Spin coherence of rubidium atoms in solid parahydrogen using dynamical decoupling

We implant rubidium atoms inside cryogenic solid parahydrogen and study their electron spin coherence. We have measured the ensemble spin dephasing time T$_2^*$ to be on the order of microseconds, six orders of magnitude below the longitudinal relaxation time T$_1$. We observe that with dynamical decoupling pulse sequences, we can achieve much longer spin coherence times. A modified Hahn echo extends T$_2$ to times on the order of milliseconds, and the alternating-phase Carr-Purcell sequence gives a T$_2$ approaching 0.1~s. The physics limiting the spin coherence will be discussed. Long spin coherence times make atoms in parahydrogen promising for applications in AC magnetometry, quantum sensing, and nano-MRI.