Two-level system
Encyclopedia : T : TW : TWO : Two-level system
In quantum mechanics, a two-level system is a system in which there are two physical states of different energy. That is, if we take the time-independent Hamiltonian to be [H], then we say that the two levels are [\psi_a] and [\psi_b] with corresponding energy eigenvalues [E_a] and [E_b], which may or may not be different. These states are always taken to be orthonormal, i.e. [\left\langle\psi_a|\psi_b\right\rangle=\delta_.] If the system is initialized in the state [\Psi(t=0)=c_a\left.|\psi_a\right\rangle+c_b\left.|\psi_b\right\rangle] then after evolving for some time [t] under the Hamiltonian [H], the state will be [\Psi(t) = c_a e^}\left|\psi_a\right\rangle+c_b e^}\left|\psi_b\right\rangle]
The set of all states in a two-level system is known as a Bloch sphere. Two-level systems are particularly important to the field of quantum computing as they can be used to implement qubits.
See also
From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.