Chapter 17: Long-lived Singlet State: From NMR Quantum Information Perspectives

NMR spectroscopy relies on the fact that nuclear spin ensembles in bulk samples under ambient conditions sustain quantum superpositions for durations long enough to implement intricate quantum dynamics. The discovery of long-lived nuclear spin order further enhanced the scope of NMR experiments paving the way for novel applications. In this chapter, we look at the long-lived singlet state (LLSS) from the perspectives of NMR quantum information, wherein the two Zeeman eigenstates of a spin-1/2 nucleus are treated as 0 and 1 states of a quantum bit. In particular, we discuss the following topics: density matrix tomography of the LLSS, initialization of a quantum register via the LLSS, noise spectroscopy of the LLSS, and numerical optimization methods to prepare the LLSS.