Towards unambiguous quantum state discrimination in an optical memory

The possibility to store and recall information encoded into quantum states of light is at the heart of many applications of quantum information processing, including a quantum repeater [1]. A recently proposed approach to such a quantum memory employs controlled reversible inhomogeneous broadening (CRIB) [2,3,4]. Beyond storage, a modified version of CRIB allows quantum state manipulations [5]. CRIB is currently still challenging, however, it is possible to study closely related atom light interaction via stimulated photon echoes [6]. Nonorthogonal state discrimination based on POVMs (positive operator valued measure) has become an interesting problem in quantum information processing from a fundamental [7] as well as applied [8] point of view. In this kind of measurement a set of nonorthogonal states is mapped onto a set of orthogonal ones by a non unitary transformation. We propose a novel, robust implementation of POVMs that combines quantum state storage with state rotations and is based on stimulated photon echoes. We will present simulations based on numerically solving Maxwell Bloch equations in an inhomogenously broadened medium, and discuss the experimental results.

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