Magnonic Combinatorial Memory

In this work, we consider a type of magnetic memory where information is encoded into the mutual arrangements of magnets. The device is an active ring circuit comprising magnetic and electronic parts connected in series. The electric part includes a broad-band amplifier, phase shifters, and attenuators. The magnetic part is a mesh of magnonic waveguides with magnets placed on the waveguide junctions. There are amplitude and phase conditions for auto-oscillations to occur in the active ring circuit. The frequency(s) of the auto-oscillation and spin wave propagation route(s) in the magnetic part depends on the mutual arrangement of magnets in the mesh. The propagation route is detected with a set of power sensors. The correlation between circuit parameters and spin wave route is the base of memory operation. The combination of input/output switches connecting electric and magnetic parts, and electric phase shifters constitute the memory address. The output of power sensors is the memory state. We present experimental data on the proof-of-the-concept experiments on the prototype with just three magnets placed on top of a single-crystal yttrium iron garnet Y3Fe2(FeO4)3 (YIG) film. The results demonstrate a robust operation with On/Off ratio for route detection exceeding 35 dB at room temperature. The number of propagation routes scales factorial with the size of the magnetic part. Coding information in propagation routes makes it possible to drastically increase the data storage density compared to conventional memory devices. MCM with just 25 magnets can store as much as 25! (10 Yotta) bits. Physical limits and constraints are also discussed

Opto-magnonic crystals: optical manipulation of spin waves

It is well-recognized in condensed matter physics that structural and magnetic properties are intimately connected; thus controlling structure has been a successful route to controlling material properties. Extending the methodologies to high frequency modulation provides a route to controlled, bidirectional modification to material properties, expanding the range of material functionality and opening new possibilities for future developments in fields as disparate as magnetic control, spintronics, and magnonics. Ultrafast optical techniques provide one manner in which elastic and magnetic dynamics can be controlled in a material, since ultrafast pulses of light are known to excite elastic deformations while also modifying the magnetic properties of the material. Optically generated elastic waves can routinely achieve the frequency range of GHz with wavelength ranges of a few micrometers, which interestingly overlaps almost perfectly with similar wavelength spin waves. In our work, we first explored the emergence of a transient magnonic crystal after the impulsive excitation of transient grating and the phase-locked elastic wave capable of preferentially driving precessional motion in different regions of the material. Secondly we have demonstrated the first instance of elastically and parametrically driven ferromagnetic oscillator, which exhibited sum and difference frequency conversion over a wide range of frequencies. Finally, we approached magnetoelastic effects from a different point of view: the study of magnetoelastic dynamics in Ni nanowires. Connecting these experiments provide possible applications in optomagnonics research which currently utilizes artificially textured materials

In situ Lorentz microscopy and electron holography in magnetic nanostructures

Nous avons développé dans cette thèse des études quantitatives et qualitatives par microscopie de Lorentz (LM) et holographie électronique (EH) des configurations magnétiques de nanostructures étudiées in-situ sous champ magnétique ou à basse température. Les trois nanostructures magnétiques étudiées sont: des nanofils de Co et de Co50Fe50, des réseaux d'antidot de Co et des couches minces de La2/3Ca1/3MnO3. Les experiences de manipulation de parois de domaine magnétique (DW) dans les nanofils ont permis l'étude de la nucleation des DW, de leur propagation, de leur piégeage et dépiegage. Par LM nous avons étudié la configuration magnétique à la remanence et les processus de retournement dans les réseau d'antidots à haute densité. Enfin, nous avons mis en evidence par EH à 100K une separation de phase magnétique et une variation de l'anisotropie magnétocristalline dans les films minces de LCMO resultant de la déformation épitaxiale induite par le substrat.In this thesis, we have developed quantitative and qualitative studies of the magnetic states of different magnetic nanostructures by in situ Lorentz Microscopy (LM) and Electron Holography (EH) experiments under application of magnetic field or working at low temperature (100 K), on three different magnetic nanostructures: L-shape Co and Co50Fe50 nanowires, Co antidot arrays and strained La2/3Ca1/3MnO3. DW manipulation experiments by magnetic field allowed characterize process such as DW nucleation, propagation, pinning and depinning in the nanowires. By in situ LM, remanent magnetic states and reversal magnetization process in high-density antidot arrays were studied. Finally, the effect of the substrate-induced strain in LCMO thin film were studied by EH at 100 K. We found that such strain effect produce a magnetic phase separation and/or variation in the magnetocrystalline anisotropy

Roadmap on all-optical processing

The ability to process optical signals without passing into the electrical domain has always attracted the attention of the research community. Processing photons by photons unfolds new scenarios, in principle allowing for unseen signal processing and computing capabilities. Optical computation can be seen as a large scientific field in which researchers operate, trying to find solutions to their specific needs by different approaches; although the challenges can be substantially different, they are typically addressed using knowledge and technological platforms that are shared across the whole field. This significant know-how can also benefit other scientific communities, providing lateral solutions to their problems, as well as leading to novel applications. The aim of this Roadmap is to provide a broad view of the state-of-the-art in this lively scientific research field and to discuss the advances required to tackle emerging challenges, thanks to contributions authored by experts affiliated to both academic institutions and high-tech industries. The Roadmap is organized so as to put side by side contributions on different aspects of optical processing, aiming to enhance the cross-contamination of ideas between scientists working in three different fields of photonics: optical gates and logical units, high bit-rate signal processing and optical quantum computing. The ultimate intent of this paper is to provide guidance for young scientists as well as providing research-funding institutions and stake holders with a comprehensive overview of perspectives and opportunities offered by this research field

Advanced detection in Lorentz microscopy: pixelated detection in differential phase contrast scanning transmission electron microscopy

Modern devices require fundamental length scales to be analysed in a maximum detail to enable research of new types of phenomena and design new materials. In this thesis, an advancement in Lorentz microscopy will be presented where the focus was placed not only onto resolution in spatial space but also onto resolution in reciprocal space. This allows greater sensitivity to measurements of the integrated magnetic induction within thin samples. This was achieved by a novel approach to the data acquisition, where instead of a segmented (annular) detector, a pixelated detector was used to measure the deflection of the scanning transmission microscopy (STEM) probe due to the in-plane integrated magnetic induction. Computer vision algorithms were researched to find an efficient, noise-robust way to register the deflection of the STEM probe. This enabled a novel approach to data analysis, where a scatter of the 2D integrated induction (a bivariate histogram) is used to show the distribution of the magnetic induction vector. The experimental results are supported by simulations, where a model of a thin polycrystalline sample causes a shift of the simulated beam due to phase modulations. The results of the detection in both the simulation and experiment showed that cross-correlation based processing can efficiently separate the low spatial frequencies (from the in-plane magnetic induction), and high spatial frequencies (from the structure of the polycrystalline sample). This work will enable quantitative analysis of a greater number of thin magnetic samples, for which the current methods are hampered by the diffraction contrast. This will be particularly helpful for the study low moment, out of plane, magnetised thin films. Currently such systems are of great interest due to the tunability of their magnetic properties and the novel magnetic structures present within them. This work also provides an important step for computational methods in transmission electron microscopy, as this is one of the first examples of 4D data acquisition of processing in STEM (where two dimensions represent the spatial scanning dimensions and other two the reciprocal space). Imaging methods developed in this thesis were applied to the topic of skyrmions in a thin layer of a FeGe cubic helimagnet, where the very fine detail of the structure of their in-plane integrated magnetic induction was shown to contain a distorted modulations of its profile. This was compared to a simple three harmonic frequency model, which was altered to fit some characteristics of the imaged magnetic skyrmions. In this work, for the first time, a direct comparison of differential phase contrast and electron holography will be shown for a simple experiment in which the integrated electric field between two needles was measured in free space in the same microscope. Although it was concluded that both methods are equivalent, some small discrepancies of measured values were present due to a long range electric field in electron holography and/or drift of the beam in between scans in STEM

Superconducting Qubit Readout via Low-backaction Electro-optomechanical Transduction

Entangling superconducting quantum processors via light would enable new means of secure communication and distributed quantum computing. However, transducing quantum signals between these disparate regimes of the electromagnetic spectrum remains an outstanding goal and interfacing superconducting qubits with electro-optic transducers presents significant challenges due to the deleterious effects of optical photons on superconductors. An ideal transducer should leave the state of the qubit unchanged: more precisely, the backaction from the transducer on the qubit should be minimal.In this work, I demonstrate readout of a superconducting transmon qubit via a low-backaction electro-optomechanical transducer. Requirements for integrating technology from circuit quantum electrodynamics are discussed, and the results of superconducting qubit readout via an electro-optic transducer are presented. The modular nature of the transducer and circuit QED system used in this work enable complete isolation of the superconducting qubit from optical photons, and the backaction on the qubit from the transducer is less than that imparted by thermal radiation from the environment. I show that only moderate improvements in transducer bandwidth and added noise should enable the transduction of non-classical signals from a superconducting qubit to the optical domain.</p