Bose–Einstein condensate

In a World-First, Scientists Have Achieved ‘Liquid Light’ at Room Temperature

Posted by

0


A Frankenstein mash-up of light and matter.

For the first time, physicists have achieved ‘liquid light’ at room temperature, making this strange form of matter more accessible than ever.

This matter is both a superfluid, which has zero friction and viscosity, and a kind of Bose-Einstein condensate – sometimes described as the fifth state of matter – and it allows light to actually flow around objects and corners.

Regular light behaves like a wave, and sometimes like a particle, always travelling in a straight line. That’s why your eyes can’t see around corners or objects. But under extreme conditions, light can also act like a liquid, and actually flow around objects.

Bose-Einstein condensates are interesting to physicists because in this state, the rules switch from classical to quantum physics, and matter starts to take on more wave-like properties.

They are formed at temperatures close to absolute zero and exist for only fractions of a second.

But in this study, researchers report making a Bose-Einstein condensate at room temperature by using a Frankenstein mash-up of light and matter.

“The extraordinary observation in our work is that we have demonstrated that superfluidity can also occur at room-temperature, under ambient conditions, using light-matter particles called polaritons,” says lead researcher Daniele Sanvitto, from the CNR NANOTEC Institute of Nanotechnology in Italy.

Creating polaritons involved some serious equipment and nanoscale engineering.

The scientists sandwiched a 130-nanometre-thick layer of organic molecules between two ultra-reflective mirrors, and blasted it with a 35 femtosecond laser pulse (1 femtosecond is a quadrillionth of a second).

“In this way, we can combine the properties of photons – such as their light effective mass and fast velocity – with strong interactions due to the electrons within the molecules,” says one of the team, Stéphane Kéna-Cohen from École Polytechnique de Montreal in Canada.

The resulting ‘super liquid’ had some strange properties.

Under normal conditions, when liquid flows, it creates ripples and swirls – but that’s not the case for a superfluid. 

As you can see below, the flow of polaritons is disturbed like waves under regular circumstances, but not in the superfluid:

liquid liquid lightThe flow of polaritons encounters an obstacle in non-superfluid (top) and superfluid (bottom). Credit: Polytechnique Montreal

“In a superfluid, this turbulence is suppressed around obstacles, causing the flow to continue on its way unaltered,” says Kéna-Cohen.

The researchers say the results pave the way not only to new studies of quantum hydrodynamics, but also to room-temperature polariton devices for advanced future technology, such as the production of super-conductive materials for devices such as LEDs, solar panels, and lasers.

“The fact that such an effect is observed under ambient conditions can spark an enormous amount of future work,” says the team.

“Not only to study fundamental phenomena related to Bose-Einstein condensates, but also to conceive and design future photonic superfluid-based devices where losses are completely suppressed and new unexpected phenomena can be exploited.”

Source:Nature Physics.

Physicists create mind-bending ‘negative mass’ that accelerates backwards and could help explain black holes

Posted by

0


A rubidium metal sample

Scientists have created a fluid with “negative mass” which they claim can be used to explore some of the more challenging concepts of the cosmos.

Washington State University physicists explained that this mass, unlike every physical object in the world we know, accelerates backwards when pushed.

The phenomenon, which is rarely created in laboratory conditions, shows a less intuitive side of Newton’s Second Law of Motion, in which a force is equal to the mass of an object times its acceleration (F=ma).

 Our everyday world sees only the positive effect of the law: if you push an object, it moves away from you.

“That’s what most things that we’re used to do,” said Michael Forbes, a WSU assistant professor of physics and astronomy and an affiliate assistant professor at the University of Washington. “With negative mass, if you push something, it accelerates toward you.”

To create the negative matter the WSU team cooled rubidium atoms to just above absolute zero, creating what is known as a Bose-Einstein condensate in which particles move very slowly and behave like waves.

First predicted theoretically by Satyendra Nath Bose and Albert Einstein, a Bose-Einstein condensate is a group of atoms cooled to such a low temperature that there is hardly any movement left in the group. At that point, the atoms begin to clump together becoming identical, from a physical point of view, and the whole group starts behaving as though it were a single atom.

Once scientists reached that stage, they used lasers to kick atoms back and forth until they started spinning backwards. When the rubidium rushes out fast enough, if behaves as if it had negative mass.

 “Once you push, it accelerates backwards,” said Mr Forbes, who acted as a theorist analysing the system. “It looks like the rubidium hits an invisible wall.”

The physicist explained that the ground-breaking aspect of their research is the “exquisite control” they have of the negative mass using their technique.

The heightened control gives researchers a new tool to engineer experiments to study similar behaviours in astrophysics, such as neutron stars, and cosmological phenomena like black holes and dark energy, where experiments are impossible.

“It provides another environment to study a fundamental phenomenon that is very peculiar,” Mr Forbes said.

What is a black hole?

Nasa artist’s impression of debris from a star being flung away from a black hole

A black hole is a region in space with a gravitational field so intense that even light can not get out. Because light can’t escape, black holes can’t be seen. They’re detected by the difference in behaviour of stars nearer to the black hole. Stellar black holes are formed by the collapse of the centre of a massive star. This collapse also causes a supernova, or an exploding star, that blasts part of the star into space.

Source:http://www.telegraph.co.uk

 

New Mind-blowing Experiment Confirms That Reality Doesn’t Exist If You Are Not Looking At It

Posted by

0


According to a well-known theory in quantum physics, a particle’s behavior changes depending on whether there is an observer or not. It basically suggests that reality is a kind of illusion and exists only when we are looking at it. Numerous quantum experiments were conducted in the past and showed that this indeed might be the case.

new-mind-blowing-experiment-confirms-that-reality-doesnt-exist-if-you-are-not-looking-at-it

Now, physicists at the Australian National University have found further evidence for the illusory nature of reality. They recreated the John Wheeler’s delayed-choice experiment and confirmed that reality doesn’t exist until it is measured, at least on the atomic scale.

Thought-provoking findings

Some particles, such as photons or electrons, can behave both as particles and as waves. Here comes a question of what exactly makes a photon or an electron act either as a particle or a wave. This is what Wheeler’s experiment asks: at what point does an object ‘decide’?

The results of the Australian scientists’ experiment, which were published in the journal Nature Physics, show that this choice is determined by the way the object is measured, which is in accordance with what quantum theory predicts.

“It proves that measurement is everything. At the quantum level, reality does not exist if you are not looking at it,” said lead researcher Dr. Andrew Truscott in a press release.

The experiment

The original version of John Wheeler’s experiment proposed in 1978 involved light beams being bounced by mirrors. However, it was difficult to implement it and get any conclusive results due to the level of technological progress back then. Now, it became possible to successfully recreate the experiment by usinghelium atoms scattered by laser light.

Dr. Truscott’s team forced a hundred of helium atoms into a state of matter called Bose-Einstein condensate. After this, they ejected all the atoms until there was only one left.

Then, the researchers used a pair of laser beams to create a grating pattern, which would scatter an atom passing through it just like a solid grating scatters light. Thus, the atom would either act as a particle and pass through one arm or act as a wave and pass through both arms.

Thanks to a random number generator, a second grating was then randomly added in order to recombine the paths. This was done only after the atom had already passed the first grate.

As a result, the addition of the second grating caused interference in the measurement, showing that the atom had traveled both paths, thus behaving like a wave. At the same time, when the second grating was not added, there was no interference and the atom appeared to have traveled only one path.

The results and their interpretation

As the second grating was added only after the atom had passed through the first one, it would be reasonable to suggest that the atom hadn’t yet ‘decided’ whether it was a particle or a wave before the second measurement.

According to Dr. Truscott, there may be two possible interpretations of these results. Either the atom ‘decided’ how to behave based on the measurement or a future measurement affected the photon’s past.

“The atoms did not travel from A to B. It was only when they were measured at the end of the journey that their wave-like or particle-like behavior was brought into existence,” he said.

Thus, this experiment adds to the validity of the quantum theory and provides new evidence to the idea that reality doesn’t exist without an observer. Perhaps further research in the field of quantum physics and more thought-provoking evidence like this will completely change our understanding of reality one day.

 

SCIENTIST THINKS HE’S PROVEN HAWKING’S THEORY THAT BLACK HOLES GLOW

Posted by

0


You might think of black holes as evil interstellar whirlpools, massive balls of who-knows-what so dense that their gravity prevents even light from escaping. But in 1974, Stephen Hawking made waves (this is a physics joke) in the science world by theorizing that maybe black holes weren’t so dark; maybe they let out a faint glow of particles that barely escape the pull. A scientist thinks he’s recreated that glow.

Black Hole Devouring Star

Jeff Steinhauer from the Technion-Israel Institute of Technology in Haifa, Israel created an analogue to a black hole in his lab, using the laws of sound, rather than light. His black hole let out a telltale signature providing compelling evidence for Hawking’s namesake theory, Hawking radiation. This research implies that black holes might not be the bottomless voids we thought they were. It also has broader implications in the field of physics as a whole, where a major goal is creating one theory that links the vast distances required by gravity theories and the tiny lengths studied in particle physics.

“I think this work stands on its own as verification of Hawking’s calculations,” Steinhauer told Popular Science.

Instead of a light-sucking behemoth, Steinhauer’s black hole is a line of cold rubidium atoms in a lab, as a form of matter called a Bose-Einstein condensate. Using lasers, he created a kind of waterfall: there’s a lot of atoms on one side moving slowly, but then pouring over the edge faster than the speed of sound to the other side. This means that phonons, individual units of sound, can’t escape past the boundary up the energy waterfall. This is like a black hole, except with space black holes, its light particles can’t escape gravity’s light-speed pull. Steinhauer published his results today in the journal Nature Physics.

Steinhauer with his black hole machine

Jeff Steinhauer

Steinhauer with his black hole-making machine

Quantum mechanics is strange, and on the smallest scales, particles will appear alongside their antiparticles and disappear. In real black holes, Stephen Hawking predicted that these particles might randomly appear on either side of the furthest extent of the black hole’s pull, so one particle gets sucked into the black hole and the other just manages to escape. Steinhauer observed this same effect on either side of his atomic waterfall; a stream of particles that fell into the black hole, and a matching stream that came out on the other side. Steinhauer was able to show that these two particles were entangled, meaning the properties are dependent on each other no matter how far away they were separated, which is a requirement of so-called Hawking radiation

It’s important to emphasize that Steinhauer isn’t using real black holes, Grant Tremblay, astrophysicist and NASA Einstein Fellow at Yale University told Popular Science in an email. You can’t immediately translate the results to say that the black holes we see in space have the same behavior. However, physicists like Brain Greene frequently discuss uniting gravity with electromagnetism and the forces inside atoms with theories like the string theory and quantum gravity to make a theory of everything. Observing the interactions of particles with gravity in the case of the black hole would add further support that these theories can actually be united, noted Steinhauer. Seeing Hawking radiation in Steinhauer’s black holes show that his sound analogues are useful tools in making models of the real thing.

“This result is an incredibly elegant example of how a Bose-Einstein condensate can act as a black hole analogue in a laboratory environment,” said Tremblay, “enabling experiments that could never be done on a real black hole.”

The fifth state of matter: Bose-Einstein condensate

Posted by

0


We all know about matter and its three states and about plasma, the hot ionized gas considered as the fourth state, but we have seldom heard of something called as the fifth state of matter. In 1924, Albert Einstein and Satyendra Nath Bose predicted the “Bose-Einstein condensate” (BEC), which is  referred as the fifth state of matter.



What is Bose-Einstein condensate (BEC)?

A Bose-Einstein condensate (BEC) is a state of matter of a dilute gas of bosons cooled to temperatures very close to absolute zero (that is, very near 0 K or ?273.14 °C). Under such conditions, a large fraction of bosons occupy the lowest quantum state, at which point macroscopic quantum phenomena become apparent.

How Bose-Einstein condensate (BEC) developed?

Bose first sent a paper to Einstein on the quantum statistics of light quanta (now called photons). Einstein was impressed, translated the paper himself from English to German and submitted it for Bose to the Zeitschrift für Physik, which published it.

The Einstein manuscript,which was once assumed to be lost, was found in a library at Leiden University in 2005. Einstein then comprehended Bose’s ideas of matter in two other papers that resulted in a concept of Bose gas, which is governed by Bose-Einstein statistics, and describes the arithmetical distribution of the same particles with figure spin, now called bosons.

Bosons, actually  include the photon as well as atoms such as helium-4 (4He), which are allowed to share a quantum state. Einstein proposed that cooling bosonic atoms to a very low temperature would cause them to fall (or “condense”) into the lowest accessible quantum state, resulting in a new form of matter.

It was Einstein who guessed that these same rules might apply to atoms. He worked out the theory for how atoms would behave in a gas if these new rules applied. What he found was that the equations said that generally there would not be much difference, except at very low temperatures. If the atoms were cold enough, something very strange was supposed to happen. It was so outlandish he was not sure it was correct

New particle might make quantum condensation at room temperature possible.

Posted by

1


Researchers from FOM Institute AMOLF, Philips Research, and the Autonomous University of Madrid have identified a new type of particle that might make quantum condensation possible at room temperature. The particles, so called PEPs, could be used for fundamental studies on quantum mechanics and applications in lasers and LEDs. The researchers published their results on 18 October in Physical Review Letters.

https://i0.wp.com/cdn.physorg.com/newman/gfx/news/2013/pepssystem.jpg

In quantum condensation (also known as Bose-Einstein condensation) microscopic with different energy levels collapse into a single macroscopic quantum state. In that state, particles can no longer be distinguished. They lose their individuality and so the matter can be considered to be one ‘superparticle’.

Quantum condensation was predicted in the 1920s by Bose and Einstein, who theorised that particles will form a condensate at very low temperatures. The first experimental demonstration of the quantum condensate followed in the 1990s, when a gas of atoms was cooled to just a few billionths of a degree above absolute zero (-273°C). The need for such an extremely low temperature is related to the mass of the particles: the heavier the particles, the lower the temperature at which condensation occurs. This motivated an ongoing search for that may condense at higher temperatures than atoms. The eventual goal is to find particles that form a condensate at .

PEPs

The researchers have created a particle that is a potential candidate for fulfilling the quest: the extremely light plasmon-exciton-polariton (PEP). This particle is hybrid between light and . It consists of photons (light particles), plasmons (particles composed of electrons oscillating in metallic nanoparticles) and excitons (charged particles in ).

The researchers made PEPs using an array of metallic nanoparticles coated with molecules that emit light. This system generates PEPs when it is loaded with energy. Through a careful design of the coupling between plasmons, excitons and photons, the researchers created PEPs with a mass a trillion times smaller than the mass of atoms.

Because of their small mass, these PEPs are suitable candidates for quantum condensation even at room temperature. However, due to losses in the system (such as absorption in the metal) PEPs have a short lifespan, which makes keeping them around long enough to condense a challenge.

First steps

The researchers have shown the first steps towards condensation of PEPs, demonstrating that PEPs cool down as their density increases. However, in the current system cooling down is limited by properties of the organic molecules used in the experiments, which lead to a saturation of the PEP density before sets in. The researchers envisage that it should be possible to overcome these challenges in the future.

Applications

To a large extent, PEPs are composed of photons. Therefore, their decay results in the emission of light. This emitted light has unique properties, which could constitute the basis of new optical devices. In view of recent advances from AMOLF and Philips Research towards improving white LEDs with similar systems, the researchers suggest that from a Bose-Einstein condensate might illuminate our living rooms in the future.