Periodic Reporting for period 4 - COQCOoN (COntinuous variables Quantum COmplex Networks)
Reporting period: 2023-12-01 to 2025-11-30
At different scales, from molecular systems to technological infrastructures, physical systems group into structures that are neither simply regular nor random, but can be represented as networks with complex shapes. In addition, individual elements of natural systems, such as atoms or electrons, are quantum objects. The objective of this project was to theoretically study and experimentally implement complex networks with quantum features using an all-optical platform based on nonlinear optical processes pumped by femtosecond lasers. This approach helps to simulate basic features of natural phenomena and to optimize future quantum technologies.
Future trusted large-scale communications and efficient big data handling, in fact, will depend on at least one of the two aspects -quantum or complex- of scalable systems, or on an appropriate combination of the two.
The results of the project have demonstrated that quantum environments can be shaped to interact with relevant quantum systems, that continuous-variable quantum networks with complex topologies can be routed for multiparty communication protocols, and that efficient quantum reservoir computing protocols can be realized in continuous-variable quantum networks.
Future trusted large-scale communications and efficient big data handling, in fact, will depend on at least one of the two aspects -quantum or complex- of scalable systems, or on an appropriate combination of the two.
The results of the project have demonstrated that quantum environments can be shaped to interact with relevant quantum systems, that continuous-variable quantum networks with complex topologies can be routed for multiparty communication protocols, and that efficient quantum reservoir computing protocols can be realized in continuous-variable quantum networks.
In he project we have mainly worked along three lines:
1) implementing two different setups based on nonlinear optical processes for producing multimode fields that can be arranged as complex quantum networks;
2) developing the theory of complex quantum systems within our specific framework, where quantum effects are encoded in the continuous variables (amplitude and phase) of the electromagnetic field;
3) devising quantum information protocols.
On the first line: we implemented two experimental setups, operating at near-infrared and telecom wavelengths, for the production of quantum states of light multiplexed both in time and frequency. The telecom-wavelength setup showed larger squeezing per mode (the quantum resource exploited in our protocols).
On the second line: we studied the complexity of large multimode quantum states, affected by non-Gaussian operations, using standard complex-network measures. We developed general theoretical tools for describing and engineering such operations, and we developed and applied experimental techniques to characterize their quantum features—such as Wigner negativity and entanglement—using machine-learning methods.
On the third line: we investigated the reconfigurability of quantum complex networks based on multimode optical resources and studied suitable quantum routing protocols for quantum communication tasks. We implemented an experimental protocol for the simulation of quantum environments. We also devised a specific quantum machine-learning protocol (quantum reservoir computing) that can be implemented using our experimental resources. We first implemented an optical protocol, then devised a quantum and measurement-based version, and finally demonstrated an experimental quantum protocol whose performance compares favorably with state-of-the-art classical techniques.
Some results have been used for a patent application. The rest of the result have been published in peer-review journals including APS journals (Physical Review A, Physical Review Research, Physical Review Letters and PRX Quantum) , Springer Nature journals ( EPJ Quantum technologies, Communication Physics, 1 just accepted in Nature Photonics); IOP journals ( Journal of Physics: complexity, New Journal of Physics, Quantum Science and Technology), Optica group ( Optics Express, Optics Letters), AIP Publishing (APL Photonics). Some results are currently under review. All the articles have also been published in an open-access electronic preprint repository (Arxiv).
The results have been disseminated in the main conferences of the field ( like CLEO US, CLEO europe, APS March Meeting, Quantum 2.0 CEWQO, ) and more dedicated workshop ( like CCS2022 Conference in Complex Systems, Bristol Quantum Information Technologies, Quantum Information in Spain ICE-7, International Workshop on Quantum Network Science, Workshop Quantum Machine Learning,..), PhD summer schools and colloquia for master students.
Outreach for general public have been delivered in quantum science fairs or events in Europe along with specific collaboration with artistic residence (French-Italian event La Science de L'art)
1) implementing two different setups based on nonlinear optical processes for producing multimode fields that can be arranged as complex quantum networks;
2) developing the theory of complex quantum systems within our specific framework, where quantum effects are encoded in the continuous variables (amplitude and phase) of the electromagnetic field;
3) devising quantum information protocols.
On the first line: we implemented two experimental setups, operating at near-infrared and telecom wavelengths, for the production of quantum states of light multiplexed both in time and frequency. The telecom-wavelength setup showed larger squeezing per mode (the quantum resource exploited in our protocols).
On the second line: we studied the complexity of large multimode quantum states, affected by non-Gaussian operations, using standard complex-network measures. We developed general theoretical tools for describing and engineering such operations, and we developed and applied experimental techniques to characterize their quantum features—such as Wigner negativity and entanglement—using machine-learning methods.
On the third line: we investigated the reconfigurability of quantum complex networks based on multimode optical resources and studied suitable quantum routing protocols for quantum communication tasks. We implemented an experimental protocol for the simulation of quantum environments. We also devised a specific quantum machine-learning protocol (quantum reservoir computing) that can be implemented using our experimental resources. We first implemented an optical protocol, then devised a quantum and measurement-based version, and finally demonstrated an experimental quantum protocol whose performance compares favorably with state-of-the-art classical techniques.
Some results have been used for a patent application. The rest of the result have been published in peer-review journals including APS journals (Physical Review A, Physical Review Research, Physical Review Letters and PRX Quantum) , Springer Nature journals ( EPJ Quantum technologies, Communication Physics, 1 just accepted in Nature Photonics); IOP journals ( Journal of Physics: complexity, New Journal of Physics, Quantum Science and Technology), Optica group ( Optics Express, Optics Letters), AIP Publishing (APL Photonics). Some results are currently under review. All the articles have also been published in an open-access electronic preprint repository (Arxiv).
The results have been disseminated in the main conferences of the field ( like CLEO US, CLEO europe, APS March Meeting, Quantum 2.0 CEWQO, ) and more dedicated workshop ( like CCS2022 Conference in Complex Systems, Bristol Quantum Information Technologies, Quantum Information in Spain ICE-7, International Workshop on Quantum Network Science, Workshop Quantum Machine Learning,..), PhD summer schools and colloquia for master students.
Outreach for general public have been delivered in quantum science fairs or events in Europe along with specific collaboration with artistic residence (French-Italian event La Science de L'art)
The experimental technique developed for characterizing Wigner negativity allows the processing of data from systems with a large number of components (up to 10), which could not be handled by previous tomographic techniques (typically limited to 3–4 components). The theoretical classification—via complex-network measures—of large multimode quantum states (up to 100 components) affected by non-Gaussian operations represents a unique approach for characterizing such large and complex quantum systems. In contrast, standard quantum optics techniques generally allow for the characterization of only few-mode (i.e. few-component) states. In addition, we revised specific quantum routing protocols for multiparty scenarios within the continuous-variable framework, uncovering functionalities that are unique to continuous-variable systems.
The experimental implementation of multiplexed quantum states is also beyond the current state of the art. We implemented the first continuous-variable (CV) multimode quantum states multiplexed simultaneously in time and frequency degrees of freedom. Moreover, the telecom setup demonstrated the first frequency-multiplexed CV quantum state with significant squeezing. We devised the first measurement-based reservoir computing protocol. Finally, the experimental implementation of quantum reservoir computing in continuous-variable photonic systems yielded results beyond the state of the art: it was unexpected that a tabletop experiment could already achieve performance comparable to state-of-the-art classical protocols of the same dimensionality.
The experimental implementation of multiplexed quantum states is also beyond the current state of the art. We implemented the first continuous-variable (CV) multimode quantum states multiplexed simultaneously in time and frequency degrees of freedom. Moreover, the telecom setup demonstrated the first frequency-multiplexed CV quantum state with significant squeezing. We devised the first measurement-based reservoir computing protocol. Finally, the experimental implementation of quantum reservoir computing in continuous-variable photonic systems yielded results beyond the state of the art: it was unexpected that a tabletop experiment could already achieve performance comparable to state-of-the-art classical protocols of the same dimensionality.