Cancer metastasis remains a critical area of study within the field of cancer research. The tumor microenvironment (TME), comprising various cell types and the extracellular matrix (ECM), plays a...Show moreCancer metastasis remains a critical area of study within the field of cancer research. The tumor microenvironment (TME), comprising various cell types and the extracellular matrix (ECM), plays a pivotal role in controlling tumor initiation and progression. Here we show an investigation into the mechanical phenotype of Hs 578T breast cancer cells within the TME, focusing particularly on the role of cell-ECM interactions in modulating cellular traction forces. Hs 578T cells with an integrin- α2 (ITGA2) stable knockout were utilized, and the resulting pressures were compared between the control and knockout at different collagen concentrations. Attention is hence given to the ITGA2 and its role in mediating cell-ECM interactions. Through the utilization of elastic hydrogel microparticles as localized stress sensors and advanced microscopy techniques, we show that increasing the collagen concentration results in increased traction forces exerted by control breast cancer cells. Conversely, the traction forces by ITGA2 Hs 578T knockout cells remain unaffected by changes in collagen concentration. Also, a linear relationship between the traction and its standard deviation, regardless of the Hs 578T cell type and collagen concentration, is observed. The findings contribute to a deeper understanding of cancer biomechanics, offering insights into potential therapeutic targets for inhibiting metastatic spread in breast cancer.Show less
Surface acoustic wave (SAW) resonators can confine and enhance the displacement associated with SAW phonons. SAW resonators are useful in quantum technology, where they are used to enhance the...Show moreSurface acoustic wave (SAW) resonators can confine and enhance the displacement associated with SAW phonons. SAW resonators are useful in quantum technology, where they are used to enhance the coupling between a single phonon and a semiconductor quantum dot (QD). In this thesis, the fabrication process of SAW resonators on GaAs with acoustic mirrors based on aluminum Bragg reflectors, and an investigation into the relation between the finesse of a resonator and the thickness of the aluminum mirrors are detailed. For this purpose, three resonators identical in design apart from the thickness of their aluminum mirrors (35 nm, 50 nm, and 100 nm) are fabricated. The finesse of these resonators is derived by examining their acoustic resonance spectra and displacement maps. Both types of measurements are performed with a fiber-based scanning Michelson interferometer. It is found that losses associated with the resonator limit the finesse. The maximal finesse is found to be F ≈ 11 for the 100 nm resonator. Based on the measurement results, it is hypothesized that reducing the resonator length will lead to a decrease in propagation loss, thereby raising the upper limit of the finesse. This project has been a step towards the optical detection of thermal phonons, with its final goal to detect single phonons.Show less
Metamaterials feature specific properties that are not commonly found in nature. An example of such a property is input sequence sensitivity, or non-Abelian behavior. Here, we study the driving...Show moreMetamaterials feature specific properties that are not commonly found in nature. An example of such a property is input sequence sensitivity, or non-Abelian behavior. Here, we study the driving sequence dependent response of a non-Abelian metamaterial with four inputs. In previous research, these inputs were actuated with equal strength. However, in this thesis we take a novel approach by first pre-stressing the metamaterial by actuating one beam with a certain strength, and then sequentially actuating and deactuating another pair of beams using a different actuation strength. This allows us to "program" the non-Abelian response by using pre-stress. We explore this two-dimensional actuation space experimentally, and collect the ensuing behavior in a "phase diagram". We find that pre-stressing allows more complex sequential responses than without pre-stressing. In particular, pre-stressing can change the response to sequential actuation from non-Abelian to Abelian and vice-versa. Our work thus uncovers a viable strategy for externally tunable, or programmable, non-Abelian behavior.Show less
Surface acoustic waves (SAWs) propagate in piezoelectric materials and are generated by interdigital transducers (IDTs). SAW devices have applications in a variety of fields, under which...Show moreSurface acoustic waves (SAWs) propagate in piezoelectric materials and are generated by interdigital transducers (IDTs). SAW devices have applications in a variety of fields, under which telecommunication, biology and chemistry. The context of SAW devices in this research project is in quantum acoustics, in which the underlying idea is that quanta of sound waves (single phonons) can be used to transfer quantum information between different systems. As these systems often operate at GHz frequencies and are fabricated on Gallium Arsenide (GaAs) substrates, the goal of this research project is to fabricate (using electron-beam lithography) and characterize 1 GHz SAW devices on GaAs. The SAW emission by the IDTs is measured in the frequency domain, where good agreement is found with the coupling of modes model, allowing us to extract the SAW amplitude, the SAW velocity and the reflection coefficient of the IDT fingers. The IDTs are also measured in the time domain, were good agreement is found with the findings of the frequency domain measurements. Finally, a first step is made towards SAW resonators, which can enhance the SAW amplitudes significantly. This amplitude enhancement is crucial for quantum acoustics experiments, as high coupling between quantum dots and SAWs is needed. This project can therefore be thought of as the foundation for future quantum acoustics experiments.Show less
FUS (FUsed in Sarcoma) is a protein involved in gene expression. When a mutation occurs, FUS can build up in the cytoplasm and form droplets and fibers because of its prion-like domain. FUS protein...Show moreFUS (FUsed in Sarcoma) is a protein involved in gene expression. When a mutation occurs, FUS can build up in the cytoplasm and form droplets and fibers because of its prion-like domain. FUS protein droplets and fibers are thought to be involved in the development with brain diseases ALS and FTD, so uncovering of the kinetics of these fibers and droplets would aid in medicine development for these diseases. In this thesis, the fiber growth rate as a function of the FUS concentration in the dilute phase surrounding the fiber is measured, using confocal microscopy, by growing the fibers from FUS coated glass beads. This showed that the fiber growth rate in linearly dependent on the FUS concentrations. Secondly, the FUS droplets have been shown to age and harden over time. Here, a tentative attempt is made to quantify this hardening over time using micro rheology. This shows that this hardening indeed happens, but it is not quantifiable yet. These findings are particularly exciting as they suggest that fibril growth rate occurs through a mechanism that is contrary to that predicted from the current paradigm. Thus, this study set the foundation for a more complete physical picture of fibril growth and its alteration by condensates.Show less
The imaging of biological tissue is an important aspect to understand the human body and the processes taking place at small scales. Existing optical and electron microscopy techniques face trade...Show moreThe imaging of biological tissue is an important aspect to understand the human body and the processes taking place at small scales. Existing optical and electron microscopy techniques face trade-offs between resolution and beam damage. Optical near-field electron microscopy (ONEM) is a newly developed technique combining optical microscopy with electron microscopy. A sample is illuminated from the back with light in the visible spectrum, a near-field shadow is cast on a low workfunction photocathode. Photons are converted into electrons by the photoelectric effect and finally, the electrons exit the photocathode towards the detection optics. As a result, ONEM allows the imaging of (biological) samples without exposure to the damaging electron beam without being diffraction limited. We explore the preparation of samples suitable for ONEM experiments consisting of a fused silica substrate with an indium tin oxide (ITO) coating and a slice of biological tissue from a mouse tail. We create a cap over the biotissue from either single-layer graphene or amorphous carbon and finally, we grow a thin caesium photocathode in situ to lower the workfunction. Using a blue laser with a wavelength of 450 nm, we show for the first time that optical near-field electron microscopy can be used to image biological tissue. We can distinguish features in ONEM matching features in PEEM when overlapping the images. The resolution of these features is in the order of 100 nm when using a 5.7 μm field of view. Furthermore, we show that a carbon or graphene layer is required for ONEM imaging, yet this layer decreases the resolution of the PEEM image.Show less
Microcavities play a significant role in the study of cavity quantum electrodynamics (CQED), as they induce efficient coupling of light and matter. Confining matter within a cavity, increases the...Show moreMicrocavities play a significant role in the study of cavity quantum electrodynamics (CQED), as they induce efficient coupling of light and matter. Confining matter within a cavity, increases the probability of deterministic interactions between e.g. a (quantum) particle and the light cast into the cavity by a laserbeam. Cavity parameters such as cavity length and radius of curvature of the micromirror define the cavity regime and consequently the physical phenomena that can be observed, from the bad-cavity (Purcell) regime to the strong coupling regime. We are looking for a highly controllable and repeatable way of producing microcavities with a small mode volume and a high finesse. This translates into the creation of micromirrors with radii of curvature between 10 μm and 50 μm and a depth of up to 1 μm. We offer an overview of micromirror production methods; CO2 laser ablation, focused ion beam milling (FIB), direct laser writing and current controlled curvature. For CO2 laser ablation the key parameters to control the dimensions of the ablated structure, are the power of the laser and the beamwaist. We perform simulations of the ablation process and show that micromirrors with the desired dimensions can be obtained by using a CO2 laser in a range between 420-440 mW and a beamwaist of 40 μm. We find that for these parameters clipping loss is negligible. Therefore, CO2 laser ablation meets the criteria and proves to be a reliable way of producing micromirrors.Show less
In the process of metastasis, cancer cells may transmigrate through the endothelium barrier of the vascular walls and into the circulatory blood system. During this process, the cancer cells...Show moreIn the process of metastasis, cancer cells may transmigrate through the endothelium barrier of the vascular walls and into the circulatory blood system. During this process, the cancer cells interact with the endothelial cells, resulting in the alternation of their mechanical properties. Although this interaction has been broadly studied from the perspective of cancer cells, no thorough investigation of the endothelial mechanical properties has been performed. In this thesis, by using a micro-rheology AFM-based approach, we show that the properties of endothelial cells change when cultured in cancer cell conditioned medium, as well as when in contact with cancer cells. We found that the stiffness of endothelial cells increased when cultured in a low-dilution cancer cell medium, while it decreased in high-dilution medium. This change was also evident on the viscoelasticity of the cells, with the endothelial cells cultured in high dilution medium showing lower viscoelastic properties. Furthermore, endothelial cells in direct contact with a cancer cell showed an increased height, as a result of the cancer cell's transmigration through the monolayer. Our findings demonstrate that the properties of endothelial cells change indirectly due to cancer cell secreted substances, and directly during the cancer cells' physical transmigration. This indicates that the endothelium is actively responding to the presence of cancer cells, rather than being a passive barrier as once believed.Show less
Cyclically driving subharmonic units can result in emergent memory effects, and such systems have the potential to store information and perform computations. For this reason, we numerically...Show moreCyclically driving subharmonic units can result in emergent memory effects, and such systems have the potential to store information and perform computations. For this reason, we numerically investigated the response to cyclic driving of two linearly coupled toggling bits, which are an inherently subharmonic unit. We found that there are 380 topologically distinct two-t-bit systems. Cyclic driving sometimes resulted in subharmonic responses with emergent periods of T=3 and T=4, as well as nonzero transients (tau>0). A variety of different orbits is possible, but the behavior (tau, T)=(0, 2) inherent to the single toggling bit, remains common in systems of two t-bits. A period of T=4 already occurred for weakly coupled systems that can be manufactured in experiments. We also found the restriction that tau + T < 4. Lastly, we conclude that coupling strength strongly affects the likelihood of avalanches occurring. The findings demonstrate both the capabilities and limitations of coupled toggling bits, which will valuable for future research.Show less
This work explores axion-photon conversion in the TeV halo of the Geminga pulsar and in neutron star magnetospheres. Based on the observed synchrotron and inverse Compton scattering radiation, the...Show moreThis work explores axion-photon conversion in the TeV halo of the Geminga pulsar and in neutron star magnetospheres. Based on the observed synchrotron and inverse Compton scattering radiation, the magnetic field inside the Geminga pulsar TeV halo is constrained to be < 2 μG, similar to literature constraints. The photon-axion conversion probability is ≲ 10−8, requiring an extreme signal-to-noise ratio for detection. In contrast, significant flux transfer can take place in the strongly magnetised anisotropic plasmas of neutron star magnetospheres. Following up on recent literature, this work provides a three-dimensional calculation of axion-photon conversion in anistropic plasmas, including the Euler-Heisenberg photon-photon scattering contribution in the limit BNS ≪ Bc = 4.4 · 1013 G. This allows for resonant double lens conversion, through which axion-like particles of arbitrarily small mass can resonantly induce photons. For relativistic axions the resonance length scale can exceed other typical scales of change in the plasma, in which case the conversion region and probability is truncated. For very light, relativistic axions, non-resonant contributions are important. In the Goldreich-Julian model with relativistic plasma, double lens resonance can occur at observable radio frequencies in the 100 GHz−1 THz regime. NB: Erratum. The derivation in chapter 3 sets magnetic permeability mu=1. For double lens resonant conversion this is inconsistent. Upon including the correct expression for mu, the EH contribution to the resonance condition (Eq. 3.28) is slightly changed:14*eta*B^2 -> 22*eta*B^2. The error should, of course, also be incorporated in the whole derivation.Show less
There is a demand for high bandwidth down links from space to earth. A cubesat in a GEO could function as a relatively cheap access point to a high bandwidth communication channel with earth. This...Show moreThere is a demand for high bandwidth down links from space to earth. A cubesat in a GEO could function as a relatively cheap access point to a high bandwidth communication channel with earth. This thesis explores new ways to increase the bandwidth by identifying bottlenecks in the GEO- Earth communication channel and how to circumvent them. The diffrac- tion limit causes large beam spreading at GEO distance, holding back ad- vanced modulation techniques due to the inability to capture the whole wave front. In this case, a modulation scheme using only a few bits should be chosen, allowing to modulate as fast as possible. The low signal inten- sity can be detected with more sensitivity by making use of a quantum enhanced receiver. From GEO to Earth, data rates around 50 Gbps are possible. Additionally, the atmosphere introduces spatial incoherence. To mitigate the effects of the atmosphere, a modulation scheme should be chosen that exploits modulation vectors which are orthogonal to the spa- tial dimension, such as polarization or wavelength. This gives a modula- tion scheme with many degrees of freedom. To deal with the complexity, a variational auto-encoder deep neural network is used to act as the modu- lator and demodulator. The variational distribution is chosen to match the noise introduced by an atmospheric channel. Using this scheme, we were able to find encodings that increase the density of symbols in phase space relative to the noise. This approach is especially promising in a bandwidth limited channel.Show less
The application of denoising machine learning to STM data has several advantages, such as improving data quality, aiding visual interpretation of data, and speeding up measurement time. With...Show moreThe application of denoising machine learning to STM data has several advantages, such as improving data quality, aiding visual interpretation of data, and speeding up measurement time. With experimental data, the absence of a ground truth poses a problem for traditional supervised learning techniques. In this work, state-of-the art self-supervised machine learning techniques are applied to reduce noise in quasiparticle interference data of overdoped cuprates, using only the noisy measurements. The machine learning methods are shown to outperform traditional denoising methods. Further ideas to improve and generalize the denoising of quasiparticle interference data are proposed.Show less
We have developed a stereo video rig able to track particles in three dimensions to study the gas-like phase of an experimental granular media system driven by contact charge electrophoresis. We...Show moreWe have developed a stereo video rig able to track particles in three dimensions to study the gas-like phase of an experimental granular media system driven by contact charge electrophoresis. We use the stereo set-up to simultaneously capture the granular media gas-like 2D dynamics and the particle motion in the perpendicular driven direction. We find that melting of the crystalline order happens when two particles anti-synchronize their oscillation phase, attract due to opposite sign charges, and collide. The repeated occurrence of such events establish a sustained mechanism of energy injection from the driven direction to the XY plane, resulting in a stationary dilute gas-like phase. We explore the change in dynamics upon an increase of the driving field and find that the dynamics of the gas-like phase are unchanged if re-normalized by the period of oscillation in the driven direction. The developed stereo system has proved itself as a robust and crucial advance in the experimental techniques used to explore the physics of driven media, opening the door to perform experiments fully capturing both the driven and horizontal dynamics.Show less
Active particles that transform energy into directed or persistent motion show collective behavior and self-organization. One type of self-organization is in the form of crystal structures. However...Show moreActive particles that transform energy into directed or persistent motion show collective behavior and self-organization. One type of self-organization is in the form of crystal structures. However, an active crystal with tunable properties has not been achieved. Inspired by an experiment in which vibrated polar discs form ordered domains, and an experiment in which metallic spheres, that move by contact charge electrophoresis, form a passive crystal, we create active particles in the shape of a cylinder composed of a metallic and a dielectric part, that move thanks to Quincke rotation on the dielectric side and an electrostatic force on the metallic side due to an external electric field. We study the behavior of these particles by characterizing the persistence of their motion, their ability to repel each other, and by studying their instantaneous speed as a function of the electric field and their size. Our results suggest that the particles have the potential to form an active crystal and seem to be compatible with the passive crystal existent at our lab.Show less
Current imaging is crucial to condensed matter physics, materials research and industry. State-of-the-art current imaging setups revolve around SQUID-on-tip (SOT) probes, that scan over a sample to...Show moreCurrent imaging is crucial to condensed matter physics, materials research and industry. State-of-the-art current imaging setups revolve around SQUID-on-tip (SOT) probes, that scan over a sample to locally measure magnetic fields and temperature. The resolution of such systems is presently limited by the lack of a robust method to control the probe-sample distance. In this thesis, we develop probes for hybrid microscopy that combine SOT with STM. We theoretically investigate interesting systems, and find that our approach would considerably improve on past magnetic investigations of vortex matter. We use focused-ion-beam milling to fabricate SOT probes on top of a commercial AFM-cantilever, and show these to be very sensitive to changes in applied magnetic field and temperature. We develop a novel readout scheme to simultaneously measure a magnetic and a tunneling signal. We present a proof-of-concept STMSOT probe that displays magnetic sensitivity inside a cryogenic STM setup, and use it as an STM probe to see the topography of a NbSe$_2$ crystal. Our approach will culminate in the development of a STMSOT setup in the near future.Show less
