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  • richardmitnick 12:37 pm on December 8, 2020 Permalink | Reply
    Tags: , Entangled quantum systems, , , , , , The Casimir effect, Three of the four fundamental forces in physics can be described in terms of quantum theory. This is not the case for the fourth force (gravity).,   

    From University of Gronigen [Rijksuniversiteit Groningen] (NL) via phys.org: “Experiment to test quantum gravity just got a bit less complicated” 

    From University of Gronigen [Rijksuniversiteit Groningen] (NL)

    via


    phys.org

    December 8, 2020

    1
    In the proposed experiment, two diamonds are each placed in superposition and studied in freefall. Apart from gravity, the Casimir effect also draws them together, causing noise in the experiment. A thin copper plate can shield this effect, reducing the noise and making the experiment more manageable. Credit: A. Mazumdar, University of Groningen.

    Is gravity a quantum phenomenon? That has been one of the big outstanding questions in physics for decades. Together with colleagues from the UK, Anupam Mazumdar, a physicist from the University of Groningen, proposed an experiment that could settle the issue. However, it requires studying two very large entangled quantum systems in freefall. In a new paper
    [Physical Review A], which has a third-year Bachelor’s student as the first author, Mazumdar presents a way to reduce background noise to make this experiment more manageable.

    Three of the four fundamental forces in physics can be described in terms of quantum theory. This is not the case for the fourth force (gravity), which is described by Einstein’s theory of general relativity. The experiment that Mazumdar and his colleagues previously designed could prove or disprove the quantum nature of gravity.

    Superposition

    A well-known consequence of the quantum theory is the phenomenon called quantum superposition: in certain situations, quantum states can have two different values at the same time. Take an electron that is irradiated with laser light. Quantum theory says that it can either absorb or not absorb the photon energy from the light. Absorbing the energy would alter the electron’s spin, a magnetic moment that can be either up or down. The result of quantum superposition is that the spin is both up and down.

    These quantum effects take place in tiny objects, such as electrons. By targeting an electron in a specially constructed miniature diamond, it is possible to create superposition in a much larger object. The diamond is small enough to sustain this superposition, but also large enough to feel the pull of gravity. This characteristic is what the experiment exploits: placing two of these diamonds next to each other in freefall and, therefore, canceling out external gravity. This means that they only interact through the gravity between them.

    Challenging

    And that is where another quantum phenomenon comes in. Quantum entanglement means that when two or more particles are generated in close proximity, their quantum states are linked. In the case of the diamonds, if one is spin up, the other, entangled diamond should be spin down. So, the experiment is designed to determine whether quantum entanglement occurs in the pair during freefall, when the force of the gravity between the diamonds is the only way that they interact.

    “However, this experiment is very challenging,” explains Mazumdar. When two objects are very close together, another possible mechanism for interaction is present, the Casimir effect. In a vacuum, two objects can attract each other through this effect. “The size of the effect is relatively large and to overcome the noise it creates, we would have to use relatively large diamonds.” It was clear from the outset that this noise should be reduced to make the experiment more manageable. Therefore, Mazumdar wanted to know if shielding for the Casimir effect was possible.

    Lockdown

    He handed the problem to Thomas van de Kamp, a third-year Bachelor’s student of Physics. “He came to me because he was interested in quantum gravity and wanted to do a research project for his Bachelor’s thesis,” says Mazumdar. During the spring lockdown, when most normal classes were suspended, Van de Kamp started working on the problem. “Within a remarkably short time, he presented his solution, which is described in our paper.”

    This solution is based on placing a conducting plate of copper, around one millimeter thick, between the two diamonds. The plate shields the Casimir potential between them. Without the plate, this potential would draw the diamonds closer to each other. But with the plate, the diamonds are no longer attracted to each other, but to the plate between them. Mazumdar: “This removes the interaction between the diamonds through the Casimir effect, and therefore removes a lot of noise from the experiment.”

    Remarkable

    The calculations performed by Van de Kamp show that the masses of the two diamonds can be reduced by two orders of magnitude. “It may seem like a small step, but it does make the experiment less demanding.” Furthermore, other parameters such as the level of vacuum needed during the experiment also become less demanding due to the shielding of the Casimir effect. Mazumdar says that a further update on the experiment, which also includes a contribution from Bachelor’s student Thomas van de Kamp, will probably appear in the near future. “So, his six-month project has brought him co-authorship on two papers, quite a remarkable feat.”

    See the full article here.

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    Stem Education Coalition

    The University of Gronigen [Rijksuniversiteit Groningen] (NL) is a public research university in the city of Groningen in the Netherlands. The university was founded in 1614 and is the second-oldest university in the Netherlands. In 2014, the university celebrated its 400th anniversary. Currently, RUG is placed in the top 100 universities worldwide according to three international ranking tables.

    The university was ranked 65th in the world, according to Academic Ranking of World Universities (ARWU) in 2019. In April 2013, according to the results of the International Student Barometer, the University of Groningen, for the third time in a row, was voted the best university of the Netherlands.

    The University of Groningen has eleven faculties, nine graduate schools, 27 research centres and institutes, and more than 175-degree programmes. The university’s alumni and faculty include Johann Bernoulli, Aletta Jacobs, four Nobel Prize winners, nine Spinoza Prize winners, one Stevin Prize winner, royalty, multiple mayors, the first president of the European Central Bank, and a secretary general of NATO.

     
  • richardmitnick 6:03 pm on July 3, 2017 Permalink | Reply
    Tags: Delbrück scattering, , , , Polarized gamma rays, , The Casimir effect, The future Extreme Light Infrastructure in Măgurele Romania, Vacuum studies, Werner Heisenberg's Uncertainty Principle   

    From Inside Science via Don Lincoln at FNAL: “A Study About Nothing” 

    Inside Science

    June 29, 2017
    Yuen Yiu

    1
    Image credits: Abigail Malate

    Scientists find new ways to measure the infinitesimally small fluctuations that exist in a vacuum.

    A vacuum is a space absolutely devoid of matter, at least according to the Merriam-Webster dictionary. But if you talk to a physicist you may get a different answer. According to quantum physics, even vacuums are not completely empty. Constant fluctuations in energy can spontaneously create mass not just out of thin air, but out of absolutely nothing at all.

    “It’s like a boiling sea of appearing and disappearing particle pairs,” said James Koga, a theoretical physicist from the National Institutes for Quantum and Radiological Science and Technology in Kyoto, Japan. The pairs, made up of one particle and one antiparticle, exist for only moments. Koga is investigating the subtle effects caused by these fluctuations.

    This peculiar nature of vacuum, sometimes referred to as “quantum vacuum,” is not just theoretical speculation. It has real, measurable effects on our physical reality. Although these effects are usually far too small to impact even the most sensitive instruments of today, scientists think the picture will change for the miniaturized technologies of tomorrow.

    “In the macroscopic world, we don’t care about these forces at all. You wouldn’t care about it when you are driving a car for instance. It’s totally negligible,” said Alejandro Manjavacas, a physicist specializing in photonics at the University of New Mexico in Albuquerque. “But in the context of nanotechnology or nanophotonics — at a super small scale, these effects will start playing a role.”

    Although the concept of a fluctuating vacuum was theorized and proven during the first half of the last century, scientists are still grappling with the implications. Two recently published papers explore two separate aspects of the same mystery — what happens when there is nothing at all?

    A glistening ocean

    The energy fluctuation in vacuum can be explained by the uncertainty principle of quantum physics. The principle, first introduced by German physicist Werner Heisenberg, states that at any definite point in space, there must exist temporary changes in energy over time. Sometimes this energy is converted into mass, generating particle-antiparticle pairs.

    Most of the time these newly born pairs recombine and vanish before interacting with anything. Because of this, physicists like to refer to these pairs as “virtual particles,” but this doesn’t mean they aren’t real — they just need something to interact with to make their presence felt.

    For this, Koga and his team envision a way to observe this boiling sea of vacuum the same way we see glistening waves in the ocean — with light. In their latest paper, published in Physical Review Letters, they lay down the theoretical groundwork needed for the experiment. Specifically, they want to study photons that bounce off an atomic nucleus in a distinctive way that wouldn’t happen without the “boiling” vacuum acting as the middleman. This peculiar light phenomenon is known as Delbrück scattering, predicted by German-American physicist Max Delbrück in 1933. The effect was later observed experimentally in 1975 — but just barely.

    “[Scientists] could kind of guess that the Delbrück scattering was there, but it was like if you include this effect in your calculation then it agrees more with the data,” said Koga.

    Koga and his team hope to take Delbrück scattering to another level by characterizing the phenomenon’s effect. It is as if scientists knew about air resistance, but still needed to study it further so that engineers could use the knowledge to build an airplane.

    The task is tricky. To measure Delbrück scattering, one must shine light onto trillions of atomic nuclei, which creates a problem. Photons bounce off nuclei, electrons and even each other in all directions, via all kinds of different interactions. How can one distinguish which photon is scattered from what?

    Koga’s team suggests that we use polarized gamma rays. Just like polarized sunglasses can help you see better by filtering out unwanted solar glares, polarized gamma rays can help scientists sift through the gazillions of photons based on their polarization, in addition to energy and scattered angle. As long as one knows where to look for the specific photons that are the results of Delbrück scattering, one should be able to pick them out from the lineup.

    “The point that we are trying to make in our paper is by using a new polarized source, you can almost see the signal isolated,” said Koga.

    But there is just one problem — such an instrument doesn’t exist. At least not yet.

    Enter the future Extreme Light Infrastructure in Măgurele, Romania. This facility will not only provide the polarized gamma rays Koga proposed, but will make some of the brightest gamma rays in the world. This is important because just like a brighter ambient light can shorten the exposure time for taking a photo, a brighter gamma ray can shorten the run time for Koga’s proposed experiment.


    Credit: ELI-NP Romania

    Kazuo Tanaka, the scientific director of the Nuclear Physics division of the future facility, is pleased with Koga’s team’s proposal.

    “I think their proposal is very crystal clear. They calculated how many days of shooting they need for the experiment, and came up with 76 days,” he said. “I think if they do the experiment we can have a very definitive measurement for Delbrück scattering.”

    While the facility is still under construction, and will not be ready for the experiment at least until 2019, a different group of physicists are studying the same nothingness of vacuum, but with a different set of eyes. Instead of beaming light into the vacuum and looking for a glint, physicist Alejandro Manjavacas and his group at the University of New Mexico want to know if the fluctuations of vacuum can actually exert an invisible force on physical objects — as if they were being moved by Jedis.


    The video shows two plates moving towards each other in a vibrating pool of water, an analogy to the Casimir effect that exist in a fluctuating vacuum. Credit: Denysbondar

    The Casimir effect, named after Dutch physicist Henrik Casimir, describes the force that pushes two objects together due to surrounding waves. The effect exists for two beads on a vibrating string, or two boats in a wavy ocean, as well as two particles in a fluctuating vacuum. Much like Delbrück scattering, the Casimir effect was theorized in 1948 and has already been confirmed, in 1996. So, what is left to be discovered?

    “Most of the work that was done on Casimir effect was for systems that weren’t moving, or if they were moving, they were moving in a uniform motion,” said Manjavacas.

    In a paper published in Physical Review Letters, Manjavacas and his colleagues calculated how the Casimir effect can nudge objects that are already spinning and moving. Through calculations, they discovered that when a tiny sphere spins near a flat surface, it will move as if it is rolling down the surface, despite never making contact with it.

    “If you try to make a nanostructure that involves moving parts that are very close together, it is crucial to know what is going to be the effect from these type of forces. You’ll need to know whether it is going to cause the moving parts to get stuck,” said Manjavacas. “Or we can use these forces to our advantage, such as using them to move objects or to force them to do the things that we want.”

    In their study, the researchers evaluated the effect for spheres with diameters ranging from 50 to 500 nanometers, much less than one hundredth the width of a human hair. As expected, the relationship between the spinning and the lateral movement isn’t straightforward — it depends on the speed that the sphere is spinning, as well as the size of the sphere and the distance between the sphere and the surface. These minute effects may soon be relevant on the frontier of technology, for example when engineers design medical nanobots.

    2
    Virtual Particles and Black Holes
    The sidebar image shows a simulated animation of a black hole moving across a galaxy in the background. Credit: Wikicommons/CC BY-SA 3.0
    Even though the quantum interpretation of vacuum — complete with strange particles popping into and out of existence — accurately describes our reality, how can we tell that this isn’t just another placeholder theory? Will the theory eventually fail just like the geocentric model, or the flat earth model, or perhaps most relevantly, the famous failed theory of ether from the 19th century?
    The theory of ether was proposed by physicists to explain how light waves can propagate through the vacuum of space. Based on intuition, scientists back then believed that a medium was necessary for light waves to travel, just like the waves in the ocean travel through the medium of water. This hypothesis was disproved in 1887 by Albert Michelson and Edward Morley, in a famous experiment, in which they measured the speed of light in perpendicular directions and found no difference. Albert Michelson was later awarded a Nobel Prize in 1907 for his achievements, and became the first Nobel laureate from the United States.

    So, will the quantum model of vacuum also be proved wrong? Most physicists today do not think so. In fact, Nobel laureate Robert Laughlin from Stanford University has written in his book “A Different Universe: Reinventing Physics from the Bottom Down” specifically about this comparison: “The word [ether] has extremely negative connotations in theoretical physics because of its past association with opposition to relativity. This is unfortunate because, stripped of these connotations, it

    Beyond its impact on nanotechnologies and particle accelerators here on earth, the fluctuating vacuum extends its effects into space. In 1968, British astrophysicist Stephen Hawking predicted that when a particle-antiparticle pair is created on the edge of a black hole’s event horizon, the pair can be pried apart by gravity — one particle falling into the black hole and the other escaping. The escape of one of the particles then contributes to an infinitesimally small, and so far purely theoretical, radiation known as Hawking radiation.
    Hawking radiation, if proven, will play a crucial role in determining the lifetime of black holes. However, even if the radiation is real, it will still be far too faint for us to detect it. There have been a few analogous models that can successfully reproduce the phenomenon in a laboratory setting, but they use light waves or sound waves instead of gravitational waves of black holes. There is hope that the Large Hadron Collider near Geneva, Switzerland, with a higher energy output, can create a super tiny black hole that lasts but a split second, and offer a more definitive answer on Hawking radiation. But for now, no direct observation for Hawking radiation has been possible, leading to some saying that the “jury is still out.”
    “This is a pity, because if they had, I would have got a Nobel prize,” said Hawking during a 2008 lecture.

    A real virtuality

    Even though the quantum interpretation of vacuum — complete with strange particles popping into and out of existence — accurately describes our reality, how can we tell that this isn’t just another placeholder theory? Will the theory eventually fail just like the geocentric model, or the flat earth model, or perhaps most relevantly, the famous failed theory of ether from the 19th century?

    The theory of ether was proposed by physicists to explain how light waves can propagate through the vacuum of space. Based on intuition, scientists back then believed that a medium was necessary for light waves to travel, just like the waves in the ocean travel through the medium of water. This hypothesis was disproved in 1887 by Albert Michelson and Edward Morley, in a famous experiment, in which they measured the speed of light in perpendicular directions and found no difference. Albert Michelson was later awarded a Nobel Prize in 1907 for his achievements, and became the first Nobel laureate from the United States.

    So, will the quantum model of vacuum also be proved wrong? Most physicists today do not think so. In fact, Nobel laureate Robert Laughlin from Stanford University has written in his book “A Different Universe: Reinventing Physics from the Bottom Down” specifically about this comparison: “The word [ether] has extremely negative connotations in theoretical physics because of its past association with opposition to relativity. This is unfortunate because, stripped of these connotations, it rather nicely captures the way most physicists actually think about the vacuum.”

    Because unlike the ether theory, the quantum model of vacuum, with all its fluctuations and peculiar features, has since been thoroughly tested and proven.

    “We see pair creation all the time actually, like in particle accelerators,” said Koga. In fact, it happens so often that for certain experiments scientists actually have to consider the phenomenon as “noise” that could obscure the signal they are looking for, according to Koga.

    “We now have experimental evidence of all kinds of particles coming in and out [of the vacuum],” said Toshiki Tajima, a physicist from the University of California, Irvine. “Muons and anti-muons, protons and anti-protons, and even quarks and anti-quarks.”

    In 1665, Robert Hooke and Antoni van Leeuwenhoek discovered microbes when they pointed their microscopes at “nothing.” In 1964, Arno Penzias and Robert Woodrow Wilson discovered the cosmic microwave background when they pointed their telescopes at “nothing.” Vacuum is perhaps the ultimate “nothing,” so if history is any indication, “nothing” is an interesting place, especially if you want to look for something.

    See the full article here .

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    Inside Science is brought to you in part through the generous support of The American Physical Society and The Acoustical Society of America and a coalition of underwriters.

     
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