Spatial Bell-State Generation without Transverse Mode Subspace Postselection

Abstract

Spatial states of single photons and spatially entangled photon pairs are becoming an important resource in quantum communication. This additional degree of freedom provides an almost unlimited information capacity, making the development of high-quality sources of spatial entanglement a well-motivated research direction. We report an experimental method for generation of photon pairs in a maximally entangled spatial state. In contrast to existing techniques, the method does not require postselection of a particular subspace of spatial modes and allows one to use the full photon flux from the nonlinear crystal, providing a tool for creating high-brightness sources of pure spatially entangled photons. Such sources are a prerequisite for emerging applications in free-space quantum communication.

Simulating Correlations of Structured Spontaneously Down‐Converted Photon Pairs

“…In addition, we recover the expected conservation laws for the optical modes in both the Hermite–Gauss basis (where we reproduce the experimental results of ref. []), as well as in the Laguerre–Gauss basis (where we recover the experiment in ref. [] and the theoretical predictions in ref.…”

“…Furthermore, interesting states (such as Bell states) can be obtained for a certain choice of the beam waist σ. This result has been experimentally confirmed by Kovlakov et al., who used a periodically poled crystal pumped with an HG‐shaped pump beam, and measured the output state projected on the HG basis. The down‐converted photon modes were determined using diffraction from an SLM.…”

“…[], which can be seen, for example, by comparing Figure b with Figure 2 in ref. [] where the expected off‐diagonal second‐order correlations of the Bell state are clearly evident.…”

“…SPDC is not limited to plane‐wave‐like beams only and was widely studied with structured pump beams, such as diverging pump beams, Laguerre Gaussian beams and Hermite Gaussian beams . Using structured light in SPDC also enables the creation of higher dimensional entanglement, for instance by employing the orbital angular momentum (OAM) as an additional degree of freedom for the photons .…”

Spatially entangled Airy photons

“…Therefore, manipulating the shape of the classical pump beam facilitates control over the twophoton spatial correlations. This interesting correspondence between the entangled photons and the pump beam has been used in various application, such as the generation of maximally entangled orbital angular momentum (OAM) states [16][17][18], cancelling the scattering of entangled photons in real time [19] and for controlling the spatial coherence of entangled states [20,21].…”