Efficient separation of the orbital angular momentum eigenstates of light

TL;DR

This paper presents a novel optical method that significantly improves the efficiency of separating light's orbital angular momentum states, reaching over 92%, which benefits quantum communication and cryptography.

Contribution

The authors introduce a series of unitary optical transformations enabling high-efficiency OAM state separation surpassing previous theoretical limits.

Findings

Achieved over 92% separation efficiency for OAM states.

Demonstrated separation of angular position modes mutually unbiased with OAM.

Enhanced potential for quantum cryptography applications.

Abstract

Orbital angular momentum (OAM) of light is an attractive degree of freedom for funda- mentals studies in quantum mechanics. In addition, the discrete unbounded state-space of OAM has been used to enhance classical and quantum communications. Unambiguous mea- surement of OAM is a key part of all such experiments. However, state-of-the-art methods for separating single photons carrying a large number of different OAM values are limited to a theoretical separation efficiency of about 77 percent. Here we demonstrate a method which uses a series of unitary optical transformations to enable the measurement of lights OAM with an experimental separation efficiency of more than 92 percent. Further, we demonstrate the separation of modes in the angular position basis, which is mutually unbiased with respect to the OAM basis. The high degree of certainty achieved by our method makes it particu- larly attractive for enhancing the information capacity of multi-level quantum cryptography systems.