Menno Poot

Quantum Technologies

Technical University of Munich

TUM School of Natural Sciences

James-Franck-Str. 1

85747 Garching


Reseatch Webpage


Research focus: nanomechanical resonators, integrated quantum optics

The research in our group focusses on Quantum Technologies in the broadest sense. In particular, we make chips using state-of-the-art nanofabrication techniques to study quantum effects in a variety of systems. For example, we look at high-frequency nanomechanical resonators at millikelvin temperatures, where these are in their quantum groundstate. Yet their tiny zero-point motion can be measured using ultra-sensitive optomechanical techniques. Another important line of research is integrated quantum optics, where photonic chips with functionality to generate, manipulate, and detect single photons are designed, made, and measured. This approach enables scalable quantum optics experiments.

Nano- and optomechanics

The field of optomechanics is rapidly developing and a wide variety of systems is currently being studied around the globe. Instead of using macroscopic resonators, our approach is to integrate both the mechanical resonator and its optical readout on a single chip. This approach takes advantage of the quickly advancing integrated-photonics technology, and enables flexible designs for the mechanical resonator: These can range from devices with length of a few hundred micrometer to nanometer-sized vibrating structures. In general, the smaller the resonator, the higher the resonance frequency and the larger their zero-point motion. Nanomechanical devices can operate at gigahertz frequencies, and this means that when such devices are cryogenically cooled in a dilution refrigerator, they will be in their groundstate. The resonator is then a true quantum mechanical object. Alternatively, one can use lower frequencies and/or higher temperatures and apply cooling techniques to bring the resonator into the quantum regime. For this, we are developing a toolbox of feedback-assisted techniques. The beauty of mechanical systems is that they couple to almost anything, for example to charge, magnetic flux, temperature, and perhaps most importantly, to light. A mechanical resonator is therefore ideally suited to act as a quantum interface between different quantum systems such as superconducting qubits and single optical photons.

Integrated quantum optics

Quantum optics has a great potential for the transition from quantum science to quantum technology. In particular, photons are ideal as carriers of quantum information since they can be transferred over large distances with low loss and small decoherence. Amazing progress have been made in the past years, but it is often challenging to scale these experiments up to larger quantum systems. One issue is number of components needed and the required space; soon one will need many optical tables to perform one experiment. In our approach, all the required functionality for performing quantum optics experiments are integrated on a single chip. This includes generation of non-classical light, routing of single photons through programmable photonic circuits that implement quantum operations, as well as sensitive detection. After detection, the results can be analyzed or be fed-forward to later parts of the circuit. For this, low loss photonic components with tight tolerances are essential. Getting the best nanofabrication results is therefore an important aspect of our research. Moreover, the detection of single photons should happen with an efficiency as large as possible. For this purpose, superconducting single photon detectors are monolithically integrated on the same chip. Finally, our optomechanical structures serve as optical phase shifters with extremely low dissipation that allow for programmable circuitry, and current research focusses on implementing feed-back and feed-forward schemes using optimized devices.

Selected Publications

  • Poot M., Schuck C., Ma X.S., Guo X., and Tang H.X.: „Design and characterization of integrated components for SiN photonic quantum circuits”, Opt. Expr. 24 6843 (2016).
  • Schick C., Gut X., Fan L., Ma X., Poot M., and Tang H.X.: „Quantum interference in heterogeneous superconducting-photonic circuits on a silicon chip“. Nature Commun. 7, 10352 (2016).
  • Poot M., van der Zant H.S.J.: „Mechanical systems in the quantum regime“. Phys. Rep. 511 273-335 (2012).
  • Poot M., Esaki S., Mahboob I., Onomitsu K., Yamaguchi H., Blanter Ya. M., and van der Zant H.S.J.: „Tunable backaction of a dc SQUID on an integrated micromechanical resonator“. Phys. Rev. Lett. 105, 207203 (2010).
  • Steele G.A., Hüttel A.K., Witkamp B., Poot M., Meerwaldt H.B., Kouwenhoven L.P., and van der Zant H.S.J.: “Strong coupling between single-electron tunneling and nano-mechanical motion” Science 325, 1103-1107 (2009).


Control over Light Emission in Low-Refractive-Index Artificial Materials Inspired by Reciprocal Design

L. Maiwald, T. Sommer, M.S. Sidorenko, R.R. Yafyasov, M.E. Mustafa, M. Schulz, M.V. Rybin, M. Eich, A.Y. Petrov

Advanced Optical Materials 2, 2100785 (2021).

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Reciprocal space engineering allows tailoring the scattering response of media with a low refractive-index contrast. Here it is shown that a quasiperiodic leveled-wave structure with well-defined reciprocal space and random real space distribution can be engineered to open a complete photonic bandgap (CPBG) for any refractive-index contrast. For these structures, an analytical estimation is derived, which predicts that there is an optimal number of Bragg peaks for any refractive-index contrast. A finite 2D or 3D CPBG is expected at this optimal number even for an arbitrarily small refractive-index contrast. Results of numerical simulations of dipole emission in 2D and 3D structures support the estimations. In 3D simulations, an emission suppression of almost 10 dB is demonstrated with a refractive index down to 1.38. The 3D structures are realized by additive manufacturing on millimeter scale for a material with a refractive index of n ≈ 1.59. Measurements confirm a strong suppression of microwave transmission in the expected frequency range.

DOI: 10.1002/adom.202100785

Efficient optomechanical mode-shape mapping of micromechanical devices

D. Hoch, K.-J. Haas, L. Moller, T. Sommer, P. Soubelet, J. Finley, M. Poot

Micromachines 12, 880 (2021).

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Visualizing eigenmodes is crucial in understanding the behavior of state-of-the-art micromechanical devices. We demonstrate a method to optically map multiple modes of mechanical structures simultaneously. The fast and robust method, based on a modified phase-lock loop, is demonstrated on a silicon nitride membrane and shown to outperform three alternative approaches. Line traces and two-dimensional maps of different modes are acquired. The high quality data enables us to determine the weights of individual contributions in superpositions of degenerate modes.

DOI: 10.3390/mi12080880

Growth of aluminum nitride on a silicon nitride substrate for hybrid photonic circuits

G. Terrasanta, M. Müller, T. Sommer, S. Geprägs, R. Gross, M. Althammer, M. Poot

Materials for Quantum Technology 1, 21002 (2021).

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Aluminum nitride (AlN) is an emerging material for integrated quantum photonics with its excellent linear and nonlinear optical properties. In particular, its second-order nonlinear susceptibility χ(2) allows single-photon generation. We have grown AlN thin films on silicon nitride (Si3N4) via reactive DC magnetron sputtering. The thin films have been characterized using x-ray diffraction (XRD), optical reflectometry, atomic force microscopy (AFM), and scanning electron microscopy. The crystalline properties of the thin films have been improved by optimizing the nitrogen to argon ratio and the magnetron DC power of the deposition process. XRD measurements confirm the fabrication of high-quality c-axis oriented AlN films with a full width at half maximum of the rocking curves of 3.9° for 300 nm-thick films. AFM measurements reveal a root mean square surface roughness below 1 nm. The AlN deposition on SiN allows us to fabricate hybrid photonic circuits with a new approach that avoids the challenging patterning of AlN.

DOI: 10.1088/2633-4356/ac08ed

On-chip quantum opticsand integrated optomechanics

D. Hoch, T. Sommer, S. Müller, M. Poot

Turkish Journal of Physics 44, 239 – 246 (2020).

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Recent developmentsin quantum computing and the growing interest in optomechanics and quantum opticsneed platforms that enable rapid prototyping and scalability. This can be fulfilled by on-chip integration, as we presenthere. The different nanofabrication steps are explained, and our automated measurement setup is discussed. We presentan opto-electromechanical device, the H-resonator, which enables optomechanical experiments such as electrostaticsprings and nonlinearities and thermomechanical squeezing. Moreover, it also functions as an optomechanical phaseshifter, an essential element for our integrated quantum optics efforts. Besides this, the equivalent of a beam splitter inphotonics-the directional coupler-is shown. Its coupling ratio can be reliably controlled, as we show with experimentaldata. Several directional couplers combined can realize the CNOT operation with almost ideal fidelity.

DOI: 10.3906/fiz-2004-20

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