Estimation of quantum-state via linear Faraday effect

One of the most important challenges of quantum information science is to reconstruct an unknown quantum state, such process is known as a quantum state tomography (QST). As the atomic vapours are a promising candidate for the processing and storage of quantum information, it is crucial to estimate their quantum state. Until now, most approaches to “atomic” quantum-state tomography have explored ultra-cold ensembles, which greatest advantage is the reduction of various relaxation processes. Nonetheless, room-temperature alkali-metal vapours enclosed in paraffin-coated cells also provide various benefits, e.g. the simplicity of experimental setup and averaging of interactions over the whole ensemble.

During presentation I will present an algorithm, enabling determination of a collective quantum-state of a room-temperature atomic vapour via weak non-demolition measurement performed by off-resonant, linearly-polarized laser light. The estimation is based on a set of a measurements of Faraday rotation of light transmitted through an atomic medium and is done by linear inversion of measured signals.