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How it works: illustration of the quantum twisting microscope in action. Electrons tunnel from the probe (inverted pyramid at the top) to the sample (bottom) in several places at once (green vertical lines) in a quantum-coherent manner. (Courtesy: Weizmann Institute of Science)

Topics: Chemistry, Entanglement, Materials Science, Nanotechnology, Quantum Mechanics

When the scanning tunneling microscope debuted in the 1980s, the result was an explosion in nanotechnology and quantum-device research. Since then, other types of scanning probe microscopes have been developed, and together they have helped researchers flesh out theories of electron transport. But these techniques probe electrons at a single point, thereby observing them as particles and only seeing their wave nature indirectly. Now, researchers at the Weizmann Institute of Science in Israel have built a new scanning probe – the quantum twisting microscope – that detects the quantum wave characteristics of electrons directly.

“It’s effectively a scanning probe tip with an interferometer at its apex,” says Shahal Ilani, the team leader. The researchers overlay a scanning probe tip with ultrathin graphite, hexagonal boron nitride, and a van der Waals crystal such as graphene, which conveniently flopped over the tip like a tent with a flat top about 200 nm across. The flat end is key to the device’s interferometer function.  Instead of an electron tunneling between one point in the sample and the tip, the electron wave function can tunnel across multiple points simultaneously.

“Quite surprisingly, we found that the flat end naturally pivots so that it is always parallel with the sample,” says John Birkbeck, the corresponding author of a paper describing this work. This is fortunate because any tilt would alter the tunneling distance and hence strength from one side of the plateau to the other. “It is the interference of these tunneling paths, as identified in the measured current, that gives the device its unique quantum-wave probing function,” says Birkbeck.

Scanning probe with a twist observes the electron’s wavelike behavior, Anna Demming, Physics World

Credit: Petrovich9/Getty Images

Topics: Entanglement, Particle Physics, Quantum Mechanics, Research, Theoretical Physics

Reference: Albert Einstein colorfully dismissed quantum entanglement—the ability of separated objects to share a condition or state—as “spooky action at a distance.” Science.org

For the first time, scientists have observed quantum interference—a wavelike interaction between particles related to the weird quantum phenomenon of entanglement—occurring between two different kinds of particles. The discovery could help physicists understand what goes on inside an atomic nucleus.

Particles act as both particles and waves. And interference is the ability of one particle’s wavelike action to diminish or amplify the action of other quantum particles like two boat wakes crossing in a lake. Sometimes the overlapping waves add up to a bigger wave, and sometimes they cancel out, erasing it. This interference occurs because of entanglement, one of the weirder aspects of quantum physics, which was predicted in the 1930s and has been experimentally observed since the 1970s. When entangled, the quantum states of multiple particles are linked so that measurements of one will correlate with measurements of the others, even if one is on Jupiter and another is on your front lawn.

Dissimilar particles can sometimes become entangled, but until now, these [mismatched] entangled particles weren’t known to interfere with one another. That’s because part of measuring interference relies on two wavelike particles being indistinguishable from each other. Imagine two photons, or particles of light, from two separate sources. If you were to detect these photons, there would be no way to determine which source each came from because there is no way to tell which photon is which. Thanks to the quantum laws governing these very small particles, this ambiguity is actually measurable: all the possible histories of the two identical photons interfere with one another, creating new patterns in particles’ final wavelike actions.

Scientists See Quantum Interference between Different Kinds of Particles for the First Time, Stephanie Pappas, Scientific American

Credit: Matt Harrison Clough (original image at link)

Topics: Entanglement, High Energy Physics, Particle Physics, Quantum Mechanics

Breaking the rules is exciting, especially if they have been held for a long time. This is true not just in life but also in particle physics. Here the rule I’m thinking of is called “lepton flavor universality,” and it is one of the predictions of our Standard Model of particle physics, which describes all the known fundamental particles and their interactions (except for gravity). For several decades after the invention of the Standard Model, particles seemed to obey this rule.

Things started to change in 2004 when the E821 experiment at Brookhaven National Laboratory on Long Island announced its measurement of a property of the muon—a heavy version of the electron—known as its g-factor. The measurement wasn’t what the Standard Model predicted. Muons and electrons are both parts of a class of particles called leptons (along with a third particle, the tau, as well as the three generations of neutrinos). The rule of lepton flavor universality says that because electrons and muons are charged leptons, they should all interact with other particles in the same way (barring small differences related to the Higgs particle). If they don’t, then they violate lepton flavor universality—and the unexpected g-factor measurement suggested that’s just what was happening.

If particles really were breaking this rule, that would be exciting in its own right and also because physicists believe that the Standard Model can’t be the ultimate theory of nature. The theory doesn’t explain why neutrinos have mass, what makes up the invisible dark matter that seems to dominate the cosmos, or why matter won out over antimatter in the early universe. Therefore, the Standard Model must be merely an approximate description that we will need to supplement by adding new particles and interactions. Physicists have proposed a huge number of such extensions, but at most one of these theories can be correct, and so far none of them has received any direct confirmation. A measured violation of the Standard Model would be a flashlight pointing the way toward this higher theory we seek.

Rule-Breaking Particles Pop Up in Experiments around the World, Andreas Crivellin, Scientific American

Image source: CERN - accelerating science

Topics: CERN, Condensed Matter Physics, Entanglement, Lasers, Quantum Mechanics

Much of modern experimental physics relies on a counterintuitive principle: Under the right circumstances, zapping matter with a laser doesn’t inject energy into the system; rather, it sucks the energy out. By cooling the system to a fraction of a degree above absolute zero, one can observe quantum effects that are otherwise invisible.

Laser cooling works like a charm, but only when a system’s ladder of quantum states is just right. Atoms of alkali metals and a few other elements are ideal. Molecules, with their multitudes of energy levels, pose a much greater challenge. And fundamental particles such as protons, which lack internal states altogether, can’t be laser-cooled at all.

Nevertheless, there’s a lot of interest in experimenting on protons at low temperature—in particular, precisely testing how their mass, magnetic moment, and other properties compare with those of antiprotons. Toward that end, the Baryon Antibaryon Symmetry Experiment (BASE) collaboration has now demonstrated a method for using a cloud of laser-cooled beryllium ions to sympathetically cool a single proton, even when the proton and ions are too distant to directly interact.

A superconducting circuit is a cooling teleporter, Johanna L. Miller, Physics Today

Image Source: Link below

Topics: Astrophysics, Electromagnetic Radiation, Entanglement, SETI

When we gaze up at the night sky, we might be accidentally eavesdropping on an alien conversation.

At least, that’s according to Imperial College London quantum physicist Terry Rudolph, who last week published preprint research theorizing that an advanced extraterrestrial civilization might alter the light coming off stars in order to communicate across a great distance, almost like a series of interstellar smoke signals.

The physics of the ordeal gets a bit dense — which is probably reasonable if aliens are rapidly communicating across star systems — but the basic idea is to use entangled photons from different stars to transmit messages that appear to be random twinkling to any nosy onlookers.

Roaming Charges

The idea, Rudolph notes, is technically possible as far as the physics are concerned, but pure speculation when it comes to any discussion of alien technology. But as he writes in the paper, any entangled communication among stars “can be rendered in principle indiscernible to those of us excluded from the conversation.”

So if there were a mega-advanced civilization out there colonizing the Milky Way galaxy, communication along the lines of what Rudolph has proposed could explain why we haven’t found any evidence of life beyond Earth.

Scientists Claim That Aliens May Be Communicating Via Starlight, Dan Robitzski, Futurism

Physicists take first-ever photo of quantum entanglement. Credit: University of Glasgow/CC by 4.0

Topics: Einstein, Entanglement, Laser, Quantum Mechanics

'Spooky' Quantum Entanglement Finally Captured in Stunning Photo
Yasemin Saplakoglu, Live Science