A team of physicists say they managed to create a new phase
of matter by shooting laser pulses reading out the Fibonacci sequence to a
quantum computer in Colorado. The matter phase relies on a quirk of the
Fibonacci sequence to remain in a quantum state for longer.

Just as ordinary matter can be in a solid, liquid, gas, or
superheated plasmic phase (or state), quantum materials also have phases. The
phase refers to how the matter is structured on an atomic level—the arrangement
of its atoms or its electrons, for example. Several years ago, physicists
discovered a quantum supersolid, and last year, a team confirmed the existence
of quantum spin liquids, a long-suspected phase of quantum matter, in a simulator.
The recent team thinks they’ve discovered another new phase.

Quantum bits, or qubits, are like ordinary computer bits in
that their values can be 0 or 1, but they can also be 0 or 1 simultaneously, a
state of ambiguity that allows the computers to consider many possible
solutions to a problem much faster than an ordinary computer. Quantum computers
should eventually be able to solve problems that classical computers can’t.

Qubits are often atoms; in the recent case, the researchers
used 10 ytterbium ions, which were controlled by electric fields and
manipulated using laser pulses. When multiple qubits’ states can be described
in relation to one another, the qubits are considered entangled. Quantum
entanglement is a delicate agreement between multiple qubits in a system, and
the agreement is dissolved the moment any one of those bits’ values is certain.
At that moment, the system decoheres, and the quantum operation falls apart.

A big challenge of quantum computing is maintaining the
quantum state of qubits. The slightest fluctuations in temperature, vibrations,
or electromagnetic fields can cause the supersensitive qubits to decohere and
their calculations to fall apart. Since the longer the qubits stay quantum, the
more you can get done, making computers’ quantum states persist for as long as
possible is a crucial step for the field.

In the recent research, pulsing a laser periodically at the
10 ytterbium qubits kept them in a quantum state—meaning entangled—for 1.5
seconds. But when the researchers pulsed the lasers in the pattern of the
Fibonacci sequence, they found that the qubits on the edge of the system
remained in a quantum state for about 5.5 seconds, the entire length of the
experiment (the qubits could have remained in a quantum state for longer, but
the team ended the experiment at the 5.5-second mark). Their research was
published this summer in Nature.

You can think of the Fibonacci sequence laser pulses as two
frequencies that never overlap. That makes the pulses a quasicrystal: a pattern
that has order, but no periodicity.

“The key result in my mind was showing the difference
between these two different ways to engineer these quantum states and how one
was better at protecting it from errors than the other,” said study co-author
Justin Bohnet, a quantum engineer at Quantinuum, the company whose computer was
used in the recent experiment.

The Fibonacci sequence is a numeric pattern in which each
number is the sum of the two previous numbers (so 1, 1, 2, 3, 5, 8, 13, and so
on). Its history goes back over 2,000 years and is connected to the so-called
golden ratio. Now, the unique series may have quantum implications.

“It turns out that if you engineer laser pulses in the
correct way, your quantum system can have symmetries that come from time
translation,” said Philipp Dumitrescu, the paper’s lead author and a quantum
physicist who conducted the work while at the Flatiron Institute. A
time-translation symmetry means that an experiment will yield the same result,
regardless of whether it takes place today, tomorrow, or 100 years from now.

“What we realized is that by using quasi-periodic sequences
based on the Fibonacci pattern, you can have the system behave as if there are
two distinct directions of time,” Dumitrescu added.

Shooting the qubits with laser pulses with a periodic (a
simple A-B-A-B) pattern didn’t prolong the system’s quantum state. But by
pulsing the laser in a Fibonacci sequence (A-AB-ABA-ABAAB, and so on), the
researchers gave the qubits a non-repeating, or quasi-periodic, pattern.

It’s similar to the quasicrystals from the Trinity nuclear
test site, but instead of being a three-dimensional quasicrystal, the
physicists made a quasicrystal in time. In both cases, symmetries that exist at
higher dimensions can be projected in a lower dimension, like the tessellated
patterns in a two-dimensional Penrose tiling.

“With this quasi-periodic sequence, there’s a complicated
evolution that cancels out all the errors that live on the edge,” Dumitrescu
said in a Simons Foundation release. By on the edge, he’s referring to the
qubits farthest from the center of their configuration at any one time.
“Because of that, the edge stays quantum-mechanically coherent much, much
longer than you’d expect.” The Fibonacci-pattern laser pulses made the edge
qubits more robust.

More robust, longer-lived quantum systems are a vital need
for the future of quantum computing. If it takes shooting qubits with a very
specific mathematical rhythm of laser pulses to keep a quantum computer in an
entangled state, then physicists had better start blasting.

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