Automated design of photonic two-qubit quantum gates and circuits via optimization and pruning

We develop an algorithm to automatically design photonic gates and circuits that is based on a combination of optimization and pruning methods. It starts with a general ansatz for optical circuits with tunable parameters that are then subjected to optimization. The algorithm simplifies the final circuit by pruning its unnecessary elements following predefined criteria. We demonstrate the algorithm by producing both approximate and numerically exact implementations of the gate and Deutsch-Jozsa, Grover, and Fourier transform two-qubit quantum circuits. All implementations of the different gates and circuits can be integrated into larger quantum information protocols.