Useful sentences

• In quantum mechanics, the electric fields are operators as explained by second quantization and Fock states. Each electrical field operator can further be expressed in terms of modes representing the wave behavior and amplitude operators, which are typically represented by the dimensionless creation and annihilation operators. In this theory, the four ports of the beam splitter are represented by a photon number state \({\displaystyle |n\rangle }|n\rangle\) and the action of a creation operation is \({\displaystyle {\hat {a}}^{\dagger }|n\rangle ={\sqrt {n+1}}|n+1\rangle }{\displaystyle {\hat {a}}^{\dagger }|n\rangle ={\sqrt {n+1}}|n+1\rangle }\).

• The most important noise in a solid-state qubit is a dephasing noise.^[1]

• However, all non-full-rank states can be approximated by full-rank states with arbitrary precision, and all states that can be generated realistically are mixed. (From paper https://journals.aps.org/pra/pdf/10.1103/PhysRevA.84.042121).

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1. DOI: 10.1103/PhysRevA.102.022602 ↩︎