arXiv subjects

D. Zoepfl

Publications and source records attributed to D. Zoepfl.

5 recordsLinked to original sources

arXiv2024

Kerr enhanced optomechanical cooling in the unresolved sideband regime

Dynamical backaction cooling has been demonstrated to be a successful method for achieving the motional quantum ground state of a mechanical oscillator in the resolved sideband regime, where the mechanical frequency is significantly larger than the cavity decay rate. Nevertheless, as mechanical systems increase in size, their frequencies naturally decrease, thus bringing them into the unresolved sideband regime, where the effectiveness of the sideband cooling approach decreases. Here, we will demonstrate, however, that this cooling technique in the unresolved sideband regime can be significantly enhanced by utilizing a nonlinear cavity as shown in the experimental work of Zoepfl et. al. (PRL, 2023). The above arises due to the increased asymmetry between the cooling and heating processes, thereby improving the cooling efficiency.

quant-ph↗

arXiv2024

Optomechanical Backaction in the Bistable Regime

With a variety of realisations, optomechanics utilizes its light matter interaction to test fundamental physics. By coupling the phonons of a mechanical resonator to the photons in a high quality cavity, control of increasingly macroscopic objects has become feasible. In such systems, state manipulation of the mechanical mode is achieved by driving the cavity. To be able to achieve high drive powers the system is typically designed such that it remains in a linear response regime when driven. A nonlinear response and especially bistability in a driven cavity is often considered detrimentally to cooling and state preparation in optomechanical systems and is avoided in experiments. Here we show, that with an intrinsic nonlinear cavity backaction cooling of a mechanical resonator is feasible operating deeply within the nonlinear regime of the cavity. With our theory taking the nonlinearity into account, precise predictions on backaction cooling can be achieved even with a cavity beyond the bifurcation point, where the cavity photon number spectrum starts to deviate from a typical Lorentzian shape.

quant-ph↗

arXiv2023

Kerr enhanced backaction cooling in magnetomechanics

Optomechanics is a prime example of light matter interaction, where photons directly couple to phonons, allowing to precisely control and measure 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 utilising 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 one 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.

quant-ph↗

arXiv2023

Single-photon cooling in microwave magneto-mechanics

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 $g_0/2 π\sim 3$ kHz, an improvement of one order of magnitude over current microwave optomechanical systems. At this coupling we measure a large single-photon cooperativity with $C_0 \gtrsim 10$, 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.

quant-ph↗

arXiv2023

Characterization of low loss microstrip resonators as a building block for circuit QED in a 3D waveguide

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.

cond-mat.supr-con↗