# How does a qubit represent the number two in quantum computing?

• Ut-Napishtim
In summary, qubits can exist in a superposition of 0 and 1, allowing for a greater number of possible states than classic bits. This superposition also allows for entanglement between multiple qubits, increasing the potential number of states even further. However, when measured, a qubit will collapse into a single defined state, either 0 or 1, with a certain probability based on its setup. This quantum aspect allows for a greater range of possibilities and applications, but for simpler tasks, regular computers may be more efficient.
Ut-Napishtim
Qubit can be ZERO and ONE at the same time. Right?

1 and 0 can represent TWO (10) in a binary system. Right? Therefore one qubit can represent number 2. Right?

My question. When this qubit is used to give a result of a calculation (is measured/evaluated somehow at the end of a calculation) it collapses into only one defined state ONE or ZERO. Right? HOW IS IT MADE THAT THE ANSWER (from this qubit) IS THE NUMBER TWO (which it was supposed to be)?

Please excuse a layman for trying to get some idea of quantum computing and many thanks for attention.

Last edited:
The difference between classic bit and qubit is that, while bit can take one of two different values ( 0 or 1) , qubit is a superposition (sum) of the two states simultaneously. When evaluated, qubit is presented in one of the two possible states ##|0\rangle## , ##|1\rangle## with a certain probability to be in one of them. The sum of the probabilities is 1 or 100%. One qubit is not equivalent to a classic bit - which has probabilities let's say p1, p2 to be 0 or 1 respectively, even though these may be equal to the probabilities of qubit, to be in the state ##|0\rangle## or ##|1\rangle##. The difference is that quantum superposition in qubit, encodes a phase between the two states - besides the probabilities, allowing interference of the two states. Also, the probability of each state is given by the square of the coefficient that define the specific set up of a qubit. As a formula: 1 qubit = ##a\cdot |1\rangle + b\cdot|0\rangle## where ##\left|{a}\right|^2 + \left|{b}\right|^2 = 1##

Well apart from all of that, one important distinction between qubits and bits is not only that the qubits can exist in superposition but they can also be entangled.

Not only can a qubit be in a superposition of 0 and 1, but a set of "N" qubits can be in a superposition of up to "2 to the N" states.
So, for example, 3 qubits can be in a state where they may code for 2 (010), 3 (011), 5(101), or 7(111), but not the other 4 codes. And 8 qubits could code for all prime numbers up to 251 or all of the composite numbers up to 255.

But simply coding for "2" may not be that useful. Most of the things you might want to do with "2" can be done with regular computers.

Hey Ut-Napishtim.

You should consider all possible states existing in super-position instead of having only one fixed value across the spectrum of states.

That is basically what the quantum aspect is - instead of having a definitive state you have everything happening at once and you have processes that decide how all of these things are entangled and eventually collapsed to some observable (single) state.

## What is a qubit?

A qubit (short for quantum bit) is the basic unit of quantum information. It is the quantum version of a classical bit, meaning it can represent both 0 and 1 at the same time, allowing for more complex calculations and faster processing in quantum computers.

## How does a qubit work?

A qubit is typically represented by the superposition of two quantum states, which can be thought of as a combination of 0 and 1. This allows for the qubit to exist in both states simultaneously, known as quantum entanglement. The manipulation of these states through quantum gates allows for complex operations and calculations to be performed.

## What is the difference between a qubit and a classical bit?

The main difference between a qubit and a classical bit is that a qubit can exist in multiple states at once, while a classical bit can only exist in either a 0 or 1 state. This allows for quantum computers to perform calculations much faster and more efficiently than classical computers.

## How are qubits measured?

Qubits are measured using quantum measurement techniques, which typically involve measuring the state of the qubit's superposition. This measurement collapses the qubit into either a 0 or 1 state and the result is recorded.

## What are the practical applications of qubits?

Qubits have a wide range of potential applications, particularly in the field of quantum computing. They can be used for faster data processing, secure communication, and simulating complex quantum systems. Qubits also have applications in other fields such as cryptography, metrology, and quantum sensing.

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