Adaptive optics for quantum technologies
Andrew Forbes · 2024
Adaptive optics in the classical realm usually implies some pre- or post-channel correction to an optical wavefront, with the objective to improve some figure of merit, perhaps transmission through noise, beam quality of high-power lasers, or bit-error-rate in optical communications. A measurement is performed on the beam, often wavefront sensing of the beam to be corrected, the error specified and fixed, either deterministically or by some iterative approach. In the quantum realm it is rather different. First, quantum communication demands low light levels, ideally single photons, so that compensating for lost signal by increasing power is not possible. Second, a measurement of the quantum state destroys the state, and unfortunately it is not possible to clone a quantum state (imperfect cloning is possible). This poses a conundrum: to fix the error one must measure the state, but if you measure the state the information of the state is destroyed. You know what is wrong, but have nothing left to fix. How then can AO be translated to the quantum realm? In this chapter we will answer this question, and in doing so widen the scope of adaptive optics to cases where there is no single beam of light but rather non-local quantum correlations between entangled photons.