59 research outputs found
Designing High-Fidelity Single-Shot Three-Qubit Gates: A Machine Learning Approach
Three-qubit quantum gates are key ingredients for quantum error correction
and quantum information processing. We generate quantum-control procedures to
design three types of three-qubit gates, namely Toffoli, Controlled-Not-Not and
Fredkin gates. The design procedures are applicable to a system comprising
three nearest-neighbor-coupled superconducting artificial atoms. For each
three-qubit gate, the numerical simulation of the proposed scheme achieves
99.9% fidelity, which is an accepted threshold fidelity for fault-tolerant
quantum computing. We test our procedure in the presence of decoherence-induced
noise as well as show its robustness against random external noise generated by
the control electronics. The three-qubit gates are designed via the machine
learning algorithm called Subspace-Selective Self-Adaptive Differential
Evolution (SuSSADE).Comment: 18 pages, 13 figures. Accepted for publication in Phys. Rev. Applie
Giant voltage control of spin Hall nano-oscillator damping
Spin Hall nano-oscillators (SHNOs) are emerging spintronic devices for
microwave signal generation and oscillator based neuromorphic computing
combining nano-scale footprint, fast and ultra-wide microwave frequency
tunability, CMOS compatibility, and strong non-linear properties providing
robust large-scale mutual synchronization in chains and two-dimensional arrays.
While SHNOs can be tuned via magnetic fields and the drive current, neither
approach is conducive for individual SHNO control in large arrays. Here, we
demonstrate electrically gated W/CoFeB/MgO nano-constrictions in which the
voltage-dependent perpendicular magnetic anisotropy, tunes the frequency and,
thanks to nano-constriction geometry, drastically modifies the spin-wave
localization in the constriction region resulting in a giant 42 % variation of
the effective damping over four volts. As a consequence, the SHNO threshold
current can be strongly tuned. Our demonstration adds key functionality to
nano-constriction SHNOs and paves the way for energy-efficient control of
individual oscillators in SHNO chains and arrays for neuromorphic computing
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