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Superconducting Quantum Circuits and Nanomechanics

Superconductivity and Superfluidity
Superconducting Quantum Circuits and Nanomechanics
Magnetism and Spintronics
Organic Metals

SFB 631
TRR 80
SPP 1458
SPP 1538
SPP 1601

Superconducting Quantum Circuits

In superconducting circuits, all superelectrons can be described by a quantum mechanical wave function with a single amplitude and phase. As a consequence, superconducting circuits can be engineered in a way to behave as macroscopic artificial atoms or quantum harmonic oscillators. For this reasons, we call our circuits superconducting quantum circuits. The wide field of applications includes the astonishing demonstration of textbook quantum mechanics and quantum information processing (QIP) and quantum simulation. Our research does not only provide the foundations of quantum information systems and quantum technology, but also addresses key fundamental questions regarding quantum coherence, quantum dynamics and decoherence processes in solid state quantum systems. Furthermore, it requires extremely sensitive measurements at millikelvin temperatures.

The research activities at the WMI are focused on:

  • Josephson junction based qubits.

    Superconducting qubits are quantum two-level systems, which consist of nanometer-sized Josephson junctions providing strong nonlinear elements and superconducting loops, with typical transition frequencies in the gigahertz regime. In superconducting flux qubits quantum mechanical superposition states of clockwise and counter-clockwise circulating persistent currents are used for the realization of solid state qubits. We are steadily working on

    • Optimizing the fabrication and measurement process of superconducting flux and transmon qubits
    • Develop advanced qubit designs best suited for our experiments
    • Realization of flux qubits with tunable tunnel splitting which offer more flexibility in circuit design
    • The challenge is to engineer qubits with long enough coherence times to study quantum effects

    Recent Publications:

    Gradiometric flux qubits with tunable gap
    M. J. Schwarz, J. Goetz, Z. Jiang, T. Niemczyk, F. Deppe, A. Marx, R. Gross, New Journal of Physics 15, 045001 (2013)

    Fabrication technology of and symmetry breaking in superconducting quantum circuits
    T. Niemczyk, F. Deppe, M. Mariantoni, E.P. Menzel, E. Hoffmann, G. Wild, L. Eggenstein, A. Marx, R. Gross, Supercond. Sci. Techn. 22, 034009 (2009)

  • Superconducting resonators.

    Superconducting resonators are boxes for microwave photons and behave as quantum harmonic oscillators. In contrast to the fermionic qubits they behave as bosons. Resonators are attractive systems to study quantum correlations. We work both on superconductung transmission line resonators which act as photon boxes on a chip and three-dimensional (3D) superconducting cavites providing very high single photon lifetims. Here we focus on

    • Microwave engineering of advanced single and multi resonator setups
    • Control the decay rates
    • Investigation of different coupling schemes
    • Flux driven Josephson parametric amplifiers

    Recent Publications:

    Fast microwave beam splitters from superconducting resonators
    M. Haeberlein, D. Zueco, P. Assum, T. Weißl, E. Hoffmann, B. Peropadre, J.J. Garc\ia-Ripoll, E. Solano, F. Deppe, A. Marx, R. Gross, arXiv:1302.0729 (2013)

    Squeezing with a flux-driven Josephson parametric amplifier
    L. Zhong, E. P. Menzel, R. Di Candia, P. Eder, M. Ihmig, A. Baust, M. Haeberlein, E. Hoffmann, K. Inomata, T. Yamamoto, Y. Nakamura, E. Solano, F. Deppe, A. Marx, R. Gross, New Journal of Physics 15, 125013 (2013)

    Networks of nonlinear superconducting transmission line resonators
    M. Leib, F. Deppe, A. Marx, R. Gross, M. Hartmann, New Journal of Physics 14, 075024 (2012)

  • Circuit quantum electrodynamics (cQED) in the strong and ultrastrong coupling regime: quantum optics on a chip.

    Coupled qubit-resonator systems are an ideal playground for investigating the interaction between light and matter and thus to perform quantum optics on a chip experiments. The coupling rates can be made larger than the decoherence rates of qubit and resonator (strong coupling regime). In particular for flux based circuits we have reached the new regime of ultrastrong coupling where the coupling rate becomes the dominating energy scale of the system. Main interests are

    • Multi-photon physics
    • Quantum state generation
    • Josephson and kinetic inductance enhancement of the coupling
    • Fascinating counter intuitive physics beyond the rotating wave approximation

    Recent Publications:

    Selection rules in a strongly coupled qubit-resonator system
    T. Niemczyk, F. Deppe, E. P. Menzel, M. J. Schwarz, H. Huebl, F. Hocke, M. Häberlein, M. Danner, E. Hoffmann, A. Baust, E. Solano, J. J. Garcia-Ripoll, A. Marx, R. Gross, arXiv:1107.0810v1 (2011)

    Circuit quantum electrodynamics in the ultrastrong-coupling regime
    T. Niemczyk, F. Deppe, H. Huebl, E. P. Menzel, F. Hocke, M. J. Schwarz, J. J. Garcia-Ripoll, D. Zueco, T. Hümmer, E. Solano, A. Marx, R. Gross, Nature Physics 6, 772-776 (2010)

    Two-photon Probe of the Jaynes-Cummings Model and Controlled Symmetry Breaking in Circuit QED
    F. Deppe, M. Mariantoni, E. Menzel, A. Marx, S. Saito, K. Kakuyanagi, H. Tanaka, T. Meno, K. Semba, H. Takayanagi, E. Solano, R. Gross, Nature Physics 4, 686 - 691 (2008)

  • Tunable coupling between microwave resonators.

    To realize quantum gates and quantum information and simulation protocols, the coupling between the individual circuit elements needs to be tunable in situ. The coupling between two circuit QED building blocks can be mediated by additional coupling circuits. We work on tunable and switchable coupling between two superconducting transmission line resonators mediated by both superconducting flux qubits and RF SQUDS. We aim at

    • Fabricating and characterizing tunable and switchable coupling
    • Entanglement generation between two resonators
    • Generation of interesting quantum states (Schrodinger cats, GHZ states)

    Recent Publications:

    Tunable and Switchable Coupling Between Two Superconducting Resonators
    A. Baust, E. Hoffmann, M. Haeberlein, M. J. Schwarz, P. Eder, E. P. Menzel, K. Fedorov, J. Goetz, F. Wulschner, E. Xie, L. Zhong, F. Quijandria, B. Peropadre, D. Zueco, J.-J. Garcia Ripoll, E. Solano, F. Deppe, A. Marx, R. Gross, arXiv:1405.1969 (2014)

    Tunable coupling engineering between superconducting resonators: from sidebands to effective gauge fields
    B. Peropadre, D. Zueco, F. Wulschner, F. Deppe, A. Marx, R. Gross, J.J. García-Ripoll, Phys. Rev. B 87, 134504 (2013)

    Two-resonator circuit quantum electrodynamics: Dissipative theory
    G. M. Reuther, D. Zueco, F. Deppe, E. Hoffmann, E. P. Menzel, T. Weißl, M. Mariantoni, S. Kohler, A. Marx, E. Solano, R. Gross, P. Hänggi, Phys. Rev. B 81, 144510 (2010)

    Two-resonator Circuit Quantum Electrodynamics: A Superconducting Quantum Switch
    M. Mariantoni, F. Deppe, E. Menzel, A. Marx, F.K. Wilhelm, R. Gross & E. Solano, Phys. Rev. B 78, 104508 (2008)

  • Propagating quantum microwaves.

    In propagating quantum microwave photonics one aims at the the generation, control, detection, and interaction of quantum microwave beams using superconducting quantum circuits. Our goal is to merge the possibilities of all-optical quantum computing with superconducting circuits to perform useful tasks such as scalable quantum gates or quantum simulation. Our efforts employ superconducting quantum circuits to explore novel paths in engineering strong and ultrastrong controlled interactions between propagating microwave photons and their environment as well as among photons themselves. To this end, we aim at

    • Tomography of arbitrary propagating quantum microwaves
    • Manipulation of propagating quantum microwaves
    • The development and understanding of microwave beam splitters with a similar degree of tunability
    • Characterization of propagating squeezed microwave light

    Recent Publications:

    Dual-Path Methods for Propagating Quantum Microwaves
    R. Di Candia, E. P. Menzel, L. Zhong, F. Deppe, A. Marx, R. Gross, E. Solano, New Journal of Physics 16, 015001 (2014)

    Path Entanglement of Continuous-Variable Quantum Microwaves
    E. P. Menzel, R. Di Candia, F. Deppe, P. Eder, L. Zhong, M. Ihmig, M. Haeberlein, A. Baust, E. Hoffmann, D. Ballester, K. Inomata, T. Yamamoto, Y. Nakamura, E. Solano, A. Marx, R. Gross, Phys. Rev. Lett. 109, 250502 (2012)

    Dual-path state reconstruction scheme for propagating quantum microwaves and detector noise tomography
    E. P. Menzel, F. Deppe, M. Mariantoni, M. Á. Araque Caballero, A. Baust, T. Niemczyk, E. Hoffmann, A. Marx, E. Solano, R. Gross, Phys. Rev. Lett. 105, 100401 (2010)

    Planck Spectroscopy and the Quantum Noise of Microwave Beam Splitters
    M. Mariantoni, E. P. Menzel, F. Deppe, M. A. Araque Caballero, A. Baust, T. Niemczyk, E. Hoffmann, E. Solano, A. Marx, R. Gross, Phys. Rev. Lett. 105, 133601 (2010


For all above described research areas we are constantly providing fascinating topics for diploma/master and bachelor students. If you are interested in doing exciting new physics in our QIP team please contact Frank Deppe, Achim Marx or Rudolf Gross.

An introducting into the field of superconducting quantum circuits can be found in the lecture notes "Applied Superconductivity".

The QIP research activites at the WMI are embedded in the Collaborative Research Center (Sonderforschungsbereich) 631 entitled "Solid-State Quantum Information Processing: Physical Concepts and Material Aspects", the Excellence Cluster "Nanosystems Initiative Munich", the FP7 Project Circuit and Cavity Quantum Electro-Dynamics (CCQED), and the FP7-STReP Project PROMISCE: Quantum Propagating Microwaves in Strongly Coupled Environments.

NIM_Logo SFB_Logo ExQM_Logo CCQED Promisce
Cluster of Excellence
Nanosystems Initiative Munich
DFG Collaborative Research Center 631
Solid State Quantum Information Processing
ExQM: Exploring Quantum Matter
(International PhD Program of Excellence)
CCQED: Circuit and Cavity Quantum Electro-Dynamics
(Marie Curie Initial Training Networks)
PROMISCE: Quantum Propagating Microwaves
in Strongly Coupled Environments (FP7-STReP)


Nanomechanical quantum hybrid systems offer promising perspectives to test macroscopic objects for their quantum mechanical behavior. Key experiments are the cooling of mechanical harmonic oscillators to their ground-state, squeezing of quantum states and conversion of quantum information between energy-scales (e.g. frequency conversion).

The research activities at the WMI are focussed on:


  • Sideband control of electromechanical hybrids
    We investigate electromechanical hybrids based on superconducting (Nb) microwave resonators combined with nanomechanical beams based on SiN-Nb sandwich layers. This combines important key parameters of the beam like the excellent conduction with high mechanical resonance frequencies and quality factors. The structures are pre-characterized at liquid helium temperatures followed by microwave spectroscopy in dilution-refrigerator environments.
    Here we focus on:
    • the investigation of the properties of the mechanical, electrical and coupled system at millikelvin temperatures.
    • benchmarking the performance of sideband cooling and heating.


nanomechanical hybrid
  • Optomechanically induced transparency and absorption in electromechanical hybrids
    Optomechanically induced transparency is an interference effect which occurs when the electromechanical system is investigated with multiple microwave tones. In particular, a so-called transparency window opens in the otherwise absorptive signature of the microwave cavity if the beam is driven by a microwave signal which is red detuned. In this experiment the microwave cavity is simultaneously probed by a low intensity microwave tone.
    In the hybrid structures described above, we test the existing models of optomechanical induced transparency towards:
    • the red and the blue detuned regime.
    • high pump and probe intensities resulting in a nonlinear response of the system and duffing like oscillations.

For all above described research areas we are constantly providing fascinating topics for diploma/master and bachelor students. If you are interested in doing exciting new physics in our nanomechanics team please contact Hans Hübl, Achim Marx or Rudolf Gross.

The nanomechanical hybrid systems research activites at the WMI are embedded in the Excellence Cluster "Nanosystems Initiative Munich".


For further information contact Hans Hübl.