Research Phase and Master’s Thesis in the M.Sc. Quantum Science & Technology

An essential step for implementation of quantum computing architectures is an efficient readout of qubits. In the field of superconducting quantum circuits, this is typically realized by dispersively coupling a superconducting qubit to a microwave resonator. Then, the frequency of the resonator depends on the state of the qubit. The former can be extracted by probing the resonator with a coherent  tone. However, efficiency of this readout approach is fundamentally limited by quantum  laws. The corresponding threshold is commonly known as the standard quantum limit and bounds quantum efficiency of the readout process by 50%. Nevertheless, recent investigations have shown that it is possible to circumvent this limit and reach quantum efficiency of the qubit readout of 100% by exploiting broadband readout signal combined with Josephson parametric amplifiers.

The goal of this Master project is to build a proof-of-principle experimental setup and perform microwave cryogenic measurements on a superconducting transmon qubit in the broadband regime in order to demonstrate violation of the standard quantum limit in the dispersive readout.

Quantum technologies are on the verge of revolutionizing high-security communication owing to advanced protocols such as teleportation and remote-state preparation. Development of quantum local area networks (QLAN) is an important milestone in this field. Such a microwave QLAN can be realized as  superconducting transmission line cooled down to millikelvin temperatures.  In practice, this system requires careful characterization measurements with quantum signals propagating over the cryogenic link in order to determine the effective losses, noise level, and other imperfections.

In this work, the main goal is to investigate a new prototype of a quantum local area network (QLAN) established between two neighboring laboratories. This includes analysis of experimental results with theoretical and numerical methods. This project will provide you an excellent opportunity to gather expertise in a broad range of topics from quantum physics to microwave engineering and cryogenic techniques.

Quantum experiments often require fast and versatile data processing which allows for a quantum feedback operation. This approach opens the road to many fascinating experiments such as quantum teleportation, entanglement purification,  quantum error correction, among others. Here, we would like to develop a specific measurement and feedback setup, based on a field programmable gate array (FPGA), for experiments with propagating quantum microwaves.

The main goal is to program and experimentally test a specific image for an FPGA  which would allow for acquisition of microwave signals and feedback generation over few hundred of nanoseconds. This timescale is the prerequisite for exploiting quantum correlations effects for quantum communication and cryptography protocols with propagating squeezed microwaves which are conducted in our lab. This project will offer a deep insight into the state‑of‑the‑art FPGA devices, microwave measurements, and cryogenic experiments with superconductors.

The smaller a device is, the higher its resonance frequency becomes. For our future quantum optomechanics experiments we will be working with mechanical resonators that operate at GHz frequencies and simultaneously couple strongly to light. Using mechanical and optical band structure calculations, you will design, make, and measure phononic and photonic cavities. The project involves nanofabrication in the cleanroom, as well as using the extreme sensitivity offered by on-chip optomechanics. We are aiming for devices made from silicon nitride, which has a lot of tensile stress in it. For micromechanical structures this material gives much better mechanical properties compared to, for example, silicon devices. An important aspect of the project is to understand if this is also true for the high frequency devices.

In optomechanics, light is used to measure and alter the dynamics of mechanical resonators. It is by far the most sensitive method to observe the tiny vibrations that nanomechanical devices perform: in one second one can determine their position with femtometer precision! Using light to measure the mechanics is not the only aspect of optomechanics. The same light can also be used to change the dynamics of the mechanical device through a process called cavity backaction. The photons exert a force on the resonator, the so-called radiation pressure. In this project we want to explore the ultimate limits to this force. The goal is to measure the force originating from a single photon! For this it is required that the photon interacts with the mechanical resonator as strongly as possible. For this we need to the design and make very low loss optical cavities, such as microring resonators. Also, the mechanical device should have a quality factor as high as possible. You will make both the optical and mechanical components from chips with highly-stressed silicon nitride using state-of-the-art nanofabrication in the cleanroom. Then the devices are placed in a vacuum chamber for their measurement. In our highly-automated setup you can very quickly characterize many of the devices on your chip. Then, with the perfect device parameters you can start to explore the more advanced measurements. Initially we can measure the devices in with pulsed light, but by using single photons we want to explore the ultimate limits to optomechanical forces.

See http://www.groups.ph.tum.de/en/qtech/openings/ for a detailed description of this project.

Für den Betrieb des MADMAX Experimentes wurden Piezo Motoren entwickelt, die bei kryogenen Temperaturen (4 K) funktionieren und einen Hub von bis zu 1 m haben. Die ersten gelieferten Prototypmotoren müssen bei kryogenen Temperaturen getestet und auf verschiedene Betriebsparameter untersucht werden. Qualification of Piezo motors at cryogenic temperatures for the MADMAX axion dark matter experiment In the context of the MADMAX dark matter axion search experiment Piezo motors have been developed for operation at cryogenic temperatures (4 K) for a stroke of up to 1 m. The first prototype motors that have been delivered will need to be tested at cyrogenic temperatures and several parameters need to be investigated.

Masterarbeit: Simulation und Aufbau einer Überhöhungskavität für hohe optische Leistungen

Hast Du Dich schon mal gefragt, was passieren würde, wenn man einen Lichtpuls zwischen zwei Spiegeln einfängt? Genau das wollen wir versuchen und damit die Grenzen der Physik im Bereich der hohen Laserleistungen ausloten. Ziel des Projektes ist eine Verbesserung von MuCLS, einer kompakten, aber brillanten Lichtquelle. Diese liefert Röntgenpulse durch inverse Comptonstreuung von Elektronen an Laserpulsen. Um die Intensität, die Wellenlänge und allgemeine Einsatzmöglichkeiten der Lichtquelle zu erweitern, beschäftigen wir uns mit einem Upgrade der Überhöhungskavität.

Aktuell sind wir dabei das Design des experimentellen Aufbaus zu finalisieren. Deine Aufgabe wird es sein, mit uns das Konzept umzusetzen. Das beinhaltet das Setup aufzubauen und zu testen. Gleichzeitig werden Simulationen durchgeführt werden, zum Beispiel um den Einfluss der Krümmungsradien der Spiegel besser zu verstehen. Die Ergebnisse werden direkt auf die Verbesserung des Aufbaus übertragen. Schlussendlich erhoffen wir uns das erste Mal eine Finesse von 30.000 in der grünen Überhöhungskavität zeigen zu können.

Alles Weitere erfährst Du bei einem persönlichen Gespräch.

Masterthesis: Simulation and Setup of a high-power laser enhancement cavity

Have you ever asked yourself what would happen if you trap a pulse of light in between two mirrors? This is exactly what we are planning to do and thereby determine the boundaries of high-power laserphysics. The project as a whole is embedded in the frame of MuCLS, a compact but brilliant light source. This light source generates X-ray pulses by inverse Compton scattering of electron on a laser pulse. Upgrading the intensity, wavelength and overall quality of the laser pulse is the goal here in order to extend the range of applications.

Currently, we are finalizing the design of the overall experimental setup. Your task would be to support us in transforming the concept into reality. This includes building the setup and testing it. Meanwhile some simulations on different parameters such as the radius of curvature of the mirrors will have to be performed. The results will directly influence and improve the setup. In the end, we hope to show a finesse of 30.000 in the laser cavity.

If you are interested, feel free to get in touch.

Im Rahmen des MADMAX Projektes zur Suche nach dunkler Materie Axionen werden verschiedene
Testaufbauten bei Raumtemperatur und in flüssigem Helium (4 K)
zur Kalibrierung und zur Untersuchung der genauen Signalantwort des
experimentellen Aufbaus betrieben. Es werden Reflektionsdaten Daten
genommen und ausgewertet.

In the frame work of the MADMAX projects several test stands at room tamperature and in liquid helium
for the investigation of the detailled system response and for calibration of the setup are being operated. Reflectivity data will be atken and analyzed.