Object Identification Using Correlated Orbital Angular Momentum States

Using spontaneous parametric down-conversion as a source of correlated photon pairs, correlations are measured between the orbital angular momentum (OAM) in a target beam (which contains an unknown object) and that in an empty reference beam. Unlike previous studies, the effects of the object on off-diagonal elements of the OAM correlation matrix are examined. Because of the presence of the object, terms appear in which the signal and idler OAM do not add up to that of the pump. Using these off-diagonal correlations, the potential for high-efficiency object identification by means of correlated OAM states is experimentally demonstrated for the first time. The higher-dimensional OAM Hilbert space enhances the information capacity of this approach, while the presence of the off-diagonal correlations allows for recognition of specific spatial signatures present in the object. In particular, this allows the detection of discrete rotational symmetries and the efficient evaluation of multiple azimuthal Fourier coefficients using fewer resources than in conventional pixel-by-pixel imaging. This represents a demonstration of sparse sensing using OAM states, as well as being the first correlated OAM experiment to measure properties of a real, stand-alone object, a necessary first step toward correlated OAM-based remote sensing.

Figure 1

Setup for the sensing of the object via orbital angular momentum of correlated photons.

Figure 2

(a) Histogram of the main diagonal and (b) complete two-dimensional OAM joint spectrum for our configuration with no object. (c) $P(l_o|l_r=0)$ cross section. The blue (vertical) box in the joint spectrum denotes the section in (a) and the green (diagonal) box denotes the section in (c).

Figure 3

(a) Image of the target, (b) experimental joint spectrum, (c) histogram of the main diagonal, and (d) $P(l_o|l_r=0)$ cross section of the joint spectrum.

Figure 4

(a) Image of the target, (b) experimental joint spectrum, (c) histogram of the main diagonal, and (d) $P(l_o|l_r=0)$ cross section of the joint spectrum.