Getting a Grip on the Environment of a Quantum Particle

Researchers of the Kavli Institute of Nanoscience at the TU Delft have succeeded in getting a grip on the environment of a quantum particle, thereby increasing the control over single electrons. With this result, the team of researchers led by Vidi-laureate and FOM-workgroup leader Lieven Vandersypen has brought the superfast quantum computer another step closer. Their results were published August 16th in Nature Physics.

One of the unique properties of quantum particles is that they can occupy multiple states at the same time. An atom or electron is then in a so-called superposition of two states. For instance, the so-called 'spin' of an electron can point in two different directions simultaneously. In terms of bits: a 'quantum bit' can be both 0 and 1 at the same time, as opposed to the usual 'classical' bits which can only be 0 or 1. These quantum particles would allow for superfast computations. Up to now, however, it was impossible to keep a quantum particle in some specific state long enough, because the environment - also consisting of quantum particles - constantly disturbs the state. Precisely this environment is what researchers were unable to get a grip on so far.

Stabilizing the 'pushing and pulling'
The researchers from Delft tackled the problem by stabilizing the environment. Before, they had already shown that it is possible to manipulate the spin of an electron using a quantum dot, a nanoscale sized box. The problem was that all atomic nuclei in the host material also possess spin. Since these nuclear spins behave as tiny magnets, they constantly push and pull on the spin of the electron in the box. The electron, however, also pushes and pulls back.

Precisely this interaction between the electron spin and the spins of the surrounding nuclei enabled the researchers to fix the state of the spins. They sent an electric current through the nanobox and thereby influenced the spin direction of the nuclear spins. Due to the interaction between the electron and nuclear spins they managed to create a situation where the nuclear spins no longer fluctuated randomly, but actually became relatively stable. This stable environment now allows the fragile but important superposition states to be preserved for a longer time.

Publication in Nature
The paper by Ivo Vink and Lieven Vandersypen was published on August 16th as an Advance Online Publication on the website of Nature Physics. A detailed theory describing the mechanism behind these experimental observations was developed by Jeroen Danon, and was published a few weeks ago in Physical Review Letters. This research was funded by NWO and Stichting FOM.

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