All-optical control of ferromagnetic thin films and nanostructures

The interplay of light and magnetism has been a topic of interest since the original observations of Faraday and Kerr where magnetic materials affect the light polarization. While these effects have historically been exploited to use light as a probe of magnetic materials there is increasing research on using polarized light to alter or manipulate magnetism. For instance deterministic magnetic switching without any applied magnetic fields using laser pulses of the circular polarized light has been observed for specific ferrimagnetic materials. Here we demonstrate, for the first time, optical control of ferromagnetic materials ranging from magnetic thin films to multilayers and even granular films being explored for ultra-high-density magnetic recording. Our finding shows that optical control of magnetic materials is a much more general phenomenon than previously assumed. These results challenge the current theoretical understanding and will have a major impact on data memory and storage industries via the integration of optical control of ferromagnetic bits.Comment: 21 pages, 11 figure

Fast spin exchange between two distant quantum dots

The Heisenberg exchange interaction between neighboring quantum dots allows precise voltage control over spin dynamics, due to the ability to precisely control the overlap of orbital wavefunctions by gate electrodes. This allows the study of fundamental electronic phenomena and finds applications in quantum information processing. Although spin-based quantum circuits based on short-range exchange interactions are possible, the development of scalable, longer-range coupling schemes constitutes a critical challenge within the spin-qubit community. Approaches based on capacitative coupling and cavity-mediated interactions effectively couple spin qubits to the charge degree of freedom, making them susceptible to electrically-induced decoherence. The alternative is to extend the range of the Heisenberg exchange interaction by means of a quantum mediator. Here, we show that a multielectron quantum dot with 50-100 electrons serves as an excellent mediator, preserving speed and coherence of the resulting spin-spin coupling while providing several functionalities that are of practical importance. These include speed (mediated two-qubit rates up to several gigahertz), distance (of order of a micrometer), voltage control, possibility of sweet spot operation (reducing susceptibility to charge noise), and reversal of the interaction sign (useful for dynamical decoupling from noise).Comment: 6 pages including 4 figures, plus 8 supplementary pages including 5 supplementary figure

Strain dependence of bonding and hybridization across the metal-insulator transition of VO2

Soft x-ray spectroscopy is used to investigate the strain dependence of the metal-insulator transition of VO2. Changes in the strength of the V 3d - O 2p hybridization are observed across the transition, and are linked to the structural distortion. Furthermore, although the V-V dimerization is well-described by dynamical mean-field theory, the V-O hybridization is found to have an unexpectedly strong dependence on strain that is not predicted by band theory, emphasizing the relevance of the O ion to the physics of VO2

Study of deuterium plasma interaction with a tungsten target within RPI-IBIS facility

The paper presents results of experimental research on the interaction of a pulsed plasma-ion stream with a tungsten (W) target. The pulsed deuterium plasma was produced within the RPI-IBIS (Multi-Rod Plasma Injector) facility at IPJ in Swierk. Measurements were carried out by means of optical spectroscopy and corpuscular diagnostic techniques. Structural changes in the irradiated targets were investigated with a SEM. Before experiments with the W-target there were determined operational conditions, when clean deuterium plasma streams can be generated. For that purpose a so-called “slow or PID (Plasma Ion Deposition) mode” of the RPI-IBIS operation was chosen. Particular attention was paid to the identification of spectral lines from WI and WII species. The obtained results, i.e. optical spectra and other characteristics have demonstrated applicability of the RPI-IBIS facility for research on the interaction of plasma streams with W-targets, e.g. those constituting some internal parts of fusion facilities.Представлено результати експериментальних досліджень по взаємодії імпульсного плазмово-іонного потоку з вольфрамовою мішенню. Імпульсні дейтерієві потоки плазми генерувались в СПІ-ІБІС (стержневий плазмовий інжектор), який знаходиться в ІЯП у Шверку. Виміри проводились за допомогою оптичної спектроскопії та корпускулярної діагностики. Структурні зміни облучаємої мішені досліджувались за допомогою SEM. Перед експериментами з вольфрамовою мішенню визначались робочі умови, коли генерувались чисті дейтерієві плазмові потоки. Був вибраний так званий режим “повільний або PID-моди” (плазмового іонного осадження). Частична увага приділялась ідентифікації спектральних ліній WI та WII. Отримані результати, оптичні спектри та інші характеристики, продемонстрували можливість застосовувати установку СПІ-ІБІС для досліджень взаємодії плазмових потоків з W-мішенню, які складають деякі внутрішні частини термоядерного реактору.Представлены результаты экспериментальных исследований по взаимодействию импульсного плазменно-ионного потока с вольфрамовой мишенью. Импульсные дейтериевые потоки плазмы генерировались внутри СПИ-ИБИС (стержневой плазменный инжектор), который расположен в ИЯП в Шверке. Измерения проводились с помощью оптической спектроскопии и корпускулярной диагностики. Структурные изменения облучаемой мишени исследовались с помощью SEM. Перед экспериментами с вольфрамовой мишенью определялись рабочие условия, когда генерировались чистые дейтериевые плазменные потоки. Для этой цели был выбран так называемый режим “медленной или PID-моды” (плазменного ионного осаждения). Частичное внимание уделялось идентификации спектральных линий WI и WII. Полученные результаты, оптические спектры и другие характеристики, продемонстрировали применимость установки СПИ-ИБИС для исследований взаимодействия плазменных потоков с W-мишенью, которые составляют некоторые внутренние части термоядерного реактора

Unifying the Phase Diagrams of the Magnetic and Transport Properties of La_(2-x)Sr_xCuO_4, 0 < x < 0.05

An extensive experimental and theoretical effort has led to a largely complete mapping of the magnetic phase diagram of La_(2-x)Sr_xCuO_4, and a microscopic model of the spin textures produced in the x < 0.05 regime has been shown to be in agreement with this phase diagram. Here we use this same model to derive a theory of the impurity-dominated, low temperature transport. Then, we present an analysis of previously published data for two samples: x = 0.002 data from Chen et. al., and x = 0.04 data from Keimer et. al. We show that the transport mechanisms in the two systems are the same, even though they are on opposite sides of the observed insulator-to-metal transition. Our model of impurity effects on the impurity band conduction, variable-range hopping conduction, and coulomb gap conduction, is similar to that used to describe doped semiconductors. However, for La_(2-x)Sr_xCuO_4 we find that in addition to impurity-generated disorder effects, strong correlations are important and must be treated on a equal level with disorder. On the basis of this work we propose a phase diagram that is consistent with available magnetic and transport experiments, and which connects the undoped parent compound with the lowest x value for which La_(2-x)Sr_xCuO_4 is found to be superconducting, x about 0.06.Comment: 7 pages revtex with one .ps figur

Time-domain characterization and correction of on-chip distortion of control pulses in a quantum processor

We introduce Cryoscope, a method for sampling on-chip baseband pulses used to dynamically control qubit frequency in a quantum processor. We specifically use Cryoscope to measure the step response of the dedicated flux control lines of two-junction transmon qubits in circuit QED processors with the temporal resolution of the room-temperature arbitrary waveform generator producing the control pulses. As a first application, we iteratively improve this step response using optimized real-time digital filters to counter the linear-dynamical distortion in the control line, as needed for high-fidelity, repeatable one- and two-qubit gates based on dynamical control of qubit frequency

Entropy of vortex cores on the border of the superconductor-to-insulator transition in an underdoped cuprate

We present a study of Nernst effect in underdoped $La_{2-x}Sr_xCuO_4$ in magnetic fields as high as 28T. At high fields, a sizeable Nernst signal was found to persist in presence of a field-induced non-metallic resistivity. By simultaneously measuring resistivity and the Nernst coefficient, we extract the entropy of vortex cores in the vicinity of this field-induced superconductor-insulator transition. Moreover, the temperature dependence of the thermo-electric Hall angle provides strong constraints on the possible origins of the finite Nernst signal above $T_c$, as recently discovered by Xu et al.Comment: 5 Pages inculding 4 figure