# A qubit walks into a bar

### Inside a crazy Quantum world - first it rewrote Physics and now it's rewiring Computing

A qubit walks into a bar and orders a drink. The bartender asks, “Will that be a 0 or a 1?” The qubit says, “Yes.”

🤣

Buckle up! 5 minutes from now not only will you get the joke but also why quantum computing is a big deal. Hold off on that white lab coat though - reading this will not get you any closer to being a for real physicist.1

Before computer science heard of quantum mechanics it messed with the biggest brains in physics. Albert Einstein - not a fan. He didn’t like that quantum physics isn’t precise or deterministic like classical physics. He said “God does not play dice with the universe2 🎲.” Emoji’s mine because I need AI Einstein to chat with.

Einstein particularly disliked quantum entanglement where two or more particles behave like a single entity even when far apart. Without Entanglement, there are no quantum computers. “Spooky action at a distance 👻” is what Einstein called it.

This from the dude who came up with the totally nutso theory of Relativity, that includes light bending, space warping, black holes sucking and of course time itself slowing down when you travel close to the speed of light.

Don’t be like Einstein. Suspend disbelief, trust science. Quantum mechanics is real and proven and coming soon to a computer near you. The world of the very small - that our large(r) world is entirely comprised of - just doesn’t behave as you’d expect and that’s the magic of nature, the magic of the universe.

Ironically, Einstein’s Theory of Relativity which enables us to understand the biggest thing (the Universe) led to the field of quantum mechanics that explains the smallest sub-atomic particles.

Classical physics starting with Newton brilliantly describes everything we see around us. For example, if you throw a thing or launch a thing, classical mechanics will tell you with precision where it will end up based on its trajectory.

Remember last week the Dali container ship that took out the Francis Scott Key bridge? The New York Times did the math and figured out it hit the bridge with the force of a rocket launch. Newton’s second law F=ma or Force = mass times acceleration3 is the math.

It’s pretty wonderful to have physics around to explain how the world we see works in predictable ways. Newton’s third law - “for every action there is an equal and opposite reaction,” nicely jives with our mental models of cause and effect.

But classical physics doesn’t explain the behavior of the tiniest things - atoms and sub-atomic particles - that make up everything everywhere. For example, if you heat up a bit of metal why does it give off radiation? As it gets hotter why does it turn red then yellow then white?

Without quantum mechanics we wouldn’t have MRIs or Lasers or Electron Microscopes. Oh and chips! Computers are not possible without quantum mechanics describing the properties of silicon that make it a semiconductor.

Transistors made of silicon form the basis of all classical computers today. Transistors corral electrons to represent one of two states: on or off, zero or one. This is a single **bit**** **- the fundamental unit of all computing today. We pack billions of transistors on a chip, capable of processing billions of bits. Everything on a computer, a phone, a game console, any piece of software - ultimately gets translated into a bunch of zeros and ones or bits.

Bits are kinda like minions - simple minded but effective and when you get enough of them together you can build super cool things like … a quantum computer.

The fundamental unit of a quantum computer is a * qubit *and they have properties that behave very differently than bits. Unlike the physics of what we can see, quantum mechanics is bizarre and does

*not*fit within our mental models of how the world works.

Qubits come in different flavors - we’re still trying to find the most efficient way to build them comparable to a transistor - but they all are made of subatomic particles and share the same mind-blowing properties:

Qubits aren’t one thing. They can be a zero, they can be a one, they can be everything in between. Imagine a coin that’s neither heads nor tails but constantly spinning - you don’t know the value until you pluck it from the air and slap it on your wrist. This is called

and it’s very powerful because all of a sudden, our unit of compute can represent a bunch of states versus just one. That’s why our qubit tells the bartender “Yes, I’ll take a 0 and a 1 on the rocks please.”**Superposition**Qubits are tightly correlated, meaning if you know the state of one you immediately know the state of the other ones they are correlated with. More than correlation - once Qubits are tied together in this way, they are effectively the same entity with the same wavelength, even if they are on opposite sides of the planet! This is what Einstein called Spooky action 👻 and it’s called

**Entaglement****.**While nature manipulates subatomic particles at will, we have a harder time. Coaxing qubits into Superposition

and it’s a fragile state. 99% of what you see in a Quantum Computer is the cooling system to keep the qubits chilling at absolute zero4 to minimize interference.5**Coherence**

The combination of #1 and #2 - Superposition & Entanglement is where the magic happens. This is how quantum computers do a bunch of complex calculations* at the same time*. Something no classical computer will ever do.

Check this example:

Mickey mouse on the left is using a classical computer to get through the maze and eat yummy cheese. Mickey’s computer has to try every turn, sequentially testing every possible path through the maze.

Mighty mouse on the right got himself a quantum computer and he’s gunna eat the yummy cheese a *lot *sooner. Rather than trying each path one by one, Mighty’s quantum computer evaluates every path simultaneously!

The more qubits, the more complex tasks can be executed in parallel. This is why quantum computers represent a massive jump in computing capability to take on our toughest problems in medicine, energy, AI, and of course physics.

Maybe you’ve seen a headline about how China is going to solve quantum computing first and steal all our secrets? It’s true that scale quantum computers will crack some of today’s most complex ciphers like RSA. Don’t sweat it, post quantum cryptography is already baked, and it’ll take a quantum computer with about 20 million qubits to crack RSA. The largest quantum computer we’ve ever built is 1,000 qubits.

Quantum computer magic may still be a few years off, but the race is heating up and we’re watching.

Why did the qubit cross the road? Because it was already on the other side.

🤣

best, Andrew

Last week’s article was a hit! Twice as many of you read it (500) then my previous most popular article. I don’t know why but it’s pretty awesome so check it out if you missed it.

When I was a kid I wanted to be an Astrophysicist. I read some books, got hyped, went to Berkeley, got crushed. Physics 1A was not kind to me, hello computer science. Caltech has the best primer on quantum physics if you want to get hyped: Quantum Physics Explained

Einstein was agnostic but believed in a cosmic religion that is revealed “… in the harmony of all that exists, not in a God who concerns himself with the fate and the doings of mankind.”

The Dali was a fully loaded massive container ship weighing an estimated 100,000 metric tons

Absolute Zero is Zero kelvin and that’s -273 Celsius or -460 Farenheit 🥶

Even so, qubits frequently fall out of Coherence into a state called, shockingly, Decoherence. This introduces errors. Classical computers have similar problems but much less frequently. Error correction addresses this and quantum error correction is one of the key problems that has to be addressed to scale quantum computers.