Quantum technology could one day revolutionize computing, communications and sensing by solving problems that are impossible for today’s computers.
However, one of the biggest challenges has been finding a practical way to control individual quantum bits, or qubits, at the scale of single atoms and molecules.
Now, researchers at the Center for Quantum Nanoscience (QNS) of the Institute for Basic Science (IBS), working with scientists from the Karlsruhe Institute of Technology (KIT), have demonstrated a new way to control the quantum state of a single magnetic molecule using electricity instead of magnetic fields.
Their findings were published in Nature Physics.
Many current quantum systems rely on magnetic fields to control the tiny magnetic property called spin, which acts as a qubit. While this method works, magnetic fields are difficult to focus on a single molecule without also affecting nearby molecules, making it challenging to build large-scale quantum devices.
Magnetic molecules are attractive candidates for future quantum technologies because they are incredibly small, measuring only a few billionths of a meter across. They can also naturally arrange themselves into organized patterns and can be chemically designed to have specific quantum properties.
Despite these advantages, controlling the spin of an individual molecule has remained difficult. Earlier experiments showed that electric fields could influence molecular spins, but the effect was too weak to be useful for practical quantum operations.
To solve this problem, the researchers studied individual molecules called iron phthalocyanine using an advanced instrument that combines scanning tunneling microscopy with electron spin resonance. This allowed them to observe and manipulate a single molecule with extremely high precision.
By carefully adjusting the electrical voltage applied to the molecule, the team discovered a new way to strengthen electrical control. Instead of responding gradually, the molecule’s spin changed dramatically when the voltage approached one of its natural energy levels.
The researchers found that this strong response was caused by a special interaction between the molecule and the magnetic tip of the microscope. This newly identified exchange-mediated effect created a highly localized magnetic influence using electricity rather than external magnets.
The effect was far stronger than previous methods. The researchers measured changes in the molecule’s resonance frequency of nearly 30%, about ten times greater than the electrical tuning effects reported in most earlier studies of similar molecular systems.
The team then showed that electricity could do more than simply change the molecule’s energy levels. Using experiments known as Rabi oscillations, they demonstrated that electrical signals could directly control the quantum state of an individual molecular spin.
They also successfully controlled one molecular spin without disturbing another nearby molecule. This level of precision is considered essential if future quantum computers are to contain many closely packed qubits that operate independently.
Unlike some earlier techniques, this new method does not require physically bending or deforming the molecule. Instead, the control comes entirely from the interaction between the molecule and a nearby magnetic electrode, making it much easier to apply in future devices.
The researchers believe this approach could also work with other quantum systems, including quantum dots and solid-state spin defects. Because electrical signals are much easier to generate, direct and integrate into electronic circuits than magnetic fields, the technique offers a practical path toward building more compact and scalable quantum technologies.
Although practical quantum computers are still years away, this research represents an important advance.
By showing that a single molecule can be controlled efficiently using electricity alone, the study provides a promising new strategy for developing future quantum computers, quantum sensors and other powerful technologies based on the strange behavior of the quantum world.
