Clarification on what we can consider a qubit to be

In summary, a qubit in a 2 level quantum system can be represented by a pair of states, such as |0> and |1>, or by the superposition of these states, such as α|0> + β|1>. Both the individual states and the superposition are considered to be qubits, and they form a useful pair in anti-commuting observables.
  • #1
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In a 2 level quantum system, should I consider the states

[tex] |0> [/tex]

and

[tex] |1|> [/tex]

to be qubits by themselves?

Or is only the SUPERPOSITION of these two states,

[tex] \alpha |0> + \beta |1> [/tex]

considered to be a qubit?
 
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  • #2
Nevermind, they have to be qubits as well. If we consider our superposition to be a qubit, then we can set ## \alpha = 1 ## and ## \beta = 0 ## and that should be an appropriate qubit state.
 
  • #3
eprparadox said:
In a 2 level quantum system, should I consider [...] to be qubits by themselves?
The qubit is the 2-state system, just like a classical bit is a binary variable. The states are not qubits, but the qauntum analogues of the classical values.
 
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  • #4
You should consider the pair to form a qubit. On their own they're not very useful.

Another useful way to think about what a qubit is is as an anti-commuting pair of observables, such as the observable ##|0\rangle##-vs-##|1\rangle## paired with the observable ##\frac{1}{\sqrt{2}} \left( |0\rangle + |1\rangle \right)##-vs-##\frac{1}{\sqrt{2}} \left( |0\rangle - |1\rangle \right)##.
 
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1. What is a qubit?

A qubit, short for quantum bit, is the basic unit of information in quantum computing. It is the quantum mechanical equivalent of a classical bit, and can represent a 0, 1, or a superposition of both states simultaneously.

2. How is a qubit different from a classical bit?

A classical bit can only represent one of two states (0 or 1) at a time, while a qubit can represent both states simultaneously in a superposition. This allows for more complex and powerful computations to be performed in quantum computing.

3. What physical systems can be used to implement a qubit?

There are multiple physical systems that can be used to implement a qubit, such as photons, ions, and superconducting circuits. Each system has its own advantages and challenges, and the choice depends on the specific application and requirements.

4. How is information stored and manipulated in a qubit?

Information is stored in the state of a qubit, which can be manipulated using quantum gates such as the Hadamard gate, CNOT gate, and others. These gates can change the state of a qubit and perform operations on it, similar to how logic gates work in classical computing.

5. Can a qubit be in more than two states simultaneously?

Yes, a qubit can be in a superposition of multiple states simultaneously. This is one of the key properties of qubits that allows for more complex and powerful computations in quantum computing.

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