Strong light–matter interaction constitutes the bedrock of all photonic applications, empowering material elements with the ability to create and mediate interactions of light with light. Amidst the quest to identify new agents facilitating such efficient light–matter interactions, a class of promising materials has emerged, featuring highly unusual properties deriving from their dielectric constant ε being equal, or at least very close, to zero. Works so far have shown that the enhanced nonlinear optical effects displayed in this epsilon-near-zero (ENZ) regime make it possible to create ultrafast albeit transient optical switches. An outstanding question, however, relates to whether one could use the amplification of light–matter interactions at the ENZ conditions to achieve permanent switching. Here we demonstrate that an ultrafast excitation under ENZ conditions can induce permanent all-optical reversal of ferroelectric polarization between different stable states. Our reliance on ENZ conditions that naturally emerge from the solid’s ionic lattice suggests that the demonstrated mechanism of reversal is truly universal, being capable of permanently switching order parameters in a wide variety of systems.

强烈的光与物质相互作用构成了所有光子应用的基石，使材料元素能够产生和介导光与光之间的相互作用。在寻找促进这种有效的光与物质相互作用的新试剂的过程中，一类有前途的材料出现了，它们具有非常不寻常的特性，因为它们的介电常数ε等于或至少非常接近于零。迄今为止的工作表明，在这种ε近零（ENZ）状态下显示出的增强的非线性光学效应使得创建超快但瞬态的光学开关成为可能。然而，一个悬而未决的问题涉及是否可以利用 ENZ 条件下光与物质相互作用的放大来实现永久切换。在这里，我们证明了 ENZ 条件下的超快激发可以引起不同稳定状态之间铁电极化的永久全光反转。我们对固体离子晶格自然产生的 ENZ 条件的依赖表明，所证明的反转机制是真正普遍的，能够在各种系统中永久切换有序参数。