Dark Matter Detection with the Dark Matter Time Projection Chamber Collaboration

Evidence from many sources suggests that dark matter (matter that does not interact electromagnetically) accounts for a significant fraction of the mass density of the universe. The fact that dark matter has yet to be observed directly is one of the biggest outstanding problems in modern physics. Directional detection, one of the many branches of dark matter searches, involves reconstructing the direction of an incoming dark matter particle through observations of its interaction with a standard model particle. The work described in this thesis was completed as a part of the Dark Matter Time Projection Chamber (DMTPC) collaboration, a group working to create a directional dark matter detector. DMTPC detectors are designed to produce both a charge signal and scintillation light (detected by PMTs and CCDs) when an ionization event occurs within the volume of the detector. In this thesis, we present the results of a study conducted to characterize the radial decrease in image intensity (termed “vignetting”) for the CCD/lens system used in DMTPC’s directional detector at Bryn Mawr College. Additionally, we describe the work involved in setting up this detector, including upgrading the time projection chamber hardware and designing a light-tight mount for the optical instruments

Dark Matter Detection with the Dark Matter Time Projection Chamber Collaboration

Evidence from many sources suggests that dark matter (matter that does not interact electromagnetically) accounts for a significant fraction of the mass density of the universe. The fact that dark matter has yet to be observed directly is one of the biggest outstanding problems in modern physics. Directional detection, one of the many branches of dark matter searches, involves reconstructing the direction of an incoming dark matter particle through observations of its interaction with a standard model particle. The work described in this thesis was completed as a part of the Dark Matter Time Projection Chamber (DMTPC) collaboration, a group working to create a directional dark matter detector. DMTPC detectors are designed to produce both a charge signal and scintillation light (detected by PMTs and CCDs) when an ionization event occurs within the volume of the detector. In this thesis, we present the results of a study conducted to characterize the radial decrease in image intensity (termed “vignetting”) for the CCD/lens system used in DMTPC’s directional detector at Bryn Mawr College. Additionally, we describe the work involved in setting up this detector, including upgrading the time projection chamber hardware and designing a light-tight mount for the optical instruments

Quantum control via a genetic algorithm of the field ionization pathway of a Rydberg electron

Quantum control of the pathway along which a Rydberg electron field ionizes is experimentally and computationally demonstrated. Selective field ionization is typically done with a slowly rising electric field pulse. The $(1/n^*)^4$ scaling of the classical ionization threshold leads to a rough mapping between arrival time of the electron signal and principal quantum number of the Rydberg electron. This is complicated by the many avoided level crossings that the electron must traverse on the way to ionization, which in general leads to broadening of the time-resolved field ionization signal. In order to control the ionization pathway, thus directing the signal to the desired arrival time, a perturbing electric field produced by an arbitrary waveform generator is added to a slowly rising electric field. A genetic algorithm evolves the perturbing field in an effort to achieve the target time-resolved field ionization signal.Comment: Corrected minor typographic errors and changed the titl

Improving the State Selectivity of Field Ionization With Quantum Control

The electron signals from the field ionization of two closely spaced Rydberg states of rubidium-85 are separated using quantum control. In selective field ionization, the state distribution of a collection of Rydberg atoms is measured by ionizing the atoms with a ramped electric field. Generally, atoms in higher energy states ionize at lower fields, so ionized electrons which are detected earlier in time can be correlated with higher energy Rydberg states. However, the resolution of this technique is limited by the Stark effect. As the electric field is increased, the electron encounters numerous avoided Stark level crossings which split the amplitude among many states, thus broadening the time-resolved ionization signal. Previously, a genetic algorithm has been used to control the signal shape of a single Rydberg state. The present work extends this technique to separate the signals from the 34s and 33p states of rubidium-85, which are overlapped when using a simple field ramp as in selective field ionization

Improving the state selectivity of field ionization with quantum control

The electron signals from the field ionization of two closely-spaced Rydberg states of \mbox{rubidium-85} are separated using quantum control. In selective field ionization, the state distribution of a collection of Rydberg atoms is measured by ionizing the atoms with a ramped electric field. Generally, atoms in higher energy states ionize at lower fields, so ionized electrons which are detected earlier in time can be correlated with higher energy Rydberg states. However, the resolution of this technique is limited by the Stark effect. As the electric field is increased, the electron encounters numerous avoided Stark level crossings which split the amplitude among many states, thus broadening the time-resolved ionization signal. Previously, a genetic algorithm has been used to control the signal shape of a single Rydberg state. The present work extends this technique to separate the signals from the $34s$ and $33p$ states of rubidium-85, which are overlapped when using a simple field ramp as in selective field ionization

Perturbed Field Ionization for Improved State Selectivity

Selective field ionization (SFI) is used to determine the state or distribution of states to which a Rydberg atom is excited. By evolving a small perturbation to the ramped electric field using a genetic algorithm, the shape of the time-resolved ionization signal can be controlled. This allows for the separation of signals from pairs of states that would be indistinguishable with unperturbed SFI. Measurements and calculations are presented that demonstrate this technique and shed light on how the perturbation directs the pathway of the electron to ionization. Pseudocode for the genetic algorithm is provided. Using the improved resolution afforded by this technique, quantitative measurements of the 36p3/2 + 36p3/2 --\u3e 36s1/2 + 37s1/2 dipole–dipole interaction are made