UVC Experiment

Quantum networks are expected to be the future of information exchange and cryptography. An important component of these networks are nodes where quantum states can be stored, and manipulated. We are investigating such quantum communication nodes formed by trapped Ytterbium ions coupled to an optical cavity.

Paul Trap
Paul trap with fibre cavity © AG Köhl

We trap single Ytterbium ions in a radio-frequency paul trap (originally invented at the Physikalisches Institut by W. Paul). Using techniques of laser cooling, we cool these ions to few Millikelvin. In combination with Ultra High Vacuum (UHV) apparatus, our system is very well isolated from the environment. In this way, the coherences in the ionic internal states are maintained over a long time span, making them good quantum memory "qubits".

Using picosecond laser pulse excitation of the ion, we create single photons that are entangled with the internal state of the ion. These photons are efficiently collected by a fibre optic resonator, where the photons are inherently fiber coupled. Using the principle of Prucell effect, the photon emission is enhanced into the fibres, hence we have a high bandwidth source of entangled photons that are fiber coupled. Distributing the photons across such fiber optic networks allows one to distribute the entanglement across distance. Using quantum communication protocols such as BBM92, we can then distribute "Quantum keys" that are inherently secure by laws of Physics.

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