When levitated using laser light, glass nanoparticles exhibit surprising coupling.

Jakob Rieser showed non-reciprocal optical interaction between two optically imprisoned nanoparticles. Iurie Coroli, Vienna

The interaction between optically levitated nanoparticles is fundamentally altered by a novel mechanism discovered by researchers at the University of Vienna, the Austrian Academy of Sciences, and the University of Duisburg-Essen. 

By demonstrating previously unachievable levels of control over the coupling in arrays of particles, they have established a new platform to investigate the intricacies of physics. This week's edition of Science reveals the findings. Picture specks of dust in the air, drifting aimlessly. 

Light pressures are exerted on particles when a laser is activated, and if a particle gets too close to the beam's focal point, it gets caught. Optical tweezers were developed on this principle by Nobel laureate Arthur Ashkin. 

When two or more particles are near one another, standing waves of light can be created between them, causing the particles to align in a crystalline pattern similar to that formed when light is bonded to a crystal of particles. There have been numerous studies on this for over 30 years.

When investigating the interactions between two glass nanoparticles, researchers in Vienna were taken aback to observe behavior that exceeded their expectations. They were able to alter the magnitude and direction of the binding force and even observe one particle (let's say the left) acting on another (the right) without the right particle reacting. 

Non-reciprocal behavior happens when a system loses energy to its surroundings, such as the laser, and appears to go against Newton's third rule (anything acted upon acts back with the same strength but opposite sign). Our existing theory of optical binding was lacking.

This unexpected pattern of activity can be attributed to a phenomenon called "coherent scattering," which scientists in Vienna have been studying for years. When a nanoparticle is exposed to laser light, the atoms and molecules inside the particle become polarised and move in sync with the laser's electromagnetic wave. 

As a result, the dispersed light from the particle has the same frequency as the incident laser. Interference can be created between in-phase waves. For the first time, scientists in Vienna have harnessed the interference effect offered by coherent scattering to cool a single nanoparticle to its quantum ground state of motion while keeping it at ambient temperature.

A further interference effect was discovered by Uro Deli, a senior researcher in the laboratory of Markus Aspelmeyer at the University of Vienna and the initial author of the previous cooling work when he began applying coherent scattering to two particles. "Light dispersed from one particle can interfere with the light that traps the other," explains Deli. The strength and nature of the forces in between the particles can be adjusted if the phase between these light fields can be altered.

It is possible to re-establish the classic optical binding for a particular configuration of phases. However, for some phases, never-before-seen effects like non-reciprocal forces exist. "Unfortunately, coherent scattering and the fact that photons are lost were not accounted for in earlier theories. 

It turns out that when you combine these two processes, you get more complex interactions than you ever imagined. "A German team member working on the enhanced theoretical description, Benjamin Stickler, explains their findings. 

"...and neither were previous trials responsive to these effects."

The team in Vienna sought to change that, so they experimented with investigating these novel light-induced forces. They did this by splitting the light from a single laser into two optical beams, trapping a single glass nanoparticle roughly 200 nm (about 1,000 times smaller than a typical grain of sand). All three variables (distance, intensity, and relative phase) were modified in their experiment. 

The position of each particle, which is being tracked with exquisite precision, oscillates at a rate determined by the trap. Since every force on the trapped particle affects this frequency, it is possible to monitor the forces between them while phase and distance are being adjusted.The experiment was conducted in a vacuum to rule out the possibility that gas between the particles induced the forces instead of light. 

This allowed them to verify that the novel light-induced forces between the confined particles were present. Ph.D. student and primary author Jakob Rieser states, "The couplings that we find are more than 10 times bigger than expected from conventional optical binding." And as predicted by our new model, when we alter the laser phases, non-reciprocal forces leave telltale traces. Hopefully, these findings will inspire novel approaches to investigating complicated processes in multiparticle systems. 

Research leader Uro Deli believes studying model systems with well-controlled interactions are the norm when trying to comprehend what is happening in truly complex systems. This is so interesting because it gives us a whole new set of tools for manipulating interactions amongst levitated particle arrays. 

The capacity to manipulate atomic interactions in optical lattices was the impetus for developing quantum simulators, which the researchers acknowledge as an important source of inspiration. 

Similarly, "being able to use this immediately on the level of solid-state systems might be a similar game changer."

What is A New, Surprising Insight into the greatest star

 What is A New, Surprising Insight into the greatest star?

This view of R136 from the Hubble Space Telescope shows the central region of the Tarantula Nebula. Wide Field Camera 3 Science Oversight Committee (NASA, ESA, F. Paresce/INAF-IASF, R. O'Connell/University of Virginia)

Can a star go that big? It's not nearly as big as we thought it would be.

The clearest pictures yet acquired of the brightest star suggest that the maximum mass attributed to the Sun is likely much lower than prior estimations.

Initially, the mass of this star ( R136a1) was estimated to be between 250 and 320 times that of the Sun. This latest calculation puts its mass between 150 and 230 times that of the Sun.

The star's mass has been revised and reduced to around 200 solar masses, which is still a heavyweight record, but this new estimate may have more far-reaching consequences.

This study was conducted as part of a larger effort to learn more about the R136 cluster. It is located in the Large Magellanic Cloud, a satellite galaxy of our Milky Way, and home to the star-forming Tarantula Nebula.

Some massive stars in the universe are located in this cluster, and their masses have recently been revised downwards along with everything else. Our previous stellar upper mass limitations may be incorrect, as these masses are crucial anchor points for the upper mass function of massive stars, which was predicted by this work.

Observations made at the Gemini Observatory have led astronomer and astrophysicist Venu Kalari to conclude that the most massive star currently known is not as large as was previously supposed. Because of this, the maximum allowed star mass may be lower than was previously believed.

Calculations and models show that there must be a maximum star mass, but we don't know what it is. At a certain point, called the Eddington limit, it is generally agreed that the outward pressure from the core's radiation will exceed the inward gravitational pressure, causing material in the star's outer layers to be ejected.

In the past, researchers have determined that the Eddington limit cannot exceed 150 solar masses. Later, more accurate mass estimates for the R136 stars were obtained.

These young, extremely hot, and enormous stars contradicted the Eddington limit and stellar formation theories. We still don't have a solid answer to the Eddington limit problem, even though subsequent studies established that such chokers can arise due to star mergers.

A significant step toward resolving this vexing mystery would be to agree on a maximum mass based on reliable reference points. Accurate measurements of a star's luminosity and temperature estimate its mass. So Kalari and his team set out to get new, higher-resolution photos of the cluster and R136a1.

It provided the data necessary for the researchers to determine that R136a1 has a new mass of 196 solar masses (plus or minus a few dozen sun masses). R136a2 and R136a3 had new masses of 151 and 155 solar masses, down from 195-211 and 180-181, respectively.

It affects the heavy element production in the universe. You may know that large stars can eventually collapse into black holes after ejecting their outer material. But there is a limit: if the star's mass is greater than 130 solar masses, it can undergo a pair-instability supernova and explode completely, core and all.

Subatomic reactions create heavy materials during these extremely intense occurrences. We must reevaluate the possible contribution of pair-instability supernovae to the heavy elements we witness in space if fewer stars exist in this mass range.

Because a single pair-instability supernova from a star of 300 solar mass would release more metals into the interstellar medium than an entire stellar mass function below it, the existence or absence of such events "cannot be overemphasised," the researchers write in their paper.

This discovery was obtained using the Zorro instrument on the Gemini South telescope to its maximum capacity. Hence the researchers advise against jumping to any hasty conclusions.

The following step would be validating the findings by obtaining and comparing observations from a different instrument.

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Increasing brain cell size using 6G radiation, say Chinese researchers.

 Increasing brain cell size using 6G radiation, say Chinese researchers.

I have some fascinating information to share today: 6G radiation can cause brain cells to grow in size. Isn't that incredible? Right? Some Chinese researchers have found evidence of rapid neuronal development in mice, which could be helpful in future electronic communication.

New therapies for treating brain diseases can be developed using 6G radiation.

Radio waves in the terahertz spectrum can increase a smartphone's bandwidth to 1 terabit per second, as recently reported (Tbps). It looks like a promising contender for use with 6G and other forms of cutting-edge wireless networking.

The neurons of a mouse grew approximately 150 percent quicker than normal after being exposed for three minutes to 100 microwatts of pulse radiation at frequencies ranging from 0.3 to 3 terahertz. In addition, the overall connection length between these neurons doubled in just three days, which is quite remarkable. Researchers also found that, unlike the control group, the exposed brain cells were in good health despite the rapid expansion.

The study's primary investigator, Li Xiaoli, reported in the academic journal Acta Physica Sinica that:

Terahertz radiation protocol safety is of the utmost importance.

Researchers claim their new findings will aid in gauging future communication technologies' security and creating treatments for neurological disorders. The findings suggest that "terahertz waves of specified frequencies and energies can be developed as a revolutionary neuromodulation technique to treat or intervene in conditions like neurodevelopmental disorders."

Researchers at the Russian Academy of Sciences elaborated in 2009 that prolonged exposure to powerful terahertz radiation (with strength reaching a few watts) for many hours each day might increase brain cell temperature, disrupt growth, and cause dehydration that affects cell size, and more. There is evidence that low-level terahertz radiation can promote neuron development by increasing the production and activity of specific proteins.