內容：

The relation between projective measurements and generalized quantum measurements is a fundamental problem in quantum physics, and clarifying this issue is also important to quantum technologies. While it has been intuitively known that projective measurements can be constructed from sequential generalized or weak measurements [1, 2], there is still lack of a proof of this hypothesis in general cases. Here we prove it from the perspective of quantum channels [3]. We show that projective measurements naturally arise from sequential generalized measurements in the asymptotic limit. Specifically, a selective projective measurement arises from a set of typical sequences of sequential generalized measurements. We provide an explicit scheme to construct projective measurements of a quantum system with sequential generalized quantum measurements. Remarkably, a single ancilla qubit is sufficient to mediate sequential generalized measurements for constructing arbitrary projective measurements of a generic system, which can have applications in readout, initialization, and feedback control of a quantum system. As an example, we present a protocol to measure the modular excitation numbers of a bosonic mode with an ancilla qubit, which are exactly the error syndromes of rotation-symmetric bosonic quantum error correction codes.

References:

1. Wen-Long Ma, Ping Wang, Weng-Hang Leong, Ren-Bao Liu*, Phys. Rev. A 98, 012117 (2018).
2. Gang-Qin Liu, Jian Xing, Wen-Long Ma, Ping Wang, Chang-Hao Li, Hoi Chun Po, Yu-Ran Zhang, Heng Fan, Ren-Bao Liu, Xinyu Pan*, Phys. Rev. Lett. 118, 150504 (2017).
3. Wen-Long Ma*, Shu-Shen Li, Ren-Bao Liu, Phys. Rev. A 107, 012217 (2023).

人物介紹：

馬穩龍，現為中國科學院半導體所研究員、博士生導師，中國科學院大學崗位教授。2015年在中科院半導體所獲得博士學位，2015年2020年先后在香港中文大學、耶魯大學和芝加哥大學從事博士后研究, 隨后加入中科院半導體所超晶格國家重點實驗室，并入選國家高層次人才引進計劃青年項目。研究領域為固態量子信息理論，在量子退相干、量子控制、量子糾錯和量子測量等領域取得了一系列創新成果，在包括PRL的PR系列, Nature Physics, Nature Communications等期刊上發表文章二十余篇。