Nobuyasu Shiga

Optimized dynamical decoupling in a model quantum memory

Any quantum system, such as those used in quantum information or magnetic resonance, is subject to random phase errors that can dramatically affect the fidelity of a desired quantum operation or measurement. In the context of quantum information, quantum error correction techniques have been developed to correct these errors, but resource requirements are extraordinary. The realization of a physically tractable quantum information system will therefore be facilitated if qubit (quantum bit) error rates are far below the so-called fault-tolerance error threshold, predicted to be of the order of 10-3–10-6. The need to realize such low error rates motivates a search for alternative strategies to suppress dephasing in quantum systems. Here we experimentally demonstrate massive suppression of qubit error rates by the application of optimized dynamical decoupling pulse sequences, using a model quantum system capable of simulating a variety of qubit technologies. We demonstrate an analytically derived pulse sequence, UDD, and find novel sequences through active, real-time experimental feedback. The latter sequences are tailored to maximize error suppression without the need for a priori knowledge of the ambient noise environment, and are capable of suppressing errors by orders of magnitude compared to other existing sequences (including the benchmark multi-pulse spin echo). Our work includes the extension of a treatment to predict qubit decoherence under realistic conditions, yielding strong agreement between experimental data and theory for arbitrary pulse sequences incorporating nonidealized control pulses. These results demonstrate the robustness of qubit memory error suppression through dynamical decoupling techniques across a variety of qubit technologies.

Experimental Uhrig dynamical decoupling using trapped ions

We present a detailed experimental study of the Uhrig dynamical decoupling UDD sequence in a variety of noise environments. Our qubit system consists of a crystalline array of 9 Be + ions confined in a Penning trap. We use an electron-spin-flip transition as our qubit manifold and drive qubit rotations using a 124 GHz microwave system. We study the effect of the UDD sequence in mitigating phase errors and compare against the well known Carr-Purcell-Meiboom-Gill-style multipulse spin echo as a function of pulse number, rotation axis, noise spectrum, and noise strength. Our results agree well with theoretical predictions for qubit decoherence in the presence of classical phase noise, accounting for the effect of finite-duration pulses. Finally, we demonstrate that the Uhrig sequence is more robust against systematic over- or under-rotation and detuning errors than is multipulse spin echo, despite the precise prescription for pulse timing in UDD.

Diamagnetic correction to the 9Be+ ground-state hyperfine constant

We report an experimental determination of the diamagnetic correction to the

Prolonging qubit coherence: dynamical decoupling schemes studied in a Penning ion trap

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High-fidelity quantum control using ion crystals in a penning trap

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Dynamical Decoupling Using Trapped Ions

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Diamagnetic correction to the {sup 9}Be{sup +} ground-state hyperfine constant

ground state hyperfine constant

Preserving quantum coherence using optimized open-loop control techniques

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Optimized Dynamical Decoupling in a Model Quantum Memory

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Optimization of Dynamical Decoupling Using Measurement Feedback

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