Behind the Scenes: Quantum Computing

What is behind the efficiency of Quantum Computers? Quantum Physics.

So, what is it?

To explain at a very basic level, a quantum computer is a computational device that relies on the phenomena of quantum physics. By using the unusual occurrences in the quantum realm to its advantage, the computer is allowed to perform computations in a much faster and effective way.

Quantum Mechanics

Quantum physics describes how all the molecules, atoms, and subatomic particles act. These particles don’t work the way that we are used to in our reality, and the smartest quantum physicists (think Albert Einstein level) still don’t have explanations for the occurrence of certain phenomena.

Thankfully, you only really need to know quantum mechanics at a basic level to understand how quantum computers work!

Superposition

Our regular computers work with binary bits which store 1 of 2 states — 0 or 1. Combinations of these bits are used to store more complex information. A large enough amount of bytes (8 bits) allows for them to store a finite number of states, like the words on your screen as you read this article.

But what if you could use something that in addition to being, 0 or 1, could also be both a 0 and 1 at the same time.

In comes the Qubit.

Regular computer store their information in bits, and quantum computers store it in qubits.

Quantum computers use qubits to store information. Qubits include photons, atoms, ions, electrons, and other quantum particles which can exist in 1 of 2 values, as well as the superposition of those values.

Superposition is a quantum physics phenomenon that allows quantum particles to be both of 2 possible states at the same time.

So whereas 4 regular bits represent 1 of the16 combinations at one time, 4 qubits in superposition can be all 16 combinations at once.

The incorporation of superposition into computers is a game-changer. It is what allows qubits to have parallelism. Parallelism allows quantum computers to work a million computations at once, whereas desktop computers would only be able to do 1.

Spin

The spin of a qubit is a quantum behavior that describes its angular momentum/trajectory. If the quantum particle spins clockwise on its axis, it is described as spin-up; counterclockwise is spin-down. In terms of computation, spin-up can correspond to a 0 and spin-down to a 1.

Bloch Sphere

As mentioned before, superposition allows qubits to be 2 possible states at the same time. This is a little hard to imagine, after all how can something be up and down, or on and off, or 0 and 1 all at the same time! Even more confusing, how can we even measure this quantum state, that isn’t in 1 single state, to make calculations?

The answer is we can’t. When a qubit passes through a quantum gate (like a transistor) in order to measure it, it collapses into one of the two possible states, either a 0 or 1.

Entanglement

Quantum entanglement is a close connection between a pair or groups of quantum systems.

When observing a single particle, we say it has its own quantum state. But when 2 of these particles get close together and act on one another, they become entangled, or an entangled system.

So, if 2 qubits were to get entangled, it would cause each qubit to react to a change in the others’ state, instantaneously, no matter how far apart.

Implementing the phenomenon that is quantum entanglement into a quantum computer solves this problem. If scientists use outside forces to entangle 2 qubits, and the second qubit can take on the properties of the first qubit.

When left alone, the qubits will spin in all directions. But, the instant one of the qubits in the pair is disturbed it will choose one state/value. At the same time, the second entangled qubit will react and choose an opposite state/value. This allows scientists to measure the properties of one entangled qubit to figure out the properties of the other half of its pair.

Key Takeaways

• By tapping into the strange and unknown realities of quantum mechanics, we can use quantum computing to solve problems that would take traditional computer lifetimes.
• A qubit can be either — 0 or 1, or 0 and 1, which describes superposition before measurements are made.
• Quantum entanglement allows scientists to only measure 1 qubit and figure out the value of the other qubit in the pair instantaneously because they are a part of the same entangled system.
• Implementing the phenomena of superposition and entanglement would make quantum computers more efficient than a regular computer.