Somewhere in the 2000s, I started hearing people use the word “Quantum” in ways I suspected were incorrect. I was intrigued, and I decided to study the concept. A friend, Andy Wolfe, lent me QED – The Strange Theory of Light and Matter by Richard P. Feynman, which truly blew my mind. (QED stands for Quantum Electrodynamics.) The book explains how light can act as both a particle (a photon) and a wave at the same time. Further studies revealed even stranger phenomena: some subatomic particles change their behavior when observed. Look away, and they act differently. What?! How do they know when they are being monitored? Welcome to quantum mechanics!
What is Quantum Mechanics?
Quantum mechanics is the branch of physics that describes the behavior of matter and energy at microscopic scales, such as atoms and subatomic particles. At this level, particles exist in multiple states until measured, can interact instantaneously across distances, and obey probabilistic rather than deterministic laws. This means we can only guess their states using probabilities until we observe them—and observing might alter the outcome.
Why is This a Big Deal?
Classic computers are binary. They operate through billions of switches that are either on or off, processing tasks sequentially (even multitasking is just rapid task-switching). In the quantum world, particles can exist in multiple states simultaneously. A switch is no longer just on or off; it can be both simultaneously.
To understand this better, let’s do some simple math.
Binary Systems
If I have three binary switches (bits), each can be either off (0) or on (1). The possible combinations are:
000 (off, off, off)
001 (off, off, on)
010 (off, on, off)
011 (off, on, on)
100 (on, off, off)
101 (on, off, on)
110 (on, on, off)
111 (on, on, on)
This results in 8 unique combinations for 3 bits.
Quantum Systems
Using quantum bits (qubits), which can be on, off, or both simultaneously, the possibilities expand exponentially. With three qubits, if we observe each, we still see the same eight combinations. But because qubits exist in superposition (both on and off), the system represents 27 possible combinations simultaneously, based on probabilities. And it gets even more astonishing: quantum computers process all these combinations at once, unlike classical computers, which process sequentially. Instead of eight lines of code running sequentially to print out all combinations of bits, I could run a single line of code with all 27 qubit combinations represented at the same time.
The Power of Quantum Computing
Imagine scaling this up to five, ten, or a hundred qubits. For example, Google’s Willow Quantum Computer recently solved a computational problem in under five minutes using 105 qubits—a task that would take a classical supercomputer approximately 10,000,000,000,000,000,000,000,000,000,000 years to complete! That’s the transformative potential of quantum computing.
A Little More Detail on Quantum Mechanics
In 1801, a simple question turned science upside down: Why, when looking through a window, do we see both the outside world and a reflection of ourselves in the glass? This paradox makes sense when you understand that light acts as both a wave and a particle simultaneously.
Richard Feynman’s QED discusses the famous double-slit experiment, where light exhibits this dual behavior. (Read more about it here.)
Atoms and Energy Levels
Let’s revisit high school chemistry. Atoms have protons, neutrons, and electrons. Electrons exist in energy levels (covalence levels) around the nucleus. Adding energy can excite an electron to a higher level, or even eject it from the atom entirely, changing the atom’s makeup. For example, if a helium atom loses an electron, it becomes hydrogen.
Here’s where it gets interesting: electrons transition between energy levels without moving through the space in between. Some physicists propose that the electron momentarily disappears into another universe before reappearing in its new state, a concept supported by theories like string theory and the Many-Worlds Interpretation. While fascinating, these remain unproven. For now, we will stick with what is proven.
Wavefunctions and Probabilities
Quantum mechanics describes electrons using a wavefunction, which represents the probability of finding the electron in a specific region around the nucleus. When an electron transitions between energy levels, its wave function changes instantaneously. This probabilistic behavior means we can predict the likelihood of a jump but not its exact timing.
This is similar to Schrödinger’s Cat—a thought experiment illustrating how a quantum system can exist in multiple states simultaneously until observed. (Read more about Schrödinger’s Cat here.)
In quantum computing, we leverage these probabilistic states. For example, if an atom transitions from helium to hydrogen over an hour, there’s a point where it exists as both simultaneously. The electron changes, a similar analogy to ice that changes to water. It is still H2O but in different forms. It isn’t until we look at it that we know if we have an ice cube or a puddle of water, but during the transition, we have both. Understanding this duality forms the basis of quantum computing.
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