Optical Crosstalk Mitigation for Individual Addressing in a Cryogenic Ion Trap
Jeremy Flannery, Roland Matt, Luca I. Huber, R. Oswald, Kaizhao Wang, Jonathan Home · 2022 IEEE International Conference on Quantum Computing and Engineering (QCE) · 2022
We present an experimental realization of coherent crosstalk cancellation in a trapped ion cryogenic system. The qubit register consists of a linear string of calcium ions which are individually addressed using tightly focused laser beams oriented perpendicular to the crystal axis. This individual control is provided by a multi-core photonic crystal fiber that allow for cancellation pulses to be applied to neighbouring ion sites to destructively interfere with crosstalk from addressing pulses on target qubits. With this technique we find > 104fold reduction in intensity crosstalk.In order for this novel method of crosstalk elimination to be stable, phase coherence must be preserved between the cancellation and addressing beams. We further develop the appropriate calibration methods and procedures to mitigate phase drifts between these different optical paths. This includes a method to minimize the effects of variable duty cycles of individual pulses that may cause for differential phase noise.In addition, we extended this work by including the results a laser written waveguide array used to provide single-ion addressing capability, which is found to produce intensity crosstalk on the order of 10−4. This device may be used in combination with the approach of optical cancellation developed for crosstalk compensation to result in negligible crosstalk errors between neighbouring qubit. As a consequence, such a system may allow for quantum error correction and fault-tolerant circuits to be viable as the system scales up to larger numbers of qubits.