1] London Centre for Nanotechnology, University College London, London WC1H 0AH, UK [2] Department of Physics and Astronomy, University College London, London WC1E 6BT, UK [3].
1] London Centre for Nanotechnology, University College London, London WC1H 0AH, UK [2] [3].
Nat Nanotechnol. 2014 Jan;9(1):64-8. doi: 10.1038/nnano.2013.264. Epub 2013 Dec 8.
The properties of quantum systems interacting with their environment, commonly called open quantum systems, can be affected strongly by this interaction. Although this can lead to unwanted consequences, such as causing decoherence in qubits used for quantum computation, it can also be exploited as a probe of the environment. For example, magnetic resonance imaging is based on the dependence of the spin relaxation times of protons in water molecules in a host's tissue. Here we show that the excitation energy of a single spin, which is determined by magnetocrystalline anisotropy and controls its stability and suitability for use in magnetic data-storage devices, can be modified by varying the exchange coupling of the spin to a nearby conductive electrode. Using scanning tunnelling microscopy and spectroscopy, we observe variations up to a factor of two of the spin excitation energies of individual atoms as the strength of the spin's coupling to the surrounding electronic bath changes. These observations, combined with calculations, show that exchange coupling can strongly modify the magnetic anisotropy. This system is thus one of the few open quantum systems in which the energy levels, and not just the excited-state lifetimes, can be renormalized controllably. Furthermore, we demonstrate that the magnetocrystalline anisotropy, a property normally determined by the local structure around a spin, can be tuned electronically. These effects may play a significant role in the development of spintronic devices in which an individual magnetic atom or molecule is coupled to conducting leads.
与环境相互作用的量子系统的性质，通常称为开放量子系统，可能会受到这种相互作用的强烈影响。虽然这可能会导致不需要的后果，例如导致量子计算中使用的量子比特退相干，但它也可以被用来探测环境。例如，磁共振成像（MRI）就是基于水在组织中的质子的自旋弛豫时间对磁场的依赖性。在这里，我们表明，单个自旋的激发能（由磁各向异性决定）可以通过改变自旋与附近导电电极的交换耦合来改变。通过扫描隧道显微镜和光谱学，我们观察到随着自旋与周围电子浴的耦合强度的变化，单个原子的自旋激发能变化高达两倍。这些观察结果与计算结果结合表明，交换耦合可以强烈地改变磁各向异性。因此，该系统是少数几个可以对能级进行控制调整（而不仅仅是调整激发态寿命）的开放量子系统之一。此外，我们还证明了磁各向异性（通常由自旋周围的局部结构决定的性质）可以通过电子方式进行调整。这些效应可能在开发自旋电子器件中发挥重要作用，其中单个磁性原子或分子与导电引线耦合。
