Title:	Entropy and geometry of quantum states
Authors:	Shivam, Kumar Reddy, Anirudh Samuel, J. Sinha, Supurna
Keywords:	Quantum measurement metric distinguishability
Issue Date:	17-May-2018
Publisher:	World Scienti¯c Publishing Company
Citation:	International Journal of Quantum Information, 2018 Vol. 16(4), p 1850032
Abstract:	We compare the roles of the Bures–Helstrom (BH) and Bogoliubov–Kubo–Mori (BKM) metrics in the subject of quantum information geometry. We note that there are two limits involved in state discrimination, which we call the “thermodynamic” limit (of NN, the number of realizations going to infinity) and the infinitesimal limit (of the separation of states tending to zero). We show that these two limits do not commute in the quantum case. Taking the infinitesimal limit first leads to the BH metric and the corresponding Cramér–Rao bound, which is widely accepted in this subject. Taking limits in the opposite order leads to the BKM metric, which results in a weaker Cramér–Rao bound. This lack of commutation of limits is a purely quantum phenomenon arising from quantum entanglement. We can exploit this phenomenon to gain a quantum advantage in state discrimination and get around the limitation imposed by the Bures–Helstrom Cramér–Rao (BHCR) bound. We propose a technologically feasible experiment with cold atoms to demonstrate the quantum advantage in the simple case of two qubits.
Description:	Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)
URI:	http://hdl.handle.net/2289/6941
ISSN:	0219-7499 1793-6918 (Online)
Alternative Location:	https://arxiv.org/abs/1609.07279 https://doi.org/10.1142/S0219749918500326
Copyright:	2018. World Scienti¯c Publishing Company
Appears in Collections:	Research Papers (TP)

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