Guinea-Bissau will implement a universal birth-dose policy for the Hepatitis B vaccine in 2027.Credit: Enrique Lopez-Tapia/Nature Picture Library/Alamy Public health authorities in Guinea-Bissau say that they have suspended a controversial US-funded hepatitis B vaccine study that has raised questions about who has authority over clinical research conducted in Africa. At a press conference held today, officials from Guinea-Bissau’s ministry of health said that the study was being suspended pending a technical and ethical review by its national public health institute. The announcement followed weeks of conflicting statements as to whether or not the trial would proceed. “There has been no sufficient coordination in order to take a final decision regarding the study,” said Quinhin Nantote, the minister of public health for Guinea-Bissau. “Faced with this situation, we decided to suspend it.” Mixed messages The meeting, convened by the Africa Centres for Disease Control and Prevention (Africa CDC), comes after an official with the organization signalled last week that the trial would not proceed. In an email to Nature today, officials at the US Department of Health and Human Services (HHS), a prominent funder of the research, said that the study was still on track, leaving the trial’s status still uncertain. Hotly anticipated US vaccine meeting ends with confusion — and a few decisions “The study is proceeding as planned and we continue to work with our partners to finalize the study’s protocols,” wrote Emily Hilliard, a spokesperson for the HHS. The continuing row shines a spotlight on long-standing tensions for clinical research trials in Africa. African scientists say that the Guinea-Bissau study shows how political pressure, funding interests and fragmented oversight can push local health priorities aside. The hepatitis B vaccine trial was designed by researchers at the Bandim Health Project (Projecto de Saúde) out of the University of Southern Denmark, and funded in part through a US$1.6 million research grant from the US Centers for Disease Control and Prevention, part of the HHS. The study aims to randomize 14,000 newborns in Guinea-Bissau starting in early 2026 to either receive the hepatitis B vaccine at birth or not, before the country’s planned universal birth-dose vaccine policy begins in 2027. The Bandim researchers have said that the study is a chance to investigate whether the vaccine has broader effects on infant health outcomes. But several scientists have argued that by randomizing newborns to not receive the vaccine, the trial denies a safe and life-saving intervention to infants in Guinea-Bissau, which has a hepatitis B prevalence of about 19%. The immune systems of newborns are immature and about 90% of people infected at birth go on to develop chronic, lifelong infections which may lead to liver disease and early death. Researchers who oppose the study argue that it is structured in a way that increases the likelihood of detecting harm from the birth dose, even if that harm is not real or clinically meaningful. “They’re trying to use African children to prove a case for reducing vaccines in the US,” says Seye Abimbola, a professor of health systems at the University of Sydney in Australia, who researches decolonizing global health. “That’s problematic.” The United States removed its own recommendations for a birth dose of the hepatitis B vaccine earlier this year. Bandim Health did not respond to Nature’s request for comments on the study design. Hilliard at the HHS said that the research “is based on the highest scientific and ethical standards”. “We are not guinea pigs” Speaking to Nature hours before the Africa CDC press conference, public health physician and former minister of health of Guinea-Bissau, Magda Robalo, said that the study should be halted. “It’s not acceptable and it should not go on,” says Robalo. “Guinea-Bissauans are not guinea pigs.” The country’s hepatitis B programme, its national public-health institute and its immunization officials were not consulted and were unaware of the study, prior to its announcement in December, says Robalo. Hepatitis B vaccine guidance set to be rolled back for US babies: what the science says Shortly after that announcement, Boghuma Titanji, a Cameroon medical doctor and clinical researcher at Emory University School of Medicine in Atlanta, Georgia, warned that the public furore over the controversial trial poses broader risks for vaccination efforts in Guinea-Bissau and across Africa. Running a trial in a poor country that wouldn’t be run in a wealthy one reinforces narratives about Africans being used for nefarious research projects and fuels mistrust in vaccination more generally, Titanji argued. Robalo says that the case underscores the need for urgent reform in global public health governance, arguing that entrenched power imbalances continue to allow unethical research practices in poorer countries. “We need to continue to call off the power structures that believe they can do whatever they want in countries like Guinea-Bissau,” says Robalo.

Exhaled breath can have hundreds of different compounds in it, some of which could have diagnostic potential.Credit: Getty The chemicals found in a person’s breath might reveal the identity of the microbes in their guts, according to a study published today in Cell Metabolism1. Using mice and a group of 41 children, Andrew Kau, an immunologist at Washington University in St. Louis, Missouri, and his colleagues measured the levels of molecules in exhaled breath and showed how they could be used to partially predict the identity and abundance of certain gut bacteria, including one species that is associated with asthma. “The gut-microbiome composition can shape the type of compounds you see in breath,” says Kau. This was suspected, he says, but “it was never certain”. AI’s keen diagnostic eye The work might lead to devices for diagnosing infections and help to guide treatment of conditions influenced by gut bacteria. Existing methods that test stool samples are time-consuming and more complicated. “I love the idea of using breath measurements to get more information about health,” says Katrine Whiteson, a biochemist at the University of California, Irvine. “Breath is an amazing measurement because it’s aggregate information from the lung and the whole body.” Volatile research Scientists have long wondered about the possibility of using the chemical metabolites in breath to diagnose disease. Human cells and bacteria produce more than 250,000 molecules, or metabolites, as they grow and survive. Some of these can enter the bloodstream, circulate to the lungs and diffuse into exhaled air. The work has proven daunting, however, says Kelly Redeker, a chemist at the University of York, UK, who was not involved in the study. “The complexity of the system is massive.” To show a correlation between gut bacteria and exhaled molecules, the authors used mice that had no gut bacteria and transplanted one of five common species into them. They found that exhaled molecules in the mice’s breath significantly differed depending on which species of bacteria they received. For example, a compound called ethyl acetate was associated with colonization by Escherichia coli. The researchers then collected stool and breath samples from healthy children, as well as children with asthma. They found that gut-microbiome composition explained at least 20% of the variation in 35 breath compounds that they tested. The researchers also trained and optimized a model to predict the abundance of Eubacterium siraeum, a species that is associated with wheezing in asthma2. The concentration of four molecules in the breath samples accounted for slightly more than half of the variation in E. siraeum populations. Researchers still don’t understand how each metabolite is formed and makes it to the lungs. “One of the frustrating things, when you start analysing breath in humans, is that you get 200 to 400 different compounds,” says Audrey Odom John, chief of paediatric infectious diseases at the Children’s Hospital of Philadelphia, Pennsylvania, and a senior author of the study. “If you look at human metabolic maps, we have almost no idea where most of those come from.” The researchers hope that their work might inform life-saving diagnostics for conditions such as sepsis. Preterm infants in intensive care are at high risk of developing deadly infections, says Odom John, and the bacteria responsible start to thrive days before any outward clinical signs. “That’s a real opportunity for intervention,” she says.

Membership at many of the high-level advisory coucils for the US National Institutes of Health is dwindling ― a decline that could trigger a freeze in issuance of some grants.Credit: Grandbrothers/Alamy Crucial grant-review panels for more than half of the institutes that make up the US National Institutes of Health (NIH) are on track to lose all their voting members within the year. Federal law requires these panels to review applications for all but the smallest grants before funding can be awarded, meaning that the ability of those institutes to issue new grants could soon be frozen. All of the NIH’s 21 institutes and three of its six centres have their own panel, called an advisory council. Membership on the councils has been dwindling as members serve out their terms without replacements being appointed. At 12 of the institutes and one of the centres, the last voting member’s term is set to expire by the end of this year, according to rosters on federal websites (see ‘Shrinking pool of advisers’). It typically takes several years for a new member to be onboarded. How Trump 2.0 is slashing NIH-backed research — in charts Dozens of scientists who were poised to fill these vacancies were dismissed last year by the administration of US President Donald Trump, Nature reported in July. If the advisory councils go dormant, “this could lead to some very big problems for the agency”, says Michael Lauer, who for about ten years ran the NIH’s ‘extramural’ arm, which funds researchers at institutions across the United States. “No grants can get funded without approval from council.” This comes after the Trump administration blocked and delayed NIH funding in several ways. For example, in early 2025, the administration barred the agency from publishing the notices required to hold grant-review sessions, contributing to a federal watchdog’s finding that the NIH was illegally withholding money allocated by the US Congress. A spokesperson for the NIH's parent agency, the Department of Health and Human Services, responds that she does not “anticipate any lapse in our ability to make awards”, adding that “we are actively appointing new council members”. Publicly available advisory-council rosters have not been updated with any new members since September, Nature's analysis shows. Independent scrutiny NIH grant applications are considered in two stages, by separate panels. The first is a study in which a group of independent scientists meets to score applications. The second is a review by the awarding institute’s advisory council, which consists of scientists and other advisers inside and outside the NIH. Advisory councils meet three times a year — generally in January, May and either August or October — and make recommendations on applications to the institute’s director, who holds the authority to make the final funding decision. Federal law states that the director of an NIH institute can issue an award only if the grant has been recommended for approval by the advisory council. Nature examined the official advisory council rosters on the websites of the NIH and the individual institutes, as well as a separate database of federal advisory committees. These sources show that advisory councils for institutes specializing in research on topics such as infectious diseases, ageing and mental health, among others, are on track to have no voting members by the end of the year. Office of Federal Advisory Committee Policy at US National Institutes of Health At the advisory council for the National Institute on Minority Health and Health Disparities, the final voting members’ terms end next month. Without extraordinary action, the council will have no members by its May meeting, when it is scheduled to review grant applications submitted as early as last September — meaning those applications would be effectively frozen. “Everybody is concerned,” says Jennifer Troyer, who oversaw extramural operations at the National Human Genome Research Institute and resigned in December over concerns about political interference in scientific review at the NIH. When she was at the agency, she regularly met with her counterparts at other NIH institutes and centres and says that “this was a topic that came up every time”. Staff members are using every tool at their disposal to prevent panels from losing all their members, Troyer says. For example, federal law allows for a single 180-day extension of a panellist’s term if their replacement has not yet joined the council. Nature’s analysis of the rosters finds that about 44% of the 147 members whose terms are set to expire this year have already received this 180-day extension. Helene Benveniste, a neuroscientist at the Yale School of Medicine in New Haven, Connecticut, whose term on the National Center for Complementary and Integrative Health council will end in July, says she received an inquiry from the NIH about extending her appointment by 180 days. The extension has not been finalized, she says. Exhaustive vetting The process to place new members on these councils is prolonged, typically spanning several years. Staff must screen candidates, seek approval from the NIH and HHS and shepherd candidates through background and ethics checks. US science in 2026: five themes that will dominate Trump’s second year The problem is not new: 13 advisory councils have gained no new voting members since June 2024, when Trump’s predecessor, Joe Biden, was president. Troyer says the Biden administration was slow to investigate and approve candidates. But after Trump began his second presidential term last January, his team dismissed dozens of academic scientists who had been nominated by Biden and had undergone the full vetting process. Staff were instead directed to recommend individuals aligned with the Trump administration’s priorities. Staff members at many institutes have submitted alternative candidates to NIH and HHS leadership, but they have heard “radio silence” on these nominations, Troyer says. The statute allows the HHS secretary, Robert F. Kennedy Jr, to circumvent the vetting process and handpick panellists. This practice is very rare but not unprecedented, Lauer says. The HHS spokesperson did not respond to Nature's queries about whether Kennedy plans to do this. In the interim, councils at all but nine institutes and centres have half or fewer of their allotted voting members, meaning that they cannot provide the breadth of knowledge they have been commissioned to offer, Lauer says. “When you have the best people on them, councils can be a great source of guidance and advice,” he adds. “It would be a shame to lose that.”

Research on fetal tissue (pictured, fetal neurons) from elective abortions will no longer be funded by the US National Institutes of Health. Credit: Riccardo Cassiani-Ingoni/Science Photo Library The world’s largest public funder of biomedical research will no longer support studies that use human fetal tissue derived from elective abortions. The US National Institutes of Health (NIH) will continue to fund research on fetal tissue from miscarriages and stillbirths, according to an announcement made on 22 January. But researchers say the new restrictions, which were applauded by opponents of abortion, will make it more difficult to study fetal development and stem cell biology, and will slow the hunt for new medical treatments. “It’s clearly a political decision, not a scientific one,” says Lawrence Goldstein, a neuroscientist at the University of California, San Diego. How Trump 2.0 is slashing NIH-backed research — in charts But it is also not a dead end for all such research, he adds: some scientists will turn to a much smaller pool of private funding in lieu of government grants. “Research is going to go ahead, [the decision is] just slowing it down,” Goldstein says. The NIH says that it funded 77 projects involving human fetal tissue in the fiscal year that began in September 2023, and that researchers can harness recent technological advances in alternative methods, such as computational biology and three-dimensional cell cultures, to conduct their studies. Goldstein says that not all research can be done using alternative methods. "If you want to make fetal kidney cell types for further development for a disease study, you have to have actual fetal kidney to compare the stuff you made," he says. "To not realize that reflects a complete lack of understanding of the field." A researcher who had a grant in fiscal year 2024 that included a proposal for fetal-tissue research echoes Goldstein. Steven Finkbeiner, a neurologist at the University of California, San Francisco, says his team uses stem cells to study Alzheimer’s disease. “The human fetal tissue work is also critical because it remains the gold standard,” he says. Stem cells are useful, “but it remains very difficult to fully recapitulate the complexity of human tissue.” The NIH did not immediately respond to a request for comment. The agency also suggested that it might be considering future changes to funding for some stem cell research. “NIH will soon seek public comment on the robustness of emerging biotechnologies to reduce or potentially replace reliance on human embryonic stem cells,” NIH director Jayanta Bhattacharya said in a statement. Changes of course The policy shift is the latest salvo in a long-running political battle over the funding of fetal tissue research. In 2019, during US President Donald Trump’s first term in office, the NIH halted fetal tissue research by federal scientists and placed restrictions on grants to academics in the field. Those changes were reversed two years later, after Trump left office. These intermittent restrictions have already scared some researchers away from the field, says Goldstein, and the NIH says that its funding of fetal tissue research has been declining since 2019. For some researchers, it is not funding uncertainty, but fears for personal safety that have led them to abandon projects involving human fetal tissue. “My concern is that I’m going to be harmed, to be targeted,” says one researcher who spoke on condition of anonymity for fear of harassment, and says that they have received threatening letters because of their research. “We’re not attracting junior scientists to this field because they know how inflammatory it can be.” And although the current funding change affects only those who use fetal tissue from elective abortions, the re-evaluation of human embryonic stem cell research hints at a larger overhaul that could affect more researchers, they add. “This can really spread. It’s like a forest fire,” they say. “Where does this end?”

Amyloid plaques (light pink; artist’s illustration) speckle neurons in a brain affected by Alzheimer’s disease.Credit: Artur Plawgo/Science Photo Library For decades, researchers have noted that cancer and Alzheimer’s disease are rarely found in the same person, fuelling speculation that one condition might offer some degree of protection from the other. Now, a study in mice provides a possible molecular solution to the medical mystery: a protein produced by cancer cells seems to infiltrate the brain, where it helps to break apart clumps of misfolded proteins that are often associated with Alzheimer’s disease. The study, which was 15 years in the making, was published on 22 January in Cell1 and could help researchers to design drugs to treat Alzheimer’s disease. “They have a piece of the puzzle,” says Donald Weaver, a neurologist and chemist at the Krembil Research Institute at the University of Toronto in Canada, who was not involved in the study. “It’s not the full picture by any stretch of the imagination. But it’s an interesting piece.” Alzheimer’s mystery Weaver has been interested in that puzzle ever since he began his medical training, when a senior pathologist made an offhand comment: “If you see someone with Alzheimer’s disease, they’ve never had cancer.” The remark stuck with Weaver over the years as he diagnosed thousands of people with Alzheimer’s disease. “I can’t remember a single one that has had cancer,” he says. How common is Alzheimer’s? Blood-test study holds surprises Epidemiological data do not draw such a clear divide, but a 2020 meta-analysis of data from more than 9.6 million people found that cancer diagnosis was associated with an 11% decreased incidence of Alzheimer’s disease2. It has been a difficult relationship to unpick: researchers must control for a variety of external factors. For example, people might die of cancer before they are old enough to develop symptoms of Alzheimer’s disease, and some cancer treatments can cause cognitive difficulties, which could obscure an Alzheimer’s diagnosis. Over the years, however, the data converged enough to convince Youming Lu, a neurologist at Huazhong University of Science and Technology in Wuhan, China, to take a closer look at the biology underlying this trend. Long search Researchers in Lu’s laboratory spent the next six years searching for the best way to model the two conditions in mice. Eventually, the team decided to transplant three different types of human tumour — lung, prostate and colon — into mouse models of Alzheimer’s disease. The mice with cancer did not develop the brain plaques characteristic of Alzheimer's disease, says Lu. “So then we asked, ‘why’?” The researchers sifted through the proteins that were secreted by these cancer cells, searching for those that can cross the protective boundary known as the blood–brain barrier to infiltrate the brain. This search, which took more than six years, narrowed the list to one: a protein called cystatin C. How cancer hijacks the nervous system to grow and spread Further experiments in mice showed that cystatin C binds to the molecules that make up the hallmark brain plaques of Alzheimer’s disease. This interaction activates a signalling protein, called TREM2, that is found on certain immune cells that patrol the brain. Those immune cells then degrade the plaques. In Lu’s mice, this plaque degradation was linked to an improved performance on cognitive tests. If confirmed and replicated in humans, the findings could suggest a path to finding new therapies, says Jeanne Mandelblatt, a cancer researcher at Georgetown University in Washington DC. Breaching the barrier Weaver says he was particularly surprised to see that cystatin C can infiltrate the brain: “It’s like trying to drive a bus across the blood–brain barrier,” he says. Lu explains that research has found that the blood–brain barrier weakens in people with early Alzheimer’s disease, but Weaver says it remains unclear whether that occurs early enough to allow cystatin C to enter the brain before symptoms of Alzheimer’s disease become apparent. Regardless, the finding that cystatin C can activate TREM2 is valuable, he says. Researchers have been trying to find drugs that can activate the protein, which could be used as a potential therapy for Alzheimer’s disease, but have struggled: most drugs disable proteins rather than activate them. “It’s always easier to break something than to make it better,” Weaver says. So far, early clinical trials of molecules that activate TREM2 have met with mixed results, he says. But that doesn’t mean it’s a dead end. “It’s going to take a cocktail of drugs to treat Alzheimer’s disease,” he says. “There’s not going to be a single magic bullet.”

Microplastics are ubiquitous, but studies disagree on how much of the pollutants are in the atmosphere.Credit: Milos Bicanski/Getty The amount of microplastic particles in the atmosphere might be lower than some studies have suggested, possibly even by several orders of magnitude. The finding, published on 21 January in Nature1, comes after a high-profile study, which was published in February, that suggested that the concentration of microplastics in the human brain might have been overestimated2. “This doesn’t mean we don’t have a lot of microplastics in the atmosphere,” says Ioanna Evangelou, an environmental scientist at the University of Vienna. But it does point to a need to broaden and standardize the measurements of microplastics globally, she adds. Many human activities — from improper disposal of waste to the degradation of car tyres — release small plastic particles, which have infiltrated the atmosphere, oceans and other ecosystems. These include nanoplastics — particles measuring less than 1 micrometre across — and microplastics, which range from 1 micrometre to around 5 millimetres. They’ve entered our bodies and brains, and scientists are still working to understand their effects on people’s health. “We should not believe that this is not an issue,” says Evangelou. She hopes that the main message of the results will not be used to dismiss the problem of atmospheric microplastics. Research on the biological effects of microplastics is still in its infancy, which means that it is not clear whether the levels humans are exposed to — whatever those levels are — are safe. Microplastic emissions Studies that have estimated the concentration of microplastics in the atmosphere show high levels of variability, with results ranging across several orders of magnitude. And studies that have taken measurements from a region in the western United States have been used to infer global emissions. Evangelou and her team aimed to get a better handle on microplastic concentrations by compiling two sets of existing studies — those that estimated global microplastic emissions, and those that measured the particles found in environmental samples. They then used the second set to assess the validity of the first. The researchers fed the estimated emissions data into a computer simulation of how the atmosphere transports pollutants. The simulation gave predictions of the concentrations of microparticles that would be found across the globe. But the predicted amounts did not match those found in samples at 283 different locations worldwide. The difference was stark — in some cases, the microplastic measurements from environmental samples were orders of magnitude smaller than the models predicted. The team also estimated that 27 times more microplastic particles are emitted from activities on land than from the ocean. Are microplastics bad for your health? More rigorous science is needed In particular, the study estimates that the amount of microplastics released from the ocean into the atmosphere is less than estimated in some previous studies, including one co-authored by Natalie Mahowald4, an atmospheric scientist at Cornell University in Ithaca, New York. Mahowald says her team’s estimates had “huge uncertainty bars”, and they are still compatible with the new findings1. “As stated in the paper, there are many continuing uncertainties in microplastics, and more data are needed, especially in new locations, and more information about the size distributions,” adds Mahowald. Stephanie Wright, an environmental toxicologist at Imperial College London, says that one limitation of the study is that it included models of emissions from the degradation of tyres among the inputs — and that the microplastic particles released from tyres would not normally show up in environmental samples. Evangelou agrees, but she adds that her team included tyre particles as a proxy for general human activities that can release microplastics. Accurate measurements Microplastics have received media interest in the past few months, and some coverage has questioned the methods available for measuring them accurately in the environment and in organisms, including the human body. “Contrary to some general impressions, we do have good methods for analysing micro- and nanoplastics,” says Dušan Materić, an analytical chemist at the Helmholtz Centre for Environmental Research in Leipzig, Germany. Measurements of microplastics in the environment usually use proper controls to avoid contamination and false positives, but studies involving human organs sometimes lack those safeguards, some researchers say. In November, Materić co-authored a letter3 to Nature Medicine that raised concerns about a widely covered study of microplastics in the brain2. “The key question for the scientific community,” Materić says, “is how to respond to high-impact and widely disseminated studies whose quantitative conclusions are not supported, even when they were produced with good intentions.” Scientists say the latest research suggests a need to improve the monitoring of microplastics, and to better understand the health effects of microplastic exposure.

Large objects, including cats, don’t show quantum effects. But physicists aren’t sure where the size limit lies. Credit: Getty Schrödinger’s cat just got a little bit fatter. Physicists have created the largest ever ‘superposition’ — a quantum state in which an object exists in a haze of possible locations at once. A team based at the University of Vienna put individual clusters of around 7,000 atoms of sodium metal some 8 nanometres wide into a superposition of different locations, each spaced 133 nanometres apart. Rather than shoot through the experimental set up like a billiard ball, each chunky cluster behaved like a wave, spreading out into a superposition of spatially distinct paths and then interfering to form a pattern researchers could detect. “It’s a fantastic result,” says Sandra Eibenberger-Arias, a physicist at the Fritz Haber Institute in Berlin. Physicists disagree wildly on what quantum mechanics says about reality, Nature survey shows Quantum theory doesn’t put a limit on how big a superposition can be, but everyday objects clearly do not behave in a quantum way, she explains. This experiment — which puts an object as massive as a protein or small virus particle into a superposition — is helping to answer the “big, almost philosophical question of ‘is there a transition between the quantum and classical?’” she says. The authors “show that, at least for clusters of this size, quantum mechanics is still valid”. The experiment, described in Nature on 21 January1, is of practical importance, too, says Giulia Rubino, a quantum physicist at the University of Bristol, UK. Quantum computers will ultimately need to maintain perhaps millions of objects in a large quantum state to perform useful calculations. If nature were to make systems collapse past a certain point, and that scale was smaller than what is needed to make a quantum computer,, “then that’s problematic,” she says. Superposition size limit Physicists have long debated how the classical, everyday world emerges from an underlying quantum one. Quantum theory “never states it stops working above a certain mass or size”, says Sebastian Pedalino, a physicist at the University of Vienna and a co-author of the study. In 1935, the Austrian physicist Erwin Schrödinger showed the absurdity of common interpretations of quantum mechanics with his famous cat-based thought experiment. The cat is put into a box with vial of poison, which will be released if a radioactive atom decays. If the box remains isolated from its environment, the atom exists in a superposition of both decayed and not-decayed, and until observed, the cat is an undefined state of both dead and alive. ‘Levitating’ nanoparticles could push the limits of quantum entanglement In the real world, objects eventually become too complex or interact too much to maintain a superposition, an idea known as decoherence. But there are also extensions to quantum mechanics, known as collapse theories, that suggest that beyond a certain point, a system will inevitably reduce to a classical state, even in isolation. These theories were picked by 4% of researchers as their favourite interpretation of quantum mechanics in a 2025 Nature survey. “The only way to answer this question is by scaling up" quantum experiments, says Rubino. To do this, Pedalino and his team generated a beam of clusters at 77 degrees kelvin (-196 ºC) in an ultra-high vacuum. The researchers put the beam through an interferometer consisting of three gratings constructed with laser beams. The first channelled the clusters through narrow gaps, from which they spread out and travelled in sync as waves; they then passed through a second set of slits that made the waves interfere in a distinctive pattern, which could be detected using the final grating. Painstaking process Viewing such quantum effects at scale is difficult, because stray gas molecules, light or electric fields can disrupt the delicate quantum state, and the slightest misalignment of the gratings or minute force can blur the fine interference pattern. It took two years for the team to be able to see the signal, says Pedalino. Before that, he spent “thousands of hours” in a basement laboratory looking at “flat lines and noise”, he says. The team’s superposition is ten times bigger than the previous record. That’s according to a measure known as ‘macroscopicity’, which combines mass with how long the quantum state lasts and how separated the states are. However, this doesn’t mean it’s the largest mass ever put into a superposition, says Rubino. In 2023, another team put a 16-microgram vibrating crystal into a superposition — but that was only over a distance of two billionths of a nanometre2. Physicists coax molecules into exotic quantum state — ending decades-long quest Scaling up further will not be easy, says co-author Stefan Gerlich, also at the University of Vienna. More-massive particles have shorter wavelengths, which make it harder to distinguish quantum predictions from classical ones. However, Gerlich says that, 15 years ago, he thought today’s experiment was “not possible”. The team is also working on putting biological matter through the same experimental set-up. Some viruses are a similar size to the clusters, but they tend to be more fragile and can fragment during flight, which makes the experiment harder to do — although not impossible. “I think that it’s not so far out of reach anymore,” says Pedalino. Although a virus is not considered to be alive, experiments with biological matter “would move the entire quantum interference into a new regime”, he adds.