论文标题
测量引起的核自旋极化
Measurement-induced nuclear spin polarization
论文作者
论文摘要
我们在一般的进化和测量框架中提出了一种核旋转偏振方案。该协议以自旋型构型起作用，其中中央自旋通过相等强度的触发器相互作用耦合到周围的浴缸（核）旋转，并受到其基态下的一系列投影测量。然后，可以通过测量来减少熵来实现非确定的核自旋极化。优化的测量间隔$τ_ {\ rm opt} $是在近谐振条件下分析获得的，这与核自旋的最后一轮测量，核自旋的数量，核自旋的数量以及中央旋转强度之间的耦合强度有关。在热状态下，数百甚至数千个随机排列的核自旋几乎可以完全极化，优化的序列小于$ 20 $不等的时间间隔测量。与常规方法相比，我们的方案对磁场强度不敏感，并且在近乎震动的情况下，它与额外的反射相互作用是可靠的。
We propose a nuclear-spin-polarization protocol in a general evolution-and-measurement framework. The protocol works in a spin-star configuration, where the central spin is coupled to the surrounding bath (nuclear) spins by flip-flop interaction of equal strength and is subject to a sequence of projective measurements on its ground state. Then a nondeterministic nuclear spin polarization could be implemented by entropy reduction through measurement. The optimized measurement-interval $τ_{\rm opt}$ is analytically obtained in the near-resonant condition, which is relevant to the nuclear spins' polarization degree of the last-round measurement, the number of nuclear spins, and the coupling strength between the central spin and nuclear spins. Hundreds and even thousands of randomly aligned nuclear spins at the thermal state could be almost fully polarized with an optimized sequence of less than $20$ unequal-time-spacing measurements. In comparison to the conventional approaches, our protocol is not sensitive to the magnetic-field intensity, and it is robust against the extra counterrotating interaction in the near-resonant situation.
