SYMPHY 2021

ABSTRACT: A quantum computer promises to revolutionize many areas of science and technology with the potential for discovery of new molecules, novel materials, clean energy, effective medicines and a deeper understanding of nature. There is an enormous effort throughout the world to build powerful machines. In this talk, I will discuss the challenges in building such a machine. I will start by introducing a few different approaches to build a quantum computer which essentially differ in the construction of the elementary building block: the quantum bit or qubit. A qubit is essentially a quantum two level system and can be implemented using different physical systems like trapped ions or superconducting circuits. I will then describe the essential requirements for building a quantum computer using such qubits with a particular focus on the engineering challenges and the classical control circuitry. This discussion will be based on the superconducting circuit approach but the general principles will apply to all other approaches as well. I will then conclude by giving an overview of the status of this field in India, including our own work at TIFR, and the opportunities and challenges in the future.

ABSTRACT: The standard model of particle physics relies on the framework of quantum field theory (QFT). Several calculations in this framework relies on the use of Feynman diagrams. While calculationally and conceptually powerful, this approach becomes quickly cumbersome beyond the first few leading orders. In fact, some of the founding fathers of quantum theory like Dirac were vocal in their dislike for this approach and disowned this framework. I will talk about an approach called the Bootstrap which was once popular in the 1960s, abandoned in the 1970s, but has come back into fashion over the last decade or so. As an example I will review how one calculates in a manifestly finite manner, without using Feynman diagrams, critical exponents in the so-called epsilon expansion at the Wilson-Fisher fixed point (eg. critical point of water). I will also discuss how century old mathematics relying on the so-called Bieberbach conjecture gives rise to constraints on low energy physics arising from the S-matrix Bootstrap.

Abstract: Collisions of highly relativistic nuclei offer the possibility of producing quasimacroscopic systems of dense nucleonic and/or quark-gluon matter at relatively high temperature. This extreme state of color-deconfined matter is usually called the quark-gluon plasma (QGP). Hydrodynamical models treat the hot system created in a collision as a fluid. In this talk, I will discuss the experimental results on how the QGP undergoes a nearly ideal hydrodynamical expansion when created.

ABSTRACT: Observations of the 21-cm line from the hyperfine transition in neutral hydrogen hold the potential to allow us to probe the Universe over a large redshift range. This talk will review our present understanding of the expected signal and highlight what we hope to learn from such observations. Various observational challenges, and some of the current and upcoming observational efforts will also be discussed.

ABSTRACT: On September 14, 2015, our ability to observe the universe dramatically changed by adding a new tool to explore the cosmos. The Laser Interferometer Gravitational-Wave Observatory (LIGO) in the US for the first time detected gravitational waves produced by two colliding black holes more than a billion light years away. Since that first observation, LIGO and the European Virgo observatory have discovered dozens of black hole and neutron star collisions across the cosmos. This talk will highlight the science impact of the discoveries so far and the potential of future observatories to address unsolved problems in numerous areas of physics and astronomy, from cosmology to Beyond the Standard Model of particle physics, and how they could provide insights into the nature of black holes and of ultra dense matter as may be found in neutron star cores.

ABSTRACT: With a goal to expand on the candidate materials exhibiting two-dimensional (2D) magnetism, we explore the possible stabilization of 2D ferromagnetism in two different systems, a) Boronated holey graphene [1] and b) Layered inorganic-organic hybrid perovskites.[2,3]

In the first problem,[1] motivated by the existence of nitrogenated monolayer holey graphene (C2 N), we consider the boronated counter part (C2B), and show through first-principles simulation while C2N is nonmagnetic and semiconducting, C2B is ferromagnetic and metallic. We provide microscopic understanding of this contrasting behavior. In the second problem, considering the Cu based layered inorganic-organic hybrid perovskites, we derive their 2D counterparts which are found to be stable, the corresponding cleavage energies being a factor of 2-2.5 smaller than that to derive graphene from graphite. The antiferrodistortive arrangement of Cu2+ ions in the inorganic layer of the 2D structure promotes ferromagnetism, which together with single ion anisotropy is found to give rise to finite-temperature long-range ordering of Cu spins, as established through solution of a generalized spin Hamiltonian. [2] We further propose a yet-unexplored class of 2D ferromagnets derived out of Cr-based organic-inorganic layered compounds. [3]

References

• [1] Dhani Nafday, Hong Fang, Puru Jena, Tanusri Saha-Dasgupta, Phys. Chem. Chem Phys. 21, 21128 (2019).
• [2] Dhani Nafday, Dipayan Sen, Nitin Kaushal, Anamitra Mukherjee, Tanusri Saha-Dasgupta, Phys. Rev. Res (Rapid Commun), 1, 032034 (R) (2019).
• [3] Dipayan Sen, Gour Jana, Nitin Kaushal, Anamitra Mukherjee, and Tanusri Saha-Dasgupta, Phys. Rev. B 102, 054411 (2020).
  

ABSTRACT: The talk will discuss selected case studies of technologies developed at the Neuro-Robotic Touch Laboratory, The BioRobotics Institute of Sant'Anna School of Advanced Studies in Pisa Italy, for endowing robots with artificial tactile sensors that are distributed over large areas. In the presented scientific approach, robotic systems are developed by capitalizing on a fertile interaction between robotics and neuroscience, so that the advancements of neuroscientific research can lead to the development of more effective technologies, which in turn contribute to the fundamental understanding of physiological processes.

A first case study proposed is with piezoresistive MEMS sensors, applied to bionic hand prostheses to restore rich tactile skills, such as texture discrimination, in upper limb amputees. The developed biorobotic technologies and artificial intelligence methods, based on information encoding with neuromorphic spikes emulating physiological tactile representation, can be applied to a variety of scenarios. Additional technologies were explored in order to cover large areas of robot bodies, including sensors based on cultured biological cells such as MDCK, piezoelectric ZnO nanowires grown with seedless hydrothermal method, and Fiber Bragg Grating (FBG) sensors.

Selected achievements are shown in the talk, discussing the application of tactile sensing technologies in a gripper able to manipulate fragile and deformable objects, or for covering the full area of an anthropomorphic robotic arm. Particularly, covering a robotic arm with a large sensorized skin allows the implementation of smart collaborative policies, such as safe interaction and programming by demonstration, that can be deployed in the factories of the future.

ABSTRACT: When it comes to ranking the most manipulated materials on earth, granular matter is second only to water. From a basic physics standpoint, the ease with which granules of well-defined shape and size can be made, imaged, and also driven by external fields has contributed immensely to our understanding of the structure of liquids [1], amorphous solids and jamming [2], and most recently active matter [3] to name a few. In my talk, I will describe recent results wherein we exploit the versatility offered by 3D printing to encode chiral activity in shape achiral granules. In vertically agitated assemblies of these chiral active particles we observed emergent stereoselective interactions that had a profound influence on the dynamics of the liquid state [4]. If time permits, I will describe findings from experiments on dense assemblies of achiral active ellipsoids [5].
References:

• [1] A geometrical approach to the structure of liquids, J. D. Bernal, Nature183,141(1959)
• [2] Granular solids, liquids, and gases, H. M. Jaeger, S. R. Nagel, and R. P. Behringer, Rev. Mod. Phys. 68, 1259 (1996)
• [3] Long-Lived Giant Number Fluctuations in a Swarming Granular Nematic, V. Narayan, S. Ramaswamy, N. Menon, Science 317, 105 (2007)
• [4] Emergent stereoselective interactions and self-recognition in polar chiral active ellipsoids, P. Arora, A. K. Sood and R. Ganapathy, Sci. Adv. 7, eabd0331 (2021)
• [5] Motile topological defects hinder dynamical arrest in dense liquids of active ellipsoids, P. Arora, A. K. Sood and R. Ganapathy (submitted 2021)

ABSTRACT:The optical properties of plasmonic structures can be controlled by resonant excitation of desired modes at, and around the interfaces of these structures. These resonant phenomena lead to enhanced electromagnetic fields by several orders of magnitude, thereby leading to intriguing vast range of applications. In my talk, starting from the basics of plasmons, sensing principles and parameters, we would discuss the recent developments on plasmonic sensors. The basic aspects of design and development of nanostructures for enhanced sensors will be discussed. The talk will span topics from surface plasmon resonance/surface enhanced fluorescence/extra-ordinary transmission and their applications on sensing of glycated hemoglobin and pollutant in water.

ABSTRACT:Diversity in the natural world emerges from the collective behavior of large numbers of interacting objects. Statistical physics provides the framework relating microscopic to macroscopic properties. A fundamental assumption underlying this approach is that we have complete knowledge of the interactions between the microscopic entities. But what if that, even though possible in principle becomes impossible in practice ? Can we still construct a framework for describing their collective behavior ? Dense suspensions and granular materials are two often quoted examples where we face this challenge. These are systems where because of the complicated surface properties of particles there is extreme sensitivity of the interactions to particle positions. In this talk, I will present a perspective based on notions of constraint satisfaction that provides a way forward. I will focus on our recent work on the emergence of elasticity in the absence of any broken symmetry, and sketch out other problems that can be addressed using this perspective.