Rydberg Quantum Gates Free from Blockade Error

Accurate quantum gates are basic elements for building quantum computers. There has been great interest in designing quantum logic gates by using blockade effect of Rydberg atoms recently. The fidelity and operation speed of these gates, however, are fundamentally limited by an intrinsic blockade error. Here we propose a type of quantum gates, which are based on Rydberg blockade effect, yet free from any blockade error. In contrast to the "blocking" method in previous schemes, we use Rydberg energy shift to realize a rational generalized Rabi frequency so that a $\pi$ phase for one input state of the gate emerges. This leads to an accurate Rydberg quantum logic gate that can operate on a 0.1-$\mu s$ timescale or faster because it works by a Rabi frequency which is comparable to the blockade shift.