Davis Emily J, Periwal Avikar, Cooper Eric S, Bentsen Gregory, Evered Simon J, Van Kirk Katherine, Schleier-Smith Monika H
Department of Physics, Stanford University, Stanford, California 94305, USA.
Department of Physics, Princeton University, Princeton, New Jersey 08540, USA.
Phys Rev Lett. 2020 Aug 7;125(6):060402. doi: 10.1103/PhysRevLett.125.060402.
Using an ensemble of atoms in an optical cavity, we engineer a family of nonlocal Heisenberg Hamiltonians with continuously tunable anisotropy of the spin-spin couplings. We thus gain access to a rich phase diagram, including a paramagnetic-to-ferromagnetic Ising phase transition that manifests as a diverging magnetic susceptibility at the critical point. The susceptibility displays a symmetry between Ising interactions and XY (spin-exchange) interactions of the opposite sign, which is indicative of the spatially extended atomic system behaving as a single collective spin. Images of the magnetization dynamics show that spin-exchange interactions protect the coherence of the collective spin, even against inhomogeneous fields that completely dephase the noninteracting and Ising systems. Our results underscore prospects for harnessing spin-exchange interactions to enhance the robustness of spin squeezing protocols.
利用光学腔中的一组原子，我们设计了一族具有连续可调自旋 - 自旋耦合各向异性的非局域海森堡哈密顿量。由此，我们得以探究丰富的相图，其中包括顺磁到铁磁的伊辛相变，该相变在临界点表现为磁导率发散。磁导率在相反符号的伊辛相互作用和XY（自旋交换）相互作用之间呈现对称性，这表明空间扩展的原子系统表现为单个集体自旋。磁化动力学图像显示，自旋交换相互作用保护集体自旋的相干性，即使在完全使非相互作用和伊辛系统去相位的非均匀场中也是如此。我们的结果强调了利用自旋交换相互作用增强自旋压缩协议稳健性的前景。
