527 research outputs found
What Can We Learn from Noise? -- Mesoscopic Nonequilibrium Statistical Physics --
Mesoscopic systems -- small electric circuits working in quantum regime --
offer us a unique experimental stage to explorer quantum transport in a tunable
and precise way. The purpose of this Review is to show how they can contribute
to statistical physics. We introduce the significance of fluctuation, or
equivalently noise, as noise measurement enables us to address the fundamental
aspects of a physical system. The significance of the fluctuation theorem (FT)
in statistical physics is noted. We explain what information can be deduced
from the current noise measurement in mesoscopic systems. As an important
application of the noise measurement to statistical physics, we describe our
experimental work on the current and current noise in an electron
interferometer, which is the first experimental test of FT in quantum regime.
Our attempt will shed new light in the research field of mesoscopic quantum
statistical physics.Comment: 15 pages, 10 figures. Review articl
Switching magnetic vortex core by a single nanosecond current pulse
In a ferromagnetic nanodisk, the magnetization tends to swirl around in the
plane of the disk and can point either up or down at the center of this
magnetic vortex. This binary state can be useful for information storage. It is
demonstrated that a single nanosecond current pulse can switch the core
polarity. This method also provides the precise control of the core direction,
which constitutes fundamental technology for realizing a vortex core memory.Comment: 13 pages, 4 figure
Fano Resonance in a Quantum Wire with a Side-coupled Quantum Dot
We report a transport experiment on the Fano effect in a quantum connecting
wire (QW) with a side-coupled quantum dot (QD). The Fano resonance occurs
between the QD and the "T-shaped" junction in the wire, and the transport
detects anti-resonance or forward scattered part of the wavefunction. While in
this geometry it is more difficult to tune the shape of the resonance than in
the previously reported Aharonov-Bohm-ring type interferometer, the resonance
purely consists of the coherent part of transport. By utilizing this advantage,
we have qualitatively explained the temperature dependence of the Fano effect
by including the thermal broadening and the decoherence. We have also proven
that this geometry can be a useful interferometer to measure the phase
evolution of electrons at a QD.Comment: REVTEX, 6 pages including 5 figures, final versio
Current-driven resonant excitation of magnetic vortex
A magnetic vortex core in a ferromagnetic circular nanodot has a resonance
frequency originating from the confinement of the vortex core. By the
micromagnetic simulation including the spin-transfer torque, we show that the
vortex core can be resonantly excited by an AC (spin-polarized) current through
the dot and that the resonance frequency can be tuned by the dot shape. The
resistance measurement under the AC current successfully detects the resonance
at the frequency consistent with the simulation.Comment: 16 pages, 4 figure
Nitrogen isotope effects on boron vacancy quantum sensors in hexagonal boron nitride
Recently, there has been growing interest in researching the use of hexagonal
boron nitride (hBN) for quantum technologies. Here we investigate nitrogen
isotope effects on boron vacancy (V) defects, one of the candidates
for quantum sensors, in N isotopically enriched hBN synthesized using
metathesis reaction. The Raman shifts are scaled with the reduced mass,
consistent with previous work on boron isotope enrichment. We obtain nitrogen
isotopic composition dependent optically detected magnetic resonance spectra of
V defects and determine the hyperfine interaction parameter of
N spin to be -64 MHz. Our investigation provides a design policy for
hBNs for quantum technologies
Optical-power-dependent splitting of magnetic resonance in nitrogen-vacancy centers in diamond
Nitrogen-vacancy (NV) centers in diamonds are a powerful tool for accurate
magnetic field measurements. The key is precisely estimating the
field-dependent splitting width of the optically detected magnetic resonance
(ODMR) spectra of the NV centers. In this study, we investigate the optical
power dependence of the ODMR spectra using NV ensemble in nanodiamonds (NDs)
and a single-crystal bulk diamond. We find that the splitting width
exponentially decays and is saturated as the optical power increases.
Comparison between NDs and a bulk sample shows that while the decay amplitude
is sample-dependent, the optical power at which the decay saturates is almost
sample-independent. We propose that this unexpected phenomenon is an intrinsic
property of the NV center due to non-axisymmetry deformation or impurities. Our
finding indicates that diamonds with less deformation are advantageous for
accurate magnetic field measurements.Comment: 9 pages, 7 figure
Observation of the Fano-Kondo Anti-Resonance in a Quantum Wire with a Side-Coupled Quantum Dot
We have observed the Fano-Kondo anti-resonance in a quantum wire with a
side-coupled quantum dot. In a weak coupling regime, dips due to the Fano
effect appeared. As the coupling strength increased, conductance in the regions
between the dips decreased alternately. From the temperature dependence and the
response to the magnetic field, we conclude that the conductance reduction is
due to the Fano-Kondo anti-resonance. At a Kondo valley with the Fano parameter
, the phase shift is locked to against the gate voltage
when the system is close to the unitary limit in agreement with theoretical
predictions by Gerland {\it et al.} [Phys. Rev. Lett. {\bf 84}, 3710 (2000)].Comment: 4 pages, 4 figure
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