There are 2 types of computers: Classical and Quantum Computers
- Classical computers are the computers that you’re using right now. Ones that use electrical transistors to represent bits. They’ve been around since 1936, when Alan Turing proposed the “Universal Turing machine”.
- Quantum Computers are computers that use quantum phenomena to represent and compute their data. It was first proposed in 1980 by Paul Benioff to create a quantum model of Turing machines.
The reason why quantum computers have such a ridiculous speed advantage is due to their quantum properties. These quantum properties allow for quantum computers to be extremely fast compared to classical computers.
Since quantum computers are based on classical computers, many of the concepts and components of quantum computers are similar to classical computers.
In classical computers, the lowest level of computation is within the bits. Everything that you’re seeing right now is due to the transistors in your computer switching the bits on or off. These bits are represented in 0s and 1s.
Now here’s the cool part. By themselves, they can only represent 2 states: 0 & 1. But if you have 2 bits, you can represent 4 states: 00, 01, 10, 11. The number of states is equal to 2 to the power of the number of bits there are.
The property of regular bits is that they can only represent 1 state at a time. But quantum bits take that property to the next level…
A quantum phenomenon that quantum computers use extensively is called superposition. Let’s use an analogy! A coin has 2 states: heads or tails. But when you spin the coin, what state is it? It’s both heads and tails!
Now replace a coin with a bit. A qubit is just a bit that’s both 0 and 1 at the same time! This enables it to take many states at once. For example, with 1 qubit you can be in 2 states at once. But with 2 qubits it’s 4 states at the same time, and with 4 qubits it’s 16!
The major difference between classical and quantum bits is classical bits can only be in 1 state at a time, while qubits can be in many states at the same time!
This has lots of benefits that we’ll get into later, but let’s get into what exactly we do with bits and qubits in a computer.
By themselves, bits are rather useless. But with the help of classical gates, we’re able to transform them into powerful and useful tools. Gates are like a function, they take in 1 or multiple bits and then spit out a result.
It is through the combination of these logic gates that give rise to functions like multiplication, division, displaying images, and playing sounds!
Much like how classical gates manipulate classical bits, quantum gates manipulate qubits. But there’s a big difference! Since qubits have quantum properties we can have a lot more different gates and functions for them!
When qubits are in a superposition, they have a certain probability to be a 0 or a 1. It can have a 50/50 percent to be a 0 or 1, but it can also take on different states like 30/70 or 5/95. We refer to this as the qubit having different rotations.
There are lots of gates that play around with the rotation of the qubit like the Not, Pauli-Z and Hadamard gates! These gates rotate the qubit, but also play with the probabilities and states of the qubit. These gates are very similar to classical gates.
Another cool property of qubits is entanglement! This is when 2 qubits are intertwined with each other, such that when you look at 1 qubit, you automatically know the state of the other qubit!
Several gates use this property — all of which are unique to quantum computing! There are CNOT, CZ, and Toffoli gates! These gates also use multiple qubits to produce an output.
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