Applied group

We study the applications of quantum entanglement.

The probabilistic nature of quantum mechanics
In classical Newtonian mechanics, the world is deterministic. This means that if the conditions of a system are known (e.g. mass, velocity, etc.), then we can accurately know the motion of objects at all points in time, and they move in perfectly determined ways. This idea is illustrated by Laplace's demon, a hypothetical creature that knows the position and momentum of every atom in the universe and thus knows the past and future motion of all those atoms.

On the other hand, quantum mechanics is probabilistic. The motion of objects on a quantum scale is not perfectly determined. This is a result of Heisenberg's uncertainty principle, ΔxΔp ≥ ħ/2, which states that the position (whose uncertainty is Δ x ) and momentum ( whose uncertainty is  Δ p ) of a particle cannot both be measured exactly - knowing one automatically leads to high uncertainty in the other.

As such, we can never truly know where a quantum particle is or how fast it is moving at any point in time - we can only know the probability of it having a particular momentum and position at a time. This probability is given by |ψ|2, when the particle is represented by a wavefunction ψ.

What happens when we measure something in quantum mechanics? (all this is too simple and has to be rewritten)
Like everything in science, quantum mechanics would be useless if we couldn't use it to make predictions about real life. To see if the predictions it makes are good, (do you mean accurate?) we have to compare it to what we measure when we observe quantum systems, i.e. systems that we believe can be modeled by quantum mechanics.

The easiest way to visualise this is to think about flipping a coin as a quantum system. After we flick the coin into the air, and before it lands, we can't tell if it's going to be heads or tails, so it might as well be both at once!

This is very similar to the concept of superposition explained in the abstract group's page. What we are interested in however is what happens as soon as the coin lands on the table. We say that the state of the coin (either "heads" or "tails") has to be chosen, because you can't have a coin spinning through the table!

In the same way that the table "forces" the coin to become in one of the two "heads" or "tails" states, a measurement in quantum mechanics "collapses" a quantum system into a state that we hope to have predicted.