A research team including ones from Stanford and Google have created and observed a new phase of matter, popularly known as a time crystal. A huge global effort to engineer a computer capable of harnessing the power of quantum physics to carry out computations of unprecedented complexity. While formidable technological obstacles still stand in the way of creating such a quantum computer, today’s early prototypes are still capable of remarkable feats. For example, the creation of a new phase of matter called a “time crystal.” Just as a crystal’s structure repeats in space, a time crystal repeats in time and, importantly, does so infinitely and without any further input of energy – like a clock that runs forever without any batteries. The quest to realize this phase of matter has been a longstanding challenge in theory and experiment – one that has now finally come to fruition.
A team of scientists from Stanford University, Google Quantum AI, the Max Planck Institute for Physics of Complex Systems, and Oxford University detail their creation of a time crystal using Google’s Sycamore quantum computing hardware. For the team, the excitement of their achievement lies not only in creating a new phase of matter but in opening up opportunities to explore new regimes in their field of condensed matter physics, which studies the novel phenomena and properties brought about by the collective interactions of many objects in a system. (Such interactions can be far richer than the properties of the individual objects.)
Matteo Ippoliti, a postdoctoral scholar at Stanford and co-lead author of the work commented “the big picture is that we are taking the devices that are meant to be the quantum computers of the future and thinking of them as complex quantum systems in their own right and instead of computation, we’re putting the computer to work as a new experimental platform to realize and detect new phases of matter.”
The fascination about the time crystal
Some ingredients to make this time crystal are as follows: The physics equivalent of a fruit fly and something to kick it. The fruit fly of physics is the Ising model, a longstanding tool for understanding various physical phenomena – including phase transitions and magnetism – which consists of a lattice where each site is occupied by a particle that can be in two states, represented as a spin up or down. “Time-crystals are a striking example of a new type of non-equilibrium quantum phase of matter,” said Vedika Khemani, an assistant professor of physics at Stanford and a senior author of the paper. “While much of our understanding of condensed matter physics is based on equilibrium systems, these new quantum devices are providing us a fascinating window into new non-equilibrium regimes in many-body physics.”
Khemani and her collaborators, took the final step to time crystal success were working with a team at Google Quantum AI. Together, this group used Google’s Sycamore quantum computing hardware to program 20 “spins” using the quantum version of a classical computer’s bits of information, known as qubits. While this may sound suspiciously close to a “perpetual motion machine,” a closer look reveals that time crystals don’t break any laws of physics. Entropy – a measure of disorder in the system – remains stationary over time, marginally satisfying the second law of thermodynamics by not decreasing.
With the development of this plan for a time crystal and the quantum computer experiment that brought it to reality, many experiments by many different teams of researchers achieved various almost-time-crystal milestones. However, providing all the ingredients in the recipe for “many-body localization” (the phenomenon that enables an infinitely stable time crystal) had remained an outstanding challenge.)
Opportunities of Quantum Computers
The finite size and coherence time of the (imperfect) quantum device meant that their experiment was limited in size and duration – so that the time crystal oscillations could only be observed for a few hundred cycles rather than indefinitely – the researchers devised various protocols for assessing the stability of their creation. These included running the simulation forward and backward in time and scaling its size.
Co-author of the paper and director at the Max Planck Institute for Physics of Complex Systems says “It essentially told us how to correct for its errors, so that the fingerprint of ideal time-crystalline behavior could be ascertained from finite time observations.”
A new phase of matter is unquestionably exciting on a fundamental level. In addition, the fact that these researchers were able to do so points to the increasing usage of quantum computers for applications other than computing. “I am optimistic that with more and better qubits, our approach can become the main method in studying non-equilibrium dynamics,” said Pedram Roushan, a researcher at Google and senior author of the paper. “We think that the most exciting use for quantum computers right now is as platforms for fundamental quantum physics,” said Ippoliti.“With the unique capabilities of these systems, there’s hope that you might discover some new phenomenon that you hadn’t predicted.”