Quantum Entanglement: The Spooky Science Behind Tomorrow’s Technology
I envy people who understand physics. I think maybe one day, if I ever get any of that elusive “spare time” I keep hearing about, maybe I’ll be able to start learning about it. One branch of physics, though, has captured my attention, because of its application to cybersecurity, and that’s quantum physics. In order for any of the rest of this to make sense, I have to go back to some basics. (Not as far back as “It was a warm summer evening” from The Big Bang Theory.)
Physics as a scientific field explains how things move and interact on a large scale. Think planets, cars, or falling objects. Quantum physics deals with the behavior of particles at the smallest scales; atoms, and even subatomic particles. What we come to understand as we explore and study physics doesn’t prepare us for what we experience when we start to look at quantum physics.
Enter the Entanglement
I stumbled on the term Quantum Entanglement and became captivated by it, so what do I do when something captivates me? I write about it in an attempt to understand it. Here’s a super-basic definition: Quantum Entanglement is a situation where two or more particles link in a way such that the state of one particle affects the state of another particle, and it doesn’t matter how close together or far apart the particles are. Their states interconnect. If you measure the spinning action of one particle, you know the action of the other.
Exploring quantum physics is very different from exploring classical physics, where everything follows a deterministic and easy-to-visualize path. In classical physics, objects are influenced only by their immediate surroundings; in quantum entanglement, there’s an instantaneous correlation between particles, regardless of proximity or distance. Classical physics is largely deterministic, such that if we know the initial conditions of something, we can predict its future state; Quantum physics introduces a level of inherent randomness. In classical physics, measurement doesn’t alter the thing being measured; in quantum mechanics, the act of measuring something can change the state of it.
Mind blown yet? Just wait. It gets even better.
A Bit of History: How Did We Discover Entanglement?
There are three key players in the discovery of Quantum Entanglement: Albert Einstein (of course), Erwin Schrodinger (of Schrodinger’s Cat, and yes, I have watched every episode of The Big Bang Theory), and John Stewart Bell. Einstein challenged the completeness of quantum mechanics, and in 1935 he wrote a paper with Boros Podolsky and Nathan Rosen. The title of the paper was “Can Quantum-Mechanical Description of Physical Reality be Considered Complete?” and it expressed a lot of challenges and questions to the contemporary concepts of quantum mechanics. The paper also proposed the existence of “local hidden variables” to explain some of the quantum weirdness. Lemme explain that.
Let’s say that you and I each have a coin. If you and I flip them simultaneously, they always come up opposite – one heads and one tails. Always. No matter how far apart we are or how close we are. Always one heads and one tails. It’s bizarre. It’s unexplainable (maybe?). That’s the sort of strange behavior we see with certain quantum particles.
Local Hidden Variables
Now let’s introduce the idea of a local hidden variable. Local means that information can’t travel faster than light between the two coins. Hidden means that there’s some unseen thing affecting the two coins. Variables would be that unseen or unknown thing that affects the outcome. Pulling in a local hidden variable might be that there’s a teeny, tiny computing mechanism in each coin. The mechanism was programmed before you and I separated to go across the world from each other, and it creates the conditions for the coin toss results.
This concept of local hidden variables was introduced as a way to explain the inexplicable behavior of these tiny particles. The problem with the explanation is that in experiments, the particles behave in ways that can’t be explained even by local hidden variables. The quantum world is even stranger than we initially believed it to be, and I’m sure you’re glad you know that now.
Schrodinger disagreed. In the same year, he wrote a paper arguing against hidden variables and introduced the concept of entanglement. His thoughts on the hidden variables were upheld by John Stewart Bell in 1964, and subsequent and recent research have strengthened support for quantum entanglements.
What does this mean for us? Well, it sort of demonstrated that quantum correlations can’t be explained by classical physics; quantum physics is really something very different. But the real significance isn’t just theoretical, because it opened up whole new fields of research like quantum information and quantum computing.
The Science Behind Entanglement
Quantum States and Superposition
Superposition is exactly what defines Schrodinger’s Cat. In quantum physics, particles can exist in multiple states at the same time. A particle’s spin can be in a superposition of both “up” and “down.” Now, this really requires some bending of everything you think you know about reality. Think of a coin spinning on a table. While it’s spinning, you don’t know if it’s head or tails; in a way, it’s both heads and tails, until it stops spinning. So, during that spinning state, it’s both.
Quantum superposition is like that, but with many possible states instead of being limited to just two. It’s not because we can’t see which state it’s in, but because it truly exists in all the states simultaneously. In classical physics, an electron orbits the nucleus like a planet orbits the sun. In quantum mechanics, the electron is in a cloud of probabilities around the nucleus, and the cloud represents all of the possible states that the electron could be in, all at one time.
Now, when we go to observe or measure the quantum system, that superposition breaks or collapses, and the particle will present itself in only one state. It isn’t just that we didn’t know what state it was in, it really was in all states at once.
Entanglement Explained
Remember that entanglement is a connection between two particles. The state of each particle cannot be described independently. When we measure one particle in an entangled pair, we know the state of the other particle. And the act of measuring one entangled particle seems to instantaneously affect the other particle — which calls our whole understanding of cause and effect into question, doesn’t it? These properties of entanglement don’t have any reflection in classical physics, so quantum mechanics ends up describing a very different reality than what we experience in our everyday, macroscopic world.
Real-World Applications of Entanglement
All of this sounds really Star-Trekky, doesn’t it? I mean, how freakin’ powerful is that microscope that can determine these states? And how do we measure stuff that small? Tiny rulers? More importantly, what can we do with knowing this? I’m so glad you asked!
Quantum Computing
By now, you’ve likely heard of Quantum Computing. Entanglement is what gives quantum computing such power. Quantum computing relies on quantum bits, called qubits. Entanglement allows multiple qubits to be correlated, so that the computers can perform many calculations simultaneously. A standard computer doesn’t really do that, even with what we call “multitasking.” (I’ve got a blog post on that here.) Because of that, the entangled qubits can represent and process so much more information than the same number of classical bits. Factoring large numbers and searching unsorted databases now becomes easy-peasy. Pulling together information from unstructured data is another gift to us from quantum computing. (What’s unstructured data? Check here for an explanation.)
Quantum Cryptography
This is the part that fascinates me, because it directly influences cybersecurity. We’re always hearing about how super fast computers are going to kill standard encryption. Well, this entanglement will make it possible to generate more secure encryption keys. The measurement collapse I talked about would alert the communication parties to the potential eavesdropping. Traditional cryptography is based on mathematical complexity, but when we bring in physics instead, we could end up with unbreakable encryption.
Quantum Teleportation
Quantum teleportation doesn’t transport matter (things like, oh, people, for instance). It deals with transporting quantum information. It uses the entanglement to transfer the exact quantum state of one particle to another particle, at any distance. Of course, the process destroys that original particle’s quantum state, and that preserves the no-cloning property of quantum mechanics. We’ll see this implemented in quantum computing and quantum internet applications, which will transfer quantum information between different parts of a quantum computer system or a network.
Challenges to Quantum Entanglement
It’s not easy doing quantum work. Entangled quantum systems are extremely sensitive to external influences, like electromagnetic fields, temperature fluctuations, mechanical vibrations, and interactions with other particles (even air). Maintaining isolation from the environment is crucial, but it’s so challenging that a quantum computer doesn’t yet exist that can stay running for long.
It’s also really hard to create and manage large-scale entangled systems. As the number of entangled particles increases, the complexity of control increases with it. Add to that the fact that manipulating quantum states is a precision-reliant act, and even tiny errors can disrupt that entanglement.
Decoherence
What is that? Lemme take a deep breath. Okay, decoherence is when a particle loses its quantum properties because of an interaction with the environment. Entangled states rapidly decay (decay? Yes, decay) into classical states. We can see, then, that quantum information has a really short lifespan, and that decoherence also means a limit on the scale of quantum systems.
Quantum physicists are working to manage decoherence using several methods. One is error correction codes, allowing the qubit to recover to its original state after an error. Another prospect is topological quantum computing, which would encode information into topological properties of the system rather than in the individual particles. They’re also looking to improve the isolation techniques to limit the environmental interference.
Why Should We Care?
We’ve looked at some aspects of why quantum entanglement and its applications are important, but there are a few other things we want to look at. Quantum entanglement is a cornerstone of quantum computing, and because of it, we can see solutions to complex problems come forth much faster. It can offer breakthroughs in cryptography, drug discovery, and materials science.
Quantum entanglement challenges our classical intuitions about reality and locality. Remember that mind bend above? Yeah, it’s like that, only deeper. It enhances our understanding of the fundamental principles that govern the universe, and that’s what physics in general does for us.
As a result, we could end up with new industries and job opportunities in fields like quantum computing, telecommuncations, and materials science. We can come to quicker resolutions of complex optimization problems, logistics issues, enhanced AI algorithms, and more efficient energy systems.
Healthcare could benefit greatly from quantum entanglement, because it could accelerate drug discovery processes and improve personalized medicine by simulating molecular interactions at a scale we can only imagine today. I’ve written about personalized medicine here. Quantum technologies might also take us to better models for climate predictions, energy efficiency, and sustainability efforts.
Your Turn
Well, this was a fun romp, wasn’t it? I’ve learned more writing this than I ever thought I wanted to know, but it’s been a fascinating ride! Drop a comment below on your thoughts about it. There’s a lot going on at a particular level — I mean at a particle level.
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