We present an ultra-compact source of maximally entangled on-demand photon pairs. Our results are based on coupling of single GaAs quantum dots that are embedded in monolithic micro-lenses to a single-mode fiber with directly attached to 3D-printed micro-optics (NA of 0.6) inside a cryogenic environment. This approach, which is geared towards future integration into industrial environments, yields state-of-the-art entangled photon pair creation performance while retaining flexibility and adjustability required for long-term operation of such a device - all while dramatically reducing the overall system footprint. We demonstrate near diffraction-limited performance and hyperspectral imaging utilizing a 3D-printed micro-objective with a full width at half maximum resolution limit of 604(16) nm when operating the system at a cryogenic temperature of 3.8 K. Furthermore, we prove that this system can be used to achieve single photon emission rates of 392(20) kHz at a 76 MHz pump rate and purities of 99.2(5) % using two-photon resonant excitation. Utilizing the exciton-biexciton emission cascade available in GaAs quantum dots under resonant excitation, near maximally entangled photon pairs with peak entanglement negatives 2n of 0.96(2) in a 4 ps time window, and 0.81(1) when averaged over one exciton lifetime, are demonstrated.
@article{arxiv.2502.11623,
title = {An ultra-compact deterministic source of maximally entangled photon pairs},
author = {M. Langer and P. Ruchka and A. Rahimi and S. Jakovljevic and Y. G. Zena and A. Danilov and M. Pal and R. Bassoli and F. H. P. Fitzek and O. G. Schmidt and H. Giessen and C. Hopfmann},
journal= {arXiv preprint arXiv:2502.11623},
year = {2025}
}