The Fundamentals of Quantum Computing
Qubits. Quantum bits. Are they really all that spectacular? Now I may be a bit biased but yes, yes they are.
Despite our reverence for the power of our modern technology, there are still some things conventional, classical computers aren’t great at — and may not even be able to do.
A computer is made up of very simple components doing very simple things; representing data, the means of processing it, and control mechanisms. The classical, very limited model of computing with which our conventional computers are built upon will only support our innovation for so long. Moore’s law (the observation that the number of transistors in a dense integrated circuit doubles about every two years) is about to reach its physical limits, and understanding our tech at a subatomic level is the next step to our technological progression.
This article is going to give you a brief, high-level understanding of the weird but exciting world of quantum mechanics by exploring properties displayed by sub-atomic particles and the fundamental unit of information in a quantum computer: the qubit.
Classical computers are defined by bits, and Quantum Computers — qubits
Simple, right?
Not really…
Classical computers contain computer chips which contain modules, which contain logic gates, which contain transistors. (Talk about a tongue twister.)
In computers, a transistor is the simplest form of a data processor that can block or open the way for information to come through. This information is made up of bits, which can be set to a series of 0s or 1s in a specific sequence that is used to represent much more complex data.
As transistors shrink to the size of a couple of atoms, the magical powers of quantum physics start to appear.
Qubit = quantum form of a bit
Qubits can present 3 main ‘special’ properties:
- Superposition (ability to be in a state of 0 and 1 at the same time)
- Entanglement (spooky action at a distance) — Einstein’s words…not mine…
- Tunnelling (finite probability of a particle moving through barriers it classically cannot)
Wait, what?
So, you’re saying… if I harness the imperial powers of qubits, I can be in two places at once, be psychic, and teleport? Where do I sign??
Not so fast.
Firstly, quantum computers harness the power of superposition and entanglement… we haven’t even gotten to figuring out quantum tunnelling!
As famed theoretical physicist Richard Feynman once said:
“I think I can safely say that nobody understands quantum mechanics.”
But let's try anyway.
Superposition (creative subtitle here)
Ah, superposition. The reason why quantum computer engineers feel excited and put down at the same time…
Remember when we recapped how bits are set to be in a state either of 1 or 0, and how qubits can be in a superposition of 1 and 0? Let’s visualize this:
Imagine having a coin. Unless you’re Two-Face from Batman, you have heads and tails, the same way a bit has 1s and 0s. Now spin the coin. Can you still tell if the coin is heads or tails? It’s sorta both… at the same time.
The same goes for a qubit. You can have a 1 or a 0 like a regular bit, and something sort of… in between (a superposition).
To know whether an electron/photon/neutron/any-other-tron is in a state of 1, 0 or superposition, they must be measured. But qubits are awfully dainty. They like to be in complete isolation when they do their own thing. Any interference from its environment will immediately force it to collapse out of its superposition. In the coin analogy, this would be a hand smacking the coin down — forcing it to read either heads or tails.
This phenomenon is called decoherence.
When measured, the qubit doesn’t randomly decohere into 1 or 0. The probability of the measured qubit being either 1 or 0 is related to the state that the qubit was originally in. Hence, why you’ll sometimes hear fancy people talk about quantum physics being “probabilistic”, rather than “deterministic”.
Going back to the coin analogy, the more the coin is tipping towards heads, the more likely you’ll measure heads. The same idea applies to tails.
Entanglement
You know that propaganda that romance novels try to sell you when they talk about you and your soulmate being connected down to the very soul? How when you’re scared/in danger/hungry, your S.O. knows how you feel and what to do in that exact location in space, at that exact time? If playing copy-cat were what constitutes a happy relationship, it turns out that the particles residing under the kingdom of quantum mechanics live better love lives than us.
What Einstein called “(spoopy) action at a distance” is actually what we now call “quantum entanglement” or, the connection of qubits across space.
Going back to the coin analogy: you’re walking down the sidewalk and *gasp* you find a lucky nickel! Feeling rich, you now have two coins to understand quantum mechanics. If you were to spin both coins and they were to interact in a very specific way, they would automatically get hopelessly entangled. Now, the state of your lucky nickel will give you precise information about the state of your other coin — no matter either location in space. If you were to measure your nickel to be head, fly yourself to Antarctica, then observed your other coin, it would be heads! Despite being thousands of miles (or even light years) apart, it’s been proven that if you measure an entangled qubit, you will know instantly the state of its partner.
Tunnelling
So, remember when I pointed out how quantum physics is probabilistic, rather than deterministic? This means we can never pinpoint where an electron (or any other subatomic particle) really is. We can merely guess with a fairly high probability that the electron is at a certain location. This range of probabilities can be described by a mathematical wave function that allows you to determine all the possible positions a particle can occupy, and the likelihood of it occupying any one of them.
Particle-wave functions (or ‘probability waves, for the sake of saving brain cells) can ‘leak’ across barriers, if the barrier is thin enough.
Instead of there being an abrupt drop-off where the particle wave hits the barrier, there is a very quick exponential drop-off or— to be more professional — the evanescent wave. The evanescent wave decays incredibly quickly and lasts only a few wavelengths before disappearing.
This, ‘evanescent wave’ is the reason behind why quantum tunneling is possible. Remember: we’re trading our electron for probability waves, meaning when our wave comes into contact with the potential boundary, an evanescent wave is formed. If the barrier is thin enough, some of the wave could go through the barrier, and actually appear on the other side.
So, if some of our probability wave makes it past the barrier, and our probability wave represents our electron… there is a small, but non-zero chance that our electron has surpassed the barrier!
If you would like to get into the specifics of the who what where and why’s of this phenomenon, the best, most valid explanation I could give you is… “because, math.”
While extremely fascinating, it’s complexity leads me to think… this can be a discussion for another day.
To recap, we’ve learned 3 things:
- Qubits are the fundamental unit of information for quantum computers
- Superposition, Entanglement, and Tunnelling are all special properties that define a qubit
- Decoherence is sometimes a pain in the butt and won’t let us truly observe qubits
If you’ve gotten this far into my article, you might be asking… but how does all this affect me? Well, I’m glad I asked for you.
Quick Math Session
So you’re sitting in your grade 4 math class, writing out equations, number trees and (ugh) prime factorization. Your pencil drags across the grid answer sheet, your mind begging you to finish the seemingly harmless process of dividing and multiplying numbers that would never have any real-world value… all of which turns out to be the fundamental concept that keeps your facebook messages, bank digits, and Netflix password safe.
Cryptography.
If this definition didn’t really help you, that’s ok… it didn’t help me either. Cryptography is basically a technique used in encryption, used because of its ability to evade the seemingly all-powerful digital computer.
Let's take 15 for an example. How long does it take for you to find two prime numbers that, when multiplied, generate the number 15? It doesn’t really take any special mathematical methods to figure out 5 and 3, both prime numbers, generate 15 when multiplied. So what about 93847? Aha. Successfully triggered your disdain for math. Even with fancy methods and strategies, it’s bound to take you a couple of minutes to find out 13 x 7219 are the prime factors of 93847. Don’t worry though… it turns out your conventional computer/device is terrible at prime factorization too. In fact, if given really really really large numbers, as our keys generally are, it could take weeks, months, even years, for decryption to occur.
This is because of the fundamental way digital computers receive and process information — through bits that only read 1s and 0s. When encountering a problem, or in our case, an extremely large number, the digital computer must work through every single possibility, one at a time, before finding the correct prime factors.
Because of superposition, qubits enable quantum computers to test each possible solution at the same time. My super amazing friend Tanisha Bassan gives a great analogy in her article, Brief Introduction to Quantum Computing:
Imagine the following example, I write an X on a random page in a random book in a library with 1 million books and tell a quantum and classical computer to find the X. For a classical computer, it would have to sort through every page of every book one by one to find the X which would consume a lot of time. For a quantum computer, a qubit in superposition can be in a multiple places at once so it can analyze every page at the same time and find the X instantly.
Boom.
Incredible, right?
The lil’ powerhouses of a computer could also allow us to work on so many other scientific affairs:
- General optimization problems
- Significantly improving AI
- Drug simulation
But going into detail with all this can be a time for another article (*hint hint wink wink)
So you see, comparing a qubit to a moody teen isn’t so difficult. Both are really, quite fragile, difficult to observe/understand, and love to act out when you come into contact with it. But when you give it some direction and manage its potential… the outcome can be spectacular.
Cool companies to note
Xanadu
Photonic quantum computing and advanced artificial intelligence company that designs and integrates quantum silicon photonic chips into existing hardware to create truly full-stack quantum computing.
1QBit
Looking to use quantum algorithms to apply computation breakthroughs to machine intelligence and optimization science while being widely accessible.
D-Wave
World’s first quantum computing company and leads the industry when it comes to the development and delivery of quantum computing systems and software.
For the love of…
All that being said, there’s still a long way to go for quantum computers. Qubits are difficult to control, and physicists are still tryna get the darn thing to do what they’re told. But, progress is being made. The incredible field of quantum physics is still young, and as with any technology in its infancy, there are likely many innovative ways to use it that haven’t been conceived. Prepare for the future… this is all part of the seemingly never-ending march of technological advancement.
If you liked this article I would be super excited if you hit the clap button :) (I just learned you can clap an article 50 times continuously) or share with your other amazing and curious friends! I love having conversations about all things tech/philosophy/life related so feel free to reach out to me via the comment section or subscribe to my medium profile! I also write monthly newsletters and would love to bring you on for my journey. :)
Anyways, thanks so much for reading and have a lovely day!
If you enjoyed this article:
- Share it with your network
- Follow my Linkedin and Medium to keep updated with my progress in quantum computing
- Join my monthly newsletter via DM’ing me!
This story is published in Noteworthy, where 10,000+ readers come every day to learn about the people & ideas shaping the products we love.
Follow our publication to see more product & design stories featured by the Journal team.
