How do surrounding atoms tune the energy of a single electron?

Quantum dance to the beat of a drum.

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Particles, such as electrons, can frequently only take on quantized energy values, one of the peculiarities of quantum physics. Qubits, quantum computers, and light-emitting quantum dots use this principle. Collisions with other electrons or atoms, however, can change the electronic energy levels. In the quantum realm, processes typically occur at highly high atomic-scale speeds.

Using an ultrafast microscope, scientists at the University of Regensburg have successfully observed how the energy of a single electron is tuned by the vibrations of the surrounding atoms on ultrafast timescales with atomic resolution. They are also able to control this process.

According to scientists, the findings could be crucial for developing super-fast quantum technologies.

The physicists studied the behavior of a discrete energy level when this atomic layer oscillates like a drum membrane using an atomically thin material. This was noticed at a vacancy, or the space created when an individual atom is eliminated.

Future nanoelectronics will find these atomically thin two-dimensional crystals particularly intriguing due to their adaptable and changeable electrical characteristics. Since vacancies in crystals have discrete electrical energy levels similar to those of atoms, they are intriguing candidates for qubits, the primary information bearers of quantum computers.

Scientists found that inducing a drum-like vibration of the atomically thin membrane can change a discrete energy level of the defect. This is achieved by shifting the atomic motion of the surrounding atoms, which regulates the vacancy’s energy level.

The scientists had to overcome several obstacles to make this important finding. To detect the dynamics of atomically localized energy levels, an atomic resolution of 1 Ångström is necessary. Furthermore, movement in the nanoworld occurs at a very high speed.

First author Carmen Roelcke said, “To track how an energy level shifts, it is necessary to take stroboscopic snapshots of the energy level, with each snapshot being recorded in less than a trillionth of a second, faster than picoseconds.”

Scientists met these challenges in an elaborate method that uses a scanning tunneling microscope’s energy and spatial resolution. Simultaneously, slow-motion recording of the incredibly quick dynamics is achievable with the use of specially designed ultrashort laser pulses. The critical synergy for the necessary ultrafast atom-scale spectroscopy was produced by the joint experience of the groups led by Jascha Repp and Rupert Huber.

Yaroslav Gerasimenko says“With our novel approach, we can decipher the structural movement of the atomic drum membrane and the shift of the localized energy level in slow motion.”

Maximilian Graml and Jan Wilhelm’s first-principles calculations provide a definitive explanation for how the atoms in the atomically thin layer move during the oscillation and how this can affect the discrete energy levels.

The research ushers in a new chapter in understanding the dynamics of atomically confined energy levels and how they interact with their surroundings. This finding provides the most direct means of local control over discrete energy levels. For example, the movement of individual atoms may alter a material’s energy structure, resulting in new functionalities or, in particular, modifying the characteristics of molecules and semiconductors that emit light.

Journal Reference:

  1. Carmen Roelcke et al., Ultrafast atomic-scale scanning tunneling spectroscopy of a single vacancy in a monolayer crystal. Nature Photonics. DOI: 10.1038/s41566-024-01390-6
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