27 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
Current experimental upper bounds on spacetime diffusion
A consistent theory describing the dynamics of quantum systems interacting on
a classical space-time was recently put forward by Oppenheim et al..[1, 2].
Quantum states may retain their coherence, at the cost of some amount of
stochasticity of the spacetime metric, characterized by a spacetime diffusion
parameter. Here, we report existing experimental upper bounds on such
space-time diffusion, based on a review of several types of experiments with
very low force noise over a broad range of test masses from single atoms to
several kilograms. We find an upper bound at least 15 orders of magnitude lower
as compared to the initial bounds for explicit models presented by Oppenheimn
et al. The results presented here provide a path forward for future experiments
that can help evaluate classical-quantum theoriesComment: 8 pages, 1 figure, 1 tabl
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
Measuring gravity with milligram levitated masses
Gravity differs from all other known fundamental forces since it is best
described as a curvature of spacetime. For that reason it remains resistant to
unifications with quantum theory. Gravitational interaction is fundamentally
weak and becomes prominent only at macroscopic scales. This means, we do not
know what happens to gravity in the microscopic regime where quantum effects
dominate, and whether quantum coherent effects of gravity become apparent.
Levitated mechanical systems of mesoscopic size offer a probe of gravity, while
still allowing quantum control over their motional state. This regime opens the
possibility of table-top testing of quantum superposition and entanglement in
gravitating systems. Here we show gravitational coupling between a levitated
sub-millimeter scale magnetic particle inside a type-I superconducting trap and
kg source masses, placed approximately half a meter away. Our results extend
gravity measurements to low gravitational forces of attonewton and underline
the importance of levitated mechanical sensors. Specifically, at a frequency of
26.7 Hz, a mass of 0.4 mg and showing Q-factors in excess of 10, we
obtained a force noise of 0.5 . We simultaneously detect the
other 5 rotational and translational degrees of freedom.Comment: 13 pages, with 13 pages supplementary material
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