Student Projects

Laser-induced acoustic desorption (LIAD) makes use of intense laser pulses to desorb materials from a surface. In particular, it can be employed to knock away nanoparticles deposited on a reflecting substrate [1]. The objective of this project is to desorb 100nm SiO2 nanoparticles from a target and to trap a single one in a near-by optical trap (a strongly focused laser beam) [2]. In this project, an existing setup will be further developed and the efficiency of desorption and trapping will be investigated as a function of system parameters, such as local potentials, distance between target and trap, vacuum pressure and laser intensities. References: [1] D. S. Bykov et al., “Direct loading of nanoparticles under high vacuum into a Paul trap for levitodynamical experiments”, Appl. Phys. Lett. 115, 034101 (2019). [2] J. Gieseler, B. Deutsch, R. Quidant and L. Novotny, “Sub-Kelvin parametric feedback cooling of a laser-trapped nanoparticle,” Phys. Rev. Lett. 109, 103603 (2012). Prerequisites: Experimental skills, electronics and measurement techniques.

Thomas Dinter (dinter@ethz.ch), Lorenzo Dania (ldania@ethz.ch)

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)

An elongated nanoparticle in a linearly polarized electric field aligns its axis of largest polarizability with the field’s polarization direction. Small angular motion from equilibrium -or librations- can be modelled as excitations in a harmonic potential [1]. Recently, the libration motion of optically-levitated nanoparticles has been cooled to the quantum ground state [2], opening the door to using levitated librators as a quantum technology. However, to preserve quantum coherence for a useful duration, the libration frequency must remain stable. The libration frequency of a nanoparticle scales with the intensity of the electric field. Therefore, a noisy electric field results in a gittering libration frequency. The objective of this project is to build an intensity-noise eater and use it to stabilize the libration frequency of an optically levitated nanoparticle. Figure 1 shows a sketch of the experimental setup. The work is divided into two steps: 1) The first step consists of measuring the intensity noise of a laser beam and build a feedback system to stabilize the laser power. The feedback is composed of an optical modulator controlled by a FPGA card; 2) The second step consists of using the intensity-stabilized laser to trap a nanoparticle, and study how the feedback affects its libration-frequency stability. References: [1] Thai M. Hoang et al., “Torsional Optomechanics of a Levitated Nonspherical Nanoparticle”, Phys. Rev. Lett. 117, 123604 (2016) [2] L. Dania et al., “High-purity quantum optomechanics at room temperature”, arXiv:2412.14117 (2024). Prerequisites: Knowledge and interest in optics and electronics, practical lab skills, quantitative approach.

Supervisors: Oscar Schmitt Kremer (oschmitt@ethz.ch), Lorenzo Dania (ldania@ethz.ch)

Ultra-high-vacuum (UHV) cryogenic experiments require vibration levels below the picometre scale. This requirement is especially critical in hybrid levitodynamics, where even sub-nanometre motion can significantly heat a levitated nanoparticle and destroy its coherence. In earlier work, we showed that a six-spring suspended optical trap operated in air effectively attenuates vibrations introduced by external shakers. The logical next step is to install this suspension inside a cryostat-compatible UHV chamber and verify that optical trapping remains stable while the platform suppresses pump-induced noise. This project aims to integrate the existing isolation stage into the vacuum chamber and demonstrate that it supports sustained optical levitation of nanoparticles. This effort entails re-measuring the springs’ resonances and quality factors at reduced pressure, aligning a high-numerical-aperture optical trap inside the chamber, and recording the particle displacement spectrum. By correlating the particle’s centre-of-mass motion with the measured platform dynamics under different conditions, we will quantify how efficiently the isolation scheme rejects vibrations transmitted through the vacuum hardware. Reaching these objectives will confirm that the suspended platform satisfies the stringent demands of hybrid trapping [1], enabling long-term coherent control, reheating measurements in the dark using the Paul trap, and ultimately efficient frequency jump protocols involving optical and RF traps. The work requires for expertise in experimental physics, mechanical design, and optics. References: [1] Gonzalez-Ballestero, Carlos, et al. Levitodynamics: Levitation and control of microscopic objects in vacuum. Science, 2021, vol. 374 Prerequisites: Good knowledge of and strong interest in optics and practical lab skills.

Supervisor: Martin Colombano (mcolombano@ethz.com)