One of the obstacles that has kept quantum computers on the distant horizon is the fact that quantum bits -- the building blocks with which they're made -- are prone to magnetic disturbances. Such "noise" can interfere with the work qubits do, but on Wednesday, scientists announced a new discovery that could help solve the problem.
Specifically, by tapping the same principle that allows atomic clocks to stay accurate, researchers at Florida State University’s National High Magnetic Field Laboratory (MagLab) have found a way to give qubits the equivalent of a pair of noise-canceling headphones.
The approach relies on what are known as atomic clock transitions. Working with carefully designed tungsten oxide molecules that contained a single magnetic holmium ion, the MagLab team was able to keep a holmium qubit working coherently for 8.4 microseconds -– potentially long enough for it to perform useful computational tasks.
“I know 8.4 microseconds doesn’t seem like a big deal,” said MagLab physicist Dorsa Komijani. “But in molecular magnets, it is a big deal, because it’s very, very long."
A paper describing the discovery will be published Thursday in the journal Nature.
One of the Holy Grails of modern applied physics, quantum computers are widely expected to open up a world of new possibilities. Whereas today’s computers rely on transistors to process bits of information in the form of binary 0s or 1s, quantum computing relies on atomic-scale qubits that can be simultaneously 0 and 1 -- a state known as a superposition that's far more efficient.
By offering exponential performance gains, quantum computers could have enormous implications for cryptography and computational chemistry, among many other fields.
MagLab's new discovery could put all this potential within much closer reach, but don't get too excited yet -- a lot still has to happen. Next, researchers need to take the same or similar molecules and integrate them into devices that allow manipulation and read-out of an individual molecule, Stephen Hill, director of the MagLab’s Electron Magnetic Resonance Facility, said by email.
"The good news is that parallel work by other groups has demonstrated that one can do this, although with molecules that do not have clock transitions," Hill said. "So it should be feasible to take the molecule we have studied and integrate it into a single-molecule device."
After that, the next step will be coming up with schemes involving multiple qubits that make it possible to address them individually and to switch the coupling between them on and off so that quantum logic operations can be implemented, he said.
That's still in the future, "but it is this same issue of scalability that researchers working on other potential qubit systems are currently facing," he added.
Magnetic molecules hold particular promise there because the chemistry allows self-assembly into larger molecules or arrays on surfaces, Hill explained. Those, in turn, could form the basis for a working device.