1,450 research outputs found
Building a 3.5 m prototype interferometer for the Q & A vacuum birefringence experiment and high precision ellipsometry
We have built and tested a 3.5 m high-finesse Fabry-Perot prototype
inteferometer with a precision ellipsometer for the QED test and axion search
(Q & A) experiment. We use X-pendulum-double-pendulum suspension designs and
automatic control schemes developed by the gravitational-wave detection
community. Verdet constant and Cotton-Mouton constant of the air are measured
as a test. Double modulation with polarization modulation 100 Hz and
magnetic-field modulation 0.05 Hz gives 10^{-7} rad phase noise for a 44-minute
integration.Comment: This draft has been presented in the 5th Edoardo Amaldi Conference on
Gravitational Wave
Effect of Spin-Orbit Interaction in Spin-Triplet Superconductor: Structure of -vector and Anomalous O-NQR Relaxation in SrRuO
Supposing the spin-triplet superconducting state of SrRuO, the
spin-orbit (SO) coupling associated with relative motion in Cooper pairs is
calculated by extending the method for the dipole-dipole coupling given by
Leggett in the superfluid He. It is shown that the SO coupling works only
in the equal-spin pairing (ESP) state to make the pair angular momentum
and the pair spin angular momentum parallel with each other. The SO coupling gives rise to the internal
Josephson effect in a chiral ESP state as in superfluid A-phase of He with
a help of an additional anisotropy arising from SO coupling of atomic origin
which works to direct the {\bf d}-vector into -plane. This resolves the
problem of the anomalous relaxation of O-NQR and the structure of {\bf
d}-vector in SrRuO.Comment: Accepted for publication in J. Phys. Soc. Jpn. vol.79 (2010), No.2
(February issue); 18 pages, 2 figure
Improved Simulation of the Mass Charging for ASTROD I
The electrostatic charging of the test mass in ASTROD I (Astrodynamical Space
Test of Relativity using Optical Devices I) mission can affect the quality of
the science data as a result of spurious Coulomb and Lorentz forces. To
estimate the size of the resultant disturbances, credible predictions of
charging rates and the charging noise are required. Using the GEANT4 software
toolkit, we present a detailed Monte Carlo simulation of the ASTROD I test mass
charging due to exposure of the spacecraft to galactic cosmic-ray (GCR) protons
and alpha particles (3He, 4He) in the space environment. A positive charging
rate of 33.3 e+/s at solar minimum is obtained. This figure reduces by 50% at
solar maximum. Based on this charging rate and factoring in the contribution of
minor cosmic-ray components, we calculate the acceleration noise and stiffness
associated with charging. We conclude that the acceleration noise arising from
Coulomb and Lorentz effects are well below the ASTROD I acceleration noise
limit at 0.1 mHz both at solar minimum and maximum. The coherent Fourier
components due to charging are investigated, it needs to be studied carefully
in order to ensure that these do not compromise the quality of science data in
the ASTROD I mission.Comment: 20 pages, 14 figures, submitted to International Journal of Modern
Physics
A theory of new type of heavy-electron superconductivity in PrOs_4Sb_12: quadrupolar-fluctuation mediated odd-parity pairings
It is shown that unconventional nature of superconducting state of
PrOs_4Sb_12, a Pr-based heavy electron compound with the filled-Skutterudite
structure, can be explained in a unified way by taking into account the
structure of the crystalline-electric-field (CEF) level, the shape of the Fermi
surface determined by the band structure calculation, and a picture of the
quasiparticles in f-configuration with magnetically singlet CEF ground
state. Possible types of pairing are narrowed down by consulting recent
experimental results. In particular, the chiral "p"-wave states such as
p_x+ip_y is favoured under the magnetic field due to the orbital Zeeman effect,
while the "p"-wave states with two-fold symmetery such as p_x can be stabilized
by a feedback effect without the magnetic field. It is also discussed that the
double superconducting transition without the magnetic field is possible due to
the spin-orbit coupling of the "triplet" Cooper pairs in the chiral state.Comment: 12 pages, 2 figures, submitted to J. Phys.: Condens. Matter Lette
Spin-fluctuation exchange study of superconductivity in two- and three-dimensional single-band Hubbard models
In order to identify the most favorable situation for superconductivity in
the repulsive single-band Hubbard model, we have studied instabilities for
d-wave pairing mediated by antiferromagnetic spin fluctuations and p-pairing
mediated by ferromagnetic fluctuations with the fluctuation exchange
approximation in both two dimensions and three dimensions. By systematically
varying the band filling and band structure we have shown that (i) d-pairing is
stronger in two dimensions than in three dimensions, and (ii) p-pairing is much
weaker than the d-pairing.Comment: RevTex, 5 figures in Postscript, to be published in Phys. Rev.
Suspension of the fiber mode-cleaner launcher and measurement of the high extinction-ratio (10^{-9}) ellipsometer for the Q & A experiment
The Q & A experiment, first proposed and started in 1994, provides a feasible
way of exploring the quantum vacuum through the detection of vacuum
birefringence effect generated by QED loop diagram and the detection of the
polarization rotation effect generated by photon-interacting (pseudo-)scalar
particles. Three main parts of the experiment are: (1) Optics System (including
associated Electronic System) based on a suspended 3.5-m high finesse
Fabry-Perot cavity, (2) Ellipsometer using ultra-high extinction-ratio
polarizer and analyzer, and (3) Magnetic Field Modulation System for generating
the birefringence and the polarization rotation effect. In 2002, the Q & A
experiment achieved the Phase I sensitivity goal. During Phase II, we set (i)
to improve the control system of the cavity mirrors for suppressing the
relative motion noise, (ii) to enhance the birefringence signal by setting-up a
60-cm long 2.3 T transverse permanent magnet rotatable to 10 rev/s, (iii) to
reduce geometrical noise by inserting a polarization-maintaining optical fiber
(PM fiber) as a mode cleaner, and (iv) to use ultra-high extinction-ratio
(10^{-9}) polarizer and analyzer for ellipsometry. Here we report on (iii) &
(iv); specifically, we present the properties of the PM-fiber mode-cleaner, the
transfer function of its suspension system, and the result of our measurement
of high extinction-ratio polarizer and analyzer.Comment: 8 pages, 6 figures, presented in the 6th Edoardo Amaldi Conference on
Gravitational Waves, Okinawa, Japan, June 2005, and accepted by "Journal of
Physics: Conference Series". Modifications from version 2 were made based on
the referees' comments on figures. Ref. [31] were update
Josephson Current between Triplet and Singlet Superconductors
The Josephson effect between triplet and singlet superconductors is studied.
Josephson current can flow between triplet and singlet superconductors due to
the spin-orbit coupling in the spin-triplet superconductor but it is finite
only when triplet superconductor has , where and
are the perpendicular components of orbital angular momentum and spin angular
momentum of the triplet Cooper pairs, respectively. The recently observed
temperature and orientational dependence of the critical current through a
Josephson junction between UPt and Nb is investigated by considering a
non-unitary triplet state.Comment: 4 pages, no figure
Parity-sensitive measurements based on ferromagnet/superconductor tunneling junctions
A method to identify the parity of unconventional superconductors is proposed
based on tunneling spectroscopy. For a model of calculation, we adopt a
ferromagnet/superconductor (F/S) junction of which tunneling current is spin
polarized. The tunneling conductance spectra are shown to be quite sensitive to
the direction of the magnetization axis in the ferromagnet only when the
superconductor has odd parity. Therefore, it is possible to distinguish the
parity of the superconductor by measuring the tunneling spectroscopy in F/S
junctions.Comment: 4 pages, 5 figure. To appear in J. Phys. Soc. Jp
Ellipsometry noise spectrum, suspension transfer function measurement and closed-loop control of the suspension system in the Q & A experiment
The Q & A experiment, aiming at the detection of vacuum birefringence
predicted by quantum electrodynamics, consists mainly of a suspended 3.5 m
Fabry-Perot cavity, a rotating permanent dipole magnet and an ellipsometer. The
2.3 T magnet can rotate up to 10 rev/s, introducing an ellipticity signal at
twice the rotation frequency. The X-pendulum gives a good isolation ratio for
seismic noise above its main resonant frequency 0.3 Hz. At present, the
ellipsometry noise decreases with frequency, from 1*10^{-5} rad Hz^{-1/2} at 5
Hz, 2*10^{-6} rad Hz^{-1/2} at 20 Hz to 5*10^{-7} rad Hz^{-1/2} at 40 Hz. The
shape of the noise spectrum indicates possible improvement can be made by
further reducing the movement between the cavity mirrors. From the preliminary
result of yaw motion alignment control, it can be seen that some peaks due to
yaw motion of the cavity mirror was suppressed. In this paper, we first give a
schematic view of the Q & A experiment, and then present the measurement of
transfer function of the compound X-pendulum-double pendulum suspension. A
closed-loop control was carried out to verify the validity of the measured
transfer functions. The ellipsometry noise spectra with and without yaw
alignment control and the newest improvement is presented.Comment: 7 pages, 5 figures, presented in 6th Edoardo Amaldi Conference on
Gravitational Waves, June 2005, Okinawa Japan and submitted to Journal of
Physics: Conference Series. Some modifications are made according to the
referee's comments: mainly to explain the relation between the displacement
of cavity mirror and the ellipticity noise spectru
ASTROD, ASTROD I and their gravitational-wave sensitivities
ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) is a
mission concept with three spacecraft -- one near L1/L2 point, one with an
inner solar orbit and one with an outer solar orbit, ranging coherently with
one another using lasers to test relativistic gravity, to measure the solar
system and to detect gravitational waves. ASTROD I with one spacecraft ranging
optically with ground stations is the first step toward the ASTROD mission. In
this paper, we present the ASTROD I payload and accelerometer requirements,
discuss the gravitational-wave sensitivities for ASTROD and ASTROD I, and
compare them with LISA and radio-wave PDoppler-tracking of spacecraft.Comment: presented to the 5th Edoardo Amaldi Conference (July 6-11, 2003) and
submitted to Classical and Quantum Gravit
- …