The road to quantum supremacy is complicated by a fabulous challenge – how to wear a cloud without changing its shape?
The potential solution sounds almost as fantastic as the problem. You can make the cloud dance as it travels to the beat of a unique material known as a time crystal.
Krzysztof Giergiel and Krzysztof Sacha of the Jagiellonian University in Poland and Peter Hannaford of Swinburne University of Technology in Australia propose a new kind of “time” circuit that can handle the task of preserving the nebulous states of qubits as they drift through storms of quantum logic .
In contrast to descriptions of objects as having well-defined locations and motions, the same-particle quantum perspective describes features such as its position, momentum, and spin as fuzzy probabilities.
This “cloud” of possibilities is best understood in isolation. After the particle interacts with its environment, its probability distribution changes like a runner’s chances of 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 use the propagation of uncertainties in a particle to quickly 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 keeping this quantum cloud of possibilities—called a qubit—coherent for as long as possible. With every bump, every electromagnetic whiff comes an increased risk of mistakes that spoil the number crunching process.
Practical quantum computers require hundreds, if not thousands, of qubits to remain intact for extended periods, making a full-scale system a monumental challenge.
Researchers have looked at various ways to make quantum computing more stable, from blocking individual qubits to keep 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 conducted by the baton of a very strange kind of wire.
Time crystals are materials that transform into repeating patterns over time. Theorized as a curiosity just over a decade ago, versions of these “ticking” systems have since been developed using the gentle nudge of a laser and ultracold clusters of atoms, where bursts of light send particles into periodic oscillations that defy the laser’s timing.
In a paper available on the arXiv peer-review server, the trio of physicists propose using the time crystal’s unique periodicity as the basis for a new kind of “time-tronics” scheme. Used to guide the delicate waves of vast numbers of information-laden qubits, this periodicity can help reduce the random collisions that are responsible for many errors.
Such a temporal chain of constantly moving qubits would make it easy to guide almost any of the computer’s particles into the path of another, entangling their quantum capabilities in useful rather than error-inducing ways.
Although 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 pulse could provide an “orchestra” for the qubits to dance to.
Translating the idea into a practical, full-scale quantum computer will require years of innovation and experimentation, if it works at all.
Still, now that we know that at least some types of time crystals exist and can be used for practical purposes, the challenge of wearing a cloud just might not be such a fairytale quest after all.
This study is available on the arXiv peer review server.
