An entangled-light-emitting diode

Entanglement to order For optical quantum computation and related information technologies to fulfil their promise, they will require a source of entangled photons that can be delivered efficiently on demand. Existing entangled-light sources are laser driven, and involve bulky and complicated optics. Salter et al . have now developed a compact light-emitting diode with an embedded quantum dot that can be driven electrically to generate entangled photon pairs. Much simpler than its laser-driven counterparts, this ELED (entangled-light-emitting diode) device, based on conventional semiconductor materials, is a promising start point for the development of an entangled light source for quantum information applications. A quantum computer based on optical processes requires a source of entangled photons that can be delivered efficiently on demand. Such a source has now been developed: it involves a compact light-emitting diode with an embedded quantum dot that can be driven electrically to generate entangled photon pairs. 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 , 4 , 5 , 6 , 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 , 13 , 14 , and in entanglement swapping 15 , 16 . The a.c. ope