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Software but Quantum - Part 1

Welcome to the Software but Quantum series. We're going to take a look at how Quantum Computers work and how algorithms and general software work on them. We're going to get into the little details, from the physics to the code and more.

Some might say that going in depth is unnecessary, but I always prefer to know how something works before I use it. So brace yourselves, there's going to be a lot of physics.

Let's get to work!

Quantum Mechanics are a bit of a mysterious art, but it tells a really beautiful story, the story of the really small. The most important concepts are something called Wave-Particle duality, (we'll call this WPD) and Superposition.

You may have learnt in school that Light travels as an electromagnetic wave, with a electric and magnetic oscillation field, and for a while in history, this theory worked all right. The double slit experiment demonstrated that light diffracts, and the only way to explain this was that light waves interfered with each other.

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But then a certain theoretical physicist by the name of Einstein discovered something called the photo-electric effect. It was known that hitting an electron with a wave of energy caused it to gain energy or be ejected entirely.

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But there was a bit of a problem. How much light? There needed to be a minimum amount (this is called the work-function 'Φ' or (Greek) 'phi'). A small amount of anything is called a Quanta. For example, I'm a Quanta of humankind, and a drop of water is a Quanta of the ocean.

So a Quanta of light is called the Photon. This is why Light behaves both as a particle and a wave, duality in essence. So, how does this matter? Well, at this point, if waves can become a particle, then can a particle behave as a wave?

Yes, yes they can.

I'm going to skip over this part, mostly because it's pretty simple. Physicists found that the double slit experiment also works for launched electrons, creating interference bands reminiscent of waves.

Luis De Broglie also proposed the following equation:

Let λ be the wavelength of the matter
Let h be Planck's Constant
Let v be the velocity of the particle

λ = h / mv.

So, this was established, and the physics world was changed forever. With such a groundbreaking theory, some interesting assumptions can be made. Do we ever really know where the particle is? How do waves become particles (called Wavefunction Collapse)? If particles like electrons are now also waves, how can we possibly know where they will be?

All this will lay the foundation for the concept of superposition, and how Quantum Computers use Quantum Bits (Qubits) to do math.


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