Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Appreciating the classical elegance of time crystals

20.09.2019

Physicists at ETH Zurich have developed a versatile framework for studying periodically driven systems, providing a unifying platform to explore so-called 'time crystals' in both the classical and the quantum regime

In a crystal, atoms are highly ordered, occupying well-defined locations that form spatial patterns. Seven years ago, the 2004 Physics Nobel laureate Frank Wilczek pondered the possibility of a 'time analogue of crystalline spatial order' - systems that display sustained periodic temporal modulations in their lowest-energy state.


Quasi potentials of six parametric oscillators with weak all-to-all coupling. Stable solutions are located at the minima. The balls indicate the symmetric solution, where all oscillators are in phase. (Screenshot from accompanying animation)

Credit: ETH Zurich/D-PHYS Toni Heugel


Quasi potentials of six parametric oscillators with weak all-to-all coupling. Stable solutions are located at the minima. The balls indicate the symmetric solution, where all oscillators are in phase. The Hamiltonian H govern the motion of the system has period T, while the solution itself has period 2T. This discrete time translation symmetry breaking makes the system a discrete time crystal.

Credit: ETH Zurich/D-PHYS Toni Heugel

The concept of such structures with an oscillating ground state is highly intriguing. Alas, not long after the idea has been published, it was proven that such time crystals are not possible without breaking fundamental laws of physics.

Not all was lost, though. Subsequent theory work suggested that when quantum many-body systems are periodically driven, then new persistent time correlations emerge that are evocative of Wilczek's time crystals.

These driven systems were dubbed 'discrete time crystals', and in 2017 the first experimental realizations of such states were reported in ensembles of coupled particles (ions, electrons and nuclei) that display quantum-mechanical properties.

A not-so-brief history of time crystals

Before long, astute observers spotted distinct similarities between discrete time crystals in quantum systems and so-called parametric resonators, a concept in classical physics reaching back to work by Michael Faraday in 1831. The connection between these two bodies of work remained, however, opaque.

Now, a new framework goes a long way towards lifting the ambiguities surrounding the similarities between periodically driven classical and quantum systems.

Writing in an article published today in the journal Physical Review Letters, Toni Heugel, a PhD student in the Department of Physics at ETH Zurich, and Matthias Oscity, a Master student there, working with Dr. Ramasubramanian Chitra and Prof. Oded Zilberberg form the Institute for Theoretical Physics and with Dr. Alexander Eichler from the Laboratory for Solid State Physics, report theoretical and experimental work that establishes how discrete time crystals can be generated that, on the one hand, require no quantum mechanical effects and, on the other hand, display genuine many-body effects, which is a characteristic of discrete time crystals reported in quantum systems.

Many ways to subharmonic frequencies

There is one obvious similarity between classical parametric resonators and experimentally realized discrete time crystals in quantum many-body systems: Both display emergent dynamics at frequencies that are fractions of the drive frequency. In the context of discrete time crystals, the emergence of oscillations at such subharmonic frequencies breaks the temporal periodicity of the driven system, providing a form of 'time analogue' to crystalline spatial order, where the symmetry of space is broken.

In classical parametrically driven systems, subharmonic frequencies appear in more familiar ways: A child on a swing, for instance, modifies the centre of gravity at twice the frequency of the resulting oscillation; or the ponytail of a runner oscillates at half the frequency of the vertical head movement.

But do these dissimilar phenomena have anything to do with one another? Yes, say the ETH physicists. In particular, they pinpoint where many-body aspects appear in classical systems. To do so, they considered classical nonlinear oscillators with tunable coupling between them.

Unifying framework for periodically driven classical and quantum systems

It is well known that for certain driving frequencies and strengths, parametric oscillators become unstable and then undergo a so-called period-doubling bifurcation, beyond which they oscillate at half their driving frequency. Heugel, Oscity and their colleagues explore what happens as several such oscillators are coupled together. In calculations as well as in experiments -- using two strings with variable coupling between them -- they find two distinct regimes.

When the coupling is strong, the two-string system moves collectively, recreating in essence the movements of the child on a swing or the ponytail of a runner. However, in the case of weak coupling between the strings, the dynamics of each string is close to that displayed by the uncoupled system. As a consequence, the coupled oscillators do not bifurcate collectively but bifurcate individually at slightly different parameters of the drive, leading to richer overall dynamics, which gets ever more complex as the systems get larger.

The ETH researchers argue that such weakly-coupled modes are similar to the ones that emerge in quantum many-body systems, implying that their framework might explain the behaviours seen experimentally in these systems. Moreover, the new work prescribes general conditions for generating classical many-body time crystals. These could ultimately be used to both interpret and explore features of their quantum counterparts.

Taken together, these findings therefore provide a powerful unifying framework for periodically driven classical and quantum systems displaying dynamics at emergent subharmonic frequencies -- systems that have been so far described in very different contexts, but might be not that dissimilar after all.

Media Contact

Andreas Trabesinger
trabi@ethz.ch
41-791-289-860

 @ETH_physics

https://www.phys.ethz.ch/ 

Andreas Trabesinger | EurekAlert!
Further information:
https://www.phys.ethz.ch/news-and-events/d-phys-news/2019/09/appreciating-the-classical-elegance-of-time-crystals.html
http://dx.doi.org/10.1103/PhysRevLett.123.124301

More articles from Physics and Astronomy:

nachricht Double layer of graphene helps to control spin currents
18.10.2019 | University of Groningen

nachricht Analysis of Galileo's Jupiter entry probe reveals gaps in heat shield modeling
17.10.2019 | American Institute of Physics

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Solving the mystery of quantum light in thin layers

A very special kind of light is emitted by tungsten diselenide layers. The reason for this has been unclear. Now an explanation has been found at TU Wien (Vienna)

It is an exotic phenomenon that nobody was able to explain for years: when energy is supplied to a thin layer of the material tungsten diselenide, it begins to...

Im Focus: An ultrafast glimpse of the photochemistry of the atmosphere

Researchers at Ludwig-Maximilians-Universitaet (LMU) in Munich have explored the initial consequences of the interaction of light with molecules on the surface of nanoscopic aerosols.

The nanocosmos is constantly in motion. All natural processes are ultimately determined by the interplay between radiation and matter. Light strikes particles...

Im Focus: Shaping nanoparticles for improved quantum information technology

Particles that are mere nanometers in size are at the forefront of scientific research today. They come in many different shapes: rods, spheres, cubes, vesicles, S-shaped worms and even donut-like rings. What makes them worthy of scientific study is that, being so tiny, they exhibit quantum mechanical properties not possible with larger objects.

Researchers at the Center for Nanoscale Materials (CNM), a U.S. Department of Energy (DOE) Office of Science User Facility located at DOE's Argonne National...

Im Focus: Novel Material for Shipbuilding

A new research project at the TH Mittelhessen focusses on the development of a novel light weight design concept for leisure boats and yachts. Professor Stephan Marzi from the THM Institute of Mechanics and Materials collaborates with Krake Catamarane, which is a shipyard located in Apolda, Thuringia.

The project is set up in an international cooperation with Professor Anders Biel from Karlstad University in Sweden and the Swedish company Lamera from...

Im Focus: Controlling superconducting regions within an exotic metal

Superconductivity has fascinated scientists for many years since it offers the potential to revolutionize current technologies. Materials only become superconductors - meaning that electrons can travel in them with no resistance - at very low temperatures. These days, this unique zero resistance superconductivity is commonly found in a number of technologies, such as magnetic resonance imaging (MRI).

Future technologies, however, will harness the total synchrony of electronic behavior in superconductors - a property called the phase. There is currently a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

International Symposium on Functional Materials for Electrolysis, Fuel Cells and Metal-Air Batteries

02.10.2019 | Event News

NEXUS 2020: Relationships Between Architecture and Mathematics

02.10.2019 | Event News

Optical Technologies: International Symposium „Future Optics“ in Hannover

19.09.2019 | Event News

 
Latest News

Energy Flow in the Nano Range

18.10.2019 | Power and Electrical Engineering

MR-compatible Ultrasound System for the Therapeutic Application of Ultrasound

18.10.2019 | Medical Engineering

Double layer of graphene helps to control spin currents

18.10.2019 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>