Quantum particles timed as they tunnel through a solid
A clever new study definitively measures how long it takes for quantum particles to pass through a barrier.
- Quantum particles can tunnel through seemingly impassable barriers, popping up on the other side.
- Quantum tunneling is not a new discovery, but there's a lot that scientists don't know.
- By super-cooling rubidium particles, researchers use their spinning as a magnetic timer.
When it comes to weird behavior, there's nothing quite like the quantum world. On top of that world-class head scratcher entanglement, there's also quantum tunneling — the mysterious process in which particles somehow find their way through what should be impenetrable barriers.
Exactly why or even how quantum tunneling happens is unknown: Do particles just pop over to the other side instantaneously in the same way entangled particles interact? Or do they progressively tunnel through? Previous research has been conflicting.
That quantum tunneling occurs has not been a matter of debate since it was discovered in the 1920s. When IBM famously wrote their name on a nickel substrate using 35 xenon atoms, they used a scanning probe microscopes to see what they were doing. And tunnel diodes are fast-switching semiconductors that derive their negative resistance from quantum tunneling.
"Quantum tunneling is one of the most puzzling of quantum phenomena," says Aephraim Steinberg of the Quantum Information Science Program at Canadian Institute for Advanced Research in Toronto to Live Science. Speaking with Scientific American he explains, "It's as though the particle dug a tunnel under the hill and appeared on the other."
Steinberg is a co-author of a study just published in the journal Nature that presents a series of clever experiments that allowed researchers to measure the amount of time it takes tunneling particles to find their way through a barrier. "And it is fantastic that we're now able to actually study it in this way."
Frozen rubidium atoms
Image source: Viktoriia Debopre/Shutterstock/Big Think
One of the difficulties in ascertaining the time it takes for tunneling to occur is knowing precisely when it's begun and when it's finished. The authors of the new study solved this by devising a system based on particles' precession.
Subatomic particles all have magnetic qualities and they spin, or "precess," like a top when they encounter an external magnetic field. With this in mind, the authors of the study decided to construct a barrier with a magnetic field, causing any particles passing through it to precess as they did so. They wouldn't precess before entering the field or after, so by observing and timing the duration of the particles' precession, the researchers could definitively identify the length of time it took them to tunnel through the barrier.
To construct their barrier, the scientists cooled about 8,000 rubidium atoms to a billionth of a degree above absolute zero. In this state, they form a Bose-Einstein condensate, AKA the fifth-known form of matter. When in this state, atoms slow down and can be clumped together rather than flying around independently at high speeds. (We've written before about a Bose-Einstein experiment in space.)
Using a laser, the researchers pushed about 2,000 rubidium atoms together in a barrier about 1.3 micrometers thick, endowing it with a pseudo-magnetic field. Compared to a single rubidium atom, this is a very thick wall, comparable to a half a mile deep if you yourself were a foot thick.
With the wall prepared, a second laser nudged individual rubidium atoms toward it. Most of the atoms simply bounced off the barrier, but about 3 percent of them went right through as hoped. Precise measurement of their precession produced the result: It took them 0.61 milliseconds to get through.
Reactions to the study
Scientists not involved in the research find its results compelling.
"This is a beautiful experiment," remarked Igor Litvinyuk of Griffith University in Australia. "Just to do it is a heroic effort." Drew Alton of Augustana University in South Dakota tells Live Science, "The experiment is a breathtaking technical achievement."
What makes the researchers' results so exceptional is their unambiguity. Says Chad Orzel at Union College in New York, "Their experiment is ingeniously constructed to make it difficult to interpret as anything other than what they say." He calls the research, "one of the best examples you'll see of a thought experiment made real." Litvinyuk agrees: "I see no holes in this."
As for the researchers themselves, enhancements to their experimental apparatus are underway to help them learn more. "We're working on a new measurement where we make the barrier thicker," Steinberg said. In addition, there's also the interesting question of whether or not that 0.61-millisecond trip occurs at a steady rate: "It will be very interesting to see if the atoms' speed is constant or not."
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Hungarian cartographer travels the world while mapping its treasures.
- Simple idea, stunning result: the world's watersheds in glorious colors.
- The maps are the work of Hungarian cartographer Robert Szucs.
- His job: to travel and map the world, one good cause at a time.
The world<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTE0MjUyNS9vcmlnaW4ucG5nIiwiZXhwaXJlc19hdCI6MTYzMzU3Njk1M30.rRdZpcl0bfVi4oBsljHdZSbcX0New9rdLcx6fr2mD7Y/img.png?width=980" id="f982a" class="rm-shortcode" data-rm-shortcode-id="fa67421340f881d5ab91463514cf9a6d" data-rm-shortcode-name="rebelmouse-image" />
Can you spot the world's ten largest drainage basins? In order of magnitude: Amazon, Congo, Nile, Mississippi, Ob, Parana, Yenisei, Lena, Niger, Amur. Image source: Grasshopper Geography
Africa<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTE0MjUyNi9vcmlnaW4ucG5nIiwiZXhwaXJlc19hdCI6MTYzOTI2MzI0MX0.OeTS-scZwBES4AlZAan7fBlaBkznkig5hPjgcd1j6hw/img.png?width=980" id="e987c" class="rm-shortcode" data-rm-shortcode-id="2d3a8999ed4071a123b30efc5652fee9" data-rm-shortcode-name="rebelmouse-image" />
Africa is home to the rivers with the world's second- and third-largest catchment areas: the Congo (in blue), with a basin of 1.44 million square miles (3.73 million km2), and the Nile (in red), with basin area of 1.26 million square miles (3.25 million km2). The Nile is the longest river in Africa, though (4,130 miles; 6,650 km), followed by the Congo: 2,900 miles (4,700 km). The Congo River's alternative name, Zaire, comes from the Kikongo nzadi o nzere ('river swallowing rivers'). Image source: Grasshopper Geography
Europe<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTE0MjUyOS9vcmlnaW4ucG5nIiwiZXhwaXJlc19hdCI6MTY0NTkzOTMyMH0.tq5fjnq8wvLqXY0C9gzfoUd0ahOAQ7IZQxbpVnC1FdY/img.png?width=980" id="a8ec4" class="rm-shortcode" data-rm-shortcode-id="1ce5f59691501103343e080905ce74a3" data-rm-shortcode-name="rebelmouse-image" />
The Volga (in yellow) is the river with the biggest catchment area in Europe (just under 545,000 square miles; 1.41 million km2). It flows exclusively through Russia, and the catchment area is entirely within Russia as well. Europe's number two is the Danube (in orange), which flows through 10 countries — more than any other river in the world. Its drainage basin (just over 307,000 square miles; almost 796,000 km2) includes nine more countries. Image: Grasshopper Geography
Germany<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTE0MjUzMC9vcmlnaW4ucG5nIiwiZXhwaXJlc19hdCI6MTY0Mzk4ODA3Nn0.qX1sOfJWAI7TUbTQCiIob-R5p4_wj299wEtrYAUREmg/img.png?width=980" id="d5efa" class="rm-shortcode" data-rm-shortcode-id="8e73c53d75840f21b4f2ca4b8a1e7f51" data-rm-shortcode-name="rebelmouse-image" />
The hydrographic map of Germany is dominated by just four major drainage systems: the Danube (in orange) in the south, the Rhine (in blue) in the west, the Elbe (in purple) in the east and the Weser (in green) between the latter two. In Antiquity, the Rhine was the border between the Roman Empire and the Germans. Rome once attempted to shift the border to the Elbe, which would have radically altered the course of history, but it suffered a massive defeat in 9 CE at the Teutoburger Wald (roughly between both rivers). Image: Grasshopper Geography
Great Britain and Ireland<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTE0MjUzMS9vcmlnaW4ucG5nIiwiZXhwaXJlc19hdCI6MTY1OTk2MjM3MX0.nDy__OLIyC1arty4_2xd54fjTzmfsIZo-2pe5QRjjA4/img.png?width=980" id="31a6f" class="rm-shortcode" data-rm-shortcode-id="d089f66097f37a10ab854eaccdac3581" data-rm-shortcode-name="rebelmouse-image" />
Both Ireland and Great Britain are islands, as a result of which neither boasts a continental-class river. Twenty of the 30 longest British rivers are less than 100 miles (160 km) long. The longest river in Britain is the Severn (220 miles, 354 km), its catchment area shown in blue in the southwest. Ireland's longest river is the Shannon (224 miles, 360 km). Even combined they're not as long as France's Seine (483 miles, 777 km). Image: Grasshopper Geography
United States<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTE0MjUzNC9vcmlnaW4ucG5nIiwiZXhwaXJlc19hdCI6MTY2MDYyMzEyM30.7S_83dA6bcLyID_7BhH1R_OTy61tpgDZrBMQ_iPwnjM/img.png?width=980" id="a879d" class="rm-shortcode" data-rm-shortcode-id="a7c74a7b5a7887fb2d13b40d5d96223c" data-rm-shortcode-name="rebelmouse-image" />
Spread-eagled across the central part of the United States, the Mississippi's drainage basin covers all or parts of 32 U.S. states (and two Canadian provinces). The easternmost point of Ol' Man River's catchment area is really far east: Cobb Hill in northern Pennsylvania. Here rises the Allegheny, tributary of the Ohio, which in turn flows into the Mississippi at Cairo, Illinois. Image: Grasshopper Geography
Washington State<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTE0MjUzNS9vcmlnaW4ucG5nIiwiZXhwaXJlc19hdCI6MTY0MzU2MzM4OH0.mniqbkEQq84rNaWOQIl4fB4mOhNdJf5WactNyE_VsyM/img.png?width=980" id="adc4d" class="rm-shortcode" data-rm-shortcode-id="97eb5a5add49c06ef00ff0bca812b380" data-rm-shortcode-name="rebelmouse-image" />
Even leaving out the Mississippi, there's enough going on in the rest of North America to keep the eye occupied. Here's a drainage map of Washington State. The big fish in this much smaller pond is the Columbia River (drainage area in blue), the largest river in the Pacific Northwest. Only in the western third of the state is there a colourful counterpoint, in the multitude of smaller river basins that are draining into the Pacific or into Puget Sound. Image: Grasshopper Geography
Australia<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTE0MjUzNi9vcmlnaW4ucG5nIiwiZXhwaXJlc19hdCI6MTYzOTM0ODM2NH0.U7vckwnoNoxf-bk8SuYO246hNMpR2zXILILsd4pas9o/img.png?width=980" id="38c2b" class="rm-shortcode" data-rm-shortcode-id="0c44d30d61c6cb94b8d5c7205cbabd58" data-rm-shortcode-name="rebelmouse-image" />
At 1,558 miles (2,508 km), the Murray is Australia's longest river. It is often considered in conjunction with the Darling (915 miles, 1,472 km), the country's third-longest river, which flows into the Murray. The Murray-Darling basin (in blue, in the southeast) covers just under 410,000 square miles (1.06 million km2), or 14 percent of Australia's total territory. Don't let that spidery network of river courses in the interior fool you: Australia is the world's driest inhabited continent (Antarctica, bizarrely, is drier). Image: Grasshopper Geography
Russia<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTE0MjUzNy9vcmlnaW4ucG5nIiwiZXhwaXJlc19hdCI6MTYwNzg5MzIxOX0.WhShHLjjWdEh4FF_OZsY1oTN3Vc77X29TbMYbVHrHqA/img.png?width=980" id="f5cee" class="rm-shortcode" data-rm-shortcode-id="53acd93f1ab67be979e6ab128c144ce6" data-rm-shortcode-name="rebelmouse-image" />
Four of the world's largest drainage basins are in Russia: the Ob, Yenisei and Lena (origin of Vladimir I. Ulyanov's nom de guerre, Lenin) entirely and the Amur, shared with China. The Volga may be Europe's longest river, but 84 percent or Russia's surface water is east of the Urals, in Siberia. The sparsely-populated region is traversed by 40 rivers longer than 1,000 km. Combined, the Ob, Yenisey and Lena rivers cover a drainage area of about 8 million km2, discharging nearly 50,000 m3 of water per second in the Arctic. Image: Grasshopper Geography
The images and our best computer models don't agree.
A trio of intriguing galaxy clusters<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yNDQzNDA0OS9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYxNTkzNzUyOH0.0IRzkzvKsmPEHV-v1dqM1JIPhgE2W-UHx0COuB0qQnA/img.jpg?width=980" id="d69be" class="rm-shortcode" data-rm-shortcode-id="2d2664d9174369e0a06540cb3a3a9079" data-rm-shortcode-name="rebelmouse-image" />
The three galaxy clusters imaged for the study
Mapping dark matter<span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="d904b585c806752f261e1215014691a6"><iframe type="lazy-iframe" data-runner-src="https://www.youtube.com/embed/fO0jO_a9uLA?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span><p>The assumption has been that the greater the lensing effect, the higher the concentration of dark matter.</p><p>As scientists analyzed the clusters' large-scale lensing — the massive arc and elongation visual effects produced by dark matter — they noticed areas of smaller-scale lensing within that larger distortion. The scientists interpret these as concentrations of dark matter within individual galaxies inside the clusters.</p><p>The researchers used spectrographic data from the VLT to determine the mass of these smaller lenses. <a href="https://www.oas.inaf.it/en/user/pietro.bergamini/" target="_blank" rel="noopener noreferrer">Pietro Bergamini</a> of the INAF-Observatory of Astrophysics and Space Science in Bologna, Italy explains, "The speed of the stars gave us an estimate of each individual galaxy's mass, including the amount of dark matter." The leader of the spectrographic aspect of the study was <a href="http://docente.unife.it/docenti-en/piero.rosati1/curriculum?set_language=en" target="_blank">Piero Rosati</a> of the Università degli Studi di Ferrara, Italy who recalls, "the data from Hubble and the VLT provided excellent synergy. We were able to associate the galaxies with each cluster and estimate their distances." </p><p>This work allowed the team to develop a thoroughly calibrated, high-resolution map of dark matter concentrations throughout the three clusters.</p>
But the models say...<p>However, when the researchers compared their map to the concentrations of dark matter computer models predicted for galaxies bearing the same general characteristics, something was <em>way</em> off. Some small-scale areas of the map had 10 times the amount of lensing — and presumably 10 times the amount of dark matter — than the model predicted.</p><p>"The results of these analyses further demonstrate how observations and numerical simulations go hand in hand," notes one team member, <a href="https://nena12276.wixsite.com/elenarasia" target="_blank">Elena Rasia</a> of the INAF-Astronomical Observatory of Trieste, Italy. Another, <a href="http://adlibitum.oats.inaf.it/borgani/" target="_blank" rel="noopener noreferrer">Stefano Borgani</a> of the Università degli Studi di Trieste, Italy, adds that "with advanced cosmological simulations, we can match the quality of observations analyzed in our paper, permitting detailed comparisons like never before."</p><p>"We have done a lot of testing of the data in this study," Meneghetti says, "and we are sure that this mismatch indicates that some physical ingredient is missing either from the simulations or from our understanding of the nature of dark matter." <a href="https://physics.yale.edu/people/priyamvada-natarajan" target="_blank">Priyamvada Natarajan</a> of Yale University in Connecticut agrees: "There's a feature of the real Universe that we are simply not capturing in our current theoretical models."</p><p>Given that any theory in science lasts only until a better one comes along, Natarajan views the discrepancy as an opportunity, saying, "this could signal a gap in our current understanding of the nature of dark matter and its properties, as these exquisite data have permitted us to probe the detailed distribution of dark matter on the smallest scales."</p><p>At this point, it's unclear exactly what the conflict signifies. Do these smaller areas have unexpectedly high concentrations of dark matter? Or can dark matter, under certain currently unknown conditions, produce a tenfold increase in lensing beyond what we've been expecting, breaking the assumption that more lensing means more dark matter?</p><p>Obviously, the scientific community has barely begun to understand this mystery.</p>
Scientists have found evidence of hot springs near sites where ancient hominids settled, long before the control of fire.