Beating the diffraction limit in astronomy via quantum cloning

Abstract

Context. The diffraction limit is considered as the absolute boundary for the angular resolution of a telescope. Non-linear optical processes, however, allow the diffraction limit to be beaten non-deterministically. Aims. We examine the possibility of overcoming the diffraction limit of a telescope through photon cloning processes, heralded by trigger events. Whilst perfect cloning is ruled out by quantum mechanics, imperfect cloning is attainable and can beat the diffraction limit on a reduced fraction of photons.Methods. We suggest to insert a layer of excited atoms in a pupil plane of the telescope. When a photon from the astronomical source passes the pupil, it stimulates the emission of identical photons by the excited atoms. The set of photons arrives on a coincidence detector, and the average position of simultaneously arriving photons is recorded. The contribution of spontaneous emissions is minimized by use of a trigger signal, implemented via a quantum-non-demolition measurement. Results. The proposed set-up – an optical amplifier triggered by a quantum-non-demolition measurement – allows to beat the diffraction limit of a telescope, at the price of a loss in efficiency. The efficiency may, however, be compensated for through increased exposure times. Conclusions. The main conclusion is the possibility in principle to improve the angular resolution of a telescope beyond the diffraction limit and thus to achieve high-angular resolutions with moderately sized telescopes.