Semiconductor quantum dots proved to be an extremely interesting source for single and entangled photons for the emerging fields of quantum information and quantum communication. The possibility to tune their light emission properties via strain engineering, to integrate them in the mature semiconductor technology, and the potential to work on-demand raised a high interest from the quantum optics community. Still, the amazing properties of these physics toy-models remain unexploited due to few current limitations. Most of the light emitted by a quantum dot is confined inside the semiconductor host matrix due to refraction index mismatch; moreover, static and dynamic fluctuations in the electronic structure of the individual quantum dot negatively impact the signal repeatability. This hinders optimal match between different emitters, a fundamental requirement for distant nodes in communication networks.
After discovering their fundamental properties, the efforts of the quantum dot community all concentrated in facing the above-mentioned challenges. These efforts recently produced a novel photonic device, i.e. the circular Bragg resonator or Bullseye, which finally helped to unlock the full potential of this promising quantum emitter.
The Nanophotonics group at Sapienza University of Rome already achieved experimental demonstrations of entanglement-based quantum information protocols with semiconductor quantum dots. We at the Nanophotonics group believe to be eligible candidates to implement a Bullseye photonic structure around a single quantum dot coupled with piezoelectric strain engineering to tune its emission energy to the one of another quantum dot. This would allow the demonstration of fundamental quantum information protocols such as quantum teleportation and entanglement swapping with remote quantum dots, a task never reached before.
The publication of the two papers describing the outstanding properties of CBG cavities represent the verge of years of research in the QD community. The terrific improvement in the emitter properties will enable new scientific breakthroughs which will eventually lead to the creation of a full-functioning worldwide quantum network. However, this scientific result represents just the beginning of the journey and we would like to be part of it. Our laboratory, in collaboration with JKU in Linz and KTH in Stockholm, performed for the first time both quantum teleportation [1] and entanglement swapping [2] using entangled light coming from a single QD. These quantum communication protocols are at the basis of a crucial part of a quantum network, i.e. the quantum repeater. A quantum repeater would allow to cut the distance travelled by a quantum signal into shorter legs thus reducing losses.
The expertise developed in our group after working on these projects makes us eligible candidates to exploit the potential carried by these novel photonic structures. It is important to stress out that no all-photonic entanglement swapping and quantum teleportation protocols with remote and distant quantum light emitters has ever been performed before. Our aim is then to reproduce these photonic structures and to integrate them in the well-developed piezoelectric devices.
With such a device, which alone would already represent a further step in the field of quantum light emitters, we will then perform quantum teleportation and entanglement swapping protocols with light coming from two QDs placed in two different cryostats. The success of these experiments would eventually prove that semiconductor QDs are the true candidates as future entangled-light sources for quantum technologies.