Pull to refresh
Logo
What Changed
Following Why Sign Up
Bethe strings, predicted in 1931, created in ultracold cesium gas

Bethe strings, predicted in 1931, created in ultracold cesium gas

New Capabilities

Innsbruck team binds atoms in one-dimensional tubes without chemical bonds; earlier sightings came in magnetic crystals and superconducting circuits

September 14th, 2026: Innsbruck announces the result

Overview

Updated Oct 28

A quantum state predicted in 1931 now exists in a laboratory. Physicists in Innsbruck cooled cesium atoms near absolute zero, squeezed them into thousands of one-dimensional tubes, and watched them bind into clusters called Bethe strings.

The atoms hold together through their interactions alone, with no chemical bonds, and clusters of six or more particles survive collisions. Earlier sightings came in magnetic crystals and superconducting circuits, one string at a time. The gas-phase evidence is indirect, an energy signature from clusters breaking apart, and the strings are short-lived, decaying into ordinary cesium molecules; the coldest runs lost about 40% of the atoms.

Why it matters

Bethe strings give physicists a knob-controlled laboratory system to test quantum many-body theory, the mathematics behind superconductors and other complex materials.

Questions about this story

Free account needed to ask — your question is kept and asked for you right after sign-up. Answers are public.

No questions yet — be the first to ask.

Key Indicators

a few
Cooling temperature of cesium atoms
Atoms were held within a few billionths of a degree of absolute zero.
6+
Atoms per bound cluster
Some of the bound states held six or more particles.
~40%
Atoms lost in the coldest runs
The team lost about 40% of its cesium atoms as strings decayed into ordinary molecules.

Voices

Curated perspectives — historical figures and your fellow readers.

Sign up to generate historical perspectives on this story.

Log in Sign Up

People Involved

Hans Bethe
Hans Bethe
Physicist who predicted Bethe strings in 1931
Deceased 2005; prediction confirmed in 2026
 Hanns-Christoph Nägerl
Hanns-Christoph Nägerl
Quantum physicist who led the Innsbruck experiment
Active at the University of Innsbruck
MH
Milena Horvath
Doctoral researcher and lead author of the paper
University of Innsbruck
SD
Sudipta Dhar
Doctoral researcher and lead author of the paper
University of Innsbruck
 Alvise Bastianello
Alvise Bastianello
Lead theorist on the project
Affiliated with the theory teams in the collaboration

Organizations Involved

University of Innsbruck
University of Innsbruck
University
Led the experimental creation of Bethe strings

Austrian university whose experimental quantum physics group built the Bethe strings in ultracold cesium.
Nature Communications
Nature Communications
Peer-reviewed scientific journal
Published the primary paper

Open-access journal that published the Innsbruck team's paper on 2026-08-29.

Timeline

1931 September 2026

3 events Latest: September 14th, 2026 · 2 months ago

  1. Innsbruck announces the result

    Latest Announcement

    The University of Innsbruck publicizes the experiment; Phys.org and ScienceDaily carry accounts in the weeks that follow.

  2. Bethe string experiment published

    Publication

    Innsbruck, Amsterdam, and Munich teams report creating Bethe strings in ultracold cesium gas in Nature Communications.

  3. Bethe predicts one-dimensional bound states

    Theoretical Prediction

    Hans Bethe publishes the Bethe ansatz, showing particles in one dimension can lock into collective bound states now called Bethe strings.

Scenarios

1

Innsbruck extends Bethe string experiments to new regimes

Likely Resolves by End of 2027

Discussed by: The Innsbruck team, which says the platform enables controlled study of string formation and interaction

The group continues with the cesium setup, probing how strings form, collide, and respond as interaction strength and particle density change. The paper's generalized hydrodynamics simulations give a baseline to test against, so follow-up results would likely appear in the same or related journals.

2

Independent labs build Bethe strings in other atomic gases

Possible Resolves by Q2 2028

Discussed by: The ultracold-atom community, since the method uses standard tools: optical lattices and Feshbach resonances

Other groups could reproduce the result with different species, such as lithium or potassium, because the technique is adaptable to any Bose gas with tuneable interactions. Independent confirmation would strengthen the claim that the strings are real and robust beyond one atomic species.

3

Indirect detection draws scrutiny or replication trouble

Possible Resolves by End of 2028

Discussed by: Commentators noting the evidence is an energy gap and momentum width, not direct imaging of individual strings

The detection is inferential, backed by theory rather than pictures of strings. A competing group could argue the data admit alternative explanations, or a replication attempt could fail. Such a challenge would push the Innsbruck team toward more direct probes, such as single-string imaging.

Historical Context

3 moments from history that rhyme with this story — and how they unfolded.

1924–1995

Bose-Einstein condensation (1924–1995)

Einstein predicted in 1924-25 that cooling a gas of bosons near absolute zero would collapse its atoms into a single quantum state. In 1995, Eric Cornell and Carl Wieman at JILA created the first Bose-Einstein condensate in rubidium, and Wolfgang Ketterle did the same with sodium at MIT. The three shared the 2001 Nobel Prize.

Then

The 1995 creations launched an entire field of ultracold-atom physics.

Now

BECs became workhorse tools for quantum simulation, precision measurement, and atom interferometry.

Why this matters now

Both stories show a theoretical prediction taking decades to confirm with ultracold atomic gases, then turning prediction into laboratory tools.

1916–2015

Gravitational wave detection (1916–2015)

Einstein's general relativity predicted gravitational waves in 1916. In September 2015, the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected ripples from two merging black holes, confirming the prediction a century later.

Then

The detection opened a new way to observe the universe, by listening to gravity rather than light.

Now

Gravitational-wave astronomy became a routine observing mode, with dozens of events catalogued.

Why this matters now

A theory published decades earlier was confirmed only when experimental technology caught up, the same pattern as Bethe strings.

1964–2012

Higgs boson discovery (1964–2012)

Peter Higgs and others predicted a particle that gives other particles mass in 1964. In July 2012, the Large Hadron Collider at CERN detected a particle matching the Higgs boson's predicted properties, completing the Standard Model of particle physics.

Then

The discovery confirmed the mechanism of mass generation and earned the 2013 Nobel Prize for Higgs and François Englert.

Now

It showed that predictions from abstract theory could be verified precisely, guiding where to build and look.

Why this matters now

A half-century-old theoretical prediction, confirmed only after instruments grew powerful enough to test it.

Sources

(8)
+2
ScienceDaily Quantum News x9m8.com The Clarity UA.NEWS University of Innsbruck Phys.org Live Science