Universal photonic quantum gate by Cooper-pair-based optical nonlinearity

Abstract

We propose a compact and highly efficient scheme for solid-state photonic quantum gates. At the core of our scheme is a $SWA{P}^{\ensuremath{\phi}}$ gate based on giant Cooper-pair-based optical nonlinearity we predict in a semiconductor-superconductor structure, selectively introducing a phase to the $|{\mathrm{\ensuremath{\Psi}}}_{+}\ensuremath{\rangle}$ Bell state. We theoretically demonstrate this scheme on a practical device based on a superconducting contact coupled to a GaAs/AlGaAs waveguide structure. We model the Cooper-pair-induced nonlinear change of the refractive index showing strong nonlinearities at energies close to the superconducting gap inside a semiconductor band. We calculate the fidelity of the proposed $SWA{P}^{\ensuremath{\phi}}$ gate, as well as the sensitivity of the gate to device parameters. As short photon wave packets are crucial for efficient higher-order interactions, we investigate the integrated fidelity for short wave packets with different central wavelengths and bandwidths, providing limiting factors as well as possible optimizations. This theoretically demonstrated concept can pave the way toward practical realizations of scalable photonic quantum circuits.