An entangled-light-emitting diode

An optical quantum computer, powerful enough to solve problems so far intractable using conventional digital logic, requires a large number of entangled photons(1,2). At present, entangled-light sources are optically driven with lasers(3-7), which are impractical for quantum computing owing to the bulk and complexity of the optics required for large-scale applications. Parametric down-conversion is the most widely used source of entangled light, and has been used to implement non-destructive quantum logic gates(8,9). However, these sources are Poissonian(4,5) and probabilistically emit zero or multiple entangled photon pairs in most cycles, fundamentally limiting the success probability of quantum computational operations. These complications can be overcome by using an electrically driven on-demand source of entangled photon pairs(10), but so far such a source has not been produced. Here we report the realization of an electrically driven source of entangled photon pairs, consisting of a quantum dot embedded in a semiconductor light-emitting diode (LED) structure. We show that the device emits entangled photon pairs under d.c. and a.c. injection, the latter achieving an entanglement fidelity of up to 0.82. Entangled light with such high fidelity is sufficient for application in quantum relays(11), in core components of quantum computing such as teleportation(12-14), and in entanglement swapping(15,16). The a.c. operation of the entangled-lightemitting diode (ELED) indicates its potential function as an ondemand source without the need for a complicated laser driving system; consequently, the ELED is at present the best source on which to base future scalable quantum information applications(17).