Robust quantum metrology with random Majorana constellations

Abstract: Even the most classical states are still governed by quantum theory. A number of physical systems can be described by their Majorana constellations of points on the surface of a sphere, where concentrated constellations and highly symmetric distributions correspond to the least and most quantum states, respectively. If these points are chosen randomly, how quantum will the resultant state be, on average? We explore this simple conceptual question in detail, investigating the quantum properties of the resulting random states. We find these states to be far from the norm, even in the large-number-of-particles limit, where classical intuition often replaces quantum properties, making random Majorana constellations peculiar and intriguing. Moreover, we study their usefulness in the context of rotation sensing and find numerical evidence of their robustness against dephasing and particle loss. We realize these states experimentally using light's orbital angular momentum degree of freedom and implement arbitrary unitaries with a multiplane light conversion setup to demonstrate the rotation sensing. Our findings open up new possibilities for quantum-enhanced metrology.