497 research outputs found
Coupling carbon nanotube mechanics to a superconducting circuit
The quantum behaviour of mechanical resonators is a new and emerging field
driven by recent experiments reaching the quantum ground state. The high
frequency, small mass, and large quality-factor of carbon nanotube resonators
make them attractive for quantum nanomechanical applications. A common element
in experiments achieving the resonator ground state is a second quantum system,
such as coherent photons or superconducting device, coupled to the resonators
motion. For nanotubes, however, this is a challenge due to their small size.
Here, we couple a carbon nanoelectromechanical (NEMS) device to a
superconducting circuit. Suspended carbon nanotubes act as both superconducting
junctions and moving elements in a Superconducting Quantum Interference Device
(SQUID). We observe a strong modulation of the flux through the SQUID from
displacements of the nanotube. Incorporating this SQUID into superconducting
resonators and qubits should enable the detection and manipulation of nanotube
mechanical quantum states at the single-phonon level
Pulsed quantum optomechanics
Studying mechanical resonators via radiation pressure offers a rich avenue
for the exploration of quantum mechanical behavior in a macroscopic regime.
However, quantum state preparation and especially quantum state reconstruction
of mechanical oscillators remains a significant challenge. Here we propose a
scheme to realize quantum state tomography, squeezing and state purification of
a mechanical resonator using short optical pulses. The scheme presented allows
observation of mechanical quantum features despite preparation from a thermal
state and is shown to be experimentally feasible using optical microcavities.
Our framework thus provides a promising means to explore the quantum nature of
massive mechanical oscillators and can be applied to other systems such as
trapped ions.Comment: 9 pages, 4 figure
Fate specification and tissue-specific cell cycle control of the <i>Caenorhabditis elegans</i> intestine
Coordination between cell fate specification and cell cycle control in multicellular organisms is essential to regulate cell numbers in tissues and organs during development, and its failure may lead to oncogenesis. In mammalian cells, as part of a general cell cycle checkpoint mechanism, the F-box protein β-transducin repeat-containing protein (β-TrCP) and the Skp1/Cul1/F-box complex control the periodic cell cycle fluctuations in abundance of the CDC25A and B phosphatases. Here, we find that the Caenorhabditis elegans β-TrCP orthologue LIN-23 regulates a progressive decline of CDC-25.1 abundance over several embryonic cell cycles and specifies cell number of one tissue, the embryonic intestine. The negative regulation of CDC-25.1 abundance by LIN-23 may be developmentally controlled because CDC-25.1 accumulates over time within the developing germline, where LIN-23 is also present. Concurrent with the destabilization of CDC-25.1, LIN-23 displays a spatially dynamic behavior in the embryo, periodically entering a nuclear compartment where CDC-25.1 is abundant
Culturing Pancreatic Islets in Microfluidic Flow Enhances Morphology of the Associated Endothelial Cells
Pancreatic islets are heavily vascularized in vivo with each insulin secreting beta-cell associated with at least one endothelial cell (EC). This structure is maintained immediately post-isolation; however, in culture the ECs slowly deteriorate, losing density and branched morphology. We postulate that this deterioration occurs in the absence of blood flow due to limited diffusion of media inside the tissue. To improve exchange of media inside the tissue, we created a microfluidic device to culture islets in a range of flow-rates. Culturing the islets from C57BL6 mice in this device with media flowing between 1 and 7 ml/24 hr resulted in twice the EC-density and -connected length compared to classically cultured islets. Media containing fluorescent dextran reached the center of islets in the device in a flow-rate-dependant manner consistent with improved penetration. We also observed deterioration of EC morphology using serum free media that was rescued by addition of bovine serum albumin, a known anti-apoptotic signal with limited diffusion in tissue. We further examined the effect of flow on beta-cells showing dampened glucose-stimulated Ca2+-response from cells at the periphery of the islet where fluid shear-stress is greatest. However, we observed normal two-photon NAD(P)H response and insulin secretion from the remainder of the islet. These data reveal the deterioration of islet EC-morphology is in part due to restricted diffusion of serum albumin within the tissue. These data further reveal microfluidic devices as unique platforms to optimize islet culture by introducing intercellular flow to overcome the restricted diffusion of media components
Fibroblast growth factor receptor 5 (FGFR5) is a co-receptor for FGFR1 that is up-regulated in beta-cells by cytokine-induced inflammation
Fibroblast growth factor receptor-1 (FGFR1) activity at the plasma membrane is tightly controlled by the availability of co-receptors and competing receptor isoforms. We have previously shown that FGFR1 activity in pancreatic beta-cells modulates a wide range of processes, including lipid metabolism, insulin processing, and cell survival. More recently, we have revealed that co-expression of FGFR5, a receptor isoform that lacks a tyrosine-kinase domain, influences FGFR1 responses. We therefore hypothesized that FGFR5 is a co-receptor to FGFR1 that modulates responses to ligands by forming a receptor heterocomplex with FGFR1. We first show here increased FGFR5 expression in the pancreatic islets of nonobese diabetic (NOD) mice and also in mouse and human islets treated with proinflammatory cytokines. Using siRNA knockdown, we further report that FGFR5 and FGFR1 expression improves beta-cell survival. Co-immunoprecipitation and quantitative live-cell imaging to measure the molecular interaction between FGFR5 and FGFR1 revealed that FGFR5 forms a mixture of ligand-independent homodimers (25%) and homotrimers (75%) at the plasma membrane. Interestingly, co-expressed FGFR5 and FGFR1 formed heterocomplexes with a 2:1 ratio and subsequently responded to FGF2 by forming FGFR5/FGFR1 signaling complexes with a 4:2 ratio. Taken together, our findings identify FGFR5 as a co-receptor that is up-regulated by inflammation and promotes FGFR1-induced survival, insights that reveal a potential target for intervention during beta-cell pathogenesis
Electromagnetically Induced Transparency and Slow Light with Optomechanics
Controlling the interaction between localized optical and mechanical
excitations has recently become possible following advances in micro- and
nano-fabrication techniques. To date, most experimental studies of
optomechanics have focused on measurement and control of the mechanical
subsystem through its interaction with optics, and have led to the experimental
demonstration of dynamical back-action cooling and optical rigidity of the
mechanical system. Conversely, the optical response of these systems is also
modified in the presence of mechanical interactions, leading to strong
nonlinear effects such as Electromagnetically Induced Transparency (EIT) and
parametric normal-mode splitting. In atomic systems, seminal experiments and
proposals to slow and stop the propagation of light, and their applicability to
modern optical networks, and future quantum networks, have thrust EIT to the
forefront of experimental study during the last two decades. In a similar
fashion, here we use the optomechanical nonlinearity to control the velocity of
light via engineered photon-phonon interactions. Our results demonstrate EIT
and tunable optical delays in a nanoscale optomechanical crystal device,
fabricated by simply etching holes into a thin film of silicon (Si). At low
temperature (8.7 K), we show an optically-tunable delay of 50 ns with
near-unity optical transparency, and superluminal light with a 1.4 microseconds
signal advance. These results, while indicating significant progress towards an
integrated quantum optomechanical memory, are also relevant to classical signal
processing applications. Measurements at room temperature and in the analogous
regime of Electromagnetically Induced Absorption (EIA) show the utility of
these chip-scale optomechanical systems for optical buffering, amplification,
and filtering of microwave-over-optical signals.Comment: 15 pages, 9 figure
Quantum nondemolition measurement of mechanical motion quanta
The fields of opto- and electromechanics have facilitated numerous advances
in the areas of precision measurement and sensing, ultimately driving the
studies of mechanical systems into the quantum regime. To date, however, the
quantization of the mechanical motion and the associated quantum jumps between
phonon states remains elusive. For optomechanical systems, the coupling to the
environment was shown to preclude the detection of the mechanical mode
occupation, unless strong single photon optomechanical coupling is achieved.
Here, we propose and analyse an electromechanical setup, which allows to
overcome this limitation and resolve the energy levels of a mechanical
oscillator. We find that the heating of the membrane, caused by the interaction
with the environment and unwanted couplings, can be suppressed for carefully
designed electromechanical systems. The results suggest that phonon number
measurement is within reach for modern electromechanical setups.Comment: 8 pages, 5 figures plus 24 pages, 11 figures supplemental materia
On RAF Sets and Autocatalytic Cycles in Random Reaction Networks
The emergence of autocatalytic sets of molecules seems to have played an
important role in the origin of life context. Although the possibility to
reproduce this emergence in laboratory has received considerable attention,
this is still far from being achieved. In order to unravel some key properties
enabling the emergence of structures potentially able to sustain their own
existence and growth, in this work we investigate the probability to observe
them in ensembles of random catalytic reaction networks characterized by
different structural properties. From the point of view of network topology, an
autocatalytic set have been defined either in term of strongly connected
components (SCCs) or as reflexively autocatalytic and food-generated sets
(RAFs). We observe that the average level of catalysis differently affects the
probability to observe a SCC or a RAF, highlighting the existence of a region
where the former can be observed, whereas the latter cannot. This parameter
also affects the composition of the RAF, which can be further characterized
into linear structures, autocatalysis or SCCs. Interestingly, we show that the
different network topology (uniform as opposed to power-law catalysis systems)
does not have a significantly divergent impact on SCCs and RAFs appearance,
whereas the proportion between cleavages and condensations seems instead to
play a role. A major factor that limits the probability of RAF appearance and
that may explain some of the difficulties encountered in laboratory seems to be
the presence of molecules which can accumulate without being substrate or
catalyst of any reaction.Comment: pp 113-12
Microwave amplification with nanomechanical resonators
Sensitive measurement of electrical signals is at the heart of modern science
and technology. According to quantum mechanics, any detector or amplifier is
required to add a certain amount of noise to the signal, equaling at best the
energy of quantum fluctuations. The quantum limit of added noise has nearly
been reached with superconducting devices which take advantage of
nonlinearities in Josephson junctions. Here, we introduce a new paradigm of
amplification of microwave signals with the help of a mechanical oscillator. By
relying on the radiation pressure force on a nanomechanical resonator, we
provide an experimental demonstration and an analytical description of how the
injection of microwaves induces coherent stimulated emission and signal
amplification. This scheme, based on two linear oscillators, has the advantage
of being conceptually and practically simpler than the Josephson junction
devices, and, at the same time, has a high potential to reach quantum limited
operation. With a measured signal amplification of 25 decibels and the addition
of 20 quanta of noise, we anticipate near quantum-limited mechanical microwave
amplification is feasible in various applications involving integrated
electrical circuits.Comment: Main text + supplementary information. 14 pages, 3 figures (main
text), 18 pages, 6 figures (supplementary information
Sideband Cooling Micromechanical Motion to the Quantum Ground State
The advent of laser cooling techniques revolutionized the study of many
atomic-scale systems. This has fueled progress towards quantum computers by
preparing trapped ions in their motional ground state, and generating new
states of matter by achieving Bose-Einstein condensation of atomic vapors.
Analogous cooling techniques provide a general and flexible method for
preparing macroscopic objects in their motional ground state, bringing the
powerful technology of micromechanics into the quantum regime. Cavity opto- or
electro-mechanical systems achieve sideband cooling through the strong
interaction between light and motion. However, entering the quantum regime,
less than a single quantum of motion, has been elusive because sideband cooling
has not sufficiently overwhelmed the coupling of mechanical systems to their
hot environments. Here, we demonstrate sideband cooling of the motion of a
micromechanical oscillator to the quantum ground state. Entering the quantum
regime requires a large electromechanical interaction, which is achieved by
embedding a micromechanical membrane into a superconducting microwave resonant
circuit. In order to verify the cooling of the membrane motion into the quantum
regime, we perform a near quantum-limited measurement of the microwave field,
resolving this motion a factor of 5.1 from the Heisenberg limit. Furthermore,
our device exhibits strong-coupling allowing coherent exchange of microwave
photons and mechanical phonons. Simultaneously achieving strong coupling,
ground state preparation and efficient measurement sets the stage for rapid
advances in the control and detection of non-classical states of motion,
possibly even testing quantum theory itself in the unexplored region of larger
size and mass.Comment: 13 pages, 7 figure
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