Publications David ZÖPFL

2023

Article

• David Zöpfl, Mathieu L. Juan, Nicolas Diaz-Naufal, C. Schneider, L. Deeg, A. Sharafiev, Anja Metelmann, G. Kirchmair Kerr Enhanced Backaction Cooling in Magnetomechanics, PRL 130 33601 (2023-01-17), http://dx.doi.org/10.1103/PhysRevLett.130.033601 doi:10.1103/PhysRevLett.130.033601 (ID: 720816) Toggle Abstract
  Optomechanics is a prime example of light matter interaction, where photons directly couple to phonons, allowing the precise control and measurement of the state of a mechanical object. This makes it a very appealing platform for testing fundamental physics or for sensing applications. Usually, such mechanical oscillators are in highly excited thermal states and require cooling to the mechanical ground state for quantum applications, which is often accomplished by using optomechanical backaction. However, while massive mechanical oscillators are desirable for many tasks, their frequency usually decreases below the cavity linewidth, significantly limiting the methods that can be used to efficiently cool. Here, we demonstrate a novel approach relying on an intrinsically nonlinear cavity to backaction-cool a low frequency mechanical oscillator. We experimentally demonstrate outperforming an identical, but linear, system by more than 1 order of magnitude. Furthermore, our theory predicts that with this approach we can also surpass the standard cooling limit of a linear system. By exploiting a nonlinear cavity, our approach enables efficient cooling of a wider range of optomechanical systems, opening new opportunities for fundamental tests and sensing.

2020

Article

• D. Zöpfl, M. L. Juan, C. Schneider, G. Kirchmair Single-Photon Cooling in Microwave Magnetomechanics, PRL 125 23601 (2020-07-07), http://dx.doi.org/10.1103/PhysRevLett.125.023601 doi:10.1103/PhysRevLett.125.023601 (ID: 720518) Toggle Abstract
  Cavity optomechanics, where photons are coupled to mechanical motion, provides the tools to control mechanical motion near the fundamental quantum limits. Reaching single-photon strong coupling would allow to prepare the mechanical resonator in non-Gaussian quantum states. Preparing massive mechanical resonators in such states is of particular interest for testing the boundaries of quantum mechanics. This goal remains however challenging due to the small optomechanical couplings usually achieved with massive devices. Here we demonstrate a novel approach where a mechanical resonator is magnetically coupled to a microwave cavity. We measure a single-photon coupling of g0/2π∼3  kHz, an improvement of one order of magnitude over current microwave optomechanical systems. At this coupling we measure a large single-photon cooperativity with C0≳10, an important step to reach single-photon strong coupling. Such a strong interaction allows us to cool the massive mechanical resonator to a third of its steady state phonon population with less than two photons in the microwave cavity. Beyond tests for quantum foundations, our approach is also well suited as a quantum sensor or a microwave to optical transducer.

2017

Article

• D. Zöpfl, C. Schneider, P. R. Muppalla, S. Kasemann, S. Partel, G. Kirchmair Characterization of low loss microstrip resonators as a building block for circuit QED in a 3D waveguide, AIP ADV 7 (2017-08-28), http://dx.doi.org/10.1063/1.4992070 doi:10.1063/1.4992070 (ID: 719818) Toggle Abstract
  Here we present the microwave characterization of microstrip resonators made from aluminum and niobium inside a 3D microwave waveguide. In the low temperature, low power limit internal quality factors of up to one million were reached. We found a good agreement to models predicting conductive losses and losses to two level systems for increasing temperature. The setup presented here is appealing for testing materials and structures, as it is free of wire bonds and offers a well controlled microwave environment. In combination with transmon qubits, these resonators serve as a building block for a novel circuit QED architecture inside a rectangular waveguide.