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The Physics World Breakthrough Award 2021 was awarded to two separate teams that entangled two macroscopic vibrating mechanical drums, advancing our understanding of the boundaries between quantum and classical systems. The winners are Mika Sillanp and his colleagues at Aalto University in Finland and the University of New South Wales in Australia, as well as a team led by John Teufel and Shlomi Kotler of the National Institute of Standards and Technology (NIST).
The NIST researchers entangled the beats of the two mechanical drums — tiny aluminum membranes made up of about 1 trillion atoms — and precisely measured their associated quantum properties. Entangled pairs like these ( as shown in this colored microscopic diagram ) are enormous by quantum standards and could perform calculations and transmit data in large-scale quantum networks in the future. Image credit: J. Teufel/NIST
Quantum technology has come a long way over the past two decades, and physicists are now able to build and manipulate systems that were once in the realm of thought experimentation. A particularly fascinating approach to research is the blurred boundary between quantum physics and classical physics. In the past, it was clearly divided according to size: tiny objects such as photons and electrons existed in the quantum world, while large objects such as billiard balls followed classical physics.
For the past decade, physicists have been using drum-shaped mechanical resonators about 10 microns in diameter to push the limits of quanta. Unlike electrons or photons, these mechanical drums are macroscopic objects manufactured using standard micromachining techniques that look as solid as billiard balls in electron microscope images (see image above). However, despite the tangible nature of the resonators, researchers have been able to observe their quantum properties, for example, Teufel and colleagues placed a device in a quantum ground state in 2017.
This year, the team led by Teufel and Kotler, as well as Sillanp's independent team, went one step further, becoming the first to entangle two such drums with quantum mechanics. The two teams became entangled in different ways. The Finnish/Australian team used a specially selected resonant frequency to eliminate noise in the system that could interfere with the entangled state, while the NIST team's entanglement resembles a double qubit gate, where the form of the entangled state depends on the initial state of the drum.
Both teams have overcome significant experimental challenges, and their enormous efforts could open the door to entanglement resonators being used as quantum sensors or nodes in quantum networks. As such, this work deservedly became the first annual breakthrough related to quantum since 2015.
These drums present a collective quantum movement. Image credit: Mika Sillanp research team at Aalto University
This year, the site published nearly 600 of the latest research results, from which five Physics World editors selected this year's breakthrough of the year and nine runners-up. In addition to being reported by Physics World in 2021, the following criteria must also be met:
• Significant progress in knowledge or understanding
● The importance of work to scientific progress and/or practical application development
Physics World readers are generally interested
In the top ten breakthroughs in 2021, the other nine achievements have also been highly praised.
Edward Chang, David Moses, Sean Metzger, Jessie Liu and colleagues at the University of California, San Francisco, have developed a speech neural prosthesis that enables severely paralyzed people to communicate in sentences by translating brain signals directly into text on the screen. To achieve this, the research team used a dense array of electrodes implanted on the surface of the participants' brains to record electrical activity in multiple cortical regions involved in speech formation. Based on the vocabulary of 50 words that the system can recognize from patterns in recorded cortical activity, he was able to generate hundreds of short sentences. The technique shows an encouraging median decoding rate of 15.2 words per minute — about three times the computer-based typing interface he typically uses for communication.
A neural prosthesis recorded the activity of the cerebral cortex of participants as they tried to phrase words. Image credit: Todd Dubnicoff, UCSF
Sebastian Klembt of the University of Würzburg in Germany, Mordechai Segev of the Technion-Israel Institute of Technology and colleagues created an array of 30 vertical cavity surface emitting lasers (VCSELs) that act as a single coherent light source, paving the way for large-scale, high-power applications. The team used the principle of topological photonics to ensure that the light from each laser in the array passes through all the other lasers, forcing them to emit at the same frequency. The new design overcomes the power limitations of the previous generation of devices built by Segev and collaborators in 2018 and could in principle be expanded to include hundreds of individual lasers.
Omar Hurricane, Annie Kritcher, Alex Zylstra and Debbie Callahan of the California National Ignition Unit (NIF) and colleagues are one step closer to achieving the ultimate goal of "ignition.". Since NIF opened more than a decade ago, its long-term goal has been to prove that it can ignite — fusion reactions produce at least as much energy as their lasers put in. This includes self-sustaining reactions, in which α particles emitted during fusion also release heat, triggering further fusion. Operated by lawrence Livermore National Laboratory, the NIF shoots 192 pulsed laser beams into the inner surface of a centimeter-long hollow metal cylinder called a blackbody radiation cavity (hohlraum). Inside is a fuel capsule, which is a hollow sphere about 2 mm in diameter containing a thin layer of deuterium tritium. Experiments from 2009 to 2012 were far from reaching ignition, so researchers continued to improve. On Aug. 8 of this year, the researchers obtained an energy output of more than 1.3 MJ, which is about 70% of the energy transmitted by the laser pulse to the sample, a staggering result. While still falling short of breakeven, the figure far exceeds the previous around 0.1 MJ, a result that some experts describe as the most significant advance since inertial fusion began in 1972. Some experts have described this result as the most significant advance in inertial fusion since 1972.
Scientists at the $3.5 billion U.S. National Ignition Unit (NIF) are one step closer to achieving the ultimate goal of "ignition" — fusion reactions produce at least the same amount of energy provided by the laser system. Image source: NIF
Researchers at CERN's Antihydrogen Laser Physics Device (ALPHA) and baryonic antibasyonic symmetry experiment (BASE) collaborated on two independent studies proposing new ways to cool particles and antiparticles. These techniques could pave the way for the precise study of matter-antimatter asymmetries in the universe. The ALPHA collaboration demonstrated for the first time laser cooling of antihydrogen atoms. To achieve this, physicists have developed a new type of laser that generates a laser pulse of 121.6 nm to cool the antiatoms. They then measured critical electron transitions in antihydrogen with unprecedented precision, a breakthrough that could lead to improved testing of other key properties of antimatter. Meanwhile, the BASE researchers showed how heat can be extracted from individual protons by a superconducting circuit connected to a laser that cools an ion cloud a few centimeters away. They say the technique could be easily applied to antiprotons.
The Event Horizon Telescope Collaboration (EHT) was used to create the first image showing the polarization of light in the region around a supermassive black hole. Polarization revealed the presence of a strong magnetic field in the region where matter accelerated into M87*, a black hole with a mass of more than six billion times the mass of the Sun. Further research into this polarization could provide important insights into how some black holes produce huge jets that spew matter and radiation into the surrounding space. In 2019, EHT made history by capturing the first images of the black hole's shadow, and the collaboration won the 2019 Physical World Breakthrough of the Year Award.
Image of M87's supermassive black hole under polarized light. Image credit: EHT Collaboration
J rg Evers of the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, the Electron Synchrotron in Germany, and the European Synchrotron Facility in France, and colleagues have pioneered the coherent quantum control of nuclear excitation. The team used X-rays emitted by a synchrotron to be delivered to the nucleus through two ultrashort pulses. By adjusting the phase of the pulse, the research team can switch the iron nucleus between coherent enhanced excitation and coherent enhanced emission. In addition to providing a better understanding of quantum matter, this work could accelerate the development of new technologies, such as ultra-precision nuclear clocks and batteries capable of storing large amounts of energy.
Christian Sanner and colleagues at JILA in the United States; Amita Deb and Niels Kj rgaard at the University of Otago; and Wolfgang Ketterle of the Massachusetts Institute of Technology and colleagues in the United States independently observed the Thuli blockage in the ultracool gas of the fermion atom. Pauli obstruction occurs in gases such as the composition of the atoms filled almost all available low-energy sub-states, which prevents the atoms from making small transitions to adjacent states. This affected the way light was scattered from atoms in the gas, and all three teams observed that Pauli blockage increased the transparency of the gas when it cooled. This effect could one day be used to improve ultracold atom-based technologies such as optical clocks and quantum repeaters.
The Muon g-2 experiment provides further evidence that the measurement of the muse's magnetic moment is inconsistent with theoretical predictions. An international team looped a magnetic polarization muse in a storage ring at Fermilab in the United States. The magnetic moment of the muse is rotated by the magnetic field, and the rotation rate gives the size of the mucturum magnetic moment. The difference between theory and experiment was first discovered twenty years ago at Brookhaven National Laboratory. Now, the combined results from Fermilab/Brookhaven show that the difference between experiment and theory is 4.2σ, less than the 5σ required for discovery. If this difference stands up to future experiments, it could point to new physics beyond the Standard Model.
Muon G-2 storage ring at the Fermi National Accelerator Laboratory. Image credit: Reidar Hahn/Fermilab
Reference Links:
https://physicsworld.com/a/quantum-entanglement-of-two-macroscopic-objects-is-the-physics-world-2021-breakthrough-of-the-year/
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