Quantum superposition

Quantum superposition of states and decoherence

Quantum superposition is a fundamental principle of quantum mechanics that states that linear combinations of solutions to the Schrödinger equation are also solutions of the Schrödinger equation. This follows from the fact that the Schrödinger equation is a linear differential equation in time and position. More precisely, the state of a system is given by a linear combination of all the eigenfunctions of the Schrödinger equation governing that system.

An example is a qubit used in quantum information processing. A qubit state is most generally a superposition of the basis states and :

Where is the quantum state of the qubit and , denote particular solutions to the Schrödinger equation in Dirac notation weighted by the complex numbers and . Here corresponds to the classical 0 bit and to the classical 1 bit. The probabilities of measuring the system in the or state are given by and respectively (see the Born's rule).

The interference fringes in the double-slit experiment provide another example of the superposition principle.


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