发表机构
University of Southampton（南安普顿大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文提出时间四极矩概念，利用非互易变频拓扑角态在时间调制微波超表面中实验实现无磁收发循环器，验证了高阶拓扑与频率转换的协同效应。
AI 中文摘要
我们引入时间四极矩，并利用其非互易变频拓扑角态，在拓扑时间调制微波超表面中实验实现了无磁收发循环器。在周期性驱动下，时间四极矩使体带隙晶格的角电荷在驱动周期内演化，产生两类受拓扑保护的角态：准能量ε=0的角模式和仅存在于周期性驱动下的纯动力学周期倍增模式（ε=π/T）。我们表明，产生该模式的两个时间调制耦合通道之间的相对相位充当合成规范场，打破时间反演对称性，同时保持角模式的拓扑保护不变。具体而言，从TX端口以频率f注入超表面的信号被上变频并辐射到自由空间，而频率为f'的自由空间波被优先捕获并路由——在相同频率下，不转换——到RX端口而非返回TX端口；反向路径被相同的破缺对称性禁止。我们通过制造微波原型上时间调制阵列的空间场强和角度分辨辐射测量，确认了时间四极矩、其相关的Floquet角态以及由此产生的非互易变频效应。
英文摘要
We introduce the temporal quadrupole moment and leverage its nonreciprocal frequency-converting topological corner states to experimentally realize a magnet-free transceiving circulator in a topological time-modulated microwave metasurface. Under periodic driving, the temporal quadrupole moment evolves the corner charge of a bulk-gapped lattice over the drive cycle, generating two distinct families of topologically protected corner states: a corner mode at quasienergy $\varepsilon=0$ and a purely dynamical period-doubled mode at $\varepsilon=π/T$ that exists only under periodic driving. We show that the relative phase between the two time-modulated coupling channels that generate it acts as a synthetic gauge field, breaking time-reversal symmetry while leaving the corner-mode topological protection intact. Specifically, a signal launched into the metasurface at TX port at frequency is up-converted and radiated into free space, while a free-space wave at is preferentially captured and routed --- at the same frequency, unconverted --- to RX port rather than back to TX port; the reverse itinerary is forbidden by the same broken symmetry. We confirm the temporal quadrupole moment, its associated Floquet corner states, and the resulting nonreciprocal frequency conversion through spatial field-intensity and angle-resolved radiation measurements of the time-modulated array on a fabricated microwave prototype.
