Quantum Computing With Multiphoton Entanglement

Coherent control of multiple photons with linear optics has been a promising approach to quantum computing. Recent years have witness tremedous progresses, both on theory and experiment on this approach. Major challenges ahead lies in manipulation of an increasing number of entangled photonic qubits, fighting against possible decoherence, and constructing quantum circuits for implementing quantum algorithms.Along this line, this dissertation describes four experiments on multiphoton entanglement and optical quantum computation. We have developed a high-brightness source of entangled photons based on spontaneous parametric down-conversion. Using linear optical networks we are able to entangle them into a six-photon GHZ state, which is the larget photonic Schrodinger cat so far, and a six-photon cluster state, a state-of-the-art one-way quantum computer. Next, we use the hyper-entanglement trick to entangle not only the polarization of the photons, but also their spatial modes. By doing so, we manage to create a six-, eight-and ten-qubit hyper-entangled Schrodinger cat state, expanding the effective Hilbert space up to 1024 dimensions. The third experiment aims to deal with the photon loss error which is a big headache in optical quantum computing. We show both in the quantum circuit model and the one-way model the smallest meaningful quantum codes that are able to tackle the photon-loss problem. Finally, we describe the first optical implementation of Shor's quantum factoring algorithm. We choose the simplest instance of this algorithm-factorization of 15-and exploit a simplified linear optical network to implement the quantum circuits of the modular exponential execution and semiclassical quantum Fourier transformation.These experiments are necessary steps towards scalable quantum computing with single photons and linear optics.