The modern description of elementary particles is built on gauge theories [1]. Such theories implement fundamental laws of physics by local symmetry constraints, such as Gauss's law in the interplay of charged matter and electromagnetic fields. Solving gauge theories by classical computers is an extremely arduous task [2], which has stimulated a vigorous effort to simulate gaugetheory dynamics in microscopically engineered quantum devices [3][4][5][6]. Previous achievements used mappings onto effective models to integrate out either matter or electric fields [7-10], or were limited to very small systems [11][12][13][14][15]. The essential gauge symmetry has not been observed experimentally.Here, we report the quantum simulation of an extended U(1) lattice gauge theory, and experimentally quantify the gauge invariance in a many-body system of 71 sites. Matter and gauge fields are realized in defect-free arrays of bosonic atoms in an optical superlattice. We demonstrate full tunability of the model parameters and benchmark the matter-gauge interactions by sweeping across a quantum phase transition. Enabled by high-fidelity manipulation techniques, we measure Gauss's law by extracting probabilities of locally gauge-invariant states from correlated atom occupations. Our work provides a way to explore gauge symmetry in the interplay of fundamental particles using controllable large-scale quantum simulators.

Ring exchange is an elementary interaction for modeling unconventional topological matters which hold promise for efficient quantum information processing. We report the observation of fourbody ring-exchange interactions and the topological properties of anyonic excitations within an ultracold atom system. A minimum toric code Hamiltonian in which the ring exchange is the dominant term, was implemented by engineering a Hubbard Hamiltonian that describes atomic spins in disconnected plaquette arrays formed by two orthogonal superlattices. The ring-exchange interactions were resolved from the dynamical evolutions in the spin orders, matching well with the predicted energy gaps between two anyonic excitations of the spin system. A braiding operation was applied to the spins in the plaquettes and an induced phase 1.00(3)π in the four-spin state was observed, confirming 1 2 -anynoic statistics. This work represents an essential step towards studying topological matters with many-body systems and the applications in quantum computation and simulation.Exploiting the laws of quantum mechanics, quantum information processing can be exponentially faster than the classical counterpart [1]. To make this technology a reality, scientists have to solve the crucial problem of decoherence and systematic errors in real quantum systems, which is very difficult due to the request of an extremely small error threshold to enable error corrections [2,3]. A very encouraging solution to this problem is the Kitaev model [4] of fault-tolerant quantum computation by anyons, a sort of topological quasiparticles being neither bosons nor fermions [5]. In this model, anyons are exploited to encode and manipulate information in a manner which is resistant to errors, the so-called topological protection. Unfortunately, except that signatures of anyonic statistics emerged in the fractional quantum Hall systems [6,7], there has been no conclusive observation of anyons in any existing matters. A proposal suggests to solely mimic anyonic statistics with non-interacting qubits [8] and experimental demonstrations were achieved with entangled photons [9, 10] and ions [11]. However, because the background interacting Hamiltonian does not exist in such systems, it is not possible to define anyonic excitations [12]. Therefore, the observation of anyons remains challenging.To construct the appropriate Hamiltonian for studying anyons, a practical scheme [13] was proposed to create artificial topological matters by manipulating ringexchange interactions [14] among ultracold atoms in optical lattices [15,16]. Although a large category of manybody models [17][18][19][20][21] have been realized with optical lattices, implementing the ring-exchange Hamiltonian is notoriously difficult due to its nature of the fourth-order spin interaction, which is greatly suppressed compared to the lower order processes, such as superexchange interactions [19,20]. So, generation and observation of the ring-exchange interactions and the correlated anyonic excitations become the ...

Scalable, coherent many-body systems can enable the realization of previously unexplored quantum phases and have a potential to exponentially speed up information processing. Here we report the cooling of a quantum simulator with ten thousand atoms and mass production of high-fidelity entangled pairs. In a two-dimensional plane, we cool Mott-insulator samples by immersing them into removable superfluid reservoirs, achieving an entropy per particle of 1.9−0.4+1.7×10−3kB. The atoms are then rearranged into a two-dimensional lattice free of defects. We further demonstrate a two-qubit gate with a fidelity of 0.993(1) for entangling 1250 atom pairs. Our results offer a setting for exploring low-energy many-body phases and could enable the creation of large-scale entanglement.

Ultracold atoms in optical lattices offer a great promise to generate entangled states for scalable quantum information processing owing to the inherited long coherence time and controllability over a large number of particles. We report on the generation, manipulation and detection of atomic spin entanglement in an optical superlattice. Employing a spin-dependent superlattice, atomic spins in the left or right sites can be individually addressed and coherently manipulated by microwave pulses with near unitary fidelities. Spin entanglement of the two atoms in the double wells of the superlattice is generated via dynamical evolution governed by spin superexchange. By observing collisional atom loss with in-situ absorption imaging we measure spin correlations of atoms inside the double wells and obtain the lower boundary of entanglement fidelity as 0.79±0.06, and the violation of a Bell's inequality with S = 2.21±0.08. The above results represent an essential step towards scalable quantum computation with ultracold atoms in optical lattices. arXiv:1507.05937v1 [cond-mat.quant-gas] 21 Jul 2015

The characteristics of evaporation heat transfer and pressure drop for refrigerant R134a flowing in a plate heat exchanger were investigated experimentally in this study. Two vertical counter flow channels were formed in the exchanger by three plates of commercialized geometry with a corrugated sine shape of a chevron angle of 60°. Upflow boiling of refrigerant R134a in one channel receives heat from the hot downflow of water in the other channel. The effects of the heat flux, mass flux, quality and pressure of R134a on the evaporation heat transfer and pressure drop were explored. The preliminary measured data for the water to water single phase convection showed that the heat transfer coefficient in the plate heat exchanger is about 9 times of that in a circular pipe at the same Reynolds number. Even at a very low Reynolds number, the present flow visualization in a plate heat exchanger with the transparent outer plate showed that the flow in the plate heat exchanger remains turbulent. Data for the pressure drop were also examined in detail. It is found that the evaporation heat transfer coefficient of R134a in the plates is quite different from that in circular pipe, particularly in the convective evaporation dominated regime at high vapor quality. Relatively intense boiling on the corrugated surface was seen from the flow visualization. More specifically, the present data showed that both the evaporation heat transfer coefficient and pressure drop increase with the vapor quality. At a higher mass flux the pressure drop is higher for the entire range of the vapor quality but the heat transfer is only better at high quality. Raising the imposed wall heat flux was found to slightly improve the heat transfer. While at a higher system pressure the heat transfer and pressure drop are both slightly lower.

We experimentally investigate the quantum criticality and Tomonaga-Luttinger liquid (TLL) behavior within one-dimensional (1D) ultracold atomic gases. Based on the measured density profiles at different temperatures, the universal scaling laws of thermodynamic quantities are observed. The quantum critical regime and the relevant crossover temperatures are determined through the double-peak structure of the specific heat. In the TLL regime, we obtain the Luttinger parameter by probing sound propagation. Furthermore, a characteristic power-law behavior emerges in the measured momentum distributions of the 1D ultracold gas, confirming the existence of the TLL.

We investigated the anti-tumor efficiency of sonodynamic therapy (SDT) on human tongue squamous carcinoma SAS cell line using low intensity ultrasound (LIU) of 0.6 and 0.8 W/cm², plus 5-aminolevulinic acid (ALA). Xenograft in vivo experiments using Balb/ca nude mice and MTT assays in vitro showed that ALA-LIU therapy significantly suppressed the proliferation of SAS cells. ALA-LIU therapy markedly enhanced SAS cell apoptosis rate compared to LIU alone. Based on TEM and fluorescence microscopy observations, there are notably morphology changes and seriously swollen mitochondria in xenograft tissues, and ALA-induced PpIX bond strongly to mitochondria of SAS cells. Immunohistochemical staining and western blotting demonstrated upregulation of Bax, cytochrome c and caspase-3, and downregulation of Bcl-2 for both in vivo and in vitro cases after ALA-LIU treatment. Increase of reactive oxygen species (ROS) in the ALA-LIU treatment groups were found using 2, 7-dichlorofluorescin diacetate (DCFH-DA) staining. Administration of the ROS scavenger, N-acetylcysteine (NAC), suppressed ALA-LIU-induced apoptosis and the expression of mitochondria apoptosis-related proteins, which confirmed that the ALA-LIU induced SAS cell apoptosis is through the generation of ROS. The process initially damaged mitochondria, activated pro-apoptotic factors Bax and cytochrome c and supressed the anti-apoptotic factor Bcl-2, activated caspase-3 to executed apoptosis through mitochondrial signaling pathway.

We perform two-photon photoassociation spectroscopy of the heteronuclear CsYb molecule to measure the binding energies of near-threshold vibrational levels of the X 2 Σ + 1/2 molecular ground state. We report results for 133 Cs 170 Yb, 133 Cs 173 Yb and 133 Cs 174 Yb, in each case determining the energy of several vibrational levels including the least-bound state. We fit an interaction potential based on electronic structure calculations to the binding energies for all three isotopologs and find that the ground-state potential supports 77 vibrational levels. We use the fitted potential to predict the interspecies s-wave scattering lengths for all seven Cs+Yb isotopic mixtures.