Scientists create a "time crystal" using giant atoms, a concept long thought to be impossible

In 2012, Nobel laureate Frank Wilczek asked whether the symmetry that arranges atoms in an ordinary crystal might also break in time, producing a structure that beats forever at its own pace.

More than a decade later, researchers at Tsinghua University, working with theorists from Vienna University of Technology, have watched rubidium vapor settle into just such a rhythm and report their findings.

Prof Thomas Pohl of the Institute of Theoretical Physics at TU Wien, a co‑author of the new paper, says the result brings Wilczek’s vision “very close to reality.”

How a time crystals differ

A time crystal repeats itself in time rather than in space, breaking the uniformity of the clock the way a snowflake breaks the uniformity of a lake.

The persistence of this rhythm, called spontaneous symmetry breaking, means the pattern survives even when no one is forcing it.

Laboratory evidence has grown fast, from early ion‑trap demonstrations of discrete time crystals in 2017 to optical‑cavity work that showed continuous versions in 2022.

Yet every platform had limits, such as ultracold temperatures or brief lifetimes, that left physicists wanting a clearer test bed.

The new rubidium system operates at room temperature and runs for hundreds of milliseconds at a time, long enough to watch thousands of oscillations.

That endurance turns the humble glass cell into a laboratory for fundamental questions about nonequilibrium phases of matter.

“The tick frequency is predetermined by the physical properties of the system, but the times at which the tick occurs are completely random,” Pohl notes. The statement underscores that the crystal’s clock sets itself, with no hidden conductor waiting in the wings.

Giant atoms set the stage

At the heart of the experiment are Rydberg atoms, rubidium atoms whose outer electron is lifted so far from the nucleus that the atom swells to about a micron across, roughly four‑hundredths of a human hair or 0.00004 inches.

These bloated atoms carry exaggerated electric fields that let them push and pull on one another across distances many times their size, knitting the gas into a strongly interacting community.

Because the atoms sit in a sealed vapor cell, they suffer almost no loss, avoiding the evaporation that plagues ultracold clouds.

The team drove each atom with two lasers tuned to excite two separate Rydberg levels at once. That choice created a built‑in tug‑of‑war: one level flourished only at the expense of the other, and the duel produced a limit‑cycle oscillation that showed up as a ripple in the transmitted light.

Like a roomful of people clapping until they fall into step, the atoms locked onto a single beat. The rhythm remained phase‑coherent for at least 80 periods, the longest window the detectors could track.

Time crystals and laser light

Nothing in the lasers’ intensity or frequency changed during the run, yet the transmitted light marched up and down with a period of a few microseconds. That self‑organization is the signature of a continuous time crystal.

Fourier analysis of single‑shot data revealed sharp combs of spectral peaks spaced by the fundamental oscillation frequency.

Early in each run the peaks drifted before narrowing into a stable set, marking the moment the crystal snapped into long‑range temporal order.

The autocorrelation function, a standard way to test for order, stayed flat over dozens of cycles once the drift settled.

The plateau shows that the pattern does not wash out with time, a key requirement for claiming true symmetry breaking rather than a transient quiver.

When the probe beam was deliberately shaken with random intensity noise, the crystal shrugged off weak perturbations.

Only at high noise levels did the oscillation contrast fall, and even then the fundamental frequency held firm until the signal disappeared into the background.

Why many‑body competition matters

Theorists have known that a single Rydberg level coupled to a laser often settles into a steady state or a bistable pair of steady states. Adding a second level changes the math.

Pohl and his colleagues modeled the gas with mean‑field equations that include the long‑range van der Waals forces between the giant atoms.

Their calculation shows that as soon as both levels draw enough laser power, the system crosses a Hopf bifurcation, switching from fixed points to a limit cycle. The experiment’s phase diagram matches that prediction.

The result highlights a theme running through time‑crystal research: many‑body interactions create collective timekeeping that a single particle cannot match.

Reviews of the field emphasize how this cooperative behavior extends ideas of order and phase transitions into driven, dissipative settings.

In the new system, the competition launches on a millimeter scale, far beyond the size of individual atoms, making it visible with standard optics and giving engineers a practical handle on the parameters.

Future tools and tests

Because the rubidium vapor sits at room temperature, the setup can be embedded into microfabricated chips alongside waveguides or microwave circuits, opening routes to compact sensors that read out time‑crystal beats in real time.

Recent studies have already used Rydberg vapors to detect radio‑frequency fields with extreme sensitivity.

Persistent, phase‑locked oscillations promise low‑phase‑noise signals useful for clock recovery, precision spectroscopy, and perhaps gravitational‑wave detection, where any self‑referencing oscillator could serve as a phase tag.

On the theory side, researchers now have a platform for mapping phase diagrams that include stationary, bistable, and time‑crystalline regimes.

Mapping how each region melts under noise or changes under periodic driving could test proposals for discrete time crystals that appear only under pulsed excitation.

Scaling the vapor‑cell concept to two or three dimensions may reveal whether spatial geometry feeds back into temporal order, a question still largely untouched in experiments.

Possible applications and open questions

The vapor‑cell crystal also offers a living classroom for nonequilibrium thermodynamics, showing how systems trade energy and entropy while holding a strict temporal pattern.

Lessons learned here could inform models of rhythmic behavior in chemical reactions, biological clocks, and even economic cycles.

Engineers eyeing quantum networks wonder whether time‑crystal phases can synchronize remote nodes through shared photons, reducing the overhead for entangling operations.

The long‑range Rydberg interactions and optical accessibility make the rubidium platform an attractive test case.

Still unresolved is whether a truly dissipation‑free, closed‑system time crystal can exist, or whether some coupling to an environment is always needed to stabilize the beat. The present work, like most others, relies on a balance of drive and loss.

Another question is how quantum coherence, rather than classical population oscillations, manifests in a macroscopic continuous time crystal. Experiments coupling Rydberg media to high‑finesse cavities may soon probe that regime.

The study is published in Nature Physics.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–