Quantum technologies

We demonstrate a method for determining the three-dimensional location of single atoms in a quantum gas microscopy system using a phase-only spatial light modulator to modify the point-spread function of the high-resolution imaging system. Here, the typical diffracted spot generated by a single atom as a point source is modified to a double spot that rotates as a function of the atom's distance from the focal plane of the imaging system. We present and numerically validate a simple model linking the rotation angle of the point-spread function with the distance to the focal plane. We show that, when aberrations in the system are carefully calibrated and compensated for, this method can be used to determine an atom's position to within a single lattice site in a single experimental image, extending quantum simulation with microscopy systems further into the regime of three dimensions.

In this thesis, I present a novel technique enabling three-dimensional localization of single atoms in an optical lattice up to sub-micrometer precision over an enhanced depth of field from a single experimental image. It consists of changing the microscope’s response to a point source, the so-called point spread function (PSF), such that it has an azimuthally structured shape, performing a rigid rotation along the observation axis, the angle of which provides information about the axial position. This is done by imposing on the collected fluorescence light a phase modulation built up from a superposition of Laguerre-Gauss modes in the pupil plane by a spatial light modulator (SLM). I demonstrate this method using the DQSIM quantum gas microscope with an engineered double-helix-shaped PSF. As I show, this enables axial resolution at the level of the vertical lattice separation of 532 nm even at lower numerical apertures while preserving the lateral resolution, overcoming the limitations of retrieving the axial position through the defocus alone.

In Chapter 1, I present the experimental setup of the DQSIM experiment in Chapter 2. I particularly address the aspects necessary for the understanding of the subsequent measurements, as well as my contributions to the setup. Chapter 3 is about my contributions to a deep horizontal lattice. In Chapter 4, I present the three-dimensional imaging of single atoms. I describe the technique of preparing atoms in a single plane, the concept of PSF, and the resolution limit. I then discuss existing methods of three-dimensional imaging, in particular the rotating PSFs. Finally, I present the experimental realization and the measurements performed. Chapter 5 draws a conclusion and gives an outlook to this thesis.

Diese Bachelorarbeit beschäftigt sich mit dem LCoS räumlichen Lichtmodulator (SLM). Dabei soll die durch Phasenmodulation erfolgende Holografie und der auf Amplitudenmodulation beruhende Aufbau der direkten Abbildung verglichen werden. Insbesondere liegt das Augenmerk auf der Verwendung des SLM zur Erstellung von Intensitätsmustern im zweidimensionalen optischen Gitter des 2D discrete quantum simulator (DQSIM). Es wurden dafür Muster mit beiden Modulationsmodi aufgenommen und analysiert. Die direkte Abbildung liefert im Vergleich zur Holografie Muster mit besserer Ebenheit, Auflösung und Hintergrund-Dunkelheit bei vergleichbarem Kontrast und Signal-Rausch- Verhältnis. Die Holografie kann jedoch je nach Muster eine höhere Lichtausbeute bieten.