Student Projects

A spherical nanoparticle trapped in a conservative potential (e.g. a laser tweezer or an rf Paul trap) oscillates along the x, y and z axes (translational degrees of freedom). An elongated nanoparticle (e.g. rod, ellipsoid or dumbbell) exhibits additional degrees of freedom. For example, it can librate (wiggle) around an external axis (e.g. electric field) [1] or it can rotate around its short or long axes [2]. These additional modes enrich the dynamics of trapped nanoparticles and offer exciting applications in sensing (e.g. pressure or rotation). The objective of this project is to synthesize monodisperse solutions of elongated silica nanoparticles following established recipes [3,4]. The nanoparticles will be analyzed with electron microscopy and their mode structure will be studied in optical traps operated in high vacuum.

References: [1] F. van der Laan, F. Tebbenjohanns, R. Reimann, J. Vijayan, L. Novotny and M. Frimmer, “Sub- Kelvin feedback cooling and heating dynamics of an optically levitated librator,” Phys. Rev. Lett. 127, 123605 (2021). [2] J. A. Zielinska, F. van der Laan, A. Normann, R. Reimann, M. Frimmer and L. Novotny, “Longaxis spinning of an optically levitated particle: A levitated spinning top,” Phys. Rev. Lett. 132, 253601 (2024). [3] P. M. Johnson, C. M. van Kats and A. van Blaaderen, “Synthesis of colloidal silica dumbbells,” Langmuir 21, 11510–11517 (2005). [4] H. Zhang, T. J. Bandosz and D. L. Akins, “Template-free synthesis of silica ellipsoids,” Chem. Commun. 47, 7791–7793 (2011).

Prerequisites: Chemistry, materials science and analytical techniques.

Lukas Novotny (lukas.novotny@ethz.ch), Jonas Ziegler (zieglerj@ethz.ch)

The study of quantum systems relies on effective vibration isolation, as vibrations serve as a source of environmental decoherence. Vibrational isolation is particularly challenging in cryostats, which ensure low temperature and high vacuum conditions [1,2]. This project focuses on improving the vibration isolation system for a hybrid electro-optical trap, designed to trap and manipulate nanoparticles. A key aspect of the project involves assessing the mechanical properties of the suspension springs at 4K. The main goal of this project is to measure and characterize vibrations of the suspended system with pm/Hz−1/2 sensitivity using an optical interferometer. The work will involve testing the system’s performance under various conditions, refining its design enhancing its functionality.

References: [1] Radebaugh. "Cryocoolers: the state of the art and recent developments." Journal of Physics: Condensed Matter 21.16 (2009): 164219. [2] Brandl, et al. "Cryogenic setup for trapped ion quantum computing." Review of Scientific Instruments 87.11 (2016).

Prerequisites: Knowledge of optics and electronics, practical lab skills, quantitative approach.

Supervisor: Martin Colombano (mcolombano@ethz.ch)

Interferometry is a cornerstone of experimental optics, with applications spanning from holography to gravitational wave detection [1]. Interferometers are employed in spectroscopy for analyzing the spectral composition of light with high resolution. Among various configurations, the Michelson interferometer stands out for its simplicity and versatility [2]. This project aims to construct a compact Michelson interferometer with phase stabilization [3]. The project will involve designing and building the interferometer, implementing a phase stabilization system, and demonstrating its ability to achieve stable operation above the shot noise limit. It will involve active feedback control to maintain phase stability in the presence of environmental disturbances.

References: [1] E. M. McDonnell and L. L. Deck, Opt. Manuf. and Test. 114870J (2020) [2] A. Michelson and E. W. Morley, Amer. J. Sci. 38, 181 (1889) [3] M.S. Elezov et al J. Phys.: Conf. Ser. 1124 051014 (2018)

Prerequisites: Knowledge and interest in optics and electronics, practical lab skills, quantitative approach.

Supervisor: Martin Colombano (mcolombano@ethz.ch)

High-precision measurements often require synchronization with external signals to reduce noise and ensure accurate data acquisition. In our experiment, a nanoparticle is levitated using optical fields within a cryostat operating at 4K. This setup demands a specific electronic system capable of precisely triggering measurements to align with the 50 Hz cycle of the main power line. Synchronization to this frequency is essential to minimize noise and ensure consistent experimental conditions. The aim of this project is to design and implement an electronic system to measure the 50 Hz signal from the main power line and generate an output signal at a user-defined frequency, while maintaining synchronization with the original 50 Hz signal. This system will provide the group with a robust tool for triggering measurements and stabilizing data acquisition processes. In this project, you will design a circuit, likely using a microcontroller (e.g.Arduino), to synchronize a measurement signal to a 50 Hz signal. You will test the accuracy of the system and evaluate its performance under different experimental conditions.

Prerequisites: Good knowledge of and strong interest in optics and electronics, practical lab skills, quantitative approach.

Supervisor: Martin Colombano (mcolombano@ethz.ch)

Many systems that utilize laser beams, such as most optical traps [1], operate in free space on optical tables. The optical table helps dampen vibrations, and when all components are well clamped, they are referenced to the table. In this case, any remaining vibrations will affect all optical elements in the same manner. Now consider the situation where the optical trap itself vibrates or drifts relative to the laser beam. Without a common reference point, the focus quality and, consequently, the trap performance degrade, resulting in lower trapping stiffness and reduced trapping frequencies. This can occur, for example, if the trap is placed inside a cryostat [2], where the cooling process leads to the contraction of materials. Even small contractions, such as 1-2 mm, can misalign the system significantly. Such misalignments must be corrected to maintain optimal performance. The goal of this semester project is to build a prototype of a beam tracking system. First, you will assemble a setup that simulates the drifts of the trap assembly inside a cryostat and characterize the variations in the transmitted signal through the trap as the assembly is moved. Next, using the detected signal, you will implement a feedback system to control the position of the beam by adjusting mirrors in front of the trap (see Figure 1). This step will involve coding a feedback-based mechanism. A solid understanding of optics, along with a strong interest in system integration and programming, is essential. Additionally, you should have a quantitative mindset and be a critical, independent thinker who enjoys contributing to a larger team research effort.

References: [1] Ashkin, Physical Review Letters 24.4 (1970):156 [2] Dubielzig, et al., Review of Scientific Instruments 92.4 (2021)

Prerequisites: Good knowledge of and strong interest in optics, coding skills, quantitative approach.

Supervisor: Louisiane Devaud (ldevaud@ethz.ch)

Levitated silica nanoparticles are used to explore quantum mechanics at macroscopic scales. A big scientific goal is the entanglement of two distant nanoparticles. Recently, two milestones towards entanglement have been reached: Ground state cooling of a single nanoparticle [1] and the strong coupling of two nanoparticles [2]. The interplay of coupling between nanoparticles and their cooling performance is object of current studies. As both effects are dependent on the phase of the optical tweezers [3], precise phase control is necessary to pave the way towards entanglement. The goal of this semester project is to implement a phase lock between the tweezers levitating two nanoparticles. You will build an interferometric detection of both tweezers and use the output to generate a feedback signal and set the relative phase of the light fields. During your work on an established setup, you should be able to integrate yourself into the experimental team and contribute to the larger research effort. You should bring prior knowledge of optics and electric feedback control, strong interest in independent problem solving and critical thinking to effectively complete your project.

References: [1] Piotrowski et al., Nature Physics 19, 1009 (2023) [2] Vijayan et al., Nature Physics 20, 859 (2024) [3] Rieser et al., Science 377, 987 (2022)

Prerequisites: Basic knowledge of optical components and electrical feedback circuits, ability to integrate into and communicate with the cavity team.

Supervisor: Lorenzo Dania (ldania@ethz.ch)