The most complex time crystal to date has been made inside a quantum computer

A time crystal has been created in a quantum computer that is more complex than any previously made. Exploring the properties of this unusual quantum arrangement strengthens the case for quantum computers as machines suitable for scientific discovery.

Typical crystals have atoms arranged in a specific repeating pattern in space, but time crystals are defined by a pattern that repeats itself in time instead. A time crystal repeatedly cycles through the same set of configurations and, barring harmful influences from its environment, should continue to cycle indefinitely.

This erratic movement initially made time crystals seem like a threat to the basic laws of physics, but over the past decade, researchers have created several in the lab. Now, Nicolas Lorente at the Donostia International Physics Center in Spain and his colleagues used an IBM superconducting quantum computer to create a time crystal of unprecedented complexity.

While most past studies have focused on one-dimensional time crystals, which can be likened to a neat array of atoms, the researchers set out to create a two-dimensional version. To do this, they used 144 superconducting qubits arranged in an intertwined pattern roughly like a honeycomb. Each qubit behaved much like a quantum mechanical spin, and the team could control how nearby qubits interacted with each other.

Changing these interactions over time is what gave rise to the time crystal, but the researchers could also program the interactions to have a more complex pattern of forces than in previous quantum computing experiments with time crystals.

The ability to achieve this new level of complexity has allowed the team to not only create a time crystal that is more complex than any previously produced using a quantum computer, but also begin to map the features of the entire qubit system and obtain its “phase diagram.” Completing a phase diagram is an important step in understanding the properties of a material – for example, the phase diagram of water reveals whether water is a liquid, solid or gas at a given temperature and pressure.

Jamie Garcia at IBM, who was not involved in the research, says the experiment may be the first of many steps that could eventually lead to quantum computers helping to design new materials based on a more complete picture of all the possible properties a quantum system can have, including odd ones like time crystals.

The model the researchers chose to emulate, which has a time crystal in its phase diagram, is already so complicated that conventional computers cannot simulate it without approximations. At the same time, all existing quantum computers suffer from errors, so researchers had to use these conventional methods to estimate where a quantum result might become unreliable. This alternation between approximate conventional methods and exact but error-prone quantum approaches could improve our understanding of many complex quantum models for materials going forward, Garcia says.

“Two-dimensional systems are practically very challenging to numerically simulate, so a large-scale quantum simulation with more than 100 qubits should provide an anchor point for future research,” he says. Biao Huang at the University of the Chinese Academy of Sciences. He says the new study represents an exciting experimental advance in several areas of the study of quantum matter. Specifically, it could help link time crystals that can be simulated on quantum computers with similar states that can be created in some types of quantum sensors, Huang says.

topics:

• quantum computing/
• quantum physics