Physics World 2021 Breakthrough Award: Quantum Entanglement between Macroscopic Objects
The Physics World 2021 Breakthrough Award was awarded to two independent teams who entangled two macroscopically vibrating mechanical drums, thereby advancing our understanding of the boundaries between quantum and classical systems. The winners are Mika Sillanpää 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).
Researchers at NIST entangled the beats of these two mechanical drums—a tiny aluminum film made of approximately 1 trillion atoms—and accurately measured their related quantum properties. Entangled pairs like this (shown in this color micrograph) are huge according to quantum standards, and may perform calculations and transmit data in large-scale quantum networks in the future. Image source: J. Teufel/NIST
Quantum technology has made great strides in the past two decades, and physicists are now able to build and manipulate systems that were once in the realm of thought experiments. A particularly fascinating research approach is the fuzzy boundary between quantum physics and classical physics. In the past, it was possible to make a clear division based on size: tiny objects such as photons and electrons existed in the quantum world, while large objects such as billiard balls followed classical physics.
In the past ten years, physicists have been using drum-shaped mechanical resonators with a diameter of about 10 microns to push the limits of quantum. Unlike electrons or photons, these mechanical drums are macroscopic objects manufactured using standard micromachining techniques, which look as strong as billiard balls in electron microscope images (see above). However, despite the tangible properties of 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 and Sillanpää’s independent team went further and became the first team to use quantum mechanics to entangle two such drums. The two teams entangled in different ways. The Finnish/Australian team used a specially selected resonance frequency to eliminate noise in the system that may interfere with the entangled state, while the NIST team's entanglement is similar to a two-qubit gate, where the form of the entangled state depends on the initial state of the drum.
Both teams have overcome major experimental challenges, and their tremendous efforts can open the door for entanglement resonators to be used as quantum sensors or as nodes in quantum networks. Therefore, this work deserves to be the first quantum-related annual breakthrough since 2015.
These drums exhibit collective quantum motion. Image source: Mika Sillanpää research team at Aalto University
This year, the website published nearly 600 latest research results, from which five Physics World editors selected this year's breakthrough and nine runner-ups. In addition to being reported by Physics World in 2021, the following criteria must also be met:
● Make significant progress in knowledge or understanding
● The importance of work to scientific progress and/or practical application development
● Physics World readers are generally interested
Among the ten breakthroughs in 2021, the other nine achievements were also highly praised.
Restoring speech in a paralysed man
Edward Chang, David Moses, Sean Metzger, Jessie Liu and colleagues of the University of California, San Francisco have developed a speech neuroprosthesis that directly translates brain signals into words on the screen, allowing severely paralyzed people to communicate in sentences. To achieve this goal, the research team used high-density electrode arrays implanted on the surface of the participants' brains to record electrical activity in multiple cortical regions involved in speech formation. Based on the 50-word vocabulary that the system can recognize from the patterns in the recorded cortical activity, he can generate hundreds of short sentences. This technology showed an encouraging median decoding rate of 15.2 words per minute—about three times that of the computer-based typing interface he usually uses for communication.
A neuroprosthesis recorded the participants' cerebral cortex activity as they tried to construct words and sentences. Image credit: Todd Dubnicoff, UCSF
Making 30 lasers emit as one
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 for large-scale, high-power applications Paved the way. The team used the principles of topological photonics to ensure that the light of each laser in the array passes through all other lasers, forcing them to emit at the same frequency. The new design overcomes the power limitations of previous-generation devices manufactured by Segev and collaborators in 2018, and can in principle be expanded to include hundreds of individual lasers.
Quantifying wave–particle duality
Tai Hyun Yoon and Minhaeng Cho of the Korea Institute of Basic Science; Xiaofeng Qian of Stevens Institute of Technology in the United States; and Girish Agarwal of Texas A&M University in the United States conducted experiments to quantify the “wave properties” and “particle properties” of photons. Theoretical work has proved that these two properties are related to the purity of the photon source. In their experiments, Yoon and Cho strictly controlled the quantum states of the photon pairs emitted by two lithium niobate crystals-a "signal photon" and an "idle photon". By independently changing the probability of each crystal emitting photons, they used a simple mathematical expression first clarified by Qian and Agarwal in 2020 to show the so-called source purity and the visibility of interference fringes (a wave-like property) and The discernibility of the path (a property similar to particles) is related. This result has been applied in the field of quantum information, and brought a new twist to the interpretation of complementarity-this idea originated from the 20th century quantum pioneer Niels Bohr, that is, quantum objects sometimes resemble waves and sometimes resemble particle.
Milestone for laser fusion
Omar Hurricane, Annie Kritcher, Alex Zylstra and Debbie Callahan of the National Ignition Facility (NIF) in California, USA, and their colleagues have taken a step toward the ultimate goal of "ignition." Since NIF was opened more than ten years ago, its long-term goal has been to prove that it can achieve ignition-the fusion reaction generates at least as much energy as its laser. This includes self-sustaining reactions, in which alpha particles emitted during the fusion process also release heat, triggering further fusion. NIF is operated by Lawrence Livermore National Laboratory, and shoots 192 pulsed laser beams at the inner surface of a centimeter-long hollow metal cylinder, called a black body radiation cavity (hohlraum). Inside is a fuel capsule, which is a hollow sphere with a diameter of about 2 mm and contains a thin layer of deuterium and tritium. The experiments from 2009 to 2012 were far from reaching ignition, so the researchers continued to improve. On August 8 this year, the researchers obtained an energy output of more than 1.3 MJ, which is about 70% of the energy delivered by the laser pulse to the sample. This result is amazing. Although the balance of payments is still not reached, this figure far exceeds the previous indicator of around 0.1 MJ. Some experts describe this result as the most significant improvement since the inertial fusion started in 1972. Some experts describe this result as the most significant development in inertial fusion since 1972.
Scientists at the US$3.5 billion National Ignition Facility (NIF) have taken a step toward the ultimate goal of "ignition"-the energy produced by the fusion reaction is at least the same as the energy provided by the laser system. Image source: NIF
Innovative particle cooling techniques
Researchers from the European Center for Nuclear Research (CERN) Antihydrogen Laser Physics Facility (ALPHA) and the Baryon Antibaryon Symmetry Experiment (BASE) collaborated on two independent studies to propose new methods for cooling particles and antiparticles. These technologies can pave the way for the precise study of the matter-antimatter asymmetry in the universe. The ALPHA collaboration demonstrated the laser cooling of anti-hydrogen atoms for the first time. To achieve this goal, physicists have developed a new type of laser that generates 121.6nm laser pulses to cool antiatoms. Then, they measured the key electronic transitions in antihydrogen with unprecedented accuracy. This breakthrough may lead to improved testing of other key properties of antimatter. At the same time, BASE researchers showed how to extract heat from a single proton through a superconducting circuit connected to a laser-cooled ion cloud a few centimeters away. They say that this technique can be easily applied to antiprotons.
Observing a black hole’s magnetic field
The Event Horizon Telescope Collaboration (EHT) was used to create the first image showing the polarization of light in the area surrounding the supermassive black hole. Polarization reveals that there is a strong magnetic field in the area where matter accelerates into M87*, a black hole with a mass that exceeds the mass of the sun six billion times. Further research on this polarization can provide important insights into how some black holes produce huge jets that eject matter and radiation into the surrounding space. In 2019, EHT made history by capturing the first image of the shadow of a black hole, and this collaboration won the 2019 Physics World Annual Breakthrough Award.
The image of the M87 supermassive black hole under polarized light. Image source: EHT Collaboration
Achieving coherent quantum control of nuclei
Jörg Evers of the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, the German Electron Synchrotron and the French European Synchrotron Facility, and his colleagues took the lead in realizing coherent quantum control of nuclear excitation. The team used X-rays from a synchrotron to transmit to the nucleus in two ultrashort pulses. By adjusting the phase of the pulse, the research team can switch the iron nuclei between coherent enhanced excitation and coherent enhanced emission. In addition to providing a better understanding of quantum matter, this work can also accelerate the development of new technologies, such as ultra-precision nuclear clocks and batteries that can store large amounts of energy.
Observing Pauli blocking in ultracold fermionic gases
Christian Sanner and colleagues from JILA in the United States; Amita Deb and Niels Kjærgaard from the University of Otago; and Wolfgang Ketterle and colleagues from the Massachusetts Institute of Technology in the United States independently observed the Pauli blockage in the ultra-cold gas of fermion atoms. Pauli blockage occurs in such a gas: because the constituent atoms almost fill up all available low-energy sub-states, this prevents the atoms from making small transitions to adjacent states. This affects the way light scatters from atoms in the gas, and all three teams have observed that Pauli blockage increases the transparency of the gas as it cools. This effect could one day be used to improve technologies based on ultra-cold atoms, such as optical clocks and quantum repeaters.
Confirming the muon’s theory-defying magnetism
Muon's abnormal magnetic moment experiment (Muon g-2 experiment) provides further evidence that the measured value of Muon's magnetic moment is inconsistent with the theoretical prediction. An international team circulates a bunch of magnetically polarized muses in the storage ring of Fermilab in the United States. Muzi’s magnetic moment is rotated by the magnetic field, and the rate of rotation gives the magnitude of Muzi’s magnetic moment. The difference between theory and experiment was first discovered at Brookhaven National Laboratory two decades ago. Now, the combined results of Fermilab/Brookhaven show that the difference between experiment and theory is 4.2σ, which is less than the 5σ required for discovery. If this difference can stand the test of future experiments, it may point to new physics beyond the Standard Model.
Muon g-2 storage ring at Fermi National Accelerator Laboratory. Image credit: Reidar Hahn/Fermilab
link:https://physicsworld.com/a/quantum-entanglement-of-two-macroscopic-objects-is-the-physics-world-2021-breakthrough-of-the-year/
