Scheme for teleportation of quantum states onto a mechanical resonator

We propose an experimentally feasible scheme to teleport an unkown quantum state onto the vibrational degree of freedom of a macroscopic mirror. The quantum channel between the two parties is established by exploiting radiation pressure effects.Comment: 5 pages, 2 figures, in press on PR

Momentum diffusion for coupled atom-cavity oscillators

It is shown that the momentum diffusion of free-space laser cooling has a natural correspondence in optical cavities when the internal state of the atom is treated as a harmonic oscillator. We derive a general expression for the momentum diffusion which is valid for most configurations of interest: The atom or the cavity or both can be probed by lasers, with or without the presence of traps inducing local atomic frequency shifts. It is shown that, albeit the (possibly strong) coupling between atom and cavity, it is sufficient for deriving the momentum diffusion to consider that the atom couples to a mean cavity field, which gives a first contribution, and that the cavity mode couples to a mean atomic dipole, giving a second contribution. Both contributions have an intuitive form and present a clear symmetry. The total diffusion is the sum of these two contributions plus the diffusion originating from the fluctuations of the forces due to the coupling to the vacuum modes other than the cavity mode (the so called spontaneous emission term). Examples are given that help to evaluate the heating rates induced by an optical cavity for experiments operating at low atomic saturation. We also point out intriguing situations where the atom is heated although it cannot scatter light.Comment: More information adde

The virtuous cycle of axon growth: Axonal transport of growth-promoting machinery as an intrinsic determinant of axon regeneration

Injury to the brain and spinal cord has devastating consequences because adult central nervous system (CNS) axons fail to regenerate. Injury to the peripheral nervous system (PNS) has a better prognosis, because adult PNS neurons support robust axon regeneration over long distances. CNS axons have some regenerative capacity during development, but this is lost with maturity. Two reasons for the failure of CNS regeneration are extrinsic inhibitory molecules, and a weak intrinsic capacity for growth. Extrinsic inhibitory molecules have been well characterised, but less is known about the neuron-intrinsic mechanisms which prevent axon re-growth. Key signalling pathways and genetic / epigenetic factors have been identified which can enhance regenerative capacity, but the precise cellular mechanisms mediating their actions have not been characterised. Recent studies suggest that an important prerequisite for regeneration is an efficient supply of growth-promoting machinery to the axon, however this appears to be lacking from non-regenerative axons in the adult CNS. In the first part of this review, we summarise the evidence linking axon transport to axon regeneration. We discuss the developmental decline in axon regeneration capacity in the CNS, and comment on how this is paralleled by a similar decline in the selective axonal transport of regeneration-associated receptors such as integrins and growth factor receptors. In the second part, we discuss the mechanisms regulating selective polarised transport within neurons, how these relate to the intrinsic control of axon regeneration, and whether they can be targeted to enhance regenerative capacity.ERA‐NET Neuron International Foundation for Research in Paraplegia Christopher and Dana Reeve Foundation. Grant Numbers: JFC‐2013(3), JFC‐2013(4) Gates Cambridge Trust Medical Research Council. Grant Numbers: G1000864 018556, MR/R004463/

BIOCHEMICAL STUDIES OF HUMAN MICAL1, THE FLAVOENZYME CONTROLLING CYTOSKELETON DYNAMICS

MICAL from the \u201cMolecule Interacting with CasL\u201d indicates a family of cytoplasmic multidomain proteins conserved from insects to humans, which participates in the control of cytoskeleton dynamics. A unique feature of MICAL proteins is the presence of a catalytic N-terminal flavoprotein monoonoxygenase-like (MO) domain that is followed by several protein interaction domains, namely: a calponin homology (CH) domain, a LIM domain and a C-terminal region containing potential coiled-coil motifs. In neurons MICAL1 is an essential component for the transduction of the semaphorin signaling downstream of plexin by catalyzing a NADPH-dependent F-actin depolymerization through the N-terminal flavoprotein domain. But it may also control integrin pathway and microtubules assembly through interaction with CasL and CRMP, respectively and apoptosis through interaction with NDR1. The MICAL2 and MICAL3 isoforms are implicated in vesicles trafficking and gene transcription. The aim of this project is to contribute to define the function of human MICAL1 by characterizing the catalytic properties of the MO domain and how they are modulated by its CH, LIM and C-terminal domains and, eventually, by its interacting proteins. The human MICAL1 form containing the isolated MO domain (55.1 kDa; pI 9) and the form comprising both the MO and the CH domains (MOCH; 68.5 kDa; pI 7.7) have been produced according to the procedures available in the laboratory, which were further optimized. The full-length MICAL1 (MICAL; 119 kDa; pI, 6.2) and the form lacking the C-terminal region (MOCHLIM; 86.4 kDa; pI, 6.7) were produced in E.coli cells and their purification protocols were set-up exploiting the engineered C-terminal His6-tag. All the purified MICAL forms are stable and greater than 95% homogeneous. MICAL forms are isolated with the correct complement of FAD bound to the MO domain and zinc ions bound to the LIM domain, which predicts the formation of two zinc fingers. The absorption spectra of all MICAL forms are similar to each other, with an extinction coefficient at 458 nm of 488.1 mM-1cm-1 similar to that previously determined for the isolated MO domain, indicating that the CH, LIM and C-terminal regions do not alter the conformation of the catalytic domain. However, the LIM domain causes MOCHLIM to oligomerize to yield dimers, trimers and higher order aggregates, while the full-length protein yielded stable dimers as opposed to the monomeric state of MO and MOCH forms. All MICAL forms catalyze a NADPH oxidase (H2O2-producing) activity, which is associated with the MO domain. By combining steady-state kinetic measurements of the reaction as a function of pH and of solvent viscosity we concluded that the CH, LIM and C-terminal domains lead to a progressive lowering of the catalytic efficiency (MO, 48165 s-1mM-1; MOCH, 4818.5 s-1mM-1; MOCHLIM, 4815 s-1mM-1; MICAL, 480.75 s-1mM-1) of the reaction due to an increase of Km for NADPH from 4820 \u3bcM (MO), to 48130 \u3bcM (MOCH), 48230 \u3bcM (MOCHLIM) and 48370 \u3bcM (MICAL). The 200-fold drop of the catalytic efficiency of the full-length MICAL compared to that of MO is also due to a 4810-fold decrease of kcat. The study of the pH and viscosity dependence of the NADPH oxidase reaction of MICAL forms led us to conclude that the observed changes in the values of the kinetic parameters are not due to changes in rate determining steps of the reaction taking place within MO. The increase of KNADPH correlates with a decrease of the positive charge of the protein due to the acidity of the CH, LIM and C-terminal domains. The 10-fold drop of kcat observed with full-length MICAL is consistent with the proposal of an autoinhibitory role of the C-terminal region on MICAL catalytic activity. Our experiments reveal that is likely due to a conformational equilibrium between an inactive and an active conformation of MICAL, which is shifted 9:1 toward the inactive conformation in solution. The position of the C-terminal region is crucial to make the protein fully inactive . All MICAL forms are able to depolymerize F-actin in the presence of NADPH as observed by monitoring the decrease of fluorescence of pyrenyl-actin and of the average radius of F-actin solution by dynamic light scattering. F-actin leads to an approximately 5-10-fold increase of the maximum rate of the NADPH consumption for all MICAL forms (MO, 20 s-1; MOCH, 26 s-1; MOCHLIM, 15 s-1; MICAL, 8 s-1) compared to that measured in its absence. The presence of F-actin leads to a lowering of the Km for NADPH to similar values (11-50 \u3bcM) for all the four forms. The apparent Km for F-actin is similar ( 484 \u3bcM) for MO, MOCH and MOCHLIM, but 10-fold higher for MICAL ( 4830 \u3bcM). Also this effect can beexplained by the conformational equilibrium between an inactive and an active conformation of the full-length MICAL. The actin binding site on the MO domain may be physically accessible to F-actin only when MICAL is in the active conformation, subtracting it from the inactive/active conformational equilibrium. In this case, the high apparent Km for actin of MICAL would reflect the coupled equilibria between inactive/active conformations and complex formation between actin and MICAL in the active conformation. In all cases, the amount of NADPH oxidized during the reaction exceeds that of total actin present, suggesting a case of substrate recycling or an enhancement of the NADPH oxidase activity of MICAL forms when actin is bound. This finding is in contrast with the proposal that MICAL forms catalyze a (slow) NADPH oxidase activity when isolated but a fast and specific hydroxylation of actin Met44 (and Met 47) in the presence of F-actin, which leads to filament depolymerization (Hung et al. (2013) Nat Cell Biol., 15, 1445-1454). Mass spectrometry analyses of actin samples treated with MICAL forms and NADPH support the hypothesis that actin depolymerization is mediated by the H2O2 released by the enhanced NADPH oxidase activity of MICAL in complex with actin. A maximum of two residues are oxidized per actin molecule among which are Met44 and Met47 but also several other Met and Trp residues are oxidized with similar probability. Overall it appears that MICAL in the free state can catalyze a basal NADPH oxidase reaction even in the cell. This activity is enhanced when the fraction of MICAL in the catalytically active state binds to actin leading to its depolymerization. Interaction of MICAL C-terminus with the cytoplasmic side of plexin upon semaphorin signaling would shift the equilibrium of inactive/active conformations toward the active form favoring the interaction with actin in proximity of plexin and its local depolymerization. With purified MICAL forms now available, it will possible to identify its interactors and to study their effect on its activities. As a first step in this direction we produced and purified a CRMP1 form that was found to cooperate with MICAL1 in determining COS7 cells collapse in response to semaphorin signaling. We demonstrated that CRMP1 and MICAL1 MO and MOCH interact, but in a complex way: at low ionic strength the interaction, which is largely non specific due to the strong opposite charges of the proteins, leads to inhibition of the MO and MOCH NADPH oxidase activity; at higher ionic strength, where non specific interactions are removed, CRMP stimulates the NADPH oxidase activity of MO and MOCH and competes with actin for binding MICAL, but the effect is mild. These preliminary experiments support the hypothesis that actin and microtubules dynamics may be linked through MICAL-CRMP interaction. More importantly, they show the feasibility of detailed in vitro studies for the identification of MICAL interacting proteins and their mutual modulatory effect. This approach, along with the detailed mechanistic studies of MICAL reactions thanks to the availability of various MICAL forms, will also open the way to the identification of molecules able to inhibit MICAL that could be beneficial to combat diseases in which MICAL has been implicated such as neurodegeneration, cancer and even vasculo- and cardiogenesis

Enhancement of the optomechanical coupling and Kerr nonlinearity using the Josephson capacitance of a Cooper-pair box

We propose a scheme for enhancing the optomechanical coupling between microwave and mechanical resonators by up to seven orders of magnitude to the ultrastrong coupling limit in a circuit optomechanical setting. The tripartite system considered here consists of a Josephson junction Cooper-pair box that mediates the coupling between the microwave cavity and the mechanical resonator. The optomechanical coupling can be modified by tuning the gate charge and the magnetic flux bias of the Cooper-pair box which in turn affect the Josephson capacitance of the Cooper-pair box. We additionally show that with a suitable choice of tuning parameters, the optomechanical coupling vanishes and the system purely exhibits a cross-Kerr type of nonlinearity between the cavity and the mechanical resonator. This allows the system to be used for phonon counting

Microwave Quantum Illumination with Correlation-To-Displacement Conversion

Entanglement is vulnerable to degradation in a noisy sensing scenario, but surprisingly, the quantum illumination protocol has demonstrated that its advantage can survive. However, designing a measurement system that realizes this advantage is challenging since the information is hidden in the weak correlation embedded in the noise at the receiver side. Recent progress in a correlation-to-displacement conversion module provides a route towards an optimal protocol for practical microwave quantum illumination. In this work, we extend the conversion module to accommodate experimental imperfections that are ubiquitous in microwave systems. To mitigate loss, we propose amplification of the return signals. In the case of ideal amplification, the entire six-decibel error-exponent advantage in target detection error can be maintained. However, in the case of noisy amplification, this advantage is reduced to three decibels. We analyze the quantum advantage under different scenarios with a Kennedy receiver in the final measurement. In the ideal case, the performance still achieves the optimal one over a fairly large range of error probability with only on-off detection. Empowered by photon-number-resolving detectors, the performance is further improved and also analyzed in terms of receiver operating characteristic curves. Our findings pave the way for the development of practical microwave quantum illumination systems

Optomechanical sideband cooling of a thin membrane within a cavity

We present an experimental study of dynamical back-action cooling of the fundamental vibrational mode of a thin semitransparent membrane placed within a high-finesse optical cavity. We study how the radiation pressure interaction modifies the mechanical response of the vibrational mode, and the experimental results are in agreement with a Langevin equation description of the coupled dynamics. The experiments are carried out in the resolved sideband regime, and we have observed cooling by a factor 350 We have also observed the mechanical frequency shift associated with the quadratic term in the expansion of the cavity mode frequency versus the effective membrane position, which is typically negligible in other cavity optomechanical devices.Comment: 15 pages, 7 figure

Observation of two-wave structure in strongly nonlinear dissipative granular chains

In a strongly nonlinear viscous granular chain under conditions of loading that exclude stationary waves (e.g., impact by a single grain) we observe a pulse that consists of two interconnected but distinct parts. One is a leading narrow "primary pulse" with properties similar to a solitary wave in a "sonic vacuum." It arises from strong nonlinearity and discreteness in the absence of dissipation, but now decays due to viscosity. The other is a broad, much more persistent shock-like "secondary pulse" trailing the primary pulse and caused by viscous dissipation. The medium behind the primary pulse is transformed from a "sonic vacuum" to a medium with finite sound speed. When the rapidly decaying primary pulse dies, the secondary pulse continues to propagate in the "sonic vacuum," with an oscillatory front if the viscosity is relatively small, until its eventual (but very slow) disintegration. Beyond a critical viscosity there is no separation of the two pulses, and the dissipation and nonlinearity dominate the shock-like attenuating pulse which now exhibits a nonoscillatory front

Occurrence of New Imidazolealkylamines (Spinaceamine and 6-Methylspinaceamine) in Skin Extracts of Leptodactylus pentadactylus labyrinthicus

Estratti di pelle di Leptodactylus pentadactylus labyrinthicus contengono elevati quantitativi di imidazolalchilamine, fra cui due derivati imidazo-cpiridinici finora ignoti in natura: la spinaceamina e la 6- metilspinaceamina.Material digitalizado en SEDICI gracias a la colaboración del Dr. Jorge Williams (FCNM-UNLP).Facultad de Ciencias Naturales y Muse

The Identification of New Histamine Derivatives in the Skin of Leptodactylus

Extracts of the skin of some South American amphibians belonging to the genus Leptodactylus contain, in addition to 5-hydroxyindolealkylamines and hydroxyphenylalkylamines, remarkable amounts of imidazolealkylamines. The species most rich in these compounds are Leptodactylus pentadactylus labyrinthicus and Leptodactylus laticeps. The skin of the former species contains not only histamine, N'-methyl- histamine and N', N'-dimethylhistamine but also two imidazo-c-pyridine derivatives hitherto unknown in nature: spinaceamine and 6-methylspinaceamine. The new findings permit a notable enlargement of our knowledge in the field of biogenic imidazolealkylamines and illustrate new possible metabolic pathways for histamine.Material digitalizado en SEDICI gracias a la colaboración del Dr. Jorge Williams (FCNM-UNLP).Facultad de Ciencias Naturales y Muse