222 research outputs found
Si/SiGe2重量子ドットにおけるスピン量子ビットの実験的研究
学位の種別: 課程博士審査委員会委員 : (主査)東京大学教授 樽茶 清悟, 大阪大学教授 大岩 顕, 東京大学教授 中村 泰信, 筑波大学教授 都倉 康弘, 東京大学准教授 長田 俊人University of Tokyo(東京大学
Feedback-based active reset of a spin qubit in silicon
Feedback control of qubits is a highly demanded technique for advanced
quantum information protocols such as quantum error correction. Here we
demonstrate active reset of a silicon spin qubit using feedback control. The
active reset is based on quantum non-demolition readout of the qubit and
feedback according to the readout results, which is enabled by hardware data
processing and sequencing. We incorporate a cumulative readout technique to the
active reset protocol, enhancing initialization fidelity above a limitation
imposed by accuracy of the single QND measurement fidelity. Based on an
analysis of the reset protocol, we suggest a way to achieve the initialization
fidelity sufficient for the fault-tolerant quantum computation
A shuttling-based two-qubit logic gate for linking distant silicon quantum processors
Control of entanglement between qubits at distant quantum processors using a
two-qubit gate is an essential function of a scalable, modular implementation
of quantum computation. Among the many qubit platforms, spin qubits in silicon
quantum dots are promising for large-scale integration along with their
nanofabrication capability. However, linking distant silicon quantum processors
is challenging as two-qubit gates in spin qubits typically utilize short-range
exchange coupling, which is only effective between nearest-neighbor quantum
dots. Here we demonstrate a two-qubit gate between spin qubits via coherent
spin shuttling, a key technology for linking distant silicon quantum
processors. Coherent shuttling of a spin qubit enables efficient switching of
the exchange coupling with an on/off ratio exceeding 1,000 , while preserving
the spin coherence by 99.6% for the single shuttling between neighboring dots.
With this shuttling-mode exchange control, we demonstrate a two-qubit
controlled-phase gate with a fidelity of 93%, assessed via randomized
benchmarking. Combination of our technique and a phase coherent shuttling of a
qubit across a large quantum dot array will provide feasible path toward a
quantum link between distant silicon quantum processors, a key requirement for
large-scale quantum computation
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