In general, metrology aims to increase the precision of measuring a physical quantity, such as time or the strength of a magnetic or electric field. This precision is typically limited by statistical errors and can be enhanced by repeating experiments many times and averaging their results. Quantum metrology takes fundamental limitations on the measurement process into account which are imposed by quantum mechanics and by the fact that measurement devices are described by their quantum states. For example, the entanglement of a well-designed quantum state can result in a reduced number of measurements required for reaching a certain measurement precision.
In this recent work we propose a novel variational quantum algorithm that turns a quantum computer into a quantum sensor and optimises its measurement precision. This way our quantum circuit can find the best quantum states for quantum metrology while also taking into account imperfections of the quantum computer. This devices is tailored to and can be implemented on near-term hardware.
We have simulated variational metrology experiments assuming various different imperfections of the quantum computer and found very interesting results. In particular, our algorithm found non-symmetric states that are optimal and significantly outperform permutationally symmetric states. This is a very interesting discovery because states that are symmetric under particle exchange have been assumed to be optimal previously.
Please refer to our recent arXiv (https://arxiv.org/abs/1908.08904) upload for more details and the explanation of symmetry breaking. The source code for reproducing our optimisation results is openly available on GitHub https://github.com/QTechTheory/Variational-State-Quantum-Metrology.
