Research

Quantum information with atoms and photons

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Photons are ideal carriers of quantum information, and this information can be coherently transferred to atomic ensembles via their interaction. These atomic systems work as quantum memories which can be used for quantum information processing and long-distance quantum communications. Different degrees of freedom of single photons allow for encoding information in many dimensions, resulting in higher information carrying capacity of a single photon. We investigate how to optimize the amount of information contained in single photons and entangled photon pairs by exploring different degrees of freedom allowing for multi-level encoding, and how to transfer this information to atomic ensembles to enable high-dimensional atom-photon interfaces for quantum information. [more]

Quantum measurements for communications

nphoton.2014.280-f1

The measurement of the state of a quantum system is limited by the intrinsic noise of such system. In particular, quantum mechanics prevents nonorthogonal states to be distinguished with total certainty. This intrinsic property of such states has undesirable consequences in optical communications, where the information encoded in such states cannot be perfectly decoded producing decoding errors and loss of information. On the other hand, nonorthogonal states are a fundamental component of quantum key distribution for secure communications. We study and realize optimized strategies for measuring nonorthogonal coherent states of light beyond the conventional limits of detection, such as the heterodyne limit, and investigate their potential for coherent and quantum communications.[more]