Quantum Walks of Photons on a Nonlinear Chip

Quantum entanglement underpins the realization of quantum simulators and computers, which can be used for unbreakable cryptography and powerful computational algorithms. Entangled photons are an ideal medium for creating and manipulating quantum states due to the low noise and ease of transmission. A qubit encoded into a photon can be easily sent between different photonic elements along an optical fiber, in analogy with the transmission of classical bits along electrical wires. Furthermore, logic operations can be performed on entangled photons by exploiting the nonlinearity inherent to quantum measurements [1]. The practical implementation of complex applications requires the minimization of coupling losses, as well as stable quantum interference. Low losses and interferometric stability allow strong entanglement between output photons. One of the biggest milestones in achieving these requirements is the integration of photon sources together with optical circuits on the same photonic chip.