Our research presently focuses on hybrid systems involving nano- and micromechanical oscillators in, or at the verge to, the quantum regime. Electro- magnetic fields coupled to them through high-quality resonators--optical micro- cavities, or superconducting microwave stripline resonators--are used as probes. Guided by concepts from atomic physics and quantum optics, but building on solid-state experimental platforms and low-temperature techniques, we are interested in all aspects of quantum measurements, damping and decoherence mechanisms, and control and conversion of mechanical quantum states.
A second line of research revolves around optical frequency combs, investigating both novel generators as well as their application in spectroscopy. This includes, in particular, comb generators based on microresonators, but also non- linear conversion, with spectral coverage all the way to the mid-infrared. We have further introduced several new spectroscopic techniques relying on frequency comb sources, with application potential for sensing and hyperspectral nano-imaging.
Researchers of the Schliesser Lab have demonstrated a new way to address a central problem in quantum physics: at the quantum scale, any measurement disturbs the measured object. This disturbance limits, for example, the precision with which the motion of an object can be tracked. But in a millimeter-sized membrane that vibrates like a drumhead, the researchers have managed to precisely monitor the motion with a laser—and to undo the quantum disturbance by the measurement. This allows them to control the membrane’s motion at the quantum level. The result has potential applications in ultraprecise sensors of position, velocity and force, and the architecture of a future quantum computer.Read the detailed article in Nature or on the arXiv, News and Views by Michael Vanner, have a look at the press release, or the Science Breaker story.
My group has recently introduced a new way to realise high-Q nanomechanical membrane resonators. Structures with an engineered phononic density of states confine nanomechanical modes to defects of an otherwise periodic pattern. As we show, appropriately chosen patterns not only suppress radiation of acoustic energy away from the defect. If combined with tensile stress, they also reduce internal dissipation by many orders of magnitude, by providing a "soft" clamping that reduces curvature.
As a result, we obtain nanogram-mechanical resonators with quality factors beyond 100 million at MHz frequencies at room temperature. This corresponds to Q-frequency products in excess of 100 THz, higher than any other mechanical resonator fabricated to date, including silicon MEMS, quartz, and diamond devices. Application prospects for quantum optomechanics, force and mass sensing are promising.Read the detailed article in Nature Nanotechnology or on the arXiv, and have a look at the press release.
By simultaneously coupling a nanomechanical membrane (ca. 100 nm thick) to an electronic resonance circuit and a propagating laser field, we could transduce tiny electronic signals into the optical domain, where they can be measured with unprecedented sensitivity. The mutual coupling is realised by metallising the membrane and suspending it in close proximity (ca. 1 micon) to a second electrode, so as to form a capacitor whose capacitance denpends on the position of the membrane. This, in turn, also induces displacement of the membrane through electrostatic forces if voltage signals are applied to the capacitor. By means of an optical interferometer limited only by quantum noise, these displacements can be detected with a sensitivity of 1.7 femtometers in a second of measurement time. The membrane, even though at room temperature and thus undergoing random thermal motion, only adds an insignificant amount of noise. The latter rather is entirely dominated by the electronic thermal noise in the input circuit. In applications where this noise is low--such as cryogenic MRI or radio astronomy--this novel appraoch may deliver significant improvements in sensitivity. It is also a promising approach to link superconducting microwave electronics--a highly advanced platform for quantum information processing--to flying optical photons as required to connect the nodes of a quantum network.Read more about this work in Nature (article, News & Views, News), the Scientific American, the JQI News and Ingenøren.
The propagation of pulses of electromagnetic radiation is usually governed by the properties of the medium or waveguide that hosts the field. In this work we have introduced a radically different approach to control the propagation of microwave signals. It harnesses the electromechanical interaction with the vibrations of a silicon nitride nano-string, and can be used to dynamically switch, slow down, and accelerate the propagation of microwave pulses confined to a superconducting microwave stripline. The signals can be retrieved after milliseconds' of tunable delay, with negligible loss and distortion. A coaxial cable realizing the same delay would need to be 600 km long, thus very lossy, hardly tunable and expensive.Read more about this work in Nature Physics.
Many molecules exhibit characteristic vibrational transistions in the mid-infrared region of the electromagnetic spectrum. This spectral domain, comprising wavelengths between 2 and 20 micron, is therefore often referred to as the molecular fingerpint region. While coherent light sources, and in particular optical frequency combs, have revolutionised atomic spectroscopy in the visible and near infrared spectral regions, the mid-infrared has remained notoriously difficult to access due to a lack of adequate radiation sources. Researchers' persistent efforts to remedy this situation have brought about a number of approaches for new, mid-infrared frequency comb generators, which I have reviewed in a recent article with Nathalie Picque and Theodor Hänsch.
Experimentally, we have worked on the development of mid-infrared frequency comb sources based on different techniques. The most recent work was based on a cascasde of parametric sideband generation that we discovered at MPQ. Applying this technique to a crystalline microresonator, we could demonstrate comb generation in the mid-infrared around 2.5 micron. Earlier work used nonlinear conversion in a thin GaSe crystal giving rise to a tunable comb around 10 micron.Read the review article in Nature Photonics and a research article in Nature Communications.
The optomechanical coupling in glass microtoroids is intrinsically large, due their small size similar to a human hair in their 100 micron diameter. And it can be further enhanced by a strong optical field. This leads to a periodic interconversion of optical (photons) and mechanical (phonons) excitations, at a rate faster than the individual dissipation rates. We have achieved this regime and demonstrated such swapping of an excitation containing less than one energy quantum on average. We have furthermore verified that the coupling rate exceeds both mechanical and optical decoherence rates. This allowed us to cool the mechanical degree of freedom close to its quantum ground state. Similarly, it would enable the swapping of non-classical states from the light field into the mechanics and back. A particularly exciting prospect for this research is that of using the mechanical oscillator as an intermediary, coupling light to another degree of freedom, such as a microwave or radio-frequency mode.Read more about this work in Nature and the Neue Zürcher Zeitung.
In atomic systems, interference between different pathways of electronic excitations can suppress the absorption of light by an atom. This effect is known as electromagnetically induced transparency (EIT). In my 2009 thesis I pointed out a close analogy of this effect in opto- and electromechanical systems--an optomechanically induced transparency (OMIT)--and proposed to study it experimentally. Here, the presence of a "control" light field leads to a mechanically mediated destructive self-interference of a "probe" field. This prevents the probe field from exciting the optomechanical cavity and allows it to traverse the system without absorption. As a result, the probe field transmission, and in fact also its propagation delay through the system, can be tuned by means of the control field, similar to an optical transistor. We could report the first observation of this effect soon thereafter in 2010. To this date, OMIT is widely studied for the generation of tunable group delays, frequency-dependent rotation of a (squeezed) field quadrature, the characterization of optomechanical systems, and for the theoretically expected enhancement of quantum nonlinearities.Read more about this work in Science and Popular Mechanics Russia.