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Researchers entangle quantum memory at facilities over 50km apart

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While quantum computers can do interesting things without dedicated memory, memory would provide a lot of flexibility in terms of the sorts of algorithms they could run and how quantum systems can interact with each other and the outside world. Building quantum memory is extremely challenging, as reading to and writing from it both have to be extremely efficient and accurate, and the memory has to do something that’s very atypical of quantum systems: hold on to its state for an appreciable length of time.

If we solve the problems, however, quantum memory offers some rather unusual properties. The process of writing to quantum memory is very similar to the process for quantum teleportation, meaning the memory can potentially be transmitted between different computing facilities. And since the storage device is a quantum object, there’s the possibility that two qubits of memory in different locations can be entangled, essentially de-localizing the qubit’s value and spreading it between two facilities.

In a demonstration of that promise, Chinese researchers have entangled quantum memory at facilities over 20 kilometers apart. Separately, they have also done the entanglement with photons that have traveled through 50 kilometers of optical cable. But the process of transmitting and entangling comes with an unfortunate side-effect: it takes so long that the memory typically loses its coherence in the meantime.

Quantum city

The basic outlines of the experiment are pretty straightforward for a process that’s somewhat mind-bending. The qubits being used here are small clouds of cold atoms (about a hundred million atoms for each). They are placed in a state where the atoms are indistinguishable from a quantum perspective and thus can be treated as a single quantum object. Because a quantum state will be distributed across all the atoms simultaneously, this provides a bit more stability than other forms of quantum memory. The atom cloud’s state is read and written using photons, and the atoms are placed in an optical cavity that traps these photons. This ensures that the photons have many opportunities to interact with the atom cloud, increasing the efficiency of operations.

When the memory’s state is set by a write photon, the atomic collective emits a second photon that indicates the success. The polarization of this photon contains information regarding the state of the atoms, so it serves as a tool for entangling the memory.

Unfortunately, that photon is at a wavelength that isn’t very useful, in that it tends to get lost during transmission. So the researchers sacrificed a bit of efficiency for a lot of utility. They used a device that shifts the wavelength of the photons from the near infrared to the wavelengths used in standard communications fibers. About 30 percent of the photons were lost, but the remaining ones can be transmitted at high-efficiency across existing fiber networks (provided the right hardware is put in place where the fiber ends).

There are losses from filtering noise and getting photons into the fiber, but the entire process is over 30-percent efficient, end to end. In this case, the two ends were 11km apart, at the University of Science and Technology of China and the Hefei Software Park.

For the entanglement, the authors created two qubits of quantum memory, generated photons from both, and sent those photons down separate cables to the Software Park. There, the photons were sent through a device that made them impossible to distinguish, entangling them. Since they, in turn, were entangled with the quantum memory that produced them, the two qubits of memory were then entangled. While they resided in the same lab, the geometry of the fibers could have been arbitrary—it was equivalent to entangling two bits of memory that were 22km apart.

That’s a big step up from the previous record of 1.4km.

Go long

To stretch things out a bit, the researchers then turned to a long spool of cable. Two photons were sent down the cable and then manipulated so that it was impossible to determine which path they took through the cable. This again entangled them, and thus the memories that emitted the photons in the first place. The process required that the phase of the incoming photons be tracked, which is notably more difficult, and therefore dropped the overall efficiency.

For a 50km-long fiber path, this led to some rather low efficiencies, on the order of 10-4. Which means the time to achieve entanglement went up—in this case to over half a second. And that’s a problem, because the typical lifetime of a qubit stored in this memory is 70 microseconds, much shorter than the entanglement process. So the approach definitely falls into the “not quite ready for production” category.

And that’s unfortunate because the approach opens up a host of very intriguing possibilities. One is that spreading a qubit across two facilities through this delocalization could enable a single quantum calculation to be performed at remote facilities—possibly ones employing different hardware that have distinct strengths and weaknesses. And the researchers note that there’s a technique called entanglement swapping that could extend the distance between memory qubits even further—provided the qubits hold on to their state. But if all of these involve some amount of error, that error will quickly pile up and make the whole thing useless.

None of this should undercut the achievement demonstrated here, but it does show how far we still have to go. The inefficiencies popping up at every step of the process each represent a distinct engineering and/or physics challenge we have to tackle before any of this can be applicable to the real world.

Nature, 2019. DOI: 10.1038/s41586-020-1976-7  (About DOIs).

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J&J boosters get nod from FDA advisors as agency eyes mix-and-match

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Enlarge / Boxes of Johnson & Johnson’s Janssen COVID-19 vaccine at a vaccination site in Florida.

A committee of independent advisors for the Food and Drug Administration on Friday voted unanimously in favor of authorizing a second dose of the Johnson & Johnson COVID-19 vaccine to everyone 18 years of age and older, two or more months after a person has received the first dose.

It is the third time the FDA’s advisory committee has recommended additional COVID-19 doses in recent weeks to bolster protection. But the reviewed data, discussion, and vote today were significantly different from the booster-authorization meetings for Pfizer/BioNTech and Moderna COVID-19 vaccines.

Dose two

The J&J vaccine has consistently lagged behind the two mRNA vaccines in efficacy against COVID-19. Some estimates have put the J&J vaccine’s effectiveness against COVID-19 hospitalization as low as 68 percent, while the two mRNA vaccines have seen estimates of effectiveness against hospitalization in the high 80s to low 90s. Recent data suggests that the mRNA vaccines’ protection against infection may start waning six or more months after primary doses—particularly in older and more vulnerable people. This data prompted the push for boosters. But such waning does not appear to be happening with the J&J vaccine.

The one-and-done vaccine seems to be holding steady in its effectiveness against infections and severe disease. Instead of arguing that a second shot can restore high levels of protection—as was the argument for mRNA vaccine boosters—representatives for J&J today argued for a second shot that could improve upon protection generated after the first. The company presented data suggesting that a second dose given at least two months after the first could push vaccine effectiveness against symptomatic disease from 53 percent to 75 percent and could hike antibody levels 3.5- to 6-fold.

The company also presented data on offering a second dose six months after the first dose. The data suggested even larger increases in antibody levels. But those results hinged on data from just 17 people, and the committee largely felt that study was not convincing enough to recommend a second dose only after that time period. Some also noted the practical matter that for many people who received the J&J vaccine, it has already been around six months since their first dose.

Overall, the committee—the Vaccines and Related Biological Products Advisory Committee (VRBPAC)—voted 19-to-0 in favor of the FDA authorizing a second dose of the J&J vaccine after two months. There was some discussion about whether the dose should be considered a booster or a second dose that is part of the primary immunization.

Combinations

After the vote, the committee discussed the results of a fresh mix-and-match trial. Researchers released preliminary results earlier this week from a small trial testing nine combinations of primary and booster vaccines. The main finding was that the mixed vaccination regimens (having a booster from a different company than the initial vaccine) were as good as, if not better than, the regimens that included only one type of vaccine. The data also hinted that boosting with the Moderna mRNA vaccine offered the strongest protection, regardless of the starting vaccine, and boosting with the J&J vaccine gave the weakest protection, particularly for people who had initially received a J&J vaccine.

The data presentation segued into a discussion aimed at assessing what data VRBPAC would want to see to authorize mix-and-match booster options—particularly authorizing mRNA vaccine boosters for people vaccinated with a J&J vaccine. The committee offered a range of points and perspectives. Some suggested seeing more safety data and longer term, in-depth efficacy data. Others said they were already convinced by the mix-and-match data.

A representative from the Centers for Disease Control and Prevention emphasized that the agency is not looking for a recommendation of specific mix-and-match combinations; rather, it wants to determine if mixing and matching should be generally approved. Such flexibility could come in handy in cases where the availability of a vaccine type is scarce or for people who are at risk or concerned about a side effect from a particular vaccine.

Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, made it clear at several points in today’s meeting that the agency is keen to find a path forward for mix-and-match vaccine boosting.

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The proof’s in the poop: Austrians have loved beer, blue cheese for 2,700 years

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Enlarge / A 2,700-year-old piece of human excrement found at the Hallstatt salt mines, in which beans, millet, and barley are clearly visible (assuming one wishes to look that closely).

Ancient Iron Age miners in what is now Austria were quite fond of beer and blue cheese, according to a new analysis of preserved paleo-poop published in the journal Current Biology. The researchers found evidence of two fungal species commonly used to produce blue cheese and beers, along with evidence that the miners’ diet was particularly rich in carbohydrates in the form of cereal grains.

“Genome-wide analysis indicates that both fungi were involved in food fermentation and provide the first molecular evidence for blue cheese and beer consumption during Iron Age Europe,” said co-author Frank Maixner of the Eurac Research Institute for Mummy Studies in Bolzano, Italy. “The miners seem to have intentionally applied food fermentation technologies with microorganisms which are still nowadays used in the food industry.”

For archaeologists keen on learning more about the health and diet of past populations—as well as how certain parasites evolved over the evolutionary history of the microbiome—preserved samples of ancient poo can be a veritable goldmine of information. Samples are usually found in dry caves, desert areas, frozen areas, or waterlogged environments (like bogs), according to Maixner and his co-authors, where desiccation, freezing, and similar processes preserve the fecal matter for posterity.

Four samples of preserved human fecal matter collected from the Hallstatt salt mines.
Enlarge / Four samples of preserved human fecal matter collected from the Hallstatt salt mines.

F. Maixner/Eurac Research

As we’ve reported previously, it can be difficult to determine whether fecal samples are human or were produced by other animals, particularly dogs. Usually, only those samples found with human skeletons or mummies could be designated as being of human origin with any certainty. That’s why scientists developed a tool last year (dubbed coproID) capable of determining whether paleofeces and coprolites recovered from archaeological sites are of human or animal origin. Among other discoveries, the researchers found that the archaeological record was unexpectedly “full of dog poop.”

One excellent source of human paleofeces samples is the prehistoric underground salt mines of Hallstatt-Dachstein/Salzkammergut, a UNESCO World Heritage site in Austria. The mines have high salt concentrations and a constant annual temperature of around 8 degrees Celsius, which is ideal for preserving organic materials like feces. Archaeologists have unearthed thousands of Bronze and Iron Age tools and implements made from wood and fur, as well as rawhide, woolen textile fragments, ropes—and yes, human feces, typically recovered by wet-sieving larger blocks of debris found in the mines. These artifacts have provided insight into the daily life of the miners.

The present study focused on investigating the miners’ dietary habits, as revealed by the analysis of gut microbes present in the preserved poop. Maixner et al. examined four paleofecal samples. Radiocarbon dating revealed that one was from the Late Bronze Age, two were from the Iron Age, and one dated to the 18th century AD—most likely because the mines began to be re-used around that time. The researchers were able to retrieve DNA and proteins from all four samples and determined that all four came from men. “The DNA damage is exceptionally low,” the authors noted in their paper. “This high preservation is most likely due to the rapid desiccation of the samples in the salt mine.”

An intrepid archaeologist standing in the middle of layers of mining debris—including paleofeces.
Enlarge / An intrepid archaeologist standing in the middle of layers of mining debris—including paleofeces.

D. Brander/H. Reschreiter/NHMW

The molecular and microscopic analysis showed that the miners primarily subsisted on cereals like emmer, spelt, barley, and millet—a diet rich in carbohydrates and supplemented with beans, fruits, seeds, nuts (walnut), or meats (cattle and swine). The Bronze Age sample showed almost exclusively cereal grain remains, along with a few weeds like corn cockle and poison parsley. The Iron Age samples were similar, except one sample had remains of broad beans, crabapples, and cranberries.

The 18th-century sample was notably different. The cereal remains (wheat and barley bran) were much more finely textured—evidence of grinding—with some garden beans and almost no fruits. “This suggest that the protohistoric miners consumed the cereals and legumes in a sort of gruel or porridge, whereas miners in the 18th century ate their cereals in a more processed form, e.g., as a bread or biscuit,” the authors wrote. The team also found evidence that the men who produced the Iron Age and 18th-century fecal samples suffered from intestinal infections (whipworm and roundworm).

The microbiomes of all four samples were quite similar to the gut microbiomes of non-Westernized populations today, particularly in the abundance of Prevotella copra, which is associated with the digestion of complex carbohydrates, according to the authors. This “adds weight to the hypothesis that the modern industrialized human gut microbiome has diverged from an ancestral state, probably due to modern lifestyle, diet, or medical advances,” they wrote. Analyzing fecal samples from the last two to three centuries would help pinpoint when that pivotal shift occurred.

Scientists analyzing paleofeces in the laboratory at Eurac's Institute for Mummy Studies.
Enlarge / Scientists analyzing paleofeces in the laboratory at Eurac’s Institute for Mummy Studies.

Ivo Corra/Eurac Research

All the samples showed some evidence of fungal DNA, but the Iron Age sample also had a high abundance of two species of fungi: Penicillium roqueforti—commonly used in the fermentation of cheese—and Saccharomyces cerevisiae, used for fermenting bread and alcoholic beverages like beer, mead, and wine. The former would have likely produced a cheese similar to modern blue cheese, indicating “a major step in ruminant milk processing from fresh to ripened cheese,” the authors wrote—perhaps because the ripened cheese would have lower lactose content and could be stored for longer periods.

As for the S. cerevisiae, the researchers were able to reconstruct about 90 percent of the fungal genome from the paleo-poop sample and concluded that it was most likely used to ferment beer. With the many fermentable cereals that constituted the subject’s diet, the researchers were even able to hypothesize about the likely process. The miners could have simply added water to wort and allowed fermentation to happen naturally via wild, airborne yeasts. But they didn’t find evidence of other yeast species common to this kind of natural fermentation process.

Rather, they found evidence of domestication of yeasts, either through the reuse of vessels or through the practice of “back-slopping,” in which new batches are inoculated with portions from previous batches. The team concluded that the miners were brewing the modern equivalent of pale beer, “produced mainly by top-fermenting S. cerevisiae strains,” they wrote.

“These results shed substantial new light on the life of the prehistoric salt miners in Hallstatt and allow an understanding of ancient culinary practices in general on a whole new level,” said co-author Kerstin Kowarik of the Museum of Natural History Vienna. “It is becoming increasingly clear that not only were prehistoric culinary practices sophisticated but also that complex processed foodstuffs as well as the technique of fermentation have held a prominent role in our early food history.”

DOI: Current Biology, 2021. 10.1016/j.cub.2021.09.031  (About DOIs).

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NASA’s Lucy mission will soon be in the sky, with a launch set for Saturday

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Enlarge / Atlas V with the Lucy spacecraft aboard an SLC-41 on the morning of October 15 as media set their sound-activated remote cameras.

Trevor Mahlmann

Less than five years have gone by since NASA selected the “Lucy” mission for development as part of its Discovery Mission program, and now the intriguing spacecraft is ready for launch.

The $981 million mission will fly an extremely complex trajectory over the span of a dozen years. The spacecraft will swing by Earth a total of three times for gravitational assists as it visits a main-belt asteroid, 52246 Donaldjohanson, and subsequently flies by eight Trojan asteroids that share Jupiter’s orbit around the Sun.

The Lucy mission is scheduled to launch on Saturday at 5:34 am ET (09:34 UTC) from Cape Canaveral Space Force Station in Florida. An Atlas V rocket carrying the 1.5-ton spacecraft rolled to the launch pad on Thursday in advance of the launch attempt. The weather looks fine Saturday morning, with a 90 percent chance of favorable conditions. The launch will be covered live on NASA TV.

Lucy will fly by its first asteroid target in April 2025, a main-belt asteroid named after Donald Johanson, the American anthropologist who co-discovered the famed “Lucy” fossil in 1974. The fossil, of a female hominin species that lived about 3.2 million years ago, supported the evolutionary idea that bipedalism preceded an increase in brain size.

This diagram illustrates Lucy's orbital path. The spacecraft’s path (green) is shown in a frame of reference where Jupiter remains stationary, giving the trajectory its pretzel-like shape.
Enlarge / This diagram illustrates Lucy’s orbital path. The spacecraft’s path (green) is shown in a frame of reference where Jupiter remains stationary, giving the trajectory its pretzel-like shape.

Southwest Research Institute

The Lucy asteroid mission, in turn, takes its name from the famed fossil. By visiting Trojan asteroids, scientists expect to glean information about the building blocks of the Solar System and better understand the nature of its planets today.

No probe has flown by these smallish Trojan asteroids, which are clustered at stable LaGrange points trailing and ahead of Jupiter’s orbit 5.2 astronomical units from the Sun. The asteroids are mostly dark but may be covered with tholins, which are organic compounds that could provide raw materials for the basic chemicals of life.

“When we look at nature, whether it’s looking at deep space or at these small objects, each one of these tells us a chapter of the story that we’re all a part of,” said NASA’s science chief, Thomas Zurbuchen, during a media briefing this week in advance of the launch. “When you look at one of those planetary bodies and you add science, it turns into a history book.”

So in some sense, the Lucy asteroid mission will  be looking at fossil remnants of our early Solar System. To accomplish all of these fly-bys in a single mission, scientists and engineers this year devised a complex orbital track, which necessitated a launch this month.

This gave mission planners a short deadline to complete the Lucy project after NASA selected it in January 2017. Since that time, planners experienced a government shutdown, the COVID-19 pandemic, and supply chain issues. Through it all, NASA and the spacecraft’s manufacturer, Lockheed Martin, have remained on schedule and within the mission’s budget.

Atlas V 401 features a 4-meter payload fairing, no strap-on solid rocket boosters, and 1 upper stage Centaur rocket engine.
Enlarge / Atlas V 401 features a 4-meter payload fairing, no strap-on solid rocket boosters, and 1 upper stage Centaur rocket engine.

Trevor Mahlmann

According to Donya Douglas-Bradshaw, Lucy project manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, the pandemic struck during a critical time period when the spacecraft was assembled with its four major scientific payloads. It took about 14 months to integrate the spacecraft bus with the instruments and verify that the craft could survive for a full 12-year mission in space. If Lucy is successful, the mission will travel farther on solar power than any previous spacecraft.

“I think the largest challenge in doing that certainly had to do with the pandemic,” she said. “Obviously, when you’re building hardware and integrating and testing it, there’s a lot of hands-on, and so it was particularly challenging to build it and maintain the safety of the workforce.”

But now, the spacecraft is buttoned up, and the rocket is ready to go. Somewhat ironically, although Lucy is visiting the “Jupiter trojans,” it will never be closer to Jupiter than when it is on Earth. This is because the Trojans trail Jupiter at a greater distance than that between Earth and the Solar System’s largest planet.

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