超导量子比特阵列中的混合态对称性保护拓扑及强到弱的自发对称性破缺
Mixed-State Symmetry-Protected Topology and Strong-to-Weak Spontaneous Symmetry Breaking in a Superconducting Qubit Array
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中文总结 AI 辅助
研究人员在五量子比特超导阵列中，实验探究了一维簇态的对称性保护拓扑序受测量和退相干的变化，观测到强到弱自发对称性破缺的有限尺寸特征，建立了探测混合态对称性与拓扑的超导电路平台。
中文摘要 AI 辅助
我们在一个五量子比特超导阵列中，实验研究了一维簇态下的对称性保护拓扑序如何被测量和退相干改变。首先，我们表征了该态的非局域弦序，结果显示受控退相位会选择性抑制一个对称区，而使另一个对称区保持稳健，这与平均对称性保护拓扑序一致。随后，我们在可调基下测量一个子晶格，发现剩余量子比特会在长程纠缠的GHZ态和顺磁态之间转变。当丢弃测量记录时，常规长程关联函数消失，而非线性保真度关联函数仍保持有限，这为强到弱自发对称性破缺提供了有限尺寸的特征。这些实验表明，条件化、平均和退相干如何揭示同一底层簇态中编码的不同序的表现，并建立了用于探测混合态对称性和拓扑的超导电路平台。
英文摘要
We experimentally investigate how symmetry-protected topological order in a one-dimensional cluster state is transformed by measurement and decoherence in a five-qubit superconducting array. We first characterize the state's nonlocal string order and show that controlled dephasing selectively suppresses one symmetry sector while leaving the other robust, consistent with average symmetry-protected topological order. We then measure one sublattice in a tunable basis and show that the remaining qubits are driven between a long-range-entangled GHZ state and a paramagnetic state. When the measurement record is discarded, the conventional long-range correlator vanishes while a nonlinear fidelity correlator remains finite, providing a finite-size signature of strong-to-weak spontaneous symmetry breaking. These experiments demonstrate how conditioning, averaging, and decoherence reveal distinct manifestations of order encoded in the same underlying cluster state, and establish a superconducting-circuit setting for probing mixed-state symmetry and topology.
