Department of Physics

Ashoka University is a private university located in Sonipat, Haryana, India, focusing on liberal arts and sciences. It was established in 2014.&nbsp;It is guided by an academic council of academics and scholars from around the world. The council sets the university&#39;s academic standard, advising on matters of curriculum, faculty hiring and research.&nbsp;

Ashoka University offers a full-time 3 (+ 1) year undergraduate programme. The University comprises of&nbsp;2500 plus students, with a mix of both national and international students.&nbsp; &nbsp;

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Ashoka University

Periodically kicked Floquet systems, such as the kicked rotor, are a paradigmatic and illustrative simple model of chaos. For non-integrable quantum dynamics, there are several diagnostic measures, such as Loschmidt echo, autocorrelation function and out of time order correlator (OTOC) to study the presence of (or the transition to) chaotic behaviour. We analytically compute these measures in terms of the eigensystem of the unitary Floquet operator of the driven quantum systems. We use these expressions to determine the time variation of the measures for the quantum-kicked rotor (QKR) on the torus, for the integrable as well as the chaotic case. For a simpler integrable variant of the kicked rotor, we also give a representation theoretic derivation of its dynamics.

Pramana Journal of Physics

<a href="https://inspirehep.net/literature/1806926">Quantum chaos measures for Floquet dynamics</a>

The complexity of quantum states under dynamical evolution can be investigated by studying the spread with time of the state over a predefined basis. It is known that this complexity is minimized by choosing the Krylov basis, thus defining the spread complexity. We study the dynamics of spread complexity for quantum maps using the Arnoldi iterative procedure. The main illustrative quantum many-body model we use is the periodically kicked Ising spinchain with nonintegrable deformations, a chaotic system where we look at both local and nonlocal interactions. In the various cases, we find distinctive behavior of the Arnoldi coefficients and spread complexity for regular versus chaotic dynamics: suppressed fluctuations in the Arnoldi coefficients as well as larger saturation value in spread complexity in the chaotic case. We compare the behavior of the Krylov measures with that of standard spectral diagnostics of chaos. We also study the effect of changing the driving frequency on the complexity saturation.

Physical Review E

Spread complexity and quantum chaos for periodically driven spin chains

Krylov complexity is an important dynamical quantity with relevance to the study of operator growth and quantum chaos and has recently been much studied for various time-independent systems. We initiate the study of K complexity in time-dependent (driven) quantum systems. For periodic time-dependent (Floquet) systems, we develop a natural method for doing the Krylov construction and then define (state and operator) K complexity for such systems. Focusing on kicked systems, in particular the quantum kicked rotor on a torus, we provide a detailed numerical study of the time dependence of Arnoldi coefficients as well as of the K complexity with the system coupling constant interpolating between the weak and strong coupling regimes. We also study the growth of the Krylov subspace dimension as a function of the system coupling constant.

World University root node

Krylov construction and complexity for driven quantum systems

To deliver the full science potential of the square kilometer array (SKA) telescope, several SKA regional centres (SRCs) will be required to be constructed in different SKA member countries around the world. These SRCs will provide high performance compute and storage, for the generation, of advanced science data products from the basic data streams generated by the SKA science data handling and processing system, critically necessary to the success of the key science projects to be carried out by the SKA user community. They will also provide support to astronomers to enable them to carry out analysis on very large SKA datasets. Construction of such large data centre is a technical challenge for all SKA member nations. In such a situation, each country plans to construct a smaller SRC over the next few years (2022 onwards), known as a proto-SRC. In India, we propose to construct a proto-SRC, which will be used for the analysis of data from SKA pathfinders and precursors with strong Indian involvement, such as uGMRT, Meerkat and MWA. We describe our thinking on some aspects of the the storage, compute and network of the proto-SRC and how it will be used for data analysis as well as for carrying out various simulations related to SKA key science projects led by Indian astronomers. We also present our thoughts on how the proto-SRC plans to evaluate emerging hardware and software technologies and to also begin software development in areas of relevance to SKA data processing and analysis, such as algorithm implementation, pipeline development and data visualisation software. © 2023, Indian Academy of Sciences.

Journal of Astrophysics and Astronomy

Plans for building a prototype SKA regional centre in India

We construct superconformal invariants in superspace which are used to build 3-point correlators of spinning operators in general N=2 superconformal field theories in three dimensions. Our systematic analysis includes various relations between these invariants and provides a minimal set of parity-even and parity-odd invariants which is further used to construct general 3-point functions in any 3d N=2 SCFT. For conserved (super)currents, we explicitly compute various 3-point functions using Wick contractions in the free field case, and express them in terms of the constructed parity-even invariants. We give evidence through examples for the claim that the 3-point function of conserved currents generally comprises of two parts – a parity-even piece coming from the free theory, and a parity-odd piece.

European Physical Journal C

Superconformal invariants and spinning correlators in 3d N= 2 SCFTs

We have investigated the rich dynamics of complex wave packets composed of multiple high-lying Rydberg states in He. A quantitative agreement is found between theory and time-resolved photoelectron spectroscopy experiments. We show that the intricate time dependence of such wave packets can be used for investigating quantum defects and performing artifact-free timekeeping. The latter relies on the unique fingerprint that is created by the time-dependent photoionization of these complex wave packets. These fingerprints determine how much time has passed since the wave packet was formed and provide an assurance that the measured time is correct. Unlike any other clock, this quantum watch does not utilize a counter and is fully quantum mechanical in its nature. The quantum watch has the potential to become an invaluable tool in pump-probe spectroscopy due to its simplicity, assurance of accuracy, and ability to provide an absolute timestamp, i.e., there is no need to find time zero.

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Physical review research

Quantum watch and its intrinsic proof of accuracy

We present the results of timing and spectral analysis of the high-mass X-ray binary pulsar, Cen X-3, with the help of observations carried out using the Large Area X-ray Proportional Counter onboard AstroSat. As part of our analysis, we sampled the source properties during four different observation epochs covering two widely different intensity states. We obtain a timing solution and report precise measurements of the spin and orbital parameters corresponding to these observational epochs. The pulse profiles during the two intensity states reveal dramatically varying shapes within a time span of 1 month. We report the detection of one of the lowest measured frequencies of quasi-periodic oscillations at 0.026&nbsp;±&nbsp;0.001&nbsp;Hz for Cen X-3 during its low-intensity state. We also find correlated periodic and aperiodic noise components in the power density spectra. We further carried out a phase-averaged and a pulse phase-resolved spectral study, where we find that the best-fitting continuum spectrum is well described by an absorbed Comptonization model along with a blackbody. Cen X-3 exhibited the presence of the ∼28&nbsp;keV cyclotron resonant scattering feature absorption line and a ∼6.6&nbsp;keV Fe emission line in both the intensity states. Significant variations in the line-forming regions and mode of accretion for Cen X-3 within time spans of a month make Cen X-3 a highly dynamic persistent binary.

Monthly Notices of the Royal Astronomical Society

Timing and spectral studies of Cen X-3 in multiple luminosity states using AstroSat

The control of spin waves in periodic magnetic structures has facilitated the realization of many functional magnonic devices, such as band stop filters and magnonic transistors, where the geometry of the crystal structure plays an important role. Here, we report on the magnetostatic mode formation in an artificial magnetic structure, going beyond the crystal geometry to a fractal structure, where the mode formation is related to the geometric scaling of the fractal structure. Specifically, the precessional dynamics was measured in samples with structures going from simple geometric structures toward a Sierpinski carpet and a Sierpinski triangle. The experimentally observed evolution of the precessional motion could be linked to the progression in the geometric structures that results in a modification of the demagnetizing field. Furthermore, we have found sets of modes at the ferromagnetic resonance frequency that form a scaled spatial distribution following the geometric scaling. Based on this, we have determined the two conditions for such mode formation to occur. One condition is that the associated magnetic boundaries must scale accordingly, and the other condition is that the region where the mode occurs must not coincide with the regions for the edge modes. This established relationship between the fractal geometry and the mode formation in magnetic fractals provides guiding principles for their use in magnonics applications.