We present and analyze a proposal for a macroscopic quantum delayed-choice experiment with massive mechanical resonators. In our approach, the electronic spin of a single nitrogen-vacancy impurity is employed to control the coherent coupling between the mechanical modes of two carbon nanotubes. We demonstrate that a mechanical phonon can be in a coherent superposition of wave and particle, thus exhibiting both behaviors at the same time. We also discuss the mechanical noise tolerable in our proposal and predict a critical temperature below which the morphing between wave and particle states can be effectively observed in the presence of environment-induced fluctuations. Furthermore, we describe how to amplify single-phonon excitations of the mechanical-resonator superposition states to a macroscopic level, via squeezing the mechanical modes. This approach corresponds to the phase-covariant cloning. Therefore, our proposal can serve as a test of macroscopic quantum superpositions of massive objects even with large excitations. This work, which describes a fundamental test of the limits of quantum mechanics at the macroscopic scale, would have implications for quantum metrology and quantum information processing.

我们提出并分析了具有大型机械谐振器的宏观量子延迟选择实验的建议。在我们的方法中，采用单个氮空位杂质的电子自旋来控制两个碳纳米管的机械模式之间的相干耦合。我们证明了机械声子可以处于波和粒子的连贯叠加中，从而同时表现出两种行为。我们还将讨论建议中可容许的机械噪声，并预测一个临界温度，在该温度以下，在环境引起的波动的情况下，可以有效地观察到波和粒子状态之间的形变。此外，我们描述了如何通过压缩机械模式将机械谐振器叠加态的单声子激发放大到宏观水平。该方法对应于相位协变克隆。因此，我们的建议甚至可以作为对大型物体宏观量子叠加的检验​​，即使在大激发下也是如此。这项工作描述了宏观尺度上量子力学极限的基本测试，将对量子计量学和量子信息处理产生影响。