Electrons jump between quantum dots

Just days after TU Delft scientists entangled quantum bits on distant chips, another group has successfully allowed electrons to jump between quantum dots. Both groups of the Kavli Institute of Nanoscience lay a basis for quantum information processing.

Researchers, led by Professor Lieven Vandersypen, have showed that they could make an electron jump between the ends of a chain of three small semiconducting islands (so-called quantum dots) without crossing the island in the middle (Nature Nanotechnology, 28 April 2013). Vandersypen’s group works with chips. In their experiment with three adjacent quantum dots, the scientists adjusted the voltage such that the middlemost quantum dot was not accessible for electrons. To their surprise they discovered that an electron could still disappear from the left dot and subsequently reappear on the right dot. That is possible due to the Heisenberg uncertainty principle, which states that energy and time cannot exactly be determined at the same time.

First author Floris Braakman MSc. and colleagues also demonstrated that this process can generate superpositions: the electron is simultaneously present in both the first and the third quantum dot. “This means that the interesting physical phenomena we observe in adjacent quantum dots also appears to occur in quantum dots that are located further away from each other”, says Braakman.

The findings could have consequences for the use of a future type of quantum computer based on quantum dots. Calculations can only be performed on such computers if pairs of electrons can be brought close together. Previously this could only be realised between adjacent quantum dots. Now that it appears that electrons from more distant quantum dots can also be brought together, the scaling up to larger chains of quantum dots has become far easier.

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