Quantum oscillations in a molecular magnet
Quantum oscillations in a molecular magnet
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DOI：
10.1038/nature06962
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发表时间：
2008-05-08
期刊：
影响因子：
64.8
通讯作者：
Barbara, B.
中科院分区：
文献类型：
--
作者：
Bertaina, S.;Gambarelli, S.;Barbara, B.
术语“分子磁体”通常是指含有几个磁性离子的分子实体，这些离子的耦合自旋产生集体自旋S（参考文献1）。这种复杂的多自旋系统为研究介观尺度下的量子效应提供了有吸引力的目标。在这些分子中，集体自旋态之间的大能量势垒可以通过热激活或量子隧穿来跨越，这取决于温度或施加的磁场（2-4）。有希望利用这些介观自旋态来实现量子比特，量子比特是量子计算机的基本组成部分-基于分子磁体（5-8）。但如果设想的应用要变得实用，就必须克服强退相干（9）。在这里，我们报告了在混合系统中分子磁体的拉比振荡（由电磁波驱动的光子的相干吸收和发射引起的量子振荡（10））的观察和分析，在该混合系统中，离散且分离良好的磁性V-15（IV）团簇嵌入在自组织的非磁性环境中。每个团簇包含15个反铁磁耦合的S = 1/ 2自旋，导致S = 1/ 2集体基态（11-13）。当这个系统被放置到谐振腔中时，微波场诱导基态和激发集体自旋态之间的振荡跃迁，这表明长寿命的量子相干性。目前对量子振荡的观察表明，具有100 μ s量级（在液氦温度下）相干时间的低维自组织量子比特网络是一个现实的前景。
The term 'molecular magnet' generally refers to a molecular entity containing several magnetic ions whose coupled spins generate a collective spin, S ( ref. 1). Such complex multi- spin systems provide attractive targets for the study of quantum effects at the mesoscopic scale. In these molecules, the large energy barriers between collective spin states can be crossed by thermal activation or quantum tunnelling, depending on the temperature or an applied magnetic field(2-4). There is the hope that these mesoscopic spin states can be harnessed for the realization of quantum bits 'qubits', the basic building blocks of a quantum computer - based on molecular magnets(5-8). But strong decoherence(9) must be overcome if the envisaged applications are to become practical. Here we report the observation and analysis of Rabi oscillations ( quantum oscillations resulting from the coherent absorption and emission of photons driven by an electromagnetic wave(10)) of a molecular magnet in a hybrid system, in which discrete and well-separated magnetic V-15(IV) clusters are embedded in a self- organized non- magnetic environment. Each cluster contains 15 antiferromagnetically coupled S = 1/ 2 spins, leading to an S = 1/ 2 collective ground state(11-13). When this system is placed into a resonant cavity, the microwave field induces oscillatory transitions between the ground and excited collective spin states, indicative of long-lived quantum coherence. The present observation of quantum oscillations suggests that low- dimension self- organized qubit networks having coherence times of the order of 100 mu s ( at liquid helium temperatures) are a realistic prospect.