Single electron spins in quantum dots are attractive for quantum communication because of their expected long coherence times. We propose a method to create entanglement between two remote spins based on the coincident detection of two photons emitted by the dots. Local nodes of two or more qubits can be realized using the dipole-dipole interaction between trions in neighboring dots and spectral addressing, allowing the realization of a quantum repeater. We have performed a detailed feasibility study of our proposal based on tight-binding calculations of quantum dot properties.Implementations of quantum information protocols in the solid state are of interest because they may eventually be more scalable than other approaches. Individual electron spins in quantum dots [1] are a promising system for quantum computing and quantum communication due to their expected long coherence times. Spin relaxation times as long as 20 ms have been observed at 4 T and much longer times predicted for lower magnetic fields [2]. There are theoretical predictions that in the absence of nuclear spins the decoherence time of the spins might approach their relaxation time [3]. Nuclear spins can be eliminated completely e.g. by using isotopically purified II-VI materials, since Zn, Cd, Mg, Se and Te all have dominant isotopes without nuclear spins.For quantum commmunication it is important to be able to create entanglement between remote spins [4,5]. The recent proposal of Ref.[4] relies on achieving a large Faraday rotation for a single photon due to the quantum dot spin. It requires very high-finesse micro-cavities that are switchable in a picosecond. The proposal of Ref.[5] relies on the detection of a single photon that could have been emitted by either of two remote sources [6]. This approach is attractive because it does not require a finely controlled strong spin-photon interaction. A practical drawback of the scheme of Ref.[5] is the requirement of phase stability over the whole distance. Ref.[7] proposed a scheme that creates entanglement between two remote emitters via the detection of two photons, which eliminates this stability requirement, while keeping the advantages of an emission-based scheme. In the present work we demonstrate, firstly, how to realize a similar scheme for quantum dot spins. Secondly, we show that it is possible to realize local nodes of two or more spins using dipole-dipole interactions and spectral addressing. Such nodes allow the realization of quantum repeater protocols [5,8]. We have investigated the feasibility of our proposal in detail, including numerical calculations of the electronic properties of quantum dots using tight binding methods.Our scheme applies to flat quantum dots, such as typical strain-induced quantum dots or dots in heterostructured nanowires [9]. This implies that the lowest-energy hole states will have predominantly "heavy-hole" character, and will be well separated from predominantly "light-hole" states. The dots can be charged with single electrons via tunneling controlled by...

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