The quantum decoherence

Quantum computers have shown some very unique properties that can be used in the future to make complex calculations that classical computers may require an eternity to execute, they only need the square root of the execution's time compared to normal computers and this is all due to the fact of superposing both 1 and 0 bites at the same time. This difference may seem poor but it grows remarkably stronger the more the delay increases.

If an operation needs 4 seconds with a normal computer it needs just 2 with a quantum computer but imagine an operation that requires 1.000.000 seconds with a classical computer, the square root of 1.000.000 is 1000 seconds, the difference is enormous about 277.5 hours.

All of us are using normal computers, and they seem to work pretty well, we don't even need to wait so much for data treatment because the delay is almost instantaneous and it'll be a waste to spend some extra thousand dollars to buy a quantum computer to just gain fractions of a second during information processing.

 So if you think quantum computers will replace normal computers you're wrong. However,  science does not stop on some daily life calculations, there are other mathematical problems that cannot be done manually neither by a normal computer, like quantum mechanics themselves. 

Yeah, it'll be cool if we manage to use something to make something from it that helps us solve itself!! 

We could precisely identify more wave functions, mass matrixes, we could construct a database for massive stars, black holes, dark matter and dark energy...

Impressive isn't it? But if the concept is clear, why we haven't been able to create an efficient quantum computer that possesses a significant amount of Qubits?

There is the main obstacle in quantum computing known as "Quantum Decoherence" this phenomenon is very complicated and hard to understand so I'll try explaining it with very simple yet effective way.

The quantum superposition is a characteristic of micro objects like electrons and it only vanishes by conducting an active measurement, but what's considered as a measurement? 

Measurement is a process executed by our consciousness or by machine, in other words, we can either observe instantly an electron in an arbitrary motion of spin to make its wave function collapse and have either up or down eigenstate, or a machine with electromagnetic waves or laser detectors....

The whole point is that a superposed state is when the particle is isolated from its surroundings, it's acting on its own. You may have wondered why macro objects aren't in a state of superposition,

why aren't we in various places at the same time?

 We already demonstrated using the Lewis de Broglie equation that the wavelength of a macro objects is so small to have a physical sense and so the effect is neglected. Other explanations suggest that if the quantum object is constituted by an outstanding amount of particles then the superposition is the average of these quantum states.

This somehow makes sense but what I want to believe is that macro objects are always vulnerable to an active measurement, objects are never isolated, we are exposed to air molecules, light photons, thermal waves... Interacting with these factors permanently gives us our collapsed state.

Even a collision with a single molecule can collapse our wave function. You can never escape to a 100% isolated environment even in space where no air is circulating there are a lot of measuring factors like light, radio waves and even dark energy and matter !!

To resume the concept of decoherence, we can say that it's the process when a particle loses its particle-wave duality forcing its wave function to collapse!

It's the process that causes light scattering where the light which is generally a wave becomes a particle that bounces in contact with a wall. In fact, this has a deeper meaning, because if we consider a light reflected by a mirror we can simply calculate the reflection angle by just knowing the initial position of the mirror whether it's horizontal or inclined by a certain angle. Eventually, we can determine in a very approximate way the location of light photons!!

Doesn't this remind you of something?

It's the quantum entanglement where determining the state of a single particle which is a mirror molecule is sufficient to identify the other (photon).

But what does all this shit have to do with quantum computers?

Qubits are also targeted by quantum decoherence which can have grievous consequences on the data processing, this can cause a leakage of information or even a deletion. Qubits are meant to be a superposition of the two states 1 and 0 but if this phenomenon occurs the collapse may cause them to behave like normal bits and enter the Quantum gates with a single 1 or 0 state. This may corrupt the whole system.

That's why quantum bits need to operate under extremely specific conditions that prevent them from interacting with other measuring factors like heat waves or their interaction with each other.

Cooling the computer ship to almost the absolute zero is one alternative, this helps suppress any upcoming heat waves and stabilize the motion of Qubits making them more controllable and reducing their interaction with each other.