Table-top creation of entangled multi-keV photon pairs via the Unruh effect

Electrons moving in a strong periodic electromagnetic field (e.g., laser or undulator) may convert quantum vacuum fluctuations into pairs of entangled photons, which can be understood as a signature of the Unruh effect. Apart from verifying this striking phenomenon, the considered effect may allow the construction of a table-top source for entangled photons (``photon pair laser’') and the associated quantum-optics applications in the multi-keV regime with near-future facilities. 04.62.+v, 12.20.Fv, 41.60.-m, 42.50.Dv.