Display Technologies, IIT Kanpur, a centre devoted to development of Organic Light Emitting Displays and related Organic Electronics. He has been a core member instrumental in setting up National Centre for Flexible Electronics set-up with the help of MeitY, Govt. of India. He is also deeply interested in pedagogical issues of science education and sociological issues of S&T as a human activity.

Cosmic Inflation, Large Quantum Fluctuations, and Primordial Black Holes

Dr. Swagat Mishra

23/1/24

Cosmic inflation is the leading paradigm to explain the origin of structure in the universe by seeding primordial density perturbations via tiny quantum fluctuations in the very early universe. Primordial Black Holes (PBHs) are interesting compact objects which might have formed due to the gravitational collapse of potentially large density perturbations in the early universe, which can also be generated by quantum fluctuations during inflation. In this seminar, after providing a thorough introduction to cosmic inflation, the speaker will discuss various possible mechanisms for generating such large fluctuations during inflation. Since PBHs form from rare and non-linear over-densities, their abundance is highly sensitive to the non-Gaussian tail of the primordial probability distribution function (PDF). Hence, it is important to determine the full PDF of primordial fluctuations, which can be carried out non-perturbatively using the 'Stochastic inflation' framework. The speaker will expand upon these important issues before concluding the talk.

Dr. Swagat Mishra did his PhD from IUCAA, Pune under the supervision of Prof. Varun Sahni in the year 2020. His doctoral thesis, "Some aspects of Accelerating Universe: from Inflation to Dark Energy" received the Justice Oak Outstanding Thesis Award in 2021 awarded by ASI India. He is presently a postdoctoral fellow at the Center for Astronomy and Particle Theory, University of Nottingham. His research interests are Theoretical Cosmology, Early Universe Physics, QFT in curved spacetime and Effective Field Theories.