Physical coherent cancellation of optical addressing crosstalk in a trapped-ion experiment

TL;DR

This paper demonstrates a method to significantly reduce optical crosstalk in a trapped-ion quantum register using destructive interference, achieving over 100-fold suppression and low gate errors, enhancing quantum control fidelity.

Contribution

The study introduces a coherent crosstalk cancellation technique using destructive interference in a trapped-ion setup, outperforming previous methods and providing calibration procedures for phase stability.

Findings

Crosstalk suppressed by over 10^3 times using cancellation light.

Rotation error per gate reduced to ~10^-5 on spectator qubits.

Crosstalk error suppressed by over 10^2 compared to native levels.

Abstract

We present an experimental investigation of coherent crosstalk cancellation methods for light delivered to a linear ion chain cryogenic quantum register. The ions are individually addressed using focused laser beams oriented perpendicular to the crystal axis, which are created by imaging each output of a multi-core photonic-crystal fibre waveguide array onto a single ion. The measured nearest-neighbor native crosstalk intensity of this device for ions spaced by 5 $\mu$m is found to be $\sim 10^{-2}$. We show that we can suppress this intensity crosstalk from waveguide channel coupling and optical diffraction effects by a factor $>10^3$ using cancellation light supplied to neighboring channels which destructively interferes with the crosstalk. We measure a rotation error per gate on the order of $\epsilon_{x} \sim 10^{-5}$ on spectator qubits, demonstrating a suppression of crosstalk error by a factor of $> 10^2$. We compare the performance to composite pulse methods for crosstalk cancellation, and describe the appropriate calibration methods and procedures to mitigate phase drifts between these different optical paths, including accounting for problems arising due to pulsing of optical modulators.