The path to quantum supremacy is complicated by a fairy tale challenge – how do you carry a cloud without changing its shape?
The potential solution sounds almost as fantastical as the problem. You could guide the cloud to dance as it travels, to the beat of a unique material known as a time crystal.
Krzysztof Giergiel and Krzysztof Sacha from Jagiellonian University in Poland and Peter Hannaford from Swinburne University of Technology in Australia propose a novel kind of 'time' circuit might be up to the task of preserving the nebulous states of qubits as they're carried through tempests of quantum logic.
Unlike descriptions of objects as having clearly defined locations and movements, a quantum perspective of the same particle describes features like its position, momentum, and spin as a blur of likelihoods.
This 'cloud' of possibilities is best understood in isolation. Once the particle interacts with its environment its spread of possibilities changes like the odds of a runner winning the 100-meter sprint at the Olympics, until finally only one outcome is observed.
Just as a classical computer can use the binary states of particles as 'on-off' switches in logic gates, quantum computers can theoretically exploit the spread of uncertainties in a particle to rapidly solve their own kinds of algorithms, many of which would be impractical or even impossible to solve the old-fashioned way.
The challenge lies in preserving the coherence of that quantum cloud of possibility – referred to as a qubit – for as long as possible. With every bump, every electromagnetic breeze, comes an increased risk of errors that ruin the number-crunching process.
Practical quantum computers require hundreds, if not thousands of qubits to remain intact for extensive periods, making a full-scale system a monumental challenge.
Researchers have sought a variety of ways to make quantum computing more robust, either by locking away individual qubits to protect them from decoherence to building safety nets around them.
Now physicists Giergiel, Sacha, and Hannaford have described a new approach that turns quantum computers into a qubit symphony guided by the baton of one very strange kind of conductor.
Time crystals are materials that transform in repeated patterns over time. Theorized as curiosities just over a decade ago, versions of these 'ticking' systems have since been developed using the gentle nudge of a laser and ultra-cold clusters of atoms, where bursts of light send particles into periodical swings that defy the laser's timing.
In a paper available on the pre- peer review server arXiv, the trio of physicists proposes using the unique periodicity of a time crystal as the basis for a new kind of "time-tronics" circuitry. Used to guide the delicate waves of vast numbers of information-laden qubits, this periodicity could help reduce the accidental collisions that are responsible for many errors.
Such a temporal circuit of constantly drifting qubits would make it easier to direct just about any of the computer's particles into another's path, entangling their quantum possibilities in useful rather than error-imposing ways.
While the proposal remains purely theoretical, the team showed how the physics of groups of potassium ions cooled to near absolute temperatures and directed by a laser's pulse could provide an 'orchestra' for qubits to waltz to.
Translating the idea into a practical, full-scale quantum computer would require years of innovation and experimentation, if it works at all.
Yet now that we know at least some kinds of time crystal exist and can be used for practical purposes, the challenge of carrying a cloud just might not be such a fairy tale quest after all.
This study is available on the pre-peer review server arXiv.