Ratcheting Up Energy by Means of Measurement

The destruction of quantum coherence can pump energy into a system. For our examples this is paradoxical because the destroyed correlations are ordinarily considered negligible. Mathematically the explanation is straightforward and physically one can identify the degrees of freedom supplying this energy. Nevertheless, the energy input can be calculated without specific reference to those degrees of freedom.

Figure 1

Probability distribution of bosons after 25 “encounters” for systems $\mathcal{A}$ and $\mathcal{B}$ (marked ${\rho }_a$ and ${\rho }_b$). Note that they are essentially the same.

Figure 2

Value of the average excitation level in system $\mathcal{A}$ (○’s) and $\mathcal{B}$ ($\times$’s): (a) uses the parameters of Fig. 1; for (b) slightly different parameters are used, with longer contact times and stronger coupling. In this case $⟨n_a⟩$ and $⟨n_b⟩$ grow, but do not tend to a common value.