Controlling two-photon emission from superluminal and accelerating index perturbations

Despite their relevance for quantum technology, photon-pair sources are difficult to control. A theoretical proposal shows how photon pairs can be created from vacuum fluctuations in time-dependent systems, potentially enabling heralded single-photon frequency combs. Sources of photons with controllable quantum properties such as entanglement and squeezing are desired for applications in quantum information, metrology and sensing. However, fine-grained control over these properties is hard to achieve, especially for two-photon sources. Here we propose a mechanism for the controlled generation of entangled and squeezed photon pairs using superluminal or accelerating modulations of the refractive index in a medium or both. By leveraging time-changing dielectric media, where quantum vacuum fluctuations of the electromagnetic field can be converted into photon pairs, we show that energy and momentum conservation in multimode systems give rise to frequency and angle correlations of photon pairs controlled by the trajectory of index modulation. In our examples, these radiation effects are two-photon analogues of Cherenkov and synchrotron radiation by moving charged particles such as free electrons. We find that synchrotron-like radiation into photon pairs exhibits frequency correlations that can enable a heralded single-photon frequency comb. These effects are sensitive to the local density of photonic states and can be strongly enhanced using photonic nanostructures. For example, index modulations propagating near the surface of graphene produce entangled pairs of graphene plasmons with high efficiency.

Automated summary

The article proposes a mechanism for the controlled generation of entangled and squeezed photon pairs using superluminal or accelerating modulations of the refractive index in a medium. By controlling the trajectory of index modulation in the medium, frequency and angle correlations of photon pairs can be achieved. The effects are sensitive to the local density of photonic states and can be strongly enhanced using photonic nanostructures.