Experimental setup to couple MWs to N- đâ˘s using grape dimers. A stripped optical fiber with N- đ spins, cantilevered from a rod, lies between two grapes. The grapes were positioned on a platform with a vertical straight copper wire, equidistant from each grape. Credit: Fawaz, Nair, Volz
Macquarie University researchers have demonstrated how ordinary supermarket grapes can enhance the performance of quantum sensors, potentially leading to more efficient quantum technologies.
The study, published in Physical Review Applied on 20 December 2024, shows that pairs of grapes can create strong localized magnetic field hotspots of microwaves which are used in quantum sensing applicationsâa finding that could help develop more compact and cost-effective quantum devices.
“While previous studies looked at the electrical fields causing the plasma effect, we showed that grape pairs can also enhance magnetic fields, which are crucial for quantum sensing applications,” says lead author Ali Fawaz, a quantum physics Ph.D. candidate at Macquarie University.
The research builds on viral social media videos showing grapes creating plasmaâglowing balls of electrically charged particlesâin microwave ovens.
While previous studies focused on electric fields, the Macquarie team examined magnetic field effects crucial for quantum applications.
The team used specialized nano-diamonds containing nitrogen-vacancy centersâatomic-scale defects that act as quantum sensors. These defects (one of the many defects giving diamonds their color) behave like tiny magnets and can detect magnetic fields.
“Pure diamonds are colorless, but when certain atoms replace the carbon atoms, they can form so-called ‘defect’ centers with optical properties,” says study co-author Dr. Sarath Raman Nair, who is a lecturer in quantum technology at Macquarie University.
“The nitrogen-vacancy centers in the nanodiamonds we used in this study act like tiny magnets that we can use for quantum sensing.”
The team placed their quantum sensorâa diamond containing special atomsâon the tip of a thin glass fiber and positioned it between two grapes. By shining green laser light through the fiber, they could make these atoms glow red. The brightness of this red glow revealed the strength of the microwave field around the grapes.
“Using this technique, we found the magnetic field of the microwave radiation becomes twice as strong when we add the grapes,” says Fawaz.
Senior author Professor Thomas Volz, who heads the Quantum Materials and Applications Group at Macquarie’s School of Mathematical and Physical Sciences, says the findings unlock exciting possibilities for quantum technology miniaturization.
“This research opens up another avenue for exploring alternative microwave resonator designs for quantum technologies, potentially leading to more compact and efficient quantum sensing devices,” he says.
The size and shape of the grapes proved crucial to the experiment’s success. The team’s experiments relied on precisely sized grapesâeach approximately 27 millimeters longâto concentrate microwave energy at approximately the right frequency of the diamond quantum sensor.
Quantum sensing devices traditionally use sapphire for this purpose. However, the Macquarie team theorized that water might work even better. This made grapes, which are mostly water enclosed in a thin skin, perfect for testing their theory.
“Water is actually better than sapphire at concentrating microwave energy, but it’s also less stable and loses more energy in the process. That’s our key challenge to solve,” says Fawaz.
Looking beyond grapes, the researchers are now developing more reliable materials that could harness water’s unique properties, bringing us closer to more efficient sensing devices.
More information: Ali Fawaz et al, Coupling nitrogen-vacancy center spins in diamond to a grape dimer, Physical Review Applied (2024). DOI: 10.1103/PhysRevApplied.22.064078
A research group led by Prof. Yao Baoli and Dr. Xu Xiaohao from Xi’an Institute of Optics and Precision Mechanics (XIOPM) of the Chinese Academy of Sciences have revealed a full-gray optical trap in structured light, which is able to capture nanoparticles but appears at the region where the intensity is neither maximized nor minimized. The study is published in Physical Review A.
The optical trap is one of the greatest findings in optics and photonics. Since the pioneering work by Arthur Ashkin in the 1970s, the optical trap has been employed in a broad range of applications in life sciences, physics, and engineering. Akin to its thermal and acoustic counterparts, this trap is typically either bright or dark, located at the field intensity maxima or minima.
In this study, researchers developed a high-order multipole model for gradient forces based on multipole expansion theory. Through immersing the Si particles in the structured light with a petal-shaped field, they found that the high-order multipole gradient forces can trap Si particles at the optical intensity, which is neither maximized nor minimized.
Therefore, researchers demonstrated that there may exist an intermediate trapping state, which is referred to as the full-gray optical trapping. The origin of this novel trap can be traced back to the nonlocal pondermotive effect of the optical intensity gradient, which is achieved through the excitation of higher-order multipole Mie resonances in nanoparticles.
The full-gray trap underscores the impact of Mie responses on optomechanics, and will facilitate the development of nanoparticle cooling, patterning and ultra-sensitive sorting in the future.
More information: Yanan Zhang et al, Full-gray optical trapping by high-order multipole-resonant gradient forces in structured light, Physical Review A (2024). DOI: 10.1103/PhysRevA.110.063517
Scientists from the National University of Singapore (NUS) have developed a highly effective and general molecular design that enables an enhancement in radioluminescence within organometallic scintillators by more than three orders of magnitude. This enhancement harnesses X-ray-induced triplet exciton recycling within lanthanide metal complexes.
Detection of ionizing radiation is crucial in diverse fields, such as medical radiography, environmental monitoring and astronomy. As a result, significant efforts have been dedicated to the development of luminescent materials that respond to X-rays.
However, current high-performance scintillators are almost exclusively limited to ceramic and perovskite materials, which face issues such as complex manufacturing processes, environmental toxicity, self-absorption and stability problems.
Organic phosphors present a promising alternative owing to their flexibility and cost-effectiveness. However, they are less efficient in X-ray detection because of weak X-ray absorption and limited use of molecular triplet excitons.
While halogen-doped organic phosphors and thermally activated delayed fluorescence molecules show potential, they require precise structural engineering and face absorption and reabsorption challenges, limiting their efficiency.
A research team led by Professor Liu Xiaogang from the Department of Chemistry at NUS, leveraged rare-earth Xâray absorption and ligand-mediated triplet exciton harvesting to overcome these challenges and significantly improved the performance of molecular scintillators.
The effective trapping of the energy dissipated during secondary X-ray relaxation via organic ligands led to a remarkable 1,300-fold increase in radioluminescence compared to lanthanide salts.
The study unveiled the role of triplet exciton recycling in determining scintillation efficiency, demonstrating that high photoluminescence quantum yield may not necessarily result in high scintillation efficiency.
The research was conducted in collaboration with Professor Yiming Wu from Xiamen University, China and Professor Xian Qin from Fujian Normal University, China.
The findings were published in the journal Nature Photonics.
Significantly, these organolanthanide compounds exhibit robust resistance to high-energy radiation and show scintillation efficiencies that surpassed those of well-known organic scintillators and inorganic LYSO:Ce crystals. Their performance was also comparable to those of CsI:Tl crystals.
By tailoring the metal centers and their coordination ligands, the researchers demonstrate the ability to achieve full-spectral X-ray scintillation from the ultraviolet to near-infrared range. Additionally, their methodology enables the fine-tuning of emission lifetimes, ranging from 50 nanoseconds to 900 microseconds.
These organolanthanide scintillators exhibit substantial Stokes shifts and offer the advantage of synthesis and processing at room temperature in solution form. Additionally, they demonstrate excellent solubility, stability, and flexibility, allowing molecular-level mixing for high-resolution radiographic imaging and potential applications in X-ray-mediated deep-tissue radiotherapy.
Prof Liu said, “The efficiency of triplet exciton recycling holds the key to better scintillation performance. These discoveries lend profound insights into X-ray-induced exciton migration dynamics and radioluminescence behavior, shaping the future of organic scintillators and their harnessing of high-energy X-ray quanta.
“The high stability of radioluminescence, large Stokes shift and full spectral tunability make organolanthanide molecules a promising platform for scintillation applications.”
More information: Jiahui Xu et al, Ultrabright molecular scintillators enabled by lanthanide-assisted near-unity triplet exciton recycling, Nature Photonics (2024). DOI: 10.1038/s41566-024-01586-w
The impact of a drop on a solid surface is an important phenomenon that has various applications. Especially when the drop splashes, it can cause deterioration of printing and paint qualities, erosion, and propagation of airborne virus, among others. Therefore, it is important to observe and understand the characteristics of the splashing drops of different liquids.
However, the multiphase nature of the phenomenon causes difficulties for observation when it is performed merely using the naked eye. Although the recent development of artificial intelligence (AI) has shown promise in tackling this problem, AI models usually function as a black box, where the underlying decision-making process is unknown.
At the Tokyo University of Agriculture and Technology, a research team from the Department of Mechanical Systems Engineering has developed an explainable AI to observe and understand the splashing drops of different liquids from an AI perspective.
The research team led by Prof. Yoshiyuki Tagawa and Prof. Akinori Yamanaka, which includes Jingzu Yee (former assistant professor), Pradipto (former assistant professor), Shunsuke Kumagai (1st-year master’s student), and Daichi Igarashi (former master’s student), published their findings in Flow on December 20, 2024.
The research team adopted the architecture of a feedforward neural network to develop an AI model to classify videos of splashing and non-splashing drops that were recorded using a high-speed camera.
After training, the AI model has successfully classified videos of splashing and non-splashing drops with a success rate of 92% for low-viscosity liquid and 100% for high-viscosity liquid. Then, the researchers implemented their proposed method of visualizing the AI to analyze and interpret the classification process.
Their results show that the AI classifies splashing and non-splashing drops from the contour of the drop’s main body, the ejected droplets, and the thin sheet ejected from the side of the drop called lamella. Moreover, the proposed visualization method successfully determined which frame of the video has the most influence on the classification of the AI.
The results show that the differences between splashing and non-splashing drops of low-viscosity liquids are more obvious during the earlier stage of the impact, while it is more obvious during the later stage of the impact for high-viscosity liquids.
“Our newly proposed explainable AI method provides an alternative to the conventional investigation methods for drop impact research,” said Jingzu Yee, a former assistant professor at the Tokyo University of Agriculture and Technology.
“Our method reveals the fundamental aspects of drop impact, which can be leveraged to enable various devices and systems that will benefit humankind.”
More information: Jingzu Yee et al, Morphological evolution of splashing drop revealed by interpretation of explainable artificial intelligence, Flow (2024). DOI: 10.1017/flo.2024.28
(A) Schematic illustration of PPT device consisting of a liquid medium, a lubricant layer, and an LMPs/P(VDF-TrFE) film sandwiched between top and bottom poly (methyl methacrylate) (PMMA) slides.(B) Photograph of the PPT platform containing a NIR laser light source and a portable PPT device with a large manipulation area of 12.5 cm2. Scale bar: 10 mm.(C) Schematic illustration of the PPT platform for object manipulation based on the photopyroelectric effect.(D) The output voltage of the PPT device upon exposure to NIR irradiation (power density: 100 mW mmâ2, frequency: 0.5s ON and 5s OFF).(E) The voltage changes increase from 0.26 to 3.34 V with an increase in the laser power density from 2 to 111 mW mmâ2.(F) The light-induced charge density of the PPT shows slight variation from 870 to 590 pC mmâ2 by increasing the medium (silicone oil) thickness from 1 to 10 cm. Error bars are calculated from five independent measurements.(G) Manipulating 5-Îźm SiO2 particle, 1 pL water droplet, and 10 mL water droplet in a non-conductive medium (silicone oil, Video S2).(H) Manipulating a live medaka egg cell (1 mm diameter), and the time-lapse trajectory of 1-mm POM bead in the conductive medium of water. Credit: The Innovation (2024). DOI: 10.1016/j.xinn.2024.100742
Optical tweezers and related techniques provide extraordinary opportunities for research and applications in the physical, biological, and medical fields. However, certain requirements such as high-intensity laser beams, sophisticated electrode designs, additional electric sources, and low-conductive media, significantly impede their flexibility and adaptability, thus hindering their practical applications.
In a study published in The Innovation, a research team led by Dr. Du Xuemin from the Shenzhen Institutes of Advanced Technology (SIAT) of the Chinese Academy of Sciences reported a novel photopyroelectric tweezer (PPT) that combines the advantages of the light and electric fields. The PPT enables versatile manipulation in various working scenarios.
The proposed PPT consists of two key components, a near infrared (NIR) spectrum laser light source and a PPT device that includes a liquid medium and a photopyroelectric substrate.
The photopyroelectric substrate includes a superhydrophobic ferroelectric polymer layer made of Ga-In liquid metal microparticle-embedded poly (vinylidene fluoride-co-trifluoroethylene) (LMPs/P(VDF-TrFE)) composites, and a lubricant-infused slippery layer. The polymer layer generates real-time surface charges via the photopyroelectric effect, while the lubricant layer reduces motion resistance, suppresses contamination, and prevents charge screening by conductive media.
Owing to its rationally designed structure, the PPT efficiently and durably generates surface charges when exposed to low-intensity NIR (as low as ~ 8.3 mW mm-2) irradiation. This induces a strong driving force (up to ~ 4.6Ă10-5 N) without requiring high-intensity laser beam, complex electrode designs, and additional electric sources.
“The innovation lies in the rational design of the photopyroelectric substrate, which efficiently generates charges, and the lubricant layer that prevents charge screening by conductive media. “This design imparts unparalleled flexibility and adaptability for diverse object manipulation,” said Dr. Du.
The PPT can remotely and programmably manipulate objects of diverse materials (polymer, inorganic, and metal), phases (bubble, liquid, and solid), and geometries (sphere, cuboid, and wire). Moreover, it is adaptable to various media with wide-range conductivities (0.001 mS cm-1~ 91.0 mS cm-1) and is versatile for both portable macroscopic manipulation platforms and microscopic manipulation systems. It supports on-demand manipulating areas ranging from 5 Îźm to 2.5 mm, enabling cross-scale manipulations of solid objects, liquid droplets, and biological samples from single cell to cell assemblies.
The PPT proposed in this study offers a new tool for robotics, colloidal science, organoids, tissue engineering, and neuromodulation.
More information: Fang Wang et al, Photopyroelectric tweezers for versatile manipulation, The Innovation (2024). DOI: 10.1016/j.xinn.2024.100742
Combining metallic glass with the Berreman mode of epsilon-near-zero (ENZ) thin films achieves a dual-function system for infrared camouflage and thermal management within an identical wavelength region of the atmospheric window. In recent research, metallic glasses were selected for their tunable optical properties, providing adjustable emissivity for versatile thermal camouflage while maintaining effective thermal management.
Thermal infrared camouflage aims to reduce the detectability of a target using thermal imaging devices. Given the typically high thermal emissivity in everyday environments, the thermal emissivity of the background environment must be considered. The conventional low-emissivity strategy for thermal camouflage is only effective for targets at extremely high temperatures, making it unsuitable for applications near room-to-medium-high temperature range (<350 °C).
In a study published in Materials Horizons, Professor Hsuen-Li Chen from the Department of Materials Science and Engineering at National Taiwan University led his research team in designing an innovative multilayer thin-film structure. This structure introduces metallic glass into infrared thermal camouflage technology, exploiting its adjustable emissivity to accommodate diverse infrared thermal camouflage scenarios.
Moreover, this is the first time combining metallic glass with the Berreman mode of epsilon-near-zero (ENZ) thin films.
In the long wave infrared (LWIR, 8â14 Îźm) regions, the small viewing angle exhibited the optical properties of metallic glasses. As the viewing angle increased, driven by the multiple Berreman modes of the ENZ thin films, it provided high thermal emissivity in transverse-magnetic (TM) polarization. It enabled thermal management without compromising the thermal camouflage performance.
The cooling power exhibited by ENZ thin films on metallic glass surpassed that of the conventional low-emissivity strategy for thermal camouflage by a factor of 1.79. Furthermore, the thermal images indicated over 97% similarity in thermal radiation between the target and background environments.
This presents new avenues for advancing infrared thermal camouflage technology.
More information: Pei-Chi Hsieh et al, Epsilon-near-zero thin films in a dual-functional system for thermal infrared camouflage and thermal management within the atmospheric window, Materials Horizons (2024). DOI: 10.1039/D4MH00711E
Long gone are the days where all our data could fit on a two-megabyte floppy disk. In today’s information-based society, the increasing volume of information being handled demands that we switch to memory options with the lowest power consumption and highest capacity possible.
Magnetoresistive Random Access Memory (MRAM) is part of the next generation of storage devices expected to meet these needs. Researchers at the Advanced Institute for Materials Research (WPI-AIMR) investigated a cobalt-manganese-iron alloy thin film that demonstrates a high perpendicular magnetic anisotropy (PMA)âkey aspects for fabricating MRAM devices using spintronics.
The findings were published in Science and Technology of Advanced Materials on November 13, 2024.
“This is the first time a cobalt-manganese-iron alloy has strongly shown large PMA,” says Professor Shigemi Mizukami (Tohoku University),
“We previously discovered this alloy showed a high tunnel magnetoresistance (TMR) effect, but it is rare that an alloy potentially shows both together.” For example, iron-cobalt-boron alloys, which are conventionally used for MRAM, possess both traits, but their PMA is not strong enough.
MRAM devices use magnetic storage elements instead of an electric charge to store data, which gives it several advantages such as reduced power consumption. Ideally, alloys for MRAM devices have both a high TMR and PMA, which allow them to integrate a large number of bits with high capacity and high thermal stability.
In order to find new, alternative materials to solve the issues seen with currently used alloys, researchers at Tohoku University have investigated the PMA of cobalt-manganese-iron alloy thin films, which were shown to have high TMR in their previous research.
Remarkably, the alloy they produced was found to exhibit high PMA. They also demonstrated that the PMA in their multilayer films was large enough to be capable of its intended end purpose: large memory capacity for MRAM devices using a simulation.
The results of this research will offer a new candidate for memory materials, and contribute to the continuous development of novel spintronics memory devices, with the aim of creating a more sustainable society for everyone.
More information: Deepak Kumar et al, Metastable body-centered cubic CoMnFe alloy films with perpendicular magnetic anisotropy for spintronics memory, Science and Technology of Advanced Materials (2024). DOI: 10.1080/14686996.2024.2421746
A research team led by Prof. Li Chuanfeng from the University of Science and Technology of China (USTC) has achieved a breakthrough in quantum photonics. They developed an on-chip photonic simulator capable of simulating arbitrary-range coupled frequency lattices with gauge potential. This study was published in Physical Review Letters.
The quest for effective simulators that can replicate the dynamics of real systems has been a driving force in quantum physics. Photonic systems, with their ability to control properties like polarization and frequency, have emerged as versatile candidates for quantum simulation.
However, the challenge lies in creating frequency lattices that can simulate complex structures like atom chains and nanotubes, which are crucial for understanding low-dimensional materials.
To address this challenge, the team’s innovative approach involves the use of thin-film lithium niobate chips, which are particularly suited for creating lattices in the frequency domain due to their high electro-optic coefficient. By periodically modulating an on-chip resonator, the researchers observed band structures, a significant advancement as it allows for the simulation of structures with arbitrary-range coupling.
Remarkably, their method enabled coupling up to eight and nine times the lattice constant while reducing the required modulation frequency by over five orders of magnitude. This is achieved by including multiple lattice points within one resonant peak, which alleviates the difficulty of applying and detecting multiharmonic signals conventionally of ultrahigh frequency on chips.
In this study, the special focus on low-frequency radio-frequency modulation offers a high degree of flexibility in choosing lattice points and regulating compound interaction.
This approach significantly reduces the required frequencies by more than three orders of magnitude, translating to a reduction from near 100 GHz to around 10 MHz in their examples. This not only simplifies the design and fabrication challenges but also lessens the demands on source and measurement equipment.
This work not only greatly alleviates the difficulties posed by high frequencies in on-chip synthetic dimensions but also maintains the scalability of traditional implementation methods, allowing it to be extended to higher-dimensional models. It achieves high-dimensional and complex frequency synthetic dimensions on thin-film lithium niobate optical chips.
The reviewers highly praised the achievement, stating it “opens a new avenue within the area of studying synthetic dimensions on photonic chips.”
More information: Zhao-An Wang et al, On-Chip Photonic Simulating Band Structures toward Arbitrary-Range Coupled Frequency Lattices, Physical Review Letters (2024). DOI: 10.1103/PhysRevLett.133.233805
Heat management at the nanoscale has long been a cornerstone of advanced technological applications, ranging from high-performance electronics to quantum computing. Addressing this critical challenge, we have been deeply intrigued by the emerging field of thermotronics, which focuses on manipulating heat flux in ways analogous to how electronics control electric energy. Among its most promising advancements are quantum thermal diodes, which enable directional heat control, and quantum thermal transistors, which regulate heat flow with precision.
Thermal diodes, much like their electrical counterparts, provide unidirectional heat transfer, allowing heat to flow in one direction while blocking it in the reverse. We find this capability revolutionary for heat management, as it has the potential to transform numerous fields.
For instance, thermal diodes can significantly improve the cooling of high-performance electronics, where heat dissipation is a major bottleneck. They could also enable more efficient energy harvesting by converting waste heat into usable energy, contributing to sustainability efforts.
Additionally, they offer applications such as dynamically managing building temperatures, enhancing the performance of thermoelectric generators, or even improving spacecraft thermal systems, where precisely controlled heat flow is critical.
In our research, we have noticed that most quantum thermal device models to date have relied on simple quantum systems with two stable energy levels, such as qubits. However, we see significant potential to go beyond these limitations.
At the Advanced Computing and Simulation Laboratory (AĎL), Monash University, Australia, we have been exploring higher-dimensional quantum systems that expand the capabilities of these devices. By integrating qubit-qutrit architectures, we have demonstrated directional heat flow with improved efficiency and scalability.
This breakthrough, published in APL Quantum, lays the groundwork for practical, high-performance thermotronic systems that could address challenges ranging from overheating in modern technology to advancing sustainable energy solutions. These advancements represent a critical step forward, promising to redefine heat management and energy efficiency in the quantum era.
Harnessing quantum asymmetry to regulate unidirectional heat flow
The quantum thermal diode, based on the interaction between a qutrit (a quantum system with three stable energy levels) and a qubit (a system with two stable energy levels), introduces a novel approach to unidirectional heat transfer.
This system leverages the inherent properties of quantum mechanics to create an asymmetric energy landscape that naturally favors heat flow in one direction, depending on the temperature gradient. This directional behavior is analogous to the way an electronic diode facilitates unidirectional current flow based on the potential difference across its terminals.
The key to this thermal diode lies in how the energy levels of the qubit and qutrit align and interact. By carefully configuring the combined energy levels, we can facilitate heat transfer along the desired temperature gradient while effectively blocking it in the opposite direction. This directional control is achieved through precise quantum interactions, which utilize specific shared energy levels between the qubit and qutrit to establish the necessary conditions for asymmetry in heat flow.
What makes this system particularly groundbreaking is its ability to operate as a nearly perfect thermal diode across a broad temperature range. Unlike classical thermal systems, the quantum nature of this device allows for precise tuning of its properties, including the spacing of energy levels and the coupling strengths between the qubit and qutrit. This tunability enables unprecedented control over the heat transfer process, making the device highly adaptable to various applications.
Whether improving the heat management of nanoscale devices or developing next-generation thermotronic systems, we believe this architecture represents a major step forward in thermal management technologies. By combining a qutrit and a qubit into a single system, this design not only achieves directional heat flow but also enhances efficiency, offering a practical and scalable solution for advanced thermotronics.
Shaping future technologies: The transformative potential of quantum thermal diodes
The development of a quantum thermal diode is a transformative breakthrough with significant implications for quantum thermodynamics and nanoscale engineering. By enabling precise control of heat flow at the quantum level, this innovation addresses challenges that traditional cooling methods cannot solve, particularly in quantum circuits and advanced nanoscale devices.
For example, quantum thermal diodes can regulate heat dissipation in quantum processors, ensuring stable and optimal performance where even slight overheating could lead to disruptions. Additionally, they open up new opportunities for energy harvesting by capturing waste heat generated in quantum systems and converting it into usable energy. This capability has the potential to drive sustainable energy solutions across numerous applications.
Beyond energy efficiency, we believe quantum thermal diodes could pave the way for thermal logic devicesâthermal analogs to electronic diodesâallowing computation to be performed using heat flow rather than electric current. Such a development would represent an entirely new paradigm in computation, with applications in fields requiring unique architectures for energy and heat management.
Furthermore, these devices hold significant promise in specialized areas, such as biomedical technologies, where precise thermal regulation is critical for maintaining the performance of sensitive quantum sensors. They could also prove vital in space exploration, where managing the temperature of delicate quantum instruments in extreme environments is essential.
By improving the efficiency of heat dissipation and enabling directional control, quantum thermal diodes not only enhance the functionality of nanoscale devices but also set the stage for the next generation of technologies.
With the potential to develop quantum thermal transistors and other advanced thermotronic devices, we believe this innovation has the power to redefine how we approach thermal management and energy utilization in a quantum-driven world. From nanoscale engineering to space exploration, the transformative potential of quantum thermal diodes promises to shape the technologies of tomorrow.
This story is part of Science X Dialog, where researchers can report findings from their published research articles. Visit this page for information about Science X Dialog and how to participate.
More information: Anuradhi Rajapaksha et al, Enhanced thermal rectification in coupled qutritâqubit quantum thermal diode, APL Quantum (2024). DOI: 10.1063/5.0237842
Bios: Anuradhi Rajapaksha earned her B.Sc. in electrical and electronic engineering (with first-class honors) from University of Peradeniya, Sri Lanka in 2021. Currently she is a PhD candidate and a member of the Advanced Computing and Simulations Laboratory at the Department of Electrical and Computer Systems Engineering, Monash University, Australia under the supervision of Prof. Malin Premaratne.
Sarath D. Gunapala received a Ph.D. degree in physics from the University of Pittsburgh, Pittsburgh, PA, USA, in 1986. In 1992, he joined NASA’s Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA, where he is currently the Director of the Center for Infrared Photodetectors. He is also a Senior Research Scientist and a Principal Member of the Engineering Staff with the NASA Jet Propulsion Laboratory.
Malin Premaratne earned several degrees from the University of Melbourne, including a B.Sc. in mathematics, a B.E. in electrical and electronics engineering (with first-class honors), and a PhD in 1995, 1995, and 1998, respectively. Currently, he is a full professor at Monash University Clayton, Australia. His expertise centers on quantum device theory, simulation, and design, utilizing the principles of quantum electrodynamics.
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 structuresâin 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”âtheir 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 forceâcalculating for all possible parameters, particle by particle, until the desired outcome was reachedâwould 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.”
