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light sound waves

Researchers demonstrate storage and release of mechanical waves without loss of energy

In several technologies which are used today, light and sound waves are the fundamentals for transporting energy and signals. However, until now there has been no method to store a wave for a long period of time and then redirect it to a specific location when needed. This would provide the opportunity to manipulate waves for several purposes such as quantum computing, storing information, energy harvesting and many more.

A team of scientists led by Andrea Alù, founding director of Photonics Initiative, Advanced Science Research Center, CUNY and Massimo Ruzzene, Aeronautics Engineering professor at Georgia Tech has demonstrated experimentally that it is possible to capture a wave and store it efficiently while redirecting it later to a specific location. The work appears in Science Advances journal.

Alù said that the experiment demonstrates new opportunities can be unlocked in wave scattering and propagation through unconventional scattering methods. Researchers found ways to change the basic interaction between waves and particles. On striking an obstacle, a light or sound wave can go through two processes, partial absorption or reflection and scattering. In absorption, the wave is immediately converted to different forms of energy including heat. For those who cannot absorb waves, they are reflected and scattered.

In this experiment, the aim of the researchers was to find some technique to mimic the process of absorption in which the wave would not be converted to any other form instead stored in the material. This is known as coherent virtual absorption and it was introduced by ASRC two years ago.

For proving the theory, it was necessary to tailor the time evolution of waves so that on contacting non-absorbing materials, they would not be scattered, transmitted or reflected. This would prevent the wave from escaping and store it inside the material efficiently. Then it could be released on demand. In the course of the experiment, two mechanical waves were propagated in opposite directions along a carbon steel waveguide that had a cavity. Time variations of every wave were controlled so that the cavity would retain all the energy. The excitation of one of the waves was stopped which enabled the researchers to control the stored energy and send it towards a specific direction.

The experiment was performed using elastic waves which traveled inside a solid material. It can also be replicated for light and radiowaves thus opening the doors to exciting opportunities such as efficient harvesting of energy, wireless power transfer and greater control on wave propagation.

Research Paper: Coherent virtual absorption of elastodynamic waves

Culture of rat brain cells

Researchers develop technology to control the brain cells with help of smartphone

A group of researchers in the United States and Korea have invented a device which can control neural circuits with the help of a small brain implant which is controlled by a smartphone. Scientists believe that this device can amplify the efforts to detect brain diseases like Alzheimer’s, Parkinson’s, migraine and depression. With the help of replaceable drug cartridges similar to LEGO and Bluetooth low-energy, this device can target the specific neurons for prolonged periods using drug and light. The study was published in Nature Biomedical Engineering journal.

Raza Qazi, a scientist with Korea Advanced Institute of Science and Technology (KAIST) and University of Colorado Boulder said that the wireless neural device enables optical and chemical neuromodulation which has been achieved for the first time. This technology overshadows the normal methods used by researchers which generally involve optical fibers and metal tubes for delivering light and drugs. It limits the subject’s movement due to physical connections with the heavy equipment and causes a lesion in soft brain tissue due to their rigid structure. Hence they are not suitable for long-term implantation. Efforts were put to mitigate the adverse tissue response with the incorporation of wireless platforms and soft probes however they could not deliver drugs for a prolonged time period.

For achieving chronic wireless drug delivery, researchers had to solve the challenge of evaporation and exhaustion of drugs. They invented a neural device having a replaceable drug cartridge that allowed to study the brain circuits without worrying about the factor of drug exhaustion. These drug cartridges were assembled for brain implantation in mice with an ultrathin probe which had microfluidic channels, LEDs for unlimited light delivery and drug doses.

Researchers controlled it with a user interface on a smartphone and could trigger any combination of light and drug deliveries in any implanted animal without being present in a laboratory. They could also set up automated animal studies where an animal’s behavior could affect other animals’ behavior due to the conditional triggering of drug and light delivery. This revolutionary equipment is possible due to complex electronics design and powerful nanoscale engineering. It would help scientists in several ways. It would also help to dissect the neural circuit basis of behavior and understand how neuromodulators control behavior in several ways. It would also help researchers develop therapeutics for emotional and addiction disorders.

KAIST researchers developed soft electronics for implantable devices and University of Washington scientists study brain circuits which are responsible for addiction, pain, stress. This global collaboration for three years made it possible to develop the powerful brain implant in mice which can speed up the detection of brain diseases. It was supported by grants from the National Research Foundation, Korea, National Institute of Health in the US, National Institute on Drug Abuse.

Qubit Mechanical Resonator

Researchers successful in developing quantum light sources for use in optical circuits

A team of researchers led by Alexander Holleitner, Jonathan Finley, physicists at Technical University of Munich (TUM) has succeeded in placing light sources in atomically thin material layers having an accuracy of few nanometres. It allows a series of applications in quantum technology ranging from quantum sensors, transistors to encryption technology for transmission of data. The study has been published in Nature Communications

Earlier circuits on chips relied on electrons as carriers of information. However, in the coming days, photons carrying information at the speed of light will perform this task in optical circuits. The basic building blocks for such chips are quantum light sources connected with detectors and quantum fibre optic cables. 

Julian Klein, the study’s lead author said that it is a first step in making optical quantum computers. The light sources need to coupled with photon circuits for future applications to make quantum calculations based on light possible. However, the critical point is the exact controlled placement of the light sources. Quantum light sources in materials such as diamond or silicon can be created but not precisely placed in the materials. 

Physicists used a semiconductor layer, molybdenum disulfide as the initial material with a thickness of three atoms. Then they irradiated it with a beam of helium ions focused on a surface area of less than one nanometre. For generating optically active defects, molybdenum or sulfur atoms are hammered out of layer very precisely. The imperfections are traps for electron-hole pairs which emit the desired photons. The helium ion microscope at Center for Nanotechnology and Nanomaterials, Walter Schottky Institute was used for irradiating the material with accurate lateral resolution. 

Researchers from TUM, University of Bremen, Max Planck Society developed the model for describing the energy state observed at theoretical imperfections.

In future scientists want to create complex light source patterns, in two-dimensional lateral lattice structures for researching multi-exciton phenomena. This is the experimental realisation of the theory within the context of the Bose-Hubbard model, accounting for complex processes in solids. 

As the light sources have a similar underlying defect in the material they cannot be distinguished theoretically. This opens for new opportunities which are based on the quantum-mechanical principle of entanglement. Klein said that it is very much possible for the integration of quantum light sources in the photon circuits in a very elegant manner. Because of the high sensitivity, it is possible to make quantum sensors for smartphones and also make highly secure encryption technologies to transmit data. 

Journal Reference: Nature Communications

Scientists combine light and matter to make particles with new behaviors

Scientists combine light and matter to make particles with new behaviors

Every type of atom in the universe has a unique fingerprint: It only absorbs or emits light at the particular energies that match the allowed orbits of its electrons. That fingerprint enables scientists to identify an atom wherever it is found. A hydrogen atom in outer space absorbs light at the same energies as one on Earth.

While physicists have learned how electric and magnetic fields can manipulate this fingerprint, the number of features that make it up usually remains constant. In work published July 3 in the journal Nature, the University of Chicago researchers challenged this paradigm by shaking electrons with lasers to create “doppelganger” features at new energies—a breakthrough that lets scientists create hybrid particles which are part-atom and part-light, with a wide variety of new behaviors.

The research is part of a greater effort in Assoc. Prof. Jonathan Simon’s lab to break down the walls between matter and light, in order to investigate their fundamental properties. In addition to learning about how materials behave at the quantum level, this work could one day help create more powerful computers or virtually “unhackable” quantum communications.

One step along the way to making matter out of light is to make individual packets of light, called photons, interact with each other like matter does. (Normally photons zip along at the speed of light and don’t react to each other at all.)

“In order to make photons collide with one another, we use atoms as a go-between,” said postdoctoral researcher Logan Clark, who led the research. “But we were running into a problem because the photons only interact with atoms whose electronic orbitals are at very particular energies. So we asked: What if we could make copies of the orbitals at whatever energies we wanted?”

Clark had already developed techniques to manipulate quantum matter by shaking it —called Floquet engineering—as part of his PhD project. The right sort of shaking naturally produces copies of quantum states at multiple energies along the way. “We had always viewed the copies as a side effect rather than the goal,” he said, “but this time, we shook our electrons with the specific intent of making the copies.”

“We asked: What if we could make copies of the orbitals at whatever energies we wanted?”

—Postdoctoral researcher Logan Clark

By varying the intensity of a laser field tuned precisely to an atomic resonance, the team was able to shift the orbitals of an electron. Shaking the orbitals by periodically varying this intensity produced the desired copies.

But these doppelgangers come with an important catch: “While the atomic orbital does appear at multiple distinct energies, it is important to note that these copies are actually bound to the original like puppets,” explained postdoctoral researcher Nathan Schine, a co-author on the study. “When any of the copies shifts, the original and all of the other copies shift with it.”

By allowing photons to interact with these shaken atoms, the team has created what they call “Floquet polaritons”—quasi-particles which are part-light and part-atom, and unlike regular photons, interact with each other quite strongly. These interactions are essential for making matter from light. Making polaritons with shaken atoms can give the polaritons much more flexibility to move around and collide with each other in new ways.

“Floquet polaritons are full of surprises; we’re still continuing to understand them better,” Clark said. “Our next order of business, though, will be to use these colliding photons to make topological ‘fluids’ of light. It is a tremendously exciting time.”

Having copies of an atomic state at multiple energies also offers exciting possibilities for optical frequency conversion—a key tool in creating secure quantum communication methods.

“It turns out shaking things is not only a lot of fun, but can lead to some really fascinating science,” Clark said.

Citation: “Interacting Floquet polaritons.” Clark et al, Nature, July 3, 2019. DOI: 10.1038/s41586-019-1354-5

Materials provided by the University of Chicago

light rays

Researchers discover a property of light never predicted before

A team of researchers from different institutions in Spain and the USA notified that they have found a brand new property of light known as self-torque. The team’s research paper explained how they came to know about the property and what are the uses of it and their research paper was published in the journal Science.

Researchers knew about the properties of light such as wavelength before. By the property known as angular momentum scientists in the recent times came to know that lights can also be twisted. Vortex beams are that kind of beams that have highly structured angular momentum. They also have orbital angular momentum (OAM).

Vortex beams seem to be a helix which is surrounding a common center and when the beams strike a surface which is flat, they appear as doughnut-shaped. The scientists came to know about the new property of light while researching on OAM beams and while researching they found it out surprisingly where the lights were behaving in a way they had never noticed before. The scientists conducted a lot of experiments and the experiments were to fire two laser lights at the cloud formed by argon gas and by doing this it forced the beams to overlap. Thus they joined and they were emitted as a single beam from the other side of the argon cloud. The beam which resulted was a type of vortex beam.

The scientists then thought what would have happened if the lasers were a little bit out of synchronization and if the lasers had different orbital angular momentum.  After this experiment emerged a beam which looked like a corkscrew with a twist which was gradually changing. When the beam hit the flat surface it looked similar to a crescent moon.

The researchers also noticed that it can be looked the other way round as a single photon which was at the front of the beam was revolving around its center slower than a photon which was at the back of the beam. The scientists named this new property as self-torque. This is not only a newly discovered property of light, but it is also the one which was never ever predicted. This technique can be used to modulate the orbital angular momentum of light in a way very similar to that of modulating frequencies in communicating tools. This could lead to the development of devices that are used to manipulate tiny materials.

revealing hidden features using power of light

Revealing ‘hidden’ phases of matter through the power of light

Most people think of water as existing in only one of three phases: solid ice, liquid water, or gas vapour. But matter can exist in many different phases—ice, for example, has more than ten known phases, or ways that its atoms can be spatially arranged. The widespread use of piezoelectric materials, such as microphones and ultrasound, is possible thanks to a fundamental understanding of how an external force, like pressure, temperature, or electricity, can lead to phase transitions that imbue materials with new properties.

A new study finds that a metal oxide has a “hidden” phase, one that gives the material new, ferroelectric properties, the ability to separate positive and negative charges, when it is activated by extremely fast pulses of light. The research was led by MIT researchers Keith A. Nelson, Xian Li, and Edoardo Baldini, in collaboration with Andrew M. Rappe and graduate students Tian Qiu and Jiahao Zhang. The findings were published in Science.

Their work opens the door to creating materials where one can turn on and off properties in a trillionth of a second with the flick of a switch, now with much better control. In addition to changing electric potential, this approach could be used to change other aspects of existing materials—turning an insulator into a metal or flipping its magnetic polarity, for example.

“It’s opening a new horizon for rapid functional material reconfiguration,” says Rappe.

The group studied strontium titanate, a paraelectric material used in optical instruments, capacitors, and resistors. Strontium titanate has a symmetric and nonpolar crystal structure that can be “pushed” into a phase with a polar, tetragonal structure with a pair of oppositely charged ions along its long axis.

Nelson and Rappe’s previous collaboration provided the theoretical basis for this new study, which relied on Nelson’s experience using light to induce phase transitions in solid materials, along with Rappe’s knowledge in developing atomic-level computer models.

“[Nelson is] the experimentalist, and we’re the theorists,” says Rappe. “He can report what he thinks is happening based on spectra, but the interpretation is speculative until we provide a strong physical understanding of what happened.”

With recent improvements in technology and additional knowledge gained from working with terahertz frequencies, the two chemists set out to see if their theory, now more than one decade old, held true. Rappe’s challenge was to complement Nelson’s experiments with an accurate computer-generated version of strontium titanate, with every single atom tracked and represented, that responds to light in the same manner as the material being tested in the lab.

They found that when strontium titanate is excited with light, the ions are pulled in different directions, with positively charged ions moving in one direction and negatively charged ions in the other. Then, instead of the ions immediately falling back into place, the way a pendulum would after it’s been pushed, vibrational movements induced in the other atoms prevent the ions from swinging back immediately.

It’s as if the pendulum, at the moment that it reaches the maximum height of its oscillation, is diverted slightly off course where a small notch holds it in a place away from its initial position.

Thanks to their strong history of collaboration, Nelson and Rappe were able to go back and forth from the theoretical simulations to the experiments, and vice versa, until they found experimental evidence that showed that their theory held true.

“It’s been a really awesome collaboration,” says Nelson. “And it illustrates how ideas can simmer and then return in full force after more than 10 years.”

The two chemists will collaborate with engineers on future applications-driven research, such as creating new materials that have hidden phases, changing light-pulse protocols to create longer lasting phases, and seeing how this approach works for nanomaterials. For now, both researchers are excited about their results and where this fundamental breakthrough could lead to in the future.

“It’s the dream of every scientist—to hatch an idea together with a friend, to map out the consequence of that idea, then to have a chance to translate it into something in the lab, it’s extremely gratifying. It makes us think we’re on the right track towards the future,” says Rappe.

Materials provided by the University of Pennsylvania

pumpkin toadlets

Scientists discover fluorescence in frogs of Atlantic Forest

In the Atlantic Forest in Eastern Brazil, the pumpkin toadlets use their bright colours to warn the other species which can attack them. But scientists have also discovered that these frogs display a signal which is otherwise unknown. Under ultraviolet light, they glow as bright blue. The findings were published in Scientific Reports.

The pumpkin toadlets reside in moist tropical and subtropical forests. As their ears are not developed properly, these frogs are deaf to the mating calls of their own species. Currently, they are the only known species that are deaf to mating calls. While investigating this, scientists accidentally discovered the glowing patterns in two species, Brachycephalus ephippium and  Brachycephalus pitanga.

When observed under natural light, they appear as orange, red or yellow. But when put under UV light, several blue patterns came up on head, back and legs of the toadlets. This is known as fluorescence and it is very rare in vertebrate animals which reside on the land. Scientists are still not sure how fluorescence helps these frogs. It may help them in identifying attackers from beforehand, take preventive actions or identify prospective partners for reproduction.

Fluorescence differs from bioluminescence, in which the body of the animals produces light with the help of chemical reactions. But fluorescence will not function in total darkness as in fluorescence, light is absorbed by some specific molecules and then it is emitted at larger wavelengths, such as red or green which finally creates a glow.

Animals which display fluorescence are corals, scorpions and sea turtle. Scientists also discovered in 2018, that chameleons also show fluorescence. Besides this, another team of researchers found out that two species of a tree frog found in South America have fluorescent skin. But in case of the frogs, the glow originates from the bones similar to that of chameleons.

Researchers observed through chemical analysis that the bony plates which were located on the head and back of the toadlets were very fluorescent. The cells which exhibit fluorescence are also called fluorescent chromatophores. They contain pigments called fluorosomes which contain proteins that are activated with the help of potassium ions. The fluorescent patterns arise from the motion and aggregation of these pigments within the chromatophore.

It is still not known clearly how do the toads use fluorescence for their benefit. It may serve as a warning sign to animals about the toxic nature of the skin as some birds can detect fluorescence in natural light. It can also be used for communication among themselves, as the toads lack the middle ear so they cannot hear calls from their own species.

Speed of light measurement device

Scientists develop techniques to manipulate speed of light

A group of researchers at the University of Central Florida have developed a technique to be able to control the velocity of light. Through this technique they can not only increase the speed of light pulse and decrease it, but they can also make it travel backwards. The results were published in Nature Communications.

This finding is a significant step in the research which can someday lead to the development of highly efficient optical communication techniques. The problems of data congestion and information loss can also be handled with this result. Currently, networks use congestion control and congestion avoidance techniques to avoid these problems. More and more devices are going online everyday and advanced techniques like these will be of prime importance in the future. With fall in the prices of data consumption, people in developing countries are getting easier access to data like never before.

There have been many attempts in the past to control the speed of light. For example, light was passed through different media to adjust the speed. The major breakthrough in this experiment is that speed of light can be adjusted in the open for the first time, without using any pass-through media to increase or decrease its speed.

Ayman Abouraddy, professor in UCF’s College of Optics and Photonics who is also a co-author of this study remarked that this is the first clear demonstration of controlling the speed of the light and this will open up many areas of possibilities not explored before. This is done in a simple, reliable and repetitive way which is an important aspect.

Scientists could speed up the light upto 30 times of its normal speed, reduce to half of the speed of light and also make the pulse travel backwards. The researchers managed to develop the technique with the help of a special device called as the phase-only spatial light modulator (SLM). This helps to combine the space and time properties of light, thus making it possible to manipulate the velocity of light.

SLM was used to sculpt the spatio-temporal spectrum in an efficient manner and thus modify the group velocity. When the researchers manipulated the spatial and temporal degrees of freedom simultaneously, they found out that the group velocities were varying arbitrarily, sometimes more than the speed of light and sometimes less. They were also propagating in the forward direction away from the source and even travelling backward.

The mixing of the two main properties of light was essential to the success and scientists hope that these results can be used in a fruitful way in the future.


Levitating Object Using Light

Researchers devise a way to levitate objects using only light

During childhood days we have been to the magic shows and we have always wondered as to how the objects over there fly in the air. Now we know that it wasn’t magic, but it was physics applied that made it look like magic.

Now the researchers at the California Institute of Technology claim that they have found a way to levitate and propel objects using light, even though for time being the work remains theoretical. It is believed according to a paper published in Nature Photonics that this technique could be used for trajectory control of ultra-light spacecraft and even laser propelled light sails for space exploration. It means that no fuel needed, just a powerful laser fired at a spacecraft from the earth.

Scientists developed photonic levitation and propulsion system by designing a complex pattern that could be etched into an object’s surface.

The way the concentrated light beam reflected from the etching causes the object to “self-stabilize“, they say, as it attempts to stay inside the focused laser beam.

The groundwork for the new research was the development of optical tweezers and the big downside to it was that it could manipulate tiny objects at the microscopic level only.

Generic Optical Tweezer Diagram

Generic Optical Tweezer Diagram (Credit: Wikimedia)

Ognjen Ilic, post-doctoral scholar and first author of the new study, explains the tweezer concept and its limitations in much simpler terms: “One can levitate a ping pong ball using a steady stream of air from a hairdryer. 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.

Though the theory is still untested in the real world, the researchers say that if it pans out, it could send a spacecraft to the nearest star outside our Solar System in just 20 years.

There is an audaciously interesting application to use this technique as a means for propulsion of a new generation of spacecraft,” said Harry Atwater, a professor at the Caltech Division of Engineering and Applied Science.

He also said, “We’re a long way from actually doing that, but we are in the process of testing out the principles.”

Published Research: https://www.nature.com/articles/s41566-019-0373-y