Eliminating Leakage Errors in Hyperfine Qubits

TL;DR

This paper demonstrates an optical pumping scheme using a trapped ytterbium ion to effectively suppress leakage errors in hyperfine qubits, significantly improving quantum error correction prospects.

Contribution

Introduces a novel optical pumping method leveraging quadrupole transition selection rules to reduce leakage errors in hyperfine qubits.

Findings

Leakage population reduced by a factor of ~3 per cycle

Negligible side-effects on un-leaked qubits, with errors ≤2.0×10^{-5} per cycle

Qubit population decay suppressed to ≤1.4×10^{-7} per cycle

Abstract

Population leakage outside the qubit subspace presents a particularly harmful source of error that cannot be handled by standard error correction methods. Using a trapped $^{171}$Yb$+$ ion, we demonstrate an optical pumping scheme to suppress leakage errors in atomic hyperfine qubits. The selection rules and narrow linewidth of a quadrupole transition are used to selectively pump population out of leakage states and back into the qubit subspace. Each pumping cycle reduces the leakage population by a factor of $\sim3$, allowing for an exponential suppression in the number of cycles. We use interleaved randomized benchmarking on the qubit subspace to show that this pumping procedure has negligible side-effects on un-leaked qubits, bounding the induced qubit memory error by $\leq2.0(8)\times10^{-5}$ per cycle, and qubit population decay to $\leq1.4(3)\times10^{-7}$ per cycle. These results clear a major obstacle for implementations of quantum error correction and error mitigation protocols.