Qubit channels that achieve capacity with two states

Abstract

This paper considers a class of qubit channels for which three states are always sufficient to achieve the Holevo capacity. For these channels it is known that there are cases where two orthogonal states are sufficient, two non-orthogonal states are required, or three states are necessary. Here a systematic theory is given which provides criteria to distinguish cases where two states are sufficient, and determine whether these two states should be orthogonal or non-orthogonal. In addition, we prove a theorem on the form of the optimal ensemble when three states are required, and present efficient methods of calculating the Holevo capacity.

9 pages, 2 figures

References in corpus (4)

• Two qubit copying machine for economical quantum eavesdropping
• Nonorthogonal Quantum States Maximize Classical Information Capacity
• Qubit Channels Can Require More Than Two Inputs to Achieve Capacity
• On 1-qubit channels

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• Concurrence and Entanglement Entropy of Stochastic 1-Qubit Maps
• Information-theoretic aspects of the generalized amplitude damping channel
• Improving classical capacity of qubit dynamical maps through stationary state manipulation
• Queue-Channel Capacities with Generalized Amplitude Damping