Department of Physics, University of California, Berkeley, CA 94720, USA.
Department of Physics, University of California, Berkeley, CA 94720, USA. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
Science. 2014 Jun 27;344(6191):1486-9. doi: 10.1126/science.1249850.
The Heisenberg uncertainty principle sets a lower bound on the noise in a force measurement based on continuously detecting a mechanical oscillator's position. This bound, the standard quantum limit, can be reached when the oscillator subjected to the force is unperturbed by its environment and when measurement imprecision from photon shot noise is balanced against disturbance from measurement back-action. We applied an external force to the center-of-mass motion of an ultracold atom cloud in a high-finesse optical cavity and measured the resulting motion optically. When the driving force is resonant with the cloud's oscillation frequency, we achieve a sensitivity that is a factor of 4 above the standard quantum limit and consistent with theoretical predictions given the atoms' residual thermal disturbance and the photodetection quantum efficiency.
海森堡不确定性原理为基于连续检测机械振荡器位置的力测量中的噪声设定了下限。当受外力的振荡器不受环境干扰，并且来自光子散粒噪声的测量不精确性与测量反作用的干扰相平衡时，就可以达到这个界限，即标准量子极限。我们将外力施加到高精细光学腔中冷原子云的质心运动上，并通过光学方法测量得到的运动。当驱动力与云的振荡频率共振时，我们实现了比标准量子极限高 4 倍的灵敏度，这与考虑到原子残余热干扰和光探测量子效率的理论预测一致。
