The vastly growing field on quantum computers highlights ever more that current classical communication might soon no longer meet the stringent security requirements for data transfer, making the development of new communication systems a pressing need. A promising solution is the transfer from classical networks to quantum networks based on information encoding in single photons, which would allow the exploitation of the already established communication infrastructure consisting of fibers and satellites. Long-distance communication, however, suffers from signal loss, pointing out the need for signal amplification and repetition. Since classical amplification is no longer feasible in quantum networks - due to the no-cloning theorem - quantum repeaters need to be developed. We propose a quantum repeater based on entanglement, to build up a quantum network by stringing together multiple quantum repeaters. The encrypted signal can then be transferred from quantum repeater to quantum repeater via entanglement swapping. The implementation of entanglement swapping sets stringent requirements on the efficiency, degree of entanglement, photon/indistinguishability as well as wavelength/tunability, of the entangled photon source. All these requirements have already been demonstrated using semiconductor quantum dots, thus making them promising candidates for future quantum repeaters. However, the requirements have only been achieved individually and an ultimate source combining all, in order to achieve remote entanglement swapping, is still missing. In this project we propose the first deomstration of remote entanglement swapping, enabled by a semiconductor-based quantum repeater device, and thus, setting a milestone for the generation of quantum networks.
Quantum repeater platforms are essential elements for the realization of future quantum networks. Entanglement-based quantum repeater platforms using entanglement swapping between different nodes in the network would allow for a device-independent and secure quantum network. Semiconductor QDs have already proven to individually meet all the stringent requirements set by a remote entanglement swapping task. However, a device meeting all the stringent requirements simultaneously is still lacking and consequently, also the proof of remote entanglement swapping. The achievement of remote entanglement swapping provides the missing step that would allow quantum networks being based on semiconductor-based quantum repeaters, realizing the exploitation of the firmly established semiconductor industry for the establishment of quantum networks.
The Nanophotonics Group under the supervision of Ass. Prof. Rinaldo Trotta at La Sapienza University has already developed a profound expertise on the device development for semiconductor QDs leading to outstanding results as the controlled cancelation of fine structure splitting stemming from fabrication imperfections[19] as well as the excellent achievements on entanglement fidelity of 98 %.[20] Additionally, the Nanophotonics Group has demonstrated the first experimental proof of quantum teleportation between different QDs as well as conducted the first experimental entanglement swapping between photons coming from the same QD.[10,11] Therefore, the group has developed extensive expertise in the research area and has greatly impacted the scientific community. Driven by our goal to advance semiconductor QDs to the best single- and entangled-photon sources, surpassing the limits given by the state-of-the-art source SPDC, we believe entanglement swapping between remote QDs is the next step towards the overall goal of quantum networks.
We are confident that the experimental demonstration of remote entanglement swapping from semiconductor QDs will tremendously advance semiconductor technology in quantum information experiments. During the preparation of the remote entanglement swapping experiment, multiple important milestones for the scientific community will be set. First, the development of the entangled photon device combined the strengths of already existing techniques in a single device. Such a device has never been demonstrated before and a patent application will be filed on the final de. In the course, in-depth understanding on the single techniques as well as influences introduced by the combination of the fabrication steps were already obtained and transmitted to the scientific community. Additionally, challenges arising by the experimental complexity, i.e. as adressed by the Nanophotonics Group in the quantum teleportation with imperfect QDs, will be investigated and provided to the scientific community via publications. For these reasons we are convinced that remote entanglement swapping will bring benefit to the scientific community by further insights and will inspire other researchers to new investigations to reach the goal of quantum repeaters based on semiconductor QDs.