Speaker
Description
Title: High-Fidelity Electronic $\sigma_z\sigma_z$ Gate on an Axial Mode via Near-Motional Oscillating Magnetic Field Gradients
Laser-free entangling gates using magnetic field gradients offer a promising pathway toward scalable trapped-ion quantum information processing. Here, we report the first experimental demonstration of a $\sigma_z\sigma_z$ gate implemented on an axial motional mode using a near-motional oscillating magnetic field gradient. We entangle two 171Yb+ ions in roughly 650 μs using the axial breathing mode at 470 kHz. The operations are performed in a microfabricated surface trap with an ion height of 120 μm. A known challenge with near-motional gradients is the "tickling" effect, where the finite impedance of current-carrying electrodes creates an oscillating electric potential that drives the ion's motion. To mitigate this, our trap design buries the current-carrying wires beneath the trapping electrodes with an intermediate ground layer. This configuration shields electric fields much more strongly than magnetic fields. While a nonzero presence of tickling remains on the common axial mode, the breathing mode exhibits no signs of tickling, making it an ideal bus for the entangling operation. Despite relying exclusively on Doppler cooling, our initial implementation consistently achieves gate fidelities in excess of 95%, currently limited by a number of factors including residual motional frequency errors. We present an analysis of leading causes of infidelity for the scheme, explain steps to take to raise the entanglement fidelity above the fault-tolerant threshold, and discuss potential strategies to further enhance robustness, significantly suppressing sensitivity to motional frequency drifts.
| Academic level | PhD student |
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