“We’re at the tipping point,” said electrical and computer engineering professor Daniel Blumenthal.

In an invited article that was also selected for the cover of Optica Quantum, Blumenthal, along with graduate student researcher Andrei Isichenko and postdoctoral researcher Nitesh Chauhan, lays out the latest developments and future directions for trapping and cooling the atoms that are fundamental to these experiments — and that will bring them to devices that fit in the palm of your hand.

Cold atoms are atoms that have been cooled to very low temperatures, below 1 mK, reducing their motion to a very low energy regime where quantum effects emerge. This makes them sensitive to some of the faintest electromagnetic signals and fundamental particles, as well as ideal timekeeping, navigation devices and quantum “qubits” for computing.

In order to capitalize on these properties, many researchers currently work with highly sensitive laboratory-scale atomic optical systems to confine, trap and cool the atoms. Conventionally, these systems use free-space lasers and optics, generating beams that are guided, directed and manipulated by lenses, mirrors and modulators. These optical systems are combined with magnetic coils and atoms in a vacuum to create cold atoms using the ubiquitous 3-dimensional magneto-optical trap (3D-MOT). The challenge that researchers face is how to replicate the laser and optics functions onto a small, durable device that could be deployed outside of the highly controlled environment of the lab, for applications such as gravitational sensing, precision timekeeping and metrology, and quantum computing

The Optica Quantum review article covers recent and rapid advancements in the realm of miniaturizing complex cold-atom experiments via applications of compact optics and integrated photonics. The authors reference photonics achievements across a variety of sub-fields, ranging from telecommunications to sensors, and map the technology development to cold atom science.

“There’s been a lot of really great work miniaturizing beam delivery,” said Isichenko, “but it’s been done with components that are still considered free-space optics — smaller mirrors or smaller gratings — but you still couldn’t integrate multiple functionalities onto a chip.”

Enter the researchers’ photonic integrated 3D-MOT, a miniaturized version of equipment used widely in experiments to deliver beams of light to laser cool the atoms. Embedded into a low-loss silicon nitride waveguide integration platform, it’s the part of a photonic system that generates, routes, expands and manipulates all the beams necessary to trap and cool the atoms. The review article highlights the photonic integrated 3D-MOT — or “PICMOT” demonstrated by the UC Santa Barbara team as a major milestone for the field.

“With photonics, we can make lasers on chip, modulators on chip and now large-area grating emitters, which is what we use to get light on and off the chip,” Isichenko added.

Of particular interest is the atomic cell, a vacuum chamber where the atoms are trapped and cooled. One feat the researchers accomplished was to route the input light from an optical fiber, which is less than the width of a hair, via waveguides to three grating emitters that generate three collimated free-space intersecting beams 3.5 mm wide. Each beam is reflected back on itself for a total of six intersecting beams that trap a million atoms from the vapor inside the cell and, in combination with magnetic fields, cool the atoms to a temperature of just 250 uK. The larger the beams the more atoms can be trapped into a cloud and interrogated, Blumenthal noted, and the more precise an instrument can be.

“We created cold atoms with integrated photonics for the first time,” said Blumenthal.

The implications of the researchers’ innovations are far-reaching. With planned improvements to durability and functionality, future chip-scale MOT designs can take advantage of a menu of photonic components, including recent results with chip-scale lasers. This can be used to optimize technology for applications as diverse as measuring volcanic activity to the effects of sea level rise and glacier movement by sensing the gradient of gravity on and around the Earth.

Integration of the 3D-MOT can give quantum scientists and time keepers new ways to send today’s earthbound instruments into space and conduct new fundamental science, and enable measurements not possible on Earth. Additionally, the devices could advance research projects by decreasing the time and effort spent establishing and fine tuning optical setups. They can also open the door to accessible quantum research projects for future physicists.

The study, published in Hypertension and supported by the National Institutes of Health, investigated whether mothers who reported higher perceived stress and depressive symptoms during pregnancy, developed higher blood pressure in the four-year period after birth. The findings showed higher stress and depressive symptoms during pregnancy were associated with greater blood pressure during the first year postpartum, but associations diminished thereafter.

“Pregnancy is a complex time where women experience different physiological changes,” says Noelle Pardo, the lead author of the study and third year doctoral student in the Department of Population and Public Health Sciences at Keck School of Medicine. “This study is building on maternal health research to understand how stressors impact women’s lives and their health after pregnancy.”

The study included data from 225 mothers from the MADRES pregnancy cohort which primarily consists of Hispanic women, and low-income participants living in Los Angeles. Hispanic women have a high burden of cardiovascular risk, and there is growing evidence linking psychosocial stressors to poor cardiovascular health, which is a leading cause of death among women in the US.

In addition to prenatal psychosocial stress, Pardo explored whether prenatal neighborhood social cohesion was a protective factor for postpartum hypertension risk — a first investigation of its kind. This refers to the sense of connection and trust a pregnant woman experiences in her community. According to her findings, social structures that promoted cohesion may have had a positive influence throughout pregnancy into the postpartum period and were associated with lower blood pressure.

“We chose social cohesion as a variable to understand how connected the participants felt to their community. Right now, there aren’t many programs or policies that help foster cohesion, yet such interventions may serve as a novel protective factor,” she says.

According to Pardo, maternal health research has mostly focused on pregnancy outcomes, with limited studies investigating the mother’s health after birth. Yet, her results have shown how crucial this research is in identifying conditions rooted in pregnancy.

The real-world application of this study calls for the identification of vulnerable individuals in the pregnant population, offering interventions to reduce stress and depressive symptoms. Similarly, it emphasizes the importance of monitoring women’s health after birth, through the provision of additional hypertension screenings among mothers who experience higher prenatal stress.

“Pregnancy may be important in determining a woman’s long term cardiovascular health. Similarly, more research is needed to determine how different exposures during pregnancy can convey future cardiovascular risk to women,” she concludes.

A critical nutrient for life, most phosphorus in the soil is organic — from remains of plants, microbes or animals. But plants need inorganic phosphorus — the type found in fertilizers — for food. While researchers traditionally thought only enzymes from microbes and plants could convert organic phosphorus into the inorganic form, Northwestern scientists previously discovered iron oxides in natural soils and sediments can drive the conversion.

Now, in a new study, the same research team found iron oxides don’t generate just a negligible amount of the precious resource. In fact, iron oxides are incredibly efficient catalysts — capable of driving the conversion at rates comparable to the reactions of enzymes. The discovery could help researchers and industry experts better understand the phosphorus cycle and optimize its use, especially in agricultural soils.

The study was published today (March 4) in the journal Environmental Science & Technology.

“Phosphorus is essential to all forms of life,” said Northwestern’s Ludmilla Aristilde, who led the study. “The backbone of DNA contains phosphate. So, all life on Earth, including humans, depends on phosphorus to thrive. That’s why we need fertilizers to increase phosphorus in soils. Otherwise, the crops we need to feed our planet will not grow. There is a profound interest in understanding the fate of phosphorus in the environment.”

An expert in the dynamics of organics in environmental processes, Aristilde is an associate professor of environmental engineering at Northwestern’s McCormick School of Engineering. She also is a member of the Center for Synthetic Biology, International Institute for Nanotechnology and Paula M. Trienens Institute for Sustainability and Energy. Jade Basinski, a Ph.D. student in Aristilde’s laboratory, is the paper’s first author. Other Ph.D. students and postdoctoral researchers in Aristilde’s team contributed to the work.

Paths to accessing phosphorus

For centuries, farmers have added phosphorus to their fields to improve crop yields. Not only does it improve crop quality, phosphorus also promotes the formation of roots and seeds. Plants literally cannot survive without it.

But there’s a catch. Plants have evolved to use phosphorus in its simplest, most readily available form: inorganic phosphorus. Inorganic phosphorus is like a ready-to-use molecule that plants can easily consume and incorporate into their metabolism. Most phosphorus in the environment, however, is organic, meaning it’s bound to carbon atoms. To access this phosphorus, plants rely on their own secreted enzymes or enzymes secreted by microbes to break bonds in organic phosphorus and release the usable inorganic form.

In previous work, Aristilde’s team found that enzymes are not the only vehicles that can perform this essential conversion. Naturally occurring in soils and sediments, iron oxides, too, can perform the reaction that transforms organic phosphorus to generate the inorganic form.

How much and how fast?

After proving that iron oxides offer another pathway for plants to access phosphorus, Aristilde and her team sought to understand the rates and efficiency of this catalytic conversion.

“Iron oxides trap phosphorus because they have different charges,” Aristilde said. “Iron oxides are positively charged, and phosphorus is negatively charged. Because of this, anywhere you find phosphorus, you will find it linked with iron oxides. In our previous study, we showed iron oxides can serve as a catalyst to cleave the phosphorus. Next, we wanted to know how much they can cleave and how fast.”

To explore this question, the researchers investigated three common types of iron oxides: goethite, hematite and ferrihydrite. Using advanced analytical techniques, Aristilde and her team studied the interactions between these iron oxides and various structures of ribonucleotides, which are the building blocks of RNA and DNA. In their multiple experiments, Aristilde’s team looked for inorganic phosphorus both in the surrounding solution and on the surface of the iron oxides. By running experiments over a specific period of time and with different concentrations of ribonucleotides, the team determined the reaction’s rates and efficiency.

“We concluded that iron oxides are ‘catalytic traps’ because they catalyze the reaction to remove phosphate from organic compounds but trap the phosphate product on the mineral surface,” Aristilde said. “Enzymes don’t trap the product; they make everything available. We found goethite was the only mineral that didn’t trap all the phosphorus after the reaction.”

The team discovered that each type of iron oxide exhibited varying degrees of catalytic activity for cleaving phosphorus from the ribonucleotides. While goethite was more efficient with ribonucleotides containing three phosphorus, hematite was more efficient with ribonucleotides containing one phosphorus. Hematite is found in the midwestern part of United States, while goethite is commonly found in soils in the southern United States and South America.

What’s next

Next, Aristilde’s team will seek to understand why different iron oxides have different efficiency for the catalysis process and how goethite is able to release the phosphate but ferrihydrite and hematite trap all the produced phosphate. While the researchers initially hypothesized that the phosphorus compounds’ surface structure would play a role, they did not find a clear trend. Now, they think the chemistry of the mineral itself might be the secret behind its success.

Because phosphorus is a finite resource — mined from phosphate rock found only in the United States, Morocco and China — its supply is dwindling. Farmers and researchers worry phosphorus eventually will become so expensive that it will increase overall food costs, making basic staples unaffordable.

Finding new ways to convert trapped organic phosphorus into bioavailable inorganic phosphorus, therefore, is vital for the global food supply.

“Our work is providing a steppingstone for designing and engineering a synthetic catalyst as a way to recycle phosphorus,” Aristilde said. “We uncovered a reaction that’s happening naturally. The dream will be to leverage our findings as a way to make catalysts to contribute to the production of fertilizers for our food security.”