The Mysterious Quantum Connection
Day 8 — Quantum30 challenge
We have officially entered the Week 2 of QuantumComputingIndia’s challenge and before going to the realm of Quantum Computing, we have to discuss a fundamental concept which is the domain of the field. So let’s switch the gears a bit and learn.
In the realm of quantum mechanics, where the rules defy our everyday understanding, lies a phenomenon known as entanglement. Building on the concept of superposition, where particles exist in a combination of multiple states, entanglement takes this peculiarity to a new level.
Understanding Entanglement
Imagine two particles — let’s call them Particle A and Particle B — whose fates are inexplicably intertwined. When particles become entangled, their properties, such as spin, become linked in such a way that any change/measurement in one particle instantaneously affects the other, regardless of the distance separating them. It’s as if they share a cosmic connection that transcends the limitations of space and time.
For example, if you toss a single fair coin, and you get heads, you know with 100% accuracy that the other side is a tail.
The Dance of Spins
Fundamental particles like electrons, quarks, and photons carry an intrinsic property called “spin.” This spin, a fundamental aspect of their nature, determines how they interact with magnetic fields and polarize under certain conditions. For electrons, spin can be in one of two states: “spin up” or “spin down.”
When two electrons become entangled, they no longer exist as separate entities with individual wavefunctions and properties. Instead, they share a collective wave function that binds them together, resulting in a state where the spin of one electron is correlated with the spin of the other.
Einstein’s Skepticism and the EPR Paradox
In 1935, three brilliant minds — Albert Einstein, Boris Podolsky, and Nathan Rosen — debated the implications of entanglement. They posed a thought experiment that looks somewhat as follows.
Imagine you and your friend both have a magical coin each interlinked to each other. Both of you go far away from each other and toss your coins. Now, when you both look at your coins then you find out, both of your coins show the same side no matter how far you are apart. Both of your coins seem to communicate mysteriously across the distances!
This led to the Einstein-Podolsky-Rosen (EPR) paradox, which questioned whether quantum mechanics was complete or if some “hidden variables” were at play, driving the correlated behavior of entangled particles. Einstein termed this as phenomenon as ‘Spooky action at a distance’.
Bell’s Inequalities: Unraveling the Mystery
A few decades later, John Bell wrote formulated certain inequalities which are known as Bell’s inequalities. Going back to the magical coins, the Bell’s inequality was more like a test that showed how these entangled coins behave in a way that’s beyond what normal things can do and cannot be explained by conventional physics, suggesting that there’s something mysterious going on with the way these particles are connected.
Scientists did this test with real particles (electrons, photons, etc), not coins, and found something strange. The particles sometimes matched more often than they should have if they were following normal rules. This means that the particles are doing something that regular objects can’t do. This result supports the idea that there’s something fundamentally different about how entangled particles work compared to everyday things.
The Elusive Faster-Than-Light Communication
The astonishing aspect of entanglement lies in its persistence across any distance, whether it’s a mere meter or billions of kilometers. This raises the intriguing question: can information be transmitted faster than the speed of light through entanglement? The answer, however, is, NO!
And here’s why. The outcomes of measurements are inherently random and unpredictable.
Merely observing one entangled particle does not provide complete insight into the state of its entangled counterpart. To ascertain the correlated state, conventional communication methods must be employed. Thus, despite the mysterious and instantaneous connection between entangled particles, there is no violation of the principles of general relativity.
References
Additional
What exactly is spin in quantum mechanics? The following video gives an about the concept.