On compression rate of quantum autoencoders: Control design, numerical and experimental realization

Quantum autoencoders which aim at compressing quantum information in a low-dimensional latent space lie in the heart of automatic data compression in the field of quantum information. In this paper, we establish an upper bound of the compression rate for a given quantum autoencoder and present a learning control approach for training the autoencoder to achieve the maximal compression rate. The upper bound of the compression rate is theoretically proven using eigen-decomposition and matrix differentiation, which is determined by the eigenvalues of the density matrix representation of the input states. Numerical results on 2-qubit and 3-qubit systems are presented to demonstrate how to train the quantum autoencoder to achieve the theoretically maximal compression, and the training performance using different machine learning algorithms is compared. Experimental results of a quantum autoencoder using quantum optical systems are illustrated for compressing two 2-qubit states into two 1-qubit states

Gamma-ray lines and neutrons from solar flares

The energy spectrum of accelerated protons and nuclei at the site of a limb flare was derived by a technique, using observations of the time dependent flux of high energy neutrons at the Earth. This energy spectrum is very similar to the energy spectra of 7 disk flares for which the accelerated particle spectra was previously derived using observations of 4 to 7 MeV to 2.223 MeV fluence ratios. The implied spectra for all of these flares are too steep to produce any significant amount of radiation from pi meson decay. It is suggested that the observed 10 MeV gamma rays from the flare are bremsstrahlung of relativistic electrons

Noise suppression of on-chip mechanical resonators by chaotic coherent feedback

We propose a method to decouple the nanomechanical resonator in optomechanical systems from the environmental noise by introducing a chaotic coherent feedback loop. We find that the chaotic controller in the feedback loop can modulate the dynamics of the controlled optomechanical system and induce a broadband response of the mechanical mode. This broadband response of the mechanical mode will cut off the coupling between the mechanical mode and the environment and thus suppress the environmental noise of the mechanical modes. As an application, we use the protected optomechanical system to act as a quantum memory. It's shown that the noise-decoupled optomechanical quantum memory is efficient for storing information transferred from coherent or squeezed light

Moire bands in twisted double-layer graphene

A moire pattern is formed when two copies of a periodic pattern are overlaid with a relative twist. We address the electronic structure of a twisted two-layer graphene system, showing that in its continuum Dirac model the moire pattern periodicity leads to moire Bloch bands. The two layers become more strongly coupled and the Dirac velocity crosses zero several times as the twist angle is reduced. For a discrete set of magic angles the velocity vanishes, the lowest moire band flattens, and the Dirac-point density-of-states and the counterflow conductivity are strongly enhanced

The ER morphology-regulating lunapark protein induces the formation of stacked bilayer discs

This is the final version of the article. Available from the publisher via the DOI in this recordLunapark (Lnp) is a conserved membrane protein that localizes to and stabilizes three-way junctions of the tubular ER network. In higher eukaryotes, phosphorylation of Lnp may contribute to the conversion of the ER from tubules to sheets during mitosis. Here, we report on the reconstitution of purified Lnp with phospholipids. Surprisingly, Lnp induces the formation of stacked membrane discs. Each disc is a bicelle, with Lnp sitting in the bilayer facing both directions. The interaction between bicelles is mediated by the cytosolic domains of Lnp, resulting in a constant distance between the discs. A phosphomimetic Lnp mutant shows reduced bicelle stacking. Based on these results, we propose that Lnp tethers ER membranes in vivo in a cell cycle–dependent manner. Lnp appears to be the first membrane protein that induces the formation of stacked bicelles.S Wang was supported by a fellowship from the Charles King Trust and RE Powers by a NIGMS T32 training grant (GM008313). We acknowledge the Max Planck Society and University of Exeter for supporting V Gold, in particular Werner Kühlbrandt and Deryck Mills at the Max Planck Institute of Biophysics. TA Rapoport is a Howard Hughes Medical Institute Investigator

Short poly(ethylene glycol) block initiation of poly(l-lactide) di-block copolymers: a strategy for tuning the degradation of resorbable devices

The current range of medical applications of resorbable polyesters could be hugely expanded if more effective strategies for tailoring degradation rate were available. Block copolymerisation with PEG has been shown to reduce degradation times, however, to date, this has relied on the addition of PEG to short lengths of polyester. This results in copolymers with high fractions of PEG and low molecular weights, reducing the potential range of applications. Furthermore, there has been no systematic study on the relative lengths of the blocks. In this work, we employed short hydroxyl-functionalised methoxy-terminated mPEG to initiate the synthesis of PLLA, resulting in controlled di- block copolymers with short mPEG blocks and long PLLA blocks. A controlled series of polymers was made with PLLA lengths (60 < Mn (kg/mol) < 200) and mPEG lengths (550 < Mn (g/mol) < 5000) giving very low mPEG wt% (0.1 < wt% < 1.5). We found, that, despite the low fraction of mPEG, water uptake and the rate of hydrolytic degradation, k, increased. Significantly, k, for the polymers was dependent only on the presence of mPEG, and was little affected by mPEG length or PLLA length in the ranges studied. Moreover, mass loss began in all polymers when the Mn of the polymer fell below a threshold of about 20 kg/mol and depended on both the initial molecular weight of PLLA and the presence (but not the length) of mPEG. Short chain mPEG therefore provides a new route for targeted, temporal control of resorbable polyesters for biomedical devices

Estimates of the reproduction ratio from epidemic surveillance may be biased in spatially structured populations

An accurate and timely estimate of the reproduction ratio R of an infectious disease epidemic is crucial to make projections on its evolution and set up the appropriate public health response. Estimates of R routinely come from statistical inference on timelines of cases or their proxies like symptomatic cases, hospitalizatons, deaths. Here, however, we prove that these estimates of R may not be accurate if the population is made up of spatially distinct communities, as the interplay between space and mobility may hide the true epidemic evolution from surveillance data. This means that surveillance may underestimate R over long periods, to the point of mistaking a growing epidemic for a subsiding one, misinforming public health response. To overcome this, we propose a correction to be applied to surveillance data that removes this bias and ensures an accurate estimate of R across all epidemic phases. We use COVID-19 as case study; our results, however, apply to any epidemic where mobility is a driver of circulation, including major challenges of the next decades: respiratory infections (influenza, SARS-CoV-2, emerging pathogens), vector-borne diseases (arboviruses). Our findings will help set up public health response to these threats, by improving epidemic monitoring and surveillance.Comment: 11 pages, 4 figures, plus Supplementary Informatio

Suppressing nano-scale stick-slip motion by feedback

When a micro cantilever with a nano-scale tip is manipulated on a substrate with atomic-scale roughness, the periodic lateral frictional force and stochastic fluctuations may induce stick-slip motion of the cantilever tip, which greatly decreases the precision of the nano manipulation. This unwanted motion cannot be reduced by open-loop control especially when there exist parameter uncertainties in the system model, and thus needs to introduce feedback control. However, real-time feedback cannot be realized by the existing virtual reality virtual feedback techniques based on the position sensing capacity of the atomic force microscopy (AFM). To solve this problem, we propose a new method to design real-time feedback control based on the force sensing approach to compensate for the disturbances and thus reduce the stick-slip motion of the cantilever tip. Theoretical analysis and numerical simulations show that the controlled motion of the cantilever tip tracks the desired trajectory with much higher precision. Further investigation shows that our proposal is robust under various parameter uncertainties. Our study opens up new perspectives of real-time nano manipulation.Comment: 8 pages, 10 figure