{"id":24908,"date":"2024-04-04T11:42:57","date_gmt":"2024-04-04T05:57:57","guid":{"rendered":"https:\/\/www.revoscience.com\/en\/?p=24908"},"modified":"2024-04-04T11:43:04","modified_gmt":"2024-04-04T05:58:04","slug":"mit-researchers-discover-neutronic-molecules","status":"publish","type":"post","link":"https:\/\/www.revoscience.com\/en\/mit-researchers-discover-neutronic-molecules\/","title":{"rendered":"MIT researchers discover \u201cneutronic molecules\u201d"},"content":{"rendered":"\n

Study shows neutrons can bind to nanoscale atomic clusters known as quantum dots. The finding may provide insights into material properties and quantum effects.<\/strong><\/p>\n\n\n\n

\"\"<\/figure>\n\n\n

By David L. Chandler<\/p><\/div><\/div>\n\n\n

CAMBRIDGE, Mass. — Neutrons are subatomic particles that have no electric charge, unlike protons and electrons. That means that while the electromagnetic force is responsible for most of the interactions between radiation and materials, neutrons are essentially immune to that force.<\/p>\n\n\n\n

Instead, neutrons are held together inside an atom\u2019s nucleus solely by something called the strong force, one of the four fundamental forces of nature. As its name implies, the force is indeed very strong, but only at very close range \u2014 it drops off so rapidly as to be negligible beyond 1\/10,000 the size of an atom. But now, researchers at MIT have found that neutrons can actually be made to cling to particles called quantum dots, which are made up of tens of thousands of atomic nuclei, held there just by the strong force.<\/p>\n\n\n\n

The new finding may lead to useful new tools for probing the basic properties of materials at the quantum level, including those arising from the strong force, as well as exploring new kinds of quantum information processing devices. The work is reported this week in the journal ACS Nano<\/em><\/a>, in a paper by MIT graduate students Hao Tang and Guoqing Wang and MIT professors Ju Li and Paola Cappellaro of the Department of Nuclear Science and Engineering.<\/p>\n\n\n\n

Neutrons are widely used to probe material properties using a method called neutron scattering, in which a beam of neutrons is focused on a sample, and the neutrons that bounce off the material\u2019s atoms can be detected to reveal the material\u2019s internal structure and dynamics. <\/p>\n\n\n\n

But until this new work, nobody thought that these neutrons might actually stick to the materials they were probing. \u201cThe fact that [the neutrons] can be trapped by the materials, nobody seems to know about that,\u201d says Li, who is also a professor of materials science and engineering. \u201cWe were surprised that this exists, and that nobody had talked about it before, among the experts we had checked with,\u201d he says.<\/p>\n\n\n\n

The reason this new finding is so surprising, Li explains, is because neutrons don\u2019t interact with electromagnetic forces. Of the four fundamental forces, gravity and the weak force \u201care generally not important for materials,\u201d he says. \u201cPretty much everything is electromagnetic interaction, but in this case, since the neutron doesn\u2019t have a charge, the interaction here is through the strong interaction, and we know that is very short-range. It is effective at a range of 10 to the minus 15 power,\u201d or one quadrillionth, of a meter.<\/p>\n\n\n\n

\u201cIt\u2019s very small, but it\u2019s very intense,\u201d he says of this force that holds the nuclei of atoms together. \u201cBut what\u2019s interesting is we\u2019ve got these many thousands of nuclei in this neutronic quantum dot, and that\u2019s able to stabilize these bound states, which have much more diffuse wavefunctions at tens of nanometers [billionths of a meter].  These neutronic bound states in a quantum dot are actually quite akin to Thomson\u2019s plum pudding model of an atom, after his discovery of the electron.\u201d<\/p>\n\n\n\n

It was so unexpected, Li calls it \u201ca pretty crazy solution to a quantum mechanical problem.\u201d The team calls the newly discovered state an artificial \u201cneutronic molecule.\u201d<\/p>\n\n\n\n

These neutronic molecules are made from quantum dots, which are tiny crystalline particles, collections of atoms so small that their properties are governed more by the exact size and shape of the particles than by their composition. The discovery and controlled production of quantum dots were the subject of the 2023 Nobel Prize in Chemistry, awarded to MIT Professor Moungi Bawendi<\/a> and two others.<\/p>\n\n\n\n

\u201cIn conventional quantum dots, an electron is trapped by the electromagnetic potential created by a macroscopic number of atoms, thus its wavefunction extends to about 10 nanometers, much larger than a typical atomic radius,\u201d says Cappellaro. \u201cSimilarly, in these nucleonic quantum dots, a single neutron can be trapped by a nanocrystal, with a size well beyond the range of the nuclear force, and display similar quantized energies.\u201d While these energy jumps give quantum dots their colors, the neutronic quantum dots could be used for storing quantum information. <\/p>\n\n\n\n

This work is based on theoretical calculations and computational simulations. \u201cWe did it analytically in two different ways, and eventually also verified it numerically,\u201d Li says. Although the effect had never been described before, he says, in principle there\u2019s no reason it couldn\u2019t have been found much sooner: \u201cConceptually, people should have already thought about it,\u201d he says, but as far as the team has been able to determine, nobody did.<\/p>\n\n\n\n

Part of the difficulty in doing the computations is the very different scales involved: The binding energy of a neutron to the quantum dots they were attaching to is about one-trillionth that of previously known conditions where the neutron is bound to a small group of nuclei. For this work, the team used an analytical tool called Green\u2019s function to demonstrate that the strong force was sufficient to capture neutrons with a quantum dot with a minimum radius of 13 nanometers.<\/p>\n\n\n\n

Then, the researchers did detailed simulations of specific cases, such as the use of a lithium hydride nanocrystal, a material being studied as a possible storage medium for hydrogen. They showed that the binding energy of the neutrons to the nanocrystal is dependent on the exact dimensions and shape of the crystal, as well as the nuclear spin polarizations of the nuclei compared to that of the neutron. They also calculated similar effects for thin films and wires of the material as opposed to particles.<\/p>\n\n\n\n

But Li says that actually creating such neutronic molecules in the lab, which among other things requires specialized equipment to maintain temperatures in the range of a few thousandths of a Kelvin above absolute zero, is something that other researchers with the appropriate expertise will have to undertake.<\/p>\n\n\n\n

Li notes that \u201cartificial atoms\u201d made up of assemblages of atoms that share properties and can behave in many ways like a single atom have been used to probe many properties of real atoms. Similarly, he says, these artificial molecules provide \u201can interesting model system\u201d that might be used to study \u201cinteresting quantum mechanical problems that one can think about,\u201d such as whether these neutronic molecules will have a shell structure that mimics the electron shell structure of atoms.<\/p>\n\n\n\n

\u201cOne possible application,\u201d he says, \u201cis maybe we can precisely control the neutron state. By changing the way the quantum dot oscillates, maybe we can shoot the neutron off in a particular direction.\u201d Neutrons are powerful tools for such things as triggering both fission and fusion reactions, but so far it has been difficult to control individual neutrons. These new bound states could provide much greater degrees of control over individual neutrons, which could play a role in the development of new quantum information systems, he says.<\/p>\n\n\n\n

\u201cOne idea is to use it to manipulate the neutron, and then the neutron will be able to affect other nuclear spins,\u201d Li says. In that sense, he says, the neutronic molecule could serve as a mediator between the nuclear spins of separate nuclei \u2014 and this nuclear spin is a property that is already being used as a basic storage unit, or qubit, in developing quantum computer systems.<\/p>\n\n\n\n

\u201cThe nuclear spin is like a stationary qubit, and the neutron is like a flying qubit,\u201d he says. \u201cThat\u2019s one potential application.\u201d He adds that this is \u201cquite different from electromagnetics-based quantum information processing, which is so far the dominant paradigm. So, regardless of whether it\u2019s superconducting qubits or it\u2019s trapped ions or nitrogen vacancy centers, most of these are based on electromagnetic interactions.\u201d In this new system, instead, \u201cwe have neutrons and nuclear spin. We\u2019re just starting to explore what we can do with it now.\u201d<\/p>\n\n\n\n

Another possible application, he says, is for a kind of imaging, using neutral activation analysis. \u201cNeutron imaging complements X-ray imaging because neutrons are much more strongly interacting with light elements,\u201d Li says. It can also be used for materials analysis, which can provide information not only about elemental composition but even about the different isotopes of those elements. \u201cA lot of the chemical imaging and spectroscopy doesn\u2019t tell us about the isotopes,\u201d whereas the neutron-based method could do so, he says.<\/p>\n\n\n\n

The research was supported by the U.S. Office of Naval Research.<\/p>\n","protected":false},"excerpt":{"rendered":"

Study shows neutrons can bind to nanoscale atomic clusters known as quantum dots. The finding may provide insights into material properties and quantum effects. CAMBRIDGE, Mass. — Neutrons are subatomic particles that have no electric charge, unlike protons and electrons. That means that while the electromagnetic force is responsible for most of the interactions between […]<\/p>\n","protected":false},"author":2,"featured_media":24909,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[17,121],"tags":[],"class_list":["post-24908","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-research","category-physics"],"featured_image_urls":{"full":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/04\/MIT-Neutronic-Molecule-01-press_0.jpg",900,600,false],"thumbnail":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/04\/MIT-Neutronic-Molecule-01-press_0-200x200.jpg",200,200,true],"medium":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/04\/MIT-Neutronic-Molecule-01-press_0-600x400.jpg",600,400,true],"medium_large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/04\/MIT-Neutronic-Molecule-01-press_0-768x512.jpg",750,500,true],"large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/04\/MIT-Neutronic-Molecule-01-press_0-675x450.jpg",675,450,true],"1536x1536":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/04\/MIT-Neutronic-Molecule-01-press_0.jpg",900,600,false],"2048x2048":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/04\/MIT-Neutronic-Molecule-01-press_0.jpg",900,600,false],"ultp_layout_landscape_large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/04\/MIT-Neutronic-Molecule-01-press_0.jpg",900,600,false],"ultp_layout_landscape":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/04\/MIT-Neutronic-Molecule-01-press_0-870x570.jpg",870,570,true],"ultp_layout_portrait":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/04\/MIT-Neutronic-Molecule-01-press_0-600x600.jpg",600,600,true],"ultp_layout_square":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/04\/MIT-Neutronic-Molecule-01-press_0-600x600.jpg",600,600,true],"newspaper-x-single-post":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/04\/MIT-Neutronic-Molecule-01-press_0-760x490.jpg",760,490,true],"newspaper-x-recent-post-big":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/04\/MIT-Neutronic-Molecule-01-press_0-550x360.jpg",550,360,true],"newspaper-x-recent-post-list-image":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/04\/MIT-Neutronic-Molecule-01-press_0-95x65.jpg",95,65,true],"web-stories-poster-portrait":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/04\/MIT-Neutronic-Molecule-01-press_0.jpg",640,427,false],"web-stories-publisher-logo":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/04\/MIT-Neutronic-Molecule-01-press_0.jpg",96,64,false],"web-stories-thumbnail":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/04\/MIT-Neutronic-Molecule-01-press_0.jpg",150,100,false]},"author_info":{"info":["By David L. Chandler"]},"category_info":"Research<\/a> Physics<\/a>","tag_info":"Physics","comment_count":"0","_links":{"self":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts\/24908","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/comments?post=24908"}],"version-history":[{"count":1,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts\/24908\/revisions"}],"predecessor-version":[{"id":24910,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts\/24908\/revisions\/24910"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/media\/24909"}],"wp:attachment":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/media?parent=24908"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/categories?post=24908"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/tags?post=24908"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}