Category: Physics

Quantum technologies are radically transforming our understanding of the universe. One emerging technology is macroscopic mechanical oscillators, devices that are vital in quartz watches, mobile phones, and lasers used in telecommunications. In the quantum realm, macroscopic oscillators could enable ultra-sensitive sensors and components for quantum computing, opening new possibilities for innovation in various industries.

Controlling mechanical oscillators at the quantum level is essential for developing future technologies in quantum computing and ultra-precise sensing. But controlling them collectively is challenging, as it requires near-perfect units, i.e., identical.

Most research in quantum optomechanics has centered on single oscillators, demonstrating quantum phenomena like ground-state cooling and quantum squeezing. But this hasn’t been the case for collective quantum behavior, where many oscillators act as one. Although these collective dynamics are key to creating more powerful quantum systems, they demand exceptionally precise control over multiple oscillators with nearly identical properties.

Scientists led by Tobias Kippenberg at EPFL have now achieved the long-sought goal: They successfully prepared six mechanical oscillators in a collective state, observed their quantum behavior, and measured phenomena that only emerge when oscillators act as a group. The research, published in Science, marks a significant step forward for quantum technologies, opening the door to large-scale quantum systems.

“This is enabled by the extremely low disorder among the mechanical frequencies in a superconducting platform, reaching levels as low as 0.1%,” says Mahdi Chegnizadeh, the first author of the study. “This precision allowed the oscillators to enter a collective state, where they behave as a unified system rather than independent components.”

To enable the observation of quantum effects, the scientists used sideband cooling, a technique that reduces the energy of oscillators to their quantum ground state—the lowest possible energy allowed by quantum mechanics.

Sideband cooling works by shining a laser at an oscillator, with the laser’s light tuned slightly below the oscillator‘s natural frequency. The light’s energy interacts with the vibrating system in a way that subtracts energy from it. This process is crucial for observing delicate quantum effects, as it reduces thermal vibrations and brings the system near stillness.

By increasing the coupling between the microwave cavity and the oscillators, the system transitions from individual to collective dynamics.

“More interestingly, by preparing the collective mode in its quantum ground state, we observed quantum sideband asymmetry, which is the hallmark of quantum collective motion. Typically, quantum motion is confined to a single object, but here it spanned the entire system of oscillators,” says Marco Scigliuzzo, a co-author of the study.

The researchers also observed enhanced cooling rates and the emergence of “dark” mechanical modes, i.e., modes that did not interact with the system’s cavity and retained higher energy.

The findings provide experimental confirmation of theories about collective quantum behavior in mechanical systems and open new possibilities for exploring quantum states. They also have major implications for the future of quantum technologies, as the ability to control collective quantum motion in mechanical systems could lead to advances in quantum sensing and generation of multi-partite entanglement.

All devices were fabricated in the Center of MicroNanoTechnology (CMi) at EPFL.

More information: Mahdi Chegnizadeh et al, Quantum collective motion of macroscopic mechanical oscillators, Science (2024). DOI: 10.1126/science.adr8187. www.science.org/doi/10.1126/science.adr8187

Journal information: Science 

Provided by Ecole Polytechnique Federale de Lausanne 

The magnetic moment of the muon is an important precision parameter for putting the Standard Model of particle physics to the test. After years of work, the research group led by Professor Hartmut Wittig of the PRISMA+ Cluster of Excellence at Johannes Gutenberg University Mainz (JGU) has calculated this quantity using the so-called lattice quantum chromodynamics method (lattice QCD method).

Their result agrees with the latest experimental measurements, in contrast to earlier theoretical calculations.

After the experimental measurements had been pushed to ever higher precision in recent years, attention had increasingly turned to the theoretical prediction and the central question of whether it deviates significantly from the experimental results and thus provides evidence for the existence of new physics beyond the Standard Model.

The anomalous magnetic moment is an intrinsic property of elementary particles such as the electron or its heavier brother, the muon. Calculating this quantity with sufficient accuracy within the framework of the Standard Model is an enormous challenge.

With the only exception of gravity, all fundamental interactions contribute to the anomalous magnetic moment. In particular, the contributions of the strong interaction, which describes the forces between the basic building blocks of protons and neutrons, the quarks, cause great difficulties for physicists.

The main source of uncertainty in the theoretical calculation of the anomalous magnetic moment of the muon is the contribution of the so-called hadronic vacuum polarization (HVP). Traditionally, this contribution has been determined using experimental data—this is called the “data-driven” method.

In fact, over many years, this technique provided a significant deviation from the experimental measured value and thus also one of the most promising indications of the existence of new physics.

Result of the PRISMA+ Cluster of Excellence

Wittig’s group has now published a new result for the HVP contribution as a preprint in the open access archive arXiv, which was obtained using the complementary method of lattice QCD.

“Our work confirms earlier evidence suggesting a clear divergence between the data-driven method and lattice QCD calculations,” says Wittig. “At the same time, we have to conclude from our result that the Standard Model has once again been confirmed, because our result agrees with the experimental measurement.”

In 2020, the “Muon g-2 Theory Initiative”—an international group of 130 physicists with strong participation from Mainz—published a reference value for the theoretical prediction of the anomalous magnetic moment of the muon within the framework of the Standard Model, which is based on the data-driven method.

This actually showed a clear deviation from the new direct measurements of this quantity, which have been carried out at Fermilab near Chicago since 2021.

However, since the publication of new results from the CMD-3 experiment in Novosibirsk in February 2023, this reference value has come into question, as the Standard Model prediction varies greatly depending on which data set is used.

In order to overcome the disadvantages of the data-driven method, Wittig’s group has focused on calculations using the lattice QCD method, which allows the contributions of the strong interaction to be calculated numerically using supercomputers. The advantage of such an approach is that, unlike the value published in 2020, it provides results that do not require experimental data.

Agreement with the experimental mean value

Wittig’s group focused on calculating the contribution of the HVP, which provides the largest contribution of the strong interaction to the anomalous magnetic moment of the muon. In their recent work, the team has found a new value for the muon’s anomalous magnetic moment that is consistent with the current experimental mean and far from the 2020 theoretical estimate.

“After years of work on reducing the uncertainties of our calculations and overcoming the computational challenges associated with performing such lattice QCD calculations, we have obtained the HVP contribution with an overall accuracy of just below 1% and a good balance between statistical and systematic uncertainties,” says Wittig. “This allows us to reassess the validity of the Standard Model.”

Even if the new result once again confirms the Standard Model, there are still many puzzles. Where the difference between the lattice QCD and the data-driven method comes from and how the result of the CMD-3 experiment should be evaluated is not yet fully understood.

“We still have a long way to go to achieve our long-term goal of reducing the total error to around 0.2%. No matter how you look at it, we can’t get around the fact that there are discrepancies in the anomalous magnetic moment of the muon that need to be explained. There is still a lot for us to understand,” concludes Wittig.

More information: Dalibor Djukanovic et al, The hadronic vacuum polarization contribution to the muon g-2 at long distances, arXiv (2024). DOI: 10.48550/arxiv.2411.07969

Journal information: arXiv 

Mechanical crystals, also known as phononic crystals, are materials that can control the propagation of vibrations or sound waves, just like photonic crystals control the flow of light. The introduction of defects in these crystals (i.e., intentional disruptions in their periodic structure) can give rise to mechanical modes within the band gap, enabling the confinement of mechanical waves to smaller regions or the materials—a feature that could be leveraged to create new technologies.

Researchers at McGill University recently realized a new mechanical crystal with an optically programmable defect mode. Their paper, published in Physical Review Letters, introduces a new approach to dynamically reprogram mechanical systems, which entails the use of an optical spring to transfer a mechanical mode into a crystal’s band gap.

“Some time ago, our group was thinking a lot about using an optical spring to partially levitate structures and improve their performance,” Jack C. Sankey, principal investigator and co-author of the paper, told Phys.org. “At the same time, we were watching the amazing breakthroughs in our field with mechanical devices that used the band gap of a phononic crystal to insulate mechanical systems from the noisy environment.”

After witnessing recent breakthroughs in the development of mechanical devices, Sankey and his colleagues started exploring the possibility of optically springing up the drumhead-like resonance of a membrane with a periodic array of holes punched in it. They predicted that this would allow them to drag the frequency into a band gap, drawing the vibrational energy inward like a tractor beam and significantly reducing the resonance’s inertial mass.

“We figured this weird situation in which the number of photons present affects how heavy a mechanical system ‘feels’ would present a lot of new opportunities,” said Sankey. “We did some promising calculations, notably finding that larger structures respond more to each photon, and that an average of a single photon in the apparatus could in principle have a measurable effect on the motion of a very feasible, centimeter-scale device.”

To demonstrate their approach, the team, led by Ph.D. student Tommy Clark, first patterned and released a membrane using standard photolithography techniques. They then aligned the fiber cavity near this membrane’s center, using tight-tolerance guide ferrules.

“We mounted the whole thing on a vibration-isolating stage in ultrahigh vacuum and used additional active feedback to stabilize the cavity mirrors to within the ~10s of picometers required for the laser light to enter the cavity near its natural resonance frequency,” explained Sankey. “Once the system is assembled and stabilized, we used the cavity’s resonant enhancement to create an intense optical field that applies a spring-like pressure to a small section of the membrane.”

Using this optical spring, the researchers deliberately disrupted their membrane’s periodic pattern, generating a defect. By adjusting the laser’s intensity, they could then dynamically and reversibly modify the properties of the defect they introduced.

“I have always loved the idea of coupling light to the shape and mass of a mechanical resonance, but there are a host of interesting applications as well, from new studies of mechanical dissipation to simulations of condensed matter systems,” said Sankey.

“There is also currently a great deal of interest in employing mechanical systems to store and transport quantum information on chip, and to connect nominally disparate quantum systems to each other. Mechanical systems are versatile tools, and Tommy’s (incredible) work demonstrates a qualitatively new way to manipulate motion with light.”

The team’s new approach for the in situ reconfiguration of mechanical defects could open new interesting possibilities for the creation of reprogrammable mechanical systems. For instance, arrays of such defects they generated could be used to program waveguides or other structures designed to route and reroute the flow of mechanical information.

“In the near future, we are most looking forward to exploring the idea that each photon interacts with many similar mechanical resonances simultaneously, while also connecting them all to each other through the same radiation force,” added Sankey. “This creates a dense ‘web’ of interactions that enhances the influence of each photon, and I am interested in leveraging this to generate increasingly macroscopic quantum states of motion.”

More information: Thomas J. Clark et al, Optically Defined Phononic Crystal Defect, Physical Review Letters (2024). DOI: 10.1103/PhysRevLett.133.226904

Journal information: Physical Review Letters 

© 2024 Science X Network

Results from a 2021 experiment led by a University of Alaska Fairbanks scientist have begun to reveal the particle-level processes that create the type of auroras that dance rapidly across the sky.

The Kinetic-scale Energy and momentum Transport experiment—KiNET-X—lifted off from NASA’s Wallops Flight Facility in Virginia on May 16, 2021, in the final minutes of the final night of the nine-day launch window.

UAF professor Peter Delamere’s analysis of the experiment’s results was published Nov. 19 in Physics of Plasmas.

“The dazzling lights are extremely complicated,” Delamere said. “There’s a lot happening in there, and there’s a lot happening in the Earth’s space environment that gives rise to what we observe.

“Understanding causality in the system is extremely difficult, because we don’t know exactly what’s happening in space that’s giving rise to the light that we observe in the aurora,” he said. “KiNET-X was a highly successful experiment that will reveal more of the aurora’s secrets.”

One of NASA’s largest sounding rockets soared over the Atlantic Ocean into the ionosphere and released two canisters of barium thermite. The canisters were then detonated, one at about 249 miles high and one 90 seconds later on the downward trajectory at about 186 miles, near Bermuda. The resulting clouds were monitored on the ground at Bermuda and by a NASA research aircraft.

The experiment aimed to replicate, on a minute scale, an environment in which the low energy of the solar wind becomes the high energy that creates the rapidly moving and shimmering curtains known as the discrete aurora. Through KiNET-X, Delamere and colleagues on the experiment are closer to understanding how electrons are accelerated.

“We generated energized electrons,” Delamere said. “We just didn’t generate enough of them to make an aurora, but the fundamental physics associated with electron energization was present in the experiment.”

The experiment aimed to create an Alfvén wave, a type of wave that exists in magnetized plasmas such as those found in the sun’s outer atmosphere, Earth’s magnetosphere and elsewhere in the solar system. Plasmas—a form of matter composed largely of charged particles—can also be created in laboratories and experiments such as KiNET-X.

Alfvén waves originate when disturbances in plasma affect the magnetic field. Plasma disturbances can be caused in a variety of ways, such as through the sudden injection of particles from solar flares or the interaction of two plasmas with different densities.

KiNET-X created an Alfvén wave by disturbing the ambient plasma with the injection of barium into the far upper atmosphere.

Sunlight converted the barium into an ionized plasma. The two plasma clouds interacted, creating the Alfvén wave.

That Alfvén wave instantly created electric field lines parallel to the planet’s magnetic field lines. And, as theorized, that electric field significantly accelerated the electrons on the magnetic field lines.

“It showed that the barium plasma cloud coupled with, and transferred energy and momentum to, the ambient plasma for a brief moment,” Delamere said.

The transfer manifested as a small beam of accelerated barium electrons heading toward Earth along the magnetic field line. The beam is visible only in the experiment’s magnetic field line data.

“That’s analogous to an auroral beam of electrons,” Delamere said.

He calls it the experiment’s “golden data point.”

Analysis of the beam, visible only as varying shades of green, blue and yellow pixels in Delamere’s data imagery, can help scientists learn what is happening to the particles to create the dancing northern lights.

The results so far show a successful project, one that can even allow more information to be gleaned from its predecessor experiments.

“It’s a question of trying to piece together the whole picture using all of the data products and numerical simulations,” Delamere said.

Three UAF students doing their doctoral research at the UAF Geophysical Institute also participated. Matthew Blandin supported optical operations at Wallops Flight Facility, Kylee Branning operated cameras on a NASA Gulfstream III aircraft out of Langley Research Center, also in Virginia, and Nathan Barnes assisted with computer modeling in Fairbanks.

The experiment also included researchers and equipment from Dartmouth College, the University of New Hampshire and Clemson University.

More information: P. A. Delamere et al, Alfvén wave generation and electron energization in the KiNET-X sounding rocket mission, Physics of Plasmas (2024). DOI: 10.1063/5.0228435

Read the story of the KiNET-X mission in 12 short installments that include videos, animations and additional photographs.

Journal information: Physics of Plasmas 

Provided by University of Alaska Fairbanks 

A team of physicists and engineers at China’s Hefei National Laboratory has succeeded in conducting the first instance of precise absolute distance measurement over a path exceeding 100 km. The group has written a paper describing how they achieved such a feat and posted it on the arXiv preprint server.

As scientists develop ever more sophisticated technology, the need for more precise measurement grows. One such application is satellite formation flying. For it to be done as precisely as needed, new ways to very accurately measure long distances are needed—such as from a satellite to the ground, and back. In this new effort, the research team in China has found a way to measure such distances with unprecedented precision.

The work by the team involved adding an improvement to a measuring technique involving the use of an optical comb—a device that allows for averaging the time it takes for multiple wavelengths of light to travel to a target and bounce back—while also analyzing interference patterns that may have arisen during the trip.

Such technology has proven to be very precise when measuring relatively short distances. It has not worked very well over long distances, unfortunately, because the light is subject to noise and environmental factors such as humidity and temperature. In this new effort, the team overcame these problems to extend the use of optical combs to distances over 100 kilometers.

The solution, the team found, was to add a second comb at the other end of the space to be measured. Doing so caused the beams of light to interfere with one another, resulting in patterns that could be used to measure the distance between them. The technique works, the researchers note, because while the combs are indistinguishable, the interference patterns created at each end are not.

Because the beams are traveling in reverse directions relative to each other, comparison of the differences in interference patterns can be resolved, resulting in mitigating the impacts of environmental noise. The result is an extremely precise way to measure objects that are more than a kilometer apart.

The team proved the effectiveness of their approach by using it to measure objects 113 kilometers apart with a precision of 82 nm. They also note that their test is the first to achieve such precision over such a long distance.

More information: Yan-Wei Chen et al, 113 km absolute ranging with nanometer precision, arXiv (2024). DOI: 10.48550/arxiv.2412.05542

Journal information: arXiv 

Plasmons are collective oscillations of electrons in a solid and are important for a wide range of applications, such as sensing, catalysis, and light harvesting. Plasmonic waves that travel along the surface of a metal, called surface plasmon polaritons, have been studied for their ability to enhance electromagnetic fields.

One of the most powerful tools for studying these waves is time-resolved electron microscopy, which uses ultrashort laser pulses to observe how these plasmonic waves behave. An international research team recently pushed the boundaries of this technique.

As reported in Advanced Photonics, the researchers used multiple time-delayed laser pulses of four different polarizations to capture the full electric field of these waves. This method allowed them to achieve a level of accuracy previously not possible.

To test their technique, the team investigated a specific spin texture known as a meron pair. A meron is a topological structure where the direction of the spin texture only covers half of a sphere, which distinguishes it from other similar structures, like skyrmions, whose spin covers the entire sphere.

To reconstruct the spin texture from the experiment, the researchers needed the electric and magnetic field vectors of the surface plasmon polaritons. While the electric field vectors could be directly measured, the magnetic field vectors had to be calculated based on the electric field’s behavior over time and space.

By using their precise method, the researchers were able to reconstruct the spin texture and determine its topological properties, such as the Chern number, which describes the number of times the spin texture maps onto a sphere. In this case, the Chern number was found to be one, indicating the presence of a meron pair.

The study also demonstrated that the spin texture remains stable throughout the duration of the plasmonic pulse, despite the fast rotation of the electric and magnetic field vectors. This new approach is not limited to meron pairs and can be applied to other complex surface plasmon polariton fields.

Understanding these fields and their topological properties is important, especially at the nanoscale, where topological protection can help maintain the stability of materials and devices.

This research shows that it is now possible to study complex spin textures with high precision on extremely short timescales. The ability to accurately reconstruct the full electric and magnetic fields of surface plasmon polaritons opens new possibilities for exploring the topological properties of electromagnetic near fields, which may have important implications for future technologies at the nanoscale.

More information: Pascal Dreher et al, Spatiotemporal topology of plasmonic spin meron pairs revealed by polarimetric photo-emission microscopy, Advanced Photonics (2024). DOI: 10.1117/1.AP.6.6.066007

Journal information: Advanced Photonics

Researchers at Rice University have made a meaningful advance in the simulation of molecular electron transfer—a fundamental process underpinning countless physical, chemical and biological processes. The study, published in Science Advances, details the use of a trapped-ion quantum simulator to model electron transfer dynamics with unprecedented tunability, unlocking new opportunities for scientific exploration in fields ranging from molecular electronics to photosynthesis.

Electron transfer, critical to processes such as cellular respiration and energy harvesting in plants, has long posed challenges to scientists due to the complex quantum interactions involved. Current computational techniques often fall short of capturing the full scope of these processes. The multidisciplinary team at Rice, including physicists, chemists and biologists, addressed these challenges by creating a programmable quantum system capable of independently controlling the key factors in electron transfer: donor-acceptor energy gaps, electronic and vibronic couplings and environmental dissipation.

Using an ion crystal trapped in a vacuum system and manipulated by laser light, the researchers demonstrated the ability to simulate real-time spin dynamics and measure transfer rates across a range of conditions. The findings not only validate key theories of quantum mechanics but also pave the way for novel insights into light-harvesting systems and molecular devices.

“This is the first time that this kind of model was simulated on a physical device while including the role of the environment and even tailoring it in a controlled way,” said lead researcher Guido Pagano, assistant professor of physics and astronomy. “It represents a significant leap forward in our ability to use quantum simulators to investigate models and regimes that are relevant for chemistry and biology. The hope is that by harnessing the power of quantum simulation, we will eventually be able to explore scenarios that are currently inaccessible to classical computational methods.”

The team achieved a significant milestone by successfully replicating a standard model of molecular electron transfer using a programmable quantum platform. Through the precise engineering of tunable dissipation, the researchers explored both adiabatic and nonadiabatic regimes of electron transfer, demonstrating how these quantum effects operate under varying conditions. Additionally, their simulations identified optimal conditions for electron transfer, which parallel the energy transport mechanisms observed in natural photosynthetic systems.

“Our work is driven by the question: Can quantum hardware be used to directly simulate chemical dynamics?” Pagano said. “Specifically, can we incorporate environmental effects into these simulations as they play a crucial role in processes essential to life such as photosynthesis and electron transfer in biomolecules? Addressing this question is significant as the ability to directly simulate electron transfer in biomolecules could provide valuable insights for designing new light-harvesting materials.”

The implications for practical applications are far-reaching. Understanding electron transfer processes at this level could lead to breakthroughs in renewable energy technologies, molecular electronics and even the development of new materials for quantum computing.

“This experiment is a promising first step to gain a deeper understanding of how quantum effects influence energy transport, particularly in biological systems like photosynthetic complexes,” said Jose N. Onuchic, study co-author, the Harry C. and Olga K. Wiess Chair of Physics and professor of physics and astronomy, chemistry and biosciences. “The insights we gain in this type of experiment could inspire the design of more efficient light-harvesting materials.”

Peter G. Wolynes, study co-author, the D.R. Bullard-Welch Foundation Professor of Science and professor of chemistry, biosciences and physics and astronomy, emphasized the broader significance of the findings: “This research bridges the gap between theoretical predictions and experimental verification, offering an exquisitely tunable framework for exploring quantum processes in complex systems.”

The team plans to extend its simulations to include more complex molecular systems such as those involved in photosynthesis and DNA charge transport. The researchers also hope to investigate the role of quantum coherence and delocalization in energy transfer, leveraging the unique capabilities of their quantum platform.

“This is just the beginning,” said Han Pu, co-lead author of the study and professor of physics and astronomy. “We are excited to explore how this technology can help unravel the quantum mysteries of life and beyond.”

The study’s other co-authors include graduate students Visal So, Midhuna Duraisamy Suganthi, Abhishek Menon, Mingjian Zhu and research scientist Roman Zhuravel.

More information: Visal So et al, Trapped-ion quantum simulation of electron transfer models with tunable dissipation, Science Advances (2024). DOI: 10.1126/sciadv.ads8011

Journal information: Science Advances 

Provided by Rice University 

A top-secret lab in the UK is developing the country’s first quantum clock to help the British military boost intelligence and reconnaissance operations, the defense ministry said Thursday.

The clock is so precise that it will lose less than one second over billions of years, “allowing scientists to measure time at an unprecedented scale,” the ministry said in a statement.

“The trialing of this emerging, groundbreaking technology could not only strengthen our operational capability, but also drive progress in industry, bolster our science sector and support high-skilled jobs,” Minister for Defense Procurement Maria Eagle said.

The groundbreaking technology by the Defense Science and Technology Laboratory will reduce reliance on GPS technology, which “can be disrupted and blocked by adversaries,” the ministry added.

It is not a world first, as the University of Colorado at Boulder developed a quantum clock 15 years ago with the US National Institute of Standards and Technology.

But it is “the first device of its kind to be built in the UK,” the statement said, adding it could be deployed by the military “in the next five years”.

A quantum clock uses quantum mechanics — the physics of matter and energy at the atomic and subatomic scale — to keep time with unprecedented accuracy by measuring energy fluctuations within atoms.

Accurate timekeeping is crucial for satellite navigation systems, mobile telephones and digital TV, among other applications, and may open new frontiers in research fields such as quantum science.

Companies and governments around the world are keen to cash in on the huge potential benefits quantum technology could bring.

Google last month unveiled a new quantum computing chip it said could do in minutes what it would take leading supercomputers 10 septillion years to complete.

The United States and China are investing heavily in quantum research, and the US administration has imposed tight restrictions on exporting such sensitive technology.

One expert, Olivier Ezratty, told AFP in October that private and public investment in such technology had reached $20 billion during the past five years.

The defense ministry said future research would “see the technology decrease in size to allow mass manufacturing and miniaturization, unlocking a wide range of applications, such as use by military vehicles and aircraft”.

© 2025 AFP

Detecting infrared light is critical in an enormous range of technologies, from remote controls to autofocus systems to self-driving cars and virtual reality headsets. That means there would be major benefits from improving the efficiency of infrared sensors, such as photodiodes.

Researchers at Aalto University have developed a new type of infrared photodiode that is 35% more responsive at 1.55 µm, the key wavelength for telecommunications, compared to other germanium-based components. Importantly, this new device can be manufactured using current production techniques, making it highly practical for adoption.

“It took us eight years from the idea to proof-of-concept,” says Hele Savin, a professor at Aalto University.

The basic idea is to make the photodiodes using germanium instead of indium gallium arsenide. Germanium photodiodes are cheaper and already fully compatible with the semiconductor manufacturing process—but so far, germanium photodiodes have performed poorly in terms of capturing infrared light.

Savin’s team managed to make germanium photodiodes that capture nearly all the infrared light that hits them.
The study was published on 1 Jan 2025 in the journal Light: Science & Applications.

“The high performance was made possible by combining several novel approaches: eliminating optical losses using surface nanostructures and minimizing electrical losses in two different ways,” explains Hanchen Liu, the doctoral researcher who built the proof-of-concept device.

The team’s tests showed that their proof-of-concept photodiode outperformed not only existing germanium photodiodes but also commercial indium gallium arsenide photodiodes in responsivity. The new technology captures infrared photons very efficiently and works well across a wide range of wavelengths. The new photodiodes can be readily fabricated by existing manufacturing facilities, and the researchers expect that they can be directly integrated into many technologies.

“The timing couldn’t be better. So many fields nowadays rely on sensing infrared radiation that the technology has become part of our everyday lives,” says Savin.

Savin and the rest of the team are keen to see how their technology will affect existing applications and to discover what new applications become possible with the improved sensitivity.

More information: Hanchen Liu et al, Near-infrared germanium PIN-photodiodes with >1A/W responsivity, Light: Science & Applications (2025). DOI: 10.1038/s41377-024-01670-4

Journal information: Light: Science & Applications

Provided by Aalto University

In an era of medical care that is increasingly aiming at more targeted medication therapies, more individual therapies and more effective therapies, doctors and scientists want to be able to introduce molecules to the biological system to undertake specific actions.

Examples are gene therapy and drug delivery, which for widespread use need to be both effective and inexpensive. In service of this goal, a trio of researchers has used machine learning to design a way to remove molecules inside a molecular cage. Their study is published in Physical Review Letters.

The research, whose lead author is Ryan K. Krueger of Harvard University, but to which each co-author contributed equally, uses differentiable molecular dynamics to design complex reactions to direct the system to specific outcomes.

As an example, they undertook the controlled disassembly of colloidal structures—in particular, designing a molecule that could remove a particle surrounded and bound by a complete shell or “cage” of colloidal particles. (Colloids are mixtures of substances where nanoscopic or microscopic insoluble particles are dispersed throughout another substance. Examples are milk, smoke and gelatin.)

Machine learning was used to optimize the design of the shell’s “opener” molecule, which they call the “spider” due to its geometry. As they wrote, “disassembly is central to the dynamic functions of living systems, such as defect repair, self-replication, and catalysis.”

In particular, they designed for the controlled disassembly of icosahedral shells, collection of 12 particles with 30 outside edges connecting the shell particles. This configuration is much like protein capsids that house viruses.

The shell particles are considered “patchy”—their interactions with other shell particles, and the caged particle, have specific values of parameters that dictate the interaction’s directionality and relative strength. Introduced in soft material research 20 years ago, patchiness offers a versatile tunability in the designed interactions, achieving specific behaviors, assisted by the recent development of patchy particle simulations within a differentiable library.

Patchiness may even be varied over the surface of the patchy particles; here the 12 individual shell particles. The goal was to disassemble the shell, which carried an inherent tension between accomplishing the disassembly while maintaining the integrity of the substructure that remained.

The researchers assumed a Morse potential for the potential energy of the interacting shell particles, often used as a model of the interaction between the two atoms in a diatomic molecule, and with the caged molecule.

The Morse potential is simple and has three free parameters that can (and must) be selected for the desired situation. Removing the caged particle requires removing one of the shell particles.

For their analysis, the team assumed the object removing the shell particle was a rigid pyramid-type structure that would fit on top of the 12-sphere cluster. They called this object a “spider.” It consisted of a pentagon-shaped ring of particles that formed the base of the pyramid, with a single “head particle” on top of the pyramid assembly.

In their simulation, the icosahedral shell was given and fixed, with the spider free to land on any shell particle and interact with it.

The patch parameters were tuned so the spider as a whole was neither attracted or repelled by the cluster of shells, but the top-of-the-pyramid particle was attracted to patches on the shell particles by a force that could be varied by distance and strength. The dimensions of the spider and the radii of its head particle and base particles could also be adjusted.

Krueger and his collaborators used molecular dynamics, a standard technique which calculates the motion of each particle by the interaction forces it experiences with the other particles. They wanted to determine which particular parameters of the spider would pluck out the caged molecule from the shell.

Doing this on a computer by brute force—calculating for all possible parameters, particle by particle, until the desired outcome was reached—would take far too much computational power and time. So the group turned to machine learning to minimize a loss function that represented the tension between the disassembly and the remaining substructure integrity.

This process succeeded in producing a rigid spider that could accomplish the removal task. They then allowed the spider to flex, introducing a new free parameter that represented “configurable entropy.”

When it was optimized as well, the energy required to free the caged particle decreased. They found that a spider with asymmetrically flexible base legs required less energy to release the caged particle compared with a spider with the symmetrical, pentagonal base that was first assumed.

They noted their methodology can be broadly applied. “Since we optimize directly with respect to the numerically integrated dynamics, our method is general enough to study a wide range of systems,” they wrote.

“Foremost, it may enable experimental realizations of theoretical models that were otherwise limited by an inability to finely tune interaction energies.”

More information: Ryan K. Krueger et al, Tuning Colloidal Reactions, Physical Review Letters (2024). DOI: 10.1103/PhysRevLett.133.228201

Journal information: Physical Review Letters 

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