Crosstalk Insensitive Trapped-Ion Entanglement through Coupling Matrix Engineering

Abstract: Control crosstalk due to imperfect optical addressing in trapped-ion entangling gates results in unwanted entanglement between the target ions and their neighbors. These errors are highly non-local, making them particularly difficult to correct using error correcting codes. We introduce a method to design entangling gates that are insensitive to optical crosstalk by controlling the excitation of the ions' motional modes to engineer an effective qubit-qubit coupling matrix that entirely excludes crosstalk-affected ions from the entangling operation. This method requires no knowledge of the crosstalk level and relies only on optimization of the laser pulse, avoiding the need to modify the optical setup or use additional gate operations. We experimentally demonstrate the method on a three-ion string by performing an entangling gate that is completely insensitive to optical crosstalk.