Forms of collective behavior often emerge in large ensembles of interacting units, such as a network of neurons, a flock of birds, or electrons in solids. In condensed-matter systems, the emergence of these collective phenomena is often associated with spectacular properties that could be harvested in applications. But the complexity of the underlying many-body interactions makes it difficult to both understand and control such effects.
Now, Clemens Rössler, at the Swiss Federal Institute of Technology (ETH) in Zurich, and co-workers [1] have shown that it is possible to control a prototypical many-body effect—the Kondo effect—in a system made of a quantum dot embedded in an electronic cavity. By tuning the coupling between the dot and the cavity, the researchers can bring the electrons in the dot together with the cavity’s electrons to form a unique quantum state with a total spin of 0—a spin-singlet. The scheme, which is controllable by purely electrical means, may allow the faithful transfer of quantum states across distant qubits, serving as a “quantum bus” in quantum processing architectures.
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