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
Superchirality is a property of light with not yet fully discovered future possibilities in industry and research. In this research, an attempt to obtain a bright superchiral lattice is made by...Show moreSuperchirality is a property of light with not yet fully discovered future possibilities in industry and research. In this research, an attempt to obtain a bright superchiral lattice is made by superposing four laser beams in a particular configuration. Additionally, this superposition should theoretically lead to homogeneous electric fields without modulation, which is potentially useful in microscopy. Recording the field with a simple CMOS camera and observing its fast Fourier transform gives rise to aliasing effects due to undersampling caused by the fact that interference occurs at a subpixel level. This phenomenon is investigated by numeric and analytic simulations. By rotation of the camera, pixel superresolution was achieved, which effectively enables the possibility to investigate the interference patterns at a subpixel level and hence measure the angle between pair of beams with good accuracy. With newly developed beam alignment methods we have achieved and confirmed a beam alignment that is sufficient for production of bright superchirality lattices.Show less
Efficient single-photon sources based on semiconductor quantum dots typically rely on resonant excitation schemes with a high degree of control. In particular, having access to continuous-wave (CW)...Show moreEfficient single-photon sources based on semiconductor quantum dots typically rely on resonant excitation schemes with a high degree of control. In particular, having access to continuous-wave (CW) and pulsed excitation without changing the center frequency is highly desirable. CW excitation is useful for alignment and characterization, while pulsed excitation is essential for on-demand single-photon production. We present a technique based on ultra-fast electro-optic modulation to directly synthesize optical pulses from a narrow linewidth CW laser. With custom-built ultra-fast electronics, we demonstrate tunable pulse lengths down to 50 ps. Pulses longer than 100 ps achieve a typical extinction ratio of 300, and the 50 ps pulses still show an extinction ratio of 150. We then use these pulses to excite a single InAs quantum dot in a micropillar cavity and show the generation of true single photons. This technique allows for full control over the experiment in the temporal-spectral domain, and is significantly simpler compared to using conventional Ti:Sa mode-locked laser oscillators in combination with grating-based pulse shaping.Show less
The quantum interference between two photons has been widely studied since the demonstration of the Hong-ou-Mandel effect in 1987. In this project, we focus our attention on a particular variation...Show moreThe quantum interference between two photons has been widely studied since the demonstration of the Hong-ou-Mandel effect in 1987. In this project, we focus our attention on a particular variation of the latter effect: the interference of a single photon and a coherent state. This process leads to the generation of displaced photon number (Fock) states. Here, we study the process analytically and numerically and propose an experimental realization using a highly reflective beam splitter and single photons generated by a quantum dot. We analyze the effect of single-photon brightness and find a universal behaviour in the second-order correlation function. Applying a quantum master equation approach, we can predict the effects of the partial distinguishability of the interfering light states. As a final point, we also show the possible applications of the generated displaced Fock states, from the optimization of quantum key distribution (QKD) protocols to a new way to determine the brightness of single-photon sources.Show less
Authentication of a communication channel usually requires that the parties meet physically; but there is one solution if it is enough to confirm the geographical location of a party: quantum...Show moreAuthentication of a communication channel usually requires that the parties meet physically; but there is one solution if it is enough to confirm the geographical location of a party: quantum position verification (QPV). This is based on quantum mechanics, the no-cloning theorem, and special relativity, the invariance of the speed of light. We shown an extension of a QPV protocol where quantum information is communicated via the polarization state of single photons including the effects of photon loss and polarization noise, and explore it by numerical simulations. Moreover, we have designed and implemented the first steps of a QPV demonstration using optical fibers. We have been able to calibrate the setup for horizontal and vertical polarization states where a visibility of approximately 0.85 has been measured.Show less
A common problem in Magnetic Resonance Force Microscopy (MRFM) is the spin-induced damping of the cantilever, which drastically limits the sensitivity to spin signals. In order to solve this...Show moreA common problem in Magnetic Resonance Force Microscopy (MRFM) is the spin-induced damping of the cantilever, which drastically limits the sensitivity to spin signals. In order to solve this problem, we have developed improvements to a Persistent Current Switch (PCS) that make it less dissipative and capable of creating a stronger magnetic field at the sample. On top of this, the low noise level that our detection setup requires is conserved. The improvements are based on the use of a low-temperature magnetic core material called MetGlas [1]. We have measured the full B-H curve of the MetGlas and verified that it decreases the current required to switch a Niobium wire to the resistive state by a factor of 30. Furthermore, we have used this data to calculate the performance of a transformer made using this material, and we have calculated the expected extremely low noise level that this circuit will cause in our SQUID.Show less
