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Synthesizing topological order Topologically ordered matter exhibits long-range quantum entanglement. However, measuring this entanglement in real materials is extremely tricky. Now, two groups take a different approach and turn to synthetic systems to engineer the topological order of the so-called toric code type (see the Perspective by Bartlett). Satzinger et al . used a quantum processor to study the ground state and excitations of the toric code. Semeghini et al . detected signatures of a toric code–type quantum spin liquid in a two-dimensional array of Rydberg atoms held in optical tweezers. —JS

The control of non-equilibrium quantum dynamics in many-body systems is challenging as interactions typically lead to thermalization and a chaotic spreading throughout Hilbert space. We investigate non-equilibrium dynamics following rapid quenches in a many-body system composed of 3 to 200 strongly interacting qubits in one and two spatial dimensions. Using a programmable quantum simulator based on Rydberg atom arrays, we show that coherent revivals associated with so-called quantum many-body scars can be stabilized by periodic driving, which generates a robust subharmonic response akin to discrete time-crystalline order. We map Hilbert space dynamics, geometry dependence, phase diagrams, and system-size dependence of this emergent phenomenon, demonstrating novel ways to steer complex dynamics in many-body systems and enabling potential applications in quantum information science.

The ability to engineer parallel, programmable operations between desired qubits within a quantum processor is key for building scalable quantum information systems1,2. In most state-of-the-art approaches, qubits interact locally, constrained by the connectivity associated with their fixed spatial layout. Here we demonstrate a quantum processor with dynamic, non-local connectivity, in which entangled qubits are coherently transported in a highly parallel manner across two spatial dimensions, between layers of single- and two-qubit operations. Our approach makes use of neutral atom arrays trapped and transported by optical tweezers; hyperfine states are used for robust quantum information storage, and excitation into Rydberg states is used for entanglement generation3–5. We use this architecture to realize programmable generation of entangled graph states, such as cluster states and a seven-qubit Steane code state6,7. Furthermore, we shuttle entangled ancilla arrays to realize a surface code state with thirteen data and six ancillary qubits8 and a toric code state on a torus with sixteen data and eight ancillary qubits9. Finally, we use this architecture to realize a hybrid analogue–digital evolution2 and use it for measuring entanglement entropy in quantum simulations10–12, experimentally observing non-monotonic entanglement dynamics associated with quantum many-body scars13,14. Realizing a long-standing goal, these results provide a route towards scalable quantum processing and enable applications ranging from simulation to metrology.

The charge degree of freedom in solid-state defects fundamentally underpins the electronic spin degree of freedom, a workhorse of quantum technologies. Here we study charge state properties of individual near-surface nitrogen-vacancy (NV) centers in diamond, where NV − hosts the metrologically relevant electron spin. We find that NV − initialization fidelity varies between individual centers and over time, and we alleviate the deleterious effects of reduced NV − initialization fidelity via logic-based initialization. We also find that NV − can ionize in the dark, which compromises spin measurements but is mitigated by measurement protocols we present here. We identify tunneling to a single, local electron trap as the mechanism for ionization in the dark and we develop NV-assisted techniques to control and readout the trap charge state. Our understanding and command of the NV's local electrostatic environment will simultaneously guide materials design and provide novel functionalities with NV centers. arXiv:1810.02058v1 [cond-mat.mes-hall]