Have you ever heard about quantum entanglement?
- Alexa Ines Guido
- 5 days ago
- 4 min read
Hola! I'm Alexa Guido, a young and curious woman passionate about science. Join me on an exciting journey to explore the wonders of the universe through the lens of physics.
Have you ever imagined two particles, separated by galaxies, somehow sharing a secret connection? That if you measure one, the other instantly reacts, even if it’s light-years away? It might sound like something out of a sci-fi novel, but it’s not. It’s quantum entanglement! This is the ultimate long-distance relationship; once connected, they remain forever connected!
Back in 1935, Albert Einstein, along with his colleagues Podolsky and Rosen, published a paper that challenged quantum theory. Their argument? If entanglement were real, it would mean “spooky action at a distance”, which sounded way too much like magic for Einstein’s taste.
Fast forward to 2022, when Alain Aspect, John Clauser, and Anton Zeilinger were awarded the Nobel Prize for their groundbreaking experiments that confirmed entanglement isn’t merely a bizarre concept; it’s a fundamental aspect of nature!
Albert Einstein famously referred to this phenomenon as “spooky action at a distance”, a phrase that stuck around like glitter after a birthday party. But entanglement isn’t magic or nonsense. It’s real. It’s a measurable reality that’s paving the way for groundbreaking advancements in quantum computing, unbreakable encryption, and even cutting-edge space experiments. So, let’s dig deeper and explore the fascinating world of quantum mechanics beyond the “spooky” label.
To truly grasp entanglement, we first need to understand superposition. Quantum entanglement occurs when a system exists in a "superposition" of multiple states. But what does that actually mean? Imagine flipping a coin and covering it before looking, it’s either heads or tails. However, in quantum mechanics, until you measure it, the coin exists in both states simultaneously. That’s superposition!
Superposition indicates that the coin's state, whether heads or tails, doesn't even exist until you take a look or perform a measurement. Entanglement is a special kind of superposition that involves two separated locations in space. The coin example is in superposition of two results in one place.
While the coin example reflects superposition in a single location, entangled particles shed their individual states and forge a new, unified quantum state that binds them eternally. In simpler terms, if something happens to one particle, it influences all the others that share its entangled connection.
In other words, if two particles are quantum-entangled, the state of one particle is tied to that of the other, no matter how far apart the particles are. This mind-bending phenomenon, which has no analogue in classical physics, has been observed in a wide variety of systems and has found several important applications.
But it’s extremely easier to understand how quantum physics works, and how it departs from the classical world, from the perspective of information, not physics.
Consider another example of quantum entanglement: a light source that emits pairs of photons[1]. These photons can be entangled in such a way that, although their polarizations can be randomly oriented, the polarizations of each pair will always match.
What is polarization? It refers to the orientation of the electric field in a light wave. As light travels, its electric field oscillates across different planes, such as vertically, horizontally, or any direction in between.
Back to those entangled pairs. So, if we measure the polarization of photon A to see if it is polarized horizontally or vertically, we get an answer and find it to be, this time, vertical.
Entanglement means that when I measure whether its twin is horizontal or vertical, we find that its polarization is vertical too. And if we do that experiment many times, we will always find that the two photons' polarizations match, even if we find that the result of which polarization they match to is random. This consistency holds true across multiple experiments, even though the specific polarization results appear random. Amazing, right?
However, there’s a catch. If photon B is measured on Pluto, it could take six hours for that information to reach us since nothing can travel faster than light. Yet, astonishingly, the measurement of photon B will always align with photon A’s state, regardless of when or where it’s measured. It seems as if the necessary information is traveling faster than light. In reality, it’s the randomness of the process that gives the illusion of faster-than-light communication.
The ability to instantaneously measure the quantum state of one particle by measuring that of its entangled partner somewhere else in the universe means that that information would have to be delivered faster than light speed, which contradicts Einstein’s theory of special relativity. What remains a mystery is how these particles communicate across such vast distances.
The Nobel Prize-winners were the first to prove this as a fundamental truth of nature. Today, you can join their legacy by creating entangled particles and processing their correlated quantum information on a real quantum computer.
Currently, at the Large Hadron Collider, scientists are investigating entangled pairs of fermions known as top quarks. They demonstrated that measuring the spin direction of one quark instantaneously leads the other to “choose” the complementary orientation. This occurs so instantaneously that it’s as if the two entangled particles are one.
NASA’s SEAQUE (Space Entanglement and Annealing QUantum Experiment) is another exciting endeavor led by Dr. Paul Kwiat from the University of Illinois. This experiment aims to establish quantum-level communication in space through the power of entanglement.
As Chris Ferrie wisely states, through the lens of quantum information, then, entanglement is not strange or rare, but rather expected!
[1] Learn more about photons in “Have you ever heard about photons?”
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