Analysis of quantum information processors using quantum metrology
Accepted in Physical Review A , (2018)
Physical implementations of quantum information processing devices are generally not unique, and we are faced with the problem of choosing the best implementation. Here, we consider how different implementations are sensitive to variations in their components. To measure this, we adopt a quantum metrological approach, and find that the sensitivity of a device to variations in a component has a particularly simple form. We give two practical examples of sensitivities of quantum devices to variations in beam splitter transmitivities: the KLM and Reverse nonlinear sign gates for linear optical quantum computing with photonic qubits, and the enhanced optical Bell detectors by Grice and Ewert & van Loock. We find that for these Bell detectors, the design that uses fewer components performs better than the design with overall lower sensitivity to component variations.