A room-temperature on-chip orbital angular momentum source that emits well-collimated single photons has been demonstrated.

Generation of single photons carrying spin and orbital angular momenta (SAM and OAM) opens enticing perspectives for exploiting multiple degrees of freedom for high-dimensional quantum systems. However, on-chip generation of single photons encoded with single-mode SAM-OAM states has been a major challenge. Here, by using carefully designed anisotropic nanodimers fabricated atop a substrate, supporting surface plasmon polariton (SPP) propagation, and accurately positioned around a quantum emitter (QE), we enable nonradiative QE-SPP coupling and the SPP outcoupling into free-space propagating radiation featuring the designed SAM and OAM. We demonstrate on-chip room-temperature generation of well-collimated (divergence < 7.5°) circularly polarized (chirality > 0.97) single-mode vortex beams with different topological charges (𝓁 = 0, 1, and 2) and high single-photon purity, g ⁽²⁾ (0) < 0.15. The developed approach can straightforwardly be extended to produce multiple, differently polarized, single-mode single-photon radiation channels and enable thereby realization of high-dimensional quantum sources for advanced quantum photonic technologies.

Channelling single-photon emission in multiple well-defined directions and simultaneously controlling its polarization characteristics is highly desirable for numerous quantum technology applications. We show that this can be achieved by using quantum emitters (QEs) nonradiatively coupled to surface plasmon polaritons (SPPs), which are scattered into outgoing free-propagating waves by appropriately designed metasurfaces. The QE-coupled metasurface design is based on the scattering holography approach with radially diverging SPPs as reference waves. Using holographic metasurfaces fabricated around nanodiamonds with single Ge vacancy centres, we experimentally demonstrate on-chip integrated efficient generation of two well-collimated single-photon beams propagating along different 15° off-normal directions with orthogonal linear polarizations.

Radially polarized optical beams are desirable in many applications because of their property to generate longitudinally polarized fields when being strongly focused. Single-photon sources are however normally limited to the generation of linearly polarized photons due to their dipolar nature. Here, we report on emission of radially polarized single photons from a nitrogen-vacancy (NV) center in a nanodiamond (ND) coupled to a bull’s-eye plasmonic antenna. Design optimization and characterization of plasmonic bull’s-eye antennas consisting of polymer circular nanoridges deterministically fabricated on a silica protected silver film around an NV-ND emitter are reported. We demonstrate with numerical simulations that the collection efficiency for photons emitted at the design wavelength can exceed 80% with optimized bull’s-eye structures. Analysis of the emission angular distribution indicates that, even when limiting the detection to the main lobe by using an 0.2 NA objective, the detection efficiency can overreach 55%. A 3-fold enhancement in the total number of detected radially polarized photons is experimentally observed with an NV-ND single-photon emitter being coupled to a bull’s-eye antenna. Generation of radially polarized single photons suggests new interesting possibilities for single-photon imaging and sensing.

Germanium vacancy (GeV) centers in diamonds constitute a promising platform for single-photon sources to be used in quantum information technologies. Emission from these color centers can be enhanced by utilizing a cavity that is resonant at the peak emission wavelength. We investigate circular plasmonic Bragg cavities for enhancing the emission from single GeV centers in nanodiamonds (NDs) at the zero phonon line. Following simulations of the enhancement for different configuration parameters, the appropriately designed Bragg cavities together with out-coupling gratings composed of hydrogen silsesquioxane ridges are fabricated around the NDs containing nitrogen vacancy centers deposited on a silica-coated silver surface. We characterize the fabricated configurations and finely tune the cavity parameters to match the GeV emission. Finally, we fabricate the cavity containing a single GeV-ND and compare the total decay-rate before and after cavity fabrication, finding a decay-rate enhancement of ∼5.5 and thereby experimentally confirming the feasibility of emission enhancement with circular plasmonic cavities.

Impurity‐vacancy centers in diamond offer a new class of robust photon sources with versatile quantum properties. While individual color centers commonly act as single‐photon sources, their ensembles have been theoretically predicted to have tunable photon‐emission statistics. Importantly, the particular type of excitation affects the emission properties of a color center ensemble within a diamond crystal. While optical excitation favors non‐synchronized excitation of color centers within an ensemble, electron‐beam excitation can synchronize the emitters excitation and thereby provides a control of the second‐order correlation function g ₂ (0). In this letter, we demonstrate experimentally that the photon stream from an ensemble of color centers can exhibit g ₂ (0) both above and below unity, thereby confirming long standing theoretical predictions by Meuret et al. [S. Meuret, L. H. G. Tizei, T. Cazimajou, et al., “Photon bunching in cathodoluminescence,” Phys. Rev. Lett. , vol. 114, no. 19, p. 197401, 2015.]. Such a photon source based on an ensemble of few color centers in a diamond crystal provides a highly tunable platform for informational technologies operating at room temperature.