Speaker
Description
The Leggett–Garg inequality (LGI) was originally proposed as a way to test “macrorealism”: the classical intuition that a system always possesses definite properties, whether or not we look. In this talk, I will describe how a trilogy of experiments on LGI takes us from precision tests of quantum reality to a practical route for certifying randomness, culminating in our QRange quantum random number generator.
In the first part, I will focus on a single-photon interferometric architecture in which we realise one of the most loophole-tight tests of macrorealism to date [1]. By combining LGI and related No-Signalling-in-Time conditions with careful control of measurement invasiveness, detector inefficiencies, multiphoton contamination and preparation/coincidence loopholes, we obtain a clear and robust violation of macrorealist bounds for a genuinely single system evolving in time.
The second part explains how such temporal correlations can be turned into a resource. By mapping the observed LGI violation to a lower bound on min-entropy, we obtain semi– device-independent guarantees on the unpredictability of the measurement outcomes, and demonstrate LGI-based quantum random number generation in a photonic platform [2]. Finally, I will show how the same temporal-correlation framework can be implemented on contemporary noisy quantum processors [3], providing a platform-agnostic route to certified randomness.
I will conclude by outlining how these ideas are engineered into QRange, a deployable QRNG module in which “testing reality” via LGI becomes the underlying certificate for high-quality randomness, with applications to cryptography, simulation and AI-oriented workloads.
1. Loophole free interferometric test of macrorealism using heralded single photons, K.Joarder, D.Saha, D.Home, U.Sinha, PRX Quantum, 3, 010307, 2022.
2. Single system based generation of certified randomness using Leggett-Garg inequality, P.P.Nath, Debashis Saha, Dipankar Home, U.Sinha, Physical Review Letters, 133, 020802, 2024.
3. Certified random number generation using quantum computers, P.P. Nath, A.Sinha, U.Sinha, Frontiers in Quantum Science and Technology, Vol.4, 2025, https://doi.org/10.3389/frqst.2025.1661544