A Strange Brand-New Phase Of Matter Developed In Quantum Computers Acts Like It Has Two-Time Dimensions

By shining a laser pulse series inspired by the Fibonacci numbers at atoms inside a quantum computer, physicists have produced a remarkable, never-before-seen phase of matter. The phase has the advantages of two-time dimensions despite there still being just one particular flow of time, as the physicists report on July 20 in Nature.

This mind-bending property offers a desired advantage: Information stored in the phase is even more protected against errors than with different setups currently utilized in quantum computers. As a result, the data may exist without obtaining garbled for a lot longer, an important milestone for making quantum computing viable, states study lead author Philipp Dumitrescu.

The technique’s use of an “additional” time dimension “is an entirely different method of thinking about phases of matter,” states Dumitrescu, that worked on the project as a study fellow at the Flatiron Institute’s Center for Computational Quantum Physics in New York City. “I have been working on these concept ideas for over 5 yrs, and seeing them come to be realized in experiments is exciting”.

Dumitrescu spearheaded the study’s theoretical part with Andrew Potter of the University of British Columbia in Vancouver, Romain Vasseur of the College of Massachusetts, Amherst, and Ajesh Kumar of the College of Texas at Austin. The experiments were conducted on a quantum computer at Quantinuum in Broomfield, Colorado, by a group led by Brian Nyenhuis.

The workhorses of the group’s quantum computer are 10 atomic ions of an element called ytterbium. Each ion is independently held and controlled by electric fields created by an ion trap and can be adjusted or determined by using laser pulses.

Each of those atomic ions works as what scientists call a quantum bit, or “qubit”. Whereas conventional computers quantify information in bits (each representing a 0 or a 1), the qubits used by quantum computers take advantage of the strangeness of quantum mechanics to keep much more data.

Just as Schrödinger’s cat pet is both dead and active in its box, a qubit can be a zero, a 1, or a mashup– or “superposition”— of both. That extra information density and the means qubits communicate with one another guarantee to enable quantum computer systems to take on computational issues much beyond the reach of conventional computers.

There is a huge issue, though: Just as peeking in Schrödinger’s box seals the cat’s fate, so does interact with a qubit. Furthermore, that interaction does not also have to be deliberate. “Even if you maintain all the atoms under tight control, they can shed their quantumness by talking to their environment, warning up or interacting with things in methods you really did not strategy,” Dumitrescu says. “In practice, experimental tools have several sources of error that can degrade comprehensibility after simply a few laser pulses”.

The difficulty, therefore, is to make qubits more robust. To do that, physicists can utilize “symmetries,” essentially properties that hold up to change. (A snowflake, for example, has rotational symmetry because it looks the same when rotated by 60 degrees.)

One means is adding time symmetry by blasting the atoms with rhythmic laser pulses. This strategy helps; however, Dumitrescu and his collaborators wondered if they could go further. So instead of just one-time symmetry, they aimed to add 2 by using ordered, however non-repeating laser pulses.

The best method to understand their approach is by considering something else ordered yet non-repeating: “quasicrystals”. A specific crystal has a regular, repeating structure, like the hexagons in a honeycomb. A quasicrystal still has an order, but its patterns never repeat. (Penrose tiling is one instance of this.) A lot more mind-boggling is that quasicrystals are crystals from higher dimensions projected or squished down into lower dimensions. Those higher dimensions can even be past physical space’s three dimensions: A 2D Penrose tiling, for instance, is a projected piece of a five-D lattice.

For the qubits, Dumitrescu, Vasseur, and Potter proposed in 2018 the creation of a quasicrystal in time rather than space. Whereas a periodic laser pulse would alternate (A, B, A, B, A, B, etc.), the researchers produced a quasi-periodic laser-pulse regimen based on the Fibonacci sequence. In such a series, each part of the sequence is the sum of the two previous parts (A, AB, ABA, ABAAB, ABAABABA, etc.).

This adjustment, just like a quasicrystal, is ordered without repeating. Moreover, akin to a quasicrystal, it is a 2D pattern squashed into a single dimension. That dimensional flattening theoretically results in two-time symmetries instead of just one: The system essentially gets a bonus proportion from a nonexistent extra time dimension.

Actual quantum computers are incredibly delicate experimental systems, though, so whether the advantages promised by the concept would endure in real-world qubits remained unproven.

Utilizing Quantinuum’s quantum computer, the experimentalists put the theory to the test. They pulsed laser light at the computer’s qubits both periodically and utilizing the sequence based on the Fibonacci numbers. The focus was on the qubits at either end of the ten-atom lineup; that is where the study researchers expected to see the new phase of matter experiencing two-time symmetries at once.

In the routine test, the edge qubits stayed quantum for around 1.5 seconds– already an impressive length given that the qubits were interacting hardly with one another. With the quasi-periodic pattern, the qubits remained quantum for the whole experiment length, concerning 5.5 secs. That is since the extra time symmetry supplied more protection, Dumitrescu states.

“With this quasi-periodic sequence, there is a complicated evolution that cancels out all the errors that live on the edge”, he says. “Because of that, the side remains quantum-mechanically systematic much longer than you would expect”.

Though the findings show that the new phase of matter can act as long-term quantum data storage, the study researchers still require to functionally integrate the stage with the computational side of quantum computing. “We have this straight, tantalizing application, but we need to find a way to hook it into the estimations,” Dumitrescu says. “That is an open problem we are working on”.

Reference:

Philipp Dumitrescu, Dynamical topological phase realized in a trapped-ion quantum simulator, Nature (2022). DOI: 10.1038/s41586-022-04853-4. www.nature.com/articles/s41586-022-04853-4

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