Quantum Entanglement of Complex Structures of Photons by Robert Fickler

Author:Robert Fickler
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

3.4.2 Limitations of Previous Experiments

So far, most of the experimental setups generating and testing OAM entanglement go back to the seminal work of Mair et al. [12]. The idea is to use the inherent momentum conservation in the down conversion process to create entanglement in the OAM degree of freedom. If one photon is measured to have quanta of OAM, the other will have quanta due to angular momentum conservation. The disadvantage of such a scheme is that the generation efficiency of the higher-order modes is directly connected to pump beam dimensions, the length of the crystal and the focusing parameters [13]. In experiments, values up to 20–30 might be achievable [14–16], however the highest OAM entanglement tested in a recent experiment was 11 [17].4 Nevertheless, a recent theoretical idea to increase the possible OAM values in the down conversion by a chirped quasi-phase-matched crystal suggests a promising enhancement [18]. The estimated increase could be tenfold, which would lead to OAM quanta of approx 200–300 after the down conversion. Although the predicted results are very promising they still rely on the phase matching conditions of the down conversion crystal. On the contrary to these theoretical studies, the presented scheme (source and transfer setups) is only limited by the devices available to generate high-order OAM modes. It can always be adapted to novel possibilities in creating spatial modes containing high quanta of OAM and for testing the limits of quantum mechanics (see e.g. spiral phase mirrors in [19, 20]).

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