Experimental implementation of the optimal linear-optical controlled phase gate

TL;DR

This paper reports the first experimental realization of a tunable, optimal linear-optical controlled phase gate that operates at maximum success probability, with success probability varying non-monotonically with phase.

Contribution

It demonstrates a flexible, optimal controlled phase gate implementation in linear optics, achieving maximum success probabilities for arbitrary phases.

Findings

Success probability is non-monotonic with phase.

The scheme is fully tunable for any phase shift.

Achieved maximum success probability within linear-optical constraints.

Abstract

We report on the first experimental realization of optimal linear-optical controlled phase gates for arbitrary phases. The realized scheme is entirely flexible in that the phase shift can be tuned to any given value. All such controlled phase gates are optimal in the sense that they operate at the maximum possible success probabilities that are achievable within the framework of any postselected linear-optical implementation. The quantum gate is implemented using bulk optical elements and polarization encoding of qubit states. We have experimentally explored the remarkable observation that the optimum success probability is not monotone in the phase.