Location: Zaal E

Time: 16:00 hrs

1 Laboratoire de Photonique Quantique et Moléculaire, ENS de Cachan, France

2 PI3 Institute, University of Stutttgart, Germany

Over the last decade, the negatively charged nitrogen-vacancy (NV) color center in diamond has attracted a lot of interest because it can be optically addressed as single quantum system and exhibits several important properties for quantum information science applications. First, its perfect photostability at room temperature enables to realize a robust single photon source for quantum cryptography applications. Furthermore, owing to the long coherence time of its electron spin, the NV defect behaves as an ultrasensitive magnetometer at the nanoscale, allowing to optically detect magnetic dipolar coupling with neighboring single spins in the diamond matrix. Such magnetic coupling has recently been used as a resource for realizing quantum registers and multipartite entanglement among single spins in diamond.

In the first part of this talk, single-photon interference experiments performed using a NV-based single photon source will be described, focusing on Wheeler’s delayed-choice gedanken experiment which is one of the most fascinating and subtle illustration of wave-particle duality. If we consider a single-photon light pulse in a Mach-Zehnder interferometer, one can either measure the interference at the output – evidencing the "wave-like" behavior of the photon– or one can detect the path followed by the photon – evidencing its "particle-like" behavior. In order to pinpoint how surprising this is, John Wheeler considered a "delayed-choice" regime where the choice of measuring either property is done only after the photon has entered the interferometer.

The second part of the talk will focus on the realization of quantum registers using the unique spin properties of NV defects in diamond. Recent results obtained at the University of Stuttgart will be presented.