Bachelor- and Master-projects

The main scientific goal in the YQO experiment is to study the quantum non-linear physics via engineering the photon-photon interaction by creating Rydberg polaritons in dense and ultracold Yb gas. Frequency noise of lasers used for Rydberg excitation can cause significant decoherence among Rydberg polaritons and photons. A standard Mach-Zehnder interferometer can be used to measure the frequency noise of a laser by translating frequency deviations to the intensity of the interference signal. In this project, you will build an interferometer for blue light at 399nm and 395nm, and use it to characterize the frequency noise of our lasers.

Optical fibers are used throughout science and technology to guide light over long distances. Standard fibers guide light inside their central core by total internal reflection. But when these fibers are heated and slowly pulled to sub-micron diameters, the light is guided as an evanescent field outside the fiber. Such nanofibers are ideal for integrated hybrid systems combining photons and atoms.

In this project, you will develop new methods to pull various fiber types to record thin diameters, aiming for >99% of the guided light to be outside the fiber. This is done in collaboration with fiber experts in Berlin and can include regular travel to or prolonged stays in Berlin.

Quantum optics experiments, including those conducted by the NQO group, rely on the efficient detection of single photons. Superconducting nanowire-based photon detectors can achieve detection efficiencies of up to 90%, representing a significant improvement over room-temperature detectors.

These detectors work by heating a nanowire when it is hit by a photon. This heating leads to a local breakdown of superconductivity. The increased resistance resulting from this breakdown leads to a change in current flow that can be detected using amplification electronics.

The NQO group has acquired a system containing eight nanowire detectors in a cryostat, to which photons are delivered via optical fibers. For this project, you will develop a data acquisition system capable of detecting photons and analyzing photon correlations with sub-nanosecond time resolution.

The current project of the Rb experiment is the study of a photon-photon interaction in a strong nonlinear medium. To make the photons interact with each other, we send them through a cold and dense atomic cloud of Rubidium 87 where they couple to a strongly interacting Rydberg state. Photons inside the medium propagate in a form of polaritons that have a strong interaction potential due to their Rydberg nature. 

The goal of our project is to study how the photons, due to the strong interaction, are evolving into different photonic modes, while propagating through the atomic cloud. This process can be imaged using a single photon sensitive camera – EMCCD camera. This camera allows us to take a snapshot of the outgoing light filed by collecting the emitted photons after the cloud on the camera chip.

Our team is looking for a Master student who will be directly involved into the main experiment. This is a great opportunity to take part in the process of a conduction of a modern scientific experiment and learn a lot of different skills in a field of experimental physics. 

In the hybrid quantum optics project, our aim is to interface ultracold Rydberg atoms and superconducting quantum circuits, including electromechanical oscillators with resonance frequencies in the gigahertz range. In order to achieve this, an ultra-cold cloud of atoms is trapped close to the surface of an atom chip that hosts the circuit. The first-generation chip to be used in the experiment features a classical microwave strip line resonator for studying the interaction between Rydberg atoms and a classical resonator positioned close to the surface of the chip.

Your project will involve designing and integrating a second-generation atom chip into the experiment. This chip will be capable of trapping ultra-cold rubidium atoms in a controllable position above the surface of the chip and will host an electromechanical oscillator close to its motional ground state, enabling the study of a large mechanical quantum system interacting with optically controlled ultra-cold Rydberg atoms.

A magneto-optical trap (MOT) is THE starting point for experiments with ultracold atoms. In the existing rubidium experiment, the MOT is loaded directly with atoms from a background gas. This is a compact and functional solution, but comes with a compromise: If the background gas pressure is ‘high’, the MOT loads fast and high atomic densities can be reached, but the probability of collisions limits the trapping time in later stages of the experiment.

Therefore, we are planning to upgrade the existing experimental setup with a two-dimensional MOT that delivers a flow of pre-cooled atoms (cooled only in two spatial directions, hence 2D) to the actual MOT region. A 2D MOT would allow the separation of the experimental setup into a high-pressure region and a low-pressure region, and greatly improve the number of atoms in the final rubidium MOT.

In this project, you will design and optimize the new 2D MOT chamber with Inventor, and design the 2D MOT optics. In this project, you will get to build and test your design for delivering ultracold atoms to the final MOT as a starting point for quantum optics experiments. 

In our YQO experiment, lasers with different wavelengths are locked to an ultralow expansion reference cavity. Other lasers are frequency stabilized by so-called offset locks relative to the cavity-stabilized master laser. The laser to be locked interferes with the master laser and the generated beatnote at hundreds of MHz is compared to a reference signal. An error signal is generated by a digital phase lock box, then sent into a PID controller that gives a feedback signal to the laser to correct any frequency drift. In this project you will lock our two new lasers at 339nm to a master laser by means of an offset lock, and characterize the lock quality in terms of short- and long-term stability.

Modern experiments in quantum optics (and virtually any other area) require the automated control of many interlinked output devices as well as precisely timed data recording. This is achieved by the combination of dedicated real-time computing hardware and custom-tailored control software. Features often include automated data taking for many days and experiment parameter adaptation via feedback, maximizing the possible data acquisition rate.

In this project, you will implement new computer control software in Python building on established concepts and hardware in our labs. This will combine device control, graphical user interface and network communication to automate the running of complex quantum optics setups.

In the YQO and RQO experiments, we create a dense atomic cloud by confining atoms in a crossed optical dipole trap. Two dipole trap beams with ~50μm waist are overlapped at a small angle at the center of the vacuum chamber to form the crossing region, and further aligned with a probe beam with 8μm beam waist.

The alignment is critical to the final atom number, atomic temperature, trap lifetime and optical depth. In this project you will develop a solution to automatize the alignment of the dipole trap and probe beams, using three reflection mirrors with motors or piezo actuators, aiming to achieve an alignment precision at ~μm level.