Homodyne tomography for quantum information: a new application for an old method

I will present a series of experiments in which we create, manipulate, characterize and apply new quantum states of the electromagnetic field for applications in quantum information processing. Our approach is unique in the way it combines traditionally discrete-variable quantum states (photons and optical qubits) as the object of investigation with homodyne tomography, a continuous-variable method of quantum state measuremnet. This method, based on phase-sensitive measurements of quantum noise staistics of the electro-magnetic field, is technically more challenging, but provides much more accurate information about optical ensembles than traditional photon-counting based techniques. By applying our approach to more and more complex quantum optical states, we not only delveop new tools of quantum information technology, but also answer some important questions of fundamental nature.