In the biggest test yet, physicists have discovered a key paradox in quantum mechanics and found that it persists even for clouds of hundreds of atoms.
Using two entangled Bose-Einstein condensates, each consisting of 700 atoms, a team of physicists led by Paolo Colciaghi and Evan Li of the University of Basel in Switzerland showed that Einstein-Podolsky-Rosen paradox (EPR) go up.
The researchers say this has important implications for quantum metrology — the study of measuring things under quantum theory.
“Our results represent the first observation of the EPR paradox with multiple spatially separated massive particle systems.” the researchers write in their paper.
“They show that the conflict between quantum mechanics and local realism does not disappear as the size of the system increases to more than a thousand massive particles.”
Although we are very good at describing the universe mathematically, our understanding of how things work is patchy at best.
One of the tools we use to fill in a gap is quantum mechanics, a theory that originated in the early 20th century, It was defended by the physicist Niels Bohr, to describe the behavior of atomic and subatomic matter. In this small world, classical physics breaks down; When old rules no longer apply, new rules must be established.
But quantum mechanics is not without its flaws, and in 1935, three famous physicists found a big gap. Albert Einstein, Boris Podolsky, and Nathan Rosen described the famous Einstein-Podolsky-Rosen paradox.
Nothing can travel faster than light, right? But it gets a little tricky with quantum entanglement, which Einstein referred to as “frightening action at a distance.” This is where you connect two (or more) particles so that their properties are related; If, for example, one particle rotates in one direction, the other rotates in the other.
These particles maintain this association even over great distances, and it is not clear how or why. Scientists know that if you measure the properties of one particle, you can infer the properties of the other particle, even at that distance.
However, under quantum mechanics, a particle will not have those properties until you measure it (an oddity that was explored by the Schrödinger thought experiment).
And under quantum mechanics, if you know one particular property of a particle, such as its location, you cannot know another, such as its momentum, with any certainty. This is Heisenberg’s uncertainty principle.
concept of classical physics local realism It also states that for one thing or energy to affect another, the two must interact.
Thus, the EPR paradox is complex. When you measure one particle in an entangled system, that measurement somehow affects the other particle, even though the measurement is not done locally.
You also know more about particles than is allowed under Heisenberg’s Uncertainty Principle. And somehow, that effect happens instantly, defying the speed of light.
Thus, the EPR paradox indicates that the theory of quantum mechanics is incomplete; It does not fully describe the reality of the universe in which we live. Physicists have mostly tested it on small, entangled systems, made up of a pair of atoms or photons, often, in what’s known as the Bell test (after its erasure, physicist John Stewart Bell).
So far, every test Bell has conducted has found that the real world behaves in a way that contradicts local realism. But how deep is this paradox?
Well, that’s where we get to Bose-Einstein condensates, which are states of matter created by cooling a cloud of bosons to a fraction above absolute zero. At such low temperatures, atoms sink to their lowest possible energy state without completely stopping.
When you reach these lower energies, the quantum properties of the particles cannot interfere with each other; They get close enough to each other to kind of interfere, resulting in a high-density cloud of atoms that behaves like a single “super atom,” or wave of matter.
Colciaggi, Lee, and fellow physicists Philipp Treutlin and Tilmann Ziebold, also from the University of Basel, produced Bose-Einstein condensates using two clouds, each consisting of 700 rubidium-87 atoms. They spatially separated these condensates by up to 100 micrometers and measured the properties.
They measured the quantum properties of condensates known as pseudospins, independently choosing which value to measure for each cloud.
They found that the properties of the capacitors appear to be correlated in a way that cannot be attributed to random chance, demonstrating that the EPR paradox is consistent on a much larger scale than previous Bell tests.
The implications of the team’s findings are highly relevant for future quantum research.
“Our experiment is particularly suitable for quantum measurement applications. One could, for example, use one of the two systems as a small sensor for probing fields and forces with high spatial resolution and the other as a reference for quantum noise reduction of the first system.” the researchers write in their paper.
“Demonstrating EPR entanglement in combination with spatial separation and individual addressability of the systems involved is not only important from a fundamental point of view but also provides the necessary ingredients for exploiting EPR entanglement in many particle systems as a resource.”
Now go have a cup of tea and sit down. You’ve got it.
Research published in X physical review.
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