234 research outputs found
Method for Cooling Nanostructures to Microkelvin Temperatures
We propose a new scheme aimed at cooling nanostructures to microkelvin
temperatures, based on the well established technique of adiabatic nuclear
demagnetization: we attach each device measurement lead to an individual
nuclear refrigerator, allowing efficient thermal contact to a microkelvin bath.
On a prototype consisting of a parallel network of nuclear refrigerators,
temperatures of mK simultaneously on ten measurement leads have been
reached upon demagnetization, thus completing the first steps toward ultracold
nanostructures.Comment: 4 pages, 3 (color) figure
Control of Multi-level Voltage States in a Hysteretic SQUID Ring-Resonator System
In this paper we study numerical solutions to the quasi-classical equations
of motion for a SQUID ring-radio frequency (rf) resonator system in the regime
where the ring is highly hysteretic. In line with experiment, we show that for
a suitable choice of of ring circuit parameters the solutions to these
equations of motion comprise sets of levels in the rf voltage-current dynamics
of the coupled system. We further demonstrate that transitions, both up and
down, between these levels can be controlled by voltage pulses applied to the
system, thus opening up the possibility of high order (e.g. 10 state),
multi-level logic and memory.Comment: 8 pages, 9 figure
Breakdown of the Korringa Law of Nuclear Spin Relaxation in Metallic GaAs
We present nuclear spin relaxation measurements in GaAs epilayers using a new
pump-probe technique in all-electrical, lateral spin-valve devices. The
measured T1 times agree very well with NMR data available for T > 1 K. However,
the nuclear spin relaxation rate clearly deviates from the well-established
Korringa law expected in metallic samples and follows a sub-linear temperature
dependence 1/T1 ~ T^0.6 for 0.1 K < T < 10 K. Further, we investigate nuclear
spin inhomogeneities.Comment: 5 pages, 4 (color) figures. arXiv admin note: text overlap with
arXiv:1109.633
Search for the ac Josephson effect in superfluid 3He
Experiments testing for the existence of the ac Josephson effect in superfluid 3He, analogous to phenomena observed in superconducting microbridges, have been performed. Small holes were employed as the weak link between two reservoirs filled with 3He; several different orifice geometries were tried. Simple model calculations suggest that steps in the flow characteristics should be observable with our resolution when an ac pressure modulation is applied across the weak link. We found that such effects do not exist for the parameter values used in our experiments.Peer reviewe
Energy Down Conversion between Classical Electromagnetic Fields via a Quantum Mechanical SQUID Ring
We consider the interaction of a quantum mechanical SQUID ring with a
classical resonator (a parallel tank circuit). In our model we assume that
the evolution of the ring maintains its quantum mechanical nature, even though
the circuit to which it is coupled is treated classically. We show that when
the SQUID ring is driven by a classical monochromatic microwave source, energy
can be transferred between this input and the tank circuit, even when the
frequency ratio between them is very large. Essentially, these calculations
deal with the coupling between a single macroscopic quantum object (the SQUID
ring) and a classical circuit measurement device where due account is taken of
the non-perturbative behaviour of the ring and the concomitant non-linear
interaction of the ring with this device.Comment: 7 pages, 6 figure
Crystal Structure and Physical Properties of U3T3Sn4 (T = Ni, Cu) Single-Crystals
Heat capacity experiments, crystal structure determination and transmission
electron microscopy have been carried out on U3Cu3Sn4 single-crystals. U3Cu3Sn4
was confirmed to be a heavy-fermion antiferromagnet (TN=13(1) K) with a low
temperature electronic heat capacity coefficient gamma=390 mJ/molUK2. Low
temperature heat capacity experiments on a U3Ni3Sn4 single-crystal indicate
that below 0.4 K there is a crossover between the previously observed non-Fermi
liquid behavior and a Fermi liquid state.Comment: 12 pages (incl. 2 tables & 4 figures), to appear in Physica
Search for the ac Josephson effect in superfluid He3
Experiments testing for the existence of the ac Josephson effect in superfluid He3, analogous to phenomena observed in superconducting microbridges, have been performed. Small holes were employed as the weak link between two reservoirs filled with He3; several different orifice geometries were tried. Simple model calculations suggest that steps in the flow characteristics should be observable with our resolution when an ac pressure modulation is applied across the weak link. We found that such effects do not exist for the parameter values used in our experiments. © 1983 The American Physical Society
Phase Diagram of the First-Order Vortex-Core Transition in Superfluid 3He-B
The phase diagram of quantized vortices in 3He-B has been obtained with two techniques. Our NMR measurements show that magnetization displays a pressure-dependent first-order phase change at TV(P). Our gyroscopic experiments reveal a transition curve TG(P) which marks an abrupt change in the critical velocity. Both curves show a weak magnetic field dependence, run similarly in the (P, T) plane, and seem to mark the same vortex-core transition.Peer reviewe
Damagnetization cooling of a gas
We demonstrate demagnetization cooling of a gas of ultracold Cr atoms.
Demagnetization is driven by inelastic dipolar collisions which couple the
motional degrees of freedom to the spin degree. By that kinetic energy is
converted into magnetic work with a consequent temperature reduction of the
gas. Optical pumping is used to magnetize the system and drive continuous
demagnetization cooling. Applying this technique, we can increase the phase
space density of our sample by one order of magnitude, with nearly no atom
loss. This method can be in principle extended to every dipolar system and
could be used to achieve quantum degeneracy via optical means.Comment: 10 pages, 5 figure
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