title: High-speed linear optics quantum computing using active feed-forward.
abstract: As information carriers in quantum computing, photonic qubits have the advantage of undergoing negligible decoherence. However, the absence of any significant photon-photon interaction is problematic for the realization of non-trivial two-qubit gates. One solution is to introduce an effective nonlinearity by measurements resulting in probabilistic gate operations. In one-way quantum computation, the random quantum measurement error can be overcome by applying a feed-forward technique, such that the future measurement basis depends on earlier measurement results. This technique is crucial for achieving deterministic quantum computation once a cluster state (the highly entangled multiparticle state on which one-way quantum computation is based) is prepared. Here we realize a concatenated scheme of measurement and active feed-forward in a one-way quantum computing experiment. We demonstrate that, for a perfect cluster state and no photon loss, our quantum computation scheme would operate with good fidelity and that our feed-forward components function with very high speed and low error for detected photons. With present technology, the individual computational step (in our case the individual feed-forward cycle) can be operated in less than 150 ns using electro-optical modulators. This is an important result for the future development of one-way quantum computers, whose large-scale implementation will depend on advances in the production and detection of the required highly entangled cluster states.
authors.affiliation: Institute for Experimental Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria. robert.prevedel@univie.ac.at
authors.forename: Robert
authors.initials: R
authors.lastname: Prevedel
authors.forename: Philip
authors.initials: P
authors.lastname: Walther
authors.forename: Felix
authors.initials: F
authors.lastname: Tiefenbacher
authors.forename: Pascal
authors.initials: P
authors.lastname: Böhi
authors.forename: Rainer
authors.initials: R
authors.lastname: Kaltenbaek
authors.forename: Thomas
authors.initials: T
authors.lastname: Jennewein
authors.forename: Anton
authors.initials: A
authors.lastname: Zeilinger