We possibly have a PhD position at the boundary between cavity-QED and quantum information available! If you have experience in experimental solid-state quantum optics and quantum information, and of course exceptional motivation, please send us a brief motivation letter, CV, and reference contacts, or contact any of the group members.
We always have possibilities for BSc and MSc projects, please contact us.
All light that we see consists of photons, however, single photons itself show fascinating different properties that enable, for instance, 100% secure communications in quantum cryptography or superresolution in microscopy. But making single photons is not an easy task. In one approach, the “photon blockade” effect, a conventional laser beam is sent to an optical cavity with a single atom (or an artificial atom aka quantum dot). Quantum effects in this device make it possible that only one photon at a time exits the device, like a turnstile for single photons. This device, however, requires very special properties and is extremely hard to fabricate. Now, we have confirmed for the first time experimentally that this can be done much easier: by using the “unconventional photon blockade” effect. This was theoretically conceived by our co-authors Vincenzo Savona and Hugo Flayac from the EPFL Lausanne. In short, we exploit the polarization property of the photons, and by cleverly using quantum interference of different polarizations, we obtain the same as in the photon blockade: a nice stream of single photons. The “unconventional photon blockade” might be very useful for future single photon sources and gives insight in the exciting photon number dependent physics of such devices. Editors suggestion: A Double Take on Unconventional Photon Blockade", Article: Phys. Rev. Lett. 121, 043601 (2018), pre-print Arxiv:1803.10992.
Cyril Vaneph and colleagues at the University of Paris-Sud have at the same time demonstrated the effect in the microwave regime.
An ordered stream of single photons is fundamentally different from conventional light which contains bunches of a random number of photons. Sources of such single-photon light are essential for emerging quantum technologies such as quantum cryptography or computing, but widespread use of recently developed bright semiconductor quantum-dot based single-photon sources was hindered by the need for complex optical setups. Here we show a fiber-integrated source of high-quality single photons; integration with conventional optical fiber technology will enable broad use in quantum photonics but it also might enable a number of new fundamental studies in various fields from microscopy to quantum metrology by reducing the experimental complexity significantly.
With a single semiconductor quantum dot in a polarization degenerate microcavity, operating in the weak coupling regime, we can transform incident coherent light into a stream of strongly correlated photons with a second-order correlation function g2(0) up to 40! This work is published in Nat. Commun. 7, 12578 (2016).
See cqed for more details.
See 4photonoam for more details.
Polarization vortices are singular points in generic light fields, different but closely connected to phase vortices. Their singular nature makes them ideal as a positional marker of light beams, we investigated this by studying how they behave while being reflected at an interface. Apart from the scientific article here that is on the cover of issue 8, you can also find a labtalk article with a bit more background, and see here for more information.
The spatial structure of light can be either pure or in an incoherent superposition, a statistical mixture. A laserpointer reflected from a rough surface shows “speckle”, and if you move the surface very quickly these speckle appear washed out; this is light with reduced spatial coherence. We studied how beam shifts depend on this by theory and experiment, click here for more information.
“Spin-Orbit Interaction for Light and Matter Waves” is a workshop which we have organized at the MPIPKS in Dresden (germany) from 15.-19. April 2013. More information here. The workshop was a great success!