New phase of matter could protect quantum computers against errors

The researchers still need to find a way to integrate the phase with the computational side of quantum computing.

An inside look at an ion trap within Quantinuum's quantum computer, which processes data using trapped-ion technology, Broomfield, US in this handout picture from 2019 (photo credit: Quantinuum/Handout via REUTERS)
An inside look at an ion trap within Quantinuum's quantum computer, which processes data using trapped-ion technology, Broomfield, US in this handout picture from 2019
(photo credit: Quantinuum/Handout via REUTERS)

A new phase of matter created with rhythmic laser pulses could use the advantage of a second dimension of time in order to protect quantum computers from errors they're prone to, according to a new peer-reviewed study published in Nature late last month.

Quantum computers work using qubits, the quantum computer equivalent to the bit used in standard computing. While a bit has a value of either a one or zero, a qubit can have both at the same time, leading to faster computing.

While the unique ability of qubits to store more data than the traditional bit allows quantum computers to compute things that conventional computers can't, qubits are highly volatile and can lose their quantum characteristics by heating up or interacting with other things in their environment. This volatility creates many possible sources for errors.

“One problem in quantum computing is that if you have qubits that are coupled to each other, but you didn’t mean them to be, they can accidentally entangle themselves,” said Dr. Andrew Potter, an assistant professor in UBC’s Department of Physics and Astronomy. “That entanglement can cause errors, or crosstalk, between the qubits. These errors represent a significant barrier to achieving a functional quantum computing platform.”

Scientists from the Flatiron Institute, the University of British Columbia, the University of Massachusetts, Amherst, and the University of Texas at Austin explored using "symmetries" (properties that hold up to change) in order to make the qubits more robust.

THE ‘BIG BEN’ bell chimes yesterday for the last time in four years ahead of restoration work on the Elizabeth Tower, which houses the Great Clock and the Big Ben bell. (credit: REUTERS)THE ‘BIG BEN’ bell chimes yesterday for the last time in four years ahead of restoration work on the Elizabeth Tower, which houses the Great Clock and the Big Ben bell. (credit: REUTERS)

The scientists realized they could use time symmetry by blasting the atoms with rhythmic laser pulses to make the qubits somewhat more robust, but decided to go even further by adding an additional time symmetry on top by using laser pulses in order, but non-repeating patterns.

The researchers went with the Fibonacci sequence - a sequence in which each part is the sum of the two previous parts - in order to create a periodic, alternating laser pulse that was ordered but did not repeat its pattern.

Using a quantum computer at Quantinuum in Broomfield, Colorado, the scientists pulsed laser light at the computer's qubits both periodically and with the sequence based on the Fibonacci sequence.

With the periodic laser pulses which created one-time symmetry, the qubits being observed stayed stable for about 1.5 seconds. With the Fibonacci sequence pulses that created two-time symmetries, the qubits stayed stable for nearly four times as long, about 5.5 seconds, the full length of the test conducted.

"A completely different way of thinking about phases of matter."

Philipp Dumitrescu of the Flatiron Institute

Lead author Philipp Dumitrescu of the Flatiron Institute called the approach a "completely different way of thinking about phases of matter," in a press statement.

“With this quasi-periodic sequence, there’s a complicated evolution that cancels out all the errors that live on the edge,” he added. “Because of that, the edge stays quantum-mechanically coherent much, much longer than you’d expect.”

While the new phase of matter can help with long-term quantum information storage, the researchers still need to find a way to integrate the phase with the computational side of quantum computing.

“We have this direct, tantalizing application, but we need to find a way to hook it into the calculations,” said Dumitrescu. “That’s an open problem we’re working on.”

Other timely quantum discoveries

The new research comes just months after a series of studies into time crystals, a phase of matter which repeats in time, similar to how a regular crystal's structure repeats in space. What that means is that the particles in the crystal perpetually switch between two states without requiring the input of more energy and without losing any energy.

These crystals are the first objects to break what is known as "time-translation symmetry," a rule in physics that says that a stable object will remain unchanged throughout time. Time crystals avoid this rule, being both stable and ever-changing.

So, for example, ice when stable will remain ice and will only change when temperature or another factor makes it unstable. A time crystal would change even when in its ground state, acting differently than all other phases of matter.

Last year, scientists from Stanford and the Max Planck Institute for Physics of Complex Systems, as well as scientists at QuTech, a collaboration between the Delft University of Technology and the Netherlands Organisation for Applied Scientific Research (TNO), figured out for the first time how to create these theoretical crystals.

In June, scientists from Lancaster University, Royal Holloway London, Landau Institute and Aalto University in Helsinki succeeded in linking two-time crystals in a two-level quantum system, in which two independent quantum states were able to occupy both states simultaneously.

These two-level quantum systems could be used like a qubit, the quantum computer equivalent to the bit used in standard computing. While a bit has a value of either a one or zero, a qubit can have both at the same time, leading to faster computing.