Speaker
Description
Open quantum systems under measurement have now been extensively studied because they exhibit interesting nonequilibrium dynamics absent in isolated quantum systems. Of particular interest is the physics of quantum trajectories, where one tracks the monitored dynamics with the measurement outcomes (i.e., quantum jumps) retained. Indeed, such quantum trajectories concerning many-body systems can exhibit interesting phenomena represented as measurement-induced phase transitions (MIPT), which cannot be obtained by the dynamics where measurement outcomes are averaged. However, the MIPT generally requires the postselection of the same quantum measurement outcomes, which causes experimentally unfriendly exponential cost. Our work shows a nontrivial crossover of subsystem fluctuations of quantum jumps in many-body dynamics, which does not require the aforementioned postselection problem because quantum jumps are directly obtained in a single quantum trajectory. Whereas the fluctuations show the conventional volume law (∼ L) following Poissonian statistics for sufficiently weak measurement strength, anomalous universal scaling law (∼ L^2.7 up to L=20) exhibiting super-Poissonian statistics appears for strong measurement strength. We also discuss that this crossover significantly affects the precision of estimating the rate of quantum jumps. That is, for strong (weak) measurement, the estimation uncertainty is enhanced (suppressed) as the system size increases. Moreover, we demonstrate that the obtained anomalous scaling of the subsystem fluctuation results from an integrated many-body autocorrelation function. We can access the measurement-induced crossover only through the postselection-free information, i.e., the time and the position of quantum jumps, which can be tested in ultracold atom experiments.