Subentropy

The '''subentropy'''JozsaRobbWootters1994 of a quantum state is defined similarly to the [[von Neumann entropy]], as :$Q(\backslash rho)\; =\; -\backslash sum\_\{k=1\}^n\; \backslash left(\; \backslash prod\_\{l\; \backslash neq\; k\}\; \backslash frac\{\backslash lambda\_k\}\{\backslash lambda\_k\; -\; \backslash lambda\_l\}\; \backslash right)\; \backslash lambda\_k\; \backslash log\; \backslash lambda\_k,$ where $\backslash \{\backslash lambda\_k\backslash \}$ is the set of eigenvalues of $\backslash rho$. In the case that some of the eigenvalues are degenerate, the limit from different eigenvalues is taken. The subentropy can be used to get a lower bound on the [[accessible information]] from an [[ensemble]] of quantum states. [[Category:Entropy]]