Ab initio quantum-enhanced optical phase estimation using real-time feedback control

Using squeezed states of light combined with a real-time Bayesian adaptive estimation algorithm, deterministic phase estimation with a precision beyond the quantum shot noise limit is demonstrated without any prior knowledge of the phase's value. Optical phase estimation is a vital measurement strategy that is used to perform accurate measurements of various physical quantities including length, velocity and displacements 1 , 2 . The precision of such measurements can be greatly enhanced by the use of entangled or squeezed states of light as demonstrated in a variety of different optical systems 3 , 4 , 5 , 6 , 7 , 8 . Most of these accounts, however, deal with the measurement of a very small shift of an already known phase, which is in stark contrast to ab initio phase estimation where the initial phase is unknown 9 , 10 , 11 , 12 . Here, we report on the realization of a quantum-enhanced and fully deterministic ab initio phase estimation protocol based on real-time feedback control. Using robust squeezed states of light combined with a real-time Bayesian adaptive estimation algorithm, we demonstrate deterministic phase estimation with a precision beyond the quantum shot noise limit. The demonstrated protocol opens up new opportunities for quantum microscopy, quantum metrology and quantum information processing.