Well isolated mechanical systems have the potential to be developed into systems for magnetic, accelerometric and gravitational sensing, as well as to investigate the limits of quantum theory. This...Show moreWell isolated mechanical systems have the potential to be developed into systems for magnetic, accelerometric and gravitational sensing, as well as to investigate the limits of quantum theory. This holds especially for mechanical resonators which consist of levitated nano- and microparticles, since an advantage of this type of system is the lack of clamping losses, potentially resulting in an extremely low energy dissipation. Here, a mechanical resonator is presented, where a magnetic microparticle is levitated in a cylindrical trap of a type I superconductor. SQUID detection has been used to measure the vibrational modes of the particle. The damping factors of the resonator have been analytically calculated, resulting in an expected quality factor Q of 10^11. The coupling and energy of the six translational and rotational rigid body modes of the particle have been simulated, based on analytical approximations. Experimentally, a resonance is detected with a damping time of 47 seconds and a Q of 2.2*10^4. These are promising first results, since this difference in damping and Q factor can be explained as the Earth's magnetic field was trapped inside the experiment. With these complications resolved, an extremely sensitive micromechanical resonator can be developed. This opens a new road in the investigation of the boundary between the quantum and classical regime and gravitational research.Show less
To find good upper bounds for the CSL model by measuring the force noise on a cantilever, the thermal noise should be minimized. To achieve millikelvin temperatures a nuclear demagnetization stage...Show moreTo find good upper bounds for the CSL model by measuring the force noise on a cantilever, the thermal noise should be minimized. To achieve millikelvin temperatures a nuclear demagnetization stage can be used, which should be thermally connected to the cantilever through a heat link. In this thesis we attempt to design a thermometer for sub-Kelvin temperatures to test this future heat link. The thermometer designed consists of an LC resonator with a high Q factor placed in series with the input coil of a dc SQUID. The inductor used is a 270 5 mH niobium wire inductor and the capacitor is an 80 pF niobium plate capacitor. A metal foil is coupled to the resonator coil, which limits the Q factor and induces a Johnson noise in the coil according to the fluctuation-dissipation theorem. This thermometer should work for temperatures down to 1 mK. However, we were not able to measure a resonance peak with the resonator attached to the SQUID input coil. To find the cause of this and determine if this thermometer design is viable, more research is needed.Show less
Multiport interferometers are an important tool in the emerging field of quantum information technologies. In theoretical work, we investigate implementing Haar-random unitary transformations in...Show moreMultiport interferometers are an important tool in the emerging field of quantum information technologies. In theoretical work, we investigate implementing Haar-random unitary transformations in increasingly large interferometers with realistic imperfections. We find that random matrices result in mostly low values of interferometer beam splitter reflectivities. We model production imperfections and we find that these severely limit the implementation of random matrices. We show the effects of the imperfection can be mitigated through optimisation of interferometer degrees of freedom and by adding additional beam splitters. In experimental work, we investigate the realisation of reconfigurable multiport interferometers in silica-on-silicon integrated photonics chips using a modular design. We show that individual modules are fully reconfigurable. We give a proof-of-principle of the design by connecting three modules for the first time and measure 5% transmission.Show less
In this thesis, the necessary elements to build up a quantum switch, the central element in a quantum random access memory, are proposed and analyzed. A network with quantum switches at its nodes...Show moreIn this thesis, the necessary elements to build up a quantum switch, the central element in a quantum random access memory, are proposed and analyzed. A network with quantum switches at its nodes forms the bifurcation path that leads an address register from a root node to an array of memory cells, activating, quantum coherently, only the quantum switches that the register encounters in its path to the memory cells. Transmon qubits and SQUIDs are used to design a superconducting device capable of routing a register of microwave photons through a bifurcation network, allowing for superposition of paths. In order to give rise to all the required interactions between the device and the address register, a non-linear capacitor, composed of two plates with carbon nanotubes in between, is introduced into the transmon. The dynamic operation of the quantum switch is analyzed using Langevin equations and a scattering approach, and probabilities of reflection and transmission of photons by (or through) the switch are computed, both for single- and two-photon processes. Computations show that, with parameters taken from up-to-date similar devices, probabilities of success are above 94%. Applications of quantum random access memories are discussed, as well as other applications of quantum switches. Also, solutions are proposed to the challenges that emerge during the study of the dynamics of the quantum switch.Show less
