Periodic Reporting for period 3 - PEQEM (Photonics for engineered quantum enhanced measurement) Reporting period: 2022-01-01 to 2023-06-30 Summary of the context and overall objectives of the project Advances in measurement always lead to dramatic advances in science and in technology. Our society is now heavily dependent on the sensors that permeate environmental monitoring, security, healthcare and commerce. Now, our rapidly growing understanding of how to control quantum systems vastly expands both the potential performance and application for measurement and sensing using quantum-enhanced techniques. But these techniques will only efficiently find disruptive use once they are engineered for robustness, deliver desired operational parameters and are shown to work in a platform that can be mass-produced.This project adopts an engineering approach to the disciplines of photonic quantum enhanced sensing and squeezed light quantum optics. We will develop new sensing protocols and implement them in integrated photonics that are tailored to enable miniature, deployable and ultimately low cost sensors that exceed the state of the art through (i) exploitation of the quantum mechanics of light and by (ii) developing the requisite high performance of components in an integrated photonics platform. The methodology is to combine quantum optics of Kerr-nonlinear materials that generate squeezed light and quantum state detection with photonic device engineering. We will benchmark device performance using quantum metrology techniques. By the end of this project, we will have developed all-integrated squeezed light generation and detection technology, that provides enhanced sensors for absorption and phase measurements beyond the shot noise limit --- the hard limit that bounds performance of state of the art “classical” sensors. Applications include next generation quantum metrology experiments, measurement of photo- sensitive samples, precise characterization of photonic components and trace gas detection. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far We have also developed the theory for a new sensing technique to simultaneously measure phase and loss, that are often linked via Kramers Kronig relations to parameterise for example the concentration of a given sample within another. Here we showed how to optimize the squeezing angle for this measurement and we explored when phase and loss was not correlated. This was published in Phys. Rev. Lett. 124, 140501 (2020). We have also explored optimal operational parameters for twin-beam absorption estimation in the presence of excess uncorrelated noise and when detection efficiency of the two beams are imbalanced --- this was published in Appl. Phys. Lett. 117, 034001 (2020). Noise suppression techniques have been developed and implemented to suppress noise in fibre lasers for possible later application for squeezed light generation. This work was published in Phys. Rev. Applied 12, 044073 (2019). The commercial potential of the noise suppression technique will be explored through support via an awarded ERC Proof of Concept grant “Shot-noise Limited Optical Waveguide MOdule (SLOW MO)”. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) Expected results until the end of the project are the full integration of squeezed light generation and measurement on one packaged photonic chip, and demonstration that this can measure parameters below the shot noise limit. Initial results will use the maturity of c-band integrated photonics, but the project will also develop capability for longer wavelengths (2.1 microns) to enable use of the technology for gas sensing. A core component in this capability will be the development of integrated Homodyne detection. Through edge-coupled photodiode geometry and reduction of overall capacitance of the detection by integration with integrated electronics, we aim for enhanced speed performance in electrical Homodyne detection beyond the state of the art that uses top-illuminated PIN diodes and free-space optics. A photonic integrated circuit for quantum state measurement
