Posted in | Quantum Physics

Breakthrough Study Demonstrates the Geometry of a Single Electron in an Artificial Atom

For the first time, physicists at the University of Basel have demonstrated the geometry of a single electron in an artificial atom.

An electron is trapped in a quantum dot, which is formed in a two-dimensional gas in a semiconductor wafer. However, the electron moves within the space and, with different probabilities corresponding to a wave function, remains in certain locations within its confinement (red ellipses). Using the gold gates applied electric fields, the geometry of this wave function can be changed. (Image credit: University of Basel, Departement of Physics)

This breakthrough discovery can be attributed to a recently developed technique that allows the physicists to show the possibility of a single electron existing in a space. This enables better control of electron spins, which can possibly act as the tiniest information unit in a next-generation quantum computer. The experiments have been reported in Physical Review Letters and the associated theory has been published in Physical Review B.

The spin of an electron is considered a potential candidate for using it as the tiniest information unit (qubit) of a quantum computer. However, it is difficult to control and switch this spin or combine it with other spins, and as a result, many research groups across the globe are working on this. The entanglement of numerous spins and the stability of a single spin rely, among other things, on the electrons’ geometry, which previously had not been possible to establish experimentally.

Only possible in artificial atoms

Now, researchers in the teams led by professor Dominik Zumbühl and professor Daniel Loss from the Department of Physics and the Swiss Nanoscience Institute at the University of Basel have come up with a novel technique, which allows them to spatially establish the electrons’ geometry in quantum dots.

A quantum dot is regarded as a possible trap, which helps in confining free electrons in a space that is approximately 1000 times larger when compared to a natural atom. Since the trapped electrons act in a way similar to the electrons adhered to an atom, quantum dots are also referred to as “artificial atoms.”

Electric fields hold the electron in the quantum dots; however, this electron moves inside the space and, with different possibilities corresponding to a wave function, continues to be in specific locations within its confinement.

Charge distribution sheds light

Spectroscopic measurements were used by the researchers to establish the energy levels in the quantum dot and to analyze the specific behavior of these levels in magnetic fields of different orientation and strength. Based on the researchers' hypothetical model, the probability density of the electron can be determined and so does its wave function with an accuracy on the sub-nanometer scale.

To put it simply, we can use this method to show what an electron looks like for the first time.

Dr Daniel Loss, Professor, Department of Physics, University of Basel

Better understanding and optimization

Working closely with associates in the US, Slovakia, and Japan, the researchers ultimately gained a better understanding of the association between the electron spin and the geometry of electrons. This electron spin should not only be stable as long as possible, but should also be rapidly switchable for use as a qubit.

We are able to not only map the shape and orientation of the electron, but also control the wave function according to the configuration of the applied electric fields. This gives us the opportunity to optimize control of the spins in a very targeted manner.

Dr Dominik Zumbühl, Associate Professor, Department of Physics, University of Basel

The electrons’ spatial orientation also has an important role to play in the entanglement of a number of spins. Likewise, when it comes to the binding of a pair of atoms to a molecule, the wave functions of both the electrons should lie on a single plane for effective entanglement of spins.

With the help of the developed technique, many previous studies can be better figured out and the spin qubits’ performance can be additionally improved in the days to come.

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