Coherent control of a classical nanomechanical two-level system
Coherent control of a classical nanomechanical two-level system
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DOI：
10.1038/nphys2666
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发表时间：
2013-08-01
期刊：
影响因子：
19.6
通讯作者：
Weig, E. M.
中科院分区：
文献类型：
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作者：
Faust, T.;Rieger, J.;Weig, E. M.
Bloch球是描述在电磁场(1，2)控制下耦合的经典或量子力学二能级系统的相干动力学的一般图像。它通常应用于自旋系综(3)、原子(4)、量子点(5)和超导电路(6)等系统。基本的Bloch方程(7)描述了二能级系统的状态演化，并允许描述能量和相松弛过程(3，8，9)。这里我们实现了一个由射频信号驱动的经典纳米机械两能级系统(2)。它是基于由介电梯度场(10)强烈耦合的高品质因数纳米弦谐振器的两个正交基模。通过Rabi(11)、Ramsey(12)和Hahn ECHO(13)的实验证明了完全Bloch球控制。此外，我们还确定了能量弛豫时间T-1和相位弛豫时间T-2和T*(2)，发现它们都是相等的。因此，消相干是由能量弛豫主导的，这意味着不仅T-1，而且T-2可以通过工程更大的机械品质因数来增加。
The Bloch sphere is a generic picture describing the coherent dynamics of coupled classical or quantum-mechanical two-level systems under the control of electromagnetic fields(1,2). It is commonly applied to systems such as spin ensembles(3), atoms(4), quantum dots(5) and superconducting circuits(6). The underlying Bloch equations(7) describe the state evolution of the two-level system and allow the characterization of both energy and phase relaxation processes(3,8,9). Here we realize a classical nanomechanical two-level system(2) driven by radiofrequency signals. It is based on the two orthogonal fundamental flexural modes of a high-quality-factor nanostring resonator that are strongly coupled by dielectric gradient fields(10). Full Bloch sphere control is demonstrated by means of Rabi(11), Ramsey(12) and Hahn echo(13) experiments. Furthermore, we determine the energy relaxation time T-1 and phase relaxation times T-2 and T*(2), and find them all to be equal. Thus decoherence is dominated by energy relaxation, implying that not only T-1 but also T-2 can be increased by engineering larger mechanical quality factors.