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High-fidelity two-qubit gates at scale are a key requirement to realize the full promise of quantum computation and simulation. The advent and use of coupler elements to tunably control two-qubit interactions has improved operational fidelity in many-qubit systems by reducing parasitic coupling and frequency crowding issues. Nonetheless, two-qubit gate errors still limit the capability of near-term quantum applications. The reason, in part, is the existing framework for tunable couplers based on the dispersive approximation does not fully incorporate three-body multi-level dynamics, which is essential for addressing coherent leakage to the coupler and parasitic longitudinal ($ZZ$) interactions during two-qubit gates. Here, we present a systematic approach that goes beyond the dispersive approximation to exploit the engineered level structure of the coupler and optimize its control. Using this approach, we experimentally demonstrate CZ and $ZZ$-free iSWAP gates with two-qubit interaction fidelities of $99.76 \pm 0.07$% and $99.87 \pm 0.23$%, respectively, which are close to their $T_1$ limits.

© 2020 American Physical Society. The dominant source of decoherence in contemporary frequency-tunable superconducting qubits is 1/f flux noise. To understand its origin and find ways to minimize its impact, we systematically study flux noise amplitudes in more than 50 flux qubits with varied superconducting quantum interference device (SQUID) geometry parameters and compare our results to a microscopic model of magnetic spin defects located at the interfaces surrounding the SQUID loops. Our data are in agreement with an extension of the previously proposed model, based on numerical simulations of the current distribution in the investigated SQUIDs. Our results and detailed model provide a guide for minimizing the flux noise susceptibility in future circuits.

Metasurface phase masks offer a new way of imaging in that the lens sizes are orders of magnitude smaller and allow for batch fabrication of a large number of miniature lenses. Unfortunately, current metasurface lens technology cannot simultaneously overcome the issues of image distortion for objects far from the optical axis and chromatic aberrations. Using simulations in Matlab, we study and design a single lens holographic system using metasurface lenses to drastically reduce both off-axis distortions and chromatic aberrations. Using a single metasurface lens, we demonstrate that a high quality image can be obtained for an object with a 30° angular diameter and 123 fractional bandwidth. We also experimentally demonstrate reduction of aberrations and 3D imaging for spare images as well as show mediocre quality reconstructed dense images.

Metasurface phase masks offer a new way of imaging in that the lens sizes are orders of magnitude smaller and allow for batch fabrication of a large number of miniature lenses. Unfortunately, current metasurface lens technology cannot simultaneously overcome the issues of image distortion for objects far from the optical axis and chromatic aberrations. Using simulations in Matlab, we study and design a single lens holographic system using metasurface lenses to drastically reduce both off-axis distortions and chromatic aberrations. Using a single metasurface lens, we demonstrate that a high quality image can be obtained for an object with a 30° angular diameter and 123 fractional bandwidth. We also experimentally demonstrate reduction of aberrations and 3D imaging for spare images as well as show mediocre quality reconstructed dense images.

Metasurface phase masks offer a new way of imaging in that the lens sizes are orders of magnitude smaller and allow for batch fabrication of a large number of miniature lenses. Unfortunately, current metasurface lens technology cannot simultaneously overcome the issues of image distortion for objects far from the optical axis and chromatic aberrations. Using simulations in Matlab, we study and design a single lens holographic system using metasurface lenses to drastically reduce both off-axis distortions and chromatic aberrations. Using a single metasurface lens, we demonstrate that a high quality image can be obtained for an object with a 30° angular diameter and 123 fractional bandwidth. We also experimentally demonstrate reduction of aberrations and 3D imaging for spare images as well as show mediocre quality reconstructed dense images.