A novel frequency conversion source for creating bichromatic entangled photons

For quantum networks to extend beyond the physical distances defined by the real-world limitations of signal loss, a sophisticated multi-modular network of quantum devices to allow for “repeating” quantum information without measuring or damaging it is required. To make these modules work efficiently within the existing telecom fiber infrastructure, it is necessary to convert a photon’s wavelength from the telecom bands, for non-lossy transmission through the fiber, to that which is optimal for the various quantum devices (e.g. quantum sources and buffers). Currently available technologies cannot efficiently convert the wavelength of single photons, preventing the realization of transparent optical quantum networks. Rather than solve the complicated problem of single-photon frequency conversion, we propose merging the frequency conversion and entanglement generation into a single device. Such a device would create pairs of entangled photons at two wavelengths, one native to atomic quantum systems and the other in the telecom band. At the heart of our device, a frequency conversion structure converts uncorrelated light pulses into polarization- entangled single photon pairs at two different frequencies. The proposed device uses the atomic transitions of a well-characterized vapor, rubidium (Rb), to access a wide variety of wavelengths, including telecom O and C bands for fiber transmission, near-Infrared for quantum storage/buffering, and near-UV for trapped-ion qubits. Our 2-in-1 module for frequency conversion and photon pair generation results in a very bright entanglement source that is simultaneously compatible with telecom fiber optics and quantum modules such as buffers and atomic processors. During Phase I, we experimentally demonstrated the production of true bichromatic entangled photons with a spectral brightness significantly larger than any available product in the market. We are now proposing a clear technical path towards improving the key parameters of the frequency converting source while investigating the most optimal designs towards a commercially available MVP. The proposed technology holds the key to building quantum buffer-assisted, all-optical quantum networks. Our approach eliminates the need for separate entanglement sources and frequency conversion systems, given that our proposed entanglement source produces photons that are natively compatible both with optical fiber networks, for the long-distance transfer of information, and atomic quantum systems, for the storing and processing of quantum information. In the near term, this technology can assist many scientists at the DOE and other agencies with their work towards the national quantum internet. In the long term, US-based and global quantum networks can use our devices in every node to distribute entanglement across the networks.