New studies stretch the boundaries of physics, achieving quantum entanglement in larger systems.
- New experiments with vibrating drums push the boundaries of quantum mechanics.
- Two teams of physicists create quantum entanglement in larger systems.
- Critics question whether the study gets around the famous Heisenberg uncertainty principle.
Recently published research pushes the boundaries of key concepts in quantum mechanics. Studies from two different teams used tiny drums to show that quantum entanglement, an effect generally linked to subatomic particles, can also be applied to much larger macroscopic systems. One of the teams also claims to have found a way to evade the Heisenberg uncertainty principle.
One question that the scientists were hoping to answer pertained to whether larger systems can exhibit quantum entanglement in the same way as microscopic ones. Quantum mechanics proposes that two objects can become "entangled," whereby the properties of one object, such as position or velocity, can become connected to those of the other.
An experiment performed at the U.S. National Institute of Standards and Technology in Boulder, Colorado, led by physicist Shlomi Kotler and his colleagues, showed that a pair of vibrating aluminum membranes, each about 10 micrometers long, can be made to vibrate in sync, in such a way that they can be described to be quantum entangled. Kotler's team amplified the signal from their devices to "see" the entanglement much more clearly. Measuring their position and velocities returned the same numbers, indicating that they were indeed entangled.
Tiny aluminium membranes used by Kotler's team.Credit: Florent Lecoq and Shlomi Kotler/NIST
Evading the Heisenberg uncertainty principle?
Another experiment with quantum drums — each one-fifth the width of a human hair — by a team led by Prof. Mika Sillanpää at Aalto University in Finland, attempted to find what happens in the area between quantum and non-quantum behavior. Like the other researchers, they also achieved quantum entanglement for larger objects, but they also made a fascinating inquiry into getting around the Heisenberg uncertainty principle.
The team's theoretical model was developed by Dr. Matt Woolley of the University of New South Wales. Photons in the microwave frequency were employed to create a synchronized vibrating pattern as well as to gauge the positions of the drums. The scientists managed to make the drums vibrate in opposite phases to each other, achieving "collective quantum motion."
The study's lead author, Dr. Laure Mercier de Lepinay, said: "In this situation, the quantum uncertainty of the drums' motion is canceled if the two drums are treated as one quantum-mechanical entity."
This effect allowed the team to measure both the positions and the momentum of the virtual drumheads at the same time. "One of the drums responds to all the forces of the other drum in the opposing way, kind of with a negative mass," Sillanpää explained.
Theoretically, this should not be possible under the Heisenberg uncertainty principle, one of the most well-known tenets of quantum mechanics. Proposed in the 1920s by Werner Heisenberg, the principle generally says that when dealing with the quantum world, where particles also act like waves, there's an inherent uncertainty in measuring both the position and the momentum of a particle at the same time. The more precisely you measure one variable, the more uncertainty in the measurement of the other. In other words, it is not possible to simultaneously pinpoint the exact values of the particle's position and momentum.
Heisenberg's Uncertainty Principle Explained. Credit: Veritasium / Youtube.com
Big Think contributor astrophysicist Adam Frank, known for the 13.8 podcast, called this "a really fascinating paper as it shows that it's possible to make larger entangled systems which behave like a single quantum object. But because we're looking at a single quantum object, the measurement doesn't really seem to me to be 'getting around' the uncertainty principle, as we know that in entangled systems an observation of one part constrains the behavior of other parts."
Ethan Siegel, also an astrophysicist, commented, "The main achievement of this latest work is that they have created a macroscopic system where two components are successfully quantum mechanically entangled across large length scales and with large masses. But there is no fundamental evasion of the Heisenberg uncertainty principle here; each individual component is exactly as uncertain as the rules of quantum physics predicts. While it's important to explore the relationship between quantum entanglement and the different components of the systems, including what happens when you treat both components together as a single system, nothing that's been demonstrated in this research negates Heisenberg's most important contribution to physics."The papers, published in the journal Science, could help create new generations of ultra-sensitive measuring devices and quantum computers.
Scientists discover a counterintuitive property of quantum particles called "backflow".
Quantum mechanics continues to provide brain-busting discoveries as mathematicians find that quantum mechanical particles can move in the opposite direction of where they are being pushed. That’s like pushing a ball forward and having it roll back towards you instead.
Scientists at Universities of York, Munich and Cardiff showed that on microscopic levels, quantum particles can travel in reverse of their momentum, exhibiting a special property called “backflow”.
Researchers were aware of such movement previously but in free” quantum particles that don’t have any force acting on them. By using analysis and numerical methods, they found that backflow is always there, but as a small hard-to-measure effect.
What’s responsible for this surprising property? Wave-particle duality, which holds that every particle may behave as a particle or a wave, and the “probabilistic nature” of quantum mechanics where particle properties are not fixated until observed.
Dr. Henning Bostelmann from the University of York Department of Mathematics elaborated on the finding:
“This new theoretical analysis into quantum mechanical particles shows that this ‘backflow’ effect is ubiquitous in quantum physics,” said Bostelmann in a press release. “We have shown that backflow can always occur, even if a force is acting on the quantum particle while it travels. The backflow effect is the result of wave-particle duality and the probabilistic nature of quantum mechanics, and it is already well understood in an idealised case of force-free motion.”
Dr. Daniela Cadamuro from the Technical University of Munich explained that while the scientists were aware of the backflow effect, it was always observed when no outside forces were acting on a particle, and the researchers showed that backflow continues to occur even with external forces present, meaning that such forces “don't destroy the backflow effect, which is an exciting new discovery.”
The practical implications of this discovery may lead to stronger computer encryption. The effect hasn’t been lab-tested yet but scientists are working on setting up appropriate experiments, perhaps with Bose-Einstein condensates. They were used earlier this year to create a superfluid with “negative mass,” where particles exhibited similarly counterintuitive behavior.
Notably, Albert Einstein remarked upon the weirdness one faces when confronted with quantum mechanics:
"It seems as though we must use sometimes the one theory and sometimes the other, while at times we may use either. We are faced with a new kind of difficulty. We have two contradictory pictures of reality; separately neither of them fully explains the phenomena of light, but together they do,” wrote Einstein in a 1938 book with Leopold Infeld.
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