Many-particle Entanglement in Multiple Quantum NMR Spectroscopy

S.I. Doronin, E.B Fel'dman, I.D. Lazarev

We use multiple quantum (MQ) NMR dynamics of a gas of spin-carrying molecules in nanocavities at high and low temperatures for an investigation of many-particle entanglement. A distribution of MQ NMR intensities is obtained at high and low temperatures in a system of 201 spins $\frac 1 2$. The second moment of the distribution, which provides a lower bound on the quantum Fisher information, sheds light on the many-particle entanglement in the system. The dependence of the many-particle entanglement on the temperature is investigated.
Almost all spins are entangled at low temperatures.