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One step beyond: recent advances in linear optical quantum computing


Linear optics (LO) has been demonstrated to be an optimal system for quantum computation and  information. Classical polarimetry makes available efficient and accurate ways to prepare and measure the polarisation of optical fields; transposing to the single-photon level, these correspond to preparation and measurement of qubits. The hardest task to achieve with single photons is to realise a nonlinear interaction of these very weak fields, for the implementation of quantum gates. This issue can be partially overcome by resorting to linear devices, measurement and post-selection; by this technique, a controlled-NOT gate has been successfully demonstrated. The next challenge is to extend the technique to slightly more complex quantum circuits. In this talk I will discuss the first steps in this direction: the demonstration of a three-qubit  Toffoli gate, and the realisation of a quantum control protocol which relies on the possibility of supplementing the action of the gate with classical feedback.

Joint Quantum Optics/AMO Seminar and QUINF Seminar