论文标题
使用SU(2)编码统一进化的多参数同时进行最佳估计
Multiparameter simultaneous optimal estimation with an SU(2) coding unitary evolution
论文作者
论文摘要
在无处不在的$ su(2)$动力学中,同时实现多个参数的最佳估计是显着的,但很困难。使用量子控制来优化此$ SU(2)$编码统一进化是解决方案之一。我们提出了一种方法,其特征在于$ su(2)$发电机的系数矢量$ \ mathbf {x} $的嵌套交叉产物及其部分导数$ \ partial_ \ ell \ ell \ ell \ mathbf {x} $,以调查控制控制量量化的多个量化量估计。我们的工作表明,量子控制并不总是在提高估计精度方面起作用,这取决于$ su(2)$动力学相对于目标参数的表征。 $ \ mathbf {x} $和$ \ partial_ \ ell \ mathbf {x} $之间的角度$α_\ ell $在$ \ mathbf {x} $之间量化了此特征。对于$α_\ ell =π/2 $的$ SU(2)$动力学,估计精度的促销可以从控件中获得最大的好处。当$α_\ ell $逐渐关闭$ 0 $或$π$时,相应地,量子控制对量子控制的贡献变得不合时宜。直到具有$α__\ ell = 0 $或$π$的动态,量子控制完全失去了优势。此外,我们发现一组条件限制了所有参数的同时最佳估计,但幸运的是,可以通过使用最大纠缠的两分四极状态作为探针状态来删除,并将辅助通道添加到配置中。最后,以旋转$ 1/2 $的系统为例,以验证上述结论。我们的建议足以表现出履行多参数估算任务的控制功能的标志,并且适用于任意$ su(2)$参数化过程。
In a ubiquitous $SU(2)$ dynamics, achieving the simultaneous optimal estimation of multiple parameters is significant but difficult. Using quantum control to optimize this $SU(2)$ coding unitary evolution is one of solutions. We propose a method, characterized by the nested cross-products of the coefficient vector $\mathbf{X}$ of $SU(2)$ generators and its partial derivative $\partial_\ell \mathbf{X}$, to investigate the control-enhanced quantum multiparameter estimation. Our work reveals that quantum control is not always functional in improving the estimation precision, which depends on the characterization of an $SU(2)$ dynamics with respect to the objective parameter. This characterization is quantified by the angle $α_\ell$ between $\mathbf{X}$ and $\partial_\ell \mathbf{X}$. For an $SU(2)$ dynamics featured by $α_\ell=π/2$, the promotion of the estimation precision can get the most benefits from the controls. When $α_\ell$ gradually closes to $0$ or $π$, the precision promotion contributed to by quantum control correspondingly becomes inconspicuous. Until a dynamics with $α_\ell=0$ or $π$, quantum control completely loses its advantage. In addition, we find a set of conditions restricting the simultaneous optimal estimation of all the parameters, but fortunately, which can be removed by using a maximally entangled two-qubit state as the probe state and adding an ancillary channel into the configuration. Lastly, a spin-$1/2$ system is taken as an example to verify the above-mentioned conclusions. Our proposal sufficiently exhibits the hallmark of control-enhancement in fulfilling the multiparameter estimation mission, and it is applicable to an arbitrary $SU(2)$ parametrization process.