Orbital-angular-momentum entangled photon emission from circular currents in semiconductor-superconductor structures

We theoretically demonstrate that a superconducting circular current induced in a semiconductor results in the emission of orbital-angular-momentum (OAM) entangled photon pairs upon carrier recombination. Combining the macroscopic Ginzburg–Landau theory and the microscopic Bardeen–Cooper–Schrieffer (BCS) theory, we investigate the emission of a superconducting light-emitting diode (SLED) with a spatially varying phase profile in the superconducting order parameter. We show that in the active region of the SLED with a circular supercurrent, radiative recombination processes inherit the order parameter phase and result in photon pairs emitted into modes of different OAM quantum numbers. We demonstrate that coherent superposition of superconducting qubit eigenstates can also be mapped onto a coherent superposition of emitted photon states. We also show that other recombination processes due to thermally excited quasi-particles do not significantly degrade the state purity. Our results introduce an original scheme for generating OAM-entangled photons, enabling a new method of transmitting superconducting qubit information to photonic channels, thereby bridging the gap between solid-state and photon-based platforms for quantum communications and information processing.