On the use of cross polarization in solid-state NMR:1 H spinlock versus adiabatic demagnetization in the rotating frame

Cross polarization(CP)is a widely used solid-state nuclear magnetic resonance(NMR)technique for enhancing the polarization of dilute S spins from much larger polarization of abundant I spins such as 1 H.To achieve such a polarization transfer,the I spin should either be spin-locked or be converted to the dipolar ordered state through adiabatic demagnetization in the rotating frame.In this work,we analyze the spin dynamics of the Hartmann-Hahn CP(HHCP)utilizing the 1 H spin-locking,and the dipolar-order CP(DOCP)having the 1 H adiabatic demagnetization.We further propose an adiabatic demagnetization CP(ADCP)where a constant radio-frequency pulse is applied on the S spin while 1 H is adiabatically demagnetized.Our analyses indicate that ADCP utilizes the adiabatic passage to effectively achieve the polarization transfer from the 1 H to S spins.In addition,the dipolar ordered state generated during the 1 H demagnetization process could also be converted into the observable S polarization through DOCP,further enhancing the polarized signals.It is shown by both static and magic-angle-spinning(MAS)NMR experiments that ADCP has dramatically broadened the CP matching condition over the other CP schemes.Various samples have been used to demonstrate the polarization transfer efficiency of this newly proposed ADCP scheme.

Measures of imaginarity and quantum state order

Complex numbers are widely used in classical and quantum physics.Further,they play an important role in describing quantum systems and their dynamical behaviors.Herein,we propose several measures of the imaginarity of quantum states based on l1 norm and convex functions in the framework of resource theory.Further,we investigate the quantum state order after a quantum system passes through a real channel.Rigorous proof shows that these proposed measures possess all the desirable properties for a measure of imaginarity.The connection between the measure of imaginarity based on the l1 norm and the measure of imaginarity based on relative entropy is derived.Moreover,we demonstrate that the l1 norm-based and the relative entropy-based measures of imaginarity are of the same order for qubit quantum states.Further we discuss the influences of the bit flip channel,phase damping channel,and amplitude flip channel on single qubit state order.