Giant magnetoresistance of Dirac plasma in high-mobility graphene

The most recognizable feature of graphene's electronic spectrum is its Dirac point around which interesting phenomena tend to cluster. At low temperatures, the intrinsic behavior in this regime is often obscured by charge inhomogeneity but thermal excitations can overcome the disorder at elevated temperatures and create electron-hole plasma of Dirac fermions. The Dirac plasma has been found to exhibit unusual properties including quantum critical scattering and hydrodynamic flow. However, little is known about the plasma's behavior in magnetic fields. Here we report magnetotransport in this quantum-critical regime. In low fields, the plasma exhibits giant parabolic magnetoresistivity reaching >100% in 0.1 T even at room temperature. This is orders of magnitude higher than magnetoresistivity found in any other system at such temperatures. We show that this behavior is unique to monolayer graphene, being underpinned by its massless spectrum and ultrahigh mobility, despite frequent (Planckian-limit) scattering. With the onset of Landau quantization in a few T, where the electron-hole plasma resides entirely on the zeroth Landau level, giant linear magnetoresistivity emerges. It is nearly independent of temperature and can be suppressed by proximity screening, indicating a many-body origin. Clear parallels with magnetotransport in strange metals and so-called quantum linear magnetoresistance predicted for Weyl metals offer an interesting playground to further explore relevant physics using this well-defined quantum-critical 2D system.Comment: 8 pages, 3 figure

High-fidelity parallel entangling gates on a neutral atom quantum computer

The ability to perform entangling quantum operations with low error rates in a scalable fashion is a central element of useful quantum information processing. Neutral atom arrays have recently emerged as a promising quantum computing platform, featuring coherent control over hundreds of qubits and any-to-any gate connectivity in a flexible, dynamically reconfigurable architecture. The major outstanding challenge has been to reduce errors in entangling operations mediated through Rydberg interactions. Here we report the realization of two-qubit entangling gates with 99.5% fidelity on up to 60 atoms in parallel, surpassing the surface code threshold for error correction. Our method employs fast single-pulse gates based on optimal control, atomic dark states to reduce scattering, and improvements to Rydberg excitation and atom cooling. We benchmark fidelity using several methods based on repeated gate applications, characterize the physical error sources, and outline future improvements. Finally, we generalize our method to design entangling gates involving a higher number of qubits, which we demonstrate by realizing low-error three-qubit gates. By enabling high-fidelity operation in a scalable, highly connected system, these advances lay the groundwork for large-scale implementation of quantum algorithms, error-corrected circuits, and digital simulations.Comment: 5 pages, 4 figures. Methods: 13 pages, 10 figure

Logical quantum processor based on reconfigurable atom arrays

Suppressing errors is the central challenge for useful quantum computing, requiring quantum error correction for large-scale processing. However, the overhead in the realization of error-corrected ``logical'' qubits, where information is encoded across many physical qubits for redundancy, poses significant challenges to large-scale logical quantum computing. Here we report the realization of a programmable quantum processor based on encoded logical qubits operating with up to 280 physical qubits. Utilizing logical-level control and a zoned architecture in reconfigurable neutral atom arrays, our system combines high two-qubit gate fidelities, arbitrary connectivity, as well as fully programmable single-qubit rotations and mid-circuit readout. Operating this logical processor with various types of encodings, we demonstrate improvement of a two-qubit logic gate by scaling surface code distance from d=3 to d=7, preparation of color code qubits with break-even fidelities, fault-tolerant creation of logical GHZ states and feedforward entanglement teleportation, as well as operation of 40 color code qubits. Finally, using three-dimensional [[8,3,2]] code blocks, we realize computationally complex sampling circuits with up to 48 logical qubits entangled with hypercube connectivity with 228 logical two-qubit gates and 48 logical CCZ gates. We find that this logical encoding substantially improves algorithmic performance with error detection, outperforming physical qubit fidelities at both cross-entropy benchmarking and quantum simulations of fast scrambling. These results herald the advent of early error-corrected quantum computation and chart a path toward large-scale logical processors.Comment: See ancillary files: five supplementary movies and captions. Main text + Method

Electrically Tunable Damping of Plasmonic Resonances with Graphene

Dynamic switching of a plasmonic resonance may find numerous applications in subwavelength optoelectronics, spectroscopy, and sensing. Graphene shows a highly tunable carrier concentration under electrostatic gating, and this could provide an effective route to achieving electrical control of the plasmonic resonance. In this Letter, we demonstrate electrical control of a plasmonic resonance at infrared frequencies using large-area graphene. Plasmonic structures fabricated on graphene enhance the interaction of the incident optical field with the graphene sheet, and the impact of graphene is much stronger at mid-infrared wavelengths. Full-wave simulations, where graphene is modeled as a 1 nm thick effective medium, show excellent agreement with experimental results

Origin of indirect optical transitions in few-layer MoS2, WS2, and WSe2

10.1021/nl403270kNano Letters13115627-5634NALE