Quantum computation through entangling single photons in multipath interferometers

Single-photon interferometry has been used to simulate quantum computations . Its use has been limited to studying few-bit applications due to rapid gr owth in physical size with numbers of bits. We propose a hybrid approach th at employs n photons, each having L degrees of freedom yielding L-n basis s tates. The photons are entangled via a quantum nondemolition measurement. T his approach introduces the essential element of quantum computing, that is , entanglement into the interferometry. Using these techniques, we demonstr ate a controlled-NOT gate and a Grover's search circuit. These ideas are al so applicable to the study of nonlocal correlations in many dimensions.