Quantum computing via active feed-forward
- Part of the experimental setup
Photonic qubits as information carriers in quantum computing have the immense advantage of suffering negligible decoherence. Their disadvantage is the absence of any significant photon-photon interaction necessary for non-trivial two-qubit gates. Yet an effective nonlinearity can be provided 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 bases of later measurements depend on earlier measurement results.
This technique is crucial for achieving deterministic quantum computation once a cluster state is prepared. In the present Letter we realize for the first time the required concatenated scheme of measurement and active feed-forward. 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 a crucial result for future developments of one-way quantum computers, whose large-scale implementation certainly depends on future advances in production and detection of the necessary highly entangled cluster states.
Robert Prevedel, Philip Walther, Felix Tiefenbacher, Pascal Böhi, Rainer Kaltenbaek, Thomas Jennewein & Anton Zeilinger
High-speed linear optics quantum computing via active feed-forward
Nature 445, 65-69 (4 January 2007)
