RelEntCoherence

From QETLAB
Revision as of 18:05, 12 January 2016 by Nathaniel (talk | contribs)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to navigation Jump to search
RelEntCoherence
Computes the relative entropy of coherence of a quantum state

Other toolboxes required none
Related functions L1NormCoherence
RobustnessCoherence
TraceDistanceCoherence
Function category Coherence and incoherence
Usable within CVX? no

RelEntCoherence is a function that computes the relative entropy of coherence of a quantum state $\rho$, defined as follows:

\[C_{r}(\rho) := -\mathrm{Tr}\big(\rho(\log_2(\rho) - \log_2(\rho_{\text{diag}}))\big),\]

where $\rho_{\text{diag}}$ is the matrix that has the same diagonal as $\rho$ but is zero elsewhere.

Syntax

  • REC = RelEntCoherence(RHO)

Argument descriptions

  • RHO: A state (either pure or mixed) to have its relative entropy of coherence computed.

Examples

Maximally coherent states

The largest possible value of the relative entropy of coherence on $d$-dimensional states is $\log_2(d)$, and is attained exactly by the "maximally coherent states": pure states whose entries all have the same absolute value.

>> d = 5;
>> v = ones(d,1)/sqrt(d); % this is a maximally coherent state
>> RelEntCoherence(v)

ans =

    2.3219

>> log(5)/log(2)

ans =

    2.3219

Source code

Click on "expand" to the right to view the MATLAB source code for this function.