Chain*

Heating of low-frequency axial modes presents a significant impediment to scaling up quantum computing and simulation based on long ion chains [1]. Sympathetic cooling offers a promising solution but requires optimal mode balance to ensure its effectiveness. Sympathetic cooling also provides controlled non-unitary dynamics, allowing more complex simulations using the available qubits.

We address both of these goals by cooling ¹⁷¹Yb⁺ ion qubits using ¹⁷²Yb⁺ in a long ion chain. We present progress in optimizing cooling procedures to mitigate both axial heating and recoil-induced radial heating. Beyond suppressing heating effects, we demonstrate how controlled sympathetic cooling facilitates qubit reset in a long chain. Additionally, we explore using our sympathetic cooling scheme to engineer dissipation in simulations of non-equilibrium phenomena in quantum systems. Our work paves the way to scaling up high-fidelity circuit-based computing and open-quantum-system simulation using long ion chains.