Coupling single atoms to form quantum states

Scientists at the London Centre for Nanotechnology have coupled single atoms to form quantum states by introducing individual silicon atom ‘defects’ using a scanning tunneling microscope.

The study, which is published in Nature Communications, suggests that engineering atomic-scale quantum states on the surface of silicon may be an important step towards creating a range of devices at the single-atom limit.

Dr Steven Schofield who led the study told Laboratory News: “There are many reasons why it is desirable to build systems of individual atoms and observe the interactions between them. These range from furthering our understanding of the physics that governs individual atoms, molecules and solids, to the potential to build novel electronic devices that exploit quantum mechanical phenomena for their operation.”

Advances in atomic physics now mean single ions can be brought together to form quantum coherent states. However, in order to build large numbers of coupled atomic systems (for processes such as quantum computing), it is desirable to develop the ability to construct coupled atomic systems in the solid state such as silicon crystal, since these are very stable, can be made extremely pure and can be integrated with existing technology.

The team exposed a silicon surface to a source of atomic hydrogen – created by heating H₂ molecules to 1500 °C. This resulted in a surface where every silicon atom had a single H atom attached to it.

“We create defects by removing individual H atoms – an electron-stimulated desorption process using the highly confined electron beam from the scanning tunnelling microscope tip,” explained Schofield. “We have created systems of dangling bonds where each dangling bond is located on a next-nearest silicon atom. The separation between them is about 0.78 nanometres.”

When these atomic defects are coupled together they produce extended quantum states that resemble artificial molecular orbitals – each structure exhibits multiple quantum states with distinct energy levels.

“The next step is to replicate these results in other material systems, for example, using substitution phosphorus atoms in silicon, which holds particular interest for quantum computer fabrication,” said Schofield.

Reference: Quantum engineering at the silicon surface using dangling bonds