Repeat-Until-Success Linear Optics Distributed Quantum Computing

We demonstrate the possibility to perform distributed quantum computing using only single-photon sources (atom-cavity-like systems), linear optics, and photon detectors. The qubits are encoded in stable ground states of the sources. To implement a universal two-qubit gate, two photons should be generated simultaneously and pass through a linear optics network, where a measurement is performed on them. Gate operations can be repeated until a success is heralded without destroying the qubits at any stage of the operation. In contrast with other schemes, this does not require explicit qubit-qubit interactions, a priori entangled ancillas, nor the feeding of photons into photon sources.

Figure 1

Schematic view of a single-photon source and level configuration of the atomic structure containing the qubit.

Figure 2

Linear optics networks for the realization of a measurement of the basis states (10) after encoding the photonic qubits in the polarization degrees of two photons (a) or into four different spatial photon modes (b) involving either a beam splitter (BS) or a $4\times 4$ Bell multiport beam splitter.