Seminar by Dr. Sharmila Balamurugan
Title: Quantum Metrology Across Scales: From Quantum Dots to Gravitational Fluctuations
Speaker: Dr. Sharmila Balamurugan, Warwick University
Abstract: Quantum metrology uses quantum resources and correlations to improve the precision with which physical parameters and signals can be measured. In this talk, I explore how these principles can reveal signatures of quantum correlations in matter and of fluctuations in the gravitational field.
First, I discuss the entanglement generation in a Cooper-pair beam splitter formed by two coupled quantum dots connected through a superconducting lead. By comparing several entanglement quantifiers, I identify an experimentally-accessible covariance-based observable that tracks the formation of entangled electrons.
Second, I discuss my work that forges a bridge between ultra-high-precision interferometer output signals and a fundamental aspect of gravity theories – the two-point correlation function of spacetime fluctuations [2]. I consider three classes of spacetime fluctuations, characterised by the decay behaviour and symmetries of their two-point correlation functions. For each, I identify low- and high-frequency behaviour of the interferometric outputs and their dependence on the interferometer's arm length. Capturing these requires sensitivity over a broad frequency range that spans the light-round-trip frequency, as provided by laboratory-scale setups, whereas detecting the presence or absence of the fluctuations can be done with high narrowband sensitivity at the light-round-trip frequency. My approach applies to interferometers with arm cavities, such as the km-long LIGO detectors, and those without, like laboratory-scale setups QUEST and GQuEST. I also assess if introducing active optical elements in the interferometric setup can enhance the sensitivity [3].
Third, I discuss the dynamics of two massive particles in the presence of quantum fluctuations of the gravitational field [4]. I find observable consequences of choosing two different position observables: (i) a frame-dependent coordinate separation and (ii) a frame-independent geodesic separation.
References:
[1] B. Sharmila, F. M. Souza, H. M. Vasconcelos, L. Sanz, Phys. Rev. A 109, 062439 (2024).
[2] B. Sharmila, S. M. Vermeulen, A. Datta, Nat. Commun. 17, 701 (2026).
[3] B. Sharmila, arXiv Preprint arXiv:2608.00907 (2026).
[4] A. Malcolm, Z.-W. Wang, B. Sharmila, A. Datta, Phys. Rev. D 111, 106022 (2025).
Venue: Seminar Room (202), Physics Department IIT Bombay, Powai, Mumbai