In previous post we show short introduction of some conceptions and great resources on the topic:

quantum computing for beginners

In this post we will continue with few others.

Uncertainty principle

As you know in classic computers:

2 + 2 = 4

but this is not always a truth about quantum computers:

In order to get the state of the system you need to perform a measurement. But it is not possible to do measurement without disturbing the system. In some ways is like a catch 22 - you can read more about it here - Catch-22 (logic)

So can we have in quantum computer:

2 + 2 = cat ?

I guess no :) But in order to get outcome you will need to carry out a measurement.

Quantum Entanglement

In previous post we discuss some ideas about it. In this post we will try to add new points to this conception. A basic explanation will be:

There is a relation between some features of entangled particles.

So imagine that you have two boxes and a pair of shoes. Let say that someone decided to hide one shoe in each box. So if you open one of the boxes and you get right shoe - you will know what is inside the other box - left shoe. Before the first try you don't know what is the first shoe. But you don't need to open the second box in order to find the second one. This is a rough explanation of quantum entanglement.

Another way to imagine is by tossing two coins. If the coins are entangled then finding that first is head - you will know that second is tail. Why this is not working for real coins. Because entanglement is property of micro / quantum world.

Superposition state

As we mention in previous post superposition can be explained as:

every state exists in any possible configuration

One way to imagine it is by the time when you wake up. You have several minutes in which you are half wake up and half sleeping. You are both at the same time. And only by pure chance you can continue to sleep or to really wake up. In order to be sure are you sleeping someone should carry out a measurement of you by Ice Bucket Challenge :)

Decoherence state

Decoherence is a process of removing the quantum characteristics and returning individual properties to each component of the system. On the other hand in coherent state all quantum properties are identified for each component of the system. The shortest explanation would be:

Quantum decoherence is the loss of quantum coherence.

If you want to go deep in decoherence you can check this article: The Role of Decoherence in Quantum Mechanics