Department of Physics, Amherst College, Amherst, Massachusetts 01002-5000, USA.
Department of Chemistry & Biochemistry, University of California at San Diego, La Jolla, California 92093, USA.
Phys Rev Lett. 2014 Mar 28;112(12):120501. doi: 10.1103/PhysRevLett.112.120501. Epub 2014 Mar 26.
We report the observation of strong coupling of a macroscopic ensemble of ∼1016 Fe8 molecular nanomagnets to the resonant mode of a microwave cavity. We use millimeter-wave spectroscopy to measure the splitting of the system's resonant frequency induced by the coupling between the spins and the cavity mode. The magnitude of this splitting is found to scale with √N, where N is the number of collectively coupled spins. We control N by changing the system's temperature and, thereby, the populations of the relevant spin energy levels. Strong coupling is observed for two distinct transitions between spin energy states. Our results indicate that at low temperatures nearly all of the spins in the sample couple with the cavity's resonant mode even though there is substantial inhomogeneous broadening of the Fe8 spin resonances.
我们报告了对约 1016 个 Fe8 分子磁体的宏观集合与微波腔的共振模式的强耦合的观察。我们使用毫米波光谱学来测量自旋和腔模之间的耦合引起的系统共振频率的分裂。发现这种分裂的幅度与 N 的平方根成正比，其中 N 是集体耦合的自旋数。我们通过改变系统的温度来控制 N，从而改变相关自旋能级的种群。在两个不同的自旋能态之间的跃迁中观察到强耦合。我们的结果表明，即使 Fe8 自旋共振存在大量的非均匀展宽，在低温下，样品中的几乎所有自旋都与腔的共振模式耦合。
