A main task in condensed-matter physics is to recognize, classify, and characterize phases of matter and the corresponding phase transitions, for which machine learning provides a new class of research tools due to the remarkable development in computing power and algorithms. Despite much exploration in this new field, usually different methods and techniques are needed for different scenarios. Here, we present SimCLP: a simple framework for contrastive learning phases of matter, which is inspired by the recent development in contrastive learning of visual representations. We demonstrate the success of this framework on several representative systems, including non-interacting and quantum many-body, conventional and topological. SimCLP is flexible and free of usual burdens such as manual feature engineering and prior knowledge. The only prerequisite is to prepare enough state configurations. Furthermore, it can generate representation vectors and labels and hence help tackle other problems. SimCLP therefore paves an alternative way to the development of a generic tool for identifying unexplored phase transitions.

The first spatial 2D quantum walk on a photonic chip with thousands of nodes is realized for future analog quantum computing.

Long-distance quantum channels capable of transferring quantum states faithfully for unconditionally secure quantum communication have been so far confirmed to be feasible in both fiber and free-space air. However, it remains unclear whether seawater, which covers more than 70% of the earth, can also be utilized, leaving global quantum communication incomplete. Here we experimentally demonstrate that polarization quantum states including general qubits of single photon and entangled states can survive well after travelling through seawater. We perform experiments with seawater collected over a range of 36 kilometers in the Yellow Sea. For single photons at 405 nm in a blue-green window, we obtain an average process fidelity above 98%. For entangled photons at 810nm, albeit very high loss, we observe the violation of Bell inequality with 33 standard deviations. Our results confirm the feasibility of a seawater quantum channel, representing the first step towards underwater quantum communication.

Quantum walks are powerful kernels in quantum computing protocols that possess strong capabilities in speeding up various simulation and optimisation tasks. One striking example is given by quantum walkers evolving on glued trees for their faster hitting performances than in the case of classical random walks. However, its experimental implementation is challenging as it involves highly complex arrangements of exponentially increasing number of nodes. Here we propose an alternative structure with a polynomially increasing number of nodes. We successfully map such graphs on quantum photonic chips using femtosecond laser direct writing techniques in a geometrically scalable fashion. We experimentally demonstrate quantum fast hitting by implementing two-dimensional quantum walks on these graphs with up to 160 nodes and a depth of 8 layers, achieving a linear relationship between the optimal hitting time and the network depth. Our results open up a scalable way towards quantum speed-up in complex problems classically intractable.Adapting well-known classical mathematical models in a way to include quantum mechanical laws has shown the emergence of new interesting behaviors. In some cases, the modified protocols have revealed an advantage with respect to the original ones in solving specific problems. This has clearly triggered the interest of the scientific community in the quest for a better understanding and exploitation of these new tools 1 . A striking example is given by quantum walks, the adaptation of the classical random walk to the world of quantum mechanics 2 . Quantum walks have already found applications in several scenarios, including spatial search problems 3,4 , the element distinctness problem 5 , testing matrix identities 6 , evaluating Boolean formulas 7 , judging graph isomorphism 8,9 , which all theoretically promise quantum speed-up and may inspire the breakthrough in real-life applications.One feature of quantum walks on complex graphs that is key in quantum algorithms is their ability to propagate from a node to a distant one in an efficient way. This is often denoted as fast hitting. In particular, fast hitting on a structure known as glued tree is extremely charming due to its exponential speed-up over its classical counterpart 10,11 . A glued tree is obtained by connecting the "final leaves" of two binary tree graphs 12 of the same depth, as shown in Fig.1(a). The process assumes a particle starting in the left-most vertex (called the Entry site), evolving through the graph, and finally hitting the right-most vertex (called the Exit site). It has been shown that, in a scenario where the central connections are randomly chosen, any algorithm exploiting a classical walker (i.e., a particle following the laws of classical mechanics) would require on average a time scaling exponentially with the graph depth to reach the Exit. On the other hand, a quantum walker will require a time that scales only linearly 11,13,14 . Due to the close relation between binary trees and decision trees in computer s...

Quantum memory capable of stopping flying photons and storing their quantum coherence is essential for scalable quantum technologies. A room-temperature broadband quantum memory will enable the implementation of large-scale quantum systems for real-life applications. Due to either intrinsic high noises or short lifetime, it is still challenging to find a room-temperature broadband quantum memory beyond conceptual demonstration. Here, we present a far-off-resonance Duan-Lukin-Cirac-Zoller (FORD) protocol and demonstrate the broadband quantum memory in room-temperature atoms. We observe a low unconditional noise level of 10 −4 and a cross-correlation up to 28. A strong violation of Cauchy-Schwarz inequality indicates high-fidelity generation and preservation of non-classical correlation. Furthermore, the achieved cross-correlation in roomtemperature atoms exceeds the key boundary of 6 above which quantum correlation is able to violate Bell's inequality. Our results open up the door to an entirely new realm of memory-enabled quantum applications at ambient conditions. arXiv:1704.06309v2 [quant-ph]

Aim The aim of the study was to compare the outcomes of robot-assisted (RAGD2) and laparoscopy-assisted gastrectomy with D2 lymphadenectomy (LAGD2) for patients with gastric cancer. Material and methods Relevant articles published up to September 2020 were searched. The weighted mean difference (WMD) was used to pool continuous variables, while risk ratio (RR) was calculated for dichotomous outcomes. Results RAGD2 required a longer operating time (WMD = 29.78, 95% confidence interval (CI): 15.97–43.59) and had less operative blood loss (WMD = − 31.93, 95% CI: − 44.03 to − 19.83), shorter time to first flatus (WMD = − 0.13, 95% CI: − 0.22 to − 0.04), shorter time to liquid diet (WMD = − 0.20, 95% CI: − 0.28 to 0.12), and fewer severe complications (RR = 0.62, 95% CI: 0.43–0.90) and overall complications (RR = 0.75, 95% CI: 0.62–0.91) than LAGD2. Conclusions RAGD2 could be beneficial in reducing operative blood loss and postoperative complications relative to LAGD2.

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