How can we minimize errors in a linear-optics quantum gate?

摘要

Possible error sources in an experimentally realized linear-optics controlled-Z gate are analyzed by considering the deviations of the beam splitting ratios from the ideal values (SRh, SRy), the polarization-dependent phase shift (birefringence) of the optical components (6φ), and the mode mismatch of input photons (Sε,). It is found that the error rate is linearly dependent on SRy and 5£, while the dependence on 8Rn and 6φ is approximately quadratic. As a practical result, the gate is much more sensitive to small errors in Ry than in Ru. Specifically, the reflectivity error for vertical polarization must be less than 0.1% to realize a gate with an error of less than 0.1%, whereas the reflectivity error for horizontal polarization can be up to 1%. The method of analysis used illustrates the basic features of errors in general linear optics quantum gates and circuits, and can easily be adapted to any other device of this type.