Correlations obtained from sequences of measurements have been employed to distinguish among different physical theories or to witness the dimension of a system. In this work we show that they can also be used to establish semi-device independent lower bounds on the purity of the initial quantum state or even on one of the post-measurement states. For single systems this provides information on the quality of the preparation procedures of pure states or the implementation of measurements with anticipated pure post-measurement states. For joint systems one can combine our bound with results from entanglement theory to infer an upper bound on the concurrence based on the temporal correlations observed on a subsystem.
Multi-time advantage for certifying quantum coherence
Center for Theoretical Physics, Polish Academy of Sciences（波兰科学院理论物理中心）；Nordita, Stockholm University and KTH Royal Institute of Technology（诺迪塔，斯德哥尔摩大学和皇家理工学院）；Institute of Theoretical Physics, University of Warsaw（华沙大学理论物理研究所）；School of Mathematics and Physics, The University of Queensland（昆士兰大学数学与物理学院）
Certifying quantum states without independence assumptions
ICFO - Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology（光子科学研究所，巴塞罗那科学技术学院）；Luxquanta Technologies S.L.（Luxquanta科技有限公司）
Coherent temporal filtering of multimode parametric down-conversion using a quantum pulse gate
Integrated Quantum Optics Group, Institute for Photonic Quantum Systems (PhoQS), Paderborn University（帕德博恩大学光子量子系统研究所）；School of Mathematics and Physics, University of Queensland（昆士兰大学数学与物理学院）
On-Chip Generation of Co-Polarized and Spectrally Separable Photon Pairs
National University of Singapore（新加坡国立大学）；Centre for Quantum Technologies, National University of Singapore（新加坡国立大学量子技术中心）；A ∗ STAR Quantum Innovation Centre (Q.InC), Agency for Science, Technology and Research (A ∗ STAR)（新加坡科技研究局A*STAR量子创新中心）；Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A ∗ STAR)（新加坡科技研究局A*STAR材料研究与工程学院）
Time evolution of correlation functions in quantum many-body systems
我们给出了严格的分析结果的时间行为的两点关联函数-也被称为动态响应函数或格林函数-在封闭的多体量子系统。我们发现，在一个大类的衰减不变模型的关联函数因式分解在晚些时候$\langle A(t) B\rangle_β\rightarrow \langle A \rangle_β\langle B \rangle_β$，从而证明耗散出现的酉动力系统。我们还表明，对于具有通用频谱的系统，该后期值周围的波动受热系综纯度的限制，该热系综通常随系统大小呈指数衰减。对于自关联函数，我们提供了一个时间尺度上的上限，在这个时间尺度上，它们达到了因式分解的后期时间值。值得注意的是，这个界限只是局部期望值的函数，并且不随系统大小而增加。我们给出的数值例子表明，这个界是一个很好的估计在不可积模型，并认为，出现的时间尺度可以理解的一个新兴的波动耗散定理。我们的研究扩展到进一步类的两个点函数，如对称的和Kubo函数，出现在线性响应理论，我们给出类似的结果。
