Quantum Sources

Crystalline WGMR with diamond incoupling prism. The green pump light is focused onto the base of the diamond coupled via evanescent coupling into the resonator. Scattering nicely shows the path of the beams.

Quantum sources are the base of quantum communication and technologies. In this group, we design quantum sources to generate specific quantum states tailored to application requirements. This adaptive generation ensures optimal performance in diverse scenarios, from long-distance data transmission to localized quantum computing tasks. Our research focuses on developing sources of quantum light, exploiting non-linear optical effects in their generation. For example, we fabricate crystalline whispering gallery mode resonators (WGMR) in order realize narrow-band and tunable parametric down-conversion sources or we use other wave-guiding structures such as crystalline waveguide or optical fibers to generate and measure squeezed states of light.

In WGMR, resonant optical cavities are used to produce non-classical light, exploiting the phenomenon of light waves traveling around a cavity’s circumference. This enables efficient generation of quantum states with a narrow bandwidth in terms of frequency. This makes them highly compatible with single atoms or other memory systems. Moreover, WGMR are compact and energy-efficient, which makes them potential sources when space and available power are limited.

Optical fibers guide light over long distances with minimal loss, ideal for quantum communication networks. Exploiting the optical Kerr-effect in glass fibers, it is possible to reliably generate squeezed states of light without requiring involved stabilization schemes. This relative experimental ease alongside their robustness and reliability makes fiber-based squeezing sources excellent choices in scenarios with adverse ambient conditions, e.g. free-space quantum key distribution.