Quantum computers promise to be more efficient and powerful than their classical counterparts. In the one-way quantum computer model, a sequence of measurements processes qubits, which are initially prepared in a highly entangled cluster state. We present here an optical implementation of a 4-qubit cluster state and we show how different algorithms can be experimentally realized by performing the corresponding sequence of measurements. We demonstrate deterministic one- and two-qubit gate operations as well as Grover's quantum search algorithm. A major advantage of optical quantum computation is the very short time for one computational step achievable by using these ultra-fast switches. With present technology this feed-forward step can be performed in less than 150 nanoseconds.
We also present how cluster states can be used to realize quantum circuits simulating simple quantum games. Finally we present the experimental realization of decoherence free subspace cluster computation where each logical qubit is encoded into two physical ones, and hence protected against phase noise.
(PLEASE NOTE NON-STANDARD DATE)