PhD student Gennaro Zanfardino

Entanglement-based efficient protocol for state discrimination among n alternatives

Current schemes for the discrimination of single-qubit states rely upon state measurements in order either to achieve unambiguous state identification or to minimize the error probability. Here we describe an alternative method based on the detection of the entanglement that is established between the qubit and an appropriate ancilla after suitable global unitary operations on the entire system. Our work is motivated by recent developments on entanglement detection with only one or few copies [1,2]. We exploit such feature to introduce a novel and more efficient state discrimination protocol. In our scheme one does not need to know the exact amount of entanglement but only to detect its presence. If one can detect entanglement with only a single copy of the state, then in order to discriminate the state of interest within a pool of N alternatives our protocol requires at most N-1 copies [3]. Our results have some far-reaching consequences in quantum communication and quantum cryptography. For instance, provided that entanglement detection can be realized in a single-copy experiment, an immediate implication is that some QKD protocols turn out to be less secure than previously assumed. Simulating the dynamics of classical spin-glass systems requires a large amount of computational resources especially for the sizes that are needed in order to provide safe estimates on the behavior in the thermodynamic limit. Here we introduce a general scheme for the quantum simulation of the dynamics of a p-spin glass interacting on an arbitrary lattice [4]. Specifically, with a composite n-qubits system, it is possible to simulate the dynamics of 2n interacting spins. Inspired by previous work with classical coherent light [5], we specialize our proposal to a concrete all-optical experimental set-up for simulating a fully connected p-spin-glass. With a state of n photons uniformly distributed over m modes, it is possible to simulate a classical disordered system where the total number of spins is equal to m and the number p of spins in the local interaction terms is 2n. For this case, we provide arguments indicating that since the computational time scales as the total number of spins m, compared to the scaling m3 that can be obtained in state-of-the-art classical Monte Carlo simulation schemes. [1] S. J. van Enk, C. W. and Beenakker, Phys. Rev. Lett. 108 110503 (2012). [2] Y. Zhou, P. Zeng, and Z. Liu, Phys. Rev. Lett 125 200502 (2020). [3] G. Zanfardino and F. Illuminati, Preprint ArXiv:2408.yyyyy (2024). [4] F. Illuminati, M. Leonetti, L. Leuzzi, S. Paesani, G. Ruocco, R. Santagati and G. Zanfardino, Preprint ArXiv:2408.yyyyy (2024). [5] M. Leonetti, E. Hörmann, L. Leuzzi, G. Parisi, and G. Ruocco, Proceedings of the National Academy of Sciences, 118 2015207118 (2021).