Hardware-Efficient Erasure Qubits With Superconducting Transmon Qutrits

TL;DR

This paper demonstrates a hardware-efficient method for implementing erasure qubits using superconducting transmon qutrits, significantly enhancing coherence times and fault-tolerance potential in quantum computing.

Contribution

It introduces a scheme that uses transmon qutrits as erasure qubits compatible with standard hardware, improving error detection and coherence times without additional overhead.

Findings

Logical qubit T1 lifetime exceeds 500 microseconds with erasure detection.

Coherence times beyond 300 microseconds achieved with dynamical decoupling.

Single-qubit gate infidelity around 10^-4.

Abstract

Quantum error correction using erasure qubits offers higher fault-tolerant thresholds and improved scaling by converting dominant physical errors into detectable erasures. In superconducting circuits, erasure qubits can be constructed using the dual-rail approach, which, however, requires additional qubit-count overhead and tailored coupling elements. Here, we demonstrate a hardware-efficient scheme that operates transmon qutrits as erasure qubits, which is compatible with standard superconducting circuit-QED hardware. The logical states $\ket{0_\text{L}}$ and $\ket{1_\text{L}}$ are represented by the ground and second excited states, while the dominant relaxation errors can be detected via an ancilla qubit using a microwave-activated two-qutrit SWAP gate. We demonstrate a logical qubit $T_1$ lifetime exceeding $500\,\mu\mathrm{s}$, post-selected with repeated mid-circuit erasure detection, which is ten times longer than the $T_1$ time of the transmon physical qubit. Coherence times beyond $300\,\mu\mathrm{s}$ are achieved using dynamical decoupling. Single-qubit gate operations reach average Clifford gate infidelity on the order of $10^{-4}$. We further demonstrate dual-purposing an ancilla qubit for both erasure detection and parity checking, showing heralded generation of Bell states between erasure qubits. These results suggest that mainstream architectures of transmon qubit arrays may already be capable of implementing erasure-based QEC strategies for hardware-efficient fault-tolerant quantum computing.