Periodic Reporting for period 2 - PHOQUSING (PHOTONICS QUANTUM SAMPLING MACHINE)
Reporting period: 2021-09-01 to 2023-02-28
Quantum theory provides a probabilistic description of nature, marking a departure from a classical picture. The intrinsic randomness of quantum processes has found applications in efficient probabilistic algorithms for simulation, integration, machine learning, and financial pricing, among other applications. Recently, a large research effort has been devoted to exploit quantum systems to generate probability distributions that are computationally hard for classical computers to obtain. In particular, several works reported the insight that devices exploiting quantum resources can generate probability distributions that are inaccessible with classical means. Hybrid Quantum Computational models combine classical processing with these quantum sampling machines to obtain computational advantage over standard classical means in some tasks. Moreover, NISQ (Noisy, Intermediate-Scale Quantum) technology may contribute to obtaining this advantage in the near term. The aim of this project is to implement PHOtonic Quantum SamplING (PHOQUSING) machines based on large, reconfigurable interferometers with active feedback.
Among the several objectives of this project, we will define the most suitable architectures enabling the generation of these hard-to-sample distributions using integrated photonics, optimizing the designs and studying the tolerance to errors. PHOQUSING aims to build working photonic quantum sampling machines, with first demonstrations of their algorithmic applications. This enables the implementation of Hybrid Quantum Computing (HQC) models that include quantum and classical elements for applications in machine learning and optimization. The results achieved within PHOQUSING will also have applications outside the scientific community. Several use cases will be addressed within the project, including development of new materials (for space technologies, surfactants, catalysts etc), financial services (portfolio optimization and management, assets scoring), computational fluid dynamics (for automotive, aeronautical) and pharma. Furthermore, we will envisage additional development of the machines to enable cloud-access, which will potentially attract interested end-users in the short term.
Among the several objectives of this project, we will define the most suitable architectures enabling the generation of these hard-to-sample distributions using integrated photonics, optimizing the designs and studying the tolerance to errors. PHOQUSING aims to build working photonic quantum sampling machines, with first demonstrations of their algorithmic applications. This enables the implementation of Hybrid Quantum Computing (HQC) models that include quantum and classical elements for applications in machine learning and optimization. The results achieved within PHOQUSING will also have applications outside the scientific community. Several use cases will be addressed within the project, including development of new materials (for space technologies, surfactants, catalysts etc), financial services (portfolio optimization and management, assets scoring), computational fluid dynamics (for automotive, aeronautical) and pharma. Furthermore, we will envisage additional development of the machines to enable cloud-access, which will potentially attract interested end-users in the short term.
During the first reporting period, the PHOQUSING consortium has progressed several steps towards the final objective of the project. Theoretical work has been performed by implementing simulation software for processes based on a Boson Sampling architecture. This software represents a fundamental step towards definition of the final applications, since it will enable testing different protocols in small-instance size classical simulations. Furthermore, the consortium has already identified optimized reconfigurable circuit designs for the first experiments to be performed with the quantum sampling machines. In particular, different architectures will be pursued for the integrated platforms employed within the project (femtosecond laser-written circuits in glass and lithographic circuits in silicon nitride), to fully exploit the advantages of each approach. Additionally, first results have been obtained on several methodologies for calibration and certification of both the intermediate components and the final hardware to be assembled. These obtained results have also started to define a first roadmap for applications of sampling processes.
During the 2nd reporting period, the PHOQUSING consortium have moved forward towards the final objective of the project starting from the work carried out in the first period. Theoretical advances have been carried on the simulation software for generalized Boson Sampling and on sampling processes with nonlinearities. Furthermore, we have completed the analysis on the appropriate architectures for circuit development, identifying suitable approaches for both experimental platforms employed within PHOQUSING (femtosecond laser-written circuits and silicon-nitride). Additionally, extensive work has been carried out regarding the calibration and certification of the photonic hardware. In particular, we have identified and tested different methodologies suitable for the characterization of integrated circuits operation, involving classical light and without the need for phase-stable operation. Furthermore, methods for the calibration of complex reconfigurable integrated circuits have been developed. Finally, several methodologies for certification of genuine multiphoton interference have been proposed and tested experimentally by the consortium. These results are merged in a unique toolbox. Finally, work has been carried out to identify applications of sampling processes within the project, including variational quantum cloning, and analyses on alternative quantum computation models.
During the 2nd reporting period, the PHOQUSING consortium have moved forward towards the final objective of the project starting from the work carried out in the first period. Theoretical advances have been carried on the simulation software for generalized Boson Sampling and on sampling processes with nonlinearities. Furthermore, we have completed the analysis on the appropriate architectures for circuit development, identifying suitable approaches for both experimental platforms employed within PHOQUSING (femtosecond laser-written circuits and silicon-nitride). Additionally, extensive work has been carried out regarding the calibration and certification of the photonic hardware. In particular, we have identified and tested different methodologies suitable for the characterization of integrated circuits operation, involving classical light and without the need for phase-stable operation. Furthermore, methods for the calibration of complex reconfigurable integrated circuits have been developed. Finally, several methodologies for certification of genuine multiphoton interference have been proposed and tested experimentally by the consortium. These results are merged in a unique toolbox. Finally, work has been carried out to identify applications of sampling processes within the project, including variational quantum cloning, and analyses on alternative quantum computation models.
Several results beyond state-of-the-art have been obtained in the first two periods of PHOQUSING project.
The implementation of software codes for computational analysis of different models and Boson sampling variations have been addressed, representing an important stepping stone through the final vision of PHOQUSING. Further analyses have been report on the Boson Sampling paradigms in terms of classification of the different variants. A complete Boson sampling experiment on a 3D integrated/reconfigurable photonic chip was successfully performed, making a step forward in the complexity of reconfigurable circuits employed in this task. Furthermore, we have devised and tested several methods for the calibration of complex integrated circuits, error modeling, and for the assessment of partial photon indistinguishability of multiphoton states. This led to the development of a complete toolbox for the validation of the sampling machines operation.
From the hardware perspective, strong improvements in the complexity of reconfigurable circuits have been achieved (both for femtosecond laser-writing technology and silicon nitride platform). Another important result obtained is the improvement of the brightness of single-photon sources (>50%). This result represents an important progress beyond current-state-of-the-art in single-photon sources. Additionally, steps ahead have been done in the experimental demonstration of quantum superposition of single-photon states encoded in two frequencies.
Finally, the assembling of both machines QOLOSSUS and QALCULUS have been completed. These machines simultaneously rely on interfacing different components: single-photon sources based on quantum dots, time-to-spatial demultiplexing systems and integrated circuits.
The implementation of software codes for computational analysis of different models and Boson sampling variations have been addressed, representing an important stepping stone through the final vision of PHOQUSING. Further analyses have been report on the Boson Sampling paradigms in terms of classification of the different variants. A complete Boson sampling experiment on a 3D integrated/reconfigurable photonic chip was successfully performed, making a step forward in the complexity of reconfigurable circuits employed in this task. Furthermore, we have devised and tested several methods for the calibration of complex integrated circuits, error modeling, and for the assessment of partial photon indistinguishability of multiphoton states. This led to the development of a complete toolbox for the validation of the sampling machines operation.
From the hardware perspective, strong improvements in the complexity of reconfigurable circuits have been achieved (both for femtosecond laser-writing technology and silicon nitride platform). Another important result obtained is the improvement of the brightness of single-photon sources (>50%). This result represents an important progress beyond current-state-of-the-art in single-photon sources. Additionally, steps ahead have been done in the experimental demonstration of quantum superposition of single-photon states encoded in two frequencies.
Finally, the assembling of both machines QOLOSSUS and QALCULUS have been completed. These machines simultaneously rely on interfacing different components: single-photon sources based on quantum dots, time-to-spatial demultiplexing systems and integrated circuits.