1,701 research outputs found
Quantum whistling in superfluid 4He
Fundamental considerations predict that macroscopic quantum systems such as
superfluids and the electrons in superconductors will exhibit oscillatory
motion when pushed through a small constriction. Here we report the observation
of these oscillations between two reservoirs of superfluid 4He partitioned by
an array of nanometer-sized apertures. They obey the Josephson frequency
equation and are coherent amongst all the apertures. This discovery at the
relatively high temperature of 2K (2000 times higher than related phenomena in
3He) may pave the way for a new class of practical rotation sensors of
unprecedented precision.Comment: 6 pages, 3 figures, to be published in Natur
Submillimeter satellite radiometer Final engineering report
All solid-state superheterodyne Dicke radiometer for submillimeter wavelength
Electron-beam-induced shift in the apparent position of a pinned vortex in a thin superconducting film
When an electron beam strikes a superconducting thin film near a pinned
vortex, it locally increases the temperature-dependent London penetration depth
and perturbs the circulating supercurrent, thereby distorting the vortex's
magnetic field toward the heated spot. This phenomenon has been used to
visualize vortices pinned in SQUIDs using low-temperature scanning electron
microscopy. In this paper I develop a quantitative theory to calculate the
displacement of the vortex-generated magnetic-flux distribution as a function
of the distance of the beam spot from the vortex core. The results are
calculated using four different models for the spatial distribution of the
thermal power deposited by the electron beam.Comment: 9 pages, 6 figures, resubmitted to PRB with referee-suggested
revisions, includes new paragraph on numerical evaluatio
Transition from synchronous to asynchronous superfluid phase slippage in an aperture array
We have investigated the dynamics of superfluid phase slippage in an array of
apertures. The magnitude of the dissipative phase slips shows that they occur
simultaneously in all the apertures when the temperature is around 10 mK below
the superfluid transition, and subsequently lose their simultaneity as the
temperature is lowered. We find that when periodic synchronous phase slippage
occurs, the synchronicity exists from the very first phase slip, and therefore
is not due to mode locking of interacting oscillators. When the system is
allowed to relax freely from a given initial energy, the total number of phase
slips that occur and the energy left in the system after the last phase slip
depends reproducibly on the initial energy. We find the energy remaining after
the final phase slip is a periodic function of the initial system energy. This
dependence directly reveals the discrete and dissipative nature of the phase
slips and is a powerful diagnostic for investigation of synchronicity in the
array. When the array slips synchronously, this periodic energy function is a
sharp sawtooth. As the temperature is lowered and the degree of synchronicity
drops, the peak of this sawtooth becomes rounded, suggesting a broadening of
the time interval over which the array slips. The underlying mechanism for the
higher temperature synchronous behavior and the following loss of synchronicity
at lower temperatures is not yet understood. We discuss the implications of our
measurements and pose several questions that need to be resolved by a theory
explaining the synchronous behavior in this quantum system. An understanding of
the array phase slip process is essential to the optimization of superfluid
`dc-SQUID' gyroscopes and interferometers.Comment: 10 pages, 4 figure
On the stability of standing matter waves in a trap
We discuss excited Bose-condensed states and find the criterion of dynamical
stability of a kink-wise state, i.e., a standing matter wave with one nodal
plane perpendicular to the axis of a cylindrical trap. The dynamical stability
requires a strong radial confinement corresponding to the radial frequency
larger than the mean-field interparticle interaction. We address the question
of thermodynamic instability related to the presence of excitations with
negative energy.Comment: 4 pages, 3 figure
Observation of Flow Dissipation in 3He-B
Anomalous dissipation is observed in 3He-B flowing in a U-tube device. The dissipation is of unknown origin and persists to the lowest measured velocity. The position of this result in the framework of other 3He-B flow experiments is discussed
Persistent-Current Experiments on Superfluid 3He-B and 3He-A
We have investigated persistent flow of superfluid 3He with an ac gyroscope filled with 20-ÎŒm powder. In 3He-B, currents circulate undiminished for 48 h at least; this implies a viscosity 12 orders of magnitude lower than in the normal fluid. In 3He-A, the current does not persist. The observed critical velocity in 3He-B at P12 bars there are two regimes in the B phase: For example, at 29.3 bars the ultimate critical velocities are 5.4 and 7.8 mm/s, respectively.Peer reviewe
Manufacture, observation, and test of membranes with locatable single pores
A method for generating single pores down to 0.1 ÎŒm diameter in the center of a large circular foil is described, based on nuclear tracks. The foil is framed by a tension ring which enables one to handle the foils in a wellâdefined precise way. The single pore has a lateral displacement of ±0.1 mm with respect to the tension ring center. The foils used are polycarbonate of the type Makrofol and have thicknesses between 2 and 10 ÎŒm. For calibration of the single pore diameters, multiple nuclear tracks between 0.1 and 3.5 ÎŒm diameter are etched and observed by microscopy. The microscopic observations are compared with gasâflow measurements, using two alternative methods: multiple holes are tested under viscous flow conditions of N2 gas at normal temperature and pressure; single holes are tested under collisionless flow conditions of 4He gas at liquidânitrogen temperature, using a capacitance method.Peer reviewe
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