ICTS

If a set of massive objects collide in space and the fragments disperse, possibly forming black holes, then this process will emit gravitational waves. Computing the detailed gravitational wave-form associated with this process is a complicated problem, not only due to the non-linearity of gravity but also due to the fact that during the collision and subsequent fragmentation the objects could undergo complicated non-gravitational interactions. Nevertheless some results in quantum theory of gravity, known as soft graviton theorems, determine the power law fall-off of the wave-form at late and early times, including logarithmic corrections, in terms of only the momenta of the incoming and outgoing objects without any reference to what transpired during the collision. In this talk I shall explain the results and very briefly outline the derivation of these results.
 

Quantum mechanics is a cornerstone of modern physics. Just as the 19th century was called the Machine Age and the 20th century the Information Age, the 21st century promises to go down in history as the Quantum Age. Quantum Computing promises unprecedented speed in solving certain classes of problems while Quantum Cryptography promises information theoretically secure communications. In this talk, I will discuss the world of single and entangled photons and also discuss ongoing work towards secure quantum communications, quantum information and precision experimental tests of principles of quantum mechanics in our Quantum Information and Computing lab at the Raman Research Institute, Bengaluru, India. I will end with our broad vision for the future, which includes establishment of long distance secure quantum communications in India and beyond involving satellite based, fibre based as well as quantum memory and repeater network based approaches towards the global quantum internet.
 

In 1924, Bose communicated a derivation of the Planck distribution, to Einstein, where Bose introduced a key notion of indistinguishability of photon quanta. This was a turning point in the history of quantum mechanics. Bose's article is considered the fourth most important article, in the development of quantum mechanics, following those of Planck, Einstein and Niels Bohr. It was Dirac, who coined the names Bosons and Fermions.  We present a brief historical account of Bose’s discovery, followed by a bird’s eye view of the impacts of boson bloom and Bose-Einstein condensation in modern science and technology.

[1] Boson Bloom, G. Baskaran and A. May, J. Physics B, 57, 142001 (2024)

Sommerfeld initiated the study of quantum matter in 1927, with his free electron theory of metals. This led to many remarkable developments, including the Bardeen-Cooper-Schrieffer theory of superconductivity in 1957. The impact of these theoretical developments on our understanding of crystalline materials, and its impact on the electronic technological revolution is well known. It is fair to state the idea of quantum entanglement was introduced by Einstein-Podolsky-Rosen in 1935, and its first serious application to quantum matter was the introduction of quantum spin liquids by Anderson in 1973. I will survey the many remarkable experimental and theoretical developments in quantum matter since then, including various quantum Hall states, spin liquids, correlated metals, and superconductors. I will also discuss the impact on other research areas, including quantum information and computing, quantum field theory, and the quantum theory of black holes.

While the formulation of quantum mechanics predates computability theory, the idea of computers based on quantum physics only arose much later, in the 1980s. Initially studied only by the curious and intrepid, quantum computation, and quantum information processing in general, came into the limelight in the 1990s. The impetus, namely, the discovery of rigorous evidence of the advantage offered by quantum computers, culminating in the Shor algorithm for Integer Factorization, is now well-known. Since then, the field has been guided by the promise of new technology while also allowing for the pursuit of ideas unfettered by practical (or even physical) considerations. I will describe some of the advances in the field in the wake of these developments.

Physicists have been trying to develop a theory that puts together general relativity and quantum mechanics. We will highlight some interesting theoretical ideas and point out a couple of concrete predictions.

The characterization of identical quantum particles as bosons or fermions goes back to the early days of quantum mechanics. It was realized much later that in two space dimensions, particles with any statistics (`anyons') can exist. Such particles can emerge as quasiparticles in quantum phases of matter. The prime experimental example is in the Fractional Quantum Hall Effect (FQHE). After a brief review of the FQHE, I will discuss recent developments on the observation of the phenomenon in zero magnetic field, and the associated questions and opportunities.

Computation is built on the fundamental laws of physics. At its heart, computation is a dance of countless interacting particles — what physicists call a many-body system — whether the computation is done by classical bits in a chip or qubits in a quantum processor. In this lecture, I will explore how ideas from many-body physics have shaped the past, present, and future of computation: from the collective behavior of electrons in semiconductors, to the spin-glass theory breakthroughs, like Hopfield neural networks, which laid the foundation for artificial intelligence and machine learning, to the importance of topological phases in enabling robust error correction for quantum processors.

We are now at the cusp of a new quantum era. Advances in quantum engineering provide unprecedented control over many-body systems, opening up entirely new frontiers for exploring quantum matter. These quantum devices allow us, for the first time, to study non-equilibrium many-body quantum systems, where novel dynamical phases — like time crystals — emerge. They also enable the creation of tunable and coherent quantum networks, leading to new phases in non-Euclidean geometries — such as topological quantum spin glasses. Beyond advancing our understanding of quantum matter, these developments are inspiring innovative paradigms for error correction, including Floquet codes and LDPC expander codes, which could transform the landscape of quantum computation.

Starting in the mid-1980s with the quantum control and detection of individual atoms/ions, we now have access to a variety of controllable quantum systems. One particular platform which has emerged as a popular choice is superconducting electrical circuits operating at ultra-low temperatures. These are micro to nanoscale electrical circuits that can be engineered to show quantum mechanical phenomena like superposition and entanglement. In this talk, I will introduce the concept of a quantum electrical circuit and how one can use superconducting materials to build them. The flexibility in circuit design allows one to create near ideal custom Hamiltonians which can be used to implement textbook measurements and explore various phenomena in previously unexplored regimes. The same flexibility also enables the possibility of large-scale chips for quantum computing applications. I will discuss some examples to illustrate the versatility of this platform and also highlight the various challenges in building a practical quantum computer.

Quantum simulation has emerged as a new and interdisciplinary research field that enables a microscopic view of quantum matter both in and out of equilibrium across different physical platforms. Recent applications of quantum simulations involving strongly correlated electronic systems using ultracold atoms in optical lattices and tweezers will be outlined. By comparing with state-of-the-art numerical methods, we show that quantum simulations with fermionic atoms can provide highly valuable and novel insights into the understanding of strongly correlated matter. As an example, we present an analysis of the emergence of the pseudogap phase in the fermionic Hubbard model. We identify a novel universal behavior of magnetic correlations upon entering the pseudogap phase, observed in both spin-spin and higher-order spin-charge correlations.

In addition to analog methods, gate-based fermionic quantum computing offers distinct advantages in quantum computations. We demonstrate the elementary operations required to manipulate the orbital degrees of freedom, which form the basis of a fermionic quantum computer.

This talk will go over the history, principles, development, and applications of inelastic light scattering, widely known as the Raman effect, concluding with some remarks on Raman and Mandelstam, the two major figures in the discovery.

Astrophysics and cosmology grew, symbiotically, alongside quantum mechanics, over the past hundred years. The developing fields of atomic, nuclear and particle physics found motivation and application to central problems in astrophysics. These included the elucidation of stellar and interstellar spectra, the powering of stars and supernovae, the origin of the chemical elements, the properties of neutron stars and the interpretation of cosmic rays.  This relationship continues and is expressed in some of the most pressing problems today, notably the nature and consequences of dark matter, the provenance of cosmic structure and baryon asymmetry, the properties of magnetars, the acceleration of the highest energy cosmic rays and the origin of life.

Although traditional astronomy was associated with visible light, it grew enormously in the twentieth century with the opening up of the electromagnetic and non-electromagnetic spectra. This happened in parallel with the development of quantum mechanics, which was employed by astrophysicists to explain planets, stars, galaxies and the history of the entire universe. Sometimes astrophysics provided a ready application for atomic, nuclear, particle and condensed matter physics; sometimes it provided an inspiration for fresh, basic understanding. This symbiotic relationship continues in the twenty-first century. In this talk, I will briefly recount some of this history and outline three contemporary observational challenges to quantum mechanics: neutron stars with ultra-strong magnetic fields, cosmic rays with individual energies comparable with that of a well-hit cricket ball and the origin of life.