Microwaves unlock power of uncontrollable diamond qubits in quantum leap

Researchers from Germany’s Karlsruhe Institute of Technology (KIT) have devised a method to precisely control diamond qubits using microwaves.

In case you’re wondering what is a diamond qubit, here’s a simple explanation —When a tin atom replaces a carbon atom in a diamond lattice, it leads to the creation of tin vacancy (SnV) centers.

The SnV centers are defects with exceptional optical and electronic properties, and therefore they can be used as qubits. Since these qubits result from defects in diamond lattices, they are called diamond qubits .

However, to harness the potential of diamond qubits, one must increase their coherence time, the time duration for which qubits can store information , and remain stable. This is where the new study could be of great help.

It reveals a way to control and stabilize qubits. “Being able to control qubits and keep them stable enough to exploit their characteristics in practical applications will be crucial to the feasibility of developing efficient and scalable quantum computers,” the study authors note .

Keeping diamond qubits in check

Diamond qubits come with many perks compared to other types of qubits . For instance, since they exist in a solid state at room temperature, the quantum operations they perform consume less power.

Also, these qubits are inside a robust diamond lattice, so they are less likely to be affected by noise and other physical factors.

Plus, they can easily connect with other diamond qubits using light, and last but not least, they tend to offer long coherence time — making them a great choice for both quantum computing and quantum sensing applications.

To harness these abilities of diamond qubits, the study authors conducted an experiment. They employed microwaves to govern the electron spin of SnV centers and tried to control the defects in diamonds with superconducting waveguides.

Superconducting waveguides are structures that guide electromagnetic waves (for example, microwave signals), without any resistance. They are made from superconducting materials , which means they can carry electrical signals with zero energy loss when cooled to very low temperatures.

The experiment turned out to be successful. “We were able to increase the coherence times of the diamond SnV centers to as long as ten milliseconds – a major improvement,” Jeremias Resch, one of the study authors and a researcher at KIT.

Controlling diamond defects without heat

Extended coherence time isn’t the only achievement of the experiment. The study authors also showed for the first time that diamond qubits can be effectively regulated with superconducting waveguides, with no heat generated in the process.

“That’s very important because these defects are generally investigated at very low temperatures near absolute zero. Higher temperatures would make the qubits useless,” Ioannis Karapatzakis, lead study author and a professor at KIT, said.

This study reveals a practical way to control qubits and keep them stable . The researchers now look forward to connecting two or more quantum computers by converting qubit quantum states into photons.

“Our results on controlling tin-vacancy centers in diamonds offer the potential for an important breakthrough in the future development of secure and efficient quantum communication,” Resch added.

The study is published in the journal Physical Review X .