probe. The environment-noise mean photon number is $4$ and object reflectivity $\epsilon=0.1$. []{data-label="fig_plot_energy"}](plot_energy1.pdf "fig:"){width="8.6cm"} ![ The accessible information and Holevo information quantities (top) and consumed Gaussian discord and quantum advantage (bottom) vs the mean energy of the probe. The environment-noise mean photon number is $4$ and object reflectivity $\epsilon=0.1$. []{data-label="fig_plot_energy"}](plot_energy2.pdf "fig:"){width="8.6cm"}

There is nothing special about our choice of probe energies of 0.01 and 0.5 used in the previous sections. To demonstrate this, Fig. \[fig\_plot\_energy\] shows the illumination performance, quantum advantage, and consumed Gaussian discord for probe mean photon numbers in the range 0 to 0.1, while the object reflectivity is kept constant at $0.1$. There is always a quantum advantage, and the consumed Gaussian discord is approximately equal to the quantum advantage in terms of Holevo information.

Comparison to discrete variables
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[17cm]{}[|X|Sc|Sc|]{} & [**DV**]{} & [**CV**]{}\
Environment noise & &\
Quantum illumination probe & &\
Accessible vs Holevo information & &\
Single-mode illumination & &\
Quantum vs single-mode illumination & &\
Single mode probe vs local measurement on idler first & &\
Consumed discord vs Holevo quantum advantage & &\
Consumed discord vs accessible info quantum advantage & &\

It is worth comparing continuous-variable (CV) illumination to discrete-variable 