FOM researchers cause electrons to jump to distant quantum dots
Scientists from Delft University of Technology and the FOM Foundation have successfully allowed electrons to jump between quantum dots located far from each other. The electron jumped between the ends of a chain of three small semiconducting islands (so-called quantum dots) without crossing the island in the middle. This process makes it easier to use quantum dots in future quantum computers. The researchers published their findings on 28 April online in the leading journal Nature Nanotechnology.
Quantum dots are semiconducting structures with dimensions of just a few nanometres in which electrons can be entrapped. That entrapment happens with the help of a negative potential difference across metal electrodes. By accurately adjusting this potential difference the electrons can be allowed to jump backwards and forwards between adjacent quantum dots. This possibility has been extensively used in experiments over the past 15 years and forms the basis for quantum calculations using quantum dots.
In the experiment with three adjacent quantum dots, the scientists adjusted the potential difference such that the middlemost quantum dot was not accessible for electrons. To their surprise the researchers from Delft, led by prof.dr.ir. Lieven Vandersypen, 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 be concomitantly determined. The research team demonstrated that this process can also 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 PhD student Floris Braakman, MSc.
The findings 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 distant quantum dots can also be brought together, the scaling up to larger chains of quantum dots has become far easier. That scaling up will make it possible for a quantum-dot computer to perform far more complex calculations. The discovery also makes it possible to investigate the behaviour of certain molecules, in which these same transport phenomena of electrons can occur, by simulating these processes with the help of quantum dot chains.
Reference
'Long-distance coherent coupling in a quantum dot array', F.R. Braakman, P. Barthelemy, C. Reichl, W. Wegscheider and L.M.K. Vandersypen. Nature Nanotechnology.
Contact
Prof.dr.ir. Lieven Vandersypen, Delft University of Technology, telephone +31 (0)15 278 24 69