We present results from the first directed search for nontensorial gravitational waves. While general relativity allows for tensorial (plus and cross) modes only, a generic metric theory may, in principle, predict waves with up to six different polarizations. This analysis is sensitive to continuous signals of scalar, vector, or tensor polarizations, and does not rely on any specific theory of gravity. After searching data from the first observation run of the advanced LIGO detectors for signals at twice the rotational frequency of 200 known pulsars, we find no evidence of gravitational waves of any polarization. We report the first upper limits for scalar and vector strains, finding values comparable in magnitude to previously published limits for tensor strain. Our results may be translated into constraints on specific alternative theories of gravity.

Bell nonlocality plays a fundamental role in quantum theory. Numerous tests of the Bell inequality have been reported since the ground-breaking discovery of the Bell theorem. Up to now, however, most discussions of the Bell scenario have focused on a single pair of entangled particles distributed to only two separated observers. Recently, it has been shown surprisingly that multiple observers can share the nonlocality from an entangled pair using the method of weak measurement without postselection [Phys. Rev. Lett. 114, 250401 (2015)]. Here we report an observation of double CHSH-Bell inequality violations for a single pair of entangled photons with strength continuous-tunable optimal weak measurement in a photonic system. Our results shed new light on the interplay between nonlocality and quantum measurements and our design of weak measurement protocol may also be significant for important applications such as unbounded randomness certification and quantum steering. arXiv:1609.01863v3 [quant-ph]

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As one of the most intriguing intrinsic properties of quantum world, quantum superposition provokes great interests in its own generation. Oszmaniec et al. [Phys. Rev. Lett. 116, 110403 (2016)] have proven that though a universal quantum machine that creates superposition of arbitrary two unknown states is physically impossible, a probabilistic protocol exists in the case of two input states have nonzero overlaps with the referential state. Here we report a heralded quantum machine realizing superposition of arbitrary two unknown photonic qubits as long as they have nonzero overlaps with the horizontal polarization state |H . A total of 11 different qubit pairs are chosen to test this protocol by comparing the reconstructed output state with theoretical expected superposition of input states. We obtain the average fidelity as high as 0.99, which shows the excellent reliability of our realization. This realization not only deepens our understanding of quantum superposition but also has significant applications in quantum information and quantum computation, e.g., generating non-classical states in the context of quantum optics and realizing information compression by coherent superposition of results of independent runs of subroutines in a quantum computation.Introduction. Quantum superposition, which makes quantum world totally different from classical world, is at the heart of quantum theory [1]. The superposition of states leads to inevitable uncertainty in the measurement outcomes, which is the fundamental feature of quantum world. Numerous nonclassical properties of quantum system such as quantum coherence [2, 3] and quantum entanglement [4], which are foundations of quantum communication and computation [5,6], also essentially stem from quantum superposition. The importance of quantum superposition is exhibited by not only its fundamental role in quantum theory but also significant applications in quantum information and quantum computation [7].As a fascinating consequence of linearity of quantum theory, quantum superposition raises great interest in its own generation, i.e., whether or not there exists a universal quantum machine that produces superposition of arbitrary two unknown input quantum states [8,9]. Unfortunately, similar to other no-go theorems [10][11][12][13], such universal protocol has been shown forbidden by quantum theory [8,9]. However, it is similar to probabilistic quantum cloning machine for linear-independent set of states [14,15] that probabilistically creating superposition of arbitrary two states is feasible given that both states have nonzero overlaps with some referential states [9].In this Letter, we experimentally demonstrate a heralded probabilistic quantum machine realizing superposition of arbitrary two photonic qubits based on the protocol in Ref. [9]. The referential state in our experiment

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