The first objective aims to advance the field of quantum metrology by developing and implementing a robust framework for multi-parameter quantum estimation. This objective is approached through two main strategies: the theoretical development of quantum measurement principles and the experimental realisation of advanced quantum imaging techniques.
A theoretical framework was developed that bridges quantum thermodynamics and quantum metrology, focusing on maximising the encoded information on quantum systems within the constraints of quantum thermodynamic laws. This furthers the understanding of entropy dynamics in quantum measurements, which is crucial when designing systems for precise parameter estimation, especially in noisy environments.
Further, an optimised protocol for quantum state verification that could be adapted for fidelity estimation in two-qubit states with minimal uncertainty was demonstrated. This is essential for ensuring the accuracy and reliability of the quantum states used in metrology. And directly improves the practical implementation of quantum metrology by enhancing the fidelity of state preparation and measurement, critical for multi-parameter estimation.
To improve the robustness of the verification process in a distributed quantum sensor network, it is crucial to ensure that the quantum states used in metrology are indeed entangled and thereby suitable for precise measurements. For this, an algorithm based on semi-definite programming was developed that was able to identify entangled resources within an experimental, noisy probability distribution. This addresses both theoretical and practical aspects of quantum metrology by optimising measurement and reducing errors due to noise and imperfections.
Complex entangled quantum probes, e.g. OAM states, have demonstrated enhanced noise-robustness compared to other states. To leverage this potential for quantum metrology, a method for generating and verifying high-fidelity entangled states with non-traditional photon configurations was demonstrated. This has potential to improve parameter estimation accuracy in quantum metrology.
Objective 2 aims to showcase the potential of multi-parameter and multiple-object estimation in quantum technology applications, specifically in contexts that demand precision measurement of sequential systems rather than single, isolated ones. This objective extends the foundational work of Objective 1 into practical applications involving complex quantum systems, such as those found in quantum computing. As the stability and noise robustness of nonlinear interferometers deteriorate with the scaling up of parameters and objects, alternative, more favourable schemes were investigated.
A theoretical framework for frequency comb absorption spectroscopy, that can be realised in integrated photonic platforms, was developed for making quantum sensing technologies more practical and adaptable to various applications.
By simplifying the process and enhancing the flexibility of measurements, this technology directly supports the multiple-object estimation capabilities essential for analysing sequential systems in quantum computing, where different parameters may need to be measured in a streamlined and efficient manner. Further, the role of entanglement in improving the precision of measurements, essential for detailed and accurate parameter estimation, was investigated.
Objective 3 focuses on harnessing the advancements in multi-parameter quantum metrology to develop ultra-precise sensors using integrated silicon photonics in collaboration with the University of Bristol. This approach aims to manage the increasing complexity and number of parameters and optical modes in quantum sensing technologies with a platform that can be realised on an industrial scale.
The optimal sensing structures were numerically identified and realised in a silicon photonic chip that has the capability of generating photonic quantum states tailored to the absorption wavelength regime of methane gas whilst simultaneously providing high detection efficiencies with available single photon detector technology. The chip's capabilities to handle complex measurements pave the way for multi-parameter and multiple-object estimation in a highly integrated format, making it a cornerstone development for Objective 3.
During the project, the fellow collaborated with 26 different scientists in 9 different universities in Europe and around the world. The 8 publications (3 of which are currently under preparation) them bear witness to the wide impact the fellow’s research has had. The fellow delivered talks at 11 different international conferences, 5 of which were invited. He also presented research seminars at 7 different universities and institutes. The research was presented at 7 different workshops and conferences in 4 different countries.
