Nonlinear and Quantum Optics

Frequency conversion

Non-linear optical phenomena require high electro-magnetic fields and highly non-linear materials. The strongest optical non-linearities are $\chi^{(2)}$ non-linearities which can only exist in crystalline materials. Whispering gallery mode resonators made out of crystalline materials combine high quality factors with small mode volumes and are thus ideal systems to study non-linear optics.

Coherent conversion between microwaves and optics

One particularly challenging, but important topic is to bridge the microwave and optical domain, coherently. Microwave photos are the quantum bits in the superconducting microwave quantum circuits. They cannot however communicate to any other quantum system outside of the cryostat, unless they are converted into the optical domain. We have shown that this is possible in 2016.

Microwave cavity with rendering of optical WGM resonator
Microwave cavity with rendering of optical WGM resonator

Fundamental quantum properties

We are working together with the QIV group at the MPL on studying the quantum properties of the emitted light from parametrically down converted light in a lithium niobate WGM resonator. A green pump photon splits into two highly tunable infra red photons and allows for heralded single photons of a single mode (2015):

In order to determine the exact modal parameters we have devised a method to clearly identify each mode (2014):

Harald G. L. Schwefel
Harald G. L. Schwefel
Associate Professor

I work on Resonant Optics.