Periodic Reporting for period 4 - SPQRel (Entanglement distribution via Semiconductor-Piezoelectric Quantum-Dot Relays)
Berichtszeitraum: 2020-11-01 bis 2021-11-30
Scalable sources of single and entangled photons are fundamental building blocks of quantum information science. They can be used for quantum communication, optical quantum computing, quantum networks and, more in general, are needed to develop future quantum technologies. It is widely accepted that these technologies have the potential to change our society significantly. In order to unlock their full potential, it is essential to go beyond proof of principle experiments performed in research laboratories. This, however, turns out to be an extremely challenging task. The main reason is that any prototype of quantum device has to meet a set of rigorous criteria to be considered for the envisioned application. The ideal source of quantum light, for example, should deliver single and entangled photons on-demand, with high purity, efficiency, indistinguishability and degree of entanglement. Moreover, it should be compatible with current photonic integration technologies and, at the same time, with other quantum systems. While a large number of non-classical light sources have been developed over the years, there is at present no source that can fulfill all these requirements simultaneously. As a consequence, optical quantum technologies have kick-start difficulties.
The SPQRel project focuses on the fabrication and study of near-ideal sources of non-classical light, which enable the construction of a quantum network for the distribution of quantum entanglement among distant parties. The sources are based on epitaxial quantum dots integrated onto innovative semiconductor-piezoelectric devices which allow for full control over the quantum-dot in-plane strain tensor. The sources can deterministically generate highly indistinguishable and strongly entangled photons with high efficiency and their emission wavelength can be finely adjusted via the application of voltages to the piezo-actuators without degrading the quality of the emitted photons. This unique feature enables the distribution of entanglement between distant parties and allows building up artificial-natural atomic interfaces where entangled photons are interfaced to absorption resonances in atomic vapors.
The findings of SPQRel have proven that it is possible to build up a quantum network in which photons from quantum dots are used to distribute entanglement over distant nodes. This research is extremely relevant for society, as it will find applications in the field of secure communication and long-distance quantum networking. Moreover, the hybrid-semiconductor piezoelectric technology developed during the SPQRel project has the potential to impact research fields beyond quantum communication, and in particular the field of strain-engineering of two-dimensional materials.
The SPQRel project focuses on the fabrication and study of near-ideal sources of non-classical light, which enable the construction of a quantum network for the distribution of quantum entanglement among distant parties. The sources are based on epitaxial quantum dots integrated onto innovative semiconductor-piezoelectric devices which allow for full control over the quantum-dot in-plane strain tensor. The sources can deterministically generate highly indistinguishable and strongly entangled photons with high efficiency and their emission wavelength can be finely adjusted via the application of voltages to the piezo-actuators without degrading the quality of the emitted photons. This unique feature enables the distribution of entanglement between distant parties and allows building up artificial-natural atomic interfaces where entangled photons are interfaced to absorption resonances in atomic vapors.
The findings of SPQRel have proven that it is possible to build up a quantum network in which photons from quantum dots are used to distribute entanglement over distant nodes. This research is extremely relevant for society, as it will find applications in the field of secure communication and long-distance quantum networking. Moreover, the hybrid-semiconductor piezoelectric technology developed during the SPQRel project has the potential to impact research fields beyond quantum communication, and in particular the field of strain-engineering of two-dimensional materials.
In the SPQRel project we have achieved several important scientific and technological results:
- We have developed a hybrid-semiconductor piezoelectric technology in which semiconductor nano- and micro-membranes are integrated onto micro-machined piezoelectric actuators. We have used this technology with different quantum emitters, including quantum dots and two-dimensional semiconductors, to fabricate non-classical light sources with tunable wavelength.
- We have fabricated and characterized several quantum dot devices and identified the system and the excitation scheme which give the best figures of merit. In particular, we showed that droplet-etched GaAs quantum dots driven under two-photon resonant excitation can deterministically generate indistinguishable entangled photons with tunable wavelength, with unprecedented single photon purity and near-unity degree of entanglement.
- We have shown that single and entangled photons generated on-demand by GaAs quantum dots can be used to implement successfully advanced quantum optics protocols, such as quantum teleportation and entanglement swapping.
- We have interfaced photons from quantum dots with clouds of natural atoms and studied the distortion of a single-photon wavepacket propagating though a dispersive and absorptive medium. Moreover, we have experimentally and theoretically investigated the possibility to interface single photons with a warm-atomic vapor quantum memory.
- We have posed the basis of a quantum-dot based quantum network: We have developed a free-space quantum communication channel and successfully performed quantum key distribution experiments in which entangled photons from quantum dots are distributed across two different buildings located few hundred meters apart. Then, we have combined photons from a quantum dot and non-linear crystal to demonstrate non-classical correlations among three nodes of primitive quantum network. Finally, we have successfully demonstrated quantum interference between photons from remote quantum dots and theoretically investigated the fidelities that can be achieved in a chain of quantum-dot relays that perform multiple swapping operations.
The results obtained within the SPQRel project are contained in several scientific publications (including Physical Review letters, Science Advances, Nature Communications, Nano Letters, etc.) and were presented at international conferences, workshops, and colloquia. They were also advertised in non-specialized journals as well as in a youtube video. The SPQRel also supported two international workshops as well as one summer school. Finally, the SPQRel project enabled the establishment of a new research group that is internationally recognized for its pioneering work on quantum optics with semiconductor nanostructures.
- We have developed a hybrid-semiconductor piezoelectric technology in which semiconductor nano- and micro-membranes are integrated onto micro-machined piezoelectric actuators. We have used this technology with different quantum emitters, including quantum dots and two-dimensional semiconductors, to fabricate non-classical light sources with tunable wavelength.
- We have fabricated and characterized several quantum dot devices and identified the system and the excitation scheme which give the best figures of merit. In particular, we showed that droplet-etched GaAs quantum dots driven under two-photon resonant excitation can deterministically generate indistinguishable entangled photons with tunable wavelength, with unprecedented single photon purity and near-unity degree of entanglement.
- We have shown that single and entangled photons generated on-demand by GaAs quantum dots can be used to implement successfully advanced quantum optics protocols, such as quantum teleportation and entanglement swapping.
- We have interfaced photons from quantum dots with clouds of natural atoms and studied the distortion of a single-photon wavepacket propagating though a dispersive and absorptive medium. Moreover, we have experimentally and theoretically investigated the possibility to interface single photons with a warm-atomic vapor quantum memory.
- We have posed the basis of a quantum-dot based quantum network: We have developed a free-space quantum communication channel and successfully performed quantum key distribution experiments in which entangled photons from quantum dots are distributed across two different buildings located few hundred meters apart. Then, we have combined photons from a quantum dot and non-linear crystal to demonstrate non-classical correlations among three nodes of primitive quantum network. Finally, we have successfully demonstrated quantum interference between photons from remote quantum dots and theoretically investigated the fidelities that can be achieved in a chain of quantum-dot relays that perform multiple swapping operations.
The results obtained within the SPQRel project are contained in several scientific publications (including Physical Review letters, Science Advances, Nature Communications, Nano Letters, etc.) and were presented at international conferences, workshops, and colloquia. They were also advertised in non-specialized journals as well as in a youtube video. The SPQRel also supported two international workshops as well as one summer school. Finally, the SPQRel project enabled the establishment of a new research group that is internationally recognized for its pioneering work on quantum optics with semiconductor nanostructures.
At the core of the SPQRel project lies the fabrication, study, and exploitation of non-classical light sources based on novel strain-tunable quantum dot devices. To achieve the goals of the project, we have developed innovative methodologies that led to a series of fundamental and technological advances: On the fundamental side, we have developed an unprecedented understanding of the effect of in-plane-strains on the optical and electronic properties of semiconductor nanostructures. On the technological side, the strain actuator that we have developed is the only (to the best of our knowledge) existing device that allows for full control over the in-plane strain tensor in semiconductors. This result has interest which goes well beyond the field of quantum communication and we have just started exploring its potential in the field of strain-engineering of two-dimensional materials.
Our results related to near-ideal sources of entangled photons that can be used for quantum teleportation and entanglement swapping certainly represent the most important breakthroughs of the SPQRel project, which firstly showed that GaAs quantum dots are one of the most promising platforms for scalable photonic quantum technologies. In the last part of the project, we have also brought the technology outside the research laboratories, with a pioneering demonstration of free-space quantum key distribution protocol in which entangled photons are distributed between distant parties in an urban communication scenario. These achievements, combined with the successful interfacing of remote quantum dots, of quantum dots and non-linear crystals, as well as quantum dots and clouds of natural atoms, show that the SPQRel project has opened the path to the forthcoming realization of a practical solid-state based quantum network for long distance quantum communication.
Our results related to near-ideal sources of entangled photons that can be used for quantum teleportation and entanglement swapping certainly represent the most important breakthroughs of the SPQRel project, which firstly showed that GaAs quantum dots are one of the most promising platforms for scalable photonic quantum technologies. In the last part of the project, we have also brought the technology outside the research laboratories, with a pioneering demonstration of free-space quantum key distribution protocol in which entangled photons are distributed between distant parties in an urban communication scenario. These achievements, combined with the successful interfacing of remote quantum dots, of quantum dots and non-linear crystals, as well as quantum dots and clouds of natural atoms, show that the SPQRel project has opened the path to the forthcoming realization of a practical solid-state based quantum network for long distance quantum communication.