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The geometry of an electron

The geometry of an electron

University of Basel physicists have demonstrated for the first time how a single electron appears in an artificial atom. They can now indicate the likelihood of an electron being present in a space using a newly discovered technique. This enables better control of electron spins, which might be the smallest information unit in a future quantum computer.

The spin of an electron is a viable contender for use as a quantum computer’s smallest information unit (qubit). Controlling and switching this spin, as well as coupling it with other spins, is a challenge on which many research organizations across the world are working. The stability of a single spin and the entanglement of many spins are dependent on the geometry of the electrons, which was previously difficult to establish experimentally.

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: University of Basel, Departement of Physics)

A quantum dot is a potential trap that may confine free electrons in an area 1000 times bigger than a normal atom. Quantum dots are also referred to as “artificial atoms” since the trapped electrons behave similarly to electrons bound to an atom.

Electric fields hold the electron in the quantum dot. It does, however, travel across space and, with varying probabilities corresponding to a wave function, stays at certain positions inside its confinement.

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

The researchers utilize spectroscopic measurements to determine the energy levels in the quantum dot and investigate how these levels behave in magnetic fields of different intensity and direction. Based on their theoretical model, they can calculate the electron’s probability density and hence its wave function with sub-nanometer precision.

“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,” says Zumbühl.

The spatial orientation of the electrons is also important in the entanglement of several spins. For effective entanglement, the wave functions of two electrons must lie on the same plane as the binding of two atoms to a molecule.

Numerous previous research can be better understood with the help of the proposed approach, and the performance of spin qubits may be further enhanced in the future.

Orbital effects of a strong in-plane magnetic field on a gate-defined quantum dot, Peter Stano, Chen-Hsuan Hsu, Leon C. Camenzind, Liuqi Yu, Dominik Zumbühl, and Daniel Loss

Published: June 2019

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