Trifa Youssef, Roscilde Tommaso
ENS de Lyon, CNRS, Laboratoire de Physique, F-69342 Lyon, France.
Phys Rev Lett. 2024 Aug 23;133(8):083601. doi: 10.1103/PhysRevLett.133.083601.
We theoretically show that the spin-spin interactions realized in two-dimensional Mott insulators of large-spin magnetic atoms (such as Cr, Er, or Dy) lead to scalable spin squeezing along the nonequilibrium unitary evolution initialized in a coherent spin state. An experimentally relevant perturbation to the collective squeezing dynamics is offered by a quadratic Zeeman shift, which leads instead to squeezing of individual spins. Making use of a truncated cumulant expansion for the quantum fluctuations of the spin array, we show that, for sufficiently small quadratic shifts, the spin squeezing dynamics is akin to that produced by the paradigmatic one-axis-twisting model-as expected from an effective separation between collective-spin and spin-wave variables. Scalable spin squeezing is shown to be protected by the robustness of long-range ferromagnetic order to quadratic shifts in the equilibrium phase diagram of the system that we reconstruct via quantum Monte Carlo and mean-field theory.
我们从理论上表明，在大自旋磁性原子（如Cr、Er或Dy）的二维莫特绝缘体中实现的自旋-自旋相互作用，会沿着以相干自旋态初始化的非平衡幺正演化导致可扩展的自旋压缩。二次塞曼频移为集体压缩动力学提供了一个与实验相关的微扰，它反而导致单个自旋的压缩。利用自旋阵列量子涨落的截断累积量展开，我们表明，对于足够小的二次频移，自旋压缩动力学类似于由典型的单轴扭转模型产生的动力学——正如从集体自旋和自旋波变量之间的有效分离所预期的那样。我们通过量子蒙特卡罗和平均场理论重建了系统平衡相图，结果表明可扩展的自旋压缩受到长程铁磁序对二次频移的鲁棒性保护。
