Quantum digital spiral imaging

Abstract

We demonstrate that the combination of digital spiral imaging with high-dimensional orbital angular momentum (OAM) entanglement can be used for efficiently probing and identifying pure phase objects, where the probing light does not necessarily touch the object, via the experimental, non-local decomposition of non-integer pure phase vortices in OAM-entangled photon pairs. The entangled photons are generated by parametric downconversion and then measured with spatial light modulators and single-mode fibers. The fractional phase vortices are defined in the idler photons, while their corresponding spiral spectra are obtained non-locally by scanning the measured OAM states in the signal photons. We conceptually illustrate our results with the biphoton Klyshko picture and the effective dimensionality to demonstrate the high-dimensional nature of the associated quantum OAM channels. Our result is a proof of concept that quantum imaging techniques exploiting high-dimensional entanglement can potentially be used for remote sensing. Photon pairs entangled in their orbital angular momentum can reveal information about an object with a complex phase profile. Lixiang Chen and co-workers from China and Scotland used entangled photons to recover the spiral spectrum of an optical fractional phase vortex. First they used a beta barium borate crystal to generate a pair of signal and idler entangled photons through spontaneous parametric downconversion. They then split the beam into two arms, each containing a programmable spatial light modulator (SLM) that can imprint any desired phase profile onto an incident photon. By encoding a fractional phase vortex on the SLM of one arm, and scanning through different orbital angular momentum values on the SLM of the other arm, the team recovered the spiral spectra of the fractional phase vortex nonlocally.