Cooper pair splitter realized in a two-quantum-dot Y-junction
Cooper pair splitter realized in a two-quantum-dot Y-junction
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DOI：
10.1038/nature08432
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发表时间：
2009-10-15
期刊：
影响因子：
64.8
通讯作者：
Schoenenberger, C.
中科院分区：
文献类型：
--
作者：
Hofstetter, L.;Csonka, S.;Schoenenberger, C.
非定域性是量子力学的一个基本性质，表现为量子系统空间分离部分之间的相关性。探索这种现象的基本途径是产生量子纠缠物体的爱因斯坦-波多尔斯基-罗森（EPR）对（1），用于检验所谓的贝尔不等式（2）。虽然这种非定域性的实验测试已经成功地用成对纠缠的光子进行了，但还不可能在固态中实现它的电子模拟，其中自旋为1/2的移动的电子是自然的量子对象（3）。困难源于这样一个事实，即电子沉浸在一个宏观的基态-费米海-这阻止了直接产生和分裂的纠缠电子对的需求。然而，超导体可以作为EPR电子对的来源，因为它的基态是由自旋单重态的库珀对组成的（4）。这些库珀对可以通过隧道效应从超导体中提取出来，但是，为了获得纠缠电子的有效EPR源，必须强制将库珀对分裂成单独的电子。这可以通过使电子通过库仑相互作用彼此“排斥”来实现（5）。因此，可以通过借助于可单独调谐的量子点将超导体耦合到两个正常金属漏极接触来实现受控的库珀对分裂。在这里，我们展示了第一个实验实现这样的可调库珀对分裂器，它显示出令人惊讶的高效率。我们的研究结果打开了一条通往EPR悖论和贝尔不等式在固态的第一次测试的路线。
Non-locality is a fundamental property of quantum mechanics that manifests itself as correlations between spatially separated parts of a quantum system. A fundamental route for the exploration of such phenomena is the generation of Einstein-Podolsky-Rosen (EPR) pairs(1) of quantum-entangled objects for the test of so-called Bell inequalities(2). Whereas such experimental tests of non-locality have been successfully conducted with pairwise entangled photons, it has not yet been possible to realize an electronic analogue of it in the solid state, where spin-1/2 mobile electrons are the natural quantum objects(3). The difficulty stems from the fact that electrons are immersed in a macroscopic ground state-the Fermi sea-which prevents the straightforward generation and splitting of entangled pairs of electrons on demand. A superconductor, however, could act as a source of EPR pairs of electrons, because its ground-state is composed of Cooper pairs in a spin-singlet state(4). These Cooper pairs can be extracted from a superconductor by tunnelling, but, to obtain an efficient EPR source of entangled electrons, the splitting of the Cooper pairs into separate electrons has to be enforced. This can be achieved by having the electrons 'repel' each other by Coulomb interaction(5). Controlled Cooper pair splitting can thereby be realized by coupling of the superconductor to two normal metal drain contacts by means of individually tunable quantum dots. Here we demonstrate the first experimental realization of such a tunable Cooper pair splitter, which shows a surprisingly high efficiency. Our findings open a route towards a first test of the EPR paradox and Bell inequalities in the solid state.