Berkeley Lab finally creates a controllable exciton quantum fluid after 60 years of trying

[KyleOReilly05]

Berkeley Lab researchers have achieved something physicists have been chasing for more than 60 years, creating a controllable Bose Einstein condensate, sometimes called a fifth state of matter, out of excitons at relatively high temperature in an atomically thin semiconductor, and discovering it has a genuinely surprising internal structure that can be switched with a magnetic field

Bose Einstein condensates are quantum states where many particles lose their individual identities entirely and behave as one single collective object, and researchers have long wanted to create these from excitons, which are essentially electron hole pairs, as a solid state pathway to macroscopic quantum coherence thats genuinely useful for building quantum technologies

The problem historically has been that optically generated excitons live for only about a billionth of a second, way too short to actually form and study a stable condensate, and BECs are normally only achieved using ultracold gases trapped in a vacuum rather than anything resembling a practical solid state device, which is exactly why this has remained unsolved for six decades despite serious effort

Principal investigator Feng Wang and his team solved this by engineering a bilayer 2D semiconducting device specifically designed to keep the excitons in their ground state rather than a short lived excited state, using molybdenum diselenide to host electrons on top and tungsten diselenide to host electron holes on the bottom, separated by an ultrathin layer of hexagonal boron nitride that lets the electrons and holes attract each other strongly enough to form stable excitons without the usual rapid decay

Wang explained why this matters beyond just finally achieving the condensate itself, saying while previous studies have shown that electrons and holes can bind into excitons there wasnt an easy way to determine whether those excitons formed a condensate nor could they ascertain what kind of internal quantum order that condensate has, and this new device design provides a way to directly access that hidden internal structure for the first time

The genuinely surprising finding is that this condensate isnt just one uniform quantum state, it has an internal two component structure that can actually be switched using an external magnetic field, revealing a level of tunable internal order in this kind of solid state quantum fluid that nobody had been able to directly observe before

Quantum Fluid Reveals Hidden Statesphys.org

[Sofia_61]

Sixty years of researchers wanting to do this but being blocked by excitons only living a billionth of a second is a genuinely long standing physics problem, solving it by engineering ground state excitons instead of relying on short lived excited ones is a clever reframing of the whole approach