University of Vienna, Faculty of Physics, Vienna Center for Quantum Science and Technology (VCQ), Boltzmanngasse 5 A-1090, Vienna, Austria.
Nat Commun. 2013;4:2295. doi: 10.1038/ncomms3295.
Observing a physical quantity without disturbing it is a key capability for the control of individual quantum systems. Such back-action-evading or quantum non-demolition measurements were first introduced in the 1970s for gravitational wave detection, and now such techniques are an indispensable tool throughout quantum science. Here we perform measurements of the position of a mechanical oscillator using pulses of light with a duration much shorter than a period of mechanical motion. Utilizing this back-action-evading interaction, we demonstrate state preparation and full state tomography of the mechanical motional state. We have reconstructed states with a position uncertainty reduced to 19 pm, limited by the quantum fluctuations of the optical pulse, and we have performed 'cooling-by-measurement' to reduce the mechanical mode temperature from an initial 1,100 to 16 K. Future improvements to this technique will allow for quantum squeezing of mechanical motion, even from room temperature, and reconstruction of non-classical states exhibiting negative phase-space quasi-probability.
在不干扰物理量的情况下对其进行观测，是对单个量子系统进行控制的关键能力。这种“反作用规避”或量子不可破坏性测量最早于 20 世纪 70 年代被用于引力波探测，而如今，此类技术已经成为整个量子科学不可或缺的工具。在这里，我们使用持续时间远小于机械运动周期的光脉冲来测量机械振荡器的位置。通过利用这种反作用规避相互作用，我们演示了机械运动状态的态制备和全态层析成像。我们已经将位置不确定性降低到 19pm，这一数值受到光脉冲量子涨落的限制，并且我们已经进行了“测量冷却”，将机械模式温度从初始的 1100K 降低到 16K。这种技术的未来改进将允许实现机械运动的量子压缩，即使是在室温下，并且可以重构具有负相空间准概率的非经典态。
