17 research outputs found
Transient Dynamics in Magnetic Force Microscopy for a Single-Spin Measurement
We analyze a single-spin measurement using a transient process in magnetic
force microscopy (MFM) which could increase the maximum operating temperature
by a factor of Q (the quality factor of the cantilever) in comparison with the
static Stern-Gerlach effect. We obtain an exact solution of the master
equation, which confirms this result. We also discuss the conditions required
to create a macroscopic Schrodinger cat state in the cantilever.Comment: 22 pages 2 figure
The Magnetic Casimir Effect
The Casimir effect results from alterations of the zero-point electromagnetic
energy introduced by boundary-conditions. For ferromagnetic layers separated by
vacuum (or a dielectric) such boundary-conditions are influenced by the
magneto-optical Kerr effect. We will show that this gives rise to a long-range
magnetic interaction and discuss the effect for two different configurations
(magnetization parallel and perpendicular to the layers). Analytical
expressions are derived for two models and compared to numerical calculations.
Numerical calculations of the effect for Fe are also presented and the
possibility of an experimental observation of the Casimir magnetic interaction
is discussed
Optomechanical scheme for the detection of weak impulsive forces
We show that a cooling scheme and an appropriate quantum nonstationary
strategy can be used to improve the signal to noise ratio for the
optomechanical detection of weak impulsive forces.Comment: 4 pages, Revtex, 1 figur
Quantum Dissipative Dynamics of the Magnetic Resonance Force Microscope in the Single-Spin Detection Limit
We study a model of a magnetic resonance force microscope (MRFM) based on the
cyclic adiabatic inversion technique as a high-resolution tool to detect single
electron spins. We investigate the quantum dynamics of spin and cantilever in
the presence of coupling to an environment. To obtain the reduced dynamics of
the combined system of spin and cantilever, we use the Feynman-Vernon influence
functional and get results valid at any temperature as well as at arbitrary
system-bath coupling strength. We propose that the MRFM can be used as a
quantum measurement device, i.e., not only to detect the modulus of the spin
but also its direction
Carbon Nanotubes as Nanoelectromechanical Systems
We theoretically study the interplay between electrical and mechanical
properties of suspended, doubly clamped carbon nanotubes in which charging
effects dominate. In this geometry, the capacitance between the nanotube and
the gate(s) depends on the distance between them. This dependence modifies the
usual Coulomb models and we show that it needs to be incorporated to capture
the physics of the problem correctly. We find that the tube position changes in
discrete steps every time an electron tunnels onto it. Edges of Coulomb
diamonds acquire a (small) curvature. We also show that bistability in the tube
position occurs and that tunneling of an electron onto the tube drastically
modifies the quantized eigenmodes of the tube. Experimental verification of
these predictions is possible in suspended tubes of sub-micron length.Comment: 8 pages, 5 eps figures included. Major changes; new material adde
Mirror quiescence and high-sensitivity position measurements with feedback
We present a detailed study of how phase-sensitive feedback schemes can be
used to improve the performance of optomechanical devices. Considering the case
of a cavity mode coupled to an oscillating mirror by the radiation pressure, we
show how feedback can be used to reduce the position noise spectrum of the
mirror, cool it to its quantum ground state, or achieve position squeezing.
Then, we show that even though feedback is not able to improve the sensitivity
of stationary position spectral measurements, it is possible to design a
nonstationary strategy able to increase this sensitivity.Comment: 25 pages, 11 figure
Whole-genome sequencing reveals host factors underlying critical COVID-19
Critical COVID-19 is caused by immune-mediated inflammatory lung injury. Host genetic variation influences the development of illness requiring critical care1 or hospitalization2,3,4 after infection with SARS-CoV-2. The GenOMICC (Genetics of Mortality in Critical Care) study enables the comparison of genomes from individuals who are critically ill with those of population controls to find underlying disease mechanisms. Here we use whole-genome sequencing in 7,491 critically ill individuals compared with 48,400 controls to discover and replicate 23 independent variants that significantly predispose to critical COVID-19. We identify 16 new independent associations, including variants within genes that are involved in interferon signalling (IL10RB and PLSCR1), leucocyte differentiation (BCL11A) and blood-type antigen secretor status (FUT2). Using transcriptome-wide association and colocalization to infer the effect of gene expression on disease severity, we find evidence that implicates multiple genes—including reduced expression of a membrane flippase (ATP11A), and increased expression of a mucin (MUC1)—in critical disease. Mendelian randomization provides evidence in support of causal roles for myeloid cell adhesion molecules (SELE, ICAM5 and CD209) and the coagulation factor F8, all of which are potentially druggable targets. Our results are broadly consistent with a multi-component model of COVID-19 pathophysiology, in which at least two distinct mechanisms can predispose to life-threatening disease: failure to control viral replication; or an enhanced tendency towards pulmonary inflammation and intravascular coagulation. We show that comparison between cases of critical illness and population controls is highly efficient for the detection of therapeutically relevant mechanisms of disease