Search results
Results From The WOW.Com Content Network
In quantum physics, a quantum state is a mathematical entity that embodies the knowledge of a quantum system. Quantum mechanics specifies the construction, evolution, and measurement of a quantum state. The result is a prediction for the system represented by the state. Knowledge of the quantum state, and the rules for the system's evolution in ...
Purity (quantum mechanics) In quantum mechanics, and especially quantum information theory, the purity of a normalized quantum state is a scalar defined as where is the density matrix of the state and is the trace operation. The purity defines a measure on quantum states, giving information on how much a state is mixed.
A pure quantum state is a state that can not be written as a probabilistic mixture, or convex combination, of other quantum states. [4] There are several equivalent characterizations of pure states in the language of density operators. [7]: 73 A density operator represents a pure state if and only if:
A quantum state for an imperfectly isolated system will generally evolve to be entangled with the quantum state for the environment. Consequently, even if the system's initial state is pure, the state at a later time, found by taking the partial trace of the joint system-environment state, will be mixed. This phenomenon of entanglement produced ...
In quantum mechanics and computing, the Bloch sphere is a geometrical representation of the pure state space of a two-level quantum mechanical system (qubit), named after the physicist Felix Bloch. [1] Mathematically each quantum mechanical system is associated with a separable complex Hilbert space . A pure state of a quantum system is ...
The fidelity between two quantum states and , expressed as density matrices, is commonly defined as: [ 1 ][ 2 ] The square roots in this expression are well-defined because both and are positive semidefinite matrices, and the square root of a positive semidefinite matrix is defined via the spectral theorem. The Euclidean inner product from the ...
The von Neumann description of quantum measurement of an observable A, when the system is prepared in a pure state ψ is the following (note, however, that von Neumann's description dates back to the 1930s and is based on experiments as performed during that time – more specifically the Compton–Simon experiment; it is not applicable to most ...
Separable state. In quantum mechanics, separable states are multipartite quantum states that can be written as a convex combination of product states. Product states are multipartite quantum states that can be written as a tensor product of states in each space. The physical intuition behind these definitions is that product states have no ...