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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - CAPABLE (Composite integrated photonic platform by femtosecond laser micromachining)

Teaser

Summary

The quantum technology revolution promises a transformational impact on the society and economics worldwide. It will enable breakthrough advancements in such diverse fields as secure communications, computing, metrology, and imaging. Quantum photonics, which recently received an incredible boost by the use of integrated optical circuits, is an excellent technological platform to enable such revolution, as it already plays a relevant role in many of the above applications. However, some major technical roadblocks needs to be overcome. Currently, the various components required for a complete quantum photonic system are produced on very different materials by dedicated fabrication technologies, as no single material is able to fulfil all the requirements for single-photon generation, manipulation, storage and detection. This project proposes a new hybrid approach for integrated quantum photonic systems based on femtosecond laser microfabrication (FLM), enabling the innovative miniaturization of various components on different materials, but with a single tool and with very favourable integration capabilities.
This project will mainly focus on two major breakthroughs: the first one will be increasing the complexity achievable in the photonic platform and demonstrating unprecedented quantum computation capability; the second one will be the integration in the platform of multiple single-photon quantum memories and their interconnection. Achievement of these goals will only be possible by taking full advantage of the unique features of FLM, from the possibility to machine very different materials, to the 3D capabilities in waveguide writing and selective material removal. The successful demonstration and functional validation of this hybrid, integrated photonic platform will represent a significant leap for photonic microsystems in quantum computing and quantum communications.

Work performed

In the first period of the project CAPABLE, a large effort has been devoted to the instalment of new labs. Nevertheless, the project already achieved many important breakthroughs. A first important result is the demonstration of very efficient waveguides in the crystal where quantum memories are made, thus enabling the realization of a single-photon integrated quantum memory with storage times that are orders of magnitude longer than any previous implementation. In addition, the stong light-matter interaction in this waveguides made it possible to use control light beams with much lower power, which opened the possibility to demonstrate frequency-multiplexed integrated quantum memories with as many as 15 modes (where each frequency mode contains 9 temporal modes for a total number of ~130 stored modes). A second important result regards the validation of quantum computations that are hard to verify classicaly, e.g. the Boson Sampling algorithm. In this framework, we have demonstrated new techniques based on machine learning that are capable to identify specific patterns in the output distributions of photons that can recognise genuine quantum interference between photons from other spurious mechanisms. From a more fundamental point of view, we have provided a first demonstration of quantum interference between single photons propagating in a topologically protected state. More on the technological side, we have developed a new femtosecond laser nanomachining process that can structure relevant crystals with nanometric resolution over millimeter scale. This technique enables the development of new and more efficient photonic nanodevices for the manipulation of photons. Finally, we have implemented a completely reconfigurable integrated photonic circuit that can be used as a testbed to implement and verify new quantum sensing protocols. In particular, we used it to assess the performance of simultaneous multi-phase estimation.

Final results

The CAPABLE project will give a boost to quantum technologies. It will create the first integrated platform encompassing all the quantum operations that are relevant in a quantum system, i.e. single photon generation, manipulation, storage and detection (the latter being developed in a parallel ongoing project).
Specific technological breakthroughs will be achieved that are worth per se, e.g. the capability to produce rapidly reconfigurable and cryo-friendly waveguide phase shifters, the significant improvement of multipoint coupling in a high-index planar light circuit, the possibility to fabricate micromechanical resonators with waveguides inside and the first demonstration of single-photon storage in a waveguide memory. Moreover, all these achievements are enabled by the same femtosecond laser microfabrication technology, thus also providing a clear vision of how they can all be combined in a single hybrid system. To further support this last claim, the last two objectives of the project will show some examples of hybrid quantum systems that will have a dramatic impact on quantum information. Efficient integration of quantum memories in fiber networks will boost current quantum cryptography applications by extending their range through quantum repeaters, and will enable distributed quantum computing schemes. The implementation of Boson Sampling at an unprecedented complexity level will approach the level where the quantum advantage with respect to classical devices will be clearly visible, although on a very specific problem. This will represent a landmark in quantum information providing a great input to the whole field and officially marking the entrance in the quantum information era.
In addition to the scientific impact, this project will provide top-level training on highly multidisciplinary topics to several students and early-stage researchers, thus helping in the creation of a new class of scientists with a holistic vision on material processing, microfabrication, device design and characterization, and quantum information.