What is a Qubit in quantum computing?
Q: What is a Qubit in quantum computing?
A: A qubit is a unit of measure used in quantum computing with two distinct states: 0 state and the 1 state, and can also have a state that is somewhere in-between, called a "superposition."
Q: Can you measure a qubit in superposition?
A: You cannot measure the superposition without the superposition going away (changing). If you try to measure a qubit that is in a superposition, the qubit will change, and become one of two states. The resulting state the qubit changes to depends on how it is measured.
Q: How is a qubit represented as a vector?
A: A qubit can be represented as a 2-element column vector. A qubit in the 0 state looks like [1, 0]. A qubit in the 1 state looks like [0, 1]. In general, a qubit state will look like [α, β] where |α|^2 + |β|^2 = 1.
Q: What are amplitudes of a qubit state?
A: α and β are called amplitudes. They can be complex numbers. Each state has an amplitude. By squaring a state's amplitude, you can get the probability of measuring that state.
Q: What is the phase of a qubit state?
A: Each state can also have a phase. The phase is part of the amplitude and is what can make the amplitude a complex number. A state's phase is like how much that state has rotated. The angle of phase is usually represented as either Φ or φ.
Q: How does the phase affect the amplitude of a qubit?
A: The phase angle becomes part of a state's amplitude, and gets multiplied with the amplitude. A phase angle of 0 makes the amplitudes positive real numbers, and a phase angle of π makes the amplitudes negative real numbers. A phase angle of π/2 makes the amplitudes positive imaginary numbers, and a phase angle of 3π/2 makes the amplitudes negative imaginary numbers.
Q: How are qubits generally written in notation?
A: Qubits are generally written as kets, which look like |ψ⟩. The 0 and 1 state are written as |0⟩ and |1⟩ respectively. A general qubit in ket notation will be written as |ψ⟩ = α|0⟩ + β|1⟩.
