The splitting of a single photon in two is one of the most useful tools in quantum photonics. It can create entangled photon pairs, single photons, squeezed light, and even more complicated states of light which are essential for optical quantum technologies. This process is known as spontaneous parametric down-conversion (SPDC).

SPDC is deeply linked to central symmetry. This is the symmetry with respect to a point — for instance, a square is centrally symmetric but a triangle is not. In its very essence — a splitting of one photon in two — SPDC breaks the central symmetry. Therefore, it is only possible in crystals whose elementary cell is centrally asymmetric. SPDC cannot happen in ordinary liquids or gases, because these materials are isotropic.

Recently, however, researchers have discovered liquid crystals that have a different structure, the so-called ferroelectric nematic liquid crystals. Despite being fluidic, these materials feature strong central symmetry breaking. Their molecules are elongated, asymmetric and, most importantly, they can be re-oriented by external electric field. Re-orientation of molecules changes the polarization of the generated photon pairs, as well as the generation rate. Given a proper packaging, a sample of such material can be a very useful device because it produces photon pairs efficiently, can be easily tuned with electric field, and can be integrated into more complex devices.

Using the samples prepared in Jozef Stefan Institute (Ljubljana, Slovenia) from a ferroelectric nematic liquid crystal synthesized by Merck Electronics KGaA, researchers at the Max-Planck Institute for the Science of Light have implemented SPDC, for the first time, in a liquid crystal. The efficiency of entangled photons generation is as high as in the best nonlinear crystals, such as lithium niobate, of similar thickness. By applying an electric field of just a few Volts, they were able to switch the generation of photon pairs on and off, as well as to change the polarization properties of these pairs. This discovery starts a new generation of quantum light sources: flexible, tunable, and efficient.

Antimicrobial resistance of pathogens is a worldwide problem, and recognized by the WHO as one of the top global public health and development threats. There are two ways to fight this: by developing new drugs, or by preventing the development of resistance. ‘We know that temperature affects the mutation rate in bacteria’, explains Timo van Eldijk, co-first author of the paper. ‘What we wanted to find out was how the increase in temperature associated with fever influences the mutation rate towards antibiotic resistance.’

Three antibiotics

‘Most studies on resistance mutations were done by lowering the ambient temperature, and none, as far as we know, used a moderate increase above normal body temperature,’ Van Eldijk reports. Together with Master’s student Eleanor Sheridan, Van Eldijk cultured E. coli bacteria at 37 or 40 degrees Celsius, and subsequently exposed them to three different antibiotics to assess the effect. ‘Again, some previous human trials have looked at temperature and antibiotics, but in these studies the type of drug was not controlled.’ In their laboratory study, the team used three different antibiotics with different modes of action: ciprofloxacin, rifampicin, and ampicillin.

The results showed that for two of the drugs, ciprofloxacin and rifampicin, increased temperature led to an increase in the mutation rate towards resistance. However, the third drug, ampicillin, caused a decrease in the mutation rate towards resistance at fever temperatures. ‘To be certain of this result, we actually replicated the study with ampicillin in two different labs, at the University of Groningen and the University of Montpellier, and got the same result,’ says Van Eldijk.

Fever-suppressing drugs

The researchers hypothesized that a temperature dependence of the efficacy of ampicillin could explain this result, and confirmed this in an experiment. This explains why ampicillin resistance is less likely to arise at 40 degrees Celsius. ‘Our study shows that a very mild change in temperature can drastically change the mutation rate towards resistance to antimicrobials,’ concludes Van Eldijk. ‘This is interesting, as other parameters such as the growth rate do not seem to change.’

If the results are replicated in humans, this could open the way to tackling antimicrobial resistance by lowering the temperature with fever-suppressing drugs, or by giving patients with a fever antimicrobial drugs with higher efficacy at higher temperatures. The team concludes in the paper: ‘An optimized combination of antibiotics and fever suppression strategies may be a new weapon in the battle against antibiotic resistance.’

As global temperatures and urban populations rise, the world’s cities have become “urban heat islands,” with tight-packed conditions and thermal radiation emitting from pavement and skyscraper trapping and magnifying these temperatures. With 68 percent of all people predicted to live in cities by 2050, this is a growing, deadly problem.

In a paper published today in Science, researchers from the UChicago Pritzker School of Molecular Engineering (PME) detail a new wearable fabric that can help urban residents survive the worst impacts of massive heat caused by global climate change, with applications in clothing, building and car design, and food storage.

In tests under the Arizona sun, the material kept 2.3 degrees Celsius (4.1 degrees Fahrenheit) cooler than the broadband emitter fabric used for outdoor endurance sports and 8.9 degrees Celsius (16 degrees Fahrenheit) cooler than the commercialized silk commonly used for shirts, dresses and other summer clothing.

This, the team hopes, will help many avoid the heat-related hospitalizations and deaths seen in global population centers this year alone.

“We need to reduce carbon emission and make our cities carbon negative or carbon neutral,” PME Asst. Prof. Po-Chun Hsu said. “But meanwhile, people are feeling the impact of these high temperatures.”

‘You have to consider the environment’

Existing cooling fabric for outdoor sports works by reflecting the sun’s light in a diffuse pattern so it doesn’t blind onlookers. But in an urban heat island, the sun is only one source of heat. While the sun bakes from above, thermal radiation emitted from buildings and pavement blast city-dwellers with blistering heat from the sides and below.

This means many materials that perform well in lab tests won’t help city-dwellers in Arizona, Nevada, California, Southeast Asia and China when predicted massive heatwaves hit them over the next few weeks.

“People normally focus on the performance or the material design of cooling textiles,” said co-first author Ronghui Wu, a postdoctoral researcher at PME. “To make a textile that has the potential to apply to real life, you have to consider the environment.”

One simple example of considering the environment is that people stand. They are wearing materials designed to reflect direct sunlight, but only their hats, shoulder coverings and the tops of their shoes — about 3 percent of their clothing — face that direct light. The other 97 of their clothes are being heated by the thermal radiation coming at them from the sides and below, which broadband emitter fabric does not fight.

The sun and sidewalk cook with different heats. Creating one material capable of protecting wearers from both provided a major engineering challenge for the team.

“Solar is visible light, thermal radiation is infrared, so they have different wavelengths. That means you need to have a material that has two optical properties at the same time. That’s very challenging to do,” said co-first author Chenxi Sui, a PhD candidate at PME. “You need to play with material science to engineer and tune the material to give you different resonances at different wavelengths.”

The costs of comfort

Cooling a home too often means warming the planet, with the carbon impact of air conditioning and refrigeration systems contributing to climate change.

“Our civilization actually uses about 10 to 15 percent of the energy in total just to make ourselves feel comfortable wherever we go,” Hsu said.

The risk from heat is not distributed evenly, however. In the U.S. and Japan, more than 90 percent of households have an air conditioner, a number that drops to 5 percent in India and parts of Africa.

The PME team’s new textile, which has received a provisional patent, can help provide a passive cooling system that can supplement and reduce the need for energy- and cost-intensive systems.

The applications go far beyond clothing.

A thicker version of the fabric protected by an invisible layer of polyethylene could be used on the sides of buildings or cars, lowering internal temperatures and reducing the cost and carbon impact of air conditioning. Similarly, the material could be used to transport and store milk and other foods that would otherwise spoil in the heat, cutting refrigeration’s impact.

“You can save a lot of cooling, electricity and energy costs because this is a passive process,” Sui said.

Three researchers at UC Santa Barbara have proposed a market-based approach to achieving the 30×30 targets in the ocean. They tested whether a system that allowed countries to trade conservation credits could reduce costs, incentivizing nations to actually meet their goals. Allowing voluntary trade always reduced the cost of conservation, sometimes by more than 90%. The study, published in Science, is the first to draft and analyze a conservation market for achieving 30×30 targets in the ocean.

The 30×30 initiative is one aspect of the Convention on Biological Diversity, a multilateral treaty developed in the early 1990s. In fact, it’s target No. 3 of the larger Global Biodiversity Framework (GBF) adopted by the 196 countries that convened for the UN Biodiversity Conference in 2022. It calls for the effective protection and management of 30% of the world’s terrestrial, freshwater, coastal and marine areas by the year 2030 — a goal that many scientists say humanity must achieve to secure our planet’s long-term health. And while the GBF requires countries to commit to conservation targets, it does not outline which areas should be protected, how to do so inclusively or how to pay for it.

“This project started just over four years ago,” said co-author Juan Carlos Villaseñor-Derbez, who completed his doctorate at UCSB’s Bren School of Environmental Science & Management. At this point, countries were falling short of the 10% protection benchmark as they drafted plans for 30% protection. “It seemed like most nations were genuinely committed to marine conservation, but that the costs of conserving were preventing some from engaging in it at all.

“At the same time,” he added, “a lot of research had already shown that if you could get nations to cooperate around conservation, you could substantially reduce the costs of conserving.” He and his co-authors realized the world needed an institution, policy or framework that could support this.

Uneven costs and benefits

The cost of protecting acres of ocean is not the only aspect that differs from place to place. The ecological benefits of conservation also vary based on location. Achieving 30×30 in the ocean will require coastal nations to consider potential trade-offs associated with these protections. Because high-value fisheries can coincide with important marine ecosystems — such as coral reefs, seagrass meadows and kelp forests — meeting the obligation could come at a high cost for some nations but not others. “Without an innovative policy solution, the cost of conservation for many nations could stall progress toward 30×30,” said Villasenor-Derbez.

This variability means that trade could incentivize additional gains. Instead of investing in areas with high conservation costs, or low benefits, nations could exchange their duties to double down on regions where protection yields higher returns.

Environmental economists and scientists at UC Santa Barbara’s Environmental Markets Lab (emLab) wondered if a conservation credit system could help meet 30×30 targets in the ocean. They devised a system whereby nations could trade their conservation obligation with other nations through a “transferable conservation market” policy built around ecological principles.

“Like existing mandates, this approach requires every country to protect a certain fraction (say 30%) of its marine habitat,” said Distinguished Professor Christopher Costello, emLab’s director. “But unlike other approaches, we allow those obligations to be traded across countries, within strict ecological constraints.” In this way, countries with higher conservation costs pay others to increase their conservation efforts. This study estimates the potential global cost savings under various trading constraints.

“For example, Norway, which has valuable fisheries, might pay Palau, a country that has already invested significantly in coastal conservation, to conserve additional areas on Norway’s behalf,” Costello said. This enables Norway to fulfill its conservation obligations in another part of the world.

Achieving 30×30 in the ocean

Costello, Villaseñor-Derbez and co-author Professor Andrew Plantinga developed a model to estimate the potential costs and benefits that could be achieved through a conservation market like this. They combined distribution data for 23,699 marine species with fisheries revenue data to build conservation supply curves for the world’s coastal nations.

They then defined “trade bubbles” based on biological and geographic factors. A country could trade conservation credits only with other nations within these predefined bubbles in order to ensure conservation was equitably spread across Earth’s different marine habitats. The authors examined five bubble policies that allow nations to trade within hemispheres, biogeographic realms, provinces, ecoregions, or globally, to determine potential costs.

Regardless of how they tweaked this setup, a market for marine conservation always reduced the costs of conservation. The model estimated savings could range from 37.4% all the way to 98% under the 30×30 target.

“It just highlighted how inefficient it is to require uniform conservation obligations from each nation,” Villaseñor-Derbez said. “After all, national boundaries don’t really overlap or line-up with the distribution patterns of marine biodiversity.”

Savings were highest in a global market, where every nation stands to gain from trade. But a global market could inadvertently focus conservation efforts on only a single type of habitat, neglecting others. That was precisely why the team introduced the trade bubble constraint.

“When nations facing large costs are allowed to trade, they can ask themselves ‘should I conserve in my waters at this high cost, or can I find someone in my bubble that has habitat just as good as mine but at a lower price?'” Villaseñor-Derbez said. The same would be true for a selling nation. They could decide whether to conserve more than they are required depending on the trading price.

Of course, a country could always go it alone, fulfilling their conservation obligations (and theirs alone) entirely within their own territory. Indeed, this is precisely how the 30×30 initiative currently looks. But the authors’ analysis suggests that very few countries will. Most find it far more economical to either buy or sell conservation obligations.

Conservation colonialism vs fair compensation

If a market system were established, some might wonder what would prevent wealthy nations from simply “paying off” their conservation obligations and offloading them onto poorer nations. For Costello, Villaseñor-Derbez and Plantinga, the market itself offers a solution. “All such exchanges are purely voluntary,” said Plantinga, who heads emLab’s Productive Landscapes Group. “The selling nation (the poor country in this example) only engages in trade if they find it advantageous.”

In fact, the market could be a boon for developing nations. The current 30×30 scheme requires even a cash-poor country with high conservation to conserve 30% of their territorial waters. The market approach offers a degree of flexibility: The country can weigh their finances against their conservation costs. They can then decide how much of their obligation to fulfill within their own waters, how much to buy from another nation, and how much to offer up for sale. This flexibility is not possible under the current approach to 30×30.

This system could also incentivize habitat restoration, target No. 2 of the GBF. Nations that tend to specialize in exploiting marine resources could compensate those who specialize in conserving marine biodiversity. “Our approach provides an explicit payment for conserving marine ecosystems,” Costello said. “Under the current system, there is rarely a payment to conserve.”

Lowering costs incentivizes action. This measurable effect is a central tenet of economics employed by governments, companies and industries across sectors and countries. So why not harness this principle for conservation? According to the authors, these savings could be redirected towards solving other pressing issues.