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Characterizing the nature of hydrodynamical transport properties in quantum dynamics provides valuable insights into the fundamental understanding of exotic non-equilibrium phases of matter. Experimentally simulating infinite-temperature transport on large-scale complex quantum systems is of considerable interest. Here, using a controllable and coherent superconducting quantum simulator, we experimentally realize the analog quantum circuit, which can efficiently prepare the Haar-random states, and probe spin transport at infinite temperature. We observe diffusive spin transport during the unitary evolution of the ladder-type quantum simulator with ergodic dynamics. Moreover, we explore the transport properties of the systems subjected to strong disorder or a tilted potential, revealing signatures of anomalous subdiffusion in accompany with the breakdown of thermalization. Our work demonstrates a scalable method of probing infinite-temperature spin transport on analog quantum simulators, which paves the way to study other intriguing out-of-equilibrium phenomena from the perspective of transport. Quantum devices offer the potential to simulate quantum phenomena, which are otherwise computationally intractable. Here, Shi, Sun, Wang and coauthors use a superconducting quantum simulator to study spin-transport at infinite temperature. [ABSTRACT FROM AUTHOR]

A hybrid system with tunable coupling between phonons and qubits shows great potential for advancing quantum information processing. In this work, we demonstrate strong and tunable coupling between a surface acoustic wave resonator and a transmon qubit based on the galvanic-contact flip-chip technique. The coupling strength varies from 2 π × 7.0 to − 2 π × 20.6 MHz, which is extracted from different vacuum Rabi oscillation frequencies. The phonon-induced ac Stark shift of the qubit at different coupling strengths is also shown. Our approach offers a good experimental platform for exploring quantum acoustics and hybrid systems. [ABSTRACT FROM AUTHOR]

Hawking radiation is one of the quantum features of a black hole that can be understood as a quantum tunneling across the event horizon of the black hole, but it is quite difficult to directly observe the Hawking radiation of an astrophysical black hole. Here, we report a fermionic lattice-model-type realization of an analogue black hole by using a chain of 10 superconducting transmon qubits with interactions mediated by 9 transmon-type tunable couplers. The quantum walks of quasi-particle in the curved spacetime reflect the gravitational effect near the black hole, resulting in the behaviour of stimulated Hawking radiation, which is verified by the state tomography measurement of all 7 qubits outside the horizon. In addition, the dynamics of entanglement in the curved spacetime is directly measured. Our results would stimulate more interests to explore the related features of black holes using the programmable superconducting processor with tunable couplers. Recently, the theory of Hawking radiation of a black hole has been tested in several analogue platforms. Shi et al. report a fermionic-lattice model realization of an analogue black hole using a chain of superconducting transmon qubits with tuneable couplers and show the stimulated Hawking radiation. [ABSTRACT FROM AUTHOR]

Quantum simulation enables study of many-body systems in non-equilibrium by mapping to a controllable quantum system, providing a powerful tool for computational intractable problems. Here, using a programmable quantum processor with a chain of 10 superconducting qubits interacted through tunable couplers, we simulate the one-dimensional generalized Aubry-André-Harper model for three different phases, i.e., extended, localized and critical phases. The properties of phase transitions and many-body dynamics are studied in the presence of quasi-periodic modulations for both off-diagonal hopping coefficients and on-site potentials of the model controlled respectively by adjusting strength of couplings and qubit frequencies. We observe the spin transport for initial single- and multi-excitation states in different phases, and characterize phase transitions by experimentally measuring dynamics of participation entropies. Our experimental results demonstrate that the recently developed tunable coupling architecture of superconducting processor extends greatly the simulation realms for a wide variety of Hamiltonians, and can be used to study various quantum and topological phenomena. [ABSTRACT FROM AUTHOR]

Random quantum states serve as a powerful tool in various scientific fields, including quantum supremacy and black hole physics. It has been theoretically predicted that entanglement transitions may happen for different partitions of multipartite random quantum states; however, the experimental observation of these transitions is still absent. Here, we experimentally demonstrate the entanglement transitions witnessed by negativity on a fully connected superconducting processor. We apply parallel entangling operations, that significantly decrease the depth of the pseudo-random circuits, to generate pseudo-random pure states of up to 15 qubits. By quantum state tomography of the reduced density matrix of six qubits, we measure the negativity spectra. Then, by changing the sizes of the environment and subsystems, we observe the entanglement transitions that are directly identified by logarithmic entanglement negativities based on the negativity spectra. In addition, we characterize the randomness of our circuits by measuring the distance between the distribution of output bit-string probabilities and the Porter-Thomas distribution. Our results show that superconducting processors with all-to-all connectivity constitute a promising platform for generating random states and understanding the entanglement structure of multipartite quantum systems. It has been predicted that entanglement phase diagrams of Haar-measure random states can show interesting phenomenology, including entanglement phase transitions. Here, the authors confirm these predictions using up to 15 qubits in a fully-connected superconducting quantum processor. [ABSTRACT FROM AUTHOR]

In this study, we introduce an online public quantum computation platform, named as ScQ, based on a 1D array of a 10-qubit superconducting processor. Single-qubit rotation gates can be performed on each qubit. Controlled-NOT gates between nearest-neighbor sites on the 1D array of 10 qubits are available. We show the online preparation and verification of Greenberger-Horne-Zeilinger states of up to 10 qubits through this platform for all possible blocks of qubits in the chain. The graphical user interface and quantum assembly language methods are presented to achieve the above tasks, which rely on a parameter scanning feature implemented on ScQ. The performance of this quantum computation platform, such as fidelities of logic gates and details of the superconducting device, is presented. [ABSTRACT FROM AUTHOR]

The Bloch oscillation (BO) and Wannier-Stark localization (WSL) are fundamental concepts about metal-insulator transitions in condensed matter physics. These phenomena have also been observed in semiconductor superlattices and simulated in platforms such as photonic waveguide arrays and cold atoms. Here, we report experimental investigation of BOs and WSL simulated with a 5-qubit programmable superconducting processor, of which the effective Hamiltonian is an isotropic XY spin chain. When applying a linear potential to the system by properly tuning all individual qubits, we observe that the propagation of a single spin on the chain is suppressed. It tends to oscillate near the neighborhood of their initial positions, which demonstrates the characteristics of BOs and WSL. We verify that the WSL length is inversely correlated to the potential gradient. Benefiting from the precise single-shot simultaneous readout of all qubits in our experiments, we can also investigate the thermal transport, which requires the joint measurement of more than one qubits. The experimental results show that, as an essential characteristic for BOs and WSL, the thermal transport is also blocked under a linear potential. Our experiment would be scalable to more superconducting qubits for simulating various of out-of-equilibrium problems in quantum many-body systems. [ABSTRACT FROM AUTHOR]

We study superconducting properties of NbN thin film samples with different thicknesses and an ultra-thin NbTiN meander nanowire sample. For the ultra-thin samples, we found that the temperature dependence of upper critical field (Hc2) in parallel to surface orientation shows bending curvature close to critical temperature Tc, suggesting a two-dimensional (2D) nature of the samples. The 2D behavior is further supported by the angular dependence measurements of Hc2 for the thinnest samples. The temperature dependence of parallel upper critical field for the thick films could be described by a model based on the anisotropic Ginzburg–Landau theory. Interestingly, the results measured in the field perpendicular to the film surface orientation show a similar bending curvature but in a much narrow temperature region close to Tc for the ultra-thin samples. We suggest that this feature could be due to suppression of pair-breaking caused by local in-homogeneity. We further propose the temperature dependence of perpendicular Hc2 as a measure of uniformity of superconducting ultra-thin films. For the thick samples, we find that Hc2 shows maxima for both parallel and perpendicular orientations. The Hc2 peak for the perpendicular orientation is believed to be due to the columnar structure formed during the growth of the thick films. The presence of columnar structure is confirmed by transmission electron microscopy (TEM). In addition, we have measured the angular dependence of magneto-resistance, and the results are consistent with the Hc2 data. [ABSTRACT FROM AUTHOR]

We study superconducting properties of NbN thin film samples with different thicknesses and an ultra-thin NbTiN meander nanowire sample. For the ultra-thin samples, we found that the temperature dependence of upper critical field (Hc2) in parallel to surface orientation shows bending curvature close to critical temperature Tc, suggesting a two-dimensional (2D) nature of the samples. The 2D behavior is further supported by the angular dependence measurements of Hc2 for the thinnest samples. The temperature dependence of parallel upper critical field for the thick films could be described by a model based on the anisotropic Ginzburg–Landau theory. Interestingly, the results measured in the field perpendicular to the film surface orientation show a similar bending curvature but in a much narrow temperature region close to Tc for the ultra-thin samples. We suggest that this feature could be due to suppression of pair-breaking caused by local in-homogeneity. We further propose the temperature dependence of perpendicular Hc2 as a measure of uniformity of superconducting ultra-thin films. For the thick samples, we find that Hc2 shows maxima for both parallel and perpendicular orientations. The Hc2 peak for the perpendicular orientation is believed to be due to the columnar structure formed during the growth of the thick films. The presence of columnar structure is confirmed by transmission electron microscopy (TEM). In addition, we have measured the angular dependence of magneto-resistance, and the results are consistent with the Hc2 data. [ABSTRACT FROM AUTHOR]

Highly uniform dispersed bimetallic Pt3Zn alloy nanocrystals (NCs) with unique geometries are obtained via a facile one‐pot synthesis process by regulating different reductants. To investigate the morphology and composition of the prepared catalysts, the transmission electron microscopy, X‐ray diffraction and X‐ray photoelectron spectroscopy are utilized. Electrochemical measurements reveal that the Pt3Zn NCs significantly exhibited larger electrochemically active surface areas and excellent catalytic activity towards electro‐oxidation of methanol and ethanol in comparison to the commercial Pt/C. The optimized Pt3Zn (AA) NCs exhibit excellent mass activities in both methanol oxidation reaction (1251.4 mA mgPt−1) and ethanol oxidation reaction (975.7 mA mgPt−1) in acidic media, which are respectively 4.28 times and 3.02 times higher than those of commercial Pt/C. Moreover, the Pt3Zn NCs show a higher stability and better resistance to the COads poisoning. The activity enhancements are attributed to electronic effects and a bifunctional mechanism. [ABSTRACT FROM AUTHOR]

The design of electrode materials with rational core/shell structures is promising for improving the electrochemical properties of supercapacitors. Hence, hierarchical FeCo2S4@FeNi2S4 core/shell nanostructures on Ni foam were fabricated by a simple hydrothermal method. Owing to their structure and synergistic effect, they deliver an excellent specific capacitance of 2393 F g−1 at 1 A g−1 and long cycle lifespan as positive electrode materials. An asymmetric supercapacitor device with FeCo2S4@FeNi2S4 as positive electrode and graphene as negative electrode exhibited a specific capacitance of 133.2 F g−1 at 1 A g−1 and a high energy density of 47.37 W h kg−1 at a power density of 800 W kg−1. Moreover, the device showed remarkable cycling stability with 87.0 % specific‐capacitance retention after 5000 cycles at 2 A g−1. These results demonstrate that the hierarchical FeCo2S4@FeNi2S4 core/shell structures have great potential in the field of electrochemical energy storage. [ABSTRACT FROM AUTHOR]

Via the hydrothermal method, we synthesized MoS2 nanosheets with varying Co dopant concentrations of 0%, 3%, 7%, using cobaltous acetate as a promoter, and marked as A, B, and C, respectively. We found that the thickness and flatness of the nanosheets increased with the increase of the Co dopant concentrations. Meanwhile, the BET surface area of samples (A, B, and C) decreased with the increase of the Co dopant concentrations. Optical absorption spectroscopy showed that, compared to sample A, the A1 and B1 excitons of samples B and C were 10 and 23 meV redshifted, respectively. Then, we performed magnetization measurement to investigate the effect of Co-doping; the unique result implied that the values of the magnetic moment decreased with the increase of the Co dopant concentrations. We performed DFT computations to address the above magnetic result. The computational result indicated that the value of the magnetic moment decreased with the increase of the Co dopant concentrations, which is in agreement with the results of the experiments described above. [ABSTRACT FROM AUTHOR]

Lead halide perovskites‐based memory devices have attracted considerable interest due to their unique current–voltage (I–V) hysteresis. Herein, all‐inorganic CsPbI3 perovskite film surviving 30 d of air storage is prepared by using a poly‐vinylpyrrolidone‐assisted passivation method under fully open‐air condition. Afterwards, a memory device with a sandwich structure of Ag/CsPbI3/indium tin oxide is manufactured. From I–V characteristics of pristine device, a spontaneous reaction between the active Ag electrode and I− ions under air exposure is suggested. Furthermore, complete degradation of Ag electrode and formation of AgIx are verified, which also accompanies with generation of more iodine vacancies (VI) in perovskite film. The memory device with AgIx layer shows a bipolar resistive switching behavior, ultrahigh ON/OFF ratio (above 106), nonvolatile, reliable, and reproducible switching performance. Cell area and temperature dependent characteristics propose that the resistive switching is dominated by VI filament in low‐resistance state and thermally assisted hopping in high‐resistance state. This study provides a new insight to understand switching behavior from the way of electrode degradation and metal iodide formation in lead iodide perovskites‐based memory devices and also suggests a potential application for AgIx‐induced resistive switching in CsPbI3‐based memory device. All‐inorganic CsPbI3 perovskite film is prepared by using a poly‐vinylpyrrolidone‐assisted passivation method. Complete degradation of Ag electrode and formation of AgIx in memory device of Ag/CsPbI3/indium tin oxide are verified which also accompanies with generation of more iodine vacancies. The memory device with AgIx layer shows a bipolar resistive switching behavior, ultrahigh ON/OFF ratio, nonvolatile, reliable, and reproducible switching performance. [ABSTRACT FROM AUTHOR]