Researchers claim they have made a breakthrough in quantum communications thanks to a new diamond stretching technique that they say greatly increases the temperature at which qubits can remain entangled, while also allowing them to be controlled with microwaves. Quantum networking is an emerging field that exploits exotic quantum phenomena to send and receive information. These networks will be impossible to hack and will use quantum entanglement to cover large distances, creating pairs of qubits that map each other's quantum states without any physical connection.
Diamond-based qubits are able to maintain their entangled state for significant periods of time, but only if they are kept incredibly cold—just a hair above absolute zero. This limits their usefulness because it means installing a huge, energy-intensive cooling device at every node of the quantum network.
But researchers from the University of Chicago, Argonne National Laboratory and the University of Cambridge say they have found a breakthrough solution by stretching diamond to change its molecular lattice.
The team laid a thin film of diamond on hot glass. As glass cools, it shrinks -- but less than diamond, exerting stretching forces on a molecular level. According to the research team, the change in the diamond's structure was "minimal" but the effect was significant.
The temperatures at which these stretched diamond qubits remain entangled rise from above absolute zero to 4 Kelvin (-452°F, -269°C). Obviously, this is still a very low temperature, but it's much easier to get to 4 Kelvin than to go below 1 Kelvin. The equipment involved is much cheaper and more compact.
"In terms of infrastructure and operating costs, it's an order of magnitude difference," said Alex High, an assistant professor at the Pritzker School of Molecular Engineering. "This technology can significantly increase the operating temperature of these systems, thereby greatly reducing the resource intensity of running these systems."
"Today, most qubits require a special refrigerator the size of a room and a highly trained team to run it," Hai said. "So if you envision an industrial quantum network where you have to build a qubit every 5 or 10 kilometers [3 or 6 miles], now you're talking about quite a bit of infrastructure and labor."
The stretched diamond structure also reduces noise and improves the fidelity of information passing through the system by 99 percent, because these qubits can be controlled with microwaves, whereas previous versions required light in the spectrum, which introduced considerable errors.
"Typically, if a system has a long coherence lifetime, it's because it's good at 'ignoring' outside interference - which means it's harder to control because it's resisting interference," said Xinghan Guo, a doctoral student and first author of the paper. "It's very exciting that through very fundamental innovations in materials science, we can bridge this conundrum."
Mete Atature, professor of physics at the University of Cambridge and co-author of the study, added: "The path is clear to develop tin-vacancy centers for diamond-based quantum network devices through a combination of extended coherence times and feasible microwave quantum control."
The paper was published in the journal Physical Review X.