The road to quantum supremacy is complicated by fairy-tale challenges: How do you transport a cloud without changing its shape?
The potential solution seems as fantastical as the problem: making moving clouds dance to the beat of a unique material called time crystals.
Krzysztof Giergiel and Krzysztof Sacha of the Jagiellonian University in Poland, and Peter Hannaford of Swinburne University of Technology in Australia, propose that a new kind of “time” circuit might be able to meet the challenge of preserving the fuzzy states of qubits as they are carried through the whirlwind of quantum logic.
Unlike describing an object’s position and motion as clearly defined, a quantum view of the same particle describes its position, momentum, spin, and other features as a blur of possibilities.
This “cloud” of possibilities is best understood in isolation: as the particle interacts with its environment, the spread of possibilities changes, like the probability of a runner winning the Olympic 100-meter sprint, until ultimately only one outcome is observed.
Just as classical computers can use the binary state of a particle as an “on/off” switch in a logic gate, quantum computers could theoretically exploit the spread of uncertainty in particles to rapidly solve algorithms that are unsolvable or impossible to solve using classical methods.
The challenge is to maintain the coherence of the quantum cloud of possibilities, called qubits, for as long as possible. Every shock, every electromagnetic wind, increases the risk of an error that could ruin the numerical process.
A practical quantum computer would require hundreds, or even thousands, of qubits to remain intact for extended periods of time, making building a full-scale system an enormous challenge.
Researchers have explored various ways to make quantum computing more robust, such as by locking individual qubits to protect them from decoherence or by building safety nets around the qubits.
Now, physicists Györgyel, Sacha and Hannaford have described a new approach that turns a quantum computer into a symphony of qubits guided by the baton of a very strange conductor.
Time crystals are materials that exhibit repeating, shifting patterns over time. They were theorized as an unusual phenomenon just over a decade ago, but since then, various versions of these “ticking” systems have been developed using the gentle stimulation of lasers and cryogenic atomic clusters, in which bursts of light send particles into periodic oscillations that counter the timing of the laser.
In the paper In the paper, published on the pre-peer-review server arXiv, the three physicists propose using the unique periodicity of time crystals as the basis for a new kind of “timetronic” circuit. Harnessing this periodicity to direct the delicate waves of vast numbers of information-packed quantum bits could help reduce the accidental collisions that are the source of many errors.
Such time circuits of constantly drifting qubits could make it easy to steer almost any particle in a computer onto the path of another, entangling quantum possibilities in useful rather than error-imposing ways.
While the proposal remains entirely theoretical, the team has demonstrated that the physics of swarms of potassium ions cooled to near absolute temperatures and directed by laser pulses could provide an “orchestra” for the quantum bits to waltz around.
Translating this idea into a practical, full-scale quantum computer, if it even works, will require years of innovation and experimentation.
But now that we know that at least some types of time crystals exist and can be used for practical purposes, maybe the challenge of transporting clouds isn’t such a fairy-tale quest after all.
This research is publicly available on a pre-peer review server arXiv.