We introduce a superconducting qubit architecture that combines high-coherence qubits and tunable qubit-qubit coupling. With the ability to set the coupling to zero, we demonstrate that this architecture is protected from the frequency crowding problems that arise from fixed coupling. More importantly, the coupling can be tuned dynamically with nanosecond resolution, making this architecture a versatile platform with applications ranging from quantum logic gates to quantum simulation. We illustrate the advantages of dynamic coupling by implementing a novel adiabatic controlled-Z gate, at a speed approaching that of single-qubit gates. Integrating coherence and scalable control, our "gmon" architecture is a promising path towards large-scale quantum computation and simulation.The fundamental challenge for quantum computation and simulation is to construct a large-scale network of highly connected coherent qubits [1, 2]. Superconducting qubits use macroscopic circuits to process quantum information and are a promising candidate towards this end [3]. Over the last several years, materials research and circuit optimization have led to significant progress in qubit coherence [4][5][6]. Superconducting qubits can now perform hundreds of operations within their coherence times, allowing for research into complex algorithms such as error correction [7,8].It is desirable to combine these high-coherence qubits with tunable inter-qubit coupling; the resulting architecture would allow for both coherent local operations and dynamically varying qubit interactions. For quantum simulation, this would provide a unique opportunity to investigate dynamic processes in non-equilibrium condensed matter phenomena [9][10][11][12][13]. For quantum computation, such an architecture would provide isolation for single-qubit gates while at the same time enabling fast two-qubit gates that minimize errors from decoherence. Despite previous successful demonstrations of tunable coupling [14][15][16][17][18][19][20][21][22][23], these applications have yet to be realized due to the challenge of incorporating tunable coupling with high coherence devices.Here, we introduce a planar qubit architecture that combines high coherence with tunable inter-qubit coupling g. This "gmon" device is based on the Xmon transmon design [5], but now gives nanosecond control of the coupling strength with a measured on/off coupling ratio exceeding 1000. We find that our device retains the high coherence inherent in the Xmon design, with the coupler providing unique advantages in constructing single-and two-qubit quantum logic gates. With the coupling turned off, we demonstrate that our architecture is protected from the frequency crowding problems that arise from fixed coupling. Our single-qubit gate fidelity is nearly independent of the qubit-qubit detuning, even when operating the qubits on resonance. By dynamically tuning the coupling, we implement a novel adiabatic controlled-Z gate at a speed approaching that of single-qubit gates.A two-qubit unit cell with tun...

Statistical mechanics is founded on the assumption that all accessible configurations of a system are equally likely. This requires dynamics that explore all states over time, known as ergodic dynamics. In isolated quantum systems, however, the occurrence of ergodic behavior has remained an outstanding question. Here, we demonstrate ergodic dynamics in a small quantum system consisting of only three superconducting qubits. The qubits undergo a sequence of rotations and interactions and we measure the evolution of the density matrix. Maps of the entanglement entropy show that the full system can act like a reservoir for individual qubits, increasing their entropy through entanglement. Surprisingly, these maps bear a strong resemblance to the phase space dynamics in the classical limit; classically chaotic motion coincides with higher entanglement entropy. We further show that in regions of high entropy the full multi-qubit system undergoes ergodic dynamics. Our work illustrates how controllable quantum systems can investigate fundamental questions in non-equilibrium thermodynamics

The discovery of topological phases in condensed matter systems has changed the modern conception of phases of matter [1, 2]. The global nature of topological ordering makes these phases robust and hence promising for applications [3]. However, the non-locality of this ordering makes direct experimental studies an outstanding challenge, even in the simplest model topological systems, and interactions among the constituent particles adds to this challenge. Here we demonstrate a novel dynamical method [4] to explore topological phases in both interacting and noninteracting systems, by employing the exquisite control afforded by state-of-the-art superconducting quantum circuits. We utilize this method to experimentally explore the well-known Haldane model of topological phase transitions [5] by directly measuring the topological invariants of the system. We construct the topological phase diagram of this model and visualize the microscopic evolution of states across the phase transition, tasks whose experimental realizations have remained elusive [6, 7]. Furthermore, we developed a new qubit architecture [8, 9] that allows simultaneous control over every term in a two-qubit Hamiltonian, with which we extend our studies to an interacting Hamiltonian and discover the emergence of an interaction-induced topological phase. Our implementation, involving the measurement of both global and local textures of quantum systems, is close to the original idea of quantum simulation as envisioned by R. Feynman [10], where a controllable quantum system is used to investigate otherwise inaccessible quantum phenomena. This approach demonstrates the potential of superconducting qubits for quantum simulation [11, 12] and establishes a powerful platform for the study of topological phases in quantum systems.Since the first observations of topological ordering in quantum Hall systems in the 1980s [1, 2], experimental studies of topological phases have been primarily limited to indirect measurements. The non-local nature of topological ordering renders local probes ineffective, and when global probes, such as transport, are used, interpretations [13] are required to infer topological properties from the measurements. Topological phases are charac- Figure 1. Dynamical measurement of Berry curvature and Ch. In this schematic drawing, brown arrows represent the ground states (adiabatic limit) for given points on a closed manifold S (green enclosure) in the parameter space, and the blue arrows are the measured states during a non-adiabatic passage. According to (2), the Berry curvature B can be calculated from the deviation from adiabaticity. Integrating B over S gives the Chern number Ch, which corresponds to the total number of degeneracies enclosed.terized by topological invariants, such as the first Chern number Ch, whose discrete jumps indicate transitions between different topologically ordered phases [14, 15]. For a quantum system, Ch is defined as the integral over a closed manifold S in the parameter space of the Hamiltonian as...

The conventional blending fabrication for thin-film nanocomposite (TFN) membranes is to disperse porous fillers in aqueous/organic phases prior to interfacial polymerization, and the aggregation of fillers may lead to the significant decrease in membrane performance. To overcome this limitation, we proposed a novel layer-by-layer (LBL) fabrication to prepare a polyamide (PA)/ZIF-8 nanocomposite membrane with a multilayer structure: a porous substrate, a ZIF-8 interlayer, and a PA coating layer. The PA/ZIF-8 (LBL) membrane for nanofiltration applications was prepared by growing an interlayer of ZIF-8 nanoparticles on an ultrafiltration membrane through in situ growth and then coating it with an ultrathin PA layer through interfacial polymerization. The obtained PA/ZIF-8 (LBL) membrane exhibited both better permeance and selectivity than did the conventional PA/ZIF-8 TFN membrane because of the ZIF-8 in situ growth producing a ZIF-8 interlayer with more ZIF-8 nanoparticles but fewer aggregates. Compared with the pure PA membrane (the flux of 11.2 kg/m(2)/h and rejection of 99.6%) for dye removal, the obtained PA/ZIF-8 (LBL) membranes achieved a significant improvement in membrane permeance and selectivity. (Flux was up to 27.1 kg/m(2)/h, and the rejection reaches 99.8%.) This LBL fabrication is a promising methodology for other polymer nanocomposite membranes simultaneously having high permeance and good selectivity.

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