Tag Archives: photon

This is what quantum entanglement looks like

Scientists have managed to take a photo of one of the most bizarre phenomena in nature: quantum entanglement.

Image credits: University of Glasgow.

There’s a reason why Einstein called quantum entanglement ‘spooky action at a distance’. Quantum entanglement, by everything that we know from our macroscopic lives, should not exist. However, the laws of quantum mechanics often defy what seems normal to us, and this bizarre phenomenon actually underpins the whole field of quantum mechanics.

Quantum entanglement occurs when a pair or a group of particles interact with each other and remain connected, instantaneously sharing quantum states — no matter how great the distance that separates them (hence the spooky action at a distance). This connection is so strong that the quantum state of each particle cannot be described independently of the state of the other(s).

Predicting, achieving, and describing this phenomenon was a gargantuan task that took decades. Photographing it is also a remarkable achievement.

Researchers from the University of Glasgow modified a camera to capture 40,000 frames per second. They operated an experimental setup at -30 degrees Celsius (-22 F) in pitch-black darkness. The experimental setup shoots off streams of photons entangled in a so-called Bell state — this is the simplest example of quantum entanglement.

The entangled photons were split up, with one of them passing through a liquid crystal material called β-barium borate, triggering four phase transitions. These four phase transitions were observed in the other, entangled photons.

A composite of multiple images of the photons as they go through the quantum transitions. Image credits: University of Glasgow.

Einstein staunchly believed that quantum mechanics does not tell the whole story and must have another, underlying physical framework. He even developed a series of experiments meant to disprove this quantum mechanics — which, ironically, ended up confirming the foundations of quantum mechanics.

However, people often forget that Einstein can also be regarded as one of the fathers of quantum mechanics. For instance, he described light as quanta in his theory of the Photoelectric Effect, for which he won the 1921 Nobel Prize. Niels Bohr and Max Planck are often regarded as the two founders of quantum mechanics, although numerous outstanding physicists worked on it over the years. For instance, physicist John Stewart Bell helped define quantum entanglement, establishing a test known as ‘Bell inequality’. Essentially, if you can break Bell inequality, you can confirm true quantum entanglement — which is what researchers have done here.

“Here, we report an experiment demonstrating the violation of a Bell inequality within observed images,” the study reads.

Lead author Dr. Paul-Antoine Moreau of the University of Glasgow’s School of Physics and Astronomy comments:

“The image we’ve managed to capture is an elegant demonstration of a fundamental property of nature, seen for the very first time in the form of an image.”

“It’s an exciting result which could be used to advance the emerging field of quantum computing and lead to new types of imaging.”

The study was published in Science Advances.

Artist concept of nano-patterned object reorienting itself to remain in a beam of light.

Physicists propose a new way to levitate and propel spacecraft-sized objects with light

Artist concept of nano-patterned object reorienting itself to remain in a beam of light.

Artist concept of nano-patterned object reorienting itself to remain in a beam of light.

In the future, spacecraft could travel to other stars faster than anything currently available by using laser light sources that are millions of miles away. For the moment, this prospect has been explored only theoretically by physicists at Caltech. In their new study, the researchers propose levitating and propelling objects using a beam of light by etching the surface of those objects with specific nanoscale patterns.

A pattern that keeps objects afloat

For decades, researchers have been using so-called optical tweezers to move and manipulate microscopic objects (i.e. nanoparticles) using a focused laser beam. Nanoparticles can be suspended mid-air due to the light scattering and gradient forces resulting from the interaction of the particle with the light. Such devices have been used to trap small metal particles, but also viruses, bacteria, living cells, and even strands of DNA. For his contributions to developing optical tweezers, Arthur Ashkin was awarded the 2018 Nobel Prize in Physics.

However, optical tweezers are limited by distance and the size of the objects. Essentially, only very small objects can be manipulated with light in this fashion and only from close range.

“One can levitate a ping pong ball using a steady stream of air from a hair dryer. But it wouldn’t work if the ping pong ball were too big, or if it were too far away from the hair dryer, and so on,” Ognjen Ilic, a postdoc at Caltech and the study’s first author, said in a statement.

In their new study, Ilic and colleagues have proposed a radical new way to use light in order to trap or even propel objects. Theoretically, their method is not limited by an object’s size or distance from the source, which means macroscopic objects such a spacecraft could be accelerated, perhaps even close to relativistic speeds, using the force of light alone.

For this to work, certain nanoscale patterns need to be etched on an object’s surface. When the concentrated laser beam hits this patterned surface, the object should begin to “self-stabilize” by generating torque to keep it in the light beam. The authors say that the patterning is designed in such a way as to encode the object’s stability.

This would work for any kind of object, from a grain of rice to a spaceship in size. The light source could also be millions of miles away which would make this technology ideal to power a light sail for space exploration.

“We have come up with a method that could levitate macroscopic objects,” said Harry Atwater, Professor of Applied Physics and Materials Science in Caltech’s Division of Engineering and Applied Science. “There is an audaciously interesting application to use this technique as a means for propulsion of a new generation of spacecraft. We’re a long way from actually doing that, but we are in the process of testing out the principles.”

The findings were reported in the journal Nature Photonics.
Surface displacement.

Scientists have calculated the force of a photon hitting an object

An international team of researchers has finally been able to calculate the momentum of light.

Light night.

Image credits Felix Mittermeier.

Light exerts a minute pressure on the objects it interacts with. Finding the exact value of this pressure is a quest that scientists have pursued for nearly 150 years now. Today, a team of researchers has finally cracked it.

A light touch

Photons, although lacking in mass, do have momentum — so when they hit an object, they apply a force onto it.

This idea first surfaced in science in 1619, in a treatise by the German mathematician and astronomer Johannes Kepler. He believed that the pressure exerted by light was the reason why a comet’s tail always pointed away from the Sun. In 1873, Scottish physicist James Clerk Maxwell proposed that light is a form of electromagnetic radiation — and thus carries momentum, allowing it to exert pressure on matter. Thus, the pressure exerted by light was linked to its momentum.

Maxwell’s hypothesis turned out to be true. However, because the momentum of light is extremely tiny, the pressure it exerts is also exceedingly low — so measuring it directly is next to impossible.

“Until now, we hadn’t determined how this momentum is converted into force or movement,” explains coauthor and engineer Kenneth Chau of the University of British Columbia, Okanagan Campus, Canada.

“Because the amount of momentum carried by light is very small, we haven’t had equipment sensitive enough to solve this.”

We still don’t have any piece of equipment sensitive enough to measure this momentum — which makes the current findings all the more impressive. Chau’s team — which includes members from Slovenia and Brazil — found a way to work around this limitation, however.

The device they built is based around a mirror. The team fitted highly-sensitive acoustic sensors to it and then encased the contraption in several layers of heat shielding material to protect it from outside interferences. The last step was to shoot laser pulses at the mirror.

As photons in the laser hit the mirror, they apply pressure which generates movement (elastic waves) across its surface. The acoustic sensors measured these waves, which the team later used to calculate the pressure generated by individual photons.

Surface displacement.

Surface displacements caused by the laser. “Displacement” is measured in femtometers (quadrillionths of a meter).
Image credits Tomaž Požar et al., 2018, Nature Communications.

“We were able to trace the features of those waves back to the momentum residing in the light pulse itself, which opens the door to finally defining and modeling how light momentum exists inside materials.”

The research provides the framework from which researchers can refine the value. An accurate value of radiation pressure could have wide-ranging applications, from better optical tweezers — scientific instruments that use highly focused laser beams to manipulate particles down to the scale of a single atom — to more efficient solar sails that will let us zip about the universe without the need for fuel.

“We’re not there yet,” Chau said, “but the discovery in this work is an important step and I’m excited to see where it takes us next.”

The paper “Isolated detection of elastic waves driven by the momentum of light” has been published in the journal Nature Communications.

Three Old Scientific Concepts Getting a Modern Look

If you have a good look at some of the underlying concepts of modern science, you might notice that some of our current notions are rooted in old scientific thinking, some of which originated in ancient times. Some of today’s scientists have even reconsidered or revamped old scientific concepts. We’ve explored some of them below.

4 Elements of the Ancient Greeks vs 4 Phases of Matter

The ancient Greek philosopher and scholar Empedocles (495-430 BC) came up with the cosmogenic belief that all matter was made up of four principal elements: earth, water, air, and fire. He further speculated that these various elements or substances were able to be separated or reconstituted. According to Empedocles, these actions were a result of two forces. These forces were love, which worked to combine, and hate, which brought about a breaking down of the elements.

What scientists refer to as elements today have few similarities with the elements examined by the Greeks thousands of years ago. However, Empedocles’ proposed quadruplet of substances bares resemblance to what we call the four phases of matter: solid, liquid, gas, and plasma. The phases are the different forms or properties material substances can take.

Water in two states: liquid (including the clouds), and solid (ice). Image via Wikipedia.

Compare Empedocles’ substances to the modern phases of matter. “Earth” would be solid. The dirt on the ground is in a solid phase of matter. Next comes water which is a liquid; water is the most common liquid on Earth. Air, something which surrounds us constantly in our atmosphere, is a gaseous form of matter.

And lastly, we come to fire. Fire has fascinated human beings for time beyond history. Fire is similar to plasma in that both generate electromagnetic radiation such as light. Most flames you see in your everyday life are not hot enough to be considered plasma. They are typically considered gaseous. A prime example of an area where plasma is formed is the sun. The ancient four elements have an intriguing correspondent in modern science.

Ancient Concept of Dome Sky vs. Simulation Hypothesis

Millennia ago, people held the notion that his world was flat. Picture a horizontal cooking sheet with a transparent glass bowl set on top of it. Primitive people thought of the Earth in much the same way. They considered the land itself as flat and the sky as a dome. However, early Greek philosophers such as Pythagoras (c. 570-495 BC) — who is also known for formulating the Pythagorean theorem — understood that Earth was actually spherical.

Fast forward to the 21st century. Now scientists are considering the scientific concept of the dome once again but in a much more complex manner.

Regardless of what conspiracy lovers would have you believe, the human race has ventured into outer space, leaving the face of the Earth to travel to the stars. In the face of all our achievements, some scientists actually question if reality is real, a mindboggling and apparently laughable idea.

But some scientists have wondered if we could be existing in a computer simulation. The gap between science and science fiction starts to become very fine when considering this.

This idea calls to mind classic sci-fi plots such as those frequently played out in The Twilight Zone in which everything the characters take as real turns out to be something entirely unexpected. You might also remember the sequence in Men in Black in which the audience sees that the entire universe is inside an alien marble. Bill Nye even uses the dome as an example in discussing hypothetical virtual reality. This gives one the feeling that he is living in a snowglobe.

Medieval Alchemy vs. Modern Chemistry

The alchemists of the Middle Ages attempted to prove that matter could be transformed from one object into an entirely new object. One of their fondest goals they wished to achieve was the creation of gold from a less valuable substance. They were dreaming big, but such dreams have not yet come to fruition. Could it actually be possible to alter one type of matter into another?

Well, modern chemists may be well on their way to achieving this feat some day. They are pursuing the idea of converting light into matter, as is expressed in Albert Einstein’s famous equation. Since 2014, scientists have been claiming that such an operation would be quite feasible, especially with extant technology.

Einstein’s famous equation.

Light is made up of photons, and a contraption capable of performing the conversion has been dubbed “photon-photon collider.” Though we might not be able to transform matter into other matter in the near future, it looks like the light-to-matter transformation has a bright outlook.

light-bulb-1644993_960_720

Scientists just turned light-based information into readable soundwaves

Australian physicists at the University of Sydney converted information encoded in pulses of light into sound waves on the same computer chip. The process also worked in reverse. The research is considered a breakthrough in light-based computing which uses photons instead of electrons to relay bits.

light-bulb-1644993_960_720

Credit: Pixabay.

Light-based electronics are very appealing to the industry since photons can theoretically enable data transmission that’s an order of magnitude greater. A photon-computer could, for instance, be up to 20 times faster than the transistors operating on electrons inside your laptop. Li-Fi, a technology which uses light in routers, can be up to 100 times faster than WiFi.

Right now, transistors are nearing the limit of miniaturization silicon can accommodate. Mass produced computer chips nowadays have embedded transistors that are only 14 nanometers across. That’s only 70 silicon atoms wide.

Light-based computers are thus one possible solution to the otherwise impending halt for “Moore’s Law” — an axiom that suggests that the electronic devices double in speed and capability about every two years. It hasn’t been proven wrong in the last 40 years but the observation can’t remain viable forever.

If we make sure Moore’s Law is still kicking another 40 years though, the possibilities could be enormous.

A very light chip

There are challenges to building a photon chip, though. Ironically, photons are too fast to be read by microprocessors. And yes, fiber optic cables do use light waves to carry information but these are immediately slowed down into electrons for computers to swallow.

Before we can achieve photon-computer status, we have to jump through some hoops. An important intermediate step was recently achieved by a team led by Dr Birgit Stiller, a research fellow at the University of Sydney.

Stiller and colleagues transferred information from the optical to the acoustic domain and back again inside a chip, as described in Nature Communications. 

“The information in our chip in acoustic form travels at a velocity five orders of magnitude slower than in the optical domain,” said Dr Stiller said in a press release.

“It is like the difference between thunder and lightning,” she said.

This delay actually proves useful considering the state of the art right now. It gives the computer chip enough breath to store and manage the information for later processing, retrieval and further transmission as light waves. The video below gives you a glimpse of how all of this works.

“This is an important step forward in the field of optical information processing as this concept fulfills all requirements for current and future generation optical communication systems,” said Professor Benjamin Eggleton, study co-author.

What exactly is a photon? Definition, properties, facts

Imagine a shaft of yellow sunlight beaming through a window. According to quantum physics that beam is made of zillions of tiny packets of light, called photons, streaming through the air. But what exactly is a photon?

photon

Photons are the stuff light is made of. Credit:JFC.

Definition

A photon is the smallest discrete amount or quantum of electromagnetic radiation. It is the basic unit of all light.

Photons are always in motion and, in a vacuum, travel at a constant speed to all observers of 2.998 x 108 m/s. This is commonly referred to as the speed of light, denoted by the letter c. 

As per Einstein’s light quantum theory, photons have energy equal to their oscillation frequency times Planck’s constant. Einstein proved that light is a flow of photons, the energy of these photons is the height of their oscillation frequency, and the intensity of the light corresponds to the number of photons. Essentially, he explained how a stream of photons can act both as a wave and particle.

Photon properties

The basic properties of photons are:

  • They have zero mass and rest energy. They only exist as moving particles.
  • They are elementary particles despite lacking rest mass.
  • They have no electric charge.
  • They are stable.
  • They are spin-1 particles which makes them bosons.
  • They carry energy and momentum which are dependent on the frequency.
  • They can have interactions with other particles such as electrons, such as the Compton effect.
  • They can be destroyed or created by many natural processes, for instance when radiation is absorbed or emitted.
  • When in empty space, they travel at the speed of light.

History

The nature of light — whether you regard it as a particle or a wave — was one of the greatest scientific debates. For centuries philosophers and scientists have argued about the matter that was barely resolved a century ago.

The disciples of a sixth century BC branch of Hindu philosophy called Vaisheshika had a surprising physical intuition about light. Like the ancient Greeks, they used to believe the world was based on ‘atoms’ of earth, air, fire, and water. Light itself was thought to be made of such very fast-moving atoms called tejas. That’s remarkably similar to our modern theory of light and its composing photons, a term coined thousands of years later in 1926 by a chemist named Gilbert Lewis and an optical physicist called Frithiof Wolfers.

Later, around 300 BC, the ancient Greek physicist Euclid made a huge breakthrough when he posited light traveled in straight lines. Euclid also described the laws of reflection and, a century later, Ptolemy complemented with writings about refraction. IT wasn’t until 1021, however, that the laws of refraction were formally established in the seminal work Kitab al-Manazir, or Book of Optics, by Ibn al-Haytham.

The Renaissance would usher in a new age of scientific inquiry into the nature of light. Of note are René Descartes’ incursions in a 1637 essay called La dioptrique, where he argued that light is made of pulses that propagate instantaneously when contacting ‘balls’ in a medium. Later writing in Traité de la lumière published in 1690, Christiaan Huygens treated light as compressible waves in an elastic medium, just like sound pressure waves. Huygens showed how to make reflected, refracted, and screened waves of light and also explained double refraction.

By this time, scientists had split into two entrenched camps. One side believed that light was a wave while the other view was of light as particles or corpuscles. The great champion of the so-called ‘corpuscularists’ was none other than Isaac Newton, widely believed as the greatest scientist ever. Newton wasn’t fond at all of the wave theory since that would mean light would be able to stray too far into the shadow.

For much of the 18th century, corpuscular theory dominated the debate around the nature of light. But then, in May 1801, Thomas Young introduced the world to his now famous two-slit experiment where he demonstrated the interference of light waves.

Young's slit experiment shows how each slit acts as a source of spherical waves, which "interfere" as they move from left to right as shown above. Credit: University of Louisville Department of Physics.

Young’s slit experiment shows how each slit acts as a source of spherical waves, which “interfere” as they move from left to right as shown above. Credit: University of Louisville Department of Physics.

In the first version of the experiment, Young actually didn’t use two slits, but rather a single thin card. The physicist simply covered a window with a piece of paper with a tiny hole in it which served to funnel a thin beam of light. With the card in his hand, Young witnessed how the beam split in two. Light passing on one side of the card interfered with light from the other side of the card to create fringes, which could be observed on the opposite wall. Later, Young used this data to calculate the wavelengths of various colors of light and came remarkably close to modern values. The demonstration would provide solid evidence that light was a wave, not a particle.

Meanwhile, this time in France, the corpuscularist movement was gaining steam after recent developments attributed the polarization of light to some kind of asymmetry among the light corpuscles. They suffered a great defeat at the hand of Augustin Fresnel who in 1821 showed that polarization could be explained if light were a transverse wave with no longitudinal vibration. Previously, Fresnel also came up with a precise wave theory of diffraction.

By this point, there was little stable ground for Newton’s followers to continue the debate. It seemed light is a wave and that’s that. The problem was that the fabled aether — the mysterious medium required to support electromagnetic fields and to yield Fresnel’s laws of propagation — was missing despite everyone’s best efforts to find it. No one ever did, actually.

A huge breakthrough came in 1861 when James Clerk Maxwell condensed experimental and theoretical knowledge about electricity and magnetism in 20 equations. Maxwell predicted an ‘electromagnetic wave’, which can self-sustain, even in a vacuum, in the absence of conventional currents. This means no aether is required for light to propagate! Moreover, he predicted the speed of this wave to be 310,740,000 m s−1 — that’s just a few percent of the exact value of the speed of light.

“The agreement of the results seems to show that light and magnetism are affections of the same substance, and light is an electromagnetic disturbance propagated through the field according to electromagnetic laws”, wrote Maxwell in 1865.

From that day forward, the concept of light was united with those of electricity and magnetism for the first time.

On 14 December 1900, Max Planck demonstrated that heat radiation was emitted and absorbed in discrete packets of energy — quanta.  Later, Albert Einstein showed in 1905 that this also applied to light. Einstein used the term Lichtquant, or quantum of light. Now, at the dawn of the 20th-century, a new revolution in physics would once again hinge on the nature of light. This time, it’s not about whether light is a crepuscule or wave. It’s whether it’s both or not.

Modern theory of light and photons

Einstein believed light is a particle (photon) and the flow of photons is a wave. The German physicist was convinced light had a particle nature following his discovery of the photoelectric effect, in which electrons fly out of a metal surface exposed to light. If light was a wave, that couldn’t have happened. Another puzzling matter is how photoelectrons multiply when strong light is applied. Einstein explained the photoelectric effect by saying that “light itself is a particle,” for which he would later receive the Nobel Prize in Physics.

The main point of Einstein’s light quantum theory is that light’s energy is related to its oscillation frequency. He maintained that photons have energy equal to “Planck’s constant times oscillation frequency,” and this photon energy is the height of the oscillation frequency while the intensity of light corresponds to the number of photons. The various properties of light, which is a type of electromagnetic wave, are due to the behavior of extremely small particles called photons that are invisible to the naked eye.

Einstein speculated that when electrons within matter collide with photons, the former takes the latter’s energy and flies out and that the higher the oscillation frequency of the photons that strike, the greater the electron energy that will come flying out. Some of you have a working proof of this idea in your very own home — it’s the solar panels!  In short, he was saying that light is a flow of photons, the energy of these photons is the height of their oscillation frequency, and the intensity of the light is related to the number of photons.

Einstein was able to prove his theory by deriving Planck’s constant from his experiments on the photoelectric effect. His calculations rendered a Planck’s constant value of 6.6260755 x 10-34  which is exactly what Max Planck obtained in 1900 through his research on electromagnetic waves. Unequivocally, this pointed to an intimate relationship between the properties and the oscillation frequency of light as a wave and the properties and momentum of light as a particle. Later, during the 1920s, Austrian physicist Erwin Schrödinger elaborated on these ideas with his equation for the quantum wave function to describe what a wave looks like.

More than a hundred years since Einstein showed the double nature of light, Swiss physicists at the École Polytechnique Fédérale de Lausanne captured the first-ever snapshot of this dual behavior. The team led by  Fabrizio Carbone performed a clever experiment in 2015 in which a laser was used to fire onto a nanowire, causing electrons to vibrate. Light travels along this tiny wire in two possible directions, like cars on a highway. When waves traveling in opposite directions meet each other they form a new wave that looks like it is standing in place. Here, this standing wave becomes the source of light for the experiment, radiating around the nanowire. The fired a new beam of electrons to image the standing wave of light, which acts as a fingerprint of the wave-nature of light. The result can be seen below.

The first ever photograph of light as both a particle and wave. Credit: EPFL.

What a photon looks like

Have you ever wondered what shape does a photon have? Scientists have been pondering this question for decades and, finally, in 2016, Polish physicists created the first ever hologram of a single light particle. The team at the University of Warsaw made the hologram by firing two light beams at a beamsplitter, made of calcite crystal, at the same time. The beamsplitter is akin to a traffic light intersection so each photon can either pass straight through or make a turn. When a photon is on its own, each path is equally probable but when more photons are involved they interact and the odds change. If you know the wave function of one of the photons, it’s possible to figure out the shape of the second from the positions of flashes appearing on a detector. The resulting image looks a bit like a Maltese cross, just like the wave function predicted from Schrödinger’s equation.

Hologram of a single photon reconstructed from raw measurements seen in the left-hand side versus the theoretically predicted photon shape on the right-hand side. Credit: FUW

Hologram of a single photon reconstructed from raw measurements seen in the left-hand side versus the theoretically predicted photon shape on the right-hand side. Credit: FUW

Facts about photons

  • Not only is light made up of photons, but all electromagnetic energy (i.e. microwaves, radio waves, X-rays) is made up of photons.
  • The original concept of the photon was developed by Albert Einstein. However, it was scientist Gilbert N. Lewis who first used the word “photon” to describe it.
  • The theory that states that light behaves both like a wave and a particle is called the wave-particle duality theory.
  • Photons are always electrically neutral. They have no electrical charge.
  • Photons do not decay on their own.

First ever optical chip to permanently store data developed

Material scientists at Oxford University, collaborating with experts from Karlsruhe, Munster and Exeter, have developed the world’s first light-based memory banks that can store data permanently. The device is build from simple materials, in use in CDs and DVDs today, and promises to dramatically improve the speed of modern computing.

A schematic of the device, showing its structure and the propagation of light through it.
Image courtesy of University of Oxford

Von-Neumann’s Bottleneck

Computing power has come a long in a very short time, with the processors that brought Apollo 11 to the Moon only 50 years ago being outmatched by your average smartphone. But in coming so far with their development, other areas of hardware have lagged behind in evolution, holding back our computers’ overall performance. The relatively slow flow of data between the processor and memory is the main limiting factor, as Professor Harish Bhaskaran, who led the research, explains.

“There’s no point using faster processors if the limiting factor is the shuttling of information to-and-from the memory — the so-called von-Neumann bottleneck,” he says. “But we think using light can significantly speed this up.”

However, simply basing the flow of information on light wouldn’t solve the problem.

Think of the processor as a busy downtown area, the data banks as being the residential areas and information bits as the cars commuting between the two. Even if the areas were to be connected by a highway with enough lanes and light-speed speed limits, the cars getting off it and driving through the neighborhoods at low speed to reach individual homes would clog up the traffic. In the same way, the need to convert the information from photons back to electrical signals would mean that the bottleneck isn’t removed, merely constrained to that particular process.

What scientists need is to base the whole system — processing, flow and memory — on light. There have been previous attempts to create this kind of photonic memory storage before, but they proved too volatile to be useful — they require power to store data. For them to be useful as computer disk drives, for example, they need to be able to store data indefinitely, with or without power.

And international team of researchers headed by Oxford University’s Department of Materials has successfully produced just that — the world’s first all-photonic nonvolatile memory chip.

A bright future for data storage

The device uses the phase-change material Ge2Sb2Te5 (GST) — the same as that used in rewritable CDs and DVDs — to store data. The material can assume an amorphous state (like glass) or a crystalline state (like a metal) when subjected to either an electrical or optical pulse.

To take advantage of this property, the team fused small sections of GST onto a silicon nitride ridge (known as a waveguide) that carries light to the chips, and successfully proved that intense pulses sent through the waveguide can produce the desired changes in the material. An intense pulse causes it to momentarily melt and quickly cool, causing it to assume an amorphous structure; a slightly less-intense pulse can put it into a crystalline state. This is how the data is stored.

Later, when the data is required, light with much lower intensity is sent through the waveguide. The two states of the GST dictates how much light can pass through the chip, the difference is read and interpreted as either 1 or 0.

“This is the first ever truly non-volatile integrated optical memory device to be created,” explains Clarendon Scholar and DPhil student Carlos Ríos, one of the two lead authors of the paper. “And we’ve achieved it using established materials that are known for their long-term data retention — GST remains in the state that it’s placed in for decades.”

And by sending out different wavelengths of light through the waveguide at the same time, a technique called wavelength multiplexing, they can use a single pulse to encode and recover the data at the same time.

“In theory, that means we could read and write to thousands of bits at once, providing virtually unlimited bandwidth,” explains Professor Wolfram Pernice from the University of Munster.

The researchers have also found that different intensities of strong pulses can accurately and repeatedly create different mixtures of amorphous and crystalline structure within the GST. When lower intensity pulses were sent through the waveguide to read the contents of the device, they were also able to detect the subtle differences in transmitted light, allowing them to reliably write and read off eight different levels of state composition — from entirely crystalline to completely amorphous. This multi-state capability could provide memory units with more than the usual binary information of 0 and 1, allowing a single bits of memory to store several states or even perform calculations themselves instead of at the processor.

“This is a completely new kind of functionality using proven existing materials,’ explains Professor Bhaskaran. ‘These optical bits can be written with frequencies of up to one gigahertz and could provide huge bandwidths. This is the kind of ultra-fast data storage that modern computing needs.”

Now, the team is working on a number of projects that aim to make use of the new technology. They’re particularly interested in developing a new kind of electro-optical interconnect, which will allow the memory chips to directly interface with other components using light, rather than electrical signals.

The world’s first image of light as both a particle and a wave

We see light every day, and yet, we don’t truly understand it; it’s either a particle or a wave, or both at the same time… and we don’t really know why. Now, for the first time, researchers have captured an image of light behaving as a particle and a wave at the same time.

Wave-Particle Duality

The wave signature is on the top of the image, while the photons are at the bottom. Image: Fabrizio Carbone/EPFL

Christian Huygens, who was a contemporary of Isaac Newton, suggested that light travels in waves. Isaac Newton, however, thought that light was composed of particles that were too small to detect individually. Strangely enough.. they were both right. In 1801 a physicist in England, Thomas Young, performed experiments which revealed that light is a wave. In the 1890s, Maxwell’s equations described light behavior in such an elegant way that many scientists thought not much was left to say about it.

Then, on Dec. 14, 1900, Max Planck came along and introduced a stunningly simple, yet strangely unsettling, concept: that light must carry energy in discrete, specific quantities. Before you know it, the particle nature came back with a vengeance; to make things even more interesting, Louis De Broglie demonstrated that every physical object actually has wave properties – in a way, everything is both a wave and matter at the same time. This is called the wave-particle duality.

As Einstein wrote:

“It seems as though we must use sometimes the one theory and sometimes the other, while at times we may use either. We are faced with a new kind of difficulty. We have two contradictory pictures of reality; separately neither of them fully explains the phenomena of light, but together they do”.

This seems to be most intriguing in the case of light – it seems that light behaves selectively depending on the environmental constraints. Sometimes it’s a wave, sometimes it’s a particle… and sometimes it’s both. Scientists have only ever been able to capture an image of light as either a particle or a wave, and never both at the same time… until now.

The first Wave-Particle image

The key to this success lies in the unusual experimental design. The team from the École Polytechnique Fédérale de Lausanne in Switzerland have managed to use electrons to image light by firing a pulse of laser light at a single strand of nanowire suspended on a piece of graphene film. This caused the nanowire to vibrate, and in turn, to send light particles (photons) along two possible directions. When light particles that are travelling on opposite directions meet and overlap on the wire, they form a wave. Known as a ‘standing wave’, this state creates light that radiates around the nanowire.

That’s a pretty creative setup in its own right, but it’s not gonna give you a wave-particle image, so they needed to take it one step further. They sent a stream of electrons into the area nearby the nanowire, forcing an interaction between the electrons and the light that had been confined on the nanowire. This caused the electrons to either speed up or slow down; using an ultrafast electron,  they could visualise the standing wave, “which acts as a fingerprint of the wave-nature of light,” the press release explains. So they were able to capture as  a wave (its fingerprint actually; at the top of the image) and as photons (in the bottom of the image).

“This experiment demonstrates that, for the first time ever, we can film quantum mechanics – and its paradoxical nature – directly,” one of the team, physicist  Fabrizio Carbone, said in a press release. “Being able to image and control quantum phenomena at the nanometer scale like this opens up a new route towards quantum computing.”

The team in Switzerland also put together the adorable video above, explaining their experiment.

Journal Reference: L Piazza, T.T.A. Lummen, E Quiñonez, Y Murooka, B.W. Reed, B Barwick & F Carbone. Simultaneous observation of the quantization and the interference pattern of a plasmonic near-field. Nature Communications 6, Article number: 6407 doi:10.1038/ncomms7407

 

 

The light in a glass fiber is coupled to a bottle resonator. (Photo Credit: TU Wien)

Scientists coax Two Photons to interact in Ultra-thin Fiber Glass

Austrian researchers at the Vienna Univ. of Technology (TU Wien) made just two photons interact with each other, a major feat that might have profound implications for quantum technology applications – computing, information teleportation and security.

Two photons, one interaction

These latest developments could prove to be essential to quantum applications, like a quantum network that allows for instant and secure transmission of information. Credit: The Connectivist

These latest developments could prove to be essential to quantum applications, like a quantum network that allows for instant and secure transmission of information. Credit: The Connectivist

In a free medium, light waves – and consequently photons – do not interact between each other. Sometimes this interaction is desirable, and in 1936 H. Euler demonstrated that a photo-photon interaction is possible in a quantum electrodynamics frame, yet this is visible only at high energies in set-ups that makes us of particle accelerators. Optically, photons can be coaxed to interact in a “non-linear” medium, where high intensity beams of light are released in vacuum. The light has an effect on the properties of these materials, and the material in turn influences the light, which leads to an indirect coupling between photons. Because of the high intensity, countless photons are present. The latest developments in Vienna, however, demonstrate an unprecedented degree of control and resolution: only two photons were manipulated to interact with one another. Theoretically, this means that a slew of quantum applications are now possible!

The light in a glass fiber is coupled to a bottle resonator.  (Photo Credit: TU Wien)

The light in a glass fiber is coupled to a bottle resonator.
(Photo Credit: TU Wien)

The researchers made use of a nifty trick to coax the two photons to interact. In fact, the interactions is so strong that the phase of the photons is changed by 180 degrees.

“It is like a pendulum, which should actually swing to the left, but due to coupling with a second pendulum, it swings to the right. There cannot be a more extreme change in the pendulum’s oscillation”, says Professor Arno Rauschenbeutel (Institute for Atomic and Subatomic Physics, TU Wien). “We achieve the strongest possible interaction with the smallest possible intensity of light.”

The system employed at TU Wien is largely made up of an ultra-thin glass fibre, coupled to a tiny bottle-like light resonator so that light can partly enter the resonator, move in circles and return to the glass fibre. This detour is what causes the photon’s phase to become inverted, but when a single rubidium atom is coupled to the resonator we’re in for an unexpected turn. Because of the rubidium atom, hardly any light enters the resonator, until two photons arrive at the same time.

[ALSO SEE] Quantum leap: bits of light successfully teleported

“The atom is an absorber which can be saturated”, says Arno Rauschenbeutel. “A photon is absorbed by the atom for a short while and then released into the resonator. During that time, it cannot absorb any other photons. If two photons arrive simultaneously, only one can be absorbed, while the other can still be phase shifted.”

Glass fiber for the quantum highway of the future!

Light runs around a bottle-shaped glass fiber, about half as thick as a human hair.  (Photo Credit: TU Wien)

Light runs around a bottle-shaped glass fiber, about half as thick as a human hair.
(Photo Credit: TU Wien)

What’s pretty funny (hey, quantum mechanics!) is that there’s no distinction between the photons. There’s absolutely no way to tell which of the two photons is getting absorbed and which is released. When both hit the resonator at the same time, both of them together experience a phase shift by 180 degrees. Two interacting photons arriving simultaneously show a completely different behaviour than single photons, according to the paper Nature Photonics.

[INTERESTING] First-ever working quantum network lays foundation for the future’s quantum internet

“That way, a maximally entangled photon state can be created”, says Arno Rauschenbeutel. “Such states are required in all fields of quantum optics – in quantum teleportation, or for light-transistors which could potentially be used for quantum computing.”

While this may sound like a big deal (it really is), the tech involved is rather rudimentary. Fiber glass has been used for decades and nowadays there are hundreds of thousands of miles worth of fiber optic installed all over the world to serve your internet needs. Nano glass fibres and bottle-resonators are perfectly compatible with existing technologies, as well, so we already have the logistics at our disposal to install the network of the future – a super-secure and super-fast (instant, as in teleportation) quantum network. We just need to work out a few tidbits … like the physics behind. Trust me, that’s no easy task. Get ready for the future, until then.

New material allows ultra-thin, transparent solar cells

Image courtesy of Vienna University of Technology, TU Vienna

Extremely thin, semi-transparent and flexible solar cells are one step closer to becoming a reality. Scientists have managed to create a semiconductor structure consisting of two ultra-thin layers which is excellent for solar panels. The solar cells are also transparent, so they could be used as windows or glass fronts.

Several months ago, the team created the first layer, an ultra-thin layer of the photoactive crystal tungsten diselenide. Now, they have successfully combined it with another layer made of molybdenum disulphide, creating a system that could be used in the future generation of solar cells.

Ultra-thin materials, having only several atoms in thickness are a hot topic in science. The most notable example is graphene, the wonder material consisting of only 1 atom of thickness arranged in a lattice. We’ve already written how graphene could make the internet 100 times faster, how it can make incredibly resistant yarn which could revolutionize the textile industry, how it can give us predator vision, develop new transistors, repair itself naturally, and many more. But the good thing about graphene studies is that they didn’t just show us what graphene can do – it also showed us what other extremely thin materials can do. At the Vienna University of Technology, Thomas Mueller, Marco Furchi and Andreas Pospischil have put that knowledge to good use:

“Quite often, two-dimensional crystals have electronic properties that are completely different from those of thicker layers of the same material,” says Thomas Mueller. His team was the first to combine two different ultra-thin semiconductor layers and study their optoelectronic properties.

Tungsten diselenide was known to be able to transform solar energy into electricity and vice versa. It had a significant problem though – a solar cell made from it would require a huge number of tiny electrodes to properly function. For this reason, it was discarded from studies for a while. However, researchers found an elegant way around that using another layer of molybdenium disulphide, which also consists of three atomic layers. The exact mechanism through which it does this is rather complicated.

When light shines upon an object, photons displace electrons from their original position. Without the electron, which is negatively charged, a positively charged hole remains in place. Both the electron and the hole can move freely in the material, but here’s the thing – they only contribute with energy when they are kept apart, so they cannot recombine. In order to prevent recombination of electrons and holes, metallic electrodes can be used to suck the charge away.

The holes move inside the tungsten diselenide layer, the electrons, on the other hand, migrate into the molybednium disulphide,” says Thomas Mueller. Thus, recombination is suppressed.

Of course, this only works if the energy is tuned just right in both layers – but this can be ensured through electrostatic fields. Florian Libisch and Professor Joachim Burgdörfer (TU Vienna) used computer models to predict what energies changes are in both layers and what voltage leads to optimum energy yields.

“One of the greatest challenges was to stack the two materials, creating an atomically flat structure,” says Thomas Mueller. “If there are any molecules between the two layers, so that there is no direct contact, the solar cell will not work.”

Another advantage of this technology is that while part of the light is absorbed and creates energy, most of it passes right through, so these solar cells could be used as glass fronts.

Scientific Reference:

  1. Marco M. Furchi, Andreas Pospischil, Florian Libisch, Joachim Burgdörfer, Thomas Mueller. Photovoltaic Effect in an Electrically Tunable van der Waals Heterojunction. Nano Letters, 2014; 140728125936002 DOI: 10.1021/nl501962c
Troy Van Voorhis, professor of chemistry (left), and Marc Baldo, professor of electrical engineering (right). Photo: MIT

Excition fission model could vastly improve solar cell efficiency

Troy Van Voorhis, professor of chemistry (left), and Marc Baldo, professor of electrical engineering (right). Photo: MIT

Troy Van Voorhis, professor of chemistry (left), and Marc Baldo, professor of electrical engineering (right). Photo: MIT

The most basic principle of a solar cell is that it works by transferring the energy from an incoming photon (light) to a molecule, which causes one or more electrons to become displaced until an electrical current is formed. That’s the absolute gist of it, only besides electricity, some of the incoming photon energy gets lost as waste heat. Oddly enough, however, there are some organic materials that behave in the opposite way: when extra energy is given, more electrons form.

Weird physics

A team of researchers at MIT used both experiments and theoretical models to explain the mechanics of this phenomenon – called singlet exciton fission – and thus help solar cells become vastly more efficient.

The phenomenon was first observed in the 1960s, yet the exact mechanism involved has become the subject of intense controversy in the field. MIT’s Troy Van Voorhis, professor of chemistry, and Marc Baldo, professor of electrical engineering, led a team which investigated this odd behaviour. They synthesized and gathered materials made of four types of exciton fission molecules decorated with various sorts of “spinach” — bulky side groups of atoms that change the molecular spacing without altering the physics or chemistry. They then subjected these to various experiments to determine their fission rate.

The MIT team turned to experts including Moungi Bawendi, the Lester Wolfe Professor of Chemistry, and special equipment at Brookhaven National Laboratory and the Cavendish Laboratory at Cambridge University, under the direction of Richard Friend.

Experimental data and theoretical models confirm once and for all what was first proposed some 50 years ago: when excess energy is available in these materials, an electron in an excited molecule swaps places with an electron in an unexcited molecule nearby. The result: one photon in, two electrons out. “

“The simple theory proposed decades ago turns out to explain the behavior,” Van Voorhis says. “The controversial, or ‘exotic,’ mechanisms proposed more recently aren’t required to explain what’s being observed here.”

As such, the results provide a solid guideline for designing solar cells with these sort of exotic materials. They show that molecular packing is important in defining the rate of fission — but only to a point. When the molecules are very close together, the electrons move so quickly that the molecules giving and receiving them don’t have time to adjust. Indeed, a far more important factor is choosing a material that has the right inherent energy levels.

David Reichman, a professor of chemistry at Columbia University who was not involved in this research, considers the new findings “a very important contribution to the singlet fission literature. Via a synergistic combination of modeling, crystal engineering, and experiment, the authors have provided the first systematic study of parameters influencing fission rates,” he says. Their findings “should strongly influence design criteria of fission materials away from goals involving molecular packing and toward a focus on the electronic energy levels of selected materials.”

The results are reported in the journal Nature Chemistry. 

Schematic for two different types of PC/SWNT photoactuators made by tuning the built-in strain of the bilayers. (c) Nature Communications

Smart ‘curtains’ open and close just by responding to light only

Schematic for two different types of PC/SWNT photoactuators made by tuning the built-in strain of the bilayers. (c) Nature Communications

Schematic for two different types of PC/SWNT photoactuators made by tuning the built-in strain of the bilayers. (c) Nature Communications

Researchers at University of California, Berkeley toyed around with novel materials and found a way to make them move and twist in response to light. A first application would be smart curtains that simply open or close according to how much light is in the room – no remote, no batteries, no electricity. It uses only the energy it absorbs from incoming light. Ali Javey, associate professor of electrical engineering and computer sciences, and colleagues, layered carbon nanotubes – atom thick rolled up carbon – onto a plastic polycarbonate membrane. When exposed to light, the carbon nanotubes absorb photon energy, part of which gets converted to heat. The rising temperature has no particular mechanical effect on the nanotubes, however the polycarbonate layer expands in response twisting and bending.

“The advantages of this new class of photo-reactive actuator is that it is very easy to make, and it is very sensitive to low-intensity light,” said Javey, who is also a faculty scientist at the Lawrence Berkeley National Lab. “The light from a flashlight is enough to generate a response.”

The researchers tweaked the size and chirality – referring to the left or right direction of twist – of the nanotubes to make the material react to different wavelengths of light. Eventually, the researchers made their combo material respond to artificial light at the flick of a switch.

“We envision these in future smart, energy-efficient buildings,” said Javey. “Curtains made of this material could automatically open or close during the day.”

Besides energy-friendly curtains, the researchers also envision other possible applications like light-driven motors and robotics that move toward or away from light, the researchers said. The novel materials were reported in a paper published in the journal Nature Communications.

Harvard and MIT scientists create photon molecules

Photons and molecules

Mikhail Lukin - image via Harvard.

Mikhail Lukin – image via Harvard.

Scientists managed to ‘trick’ photons (the elementary particles of light and all other forms of electromagnetic radiation) into forming molecules for the first time – a state of matter that until recently had been purely theoretical.

Scientists from Harvard University and the Massachusetts Institute of Technology (MIT) are challenging the current paradigm – they want physicists to rethink what they know about light, and they didn’t have to go in another galaxy to do this.

What happened is that a group led by Harvard Professor of Physics Mikhail Lukin and MIT Professor of Physics Vladan Vuletic managed to coax photons into binding together to form molecules. The discovery goes against decades of accepted theories and ideas on light. Photons have constantly been described as massless particles that don’t interact with each other (they are only considered to have a mass when they are moving). Shine two photon lasers at each other, and the rays will simply pass through each other – photonic molecules seems a nonsensical term.“Most of the properties of light we know about originate from the fact that photons are massless, and that they do not interact with each other,” Lukin said. “What we have done is create a special type of medium in which photons interact with each other so strongly that they begin to act as though they have mass, and they bind together to form molecules. This type of photonic bound state has been discussed theoretically for quite a while, but until now it hadn’t been observed.

What they did isn’t really a photon laser, but rather a… light saber.

Using the Force

"Photonic molecules" behave less like traditional lasers and more like something you might find in science fiction -- the light saber. (Credit: © Yana / Fotolia)

“Photonic molecules” behave less like traditional lasers and more like something you might find in science fiction — the light saber. (Credit: © Yana / Fotolia)

“It’s not an inapt analogy to compare this to light sabers,” Lukin said. “When these photons interact with each other, they’re pushing against and deflecting each other. The physics of what’s happening in these molecules is similar to what we see in the movies.”

But Harvard researchers can’t really rely on “The Force”, so instead, they began by pumping rubidium atoms into a vacuum chamber. After a while, they used lasers to cool the cloud of atoms to just a few degrees above absolute zero (the lowest thermodynamic temperature – −273.15° on the Celsius scale, −459.67° on the Fahrenheit scale). Then, using very weak lasers, they fired single photons into the cloud of atoms. As the photons enter the cloud, they give energy to atoms along their path, which causes them to slow dramatically. As the photons move through the cloud, that energy is handed off from atom to atom, and eventually exits the cloud with the photon.

“When the photon exits the medium, its identity is preserved,” Lukin said. “It’s the same effect we see with refraction of light in a water glass. The light enters the water, it hands off part of its energy to the medium, and inside it exists as light and matter coupled together. But when it exits, it’s still light. The process that takes place is the same. It’s just a bit more extreme. The light is slowed considerably, and a lot more energy is given away than during refraction.”

But when Lukin and his colleagues fired two photons into the cloud, they were really surprised to see the results – the two photons came out of the cloud together, as a single molecule. This is the effect of a rather strange and unintuitive effect, called the Rydberg blockade, which means that when an atom is excited, nearby atoms cannot be excited to the same degree. What this means for this case in particular, is that as the first photon excites an atom, it must move forward before the second one can excited nearby atoms. What’s interesting is that they tend to retain this molecule-like behavior even after exiting the cloud.

 

Photons with strong mutual attraction in a quantum nonlinear medium. Credit: Nature.
Photons with strong mutual attraction in a quantum nonlinear medium. Credit: Nature.

 This could prove to be valuable for developing quantum computers; quantum logic requires interactions between individual quanta so that quantum systems can be switched to perform information processing.

“What we demonstrate with this process allows us to do that,” Lukin said. “Before we make a useful, practical quantum switch or photonic logic gate, we have to improve the performance. So it’s still at the proof-of-concept level, but this is an important step. The physical principles we’ve established here are important.”

The process could be used in the future to create 3D structures, such as crystals, solely out of light.

“What it will be useful for we don’t know yet. But it’s a new state of matter, so we are hopeful that new applications may emerge as we continue to investigate these photonic molecules’ properties,” he said.

A false-color scanning electron microscope image of the etched circuit that produces the sound laser. (c) Imran Mahboob

First working phaser built: a laser that shoots sound

A false-color scanning electron microscope image of the etched circuit that produces the sound laser. (c) Imran Mahboob

A false-color scanning electron microscope image of the etched circuit that produces the sound laser. (c) Imran Mahboob

Trekkies have a reason to rejoice one again after Japanese researchers have successfully devised the first working phaser – a laser that shoots sound particles instead of light. It will take a while though until you’ll be able to zap your neighbors around with a sound canon, as the scientists still need to work around a physical problem their currently facing to allow the vibrations to be transmitted as energy.

Since their advent more than 50 years ago lasers have become indispensable to modern technology, from measurement devices, to optical tech, to of course military applications. What makes them so appealing is that they’re very efficient at displacing energy. A laser works by emitting light particles, known as photons, at a specific and very narrow wavelength, which then travel together at the same time and direction.

Previous attempts have been made of creating a sonic laser, but mostly have failed due to the immense technical difficulties associated. In 2010 a team of researchers at the Johns Hopkins University in Baltimore boasted they had created the first sound laser, however this wasn’t a full sound laser, but a hybrid. This device fooled sound particles – known as phonons – to follow photons emitted from a traditional laser to create a coherent sound emission.

Japanese researchers at NTT Basic Research Laboratories have gotten rid of the optical part and created a working, stand-alone phaser. The team’s device works by employing a mechanical oscillator that excites phonons, which become relaxed and then release their energy back into the device. This trapped energy causes the device to vibrate, however under a very narrow wavelength, similarly to how the laser emits photons. The entire device is etched onto an integrated circuit that’s about 1 cm by 0.5 cm.

Beam me up, Scotty!

However, while lasers can deliver beams of photons anywhere, even through the vacuum of space, sound waves require a medium in order to propagate. This implies that, for the time being at least, phaser waves are confined to their device.

“We would lose the lasing if we get it out,” said co-author of the paper Imran Mahboob of NTT Basic Research Laboratories in Japan. “So we will need to figure out how to build structures onto the resonator that would allow us to transmit the vibrations out as energy.”

Even so, the device is far from being useless. For instance, a tiny device inside the phaser translates the mechanical vibration into an oscillating electrical signal, which could serve as a tiny clock that is a lot more efficient than current electronics that rely on quartz crystals. The phaser could also be used to make extremely precise measurements or for ultrasound imaging purposes.

“It’s still in its infancy, but they showed it can be done, and more people will get involved,” said Jacob Khurgin of Johns Hopkins University in Baltimore.

The phaser was described in a paper published in the journal Physical Review Letters. What’s interesting however is yet again how science fiction servers to inspire and guide the world’s brightest mind to devise them into reality. Previously we’ve reported on other Star Trek gadgets and concepts that made their way to scientists’ drawing boards, like the tricorder, the holodeck and even warp-drive, currently investigated by NASA.

via Wired

Astronomers capture light from first stars using bright galaxies

I gotta say, sometimes it absolutely baffles me to see the kind of complex studies astrophysicists do, and this is definitely one of them. The light from the first stars in the Universe is still lingering around in the cosmos, and researchers have found a new way to capture it: using ultra-bright galaxies that act as cosmic beacons, capturing relict photons in a blaze of gamma rays.

 

But it’s not just these early wandering photos that are captured – every light particle can be ensnared.

“We now have constraints on the total number of stars that ever formed,” Volker Bromm, an astronomer at the University of Texas at Austin, says of the new way to see old light, described online November 1 in Science. “It provides us with a review of the entire history of cosmic star formation, including the very first epochs of star formation in the very early universe.”

The biggest interest is finding out more about the early days of the universe and its first stellar inhabitants, which are currently too far from us to provide any information directly. Now roughly 13.7 billion years old, the universe is believed to have spawned the first stars some 4-500 million years after its birth. Studying these first stars would fill in some major gaps regarding what we know of the universe.

“Detecting these stars is very important but currently impossible,” says astrophysicist Marco Ajello of the Kavli Institute for Particle Astrophysics and Cosmology at Stanford and a coauthor of a the new study. “In this way, we are already able to set constraints on the amount and role of these stars in the early universe.”

Typically, it’s quite difficult to separate this relict starlight from every other object that’s shining; black holes, dust, other stars – all these and many more are just lurking around there, hiding the photon signature of primordial stars, and since we’re well inside the galaxy, there’s not much we can do about it.

“If we were located outside the Milky Way, then we could have measured the background light more easily,” says Avi Loeb, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics. “We are embedded too deep inside the galaxy.”

To get around this problem, Ajello and his colleagues used the orbiting Fermi Large Area Telescope to study distant blazars, a type of bright, active galaxy. Like virtually all galaxies, blazars have supermassive black holes at their centers, but their black holes shoot out enormous jets of energy toward Earth. The jets include gamma rays, a high-energy form of radiation that interacts with the photons sent out by early stars. The photons interact with the gamma rays, and are converted into electrons and their antimatter equivalents – positrons. The transition produces a fade dimming effect, but one that the Fermi telescope can actually observe, and correlate it with the amount of photons between the source and the Earth.

Artist representation of a blazar

 

Since blazars are relatively common and distributed throughout the entire Universe, astronomers use them to measure the photon fog at different ages, and calculate the contributions from early stars. So far, the initial results are quite promising; they show that early stars took more time to form than previously believed, and unlike today’s stars, which also hold heavier elements, early stars were made entirely of hydrogen.

“The first stars were in general more massive — up to hundreds of times as massive as the sun — hotter, brighter, and more short-lived.”

magnetic field

Physics premiere: synthetic magnetism used to control light – new generation of electronics possible

Photons are slippery fellas. Since they don’t have any electrons, they’re free to run through any matter, no matter how intense an electric field may be. Scientists at Stanford, however, have come by a monumental breakthrough after they devised a way to exert virtual force on photons using synthetic magnetism similar to the effect of magnets on electrons. The findings could lead to a whole new generation of highly efficient electronics.

“This is a fundamentally new way to manipulate light flow. It presents a richness of photon control not seen before,” said Shanhui Fan, a professor of electrical engineering at Stanford and senior author of the study.

A fundamental principle of electronics is the ability to maneuver electrons through a given path. When an electron is met with an magnetic field, it will travel along the lines where resistance is lowest, typically in a circular path around the field. In a similar manner, the Stanford researchers have successfully managed to send photons in a circular motion around the synthetic magnetic field.

Key to their attempt were photonic crystals –  materials that can confine and release photons

magnetic fieldWith this in mind, the scientists fashioned a a grid of tiny cavities etched in silicon, which acted as their photonic crystal. By applying a precise electrical current through the grid, the researchers were able to synthesize magnetism and exert virtual force upon photons. The photons’ path is subjected to a great degree of freedom, as researchers are able to modify its radius of curvature  by varying the electrical current applied to the photonic crystal and by manipulating the speed of the photons as they enter the system.

Apparently, in their breakthrough, the scientists managed to break the law as well. Don’t call the police just yet  – the laws of physics that is. A key postulate in physics, the time-reversal symmetry of light, was broken by the researchers after they introduced a charge on the photons that reacts to the effective magnetic field the way an electron would to a real magnetic field. What this means, for engineers at least, is that a photon travelling forward will have different properties than when it is traveling backward, opening a whole new spec of technical possibilities.

 “The breaking of time-reversal symmetry is crucial as it opens up novel ways to control light. We can, for instance, completely prevent light from traveling backward to eliminate reflection,” said Fan.

Think of optical fibers, which although fast for data transmission, still reflect plenty of light and cause noise and distortion of the signal.

“Despite their smooth appearance, glass fibers are, photonically speaking, quite rough. This causes a certain amount of backscatter, which degrades performance,” said Kejie Fang, a doctoral candidate in the Department of Physics at Stanford and the first author of the study.

In essence, once a photon enters the new device it cannot go back. This means a whole new generation of electronics based on light, instead of electricity, could be developed ranging from accelerators and microscopes to speedier on-chip communications.

Findings were reported in the journal Nature Photonics.

source

 

Time travel impossible, huh? Tell that to Dr. Brown.

Time travel proven impossible by scientists

Time travel impossible, huh? Tell that to Dr. Brown.

Time travel impossible, huh? Tell that to Dr. Brown.

A team of Hong Kong scientists have proven that nothing can travel faster than the speed of light in vacuum, at the same time crushing a dream concluding that time travel is simply impossible.

Time travel has been a central theme for science fiction for many years, moving minds and imagination to all sort of places, times and possibilities. Scientists lead by Du Shengwang  from Hong Kong University of Science and Technology have experimentally shown, however, that time travel will forever remain in the realm of SciFi, as they’ve proven that even a  single photon, or unit of light still obeys Einstein’s “traffic laws of the Universe.”

“Einstein claimed that the speed of light was the traffic law of the universe or in simple language, nothing can travel faster than light,” the university said on its website.

Some years ago, an enchanting possibility of time travel emerged when a study suggested that superluminal — or faster-than-light — propagation of optical pulses in some specific medium was obtainable. After some time, the whole matter was found to be a simple visual effect, but hope still remained.

Researchers, have now proven that even a single photon, the fundamental quanta of light, can’t travel faster than the maximum speed.

“The results add to our understanding of how a single photon moves. They also confirm the upper bound on how fast information travels with light,” says Professor Du.

“By showing that single photons cannot travel faster than the speed of light, our results bring a closure to the debate on the true speed of information carried by a single photon. Our findings will also likely have potential applications by giving scientists a better picture on the transmission of quantum information.”

In a novel experiment, the researchers had to separate singular photons for their point to be made across. This required measuring what is known as an optical precursor – the waves that precede photons in a material. By passing pairs of photons through a vapour of atoms held at just 100 millionths of a degree above absolute zero – the Universe’s ultimate low-temperature limit – the team showed that the optical precursor and the photon that caused it are indeed limited to the vacuum speed of light.

The study was published in the U.S. peer-reviewed scientific journal Physical Review Letters.

Physicists create previously thought impossible super photons

Velocity-distribution data of a gas of rubidium atoms, confirming the discovery of a new phase of matter, the Bose–Einstein condensate. Via Wikipedia

A team of physicists from the University of Bonn developed a totally new type of source of light, the so called Bose-Einstein condensate; the results will be published in the upcoming edition of Nature. They managed to achieve this astonishing feat by greatly cooling Rubidium atoms and stashing them into each other, up until the point they become indistinguishable and behave like a single big particle, which researchers call a Bose-Einstein condensate.

Technically speaking, the Bose-Einstein condensate is a state of matter of a dilute gas, of weakly interacting bosons, cooled to a temperature very close to absolute zero (approximately -273 degrees Celsius). Under such conditions, a large fraction of the bosons occupy the lowest quantum state of the external potential, at which point quantum effects become apparent on a macroscopic scale. [Wikipedia]

The apparently unsolvable problem appears when talking about light; the problem is that when photons are cooled down, they just disappear; however, Bonn physicists Jan Klärs, Julian Schmitt, Dr. Frank Vewinger, and Professor Dr. Martin Weitz succeeded where so many others failed.

For a better understanding of the phenomena, we should ask ourselves how warm light really is; for example, if you warm a tungsten filament (standard light bulb filament), it starts glowing, first red, then moves on to yellow and then, finally, blue(ish). It would seem that for every temperature there is a different colour, but the problem is that different metals glow in different colours, so a common starting unit had to be found. In order to achieve this, physicists created a theoretical model, the so called black body. The black body is an idealized object that absorbs all the electromagnetic radiation directed at it. So if you take this theoretical object and theoretically heat it, it will give a common ground for a corelation between light colour and temperature. But what happens when you cool it ?

The creators of the "super-photon" are Julian Schmitt (left), Jan Klaers, Dr. Frank Vewinger and professor Dr. Martin Weitz (right). (Credit: © Volker Lannert / University of Bonn)

If you would cool it, it will at some point stop radiating in the visible spectrum – it will only give out infrared photons which are invisible for the human eye. Also, as you cool it, the radiation intensity will decrease as the number of photons gets smaller (because photons disappear when cooled). The problem seems impossible – how do you lower the temperature of the photons without “killing” them ?

The Bonn researchers used a really inventive system, basically using two highly reflective mirrors and bouncing a beam back and forth between them. What happens is that when light hits the mirrors, the molecules in the mirror absorb the photons and then spit them back, and a whole number of interesting things happen during those collisions:

“During this process, the photons assumed the temperature of the fluid,” explained Professor Weitz. “They cooled each other off to room temperature this way, and they did it without getting lost in the process.”

This should especially please chip designers, because they use laser light for etching logic circuits into their semiconductor materials; just how small and fine these structures can be is limited by the wavelength of light – the smaller the better. A big wavelength is just like writing on a piece of paper with a big paintbrush. In time, this development will pave the way for more performant microchips, which will ultimately affect us all.