“…Unfortunately, a fundamental limitation for such blockaded gate arises from an intrinsic blockade error coming from a Rydberg level shift V , which is proportional to (Ω/V ) 2 [23] (Ω is the effective Rabi frequency) accom- * jqian1982@gmail.com panied by a blockade error around 10 −3 [24], preventing from its extensive use. In the recent years, in order to suppress this blockade error, a rich variety of alternative proposals, such as construction of a novel generalized Rabi frequency by the Rydberg energy shift [25], using technique of the electromagnetically induced transparency [26], or replacing with a long-lifed circular Rydberg state [27] and a specifically-shaped laser [28][29][30], have been extensively demonstrated, proving the reduction of gate error beyond the level of 10 −4 . Especially, a recent exotic proposal describes an accurate quantum gate by spin echo to suppress the blockade error to the order of (10 −3 ) 2 by adding two anticlockwise rotations, leading to the intrinsic error of gate beyond the level of 10 −5 which is only limited by the Rydberg state decay [31].…”