Comments about "Qubit" in Wikipedia
This document contains comments about the article https://en.wikipedia.org/wiki/Qubit in Wikipedia
 The text in italics is copied from that url
 Immediate followed by some comments
In the last paragraph I explain my own opinion.
Contents
Reflection
Introduction
The article starts with the following sentence.














1 Etymology










2 Bit versus qubit

A binary digit, characterized as 0 or 1, is used to represent information in classical computers.

The importance is that a bit is either true or false.
If you ask a farmer how many cows he has and his answer his 5 than you need 3 bits to store that value. That is straight forward.
What is important when you measure these 3 bits each time the answer is the same i.e. 5



There are two possible outcomes for the measurement of a qubit—usually taken to have the value "0" and "1", like a bit or binary digit.

This sentence is not clear.

However, whereas the state of a bit can only be either 0 or 1, the general state of a qubit according to quantum mechanics can be a coherent superposition of both.

Quantum mechanics has nothing to do with this.
What you have is a physical 'object' and when you perform a measurement in certain cases the outcome is a "0" and in other cases you get a "1".
This implies that before you perform a measurement the object is in superposition of both states.
The question to answer is what are the physical pecularities of this 'object'. 8 Physical implementations












3 Standard representation










4 Qubit states
 A pure qubit state is a coherent superposition of the basis states. This means that a single qubit can be described by a linear combination of
 phi> = a0> + ß1>
where a and ß are the probability amplitudes, that are both complex numbers.

This seems easy, but it is in reality very complex, because complex numbers are in some way or another involved. See also next sentence

When we measure this qubit in the standard basis, according to the Born rule, the probability of outcome 0> with value "0" is  a ^ 2 or alpha^2 and the probability of outcome 1> with value "1" is  ß ^2 or beta^2







4.1 Bloch sphere representation










4.2 Mixed state










5 Operations on qubits










6 Quantum entanglement










6.1 Controlled gate to construct the Bell state










6.2 Applications










7 Quantum register










7.1 Qudits and qutrits










8 Physical implementations










9 Qubit storage










10. See also
Following is a list with "Comments in Wikipedia" about related subjects
Reflection 1  Physical
A clasical Qubit is a very simple physical object. . It has two physical states which are stable and the state is either defined 0 or 1. Stable in this sense means the physical state does not change if there is no extra 'outside' influence. In the normal operation is not the case because the state of a computer changes accordingly to the requests initiated by a program.
A Quantum Qubit is a very complex physical object. because the state depends about the physics of the material that it is made of and can have any value, however, I expect in reality only a limited number.
Reflection 2
Reflection 3
Feedback
If you want to give a comment you can use the following form Comment form
Created: 2 March 2019
Go Back to Wikipedia Comments in Wikipedia documents
Back to my home page Index