Star Formation is Triggered By Cloud-cloud Collisions, Study Finds (Astronomy)

Japanese researchers have found that collisions of gas clouds hovering in space bring about the birth of star clusters.

Stars form by the gravitational contraction of clouds of gas in space and can have various masses. Massive stars, together with many other stars, may form a huge star cluster (a group of more than 10,000 stars). The formation of such a star cluster requires the rapid packing of enormous amounts of gas and other materials into a small space, but the mechanism by which this occurs has yet to be clarified.

A research team led by Associate Professor Kengo Tachihara and Emeritus Professor Yasuo Fukui of Nagoya University focused on a hypothesis in which multiple gas clouds collide, which allows them to gather efficiently and thereby form a star cluster. To verify this hypothesis, the team, in collaboration with researchers from Osaka Prefecture University and the National Astronomical Observatory of Japan, conducted observational studies of a vast amount of data obtained as a result of more than a decade of research, as well as theoretical studies of numerical simulations with the data. As a result, they found that collisions of gas clouds hovering in space do, in fact, induce the birth of a star cluster.

They observed many collisions of gas clouds in our Milky Way Galaxy and also in other galaxies, suggesting that these collisions are a universal phenomenon. From this perspective, there is an increasingly likely possibility that the Milky Way Galaxy collided with other galaxies soon after its birth, which caused gas clouds in the galaxies to collide frequently, resulting in the formation of many globular clusters (groups of more than one million stars). Their findings have contributed to a deeper understanding of the formation of massive stars and the birth of globular clusters.

The studies were published in the peer-reviewed journal Publications of the Astronomical Society of Japan in January 2021 as a special issue titled “Star Formation Triggered by Cloud-Cloud Collision Ⅱ,” which contains a collection of 20 original papers based on elaborate verifications of individual astronomical bodies, as well as a review paper summarizing the latest understandings of star formation by collisions of gas clouds.

Featured image: Demonstration of typical colliding molecular clouds (represented by blue color and yellow contours) forming star clusters discovered by radio observations. Positions of the cluster-forming colliding clouds reported in the present special issue are denoted by red dots plotted on the picture of the Milky Way Galaxy on the right (the circle denotes the position of the Sun). Images of the Antennae Galaxies and the Triangulum Galaxy are shown on the left. The inset optical images show the Eagle Nebula and [DBS2003]179, where shining nebulae and newly born star clusters can be seen. (Credit: Nagoya University, National Astronomical Observatory of Japan, NASA, JPL-Caltech, R. Hurt (SSC/Caltech), Robert Gendler, Subaru Telescope, ESA, The Hubble Heritage Team (STScI/AURA), Hubble Collaboration, and 2MASS)


Provided by Nagoya University

A Barred Galaxy’s Massive Molecular Inflow (Cosmology / Astronomy)

Large amounts of gas are sometimes funneled to a galaxy’s nuclear regions, with profound consequences. The gas triggers starburst activity and can also feed the supermassive black hole, converting it into an active galactic nucleus (AGN); indeed the supermassive black holes in AGN are thought to gain most of their mass in these accretion events. Eventually, outward pressure from supernovae, shocks, and/or AGN activity terminate the inflow. Galaxy mergers are thought to be one mechanism capable of triggering these massive inflows by disrupting the medium. A less dramatic cause may result from gas flows induced by a combination of galactic rotation and the gravitational instabilities generated by galactic bars, the elongated central structures (composed of stars) found in numerous spiral galaxies including the Milky Way.

What happens to infalling gas when it encounters a nuclear region is poorly understood because the very high obscuration around galactic nuclei makes optical observations challenging. Astronomers have therefore been relying on data from far-infrared and submillimeter wavelength observations which can penetrate the dust, although longer wavelength imaging typically lacks the high spatial resolution needed. Infrared spectroscopy has been one of the premier ways to overcome both difficulties because the radiation not only penetrates the dust, the strengths and shapes of spectral lines can be modeled to infer even small dimensions as well as temperatures, densities, and other characteristics of the emitting regions.

CfA astronomers Eduardo Gonzalez-Alfonso, Matt Ashby, and Howard Smith led a team that modeled infrared spectra of water vapor from the nuclear region of the ultraluminous galaxy ESO320-G030, about 160 million light-years away, a galaxy that emits about one hundred times as much energy as the Milky Way. The data were obtained with the Herschel Space Observatory and the ALMA submillimeter facility. This galaxy shows no signs of having been in a merger, nor does it show any signs of AGN activity, but it does have a clear and complex central bar structure and infalling gas that was previously discovered through infrared spectroscopy.

The astronomers observed and modeled twenty spectral features of water vapor, enough diagnostic lines to model the complexity of the emitting regions. The successful results required a three-component nuclear model: a warm envelope (about 50 kelvin) about 450 light-years in radius within which is a second component, a nuclear disk about 130 light-years in radius, and finally a much warmer compact core (100 kelvin) about 40 light-years in radius. These three components alone emit nearly 70% of the galaxy’s luminosity from a starburst that is making about 18 solar-masses of stars a year (the Milky Way averages about one per year). The mass inflow rate into the region is about the same as the star production – about 18 solar-masses per year. In addition to these conclusions about the nuclear region, the astronomers use their best-fit results to model successfully 17 other molecular species (besides water) seen in the far infrared spectra, including ionized molecules and carbon and nitrogen-bearing molecules. The combined results, in particular the extremely high abundance of ionized molecules, suggest the strong presence of enhanced ionizing cosmic rays and shed light on the chemistry of the complex nuclear zone.

Featured image: The barred spiral galaxy NGC1300 as seen by Hubble.  Astronomers think that galactic bars help funnel material into the nuclear regions of galaxies where they help trigger star formation and feed the supermassive black hole.  The nuclear region is heavily obscured in the optical, but infrared and submillimeter wavelengths can penetrate the dust.  Analyses of new infrared spectra of water vapor and other gases have now confirmed and quantified these processes in the barred spiral ESO320-G030.NASA, ESA, and the Hubble Heritage Team; STScI/AURA


Reference: “A Proto-Pseudobulge in ESO 320-G030 Fed by a Massive Molecular Inflow Driven by a Nuclear Bar,” Eduardo González-Alfonso, Miguel Pereira-Santaella, Jacqueline Fischer, Santiago García-Burillo, Chentao Yang, Almudena Alonso-Herrero, Luis Colina, Matthew L. N. Ashby, Howard A. Smith, Fernando Rico-Villas, Jesús Martín-Pintado, Sara Cazzoli, and Kenneth P. Stewart, Astronomy & Astrophysics, 645, 49, 2021.


Provided by CFA Harvard

Planet Formation May Start Earlier Than Previously Thought (Planetary Science)

Rings in protoplanetary systems may develop much earlier than in conventional scenarios of planet formation

On their long journey to form planets, dust grains may coalesce with each other much earlier than previously thought, simulations by RIKEN astrophysicists suggest1. This may mean revisiting conventional theories of planet formation.

Massive planets start off life as specks of dust that are too miniscule to be observed by the human eye. “Planets like the Earth that are thousands of kilometers in diameter evolved from submicron particles of interstellar dust—that’s quite a jump in scale,” notes Satoshi Ohashi of the RIKEN Star and Planet Formation Laboratory. “We’re interested in discovering how dust grains come together to form objects that are thousands of kilometers in size.”

Planets are birthed from protoplanetary disks—swirling disks of gas and dust around new stars. Ring-like structures have been observed in these disks, and the rings are thought to merge into larger and larger structures over time, eventually leading to the formation of planets. But much remains unknown about the process.

Now, Ohashi and his co-workers have studied a possible scenario for the formation of these rings by performing computer simulations. The results they obtained indicate that dust may aggregate into larger particles during the protostellar stage, while the star itself is still forming and much earlier than predicted by current theories of planet formation. “We found that ring structures emerged even in the early stages of disk formation,” says Ohashi. “This suggests that the dust grains may become bigger earlier than we had previously thought.”

This is an unexpected finding because the dust disk is still in a state of considerable flux during the protostellar stage—hardly a promising place for dust to agglomerate. “It’s really surprising because during planet formation the dust grains should stay in the disk, but material is still falling into the central star during the protostellar stage,” says Ohashi. “So we are thinking that planet formation could be a highly dynamic process.”

The team found good agreement between their simulation results and observations of 23 ring structures in disks by the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile and other telescopes. Their results could also explain the recent observation of rings in protostellar disks. “Recent ALMA observations have found at least four ring structures in protostellar disks, which are consistent with our simulations,” notes Ohashi.

In the future, the team hopes to obtain images of ring structures around protoplanetary disks in multiple wavelengths, since that would enable them to better compare their simulation with observations.

Featured image: An image taken by the Atacama Large Millimeter/submillimeter Array (ALMA) of the protoplanetary disc around the nearby young star TW Hydrae. This image reveals multiple rings and gaps that indicate the presence of emerging planets as they sweep their orbits clear of dust and gas. Simulations by RIKEN astrophysicists suggest that the rings may form earlier than previously thought. © S. ANDREWS (HARVARD-SMITHSONIAN CFA); B. SAXTON (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO /SCIENCE PHOTO LIBRARYY

Reference

  • 1.Ohashi, S., Kobayashi, H., Nakatani, R., Okuzumi, S., Tanaka, H., Murakawa, K., Zhang, Y., Liu, H. B. & Sakai, N. Ring formation by coagulation of dust aggregates in the early phase of disk evolution around a protostar. The Astrophysical Journal 907, 80 (2021). doi: 10.3847/1538-4357/abd0fa

Provided by RIKEN

Spacer Cation Alloying of Homo-conformational Carboxylate trans Isomer to Boost In-plane Ferroelectricity in 2D Hybrid Perovskite (Chemistry)

Two-dimensional (2D) hybrid perovskites of Ruddlesden-Popper (RP) lattices are recently booming as a vigorous class of ferroelectrics, whereas their intrinsic van der Waals gaps exert weak interactions that destabilize the layered motifs. Thus, it is a challenge to reduce interlayered energy gap for exploring stable RP ferroelectrics. 

In a study published in J. Am. Chem. Soc., the research group led by Prof. LUO Junhua and Prof. SUN Zhihua from Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences proposed hydrogen bonds to reduce van der Waals gaps of 2D RP-type perovskite phases while retaining ferroelectricity.  

The researchers alloyed the homo-conformational trans-isomer for the first time as a cationic spacer to exploit a new molecular ferroelectric, (t-ACH)2(EA)2Pb3Br10 (t-ACH = 4-aminomethyl-1-cyclohexanecarboxylate, EA = ethylammonium).  

They found that strong O-H···O hydrogen bonds link the adjacent organic layers to form a new quasi-RP motif with reduced energy gaps and enhanced phase stability. In terms of ferroelectricity, such directional O-H···O hydrogen bonds make a crucial role to the generation of polarization or formation of polar structure, as verified by structure analyses, quadratic optical nonlinearity and electric hysteresis loops. 

Strong in-plane ferroelectricity with high Curie temperature (355 K) and spontaneous polarization (~2.9 μC/cm2) is well established for (t-ACH)2(EA)2Pb3Br10.  

Furthermore, structure analyses revealed that the mixed-cation alloying makes a crucial role to its electric polarization, which means a breakthrough for reducing energy gaps of 2D RP lattice and retaining ferroelectricity.  

Combining with the anisotropic nature of its 2D motif, such ferroelectricity creates strong linearly polarized-light sensitivity with a large dichroism ratio up to ~3.2.  

This study showed the great potentials of (t-ACH)2(EA)2Pb3Br10 for practical device application. 2D RP-type ferroelectric with trans isomer cationic spacer is unprecedented, and the concept of reducing energy gaps via H-bonding interactions sheds light on rational design of stable ferroelectrics toward photoelectric applications.

Featured image: Illustration of the Research (Image by Prof. LUO’s group)


Reference: Yi Liu, Shiguo Han, Jiaqi Wang, Yu Ma, Wuqian Guo, Xiao-Ying Huang, Jun-Hua Luo, Maochun Hong, and Zhihua Sun, “Spacer Cation Alloying of a Homoconformational Carboxylate trans Isomer to Boost in-Plane Ferroelectricity in a 2D Hybrid Perovskite”, J. Am. Chem. Soc. 2021, 143, 4, 2130–2137.
https://doi.org/10.1021/jacs.0c12513


Provided by Chinese Academy of Sciences

Damage to White Matter is Linked to Worse Cognitive Outcomes After Brain Injury (Neuroscience)

White matter vs gray matter: Damage to dense structural connections in the brain is a better predictor of poor outcomes than damage to functional hubs

A new University of Iowa study challenges the idea that gray matter (the neurons that form the cerebral cortex) is more important than white matter (the myelin covered axons that physically connect neuronal regions) when it comes to cognitive health and function. The findings may help neurologists better predict the long-term effects of strokes and other forms of traumatic brain injury.

“The most unexpected aspect of our findings was that damage to gray matter hubs of the brain that are really interconnected with other regions didn’t really tell us much about how poorly people would do on cognitive tests after brain damage. On the other hand, people with damage to the densest white matter connections did much worse on those tests,” explains Justin Reber, PhD, a UI postdoctoral research fellow in psychology and first author on the study. “This is important because both scientists and clinicians often focus almost exclusively on the role of gray matter. This study is a reminder that connections between brain regions might matter just as much as those regions themselves, if not more so.”

The new study, published in PNAS, analyzes brain scans and cognitive function tests from over 500 people with localized areas of brain damage caused by strokes or other forms of brain injury. Looking at the location of the brain damage, also known as lesions, the UI team led by Reber and Aaron Boes, MD, PhD, correlated the level of connectedness of the damaged areas with the level of cognitive disability the patient experienced. The findings suggest that damage to highly connected regions of white matter is more predictive of cognitive impairment than damage to highly connected gray matter hubs.

Network hubs and brain function

Research on cognition often focuses on networks within the brain, and how different network configurations contribute to different aspects of cognition. Various mathematical models have been developed to measure the connectedness of networks and to identify hubs, or highly connected brain regions, that appear to be important in coordinating processing in brain networks.

The UI team used these well accepted mathematical models to identify the location of hubs within both gray and white matter from brain imaging of normal healthy individuals. The researchers then used brain scans from patients with brain lesions to find cases where areas of damage coincided with hubs. Using data from multiple cognitive tests for those patients, they were also able to measure the effect hub damage had on cognitive outcomes. Surprisingly, damage to highly connected gray matter hubs did not have a strong association with poor cognitive outcomes. In contrast, damage to dense white matter hubs was strongly linked to impaired cognition.

This video is a map of edge density, a measure of the density of white matter connections between different brain regions. The color scale goes from dark purple where there are only sparse connections, to a yellowish white where the connections are most densely packed. A University of Iowa study suggest that damage to highly connected regions of white matter is more predictive of cognitive impairment than damage to highly connected gray matter hubs. © Justin Reber, University of Iowa

“The brain isn’t a blank canvas where all regions are equivalent; a small lesion in one region of the brain may have very minimal impact on cognition, whereas another one may have a huge impact. These findings might help us better predict, based on the location of the damage, which patients are at risk for cognitive impairment after stroke or other brain injury,” says Boes, UI professor of pediatrics, neurology, and psychiatry, and a member of the Iowa Neuroscience Institute. “It’s better to know those things in advance as it gives patients and family members a more realistic prognosis and helps target rehabilitation more effectively.”

UI registry is a unique resource for neuroscientists

Importantly, the new findings were based on data from over 500 individual patients, which is a large number compared to previous studies and suggests the findings are robust. The data came from two registries; one from Washington University in St. Louis, which provided data from 102 patients, and the Iowa Neurological Registry based at the UI, which provided data from 402 patients. The Iowa registry is over 40 years old and is one of the best characterized patient registries in the world, with close to 1000 subjects with well characterized cognition derived from hours of paper and pencil neuropsychological tests, and detailed brain imaging to map brain lesions. The registry is directed by Daniel Tranel, PhD, UI professor of neurology, and one of the study authors.

Reber notes that the study also illustrates the value of working with clinical patients as well as healthy individuals in terms of understanding relationships between brain structure and function.

“There is a lot of really excellent research using functional brain imaging with healthy participants or computer simulations that tell us that these gray matter hubs are critical to how the brain works, and that you can use them to predict how well healthy people will perform on cognitive tests. But when we look at how strokes and other brain damage actually affect people, it turns out that you can predict much more from damage to white matter,” he says. “Research with people who have survived strokes or other brain damage is messy, complicated, and absolutely essential, because it builds a bridge between basic scientific theory and clinical practice, and it can improve both.

I cannot stress enough how grateful we are that these patients have volunteered their time to help us; without them, a lot of important research would be impossible,” he adds.

In addition to Reber, Boes, and Tranel, the research team included UI researchers Kai Hwang, PhD, Mark Bowren, and Joel Bruss, as well as Pratik Mukherjee, MD, PhD, at the University of California, San Francisco.

The research was funded in part by grants from the National Institute of Neurological Disorders and Stroke, and the National Institute of Mental Health at the National Institutes of Health (NIH), and the INSPIRE T32 fellowship, an NIH-funded post-doctoral training program.


Reference: Justin Reber, Kai Hwang, Mark Bowren, Joel Bruss, Pratik Mukherjee, Daniel Tranel, Aaron D. Boes, “Cognitive impairment after focal brain lesions is better predicted by damage to structural than functional network hubs”, Proceedings of the National Academy of Sciences May 2021, 118 (19) e2018784118; https://doi.org/10.1073/pnas.2018784118


Provided by University of Iowa Health Care

Aluminum May Affect Climate Change by Increasing Ocean’s Carbon Sink Capacity (Earth Science)

Reducing net greenhouse gas emissions to zero as soon as possible and achieving “carbon neutrality” is the key to addressing global warming and climate change. The ocean is the largest active carbon pool on the planet, with huge potential to help achieve negative emissions by serving as a carbon sink. 

Recently, researchers found that adding a small amount of aluminum to achieve concentrations in the 10x nanomolar (nM) range can increase the net fixation of COby marine diatoms and decrease their decomposition, thus improving the ocean’s ability to absorb CO2 and sequester carbon at deep ocean depths. 

The study, published in Limnology and Oceanography on May 3, was conducted by a joint team led by Prof. TAN Yehui from the South China Sea Institute of Oceanology (SCSIO) of the Chinese Academy of Sciences and Prof. Peter G.C. Campbell from the Eau Terre Environnement Research Centre of the National Institute of Scientific Research, Canada.

Estimated effects of aluminum on the export of particulate organic carbon to ocean depths. (Image by ZHOU Linbin)

According to the earlier “iron hypothesis”, adding a small amount of iron to the iron-limited but nutrient-rich oceans could significantly promote the growth of marine phytoplankton (microalgae) and their absorption of CO2, and the consequent burial of organic matter in the ocean. However, the results of artificial iron fertilization experiments did not fully support the “iron hypothesis” and later studies suggested that ignoring the effects of aluminum and other elements may be the reason. 

“In fact, natural iron fertilization, as caused by dust deposition, upwelling and hydrothermal venting, provides the ocean not only iron, but also aluminum and other elements. Aluminum concentrations in the upper ocean are usually one order of magnitude higher than those of iron,” said Prof. TAN. 

Prof. TAN’s team and their collaborators found that aluminum may not only improve the utilization efficiency of iron and dissolved organic phosphorus by marine phytoplankton, thus enhancing carbon fixation in the upper ocean, but may also reduce the decomposition rate of biogenic organic carbon and enhance the export and sequestration of carbon in deep ocean depths. 

They also found a significant negative correlation between aluminum input to the Southern Ocean and atmospheric CO2 concentration over the past 160,000 years. 

Based on their findings about aluminum, they improved the original “iron hypothesis” by proposing the “iron-aluminum hypothesis” to better explain the roles of the two elements in climate change. 

In this study, the researchers used radiocarbon (14C) as a tracer to show that adding aluminum to seawater to achieve trace concentrations (e.g., 40 nM) increased net carbon fixation of marine diatoms 10% to 30%. 

More importantly, this study proved that environmentally relevant low concentrations of aluminum can reduce the daily decomposition rate of marine diatom-produced particulate organic carbon by 50% or more. 

Calculations based on the new data suggest that adding aluminum at a concentration of 40 nM or lower to the ocean may increase the amount of particulate organic carbon exported to depths of 1,000 m and deeper by 1–3 orders of magnitude. This will significantly increase the ocean’s carbon sink capacity and sequester carbon in the ocean for a long time, thus ameliorating climate change.

Featured image: Diagram of how aluminum may facilitate the uptake of iron and the utilization of dissolved organic phosphorus by marine phytoplankton (Image by ZHOU Linbin) 


Reference: Zhou, L., Liu, F., Liu, Q., Fortin, C., Tan, Y., Huang, L. and Campbell, P.G.C. (2021), Aluminum increases net carbon fixation by marine diatoms and decreases their decomposition: Evidence for the iron–aluminum hypothesis. Limnol Oceanogr. https://doi.org/10.1002/lno.11784


Provided by Chinese Academy of Sciences

New Design for Isolated Power Supply Chip (Engineering)

Recently, a research group led by Prof. CHENG Lin from School of Microelectronics, University of Science and Technology of China (USTC) of the Chinese Academy of Sciences has made achievements in the field of fully integrated isolated power chip design.

The researchers proposed a chip based on glass fan-out wafer-level package (FOWLP), achieving 46.5% peak transformation efficiency and 50mW/mm2 power density.

Compared with the traditional isolated power supply chip, this new design interconnects the receiving and transmitting chips through the micro transformer made of the rewiring layer, showing no need of additional transformer chips. In this way, it lowered the need for three or even four chips in the existing chip design, so as to greatly improve the efficiency of isolated power supply.

In addition, the researchers proposed a grid voltage control technology with variable capacitor, which maintains the grid peak voltage in the best safe voltage range even in a wider supply voltage range.

This design improves the conversion efficiency and power density of the chip effectively, providing a new solution for the design of isolated power chip in the future.

This work is published at the IEEE International Solid State Circuits Conference (ISSCC), and was selected as the demo demonstration at the meeting.

Featured image: Photo of Isolated power system package and chip. (Image by PAN Dongfang)


Reference: D. Pan et al., “33.5 A 1.25W 46.5%-Peak-Efficiency Transformer-in-Package Isolated DC-DC Converter Using Glass-Based Fan-Out Wafer-Level Packaging Achieving 50mW/mm2 Power Density,” 2021 IEEE International Solid- State Circuits Conference (ISSCC), 2021, pp. 468-470, doi: 10.1109/ISSCC42613.2021.9365955.


Provided by Chinese Academy of Sciences

Researchers Prepare Broadband Antireflection Laser Film Based on Deionized Water Treatment of Electron-beam Film (Material Science)

Recently, a research team from the Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences (CAS) prepared a kind of broadband anti-reflection (AR) laser film based on water bath treatment of electron-beam Al2O3 film. The work was published in Optical Materials Express

Broadband AR films with graded-refractive index are widely used in many applications. Researchers used many methods for preparing broadband AR coatings, including multilayer AR coatings, glancing angle deposition, biomimetic photonic nanostructure, and so on. However, these methods are limited by factors such as complex fabrication processes, high costs, and difficulty in large-scale implementation. 

Al2O3 film is chemically unstable in high temperature water. It has been reported that Al2O3 films transform into random microstructure with graded-refractive index and broadband antireflection property is obtained after high temperature water bath treatment. 

In this work, the researchers used electron beam evaporation to deposit Al2O3 films and systematically studied the effects of water bath treatment time on the microstructure and AR properties of Al2O3 films. 

Results show that the Al2O3 film treated in 90 ℃ deionized water for sev minutes has excellent broadband AR performance in the wavelength range of 350-1,100 nm. The average transmittance of the double-sided coated sample is about 98.8% in the wavelength range of 350-1,100 nm.

According to the fitting results by the genetic algorithm, the Al2O3 film has a parabola-like refractive index profile. The laser-induced damage threshold of the AR film shows the potential for application in lasers. 

This work was supported by the National Natural Science Foundation of China, the Youth Innovation Promotion Association of CAS and the Strategic Priority Research Program of CAS. 

Featured image: Transmittance performance of the double-sided coated sample treated for 7 minutes. (Image by SIOM) 


Reference: Chaoyi Yin, Meiping Zhu, Tingting Zeng, Jian Sun, Rongjun Zhang, Jiaoling Zhao, Longsheng Wang, and Jianda Shao, “Al2O3 anti-reflection coatings with graded-refractive index profile for laser applications,” Opt. Mater. Express 11, 875-883 (2021). https://doi.org/10.1364/OME.418174


Provided by Chinese Academy of Sciences

USTC Realizes Coherent Storage of Light over One-hour (Physics)

Remote quantum distribution on the ground is limited because of the loss of photon in optical fibers. One solution for remote quantum communication lies in quantum memories: photons are stored in the long-lived quantum memory (quantum flash drive) and then quantum information is transmitted by the transportation of the quantum memory. Given the speed of aircrafts and high-speed trains, it is critical to increase the storage time of the quantum memories to the order of hours. 

In a new study published in Nature Communications, a research team led by Prof. LI Chuanfeng and Prof. ZHOU Zongquan from University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS) extended the storage time of the optical memories to over one hour. It broke the record of one minute achieved by German researchers in 2013, and made a great stride towards the application of quantum memories. 

In the attempt to achieve optical storage in a zero-first-order-Zeeman (ZEFOZ) magnetic field, the complicated and unknown energy level structures in both the ground and excited states have challenged researchers for a long time. Recently, researchers used the spin Hamiltonians to predict the level structures. However, an error may occur in the theoretical prediction. 

To overcome the problem, researchers from USTC adopted the spin wave atomic frequency comb (AFC) protocol in a ZEFOZ field, namely ZEFOZ-AFC method, successfully implementing the long-lived storage of light signals.

Dynamical decoupling (DD) was used to protect the spin coherence and extend the storage time. The coherent nature of this device is verified by implementing a time-bin-like interference experiment after 1h storage with a fidelity of 96.4%. The result showed the great storage capacity of the coherent light and its potential in quantum memories. 

This study expands the optical storage time from the order of minutes to the order of hours. It meets the basic requirements of the optical storage lifetime for quantum memories. Through optimizing the storage efficiency and signal-to-noise ratios (SNR), researchers are expected to transmit quantum information by classical carriers in a new quantum channel.

Featured image: Schematic of the experimental setup. The probe and pump beam are emitted with single-mode fibers (SMF) and fiber collimators (FC) before entering the cryostat. The two beams are arranged in a non-collinear configuration. Half-wave plates (λ/2) control the polarization of the beams, and two pairs of lenses are used to obtain proper beam widths at the position of the crystal. A BS (beam splitter) with a reflection-to-transmission ratio of 8:92 is employed to efficiently collect the transmitted signal. The probe beam is reflected by the mirror at the bottom of the cryostat and coupled to a SMF for optical heterodyne detection after passing through the BS. A pair of coils placed at the two sides of the sample is driven by an arbitrary waveform generator (AWG) with the output amplified with a 300-W RF amplifier. © Ma et al.


Reference: Ma, Y., Ma, YZ., Zhou, ZQ. et al. One-hour coherent optical storage in an atomic frequency comb memory. Nat Commun 12, 2381 (2021). https://doi.org/10.1038/s41467-021-22706-y


Provided by Chinese Academy of Sciences