24 research outputs found
A Nanoscale Experiment Measuring Gravity's Role in Breaking the Unitarity of Quantum Dynamics
Modern, state of the art nanomechanical devices are capable of creating
spatial superpositions that are massive enough to begin to experimentally
access the quantum to classical crossover, and thus force us to consider the
possible ways in which the usual quantum dynamics may be affected. One recent
theoretical proposal describes the crossover from unitary quantum mechanics to
classical dynamics as a form of spontaneous symmetry breaking. Here, we propose
a specific experimental setup capable of identifying the source of unitarity
breaking in such a mechanism. The experiment is aimed specifically at
clarifying the role played by gravity, and distinguishes the resulting dynamics
from that suggested by alternative scenarios for the quantum to classical
crossover. We give both a theoretical description of the expected dynamics, and
a discussion of the involved experimental parameter values and the proposed
experimental protocol.Comment: 11 pages, 5 figures; final versio
A Tunable Kondo Effect in Quantum Dots
We demonstrate a tunable Kondo effect realized in small quantum dots. We can
switch our dot from a Kondo impurity to a non-Kondo system as the number of
electrons on the dot is changed from odd to even. We show that the Kondo
temperature can be tuned by means of a gate voltage as a single-particle energy
state nears the Fermi energy. Measurements of the temperature and magnetic
field dependence of a Coulomb-blockaded dot show good agreement with
predictions of both equilibrium and non-equilibrium Kondo effects.Comment: 8 pages, 4 figure
Vibration isolation with high thermal conductance for a cryogen-free dilution refrigerator
We present the design and implementation of a mechanical low-pass filter
vibration isolation used to reduce the vibrational noise in a cryogen-free
dilution refrigerator operated at 10 mK, intended for scanning probe
techniques. We discuss the design guidelines necessary to meet the competing
requirements of having a low mechanical stiffness in combination with a high
thermal conductance. We demonstrate the effectiveness of our approach by
measuring the vibrational noise levels of an ultrasoft mechanical resonator
positioned above a SQUID. Starting from a cryostat base temperature of 8 mK,
the vibration isolation can be cooled to 10.5 mK, with a cooling power of 113
W at 100 mK. We use the low vibrations and low temperature to demonstrate
an effective cantilever temperature of less than 20 mK. This results in a force
sensitivity of less than 500 zN/, and an integrated
frequency noise as low as 0.4 mHz in a 1 Hz measurement bandwidth
Towards an experimental test of gravity-induced quantum state reduction
According to the hypothesis of Penrose and Diosi, quantum state reduction is
a manifestation of the incompatibilty of general relativity and the unitary
time evolution of quantum physics. Dimensional analysis suggests that
Schrodinger cat type states should collapse on measurable time scales when
masses and lengths of the order of bacterial scales are involved. We analyze
this hypothesis in the context of modern developments in condensed matter and
cold atoms physics, aimed at realizing macroscopic quantum states. We first
consider 'micromechanical' quantum states, analyzing the capacity of an atomic
force microscopy based single spin detector to measure the gravitational state
reduction, but we conclude that it seems impossible to suppress environmental
decoherence to the required degree. We subsequently discuss 'split' cold atom
condensates to find out that these are at present lacking the required mass
scale by many orders of magnitude. We then extent Penrose's analysis to
superpositions of mass current carrying states, and we apply this to the flux
quantum bits realized in superconducting circuits. We find that the flux qubits
approach the scale where gravitational state reduction should become
measurable, but bridging the few remaining orders of magnitude appears to be
very difficult with present day technology.Comment: 12 pages, 7 figure
Size of the Localized Electron Emission Sites on a Closed Multiwalled Carbon Nanotube
036804Quantum Matter and Optic
Heterogeneous nucleation of three-dimensional protein nanocrystals
Nucleation is the rate-limiting step in protein crystallization. Introducing heterogeneous substrates may in some cases lower the energy barrier for nucleation and thereby facilitate crystal growth. To date, the mechanism of heterogeneous protein nucleation remains poorly understood. In this study, the nucleating properties of fragments of human hair in crystallization experiments have been investigated. The four proteins that were tested, lysozyme, glucose isomerase, a polysaccharide-specific Fab fragment and potato serine protease inhibitor, nucleated preferentially on the hair surface. Macrocrystals and showers of tiny crystals of a few hundred nanometres thickness were obtained also under conditions that did not produce crystals in the absence of the nucleating agent. Cryo-electron diffraction showed that the nanocrystals diffracted to at least 4 A resolution. The mechanism of heterogeneous nucleation was studied using confocal fluorescent microscopy which demonstrated that the protein is concentrated on the nucleating surface. A substantial accumulation of protein was observed on the sharp edges of the hair's cuticles, explaining the strong nucleating activity of the surface
Increased muon field at surface and substrate interface of palladium thin films
We performed depth-dependent low-energy muon spin spectroscopy (SR) studies on three palladium 100 nm thin films, both undoped and doped with 170 ppm of iron. Muons implanted in the surface and substrate interface region probe an increased local magnetic field compared to the inner part of the sample. The field increase extends over a few nanometers, it is temperature-independent (in the range of 3.7 - 100 K), stronger for the iron-doped samples and accompanied by an increase in local field inhomogeneity. We consider various potential origins for this magnetic surface state, such as adsorbents and supressed d-states. Our conclusion is that orbital moments induced at the surface / interface by localized spins and charges are the most likely explanation, potentially accompanied by magnetic moments due to crystal irregularities