Weak-value amplification (WVA) is a commonly used technique in metrology—the study of measurement—that has attracted much recent attention for its promising applications in quantum sensing. First described in 1988 by Aharonov, Albert, and Vaidman, WVA allows scientists to precisely measure extremely small values—or variations in these values—of some quantity of interest, by interfering two quantum states and observing the resulting interference pattern. This technique has a variety of uses, from direct spatial measurements, such as those of velocity or angular displacement, to more exotic ones, such as variations in temperature, chemical concentration, or magnetic field strength.
One great advantage of WVA is that it can be used to minimize many systematic errors that could creep into scientific experiments. Unfortunately, there is a stark trade-off in the quantum experimental setting: amplification of the desired quantity is always offset by a corresponding decrease in the number of detected events. In a quantum optics context, this trade-off manifests as a decrease in detected photon count rate. In a recent paper, physicists at the University of Illinois Urbana-Champaign and their colleagues have experimentally overcome this trade-off without sacrificing photon count rate, by modifying conventional WVA to include a novel photon recycling scheme.