Quantum Computing — the big picture
By: Ihssene Brahimi
Tags: Tech, Quantum Computing, Technology

Enter the realm of quantum computing

“ If quantum mechanics hasn’t profoundly shocked you, you haven’t understood it yet” — Niels Bohr

What sets quantum computing apart from the computational herd is, in fact, the three fundamental properties of quantum physics: superposition, interference, and entanglement.

It’s all about Quantum Superposition!

Superposition: (also known as coherence) expresses the ability of the quantum system to exist in all of its theoretically possible states at once. In other words — as long as no measurement is performed, there is a certain probability to have one state AND a certain probability to have another state concurrently. But once we observe, only one result is obtained. Here is an example:

Say we roll a dice with sides numbered from one to six. As long as it doesn’t stop rolling, it takes all the six values — 1,2,3,4,5, and 6. But once landed, it becomes a normal dice with only one value — 1 or 2 or 3 or 4 or 5 or 6.

One other famous example is Erwin Schrödinger’s cat.

According to what we have seen so far; when a qubit is in a state of superposition, it forms a linear combination of an infinite number of states between 1 and 0. However, you will never know which state it will take until you actually look at it, which brings up our next phenomenon, quantum measurement.

Quantum measurement: (also known as decoherence) refers to the act of observing or measuring a quantum particle. This latter collapses or ruins the superposition state and the particle takes on a classical binary state of either 1 or 0 — nothing in-between.

Entanglement — The most romantic notion in physics.

“Spukhafte Fernwirkung” or ”Spooky action at a distance”

That’s how Albert Einstein described quantum entanglement. Weird huh?

Intrigued by the mind-bending phenomenon, he derided the notion, citing it as proof that quantum theory was flawed and incomplete. Is entanglement that baffling?!

While we don’t really want to go down the rabbit hole of entanglement, here is a simple explanation:

Quantum entanglement

Unlike in classical physics, pairs of particles are said to be coupled or entangled with each other, when they form a system such that the state of one particle is dependent on the state of the other particle. Simply put, whatsoever process the particle experiences, it correlates to the other particle as well.

Not to mention that even if separated, across insanely large distances of space and time — say light-years. These entangled particles, however, can remain perfectly connected.

What if a measurement is applied?

Since there is a correlation between the entangled qubits, measuring a state of one qubit provides the information of the other qubit such that if one of them collapses — due to measurement, the other one collapses too.

Now let’s go back to Einstein’s spukhafte Fernwirkung thing.

He believed there must have been something wrong with quantum mechanics. But thanks to scientists, this phenomenon has been proved with countless quantum physics experiments.

Sorry, Einstein, you missed it.

Remember, in the quantum theory, once two particles undergo a shared state, they are no longer separate entities but exist as one. Thus if entanglement reminds you of something, it won’t be other than the experience of falling in love. Does entanglement make sense now?

Quantum entanglement is awesome. Think about it. Entangled particles are bound to each other in a way they aren’t to any other particle in the universe. And when something happens to one, it immediately affects the other.

How beautiful!

Interference: is another incredible property of quantum mechanics, one that makes you think what in the world is going on behind the scenes of our reality. The great physicist Richard Feynman once said about interference:

“The essentials of quantum mechanics could be grasped from an exploration of interference and the double-slit experiment.”

Microsoft researchers defined interference as the intrinsic behavior of a qubit, due to superposition, to influence the probability of it collapsing one way or another.

It’s considered as one of the most challenging principles of quantum theory which states that the building particles cannot only be in more than one place at any given time (due to superposition), however, that an individual particle, such as a photon (light particles) can cross its trajectory and interfere with the direction of its path.