"Nature" (20240125 published) one-week paper introduction

Compile | Feng Weiwei

Nature, 25 January 2024, Volume 625 Issue 7996

Nature, Vol. 625, No. 7996, January 25, 2024

Physics

Testing quantum electrodynamics in extreme fields using helium-like uranium

Quantum electrodynamics are tested in extreme magnetic fields using helium-like uranium

▲ 作者：R. Loetzsch, H. F. Beyer, L. Duval, U. Spillmann et al.

▲ Links:

https://www.nature.com/articles/s41586-023-06910-y

▲ Abstract:

Quantum electrodynamics (QED), the quantum field theory that describes the interaction between light and matter, is often considered the most mature quantum theory in modern physics. But this is mainly based on extremely precise studies in the field of relatively low field strengths and photoatoms and ions.

In the field of very strong electromagnetic fields, such as in the heaviest highly charged ions, the QED calculation enters a non-perturbative state with different properties. However, the corresponding experimental studies are very challenging, and the theoretical predictions have only been partially verified. The researchers propose an experiment that is sensitive to higher-order QED effects and electron-electron interactions in the high-Z region.

This is achieved by using a multi-reference method based on Doppler-tuned X-ray emissions from stored relativistic uranium ions with different charge states. The experimental results can distinguish several state-of-the-art theoretical methods and provide an important benchmark for the calculation of the strong field domain.

▲ Abstract：

Quantum electrodynamics (QED), the quantum field theory that describes the interaction between light and matter, is commonly regarded as the best-tested quantum theory in modern physics. However, this claim is mostly based on extremely precise studies performed in the domain of relatively low field strengths and light atoms and ions. In the realm of very strong electromagnetic fields such as in the heaviest highly charged ions, QED calculations enter a qualitatively different, non-perturbative regime. Yet, the corresponding experimental studies are very challenging, and theoretical predictions are only partially tested. Here we present an experiment sensitive to higher-order QED effects and electron–electron interactions in the high-Z regime. This is achieved by using a multi-reference method based on Doppler-tuned X-ray emission from stored relativistic uranium ions with different charge states. Moreover, our experimental result can discriminate between several state-of-the-art theoretical approaches and provides an important benchmark for calculations in the strong-field domain.

Observing dynamical phases of BCS superconductors in a cavity QED simulator

Observe the dynamic phase of a BCS superconductor in a cavity electrodynamics simulator

▲ 作者：Dylan J. Young, Anjun Chu, Eric Yilun Song et al.

▲ Links:

https://www.nature.com/articles/s41586-023-06911-x

▲ Abstract:

In conventional Bardeen-Cooper-Shreifer (BCS) superconductors, electrons with opposite momentum combine to form Cooper pairs due to phonon-mediated attraction interactions in the material. While superconductivity occurs naturally at thermal equilibrium, superconductivity can also occur outside equilibrium when there is a sudden change in system parameters. The resulting non-equilibrium phase is expected to occur in real materials and ultracold fermion atoms, but not all of them are directly observed.

An alternative method using cavity quantum electrodynamics (QED) to generate the proposed dynamic phase has been implemented. This system encodes the presence or absence of Cooper pairs in long-lived electron transitions coupled to an optical cavity for 88Sr atoms and represents the interaction between electrons as a photon-mediated interaction through the cavity.

This opens up exciting prospects for quantum simulation, including the design of unconventional superconductors and the exploration of potential beyond mean field effects, such as spectral shape factors, as well as increased coherence times for quantum sensing.

▲ Abstract：

In conventional Bardeen–Cooper–Schrieffer superconductors, electrons with opposite momenta bind into Cooper pairs due to an attractive interaction mediated by phonons in the material. Although superconductivity naturally emerges at thermal equilibrium, it can also emerge out of equilibrium when the system parameters are abruptly changed. The resulting out-of-equilibrium phases are predicted to occur in real materials and ultracold fermionic atoms, but not all have yet been directly observed. Here we realize an alternative way to generate the proposed dynamical phases using cavity quantum electrodynamics (QED). Our system encodes the presence or absence of a Cooper pair in a long-lived electronic transition in 88Sr atoms coupled to an optical cavity and represents interactions between electrons as photon-mediated interactions through the cavity. This opens up exciting prospects for quantum simulation, including the potential to engineer unconventional superconductors and to probe beyond mean-field effects like the spectral form factor, and for increasing the coherence time for quantum sensing.

Nozaki–Bekki solitons in semiconductor lasers

Nozaki-Baker solitons in semiconductor lasers

▲ 作者：Nikola Opačak, Dmitry Kazakov, Lorenzo L. Columbo et al.

▲ Links:

https://www.nature.com/articles/s41586-023-06915-7

▲ Abstract:

Optical frequency comb light sources, emitting perfectly periodic and coherent optical waveforms, have recently rapidly evolved into chip-level integrated solutions. Of these, two categories are particularly important – semiconductor Fabry-Perot lasers and passive ring Kerr microresonators. The researchers fused the two technologies in a ring-shaped diode laser and demonstrated a free-running soliton formation paradigm called the Nozaki-Beckage soliton.

The researchers demonstrated that the Nozaki-Baker solitons are structurally stable in ring lasers and form spontaneously as the laser bias is adjusted, eliminating the need for an external optical pump. By combining conclusive experimental results with a complementary detailed theoretical model, they reveal the salient characteristics of these solitons and provide guidance for their generation.

In addition to the basic soliton circulating inside the ring laser, the researchers demonstrated the multi-soliton state, verified its locality, and provided insight into the formation of soliton crystals. The results solidify a monolithic electro-driven platform that can be used to generate solitons directly, and open the door to interdisciplinary research areas of laser multimode dynamics and Kerr-parameter processes.

▲ Abstract：

Optical frequency-comb sources, which emit perfectly periodic and coherent waveforms of light, have recently rapidly progressed towards chip-scale integrated solutions. Among them, two classes are particularly significant—semiconductor Fabry–Perót lasers and passive ring Kerr microresonators. Here we merge the two technologies in a ring semiconductor laser and demonstrate a paradigm for the formation of free-running solitons, called Nozaki–Bekki solitons. We show that Nozaki–Bekki solitons are structurally stable in a ring laser and form spontaneously with tuning of the laser bias, eliminating the need for an external optical pump. By combining conclusive experimental findings and a complementary elaborate theoretical model, we reveal the salient characteristics of these solitons and provide guidelines for their generation. Beyond the fundamental soliton circulating inside the ring laser, we demonstrate multisoliton states as well, verifying their localized nature and offering an insight into formation of soliton crystals. Our results consolidate a monolithic electrically driven platform for direct soliton generation and open the door for a research field at the junction of laser multimode dynamics and Kerr parametric processes.

The persistence of memory in ionic conduction probed by nonlinear optics

Nonlinear optics to study the persistence of memory in ion conduction

▲ 作者：Andrey D. Poletayev, Matthias C. Hoffmann et al.

▲ Links:

https://www.nature.com/articles/s41586-023-06827-6

▲ Abstract:

Predicting the actual transport rate of condensed matter enables the rational design of materials, equipment, and processes. This is particularly important for the development of low-carbon energy technologies such as rechargeable batteries. The researchers used a single-cycle terahertz pump to pulse-trigger ion jumps in the battery's solid electrolyte.

This is visualized by inducing transient birefringence, which allows for direct detection of the anisotropy of ion skipping on picosecond time scales. The relaxation of the transient signal measures the attenuation of directed memory and the generation of diffusion entropy. The researchers extended the experimental results of silicon transient birefringence to determine the vibrational attempt frequency of ion jumping.

Using nonlinear optical methods, they explored the transport of ions at their fastest limits, distinguished between relevant conduction mechanisms and true random walks at the atomic scale, and demonstrated the connection between activated transport and information thermodynamics.

▲ Abstract：

Predicting practical rates of transport in condensed phases enables the rational design of materials, devices and processes. This is especially critical to developing low-carbon energy technologies such as rechargeable batteries. Here we use single-cycle terahertz pumps to impulsively trigger ionic hopping in battery solid electrolytes. This is visualized by an induced transient birefringence, enabling direct probing of anisotropy in ionic hopping on the picosecond timescale. The relaxation of the transient signal measures the decay of orientational memory, and the production of entropy in diffusion. We extend experimental results using in silico transient birefringence to identify vibrational attempt frequencies for ion hopping. Using nonlinear optical methods, we probe ion transport at its fastest limit, distinguish correlated conduction mechanisms from a true random walk at the atomic scale, and demonstrate the connection between activated transport and the thermodynamics of information.

Ecology

Rapid groundwater decline and some cases of recovery in aquifers globally

Rapid global groundwater decline and aquifer restoration

▲ 作者:Scott Jasechko, Hansjörg Seybold et al.

▲ Links:

https://www.nature.com/articles/s41586-023-06879-8

▲ Abstract:

Groundwater resources are essential for ecosystems and livelihoods. Overpumping groundwater can lead to a drop in the water table, as well as seawater intrusion, land subsidence, river depletion, and wells drying up. However, the current global rate and prevalence of groundwater decline is poorly constrained, as in-situ groundwater levels have not yet been synthesized globally.

The researchers analysed groundwater table trends in 170,000 monitoring wells and 1,693 aquifer systems, which account for about 75 percent of global groundwater extraction. Studies have shown that in the 21st century, a rapid decline in the water table (> 50 m/year) is widespread, especially in arid regions with large tracts of farmland.

Crucially, the study also shows that the rate of decline in groundwater levels in 30 per cent of the world's regional aquifers has accelerated over the past 40 years. The general acceleration of the deepening of groundwater levels underscores the urgent need for more effective measures to address groundwater depletion. The analysis also revealed specific cases in which the depletion trend had been reversed with policy changes, aquifer recharge management and surface water transfers, indicating that depleted aquifer systems have the potential to recover.

▲ Abstract：

Groundwater resources are vital to ecosystems and livelihoods. Excessive groundwater withdrawals can cause groundwater levels to decline, resulting in seawater intrusion, land subsidence, streamflow depletion and wells running dry. However, the global pace and prevalence of local groundwater declines are poorly constrained, because in situ groundwater levels have not been synthesized at the global scale. Here we analyse in situ groundwater-level trends for 170,000 monitoring wells and 1,693 aquifer systems in countries that encompass approximately 75% of global groundwater withdrawals. We show that rapid groundwater-level declines (>0.5 m year−1) are widespread in the twenty-first century, especially in dry regions with extensive croplands. Critically, we also show that groundwater-level declines have accelerated over the past four decades in 30% of the world’s regional aquifers. This widespread acceleration in groundwater-level deepening highlights an urgent need for more effective measures to address groundwater depletion. Our analysis also reveals specific cases in which depletion trends have reversed following policy changes, managed aquifer recharge and surface-water diversions, demonstrating the potential for depleted aquifer systems to recover.

Consistent patterns of common species across tropical tree communities

Consistent patterns of species common in tropical tree communities

▲ 作者:Declan L. M. Cooper, Simon L. Lewis et al.

▲ Links:

https://www.nature.com/articles/s41586-023-06820-z

▲ Abstract:

Trees make up the most biodiverse ecosystem on the planet – tropical forests. As little is known about most tropical tree species, the large number of tree species poses a significant challenge to understanding these forests, including their response to environmental change. A focus on common species may circumvent this challenge.

The authors studied inventory data from 1,003,805 trees with trunk diameters of at least 10 cm in tropical primeval forests in Africa, the Amazon, and Southeast Asia, examining abundance patterns for common tree species. These trees are spread over 1,568 sites and cover a closed-canopy, structurally intact tropical forest. The researchers estimate that 2.2 percent, 2.2 percent and 2.3 percent of the species each account for 50 percent of tropical trees in these areas.

By extrapolating all closed canopy tropical forests, the study estimates that only 1,053 species account for half of the 800 billion tropical trees on Earth with trunks of at least 10 centimeters in diameter. Despite different biogeographical, climatic, and anthropogenic histories, researchers have found clear patterns of common species and species abundance across continents. This suggests that the basic mechanism of tree community assemblage may be applicable to all tropical forests.

Resampling analysis suggests that the most common species may belong to a controllable list of known species, which allows targeted efforts to understand their ecology. While they do not diminish the importance of rare species, the results provide new opportunities to understand the world's most diverse forests, including by focusing on the common species that make up the majority of trees to model their response to environmental change.

▲ Abstract：

Trees structure the Earth’s most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth’s 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world’s most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees.