We have demonstrated a quantum interface based on the frequency upconversion for photons carrying orbital angular momentum (OAM) states from telecom wavelength to visible regime by sum-frequency generation with high quantum conversion efficiency.
The orbital angular momentum (OAM) of light shows great potential in quantum communication. The transmission wavelength for telecom is usually around 1550 nm, while the common quantum information storage and processing devices based on atoms, ions or NV color centers are for photons in visible regime. Here we demonstrate a quantum information interface based on the frequency upconversion for photons carrying OAM states from telecom wavelength to visible regime by sum-frequency generation with high quantum conversion efficiency. The infrared photons at 1558 nm carrying different OAM values were converted to the visible regime of 622.2 nm, and the OAM value of the signal photons was well preserved in the frequency upconversion process with pump beam in Gaussian profile.
Light carrying orbital angular momentum (OAM) has exciting applications, including the studies of fundamental quantum physics, optical manipulation and trapping of particles, astrophysics, high-precision optical measurements and optical communication, etc. In quantum information field, a photon encoded with information in its OAM degrees of freedom enables networks to carry significantly more information and increase their capacity greatly due to the inherent infinite degrees of freedom for OAM. Therefore it is no surprise that many groups and researchers are active in building up a high-dimensional quantum network and many important progresses have been achieved during the past years. To realize a long-distance quantum communication, a quantum repeater has to be used to overcome the problem of communication fidelity decreasing exponentially with the channel length, where, quantum memories for photons, used for storing quantum information, which have been realized successfully during the past decade in many systems such as a cold/hot atomic system, a solid matter, a diamond, and others, are key components consisting of a quantum repeater. Photons acted as information candidates can connect different quantum repeaters. Long distance quantum communication requires the wavelengths of photons are situated in the low-loss communication windows, but most quantum memories currently being developed for use in a quantum repeater work at different wavelengths, only few memories can work in low-loss communication windows. Furthermore, the signal stored is an attenuated coherent light and has the Gaussian mode. Though the storage of photonic entanglement at telecom wavelength is realized in an erbium-doped optical fibre recently, the spatial mode used is Gaussian mode. Quantum memories for photons with OAM have recently been realized, but all work at different wavelengths. So a quantum interface to bridge the wavelength gap is necessary.
Light-carrying orbital angular momentum (OAM) has great potential in enhancing the information channel capacity in both classical and quantum optical communications. Long distance optical communication requires the wavelengths of light are situated in the low-loss communication windows, but most quantum memories currently being developed for use in a quantum repeater work at different wavelengths, so a quantum interface to bridge the wavelength gap is necessary. So far, such an interface for OAM-carried light has not been realized yet. Here, we report the first experimental realization of a quantum interface for a heralded single photon carrying OAM using a nonlinear crystal in an optical cavity. The spatial structures of input and output photons exhibit strong similarity. More importantly, single-photon coherence is preserved during up-conversion as demonstrated.
Optical vortex beams (OVBs) carrying orbital angular momentum (OAM) offer access to an unbounded set of orthogonal states, enabling a dramatic increase in the information capacity for optical communication systems. However, practical OAM detection in telecommunication platforms remains challenging due to background noise, detector limitations at infrared communication wavelengths, and the destructive nature of conventional sampling methods. Here, we introduce an all-optical, nearly nondestructive OAM detection method based on sum-frequency generation (SFG) that overcomes these limitations by transferring the information on the OAM into a distinct frequency domain. In our scheme, two OVBs─one carrying OAM-encoded information and the other serving as a reference─are coupled within a beta-barium borate (BBO) crystal to generate an SFG signal. Our theoretical and experimental studies demonstrate that SFG efficiency is governed by the spatial overlap of the interacting vortex profiles, providing mode-selective and OAM-resolved detection. Crucially, as only a small fraction of the input photons undergo conversion into the nonlinear signal, the original beams remain functionally intact. Since detection is performed exclusively on the upconverted signal in a spectrally distinct visible wavelength region, the signal-to-noise ratio can be improved. Moreover, the SFG signal is generated only when specific OAM states and temporal overlap conditions are simultaneously satisfied, enabling ultrafast and conditionally gated access to the OAM information. This nonlinear selectivity offers enhanced physical-layer security and high-throughput capabilities. Together, our approach provides a robust and versatile platform for advanced OAM-based optical communications and high-capacity photonics applications.