Physicists Determine Geometry of Electrons in Quantum Dots

A team of physicists at the University of Basel has experimentally mapped out the shape and orientation of electrons trapped in quantum dots.

An electron is trapped in a quantum dot, which is formed in a 2D 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.

An electron is trapped in a quantum dot, which is formed in a 2D 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.

“A quantum dot is a potential trap which allows to confine free electrons in an area which is about 1,000 times larger than a natural atom,” explained University of Basel’s Professors Dominik Zumbühl and Daniel Loss and their colleagues.

“Because the trapped electrons behave similar to electrons bound to an atom, quantum dots are also known as ‘artificial atoms’.”

“The electron is held in the quantum dot by electric fields. However, it moves within the space and, with different probabilities corresponding to a wave function, remains in certain locations within its confinement.”

The scientists developed a method by which they can spatially determine the geometry of electrons in quantum dots.

They used spectroscopic measurements to determine the energy levels in the quantum dot and study the behavior of these levels in magnetic fields of varying strength and orientation.

With the team’s theoretical model, it was possible to determine the electron’s probability density and thus its wave function with a precision 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,” Professor Loss said.

“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,” Professor Zumbühl added.

“This gives us the opportunity to optimize control of the spins in a very targeted manner.”

“The spatial orientation of the electrons also plays a role in the entanglement of several spins.”

“Similarly to the binding of two atoms to a molecule, the wave functions of two electrons must lie on one plane for successful entanglement.”

“With the aid of the developed method, numerous earlier studies can be better understood and the performance of spin qubits can be further optimized in the future.”

The results of the team’s experiments were published in the journal Physical Review Letters and the related theory in the journal Physical Review B.

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Leon C. Camenzind et al. 2019. Spectroscopy of Quantum Dot Orbitals with In-Plane Magnetic Fields. Phys. Rev. Lett 122 (20): 207701; doi: 10.1103/PhysRevLett.122.207701

Peter Stano et al. 2019. Orbital effects of a strong in-plane magnetic field on a gate-defined quantum dot. Phys. Rev. B 99 (8): 085308; doi: 10.1103/PhysRevB.99.085308

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