Physicists have conducted the first quantum calculations using individual atoms on a surface, controlling titanium atoms with microwave signals from a scanning tunnelling microscope (STM), potentially paving the way for a new type of Quantum Computer. The technique, developed by Andreas Heinrich at the Institute for Basic Science in Seoul and his team, is not expected to rival quantum computing approaches by Google and IBM. However, it could be used to study quantum properties in other chemical elements or molecules. The team manipulated the spin of electrons in titanium atoms to perform a simple two-qubit quantum operation, a process that could potentially be extended to 100 qubits.
Quantum Calculations Using Individual Atoms
Scientists have successfully performed quantum calculations using individual atoms placed on a surface. This method, detailed in Science on 5 October titled “An atomic-scale multi-qubit platform”, involves controlling titanium atoms by directing microwave signals from the tip of a scanning tunnelling microscope (STM). While this technique is not expected to rival the current quantum computing methods used by tech companies such as Google and IBM, it could potentially be used to study quantum properties in various chemical elements or even molecules.
The challenge in quantum computing lies in isolating quantum states, known as qubits, from environmental disturbances and controlling them with enough precision for calculations to be achieved. Qubits are the quantum equivalent of the memory bits in a classical computer. The researchers, led by Andreas Heinrich at the Institute for Basic Science in Seoul, worked with the electron’s spin, nature’s ‘original’ qubit.
Electrons behave like tiny compass needles, and measuring the direction of their spin can yield only two possible values, ‘up’ or ‘down’, which correspond to the ‘0’ and ‘1’ of a classical bit. However, before it is measured, electron spin can exist in a continuum of possible intermediate states, known as superpositions. This is the key to performing quantum computations. To better understand the behaviour and state of the qubit, researchers often use the Bloch Sphere to represent quantum states on qubits.
The Technique: Scanning Tunnelling Microscope (STM)
An STM, or Scanning Tunneling Microscope, is a tool that allows scientists to view surfaces at the atomic level. Imagine it as a sharp needle that scans extremely close to a surface; when it’s close enough, electrons “jump” or “tunnel” between the hand and the surface. By measuring this tunnelling, the STM can create detailed images of individual atoms on the surface. It’s like feeling the bumps on a character with an incredibly sensitive fingertip but at an atomic scale.
The researchers began by scattering titanium atoms on a perfectly flat surface of magnesium oxide. They then mapped the atoms’ positions using the STM, which has atomic resolution. They used the tip of the STM probe to move the titanium atoms around, arranging three of them into a triangle.
By emitting microwave signals from the STM tip, the researchers could control the spin of a single electron in one of the titanium atoms. By tuning the frequencies of the microwaves appropriately, they could also make its spin interact with the spins in the other two titanium atoms. This interaction is similar to how multiple compass needles can influence each other through their magnetic fields.
Quantum Operation and Results
By manipulating the atoms’ spins, the team could set up a simple two-qubit quantum operation and read out its results. The process took just nanoseconds — faster than is possible with most other types of qubits (which come in a range of flavours such as Ion-Trap, Photonic, Superconducting and Semiconducting).
Future of the Technique
Heinrich believes that extending the technique to perhaps 100 qubits will be relatively straightforward, possibly by manipulating spins in a combination of individual atoms and molecules. However, it might not be easy to push it beyond that, given that the current leading qubit technologies are already being scaled up to hundreds of qubits.
While this technique is more on the primary science side, Heinrich suggests that multiple STM quantum computers could one day be linked to form a larger one. This could potentially open up new avenues in the field of quantum computing.
“At some level, everything in nature is quantum and can, in principle, perform quantum computations. The hard part is to isolate quantum states called qubits — the quantum equivalent of the memory bits in a classical computer — from environmental disturbances, and to control them finely enough for such calculations to be achieved.”
Andreas Heinrich, Institute for Basic Science in Seoul
Heinrich says that it will be fairly straightforward to extend the technique to perhaps 100 qubits, possibly by manipulating spins in a combination of individual atoms and molecules. It might be not easy to push it much beyond that, however — and the leading qubit technologies are already being scaled up to hundreds of qubits. “We are more on the basic-science side,” Heinrich says, although he adds that multiple STM quantum computers could one day be linked to form a bigger one.” – Andreas Heinrich, Institute for Basic Science in Seoul.
Summary
Physicists have successfully performed quantum calculations using individual atoms on a surface, controlling titanium atoms with microwave signals from a scanning tunnelling microscope. While not yet competitive with leading quantum computing approaches, this method could potentially be used to study quantum properties in various chemical elements or molecules.
- Physicists have successfully performed quantum calculations using individual atoms on a surface, a first in the field.
- The technique, described in Science on 5 October, utilises titanium atoms controlled by microwave signals from a scanning tunnelling microscope (STM).
- While not expected to compete with leading quantum computing approaches by Google and IBM, the method could be used to study quantum properties in other chemical elements or molecules.
- The research team, led by Andreas Heinrich at the Institute for Basic Science in Seoul, worked with electron spin, nature’s ‘original’ qubit.
- The team scattered titanium atoms on a magnesium oxide surface, then used the STM to arrange three atoms into a triangle.
- Using microwave signals, they controlled the spin of a single electron in one titanium atom and made it interact with the spins in the other two atoms.
- This allowed them to set up a simple two-qubit quantum operation and read its results in nanoseconds, faster than most other types of qubit.
- Heinrich believes the technique could be extended to around 100 qubits by manipulating spins in individual atoms and molecules.
