119 research outputs found
Robust Single-Shot Spin Measurement with 99.5% Fidelity in a Quantum Dot Array
We demonstrate a new method for projective single-shot measurement of two
electron spin states (singlet versus triplet) in an array of gate-defined
lateral quantum dots in GaAs. The measurement has very high fidelity and is
robust with respect to electric and magnetic fluctuations in the environment.
It exploits a long-lived metastable charge state, which increases both the
contrast and the duration of the charge signal distinguishing the two
measurement outcomes. This method allows us to evaluate the charge measurement
error and the spin-to-charge conversion error separately. We specify conditions
under which this method can be used, and project its general applicability to
scalable quantum dot arrays in GaAs or silicon.Comment: 13 pages, 3 figure
Quantum nondemolition measurement of an electron spin qubit
Measurement of quantum systems inevitably involves disturbance in various
forms. Within the limits imposed by quantum mechanics, however, one can design
an "ideal" projective measurement that does not introduce a back action on the
measured observable, known as a quantum nondemolition (QND) measurement. Here
we demonstrate an all-electrical QND measurement of a single electron spin in a
gate-defined quantum dot via an exchange-coupled ancilla qubit. The ancilla
qubit, encoded in the singlet-triplet two-electron subspace, is entangled with
the single spin and subsequently read out in a single shot projective
measurement at a rate two orders of magnitude faster than the spin relaxation.
The QND nature of the measurement protocol is evidenced by observing a
monotonic increase of the readout fidelity over one hundred repetitive
measurements against arbitrary input states. We extract information from the
measurement record using the method of optimal inference, which is tolerant to
the presence of the relaxation and dephasing. The QND measurement allows us to
observe spontaneous spin flips (quantum jumps) in an isolated system with small
disturbance. Combined with the high-fidelity control of spin qubits, these
results pave the way for various measurement-based quantum state manipulations
including quantum error correction protocols.Comment: This is a pre-print of an article published in Nature Nanotechnology.
The final authenticated version is available online at:
https://doi.org/10.1038/s41565-019-0426-
Development of fast-response PPAC with strip-readout for heavy-ion beams
A strip-readout parallel-plate avalanche counter (SR-PPAC) has been developed
aiming at the high detection efficiency and good position resolution in
high-intensity heavy-ion measurements. The performance was evaluated using 115
MeV/u Xe, 300 MeV/u Sn, and 300 MeV/u Ca beams. A
detection efficiency beyond 99% for these beams is achieved even at an incident
beam intensity of 0.7 billion particles per second. The best position
resolution achieved is 235 um (FWHM).Comment: 16 pages, 18 figures, 2 table
Coherence of a driven electron spin qubit actively decoupled from quasi-static noise
The coherence of electron spin qubits in semiconductor quantum dots suffers
mostly from low-frequency noise. During the last decade, efforts have been
devoted to mitigate such noise by material engineering, leading to substantial
enhancement of the spin dephasing time for an idling qubit. However, the role
of the environmental noise during spin manipulation, which determines the
control fidelity, is less understood. We demonstrate an electron spin qubit
whose coherence in the driven evolution is limited by high-frequency charge
noise rather than the quasi-static noise inherent to any semiconductor device.
We employed a feedback control technique to actively suppress the latter,
demonstrating a -flip gate fidelity as high as in a
gallium arsenide quantum dot. We show that the driven-evolution coherence is
limited by the longitudinal noise at the Rabi frequency, whose spectrum
resembles the noise observed in isotopically purified silicon qubits.Comment: 10 pages, 7 figure
Efficacy of glutathione for the treatment of nonalcoholic fatty liver disease: an open-label, single-arm, multicenter, pilot study
Background: Glutathione plays crucial roles in the detoxification and antioxidant systems of cells and has been used to treat acute poisoning and chronic liver diseases by intravenous injection. This is a first study examining the therapeutic effects of oral administration of glutathione in patients with nonalcoholic fatty liver disease (NAFLD). Methods: The study was an open label, single arm, multicenter, pilot trial. Thirty-four NAFLD patients diagnosed using ultrasonography were prospectively evaluated. All patients first underwent intervention to improve their lifestyle habits (diet and exercise) for 3 months, followed by treatment with glutathione (300 mg/day) for 4 months. We evaluated their clinical parameters before and after glutathione treatment. We also quantified liver fat and fibrosis using vibration-controlled transient elastography. The primary outcome of the study was the change in alanine aminotransferase (ALT) levels. Results: Twenty-nine patients finished the protocol. ALT levels significantly decreased following treatment with glutathione for 4 months. In addition, triglycerides, non-esterified fatty acids, and ferritin levels also decreased with glutathione treatment. Following dichotomization of ALT responders based on a median 12.9% decrease from baseline, we found that ALT responders were younger in age and did not have severe diabetes compared with ALT non-responders. The controlled attenuation parameter also decreased in ALT responders. Conclusions: This pilot study demonstrates the potential therapeutic effects of oral administration of glutathione in practical dose for patients with NAFLD. Large-scale clinical trials are needed to verify its efficacy. Trial registration: UMIN000011118 (date of registration: July 4, 2013)
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