Archishna Bhattacharyya

We show for the first time that uncloneable encryption exists with no computational assumptions, with security inverse-polynomial in the security parameter. We use properties of a monogamy-of-entanglement game associated with the Haar measure encryption to guarantee that any state that succeeds with high probability cannot be close to maximally-entangled between the referee and either of the players, whence we can apply the decoupling principle to show that either player becomes completely uncorrelated, and therefore cannot win significantly better than random guessing.

Discrete-Modulated Continuous-Variable Quantum Key Distribution (DMCVQKD) protocols are amenable for deployment in quantum communication networks due to their experimental simplicity, but pose theoretical challenges impeding their tight security analyses. Major progress has recently been made in the finite-size regime against independent and identical (iid) collective attacks (Kanitschar, F. et. al., (2023), PRX Quantum, 4(4), p.040306). However, a complete and rigorous analysis must take into account correlated rounds of attack beyond the iid-collective assumption, and must not assume a photon-number cutoff on the signal states. The difficulty of achieving this lies in the absence of an information-theoretic framework for proving security that handles infinite dimensional multipartite quantum states that are a priori unstructured, i.e., beyond the asymptotic iid setting. We present a composable security proof against coherent attacks in the finite-size regime for a general DMCVQKD protocol. We introduce a framework to handle states that are in part iid and in part unstructured (almost iid) in infinite dimensional Hilbert spaces. We use a de Finetti reduction for infinite dimensional almost iid states (Renner, R., Cirac, J. I., Phys. Rev. Lett. 102, 110504 (2009)), and generalise the acceptance test and the energy test to almost iid states handling Eve’s correlated infinite dimensional side information. As work in progress, we address the issue of a missing chain rule that formulates an explicit key rate expression. Numerical simulation of key rates (Winick, A. et. al., Quantum 2, 77 (2018)) can then be performed, demonstrating the efficacy of the security proof.