Fast, High-Fidelity Erasure Detection of Dual-Rail Qubits with Symmetrically Coupled Readout

TL;DR

This paper demonstrates a fast, high-fidelity, and scalable method for erasure detection in dual-rail qubits using symmetrically coupled dispersive readout, enabling efficient quantum error correction.

Contribution

It introduces a hardware-efficient circuit for erasure detection with single-shot speed and minimal impact, and demonstrates continuous erasure detection during quantum gates.

Findings

Single-shot erasure detection in 384 ns with residual error of 6.0(2)×10⁻⁴.

Achieved erasure error per check of 2.54(1)×10⁻².

Continuous erasure detection during gates with median error of 7.2×10⁻⁵.

Abstract

Erasure qubits are a promising platform for implementing hardware-efficient quantum error correction. Realizing the error-correction advantages of this encoding requires frequent mid-circuit erasure checks that are fast, high-fidelity, and scalable. Here, we realize erasure detection with a hardware-efficient circuit consisting of a single readout resonator dispersively and symmetrically coupled to both transmons of a dual-rail qubit. We use this circuit to demonstrate single-shot erasure detection in 384 ns with minimal impact on the dual-rail logical manifold, achieving a residual error per check of $6.0(2) \times 10^{-4}$, with only $8(3) \times 10^{-5}$ induced dephasing per check, and an erasure error per check of $2.54(1)\times 10^{-2}$. The high degree of matched dispersive readout coupling ($\chi$-matching) within the dual-rail qubit code space also allows us to realize a new modality: time-continuous erasure detection performed in parallel with single-qubit gates. Here we achieve a median $7.2 \times 10^{-5}$ error per gate with $< 1 \times 10^{-5}$ error induced by erasure detection. This demonstrates a reduction in erasure detection overhead as well as a crucial ingredient for soft information quantum error correction. Together, these results establish symmetrically coupled dispersive readout as a fast, hardware-efficient, and scalable component for erasure-based quantum error correction using transmon dual-rail qubits.