What is the accepted interpretation of quantum mechanics?

The most widely accepted interpretation of quantum mechanics seems to be the Copenhagen one. If I got it right, it’s heavily relaying on the two following principles (among others): Superposition: a quantum system is at the same time in all the states it could possibly be in.

What is outer product rule?

In linear algebra, the outer product of two coordinate vectors is a matrix. If the two vectors have dimensions n and m, then their outer product is an n × m matrix. More generally, given two tensors (multidimensional arrays of numbers), their outer product is a tensor.

Why is bra-ket notation used in quantum mechanics?

As far as I know, Dirac probably invented it while studying quantum mechanics, and so historically the notation has mostly been used to denote the vectors that show up in quantum mechanics, i.e. quantum states. Bra-ket notation is the standard in any quantum mechanics context, not just quantum computation.

What is the bra-ket formalism?

The bra-ket formalism was introduced by Paul Dirac in order to describe in a uniform manner vectors and linear operators both in the abstract Hilbert space of the state vectors, H, and in the extensions of H which are used to solve the eigenvector problem for observables with continuous spectrum.

What is the difference between a bra and a ket | ψ ⟩?

As already explained by others, a ket | ψ ⟩ is just a vector. A bra ⟨ ψ | is the Hermitian conjugate of the vector. You can multiply a vector with a number in the usual way. Now comes the fun part: You can write the scalar product of two vectors | ψ ⟩ and | ϕ ⟩ as ⟨ ϕ | ψ ⟩.

Is the scalar product of kets between kets and bras Hermitian?

This also denotes the scalar product of the ordered pair of kets ∣ψ⟩, ∣ϕ⟩ and the scalar product of the ordered pair of bras ⟨ϕ∣, ⟨ψ∣. It follows that the scalar product between kets and that between bras is Hermitian, i.e.