Quantum optics has proved a fertile field for experimental tests of quantum information science, from experimental verification of Bell inequality violations to quantum teleportation. However, quantum optics was not thought to provide a practical path to efficient and scalable quantum computation, and most current efforts to achieve this have focussed on solid state implementations. This orthodoxy was challenged recently when Knill et al. showed that, given single photon sources and single photon detectors, linear optics alone would suffice to implement efficient quantum computation. While this result is surprising, the complexity of the optical networks required is daunting. In this report we propose an efficient scheme which is elegant in its simplicity. By encoding the quantum information in multi-photon coherent states, rather than single photon states, simple optical manipulations acquire unexpected power. The required resource, which may be produced non- deterministically, is a superposition of the vacuum and a coherent state. Given this, the scheme is deterministic and requires only simple linear optics and photon counting. Qubit readout uses homodyne detection which can be highly efficient. Notes: Timothy Ralph & Gerard Milburn, Special Research Centre for Quantum Computer Technology, University of Queensland, OLD4072, Brisbane, Australia 7 Pages
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