Complete Characterization of Qubit Masking

Xiao-Bin Liang, Bo Li, and Shao-Ming Fei

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Submission date: 21. Aug. 2019
Pages: 9
published in: Physical review / A, 100 (2019) 3, art-no. 030304(R) 
DOI number (of the published article): 10.1103/PhysRevA.100.030304
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Abstract:
We study the problem of information masking through nonzero linear operators that distribute information encoded in single qubits to the correlations between two qubits. It is shown that a nonzero linear operator can not mask any nonzero measure set of qubit states. We prove that the maximal maskable set of states on the Bloch sphere with respect to any masker is the ones on a spherical circle. Any states on a spherical circle on the Bloch sphere are maskable, which also proves the conjecture on maskable qubit states given in [Phys. Rev. Lett. 120, 230501 (2018)]. Moreover, we provide explicitly operational unitary maskers for all maskable sets. As applications, new protocols for secret sharing are introduced.