Noun
von Neumann entropy
(quantum mechanics) The entropy of a quantum state. If the state is expressed as a quantum density matrix
ρ
{\displaystyle \rho }
, then this entropy can be expressed mathematically as
S
=
−
tr
(
ρ
log
ρ
)
{\displaystyle S=-{\text{tr}}(\rho \log \rho )}
where
tr
{\displaystyle {\text{tr}}}
is the trace operator and the logarithm is natural.