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First observed in liquid helium below the lambda point, superfluidity manifests itself in a number of fascinating ways. In the superfluid phase, helium can creep up along the walls of a container, boil without bubbles, or even flow without friction around obstacles. As early as 1938, Fritz London suggested a link between superfluidity and Bose–Einstein condensation (BEC)³. Indeed, superfluidity is now known to be related to the finite amount of energy needed to create collective excitations in the quantum liquid^4,5,6,7, and the link proposed by London was further evidenced by the observation of superfluidity in ultracold atomic BECs^1,8. A quantitative description is given by the Gross–Pitaevskii (GP) equation^9,10 (see Methods) and the perturbation theory for elementary excitations developed by Bogoliubov¹¹. First derived for atomic condensates, this theory has since been successfully applied to a variety of systems, and the mathematical framework of the GP equation naturally leads to important analogies between BEC and nonlinear optics^12,13,14. Recently, it has been extended to include condensates out of thermal equilibrium, like those composed of interacting photons or bosonic quasiparticles such as microcavity exciton-polaritons and magnons^14,15. In particular, for exciton-polaritons, the observation of many-body effects related to condensation and superfluidity such as the excitation of quantized vortices, the formation of metastable currents and the suppression of scattering from potential barriers^{2,16,17,18,19,20} have shown the rich phenomenology that exists within non-equilibrium condensates. Polaritons are confined to two dimensions and the reduced dimensionality introduces an additional element of interest for the topological ordering mechanism leading to condensation, as recently evidenced in ref. 21. However, until now, such phenomena have mainly been observed in microcavities embedding quantum wells of III–V or II–VI semiconductors. As a result, experiments must be performed at low temperatures (below ∼ 20 K), beyond which excitons autoionize. This is a consequence of the low binding energy typical of Wannier–Mott excitons. Frenkel excitons, which are characteristic of organic semiconductors, possess large binding energies that readily allow for strong light–matter coupling and the formation of polaritons at room temperature. Remarkably, in spite of weaker interactions as compared to inorganic polaritons²², condensation and the spontaneous formation of vortices have also been observed in organic microcavities^23,24,25. However, the small polariton–polariton interaction constants, structural inhomogeneity and short lifetimes in these structures have until now prevented the observation of behaviour directly related to the quantum fluid dynamics (such as superfluidity). In this work, we show that superfluidity can indeed be achieved at room temperature and this is, in part, a result of the much larger polariton densities attainable in organic microcavities, which compensate for their weaker nonlinearities.

Our sample consists of an optical microcavity composed of two dielectric mirrors surrounding a thin film of 2,7-Bis[9,9-di(4-methylphenyl)-fluoren-2-yl]-9,9-di(4-methylphenyl)fluorene (TDAF) organic molecules. Light–matter interaction in this system is so strong that it leads to the formation of hybrid light–matter modes (polaritons), with a Rabi energy 2 Ω_R ∼ 0.6 eV. A similar structure has been used previously to demonstrate polariton condensation under high-energy non-resonant excitation²⁴. Upon resonant excitation, it allows for the injection and flow of polaritons with a well-defined density, polarization and group velocity.

Continue reading “Room-temperature superfluidity in a polariton condensate Physics” »

CAR T cell therapy has been a major advance for treating leukemia, lymphoma and multiple myeloma. Now, it’s showing promise for solid tumors, including lung cancer, kidney cancer and bone cancer.

In a stage two clinical trial, researchers found that adding an mRNA cancer vaccine to standard treatment reduced the chances for melanoma recurrence or death by 44 percent. NBC News’ Kristen Dahlgren spoke to one of the study’s doctors and a patient for more details.

No people or satellites were aboard. There won’t be another try until at least Wednesday.

“Learned a lot today,” Musk tweeted after the flight was postponed.

The company plans to use Starship to send people and cargo to the moon and, ultimately, Mars.

A multi-institution study that included researchers from Stanford University, the University of California at San Diego, the University of Cambridge, the Fred Hutchinson Cancer Center and others has looked into the development of extrachromosomal DNA in patients with esophageal adenocarcinoma or Barrett’s esophagus.

In the paper, “Extrachromosomal DNA in the cancerous transformation of Barrett’s oesophagus,” published in Nature, researchers identify previously unknown aspects of extrachromosomal DNA presence and their potential role in Barrett’s esophagus. David H. Wang has published a News & Views piece in the same journal discussing the study.

Barrett’s esophagus is a pre-cancerous tissue abnormality that affects about 1.6% of the U.S. population. The condition is mostly harmless, defined by cells in the esophagus lining that become more intestinal-like and is frequently associated with heartburn and acid regurgitation.

No, they haven’t decided to teach themselves anything, they don’t love you back, and they still aren’t even a little bit sentient.

The ‘power couple’ of solar-plus-storage, facilitated by AIoT, will be vital to safeguarding countries’ energy security and reducing geopolitical risks.

This study investigated the effect of administering Lactobacillus probiotics (LBPs) on vaginal dysbiosis in asymptomatic women. The results showed that oral intake of LBPs improved vaginal health in women with high Nugent scores.

Recently, a team of South Korean scientists led by Director C. Justin Lee of the Center for Cognition and Sociality within the Institute for Basic Science made a discovery that could revolutionize both the diagnosis and treatment of Alzheimer’s Disease. The group demonstrated a mechanism where the astrocytes in the brain uptake elevated levels of acetates, which turns them into hazardous reactive astrocytes. They then went on to further develop a new imaging technique that takes advantage of this mechanism to directly observe the astrocyte-neuron interactions.

Alzheimer’s disease (AD), one of the major causes of dementia, is known to be associated with neuroinflammation in the brain. While traditional neuroscience has long believed that amyloid beta plaques are the cause, treatments that target these plaques have had little success in treating or slowing the progression of Alzheimer’s disease.

On the other hand, Director C. Justin Lee has been a proponent of a novel theory that reactive astrocytes are the real culprit behind Alzheimer’s disease. Reactive astrogliosis, a hallmark of neuroinflammation in AD, often precedes neuronal degeneration or death.