Institut für Theoretische Physik, Universität Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria.
Phys Rev Lett. 2013 Sep 20;111(12):123601. doi: 10.1103/PhysRevLett.111.123601. Epub 2013 Sep 18.
Ramsey interferometry is routinely used in quantum metrology for the most sensitive measurements of optical clock frequencies. Spontaneous decay to the electromagnetic vacuum ultimately limits the interrogation time and thus sets a lower bound to the optimal frequency sensitivity. In dense ensembles of two-level systems, the presence of collective effects such as superradiance and dipole-dipole interaction tends to decrease the sensitivity even further. We show that by a redesign of the Ramsey-pulse sequence to include different rotations of individual spins that effectively fold the collective state onto a state close to the center of the Bloch sphere, partial protection from collective decoherence is possible. This allows a significant improvement in the sensitivity limit of a clock transition detection scheme over the conventional Ramsey method for interacting systems and even for noninteracting decaying atoms.
拉姆齐干涉测量法在量子计量学中被常规用于对光学时钟频率进行最灵敏的测量。自发衰落到电磁真空中最终限制了询问时间，从而对最佳频率灵敏度设置了下限。在两能级系统的密集集合中，存在集体效应，如超辐射和偶极-偶极相互作用，往往会进一步降低灵敏度。我们表明，通过重新设计 Ramsey 脉冲序列，包括对单个自旋的不同旋转，这有效地将集体态折叠到接近 Bloch 球中心的态上，可以实现对集体退相干的部分保护。这使得时钟跃迁检测方案的灵敏度极限相对于相互作用系统中的传统 Ramsey 方法甚至对于非相互作用的衰变原子都有了显著提高。
