Wednesday, April 8th, 2020

Time	Event
11:00a	New “refrigerator” super-cools molecules to nanokelvin temperatures For years, scientists have looked for ways to cool molecules down to ultracold temperatures, at which point the molecules should slow to a crawl, allowing scientists to precisely control their quantum behavior. This could enable researchers to use molecules as complex bits for quantum computing, tuning individual molecules like tiny knobs to carry out multiple streams of calculations at a time. While scientists have super-cooled atoms, doing the same for molecules, which are more complex in their behavior and structure, has proven to be a much bigger challenge. Now MIT physicists have found a way to cool molecules of sodium lithium down to 200 billionths of a Kelvin, just a hair above absolute zero. They did so by applying a technique called collisional cooling, in which they immersed molecules of cold sodium lithium in a cloud of even colder sodium atoms. The ultracold atoms acted as a refrigerant to cool the molecules even further. Collisional cooling is a standard technique used to cool down atoms using other, colder atoms. And for more than a decade, researchers have attempted to supercool a number of different molecules using collisional cooling, only to find that when molecules collided with atoms, they exchanged energy in such a way that the molecules were heated or destroyed in the process, called “bad” collisions. In their own experiments, the MIT researchers found that if sodium lithium molecules and sodium atoms were made to spin in the same way, they could avoid self-destructing, and instead engaged in “good” collisions, where the atoms took away the molecules’ energy, in the form of heat. The team used precise control of magnetic fields and an intricate system of lasers to choreograph the spin and the rotational motion of the molecules. As result, the atom-molecule mixture had a high ratio of good-to-bad collisions and was cooled down from 2 microkelvins to 220 nanokelvins. “Collisional cooling has been the workhorse for cooling atoms,” adds Nobel Prize laureate Wolfgang Ketterle, the John D. Arthur professor of physics at MIT. “I wasn’t convinced that our scheme would work, but since we didn’t know for sure, we had to try it. We know now that it works for cooling sodium lithium molecules. Whether it will work for other classes of molecules remains to be seen.” Their findings, published today in the journal Nature, mark the first time researchers have successfully used collisional cooling to cool molecules down to nanokelvin temperatures. Ketterle’s coauthors on the paper are lead author Hyungmok Son, a graduate student in Harvard University’s Department of Physics, along with MIT physics graduate student Juliana Park, and Alan Jamison, a professor of physics at the University of Waterloo and visiting scientist in MIT’s Research Laboratory of Electronics. Reaching ultralow temperatures In the past, scientists found that when they tried to cool molecules down to ultracold temperatures by surrounding them with even colder atoms, the particles collided such that the atoms imparted extra energy or rotation to the molecules, sending them flying out of the trap, or self-destructing all together by chemical reactions. The MIT researchers wondered whether molecules and atoms, having the same spin, could avoid this effect, and remain ultracold and stable as a result. They looked to test their idea with sodium lithium, a “diatomic” molecule that Ketterle’s group experiments with regularly, consisting of one lithium and one sodium atom. “Sodium lithium molecules are quite different from other molecules people have tried,” Jamison says. “Many folks expected those differences would make cooling even less likely to work. However, we had a feeling these differences could be an advantage instead of a detriment.” The researchers fine-tuned a system of more than 20 laser beams and various magnetic fields to trap and cool atoms of sodium and lithium in a vacuum chamber, down to about 2 microkelvins — a temperature Son says is optimal for the atoms to bond together as sodium lithium molecules. Once the researchers were able to produce enough molecules, they shone laser beams of specific frequencies and polarizations to control the quantum state of the molecules and carefully tuned microwave fields to make atoms spin in the same way as the molecules.  “Then we make the refrigerator colder and colder,” says Son, referring to the sodium atoms that surround the cloud of the newly formed molecules. “We lower the power of the trapping laser, making the optical trap looser and looser, which brings the temperature of sodium atoms down, and further cools the molecules, to 200 billionths of a kelvin.” The group observed that the molecules were able to remain at these ultracold temperatures for up to one second. “In our world, a second is very long,” Ketterle says. “What you want to do with these molecules is quantum computation and exploring new materials, which all can be done in small fractions of a second.” If the team can get sodium lithium molecules to be about five times colder than what they have so far achieved, they will have reached a so-called quantum degenerate regime where individual molecules become indistinguishable and their collective behavior is controlled by quantum mechanics. Son and his colleagues have some ideas for how to achieve this, which will involve months of work in optimizing their setup, as well as acquiring a new laser to integrate into their setup.  “Our work will lead to discussion in our community why collisional cooling has worked for us but not for others,” Son says “Perhaps we will soon have predictions how other molecules could be cooled in this way.” This research was funded, in part, by the National Science Foundation, NASA, and the Samsung Scholarship. (Comment on this)
1:15p	Titan’s missing river deltas and an Earthly climate connection “I’ll never forget the moment when I first saw new Cassini data come down from Titan’s surface,” says Samuel Birch. “I was in awe at witnessing this brand new, never-seen-before bit of our solar system.” Birch explores and models the evolution of the surfaces of planets, moons, and small bodies in the outer solar system, including Saturn’s largest moon, Titan, and the Comet 67P/Churyumov-Gerasimenko — two very different, icy worlds investigated by the spacecraft Cassini and Rosetta. He joins MIT this summer as one of eight recipients of the 2020 Heising-Simons Foundation 51 Pegasi b Fellows bridging planetary science and astronomy, accelerating our understanding of planetary system formation and evolution, and advance new technologies for detecting Earthlike worlds. Over the years, the Heising-Simons Foundation has generously supported a growing cohort of exoplanet researchers at MIT, including Jason Dittmann, Ian Wong, Ben Rackham, Clara Sousa-Silva, and now Samuel Birch, a research associate from Cornell University. In the coming three years, with support networks, mentorship from MIT Department of Earth, Atmospheric and Planetary Science (EAPS) members like Professor Taylor Perron and Research Scientist Jason Soderblom, and a grant of up to $375,000, Birch will have the space and time to fully explore ideas, deciphering what the surfaces of those objects tell us about their climatological past and potential habitability. He’ll also develop and operate related spacecraft missions and mission concepts that seek to study edges of our solar system. “I like to think of myself as an explorer of the outer solar system, trying to figure what is shaping the weird landscapes on these icy worlds,” Birch says. Not quite familiar territory As scientists learn more about the geophysics of Saturn’s moon Titan, their findings motivate newer and bigger questions that extend to Earth and other planetary bodies, highlighting the need for its continued study. “Titan’s surface is perhaps the most intriguing in our solar system, as there are rivers and seas of liquid methane and sand dunes made of organic plastics — all the result of a dense, nitrogen-dominated atmosphere,” says Birch. With a salty liquid water ocean beneath the surface, and an icy exterior sculpted by rivers, seas, and waves, Titan’s hydrologic cycle is similar to Earth’s. However, when its coastal rivers meet the lakes and sea, they seem to be missing deltas at their ends, Birch says. This may be because deltas like those on Earth do not form (or rarely form) because of differences in materials, dynamics, and coastal conditions. Alternately, their characteristics and representation in Cassini datasets may make them difficult to identify. To solve this mystery, Birch and MIT researchers will investigate deltaic and river dynamics, using a combination of theoretical, experimental, and numerical modeling, atmospheric simulations, and a re-evaluation of Cassini data for evidence of the resulting landforms. This suite of studies will help them understand what a delta “looks” like and map their distribution, which may unveil a record of Titan’s climate history and reveal how liquid methane has molded its landscapes. “If we can understand the reasons for the stark differences between Earth and Titan — and with it, the fate of all the mass eroded by Titan’s rivers,” Birch says, “we have the chance to really advance our knowledge of the history of erosion, sea-level, and climate change on Titan.” Life extensions This work inherently informs the study of fundamental Earthlike surface processes related to climate and the search for life beyond Earth. Since Titan lacks the complex interplay of diverse physical and chemical processes of Earth’s biosphere — like active tectonics, variable bedrock lithologies, diverse climate zones, vegetation, and (as far as we know) organisms — the moon serves as a natural laboratory for studying the effects of sea-level change on shoreline, river, and delta evolution. Additionally, scientists target deltas because of their high astrobiological potential for harboring life, like those on Mars. Analogous, active environments like Titan’s offer promise for the upcoming Dragonfly mission — when a nuclear-powered, dual-quadcopter will explore the moon, and perhaps these valuable spots. In the long run, Birch would like to parlay the skills he cultivates here to develop his own research group and continue to participate in missions that address key questions regarding the evolution of planetary surfaces. “I am extremely honored by this opportunity and that the community and the Heising-Simons Foundation value my work … I am fortunate that the mentors I will have at MIT are some of the best in the field,” Birch says, acknowledging the support of his collaborators and advisor, and welcoming the challenge and rewards that the future research will bring. “It is a fantastic opportunity and can’t wait to see what we can all discover on Titan and elsewhere!” The Heising-Simons Foundation is a family foundation based in Los Altos and San Francisco, California. The foundation works with its many partners to advance sustainable solutions in climate and clean energy, enable groundbreaking research in science, enhance the education of our youngest learners, and support human rights for all people. In addition to Birch, other fellows selected in this year’s cohort will join their host institutions: Elizabeth Bailey at the University of California at Santa Cruz; Ashley Baker and Kimberly Moore at Caltech; Emilie Dunham at the University of California at Los Angeles; Emily First and Eileen Gonzales at Cornell University; and Benjamin Tofflemire at University of Texas at Austin. (Comment on this)
1:59p	Origins of Earth’s magnetic field remain a mystery Microscopic minerals excavated from an ancient outcrop of Jack Hills, in Western Australia, have been the subject of intense geological study, as they seem to bear traces of the Earth’s magnetic field reaching as far back as 4.2 billion years ago. That’s almost 1 billion years earlier than when the magnetic field was previously thought to originate, and nearly back to the time when the planet itself was formed. But as intriguing as this origin story may be, an MIT-led team has now found evidence to the contrary. In a paper published today in Science Advances, the team examined the same type of crystals, called zircons, excavated from the same outcrop, and have concluded that zircons they collected are unreliable as recorders of ancient magnetic fields. In other words, the jury is still out on whether the Earth’s magnetic field existed earlier than 3.5 billion years ago. “There is no robust evidence of a magnetic field prior to 3.5 billion years ago, and even if there was a field, it will be very difficult to find evidence for it in Jack Hills zircons,” says Caue Borlina, a graduate student in MIT’s Department of Earth, Atmospheric, and Planetary Sciences (EAPS). “It’s an important result in the sense that we know what not to look for anymore.” Borlina is the paper’s first author, which also includes EAPS Professor Benjamin Weiss, Principal Research Scientist Eduardo Lima, and Research Scientist Jahandar Ramezan of MIT, along with others from Cambridge University, Harvard University, the University of California at Los Angeles, the University of Alabama, and Princeton University. A field, stirred up Earth’s magnetic field is thought to play an important role in making the planet habitable. Not only does a magnetic field set the direction of our compass needles, it also acts as a shield of sorts, deflecting away solar wind that might otherwise eat away at the atmosphere. Scientists know that today the Earth’s magnetic field is powered by the solidification of the planet’s liquid iron core. The cooling and crystallization of the core stirs up the surrounding liquid iron, creating powerful electric currents that generate a magnetic field stretching far out into space. This magnetic field is known as the geodynamo. Multiple lines of evidence have shown that the Earth’s magnetic field existed at least 3.5 billion years ago. However, the planet’s core is thought to have started solidifying just 1 billion years ago, meaning that the magnetic field must have been driven by some other mechanism prior to 1 billion years ago. Pinning down exactly when the magnetic field formed could help scientists figure out what generated it to begin with. Borlina says the origin of Earth’s magnetic field could also illuminate the early conditions in which Earth’s first life forms took hold. “In the Earth’s first billion years, between 4.4 billion and 3.5 billion years, that’s when life was emerging,” Borlina says. “Whether you have a magnetic field at that time has different implications for the environment in which life emerged on Earth. That’s the motivation for our work.” “Can’t trust zircon” Scientists have traditionally used minerals in ancient rocks to determine the orientation and intensity of Earth’s magnetic field back through time. As rocks form and cool, the electrons within individual grains can shift in the direction of the surrounding magnetic field. Once the rock cools past a certain temperature, known as the Curie temperature, the orientations of the electrons are set in stone, so to speak. Scientists can determine their age and use standard magnetometers to measure their orientation, to estimate the strength and orientation of the Earth’s magnetic field at a given point in time. Since 2001, Weiss and his group have been studying the magnetization of the Jack Hills rocks and zircon grains, with the challenging goal of establishing whether they contain ancient records of the Earth’s magnetic field.   “The Jack Hills zircons are some of the most weakly magnetic objects studied in the history of paleomagnetism,” Weiss says. “Furthermore, these zircons include the oldest known Earth materials, meaning that there are many geological events that could have reset their magnetic records.” In 2015, a separate research group that had also started studying the Jack Hills zircons argued that they found evidence of magnetic material in zircons that they dated to be 4.2 billion years old — the first evidence that Earth’s magnetic field may have existed prior to 3.5 billion years ago. But Borlina notes that the team did not confirm whether the magnetic material they detected actually formed during or after the zircon crystal formed 4.2 billion years ago — a goal that he and his team took on for their new paper. Borlina, Weiss, and their colleagues had collected rocks from the same Jack Hills outcrop, and from those samples, extracted 3,754 zircon grains, each around 150 micrometers long — about the width of a human hair. Using standard dating techniques, they determined the age of each zircon grain, which ranged from 1 billion to 4.2 billion years old. Around 250 crystals were older than 3.5 billion years. The team isolated and imaged those samples, looking for signs of cracks or secondary materials, such as minerals that may have been deposited on or within the crystal after it had fully formed, and searched for evidence that they were significantly heated over the last few billion years since they formed. Of these 250, they identified just three zircons that were relatively free of such impurities and therefore could contain suitable magnetic records. The team then carried out detailed experiments on these three zircons to determine what kinds of magnetic materials they might contain. They eventually determined that a magnetic mineral called magnetite was present in two of the three zircons. Using a high-resolution quantum diamond magnetometer, the team looked at cross-sections of each of the two zircons to map the location of the magnetite in each crystal. They discovered magnetite lying along cracks or damaged zones within the zircons. Such cracks, Borlina says, are pathways that allow water and other elements inside the rock. Such cracks could have let in secondary magnetite that settled into the crystal much later than when the zircon originally formed. Either way, Borlina says the evidence is clear: These zircons cannot be used as a reliable recorder for Earth’s magnetic field. “This is evidence we can’t trust these zircon measurements for the record of the Earth’s magnetic field,” Borlina says. “We’ve shown that, before 3.5 billion years ago, we still have no idea when Earth’s magnetic field started.” “For me, these results cast a great deal of doubt on the potential of Jack Hills zircons to faithfully record the palaeomagnetic field intensity prior to 3.5 billion years,” says Andy Biggin, professor of paleomagnetism at the University of Liverpool, who was not involved in the research. “That said, this debate has been raging, like the palaeomagnetic equivalent to Brexit, since 2015 and I would be very surprised if this were the last word on the matter. It is nigh on impossible to prove a negative and neither methods nor interpretations are ever beyond question.” Despite these new results, Weiss stresses that previous magnetic analyses of these zircons are still highly valuable.  “The team that reported the original zircon magnetic study deserves a lot of credit for trying to tackle this enormously challenging problem,” Weiss says.  “As a result of all the work from both groups, we now understand much better how to study the magnetism of ancient geological materials. We now can begin to apply this knowledge to other mineral grains and to grains from other planetary bodies.” This research was supported, in part, by NASA. (Comment on this)
11:59p	Bluetooth signals from your smartphone could automate Covid-19 contact tracing while preserving privacy Imagine you’ve been diagnosed as Covid-19 positive. Health officials begin contact tracing to contain infections, asking you to identify people with whom you’ve been in close contact. The obvious people come to mind — your family, your coworkers. But what about the woman ahead of you in line last week at the pharmacy, or the man bagging your groceries? Or any of the other strangers you may have come close to in the past 14 days? A team led by MIT researchers and including experts from many institutions is developing a system that augments “manual” contact tracing by public health officials, while preserving the privacy of all individuals. The system relies on short-range Bluetooth signals emitted from people’s smartphones. These signals represent random strings of numbers, likened to “chirps” that other nearby smartphones can remember hearing. If a person tests positive, they can upload the list of chirps their phone has put out in the past 14 days to a database. Other people can then scan the database to see if any of those chirps match the ones picked up by their phones. If there’s a match, a notification will inform that person that they may have been exposed to the virus, and will include information from public health authorities on next steps to take. Vitally, this entire process is done while maintaining the privacy of those who are Covid-19 positive and those wishing to check if they have been in contact with an infected person. “I keep track of what I’ve broadcasted, and you keep track of what you’ve heard, and this will allow us to tell if someone was in close proximity to an infected person,” says Ron Rivest, MIT Institute Professor and principal investigator of the project. “But for these broadcasts, we’re using cryptographic techniques to generate random, rotating numbers that are not just anonymous, but pseudonymous, constantly changing their ‘ID,’ and that can’t be traced back to an individual.” This approach to private, automated contact tracing will be available in a number of ways, including through the privacy-first effort launched at MIT in response to Covid-19 called SafePaths. This broad set of mobile apps is under development by a team led by Ramesh Raskar of the MIT Media Lab. The design of the new Bluetooth-based system has benefited from SafePaths’ early work in this area. Bluetooth exchanges Smartphones already have the ability to advertise their presence to other devices via Bluetooth. Apple’s “Find My” feature, for example, uses chirps from a lost iPhone or MacBook to catch the attention of other Apple devices, helping the owner of the lost device to eventually find it.  “Find My inspired this system. If my phone is lost, it can start broadcasting a Bluetooth signal that’s just a random number; it’s like being in the middle of the ocean and waving a light. If someone walks by with Bluetooth enabled, their phone doesn’t know anything about me; it will just tell Apple, ‘Hey, I saw this light,’” says Marc Zissman, the associate head of MIT Lincoln Laboratory’s Cyber Security and Information Science Division and co-principal investigator of the project. With their system, the team is essentially asking a phone to send out this kind of random signal all the time and to keep a log of these signals. At the same time, the phone detects chirps it has picked up from other phones, and only logs chirps that would be medically significant for contact tracing — those emitted from within an approximate 6-foot radius and picked up for a certain duration of time, say 10 minutes. Phone owners would get involved by downloading an app that enables this system. After a positive diagnosis, a person would receive a QR code from a health official. By scanning the code through that app, that person can upload their log to the cloud. Anyone with the app could then initiate their phones to scan these logs. A notification, if there’s a match, could tell a user how long they were near an infected person and the approximate distance.   Privacy-preserving technology Some countries most successful at containing the spread of Covid-19 have been using smartphone-based approaches to conduct contact tracing, yet the researchers note these approaches have not always protected individual’s privacy. South Korea, for example, has implemented apps that notify officials if a diagnosed person has left their home, and can tap into people’s GPS data to pinpoint exactly where they’ve been. “We’re not tracking location, not using GPS, not attaching your personal ID or phone number to any of these random numbers your phone is emitting,” says Daniel Weitzner, a principal research scientist in the MIT Computer Science and Artificial Intelligence Laboratory (CSAIL) and co-principal investigator of this effort. “What we want is to enable everyone to participate in a shared process of seeing if you might have been in contact, without revealing, or forcing anyone to reveal, anything.” Choice is key. Weitzner sees the system as a virtual knock on the door that preserves people’s right to not answer it. The hope, though, is that everyone who can opt in would do so to help contain the spread of Covid-19. “We need a large percentage of the population to opt in for this system to really work. We care about every single Bluetooth device out there; it’s really critical to make this a whole ecosystem,” he says. Public health impact Throughout the development process, the researchers have worked closely with a medical advisory team to ensure that this system would contribute effectively to contact tracing efforts. This team is led by Louise Ivers, who is an infectious disease expert, associate professor at Harvard Medical School, and executive director of the Massachusetts General Hospital Center for Global Health. “In order for the U.S. to really contain this epidemic, we need to have a much more proactive approach that allows us to trace more widely contacts for confirmed cases. This automated and privacy-protecting approach could really transform our ability to get the epidemic under control here and could be adapted to have use in other global settings,” Ivers says. “What’s also great is that the technology can be flexible to how public health officials want to manage contacts with exposed cases in their specific region, which may change over time.” For example, the system could notify someone that they should self-isolate, or it could request that they check in through the app to connect with specialists regarding daily symptoms and well-being. In other circumstances, public health officials could request that this person get tested if they were noticing a cluster of cases. The ability to conduct contact tracing quickly and at a large scale can be effective not only in flattening the curve of the outbreak, but also for enabling people to safely enter public life once a community is on the downward side of the curve. “We want to be able to let people carefully get back to normal life while also having this ability to carefully quarantine and identify certain vectors of an outbreak,” Rivest says. Toward implementation Lincoln Laboratory engineers have led the prototyping of the system. One of the hardest technical challenges has been achieving interoperability, that is, making it possible for a chirp from an iPhone to be picked up by an Android device and vice versa. A test at the laboratory late last week proved that they achieved this capability, and that chirps could be picked up by other phones of various makes and models. A vital next step toward implementation is engaging with the smartphone manufacturers and software developers — Apple, Google, and Microsoft. “They have a critical role here. The aim of the prototype is to prove to these developers that this is feasible for them to implement,” Rivest says. As those collaborations are forming, the team is also demonstrating its prototype system to state and federal government agencies. Rivest emphasizes that collaboration has made this project possible. These collaborators include the Massachusetts General Hospital Center for Global Health, CSAIL, MIT Lincoln Laboratory, Boston University, Brown University, MIT Media Lab, The Weizmann Institute of Science, and SRI International. The team also aims to play a central, coordinating role with other efforts around the country and in Europe to develop similar, privacy-preserving contact-tracing systems. “This project is being done in true academic style. It’s not a contest; it’s a collective effort on the part of many, many people to get a system working,” Rivest says.   (Comment on this)

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