Congratulations to Yi-Tao Wang et al.

I wish to congratulate the team from China's Key Laboratory of Quantum Information and the Synergetic Innovation Center, both in Hefei.

They have published, this week, in Physical Review Letters, the paper "Experimental Demonstration of Higher Precision Weak-Value-Based Metrology Using Power Recycling", the experimental implementation of a theoretical proposal I published with my group members and colleagues Paul Kwiat and John Howell. The idea is to use weak value amplification together with a recycling step to improve the precision on a measured parameter. This allows all photons to experience the weak value amplification in principle, rather than just the postselected ones. In this scheme, the recycling is accomplished by creating a resonant cavity with a partially transmitting mirror, whereby the light exiting the "wrong" port (i.e. the not postselected one) is redirected back into the interferometer via interference until it eventually comes out the right port, experiencing the amplification effect.

Yi-Tao Wang is the lead author, and the group is led by Guang-Can Guo.

The good news: It works.

Experimental setup of the power-recycled weak-value-based beam-deflection measurement. This setup is constituted by four parts: the probe source, the measurement device, the splitting detector, and the PDH system used to stabilize the cavity length. The probe source is the beam attenuated by the neutral-density filter (NDF). This beam is focused onto the cavity mirror and sent into the measurement device. The measurement device consists of a cavity mirror and a Sagnac interferometer. The beam deflection is imposed via a pizeo-driven 50∶50 BS and is coupled to the transverse beam position when exiting from the dark port. The splitting detector is realized using a KEP, two SPADs, and a time-to-digital converter (TDC), which is used to detect the beam-position shift. The PDH system contains the reference beam modulated by the chopper, the transimpedance amplifier (TIA) used to detect the power of this beam, the following signal-processing circuits, and the servo to stabilize the cavity mirror. LPF, low-pass filter; M1, mirror 1; DP, dove prism; FR, Faraday rotator; EOM, electro-optic modulator; PBS, polarizing beam splitter; VA, variable attenuator; QWP, quarter-wave plate; HWP, halfwave plate.