Category: Physics

The peculiar topological properties of some forms of matter have been researched for decades. Now, researchers at the Institute of Science and Technology Austria (ISTA) have discovered topological properties of simple diatomic molecules driven to rotation by laser pulses.

The scientists apply similar mathematics to describe them as for solid matter systems, thus bridging two different fields of physics. Their findings promise possible applications in chemistry.

Sometimes, unforeseen connections between disparate research fields in physics can emerge. This is the case for the topological properties of quantum states in rotating molecules.

In a new study, Ph.D. student Volker Karle, Postdoc Areg Ghazaryan, and Professor Mikhail Lemeshko from the Institute of Science and Technology Austria (ISTA), have now revealed that a simple rotating molecule made from just two atoms can feature quantum states with topological properties, similar to what happens in graphene and other solid-state topological materials.

“The interesting thing is that these two systems—a single rotating molecule and a solid sheet of graphene made from millions of carbon atoms—are very different and yet, some of their properties can be described by similar mathematics,” Karle explains. “We are building a bridge between the fields of physical chemistry and solid-state physics.”

The three researchers published their new findings in the journal Physical Review Letters.

A doughnut stays a doughnut

“Topology is the study of the geometrical properties of an object which are unaffected by the continuous change of its shape and size. Realizing that one can classify quantum states not only by their energy and symmetry but also by their topology led to a real breakthrough in our understanding of solid-state physics in the last decades,” Lemeshko explains.

“A simple example of a topological property would be a doughnut. From a mathematical perspective, a doughnut is just a ring with one hole,” Karle adds. “No matter how you stretch or squeeze it, it remains a doughnut as long as you do not do anything as drastic as adding or removing a hole. The property of being a doughnut is therefore topologically protected from ‘small’ disturbances like changing its shape or size.”

In systems like topological insulators, these topological effects emerge from the effects of millions of atoms interacting with one another. However, Karle, Ghazaryan, and Lemeshko have shown that this kind of phenomenon can also be found in much simpler systems like a single molecule.

Pushing a molecule with laser light

“The system we are studying is a single molecule formed by two atoms bonded together,” Karle says. The researchers created a model that describes what happens in such a molecule being pushed by short laser pulses to make it rotate around the midpoint between the two atoms. “At just the right wavelength and timing of the laser pulses, we can create topologically nontrivial quantum states in the molecule that behave like to ones found in solid-state systems.”

For decades now, scientists have studied the topological properties of many different materials and systems—even leading to a Nobel Prize in 2016. However, finding them in a system like a simple molecule allows for new kinds of experiments and applications.

“We are envisioning an experiment where a stream of such molecules is being shot out of a source and then hit with laser pulses,” Karle says. “They then fly into a detector where we can study their quantum states in much greater detail than what’s possible with solid-state systems.” The researchers hope to gain many more insights from future experiments perhaps laying the foundations for new applications in chemistry.

Controlling reactivity

Non-trivial topological properties, like the ones described in this new publication, could lead to topologically protected quantum states. These are especially interesting for any application that needs to be resilient against outside disturbances like heat, magnetic fields, or material impurities. A well-known example that has garnered lots of research interest during the last few years are quantum computers based on topological quantum bits.

However, the molecules that Karle and his colleagues are studying would find different applications. “We hope that this research will allow us to better understand many chemical reactions and may one-day lead to new ways of controlling them,” Lemeshko says. “We could use lasers to create topologically protected quantum states in molecules that increase or decrease their reactivity with other chemicals just as we need it. The topological protection would stabilize the quantum state of the molecule which would otherwise quickly vanish.”

More information: Volker Karle et al, Topological Charges of Periodically Kicked Molecules, Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.130.103202

Journal information: Physical Review Letters 

Provided by Institute of Science and Technology Austria 

Super-resolution microscopy methods are essential for uncovering the structures of cells and the dynamics of molecules. Since researchers overcame the resolution limit of around 250 nanometers (while winning the 2014 Nobel Prize in Chemistry for their efforts), which had long been considered absolute, the methods of microscopy have progressed rapidly.

Now a team led by LMU chemist Prof. Philip Tinnefeld has made a further advance through the combination of various methods, achieving the highest resolution in three-dimensional space and paving the way for a fundamentally new approach for faster imaging of dense molecular structures. The new method permits axial resolution of under 0.3 nanometers.

The researchers combined the so-called pMINFLUX method developed by Tinnefeld’s team with an approach that utilizes special properties of graphene as an energy acceptor. pMINFLUX is based on the measurement of the fluorescence intensity of molecules excited by laser pulses. The method makes it possible to distinguish their lateral distances with a resolution of just 1 nanometer.

Graphene absorbs the energy of a fluorescent molecule that is no more than 40 nanometers distant from its surface. The fluorescence intensity of the molecule therefore depends on its distance from graphene and can be used for axial distance measurement.

DNA-PAINT increases the speed

Consequently, the combination of pMINFLUX with this so-called graphene energy transfer (GET) furnishes information about molecular distances in all three dimensions—and does this in the highest resolution achievable to date of under 0.3 nanometers. “The high precision of GET-pMINFLUX opens the door to new approaches for improving super-resolution microscopy,” says Jonas Zähringer, lead author of the paper.

The researchers also used this to further increase the speed of super-resolution microscopy. To this end, they drew on DNA nanotechnology to develop the so-called L-PAINT approach. In contrast to DNA-PAINT, a technique that enables super-resolution through the binding and unbinding of a DNA strand labeled with a fluorescent dye, the DNA strand in L-PAINT has two binding sequences.

In addition, the researchers designed a binding hierarchy, such that the L-PAINT DNA strand binds longer on one side. This allows the other end of the strand to locally scan the molecule positions at a rapid rate.

“As well as increasing the speed, this permits the scanning of dense clusters faster than the distortions arising from thermal drift,” says Tinnefeld. “Our combination of GET-pMINFLUX and L-PAINT enables us to investigate structures and dynamics at the molecular level that are fundamental to our understanding of biomolecular reactions in cells.”

The findings are published in the journal Light: Science & Applications.

More information: Jonas Zähringer et al, Combining pMINFLUX, graphene energy transfer and DNA-PAINT for nanometer precise 3D super-resolution microscopy, Light: Science & Applications (2023). DOI: 10.1038/s41377-023-01111-8

Journal information: Light: Science & Applications 

Provided by Ludwig Maximilian University of Munich 

Self-testing is a promising method to infer the physics underlying specific quantum experiments using only collected measurements. While this method can be used to examine bipartite pure entangled states, so far it could only be applied to limited kinds of quantum states involving an arbitrary number of systems.

Researchers at Sorbonne University, ICFO-Institute of Photonic Sciences and Quantinuum recently introduced a framework for the quantum network-assisted self-testing of all pure entangled states of an arbitrary number of systems. Their paper, published in Nature Physics, could inform future research efforts aimed at certifying quantum phenomena.

“I was a postdoctoral researcher in Barcelona in 2014 in the group of Antonio Acín when the first author, Ivan Šupić and I began working on self-testing quantum states together,” Matty Hoban, one of the researchers who carried out the study, told Phys.org. “That is, certifying that you have systems in particular quantum states without trusting the devices and treating them as black boxes (called the device-independent setting). Part of this work involved exploring different kinds of scenarios of trust.”

During their initial collaboration, Hoban and Šupić investigated scenarios in which quantum physicists trust some of their experimental components and distrust others. Their goal was to then identify strategies that could simplify the certification of quantum states in these different scenarios.

“I had already moved back to the U.K. and was at the University of Oxford when Ivan visited me and we started exploring a setting where you could prepare particular, simple quantum states and trust this preparation, and then use these states to probe larger systems with more complex quantum states,” Hoban said. “This is a bit like using a small magnet (e.g., a compass) to characterize the magnetic field of the Earth. With the other authors Antonio Acín and Laia Domingo Colomer, we showed how you could self-test arbitrary quantum states in a setting called the Measurement-Device-Independent setting. Meanwhile Ivan was working with Joseph Bowles and Antonio Acín and Daniel Cavalcanti on the detection of entanglement in this completely black-box setting.”

In their new studies, Hoban and his colleagues found that the self-testing of simple quantum states could be a building block for the detection of entanglement. Specifically, this could be achieved by self-testing the maximally entangled state and transferring it in a networked scenario with more systems.

Combining their research efforts, the researchers were able to remove the assumption of characterized quantum state preparation in the measurement-device-independent setting outlined in one of their previous works. They then also teamed up with Marc-Olivier Renou, who was experienced in the study of device-independent quantum systems in networked scenarios.

“In traditional self-testing, if you want to certify that N parties have a particular N-partite quantum state, you would just ask questions of N devices,” Hoban explained. “But now imagine you had a large network of M devices and they can share information, and M could be larger than N. Network-assisted self-testing allows you to ask questions of this larger network to determine the behavior of a smaller number of devices. In the classical world adding additional devices might not seem to add anything: if I ask one person what time it is, their watch shouldn’t depend on whether they had a friend with them or not. But adding quantum systems can add something more.”

A significant difference between quantum systems and classical systems lays in the connections between different systems, particularly in the concept of quantum entanglement. Quantum entanglement underpins many quantum information tasks, such as quantum teleportation.

“If we have two parties, Alice can send an arbitrary unknown quantum state to Bob if they initially share a maximally entangled state,” Hoban said. “So not only entanglement, but maximal entanglement, allows us to move quantum information around from party to party. Instead of just Alice and Bob we can have multiple parties moving this information around, in a network.”

The network-assisted self-testing strategy introduced by Hoban and his colleagues exploits the fact that devices can be entangled with other devices to implement features of quantum theory, including teleportation. As part of their study, the researchers showed that their strategy successfully enables the self-testing of arbitrary pure quantum states.

“On a more foundational level, our results show that you can treat a system as a complete black box, yet from the statistics from interacting with it, you can conclude what the properties of the system are,” Hoban said. “It’s a bit like when you ask a witness to a crime to reconstruct what the alleged criminal looks like; the resulting image can look hilariously wrong or be completely generic. Furthermore, the witness could be lying and you would not know. In our work, you can perform a perfect reconstruction of the quantum description of a system just through asking questions to a black box and you could catch the system out if it tries to lie about what’s inside.”

The recent work by this team of researchers could soon open new opportunities for the certifying quantum devices and entangled quantum states. Notably, their proposed technique is generic, so it could be used to self-test a wide range of quantum states without requiring particular adaptations. Hoban and his colleagues are now working on making their strategy increasingly applicable to real-world problems.

“Our results are more proof-of-principle and require that you achieve some task perfectly; we need to allow for the possibility of some small error,” Hoban added. “This is called robust self-testing in the literature. Also, the methods we used are generic, and we would like to adapt them to particular settings to reduce the resource requirements. I would also like to find applications in delegating quantum computation and quantum cryptography.”

More information: Ivan Šupić et al, Quantum networks self-test all entangled states, Nature Physics (2023). DOI: 10.1038/s41567-023-01945-4

Journal information: Nature Physics 

Bubbles are fun for everyone. But, it turns out, they can also be little menaces.

When a bubble pops, it can concentrate and aerosolize any particles stuck on it. Not a big deal when it’s a store-bought soapy bubble bursting in the yard or on your hand.

But it’s a major concern when the particles it carries are potentially hazardous: bubbles caught in a crashing wave can send vaporized microplastics into the air where they might mess with the Earth’s atmosphere; bubbles burst by a flushing toilet can fling bacteria meters and onto nearby surfaces; a frothing cruise ship hot tub was once shown to be a Legionnaires’ disease super-spreader.

Now, a new study by Boston University engineers illustrates why bubbles fire some contaminants into the air, while allowing others to sink harmlessly. After taking a close-up look at what happens when bubbles pop, the researchers found a new way to predict which particles are flung high—and which ones fall—overhauling a 40-year-old theory of fluid dynamics. Their results, which were published in Physical Review Letters, could help scientists track marine pollution or more accurately predict a virus’ transmissibility.

“With this new theory, we can better model potential ocean sources of pollutants or how other particles in the ocean can get into the atmosphere and act as cloud condensation nuclei, altering the climate,” says Lena Dubitsky, a doctoral student in the BU Fluid Lab and joint lead author on the paper. “In terms of public health, this model helps predict what drop size might contain the most pathogens.”

And that can be crucial in determining how easily a disease might spread or whether a small drop can sneak a virus through the defenses protecting our lower respiratory tract.

At their simplest, bubbles are a thin layer of liquid surrounding a gas. The bubbles kids love blowing, for example, are a layer of water trapped between two layers of soap molecules, with air in the middle.Play

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If you poke the bubble, it creates a hole, which quickly widens—the whole bubble pops in less than one-tenth of a second—forcing the outer soapy layer to collapse, packing its molecules together in a denser space. All of that movement and change in density—as well as the air inside flying up and out—propels drops of water and soap into the sky in a quick pop.

The retreat of that outer layer and the ejection of those drops—particularly the first, or top, drop to exit—is central to the BU Fluid Lab’s new theory. “We focus on jet drops in this study, which are created when the bubble cavity collapses and shoots up into a liquid jet, which pinches off into drops,” says Dubitsky. “In particular, we study the first jet drop since it tends to be the smallest and fastest, making it more likely to stay suspended in the atmosphere, to be transported the furthest, or be inhaled deeply into the respiratory tracts.”

Any particles trapped in that first explosive drop are also more likely to become highly concentrated.

For the past four decades, researchers studying bubbles thought the all-important top drop was drawn from a uniform fluid layer surrounding the entire bubble—only particles small enough to sit in that layer would get pulled into it, meaning bigger particles would get left behind.

“We decided to use really big particles to stress test this old theory and found it didn’t apply at all,” says Dubitsky.

Instead, they discovered that the fluid forming the top drop doesn’t always surround the whole bubble, and that a bubble’s size and where a particle sits on it also determine what gets ejected and when. If that all seems a bit esoteric and technical, just think about SARS-CoV-2. For the past couple of years, our health has been inextricably tied to droplets—how they spread, what they carry with them, how long they linger in the air.

“In order to predict the infectivity of a particular pathogen, one needs to know the infectious dose, so when these droplets become ultraconcentrated, it really matters what size is becoming ultraconcentrated,” says Oliver McRae, a joint lead author on the paper and BU College of Engineering postdoctoral associate.Play

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“If you have a 50-micron droplet [one micron is one one-thousandth of a millimeter], we don’t really care about that much. If you’re able to get larger particles and transport them much further than previously thought, that is a key takeaway.”

To capture the bubbles in action, the research team set up a container filled with fluid and small microplastic particles—little pieces of polystyrene. They then blew bubbles of different sizes into the liquid, using high-speed cameras to watch them rise to the surface and burst. The top drop would splat onto a glass slide above the fluid’s surface, allowing researchers to analyze the particles left behind. McRae then created computer simulations of the bursting bubbles so they could dissect their speedy demise.

“What we saw is that as the bubble is collapsing and the fluid is being swept down toward the base, eventually becoming a jet, the fluid layer is getting thicker,” says McRae, “and so that compression allows for larger particles to get in.”

With larger bubbles, the outer layer was pretty uniform to start with, completely surrounding the bubble; on smaller bubbles though, it barely covered the bottom half.

“That means if you’re a bacteria or a virus and you’re stuck on the upper half of the bubble, you’ll never get in the top drop in a small bubble,” says McRae. “That wasn’t taken into account or wasn’t predicted in previous theories.”

According to James Bird, an ENG associate professor of mechanical engineering and the Fluid Lab’s principal investigator, the research is exciting because it “opens up the possibility that there’s so much more going on than we had appreciated, than we even had the framework to appreciate.”

As an example, he says, the Legionella bacteria, which causes Legionnaires’ disease and is transported by bursting bubbles, has an elongated rather than circular shape. What could his team’s latest findings mean for how it gets swept up in a bubble’s pop? And what could that mean for stemming outbreaks?

“Maybe in a toilet or swimming pool there are strategies one can take to make sure some of these places aren’t going to be as pathogenic,” says Bird. “Or maybe when you have something new, a novel virus or bacteria, there’s ways to predict, just based on the chemistry and the shape, how likely it is to be aerosolized. This work is a stepping stone.”

More information: Lena Dubitsky et al, Enrichment of Scavenged Particles in Jet Drops Determined by Bubble Size and Particle Position, Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.130.054001

Journal information: Physical Review Letters 

Provided by Boston University 

From fundamental physics of light-matter interaction to fabrication of targeted optical properties in highly complex optical engineering, the femtosecond (fs) laser plays a crucial role in laser manufacturing. Ultrashort light pulses can precisely deposit light energy in a given transparent material volume by controllable focusing conditions. Nonlinear absorption of high-density photon energy leads to the creation of free electrons plasma within a few fs, before the electron-phonon energy transfer to the lattice.

At a low repetition rate, the glass network heating is decoupled from light exposure and the plasma itself, enabling localized modifications or even breakdown without surrounding damage. Such nonlinear processes contribute to multiple types of modifications according to laser parameters. The fs laser-induced modifications have found many applications in most branches of nonlinear science, ranging from plasma physics and nano-photonics to material science, bio-photonics and quantum information science.

In a new paper published in Light: Science & Applications, a team of scientists led by Professor Matthieu Lancry from the University Paris Saclay has developed a new technique to tailor chiral optical properties. Their novel procedure implements fs laser 3D direct writing on glasses.

Recent progress highlights that an fs laser beam (axially symmetric intensity distribution, linearly polarized with orthogonal incidence) can create optical chirality inside an achiral material through a direct laser writing. This concept shed light on a new approach for tailoring chiral optical properties in 3D, providing a wider landscape of laser manufacturing. A prerequisite to exploiting such new potentials is to elucidate of how one can manipulate these chiral optical properties.

In this work, they suggested that the breaking of symmetry arises from the combined action of a stress field and a form birefringence due to nanograting formation with the non-parallel non-orthogonal neutral axis. This extrinsic chiral assembly is the source of the observed optical chirality, namely optical rotation and circular dichroism.

The researchers attempted to “disassemble” the dependence of the form birefringence and stress contributions concerning the laser polarization direction. In a simple view, the slow/fast axis of the form birefringence is controlled by the laser polarization direction and the related amplitude by the laser fluence.

Whereas the orientation of stress-induced birefringence is mostly dictated by the scanning geometry. A two-layer model is then developed based on Mueller formalism. It quantitatively explains the creation of both linear and circular anisotropic optical properties.

Finally, the researchers exploited their model to engineer chiral optical properties following two different designs: multilayer “nanograting-based waveplates” and an ultralow loss design based on “stress-engineered waveplates.” The results provide clear evidence that the origin of fs laser-induced circular properties includes two contributions and propose a strategy for tailoring chiral optical properties in any glasses by fs laser direct writing.

More information: Jiafeng Lu et al, Tailoring chiral optical properties by femtosecond laser direct writing in silica, Light: Science & Applications (2023). DOI: 10.1038/s41377-023-01080-y

Journal information: Light: Science & Applications 

Provided by Chinese Academy of Sciences 

Warming a crystal of the mineral fresnoite, Oak Ridge National Laboratory scientists discovered that excitations called phasons carried heat three times farther and faster than phonons, the excitations that usually carry heat through a material.

“Neutrons were ideal for exploring these sources of heat transport because they interact with both phasons and phonons,” said Michael Manley, who led the study with Raphael Hermann.

In most crystals, atomic vibrations propagate excited waves through the lattice as phonons. However, in certain crystals, atomic rearrangements also propagate excited waves as phasons. Because phasons can move faster than sound, physicists anticipated they would excel at moving heat.

The team mapped paths of phasons and phonons and characterized their vibrations at ORNL’s Spallation Neutron Source and measured the transport of heat through the lattice in a Materials Science and Technology Division laboratory.

“We observed phasons carrying heat through the crystal by improving the experimental resolution, like going from the Hubble to the James Webb Space Telescope,” Hermann said, referring to iconic telescopes launched three decades apart.

The results may help theorists improve accuracy for heat transport simulations of energy materials.

The study is published in the journal Physical Review Letters.

More information: M. E. Manley et al, Phason-Dominated Thermal Transport in Fresnoite, Physical Review Letters (2022). DOI: 10.1103/PhysRevLett.129.255901

Journal information: Physical Review Letters 

Provided by Oak Ridge National Laboratory 

In 2018, a team of physicists at Purdue University invented a device which experimentally showed quasiparticles interfering for the first time in the fractional quantum Hall effect at filling factor v=1/3. Further development of these heterostructures has allowed the Manfra Group to expand their research to experiments that explore counterflowing charged edge modes at the 2/3 fractional quantum Hall state.

They have recently published their findings, “Half-Integer Conductance Plateau at the ν = 2/3 Fractional Quantum Hall State in a Quantum Point Contact,” in Physical Review Letters. This novel work has been selected as the Editor’s Suggestion for the forthcoming issue.

The team is led by Dr. Michael J. Manfra, Bill and Dee O’Brien Distinguished Professor of Physics and Astronomy, Professor of Electrical and Computer Engineering, Professor of Materials Engineering, and Scientific Director of the Microsoft Quantum Lab West Lafayette. The lead author of the publication is Dr. James Nakamura, senior research scientist. Dr. Geoffrey Gardner and graduate student Shuang Liang were also co-authors of this publication making valuable contributions to heterostructure growth.

In the experiment, the team produced a semiconductor material which contains a sheet of two-dimensional electrons. On top of this semiconductor, they built a quantum point contact which consists of metal gates with a very narrow 300 nanometer gap. They used the quantum point contact to direct the conducting edge states through the narrow gap.

In this configuration, demonstrated by the graphic above, they were able to measure an electrical conductance equal to half the fundamental value of e²/h. This experimental result is consistent with longstanding theoretical predictions for the edge states of the ν = 2/3 fractional quantum Hall state.

“We have a semiconductor structure that contains electrons arranged in a plane, called a two-dimensional electron system. When you cool the electrons down to low temperature and put them in a strong magnetic field, they form special states of matter called quantum Hall states,” explains Nakamura.

“At a certain value of the magnetic field, the quantum Hall state is called the ν = 2/3 fractional quantum Hall state. At all quantum Hall states, electrical current is carried by edge states that flow around the edge of the sample, and they are chiral, meaning each edge state only flows in one direction (clockwise or counterclockwise). The ν = 2/3 state is predicted by theoretical physicists to have the special property that the there are two edge states which flow in the opposite direction to each other, one clockwise and the other counterclockwise.”

“This is different from most quantum Hall states, where all the edge states flow in the same direction. We used a device with metal gates called a quantum point contact to control the edge states, and our measurements of the edge states in the quantum point contacts confirm the counterflowing edge states in our device.”

“The quantum point contact brings the edge states on opposite edges of the sample close together. We measured a value of electrical conductance across the device equal to half of the value e²/h, where e is the electron’s charge and h is Planck’s constant. This value of the conductance is strong experimental evidence that our system has the edge structure with two counterflowing edge states.”

This research is part of an ongoing quest to understand and manipulate fractionally charged anyons in fractional quantum Hall regime, a rich testbed for exploring the impact of topology in condensed matter physics which may possibly be used to create qubits.

More information: J. Nakamura et al, Half-Integer Conductance Plateau at the ν=2/3 Fractional Quantum Hall State in a Quantum Point Contact, Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.130.076205

Journal information: Physical Review Letters 

Provided by Purdue University 

Burning hydrocarbon fuels produces nano-sized soot particles and Polycyclic Aromatic Hydrocarbons (PAH)—harmful emissions that impact our environment. The carbon-made particles make up 70% of our interstellar space, and black carbon particles from flames are exciting nanomaterials for electronic devices and sustainable energy applications—making their study important.

The lifetimes of soot and PAHs are extremely short (sub nanoseconds to hundreds of nanoseconds) in turbulent flames. Therefore, it requires ultrafast imaging approaches to resolve combustion both in space (2D/3D) and time.

The current state-of-the-art planar imaging systems are limited to just a few million frames per second. To extract 2D maps of flame species, they also require multiple consecutive laser pulses, causing undesired thermal issues. Furthermore, the traditional pump-probe ultrafast imaging methods can only capture the processes which are “repeatable” because several images of the same process are taken at different time instances to extract a complete picture of spatiotemporal dynamics.

Therefore, researchers in the field of combustion science have long awaited a tool that can overcome the limitations of the current systems.

In a new paper published in Light: Science & Applications, a team of scientists, led by Dr. Yogeshwar Nath Mishra, Dr. Peng Wang and Professor Lihong V. Wang, from California Institute of Technology and their collaborators from University of Gothenburg in Sweden, and Friedrich-Alexander University Erlangen in Germany, have developed the world’s fastest planar imaging camera: laser-sheet compressed ultrafast photography (LS-CUP).

Using LS-CUP, they have captured the entire movies of laser-flame dynamics at a record imaging speed of 12.5 billion frame per second (Gfps), which is at least three orders of magnitude higher than the current state-of-the-art systems. Using only one single laser pulse, LS-CUP enabled wide-field real-time imaging of laser-induced fluorescence from PAHs, elastic light scattering and laser-induced incandescence from soot particles.

Dr. Yogeshwar Nath Mishra, one of the leading authors of this paper said, “Laser sheet imaging is one of the most popular techniques for characterizing flows and combustion in two-dimension (2D) because it preferably resolves a plane in both time and space. Using LS-CUP, we can perform many exciting studies and ‘film’ fast chemical reactions and non-repeatable flame-laser interactions using a single laser pulse in real-time beyond the MHz imaging range.”

“We can combine it with pre-existing planar imaging methods for combustion research. Further, we can apply LS-CUP for real-time observation of hydrogen combustion, plasma-assisted combustion, and metal powder combustion—some of the recent hot topics in the field. Temperature is a crucial property in many thermodynamic systems, and to the best of our knowledge, we have reported its fastest wide-field measurements.”

Dr. Peng Wang, the other major contributor to this work, said, “LS-CUP is perfect: it is single-shot, only needs a single laser pulse, has a wide field-of-view, and can be easily adapted to observe all kinds of laser-induced signals over the entire lifetime of soot particles. We extracted critical parameters from the fast dynamics, such as fluorescence lifetimes of PAH molecules, soot nanoparticle sizes and cluster sizes, particle temperature, etc.”

“LS-CUP, in general, allows us to study extremely fast phenomena from a completely new and unique perspective. Reaching far beyond combustion research, the applications of our technique are extremely broad in physics, chemistry, biology and medicine, energy, and environmental research. The capability of capturing ultrafast phenomena represents an important metric of our human’s technology development, which is also driven by the curiosity and needs of scientists and engineers across various fields.”

More information: Yogeshwar Nath Mishra et al, Single-pulse real-time billion-frames-per-second planar imaging of ultrafast nanoparticle-laser dynamics and temperature in flames, Light: Science & Applications (2023). DOI: 10.1038/s41377-023-01095-5

Journal information: Light: Science & Applications 

Provided by Chinese Academy of Sciences 

Photonic integrated circuits, or in short, PICs, utilize particles of light, better known as photons, as opposed to electrons that run in electronic integrated circuits. The main difference between the two: A photonic integrated circuit provides functions for information signals imposed on optical wavelengths typically in the near infrared spectrum.

“Actually, these PICs with many integrated photonic components are able to generate, route, process and detect light on a single chip,” says Dr. Georgy Astakhov, Head of Quantum Technologies at HZDR’s Institute of Ion Beam Physics and Materials Research. “This modality is poised to play a key role in upcoming future technology, such as quantum computing. And PICs will lead the way.”

Before, quantum photonics experiments were notorious for the massive use of “bulk optics” distributed across the optical table and occupying the entire lab. Now, photonic chips are radically changing this landscape. Miniaturization, stability and suitability for mass production might turn them into the workhorse of modern-day quantum photonics.

From random to control mode

Monolithic integration of single-photon sources in a controllable way would give a resource-efficient route to implement millions of photonic qubits in PICs. To run quantum computation protocols, these photons must be indistinguishable. With this, industrial-scale photonic quantum processor production would become feasible.

However, the currently established fabrication method stands in the way of the compatibility of this promising concept with today’s semiconductor technology.

In a first attempt reported about two years ago, the researchers were already able to generate single photons on a silicon wafer, but only in a random and non-scalable way. Since then, they have come far. “Now, we show how focused ion beams from liquid metal alloy ion sources are used to place single-photon emitters at desired positions on the wafer while obtaining a high creation yield and high spectral quality,” says Dr. Nico Klingner, physicist.

Furthermore, the scientists at HZDR subjected the same single-photon emitters to a rigorous material testing program: After several cooling-down and warming-up cycles, they did not observe any degradation of their optical properties. These findings meet the preconditions required for mass production later on.

To translate this achievement into a widespread technology, and allow for wafer-scale engineering of individual photon emitters on the atomic scale compatible with established foundry manufacturing, the team implemented broad-beam implantation in a commercial implanter through a lithographically defined mask.

“This work really allowed us to take advantage of the state-of-the-art silicon processing cleanroom and electron beam lithography machines at the Nano Fabrication facility Rossendorf,” explains Dr. Ciarán Fowley, Cleanroom group leader and Head of Nanofabrication and Analysis.

Using both methods, the team can create dozens of telecom single-photon emitters at predefined locations with a spatial accuracy of about 50 nm. They emit in the strategically important telecommunication O-band and exhibit stable operation over days under continuous-wave excitation.

The scientists are convinced that the realization of controllable fabrication of single-photon emitters in silicon makes them a highly promising candidate for photonic quantum technologies, with a fabrication pathway compatible with very large-scale integration. These single-photon emitters are now technologically ready for production in semiconductor fabs and incorporation into the existing telecommunication infrastructure.

The findings are published in the journal Nature Communications.

More information: Michael Hollenbach et al, Wafer-scale nanofabrication of telecom single-photon emitters in silicon, Nature Communications (2022). DOI: 10.1038/s41467-022-35051-5

Journal information: Nature Communications 

Provided by Helmholtz Association of German Research Centres 

Metasurfaces are highly versatile for manipulating the amplitude, phase, or polarization of light. During the last decade, metasurfaces have been proposed for a vast range of applications—from imaging and holography to the generation of complex light field patterns. Yet, most optical metasurfaces developed to date are isolated optical elements that work only with external light sources.

Despite their versatility for manipulating a light field spatially, most metasurfaces have only a fixed, time-invariant response and a limited ability to control the temporal shape of a light field. To overcome such limitations, researchers are looking into ways to use nonlinear metasurfaces for spatiotemporal light field modulation. However, most materials for constructing metasurfaces have a relatively limited nonlinear optical response on their own.

One solution to the limited nonlinearity of metasurface materials is near-field coupling to a medium with extremely large optical nonlinearity. Epsilon-near-zero (ENZ) materials, an emerging class of materials with vanishing permittivity, have drawn much attention in recent years. For instance, indium tin oxide (ITO), a conductive metal oxide widely used as transparent electrodes in solar cells and consumer electronics, typically has permittivity beyond zero in the near-infrared regime.

An ENZ material, with its linear refractive index approaching zero, is endowed with an extremely large nonlinear refractive index and nonlinear absorption coefficient.

As reported in Advanced Photonics, researchers from Tsinghua University and the Chinese Academy of Sciences recently generated laser pulses with tailored spatiotemporal profiles by directly incorporating an ENZ material coupled to a metasurface in a fiber laser cavity.

The researchers used the geometric phase of a metasurface made of spatially inhomogeneous anisotropic metallic nano-antennas to tailor the transverse mode of the output laser beam. The giant nonlinear saturable absorption of the ENZ-coupled system allows pulsed laser generation via a Q-switching process. To provide a prototype, the researchers realized a microsecond pulsed vortex laser with varying topological charges.

This work provides a new route to construct a laser with a tailored spatiotemporal mode profile in a compact form. For further system miniaturization, the metasurface may be integrated on the fiber-end face.

According to corresponding author Yuanmu Yang, professor at the Tsinghua University State Key Laboratory of Precision Measurement Technology and Instruments, “We hope that our work may further exploration of metasurface versatility for spatial light field manipulation, with its giant and tailorable nonlinearity for generating laser beams with arbitrary spatial and temporal profiles.”

Yang notes that this innovative method may pave the way for the next generation of miniaturized pulsed laser sources, which could be used in various applications, such as light trapping, high-density optical storage, superresolution imaging, and 3D laser lithography.

More information: Wenhe Jia et al, Intracavity spatiotemporal metasurfaces, Advanced Photonics (2023). DOI: 10.1117/1.AP.5.2.026002

Provided by SPIE