Cavity-enhanced single photon sources

 

Color centers in diamond represent an interesting class of solid state-based quantum emitters that allow room-temperature single-photon generation. The conventional approach, confocal microscopy, achieves only meagre collection efficiency, and the emitter’s moderate quantum yield as well as broad emission spectra limit the performance for their use as single-photon sources.
We want to improve single-photon emission properties by coupling color centers to optical microcavities. Using Purcell enhancement, directed emission into a well-defined mode with efficiency close to unity can be achieved.

In a first approach, we have studied the scaling laws of the Purcell enhancement in the regime of broadband emitters [Kaupp et al., PRA 88, 053812 (2013)]. While changes in the emission lifetime remain small in this regime, we observe an increase of the emission spectral density by up to a factor of 300. This gives a direct measure of the Purcell factor that could be achieved with this resonator and an emitter whose linewidth is narrower than the cavity linewidth.

 

Currently, we are working on nano-cavities with mode volumes of a fraction of a wavelength cubed to realize significant cavity enhancement of broadband emitters such as the NV center in diamond.

In a complementary direction, we use cavities with large quality factors to improve the spectral properties of the photons. Here we focus on the silicon-vacancy center in diamond, which shows a narrow emission linewidth also at room temperature.
Beyond the photon exctraction aspect, optical cavities offer a promising route to realize efficient spin-photon interfaces. We are considering the potential of Purcell enhancement to improve optical spin state readout, as well as the possibility to realize a quantum-coherent spin-photon interface.

This project is partly funded by the EU within the project Wavelength tunable Advanced Single Photon Sources (WASPS, www.fp7wasps.org), and by the excellence cluster Nanosystems Initiative Munich (NIM, www.nano-initiative-munich.de). In this project we are collaborating with Dr. Huan Cheng Chang, Dr. Helmut Fedder, and the WASPS consortium (Prof. Jason Smith, Prof. Christoph Becher, Dr. Alexia Auffeves, Prof. John Rarity, Prof. Oliver Williams).