Lawrence Berkeley National Laboratory scientists have realised a tunable Bose–Einstein condensate (BEC) formed from excitons in an atomically thin semiconductor, demonstrating a solid‑state quantum fluid that endures up to roughly 2 kelvin and can be controlled electrically and magnetically.
What the team observed
In work published in Nature, the researchers created long‑lived electron–hole pairs — known as excitons — in a bilayer two‑dimensional semiconducting device and found they form a macroscopic coherent state resembling the BECs more commonly produced in ultracold atomic gases. Crucially, the condensate could be tuned with an electrical bias and its internal spin–valley configuration switched using a magnetic field, offering control over the condensate's properties within a solid‑state platform.
The advance addresses two long‑standing obstacles to exciton condensation in devices. First, optically generated excitons typically exist for only about a billionth of a second, making it hard to reach and study collective quantum behaviour. Second, condensation has usually required gas‑phase atoms at microkelvin temperatures in vacuum. Here, the exciton system is stabilised in a semiconductor heterostructure and remains robust to temperatures on the order of a few kelvin.
Why the result matters
The achievement provides a controllable platform to study quantum fluids in solid materials — a class of states in which many particles lose their individual identity and move as a single, coherent object. Such macroscopic quantum coherence in a device geometry could have implications for:
- quantum simulation of many‑body physics;
- coherent optoelectronics for telecommunications and computing;
- future devices harnessing exciton superfluidity for lower‑loss information transfer.
“While previous studies have shown that electrons and holes can bind into excitons, there wasn’t a”
The press release accompanying the paper emphasises that the combination of electrical tunability and magnetic switching of internal states opens practical routes to experiment with, and ultimately exploit, exciton condensates in technologies where traditional cold‑atom systems are impractical.
Experimental detail and constraints
The condensate was observed in an atomically thin bilayer device engineered to host interlayer excitons. The exciton BEC persisted up to approximately 2 K, a temperature that is many orders of magnitude higher than the microkelvin regimes of atomic BECs, though still far below everyday temperatures. The researchers also report that the condensate's internal degrees of freedom — described in terms of spin and valley indices in these two‑dimensional materials — can be reconfigured by applying a magnetic field.
A simple summary of the reported parameters:
| Parameter | Reported value |
|---|---|
| Condensate persistence temperature | ≈ 2 K |
| Typical lifetime of optically generated excitons | ≈ 1 × 10⁻⁹ s |
These figures highlight both the promise and the limitations: exciton lifetimes and operating temperatures remain challenging for device integration, but electrical control in a solid device is a decisive step towards practicable quantum fluids.
Outlook and consequences
The discovery does not immediately translate into commercial products. However, by demonstrating a controllable exciton condensate in a device architecture, the work creates a testbed for probing collective quantum phenomena under conditions closer to those of real‑world electronics. Researchers now have a platform to explore how such condensates respond to disorder, electrical contacts and other ingredients relevant to circuits.
Longer term, if exciton condensates can be stabilised at higher temperatures and integrated with existing semiconductor processes, they could underpin novel low‑power interconnects or elements of quantum simulators. For now, the result is a substantial materials and physics milestone: a solid‑state quantum fluid whose internal structure and coherence can be engineered and manipulated within a thin, device‑friendly platform.
Reporting from the national science desk. The article is based on a Berkeley Lab press release and the published paper in Nature.
