Jeudi  26 juin

Title: Exploring Quantum Information and Many-Body Physics with Nuclear Spins: Temporal Correlations, Lee-Yang Zeros, and the Quantum Mpemba Effect 

Arijit Chatterjee (IISER, Pune, India)

Abstract:   

 In the presence of a high magnetic field, nuclear spins serve as an ideal testbed for studying quantum information processing, quantum foundations, and quantum many-body physics, due to their long classical (T1) and quantum (T2) memories and robust control via radio frequency pulses. In this talk, I will discuss some of our recent works using nuclear spins to explore these areas. First, I will address our investigations of temporal correlations, quantified by the Leggett-Garg Inequality (LGI), of a qubit evolving under the superposition of unitary operators. Using a three-qubit quantum register, we experimentally realized superposed unitaries and demonstrated the violation of LGI beyond its maximal quantum value of 1.5, indicating enhanced non-classicality. Interestingly, we found that this superposed unitary dynamics improves robustness against decoherence. Next, I will discuss our work on Lee Yang (LY) zeros, points in the complex plane of physical parameters where the partition function goes to zero, which provide insights into a system's thermodynamics and its behaviour near critical points. We propose a method to determine the full set of LY zeros of an asymmetric Ising system using a single quantum probe and demonstrate it experimentally with a three-qubit nuclear spin register. Finally, I will talk about our investigation of the quantum Mpemba effect in nuclear spin relaxation dynamics. We theoretically showed that a system far from steady state can relax faster than one nearer to equilibrium and demonstrated it experimentally. I will conclude with brief mentions of our other works in quantum shadow tomography and non-completely positive quantum dynamics with nuclear spins.   
References :
 [1] Chatterjee Arijit, T. S. Mahesh, Mounir Nisse, and Yen-Kheng Lim. "Observing algebraic variety of Lee-Yang zeros in asymmetrical systems via a quantum probe." Physical Review A 109, no. 6 (2024): 062601.
[2] Chatterjee Arijit, H. S. Karthik, T. S. Mahesh, and A. R. Devi. "Enhanced non-macrorealism: Extreme violations of Leggett-Garg inequalities for a system evolving under superposition of unitaries." arXiv preprint arXiv:2411.02301 (2024). (Submitted to Physical Review Letters)
[3] Sengupta Aniket, Chatterjee Arijit, Sreejith G. J. and T. S. Mahesh. "Partial Shadow Tomography for structured operators and its experimental demonstration using NMR." arxiv preprint arXiv:2503.14491 (2025)