Creation and manipulation of Schrödinger cat states of a nuclear spin qudit in silicon

High-dimensional quantum systems are a valuable resource for quantum information processing. They can be used to encode error-correctable logical qubits, for instance in continuous-variable states of oscillators such as microwave cavities or the motional modes of trapped ions. Powerful encodings include 'Schrödinger cat' states, and superpositions of widely displaced coherent states, which also embody the challenge of quantum effects at the large scale. Alternatively, recent proposals suggest encoding logical qubits in high-spin atomic nuclei, which can host hardware-efficient versions of continuous-variable codes on a finite-dimensional system. Here we demonstrate the creation and manipulation of Schrödinger cat states using the spin-7/2 nucleus of a single antimony (123Sb) atom, embedded and operated within a silicon nanoelectronic device. We use a coherent multi-frequency control scheme to produce spin rotations that preserve the SU(2) symmetry of the qudit, and constitute logical Pauli operations for logical qubits encoded in the Schrödinger cat states. The Wigner function of the cat states exhibits parity oscillations with a contrast up to 0.982(5), and state fidelities up to 0.913(2). These results demonstrate high-fidelity preparation of nonclassical resource states and logical control in a single atomic-scale object, opening up applications in quantum information processing and quantum error correction within a scalable, manufacturable semiconductor platform.高维量子系统是量子信息处理中的宝贵资源。其可用于编码可纠错的逻辑量子比特，例如在微波腔、囚禁离子运动模式等振荡器的连续变量态中。高效编码方案包括薛定谔猫态（Schrödinger cat state）以及大位移相干态的叠加态，这类态同时也体现了宏观尺度下量子效应的研究挑战。此外，近期的研究提案提出在高自旋原子核中编码逻辑量子比特，这类系统可在有限维体系中实现硬件高效的连续变量编码方案。本研究展示了利用嵌入并运行于硅基纳米电子器件中的单个锑-123（123Sb）原子的自旋7/2原子核，制备与操控薛定谔猫态的过程。我们采用相干多频控制方案实现自旋旋转，该方案可保留多态量子系统（qudit）的SU(2)对称性，并对应于薛定谔猫态编码逻辑量子比特的逻辑泡利操作。该猫态的维格纳函数（Wigner function）展现出对比度最高达0.982(5)的宇称振荡，且态保真度最高可达0.913(2)。上述结果证明了在单个原子尺度体系中实现高保真度非经典资源态制备与逻辑操控的可行性，为可扩展、可量产的半导体平台中的量子信息处理与量子纠错应用开辟了道路。