Measuring quantum state is fundamentally important in the development of quantum physics. Generally, quantum state tomography is a powerful way for quantum state reconstruction, which relies on a large number of projection measurements and complicated multi-parameter estimation. However, its required measurement resources increases exponentially as the dimension of quantum state increases. In this report, we developed a delta-quench measurement scheme for quantum state measurement: by weakly modulating the quantum wavefunction in a δ-function way followed by a post-selection, we may directly measure the real and imaginary parts of the wavefunction, which is expected to have important applications in situations for the high-dimension quantum state reconstrunction. Experimentally, we apply this scheme to measure the temporal wavefunction of photons, and demonstrate the robustness of this method.

Dr. Shanchao Zhang is currently a professor in School of Physics and Telecommunication Engineering at South China Normal University (SCNU, since 2017). He got his PhD degree (2009-2013) and continued PostDoc researches (2013-2017) at the Hong Kong University of Science and Technology (HKUST). His researches mainly focus on the AMO physics and its quantum applications using cold atoms and has published series paper including 2 in Nature Photonics and 10 in PRL. In his labs at SCNU, ytterbium (Yb) and rubidium (Rb) atoms are laser cooled down to temperature of nano-Kelvin, by which quantum state of atoms can be manipulated in an accurate way.  By which, he has developed the most efficient quantum memory for single photons, realized the delta-quench measurment of quantum wavefunction and recently demonstrate the topology of non-Abelian vacua.

Shanchao Zhang, Yiru Zhou, Yefeng Mei, Kaiyu Liao, Yongli Wen, Xinding Zhang, Shengwang Du, Hui Yan, Shi-Liang Zhu, δ-quench measurement of quantum wavefunctions. Phys. Rev. Lett. 123.190402 (2019)

Please contact phweb@ust.hk should you have questions about the talk.