Deterministic Logic Gates for Photonic Qubits

Quantum logic gates operating on qubits encoded in photons are highly desirable for processing quantum information as it is being transmitted through quantum networks. However, the difficulty of enabling sufficiently strong interactions between photons has hindered their experimental realization. Additionally, the multi-mode nature of finite-duration photon wave packets limits the gate fidelity if photons interact while travelling. We propose a method that converts travelling continuous-mode photons into quasi-single mode fields by absorbing them into cavities. This is enabled by strong classical control fields that perform the necessary re-distribution of photon frequency-modes. Letting the photons interact while occupying modes of a cavity with high quality factor and low mode-volume achieves a large interaction strength and simultaneously avoids gate fidelity degradations. We consider nonlinear interactions due to Χ⁽²⁾, Χ⁽³⁾, and atom-like emitters. Our numerical results show that high-fidelity gates are possible with near-term improvements in nanofabrication.