Garching bei Munchen, Germany
Garching bei Munchen, Germany

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Ballester D.,University of the Basque Country | Romero G.,University of the Basque Country | Garcia-Ripoll J.J.,Institute Fisica Fundamental | Deppe F.,Walther - Meissner Institute | And 3 more authors.
Physical Review X | Year: 2012

We propose a method to get experimental access to the physics of the ultrastrong- and deep-strongcoupling regimes of light-matter interaction through the quantum simulation of their dynamics in standard circuit QED. The method makes use of a two-tone driving scheme, using state-of-the-art circuit-QED technology, and can be easily extended to general cavity-QED setups. We provide examples of ultrastrong- and deep-strong-coupling quantum effects that would be otherwise inaccessible.


Zhou X.,Ecole Polytechnique Federale de Lausanne | Zhou X.,Max Planck Institute of Quantum Optics | Hocke F.,Walther - Meissner Institute | Schliesser A.,Ecole Polytechnique Federale de Lausanne | And 6 more authors.
Nature Physics | Year: 2013

The parametric coupling of electromagnetic and mechanical degrees of freedom gives rise to a host of optomechanical phenomena. Examples include quantum-limited displacement measurements, sideband cooling or amplification of mechanical motion. Likewise, this interaction provides mechanically mediated functionality for the processing of electromagnetic signals, such as microwave amplification. Here, we couple a superconducting niobium coplanar waveguide cavity to a nanomechanical oscillator, and demonstrate all-microwave field-controlled tunable slowing and advancing of microwave signals, with millisecond distortion-free delay and negligible losses. This is realized by using electromechanically induced transparency, an effect analogous to electromagnetically induced transparency in atomic physics. Moreover, by temporally modulating the electromechanical coupling and correspondingly the transparency window, switching of microwave signals is demonstrated and its temporal dynamics investigated. The exquisite temporal control gained over the electromechanical coupling provides the basis for realizing advanced protocols for storage of both classical and quantum microwave signals. © 2013 Macmillan Publishers Limited. All rights reserved.


Nembach H.T.,U.S. National Institute of Standards and Technology | Shaw J.M.,U.S. National Institute of Standards and Technology | Weiler M.,U.S. National Institute of Standards and Technology | Weiler M.,Walther - Meissner Institute | And 2 more authors.
Nature Physics | Year: 2015

Proposals for novel spin-orbitronic logic and memory devices are often predicated on assumptions as to how materials with large spin-orbit coupling interact with ferromagnets when in contact. Such interactions give rise to a host of novel phenomena, such as spin-orbit torques, chiral spin structures and chiral spin torques. These chiral properties are related to the antisymmetric exchange, also referred to as the interfacial Dzyaloshinskii-Moriya interaction (DMI; refs,). For numerous phenomena, the relative strengths of the symmetric Heisenberg exchange and the DMI are of great importance. Here, we use optical spin-wave spectroscopy (Brillouin light scattering) to directly determine the volume-averaged DMI vector D for a series of Ni 80 Fe 20 /Pt thin films, and then compare the nearest-neighbour DMI coupling energy with an independently measured value of the Heisenberg exchange for each sample. We show that the dependence on Ni 80 Fe 20 thickness of both the microscopic symmetric and antisymmetric exchange are nearly identical, consistent with the notion that the fundamentals of the DMI and Heisenberg exchange essentially share the same underlying physics, albeit with different symmetries, as was originally proposed by Moriya for superexchange in magnetic oxides, and by Fert and Levy for RKKY coupling in metallic spin glasses. Indeed, our result demonstrates the generality of the original DMI theory, insofar as the proportionality of the symmetric and antisymmetric exchange is robust with regard to the details of spin coupling for the material system in question. Although of significant fundamental importance, this result also leads us to a deeper understanding of DMI and how it could be optimized for spin-orbitronic applications. © 2015 Macmillan Publishers Limited. All rights reserved.


Lerf A.,Walther - Meissner Institute
Dalton Transactions | Year: 2014

Intercalation chemistry will soon be a hundred years old. The period of greatest activity in this field of solid state chemistry and physics was from about 1970 to 1990. The intercalation reactions are defined as topotactic solid state reactions and the products-the intercalation compounds-are clearly distinguished from inclusion and interstitial compounds. After a short historical introduction emphasizing the pioneering work of Ulrich Hofmann, the central topics and concepts will be reviewed and commented on. The most important ones, in my view, are: dichalcogenide intercalation compounds, the electrochemical intercalation and the search for new battery electrodes, the physics of graphite intercalation compounds, and the staging and interstratification phenomena. The relation to other fields of actual research and the demands for forthcoming research will also be addressed. This journal is © the Partner Organisations 2014.


Uhlig K.,Walther - Meissner Institute
Journal of Physics: Conference Series | Year: 2012

We review briefly our first cryogen-free dilution refrigerator (CF-DR) which was precooled by a GM cryocooler. We then show how today's dry DRs with pulse tube precooling have developed. A few examples of commercial DRs are explained and noteworthy features pointed out. Thereby we describe the general advantages of cryogen-free DRs, but also show where improvements are still desirable. At present, our dry DR has a base temperature of 10 mK and a cooling capacity of 700 μW at a mixing chamber temperature of 100 mK. In our cryostat, in most recent work, an additional refrigeration loop was added to the dilution circuit. This 4He circuit has a lowest temperature of about 1 K and a refrigeration capacity of up to 100 mW at temperatures slightly above 1 K; the dilution circuit and the 4He circuit can be run separately or together. The purpose of this additional loop is to increase the cooling capacity for experiments where the cooling power of the still of the DR is not sufficient to cool cold amplifiers and cables, e.g. in studies on superconducting quantum circuits or astrophysical applications. © Published under licence by IOP Publishing Ltd.


Muschler B.,Walther - Meissner Institute
Journal of physics. Condensed matter : an Institute of Physics journal | Year: 2010

Raman scattering cross sections depend on photon polarization. In the cuprates, nodal and antinodal directions are weighted more strongly in B(2g) and B(1g) symmetries, respectively. On the other hand, in angle-resolved photoemission spectroscopy (ARPES), electronic properties are measured along well-defined directions in momentum space rather than their weighted averages being taken. In contrast, the optical conductivity involves a momentum average over the entire Brillouin zone. Newly measured Raman response data on high-quality Bi(2)Sr(2)CaCu(2)O(8 + δ) single crystals up to high energies have been inverted using a modified maximum entropy inversion technique to extract from B(1g) and B(2g) Raman data corresponding electron-boson spectral densities (glue), and these are compared to the results obtained with known ARPES and optical inversions. We find that the B(2g) spectrum agrees qualitatively with nodal direction ARPES while the B(1g) results look more like the optical spectrum. A large peak around 30-40 meV in B(1g) and a much less prominent one in B(2g) are taken as support for the importance of (π, π) scattering at this frequency.


Hoehne F.,TU Munich | Dreher L.,TU Munich | Huebl H.,Walther - Meissner Institute | Stutzmann M.,TU Munich | Brandt M.S.,TU Munich
Physical Review Letters | Year: 2011

We demonstrate the electrical detection of pulsed X-band electron nuclear double resonance (ENDOR) in phosphorus-doped silicon at 5 K. A pulse sequence analogous to Davies ENDOR in conventional electron spin resonance is used to measure the nuclear spin transition frequencies of the P31 nuclear spins, where the P31 electron spins are detected electrically via spin-dependent transitions through Si/SiO2 interface states, thus not relying on a polarization of the electron spin system. In addition, the electrical detection of coherent nuclear spin oscillations is shown, demonstrating the feasibility to electrically read out the spin states of possible nuclear spin qubits. © 2011 American Physical Society.


Hackl R.,Walther - Meissner Institute
Zeitschrift fur Kristallographie | Year: 2011

The discovery of superconductors on copperoxygen basis in 1986 was one of the most celebrated events in condensed matter physics. The maximal transition temperature Tc close to 150 K was observed in HgBa2Ca 2Cu3O8+δ at high pressure. In spite of enormous progress in both the experimental knowledge and theoretical understanding, the origin of the high Tc remains elusive. Although the materials properties require unexpectedly complicated technical solutions several applications have been commercialized. © by Oldenbourg Wissenschaftsverlag, München.


Uhlig K.,Walther - Meissner Institute
AIP Conference Proceedings | Year: 2012

Helium-3,4 dilution refrigeration is indispensable for low temperature science and engineering as it is the only method which provides temperatures between 0.3 K and 0.005 K for unlimited working periods. Cryogen-free dilution refrigerators are about to replace traditional cryostats with liquid helium precooling. The dilution circuit is always precooled by a two-stage pulse tube cryocooler; therefore, refrigeration capacities are available to the experimentalist at the temperatures of the two stages of the pulse tube cooler, and furthermore at three temperatures of the dilution circuit (∼ 0.7 K-still, 0.1 K-heat exchanger, ∼ 0.01 K - mixing chamber). However, there are quite a few applications (e.g. quantum information processing or astro-physics) where the cooling power of the still near ∼ 1K is not sufficient to cool amplifiers and electric lines. In our work we present a dilution refrigerator where a He-4 cooling circuit has been added in the cryostat to the dilution circuit. This He-4 circuit provides up to 60 mW of refrigeration capacity in addition to the cooling capacity of ∼ 30 mW of the still. The dilution circuit and the 1K-circuit can be operated together or separately. © 2012 American Institute of Physics.


Opel M.,Walther - Meissner Institute
Journal of Physics D: Applied Physics | Year: 2012

The recent study of oxides led to the discovery of several new fascinating physical phenomena. High-temperature superconductivity, colossal magnetoresistance, dilute magnetic doping, or multiferroicity were discovered and investigated in transition-metal oxides, representing a prototype class of strongly correlated electronic systems. This development was accompanied by enormous progress regarding thin film fabrication. Within the past two decades, epitaxial thin films with crystalline quality approaching semiconductor standards became available using laser-molecular beam epitaxy. This evolution is reviewed, particularly with emphasis on transition-metal oxide thin films, their versatile physical properties, and their impact on the field of spintronics. First, the physics of ferromagnetic half-metallic oxides, such as the doped manganites, the double perovskites and magnetite is presented together with possible applications based on magnetic tunnel junctions. Second, the wide bandgap semiconductor zinc oxide is discussed particularly with regard to the controversy of dilute magnetic doping with transition-metal ions and the possibility of realizing p-type conductivity. Third, the field of oxide multiferroics is presented with the recent developments in single-phase multiferroic thin film perovskites as well as in composite multiferroic hybrids. © 2012 IOP Publishing Ltd.

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