Physicists observed a new phase of matter in a quantum computer after pulsing light on its qubits in a manner inspired by the Fibonacci series.
This bizarre quirk of quantum mechanics behaves as though it had two time dimensions, rather than one; a property that experts say makes qubits more durable, allowing them to remain stable for the duration of the experiment.
Quantum coherence refers to this steadiness, which is one of the primary aims of an error-free quantum computer — and also one of the most difficult to attain.
According to the lead author of a new publication explaining the phenomena, computational quantum physicist Philipp Dumitrescu of the Flatiron Institute, the work represents “a whole different way of thinking about phases of matter.”
“I’ve been working on these theory concepts for over five years, and it’s thrilling to see them realised in trials.”
The basis of quantum computing is qubits, the quantum version of computer bits. However, while bits process information in one of two states, 1 or 0, qubits can concurrently exist in both states, a phenomenon known as quantum superposition.
Under the correct conditions, the mathematical aspect of this superposition can be immensely potent from a computational standpoint, making problem-solving a breeze.
But the hazy, uncertain quality of a group of qubits also depends on the relationship between their uncertain states, which is known as entanglement.
Infuriatingly, qubits can become entangled with virtually everything in their environment, leading to mistakes. The more fragile a qubit’s fuzzy state is (or the more disorder there is in its environment), the greater the possibility that it will lose its coherence.
Improving coherence to the point of viability is expected to require a multi-tactic approach in order to overcome a significant barrier preventing the development of a functional quantum computer – every little bit counts.
Dumitrescu noted, “Even if you keep all the atoms under tight control, they can lose their quantumness by communicating with their surroundings, heating up, or interacting with things in unanticipated ways.”
In actuality, experimental systems contain several error sources that can weaken coherence after only a few laser pulses.
Enforcing symmetry is one method for preventing decoherence in qubits. Simply rotating a simple square by ninety degrees results in the same shape. This symmetry safeguards it against rotational impacts.
The tapping of qubits with equally spaced laser pulses maintains a symmetry based on time rather than space. Dumitrescu and his colleagues wished to determine whether this impact could be amplified by introducing asymmetrical quasiperiodicity as opposed to symmetrical periodicity.
Theoretically, this would result in the addition of two time symmetries, one effectively concealed within the other.
The concept was derived on earlier work by the team that advocated the creation of a quasicrystal in time, as opposed to space. Whereas a crystal is composed of a symmetrical lattice of atoms that repeats in space, similar to a square grid jungle gym or a honeycomb, the pattern of atoms on a quasicrystal is non-repeating, yet nevertheless organised, like a Penrose tiling.
The experiment was conducted on a cutting-edge commercial quantum computer designed by Quantinuum, a business specialising in quantum computing. This beast uses 10 ytterbium atoms for its qubits (one of the elements of choice for atomic clocks). These atoms are contained within an electrical ion trap, from which laser pulses can be used to manipulate or measure them.
Dumitrescu and his coworkers devised a sequence of laser pulses based on the Fibonacci sequence, in which each segment is the sum of the two preceding segments. This produces a sequence that is ordered but does not repeat, similar to a quasicrystal.
Mathematically, quasicrystals are lower-dimensional portions of higher-dimensional lattices. A Penrose tiling is a slice of a five-dimensional hypercube in two dimensions.
Similarly, the laser pulses of the team can be viewed as a one-dimensional representation of a two-dimensional pattern. This meant that qubits may theoretically be subject to two time symmetries.
The scientists put its work to the test by flashing lasers onto an array of ytterbium qubits, first in a symmetrical sequence and then quasiperiodically. The coherence of the two qubits at each end of the trap was then measured.
For the periodic sequence, the qubits exhibited 1.5 seconds of stability. For the length of the experiment, they stayed steady for the entirety of the quasiperiodic sequence.
According to the researchers, the new temporal symmetry provides another degree of protection against quantum decoherence.
Dumitrescu stated, “Within this quasi-periodic sequence, there is a complex evolution that wipes out all errors that live on the edge.”
“As a result, the edge retains quantum-mechanical coherence for an extraordinarily extended time.”
According to the researchers, the work is not yet suitable for integration into functional quantum computers, but it is a significant step in the right direction.