Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 7610001, Israel.
Phys Rev Lett. 2018 Jun 15;120(24):243603. doi: 10.1103/PhysRevLett.120.243603.
The use of entangled states was shown to improve the fundamental limits of spectroscopy to beyond the standard-quantum limit. Here, rather than probing the free evolution of the phase of an entangled state with respect to a local oscillator, we probe the evolution of an initially separable two-atom register under an Ising spin Hamiltonian with a transverse field. The resulting correlated spin-rotation spectrum is twice as narrow as that of an uncorrelated rotation. We implement this ideally Heisenberg-limited Rabi spectroscopy scheme on the optical-clock electric-quadrupole transition of ^{88}Sr^{+} using a two-ion crystal. We further show that depending on the initial state, correlated rotation can occur in two orthogonal subspaces of the full Hilbert space, yielding entanglement-enhanced spectroscopy of either the average transition frequency of the two ions or their difference from the mean frequency. The use of correlated spin rotations can potentially lead to new paths for clock stability improvement.
纠缠态的使用被证明可以将光谱学的基本限制提高到超越标准量子极限。在这里，我们不是探测相对于本地振荡器的纠缠态相位的自由演化，而是探测在横场中的伊辛自旋哈密顿量下初始可分离的双原子寄存器的演化。由此产生的相关自旋旋转光谱比不相关旋转的光谱窄两倍。我们使用双离子晶体在光学钟电四极跃迁上实现了这个理想的海森堡极限拉比光谱方案。我们进一步表明，根据初始状态，相关旋转可以发生在全希尔伯特空间的两个正交子空间中，从而实现对两个离子的平均跃迁频率或它们与平均频率之差的纠缠增强光谱学。相关自旋旋转的使用可能为时钟稳定性的提高开辟新的途径。
