An 87Sr-based-optical lattice clock in NICT is compared to that of The University of Tokyo using a >50 km fiber
link. In this work, we have demonstrated for the first time that two distant Sr lattice clocks generate the same
frequency with systematic uncertainty of 0.31 Hz (7.3 × 10-16 fractionally) for the 429 THz clock frequency.
We demonstrate the frequency comparison of two optical lattice clocks at the relative stabilities close to the quantum
projection noise (QPN) limit of optical lattice clocks. This stable frequency comparison is accomplished by synchronous
interrogations of two clocks by a common probe laser, which allows us to cancel out the probe laser's frequency noise.
We perform the frequency comparison of a one-dimensional (1D) optical lattice clock with spin-polarized fermions
87Sr and a three-dimensional (3D) optical lattice clock with unity-occupation bosons 88Sr and achieve the Allan standard
deviation of σγ(τ)=4×10-16 τ-1/2, which corresponds to the QPN limited stability for N=1,000 atoms and the spectrum
linewidth γ=8 Hz. The relative stability reaches 1×10-17 with an averaging time of 1,600 s. Finally, we discuss the
prospects to realize 10-18 fractional inaccuracies and the possible application of frequency comparison with synchronous
interrogations to remote clocks' comparison for relativistic geodesy.
The growth and characterization of some cubic III-nitride films on suitable cubic substrates have been done, namely, c-
GaN on GaAs by MOVPE, c-GaN and c-AlGaN on MgO by RF-MBE, and c-InN and c-InGaN (In-rich) on YSZ by RFMBE.
This series of study has been much focused on the cubic-phase purity as dependent on the respective growth
conditions and resulting electrical and optical properties. For c-GaN and c-InN films, a cubic-phase purity higher than
95% is attained in spite of the metastable nature of the cubic III-nitrides. However, for c-AlGaN and c-InGaN films, the
cubic-phase purity is rapidly degraded with significant incorporation of the hexagonal phase through stacking faults on
cubic {111} faces which may be exposed on the roughened growing or substrate surface. It has been shown that the
electron mobilities in c-GaN and c-AlGaN films are much related to phase purity.
We discuss two possible configurations for optical lattice clocks; a one-dimensional (1D) lattice loaded with spinpolarized
fermions, and a three-dimensional (3D) lattice loaded with bosons. In the former scheme, collisional frequency
shifts are suppressed by the quantum statistical property of identical fermions. This Pauli blocking of collisions is
critically dependent on the degree of spin polarization of the fermionic atoms, which we carefully investigated in the
Rabi excitation process of the clock transition. In the latter scheme, a single occupancy lattice suppresses bunching of
bosons and collisional frequency shifts. We demonstrate a frequency comparison of these two optical lattice clocks based
on fermionic 87Sr and bosonic 88Sr. Operating these clocks parallely has yielded a stability approaching 10−17. Such measurements are an important step to ascertain the lattice clocks' uncertainty at the 10−17 level and beyond.
We have developed a one-dimensional optical lattice clock with ultracold 171Yb atoms. The absolute frequency of the
1S0(F = 1/2) - 3P0(F = 1/2) clock transition in 171Yb is determined to be 518 295 836 590 864(28) Hz with respect to the
SI second. Details of the experimental setups and atom trapping results are also described.
The recent development of optical frequency standards has been performed quite rapid and the better uncertainty than
that of microwave frequency standards will be realized in very near future. We are evaluating a one-dimensional 87Sr
optical lattice clock developed and located at the University of Tokyo, Tokyo, by using UTC(NMIJ) generated at NMIJ,
Tsukuba. The baseline length between those two sites is about 50 km. We constructed a time and frequency transfer link
using GPS carrier phase method for this link. We use GIPSY software and a newly developed one for data analysis. Our
developed one works in real time using carrier phase data and broadcast navigation data which are obtained from the
carrier phase receivers.
Two "optical lattice clocks", which based on spin-polarized fermionic 87Sr trapped in a one-dimensional optical lattice
and on bosonic 88Sr in a three-dimensional lattice, were operated simultaneously. From a beat note between the two
optical clocks, stability as well as accuracy of "optical lattice clocks" were evaluated. We report the progress of the
measurements.
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