Physicists have successfully developed the first two-dimensional Bose glass, which is an innovative state of matter that poses challenges to traditional statistical mechanics.
Researchers at the Cavendish Laboratory in Cambridge have achieved a significant milestone by creating the inaugural two-dimensional version of the Bose glass, a groundbreaking state of matter that questions established concepts in statistical mechanics. The findings of this research have been documented in Nature.
The term “Bose glass” reflects its glass-like characteristics, where all particles are localized. This means that each particle tends to remain in its own position rather than mixing with nearby particles. For instance, if coffee were localized, adding milk would maintain distinct black and white stripes indefinitely, rather than blending into an average color.
To develop this new phase of matter, the researchers overlapped multiple laser beams to form a quasiperiodic pattern. This creates a structure that has long-range order akin to a typical crystal but does not repeat, resembling Penrose tiling. When ultracold atoms, cooled to nearly absolute zero (nanokelvin temperatures), filled this structure, they formed the Bose glass.
Professor Ulrich Schneider, a specialist in Many-Body Physics at the Cavendish Laboratory and the lead investigator of the study, stated, “Localisation remains one of the most challenging issues in statistical mechanics, but it could also contribute to advancements in quantum computing.” In a localized system, where particles do not mix with their environment, quantum information is better preserved over time.
Schneider added, “A significant hurdle in analyzing large quantum systems is our inability to simulate them on computers. To represent the system precisely, we must account for all particles and their potential arrangements, which increases rapidly. However, we now possess a real-world two-dimensional model that allows us to examine its dynamics and statistical properties directly.”
Schneider and his team concentrate on quantum simulation and quantum many-body dynamics, utilizing ultracold atoms to explore many-body phenomena that cannot be numerically simulated due to the lack of a large quantum computer.
This issue often becomes less complex since the system typically settles into a thermal state, where only the temperature matters, while most other details are lost. This condition is known as ergodic and forms the basis of statistical mechanics, a cornerstone of understanding matter. “For example, knowing the volume of milk added is sufficient to predict the final color of coffee after prolonged stirring,” Schneider explained. “However, to forecast the intricate patterns of white and dark swirls during stirring, precise information on how and where the milk was introduced is vital.”
Interestingly, the Bose glass does not exhibit ergodicity, meaning it retains its specifics and requires detailed modeling. This characteristic positions it as a potential candidate for many-body localization.
Dr. Jr-Chiun Yu, the lead author of the study, expressed, “It’s a long-term goal to discover a system or material exhibiting many-body localization. Such materials would present numerous exciting possibilities, not only for foundational research but also for the development of quantum computers. Quantum information stored in these systems is likely to remain localized and not leak into the surroundings, a phenomenon known as ‘decoherence’ that affects many current quantum computing approaches.”
During the experiment, the team noted a striking phase transition from a Bose glass to a superfluid, similar to ice melting as temperatures rise. “A superfluid flows effortlessly,” explained Dr. Bo Song, a former Postdoctoral Research Associate in Cambridge and now an Assistant Professor at Peking University, who was involved in the study. “Consider particles moving through a superfluid; they would experience no friction, enabling them to glide without resistance. This phenomenon, referred to as superfluidity, is closely tied to superconductivity. Together with the Mott insulator and the newly observed Bose glass, the superfluid is part of the foundational states in the Bose-Hubbard model, which describes the interactions and behaviors of bosons in disordered systems.”
Bose glasses and superfluids are distinct phases of matter, similar to ice and water. However, just like ice cubes floating in water, the atoms in their system can exhibit both states within the same experimental framework. The experimental outcomes not only align with recent theoretical predictions but also provide insights into the formation and progression of the Bose glass, prompting researchers to begin contemplating practical applications.
Despite the promising prospects ahead, Schneider urges a careful approach. “There remains much we do not fully understand regarding the Bose glass and its potential association with many-body localization, particularly regarding their thermodynamic and dynamic features. We should prioritize addressing these inquiries before exploring practical applications,” Schneider concluded.
