Fuyuhiko Shiota

A study of a superconducting magnetic levitation system for an absolute determination of the magnetic flux quantum

A study of the equilibrium positions of a superconducting magnetic lévitation system which substitutes an electromagnetic energy for a mechanical energy is in progress for the absolute determination of the magnetic flux quantum Φ0. The study on a preliminary system at ppm-level resolution has been done and the reproducibility of the trajectory turned out to be of the order of 10 ppm. The problems of the present system and ideas for the next system at the sub-ppm level are discussed.

Absolute determination of the magnetic flux quantum using superconducting magnetic levitation

The current status of our superconducting magnetic levitation experiment for determining the magnetic flux quantum is described. The flux-up system has been improved significantly by using a Josephson voltage standard. Studies are also in progress to improve the mechanical measurement relevant to the floating body with the goal of reducing the uncertainty to less than 1 ppm. >

A Study of an Absolute Determination of the Magnetic Flux Quantum Using a Superconducting Levitation System

A study on a new method of determining the magnetic flux quantum 0 possibly at subppm level using a superconducting levitation system is described with some data from a preliminary experiment. The method employs a superconducting levitation system to substitute the gravitational potential energy of the floating body for the magnetic energy. The estimation of the expected accuracy and methods of improving the experiment are discussed.

Improvement of the superconducting magnetic levitation system for the determination of the magnetic flux quantum

An improvement of the preliminary superconducting magnetic levitation system for the absolute determination of the magnetic flux quantum is described. This improvement includes the development of the flux-up method to determine the flux in terms of the Josephson voltage. The improvement is essential for the determination of the magnetic flux quantum as well as of the coil current, in terms of the Josephson voltage and quantized Hall resistance. >

Evaluation of equilibrium trajectory of superconducting magnetic levitation system for the future kg unit of mass

The superconducting magnetic levitation system for absolute determination of magnetic flux quantum /spl Phi//sub 0/, which is aimed at the future replacement of the kilogram unit of mass, has been developed at the National Research Laboratory of Metrology (NRLM) with a small floating body of approximately 25 g mass. The consistency of the relation between potential energy of the floating body and the electromagnetic energy of the superconducting magnetic levitation system has been evaluated with 1 ppm order resolution. In this paper, the results of the evaluation as well as the improvements made in the apparatus in recent years at NRLM are described.

Vertical displacement determination of a levitated superconducting mass

The determination of the vertical displacement of the center of gravity of a levitated superconducting body in the National Research Laboratory of Metrology (NRLM) superconducting magnetic levitation project, which is aimed at establishing a new definition of the unit of mass based on the fundamental constants, is discussed. The translation displacement (three degrees of freedom) and the attitude change (three degrees of freedom) of the measuring point, which is the optical center of the cube corner prism O/sub C/ of the floating body, are measured using a newly developed optical measuring system. To determine the vertical displacement of the center of gravity of the floating body G/sub C/ the relative position of G/sub C/ with respect to O/sub C/ is required, which is determined using the energy relation between the electromagnetic energy and the gravitational potential energy under levitating conditions.

A buoyancy-free mass comparator with precision better than 10/sup -6/ for use in a superconducting magnetic levitation system

A system for measuring mass without the necessity of correcting for the buoyancy of air with a relative standard uncertainty better than 10/sup -6/ has been developed. The system is intended for use in determining the mass of the floating body in the superconducting magnetic levitation system.

Mechanism for levitated superconductor experiment

A mechanism for a levitated superconductor experiment has been proposed and is being developed with the final target of defining the kilogram in terms of fundamental constants. Improving the stability of the levitated object by means of introducing a superconducting linear bearing is the aim of the work reported in this paper. The strategy of this development, results of the preparatory experiments, and further prospects are discussed.

Improvement of the Superconducting Magnetic Levitation System for an Absolute Determination of the Magnetic Flux Quantum

The superconducting magnetic levitation system for the absolute determination of the magnetic flux quantum 0 is improved. Resolution of the vertical position of the floating body with laser interferometer becomes 1/100 µm order, which corresponds to 1 ppm of the gravitational potential energy of the floating body. An outline of this system and some temporary results are described.

Phenomenological Explanations for the Unbiased Operation of Even-Harmonic Josephson Junction Mixers

Even-harmonic JJ mixers allow unbiased operation, while odd-harmonic ones do not. Phenomenological explanations are presented for this phenomenon. Based on the voltage source model, a simple analysis is given that explains this phenomenon clearly. Furthermore, based on the current source model, this is studied by using a JJ simulator. In the odd-harmonic mixing, the waveform of supplied current has an odd symmetry, therefore, there is no mean junction voltage and no IF output. In the even-harmonic mixing, there is no such symmetry in the waveform of supplied current, therefore, there is a finite mean junction voltage and IF output.