Research Proposal for an Experiment to Search for the Decay {\mu} -> eee

We propose an experiment (Mu3e) to search for the lepton flavour violating decay mu+ -> e+e-e+. We aim for an ultimate sensitivity of one in 10^16 mu-decays, four orders of magnitude better than previous searches. This sensitivity is made possible by exploiting modern silicon pixel detectors providing high spatial resolution and hodoscopes using scintillating fibres and tiles providing precise timing information at high particle rates.Comment: Research proposal submitted to the Paul Scherrer Institute Research Committee for Particle Physics at the Ring Cyclotron, 104 page

Strong-field effects on singly excited vibronic resonances in the hydrogen molecule.

Studies of the hydrogen molecule interacting with ultrashort laser pulses allow for the understanding of many molecular quantum phenomena in the simplest possible molecule. In a transient-absorption experiment with H2 in the spectral range 13-17eV, transitions from the molecular ground state to the electronically excited B, C and D states are driven by extreme-ultraviolet (XUV) light, and a second near-infrared (NIR) laser is then used to access other dark states. The aim of this project is to implement the simplest possible multi-level simulation based on light-matter interaction theory which can already reproduce the experimental results, and understand with it the importance of different excited-state couplings to the changing absorption features. The included energy levels of the eigenstates of H2 are calculated numerically, as well as the dipole matrix elements for the considered transitions. Intensity-dependent changes in the XUV absorption spectrum in the presence of a moderately strong NIR field are observed, as well as changes in the revival time of the simulated wavepacket of the D states. In order to obtain Fano line-shaped resonances, different implementations of a predissociating continuum are examined. And finally, the effects introduced by a changing time delay between the two pulses are studied

Neutron Spectroscopy of the Parity-Violating 0.734 eV Neutron Resonance in Lanthanum-139 in Preparation for the NOPTREX Time Reversal Violation Experiment

One of the most outstanding questions in physics is the matter-antimatter asymmetry of the Universe, resulting from excess baryogenesis processes during the early moments of the formation of the Universe. At present, the types of processes needed to explain this matter excess, so-called `CP-violating processes\u27 are known to exist within the present framework of the Standard Model of particle physics. However, decades of research has shown that our understanding of the origin of these processes is incomplete, as we do not presently know of enough sources of CP-violating processes to account for the large baryon asymmetry that we observe. The Neutron Optics Time Reversal EXperiment (NOPTREX) collaboration was formed to investigate the existence of possible CP-violating processes in compound neutron-nuclear resonance scattering reactions in which large parity-violating effects are observed. One of the most crucial elements of the NOPTREX experiments is defining the optimal nuclear scattering target material. This work centers on the characterization of the most promising candidate nucleus for such an investigation, 139La; in particular, we focus on the experimental efforts to measure the longitudinal parity violation present in the 0.734 eV neutron resonance that took place at Flight Path 12 at the Los Alamos Neutron Science Center (LANSCE) from 2017-2020

State readout of single Rubidium-87 atoms for a loophole-free test of Bell’s inequality

In contrast to classical physical theories, quantum mechanics - the theory describing particles and waves in the microscopic world - has very peculiar properties: The most prominent of them are the Heisenberg uncertainty principle, that makes it impossible to determine certain pairs of variables of a system simultaneously, as well as the existence of entangled states, which allow to establish non-local correlations between two particles at arbitrary distances. This lead to the derivation of the famous paradox of Einstein, Podolsky and Rosen, from which the authors con cluded that quantum mechanics cannot be a complete theory. The possibility of the existence of the thereupon postulated complete local hidden variable theories (LHV) became testable with Bell’s inequality. This theorem limits the correlations between measurements on particles from a pair of two-level systems. Until recently experiments on Bell’s inequality suffered from loopholes that impeded a conclusive exclusion of LHVs. These are the locality loophole that requires spacelike separation of the measurements and the detection loophole that requires that a mini mum number of all created particle pairs is read out. This work contributes to a Bell-experiment with a pair of single Rubidium 87 atoms that are trapped at a distance of 400 meters. It focuses on the implementation of an atom trap setup that enables a fast, efficient and precise readout of the atomic state which shall allow to close both loopholes simultaneously in one experiment. The atomic two-level system consists of two Zeeman states of the ground state atoms. The readout is based on a Zeeman state selective ionization of the atoms and subsequent fast detection of the ionization fragments with charged particle detectors. The atoms can be analyzed in arbitrary measurement bases and the experimentally determined contrast to distinct between two orthogonal Zeeman states is in the range of 90%...93%. This is sufficient for demonstrating a violation of Bell’s inequality with two entangled atoms. For every readout attempt an answer about the atomic state is obtained which allows to close the detection loophole. Furthermore, including the setting of the measurement basis the overall duration of the readout is 820 nanoseconds. Given the inter-atomic distance of 400 meters, it hence becomes also possible to close the locality loophole in the same experiment. Rubidium atoms are a commonly used carrier of qubit states in quantum information science. In the realm of quantum cryptography the presented readout scheme could for example open the path to realizing device-independent quantum key distribution with single atoms.Im Gegensatz zu klassischen Theorien hat die Quantenmechanik - die Theorie zur Beschreibung von Teilchen und Wellen in der mikroskopischen Welt - sehr eigenartige Eigenschaften: Die bekanntesten sind die Heisenbergsche Unschärferelation, die es unmöglich macht bestimmte Paare von Variablen eines Systems gleichzeitig zu bestimmen, sowie die Existenz verschränkter Zustände, die es erlauben zwischen beliebig voneinander entfernten Teilchen nichtlokale Korrelationen zu erzeugen. Dies führte zur Herleitung des Paradoxons von Einstein, Podolsky und Rosen, aus dem die Autoren schlossen, dass die Quantenmechanik keine vollständige Theorie sein kann. Die Möglichkeit der Existenz der daraufhin geforderten vollständigen lokalen versteckten Variablentheorien wurde mit Bells Ungleichung überprüfbar. Dieses Theorem beschränkt die Korrelationen zwischen Messergebnissen an Teilchen aus einem Paar von Zweiniveausystemen. Bis vor kurzem litten Experimente zur Bellschen Ungleichung an Schlupflöchern, die ein beweiskräftiges Ausschließen von lokalen versteckten Variablentheorien verhinderten. Diese sind das Lokalitätsschlupfloch, zur dessen Schließung eine raumartige Trennung der Messungen erforderlich ist, und das Detektionsschlupfloch, nach dem eine gewisse Mindestanzahl aller erzeugten Teilchenpaare ausgelesen werden muss. Diese Arbeit trägt zu einem Bellexperiment mit einem Paar von einzelnen Rubidium 87 Atomen bei, die 400 Meter voneinander entfernt gefangen sind. Sie konzentriert sich auf die Implementierung einer Atomfalle, die eine schnelle, effiziente und präzise Atomzustandsauslese erlaubt, die es ermöglichen soll beide Schlupflöcher in einem einzigen Experiment zu schließen. Das atomare Zweiniveausystem besteht aus zwei Zeemanzuständen des Atoms im Grundzustand. Die Auslese basiert auf einer zeemanzustandsabhängigen Ionisation der Atome und der darauffolgenden schnellen Detektion der Ionisationsfragmente mit Teilchendetektoren. Die Atome können in beliebigen Messbasen analysiert werden und der experimentell bestimmte Kontrast zur Unterscheidung zweier orthogonaler Zustände liegt im Bereich von 90%...93%. Dies reicht aus um eine Verletzung der Bellschen Ungleichung mit zwei verschränkten Atomen zu zeigen. Bei jedem Ausleseversuch erhält man eine Antwort über den Atomzustand, womit das Detektionsschlupfloch geschlossen wird. Darüber hinaus liegt die Gesamtdauer der Messung inklusive des Einstellens der Messbasis bei 820 Nanosekunden. Mit einem Abstand zwischen zwei Atomen von 400 Metern wird also auch ein Schließen des Lokalitätsschlupflochs in demselben Experiment möglich. Rubidiumatome sind ein viel verwendeter Träger von Qubitzuständen im Bereich der Quanteninformation. Im Zusammenhang mit der Quantenkryptographie könnte das vorliegende Ausleseschema den Weg zur Realisierung von geräteunabhängiger Quantenschlüsselverteilung mit einzelnen Atomen eröffnen.Deutsche Übersetzung des Titels: Zustandsauslese einzelner Rubidium-87 Atome für einen schlupflochfreien Test der Bellschen Ungleichun

Quantum Cryptography

Quantum cryptography could well be the first application of quantum mechanics at the individual quanta level. The very fast progress in both theory and experiments over the recent years are reviewed, with emphasis on open questions and technological issues.Comment: 55 pages, 32 figures; to appear in Reviews of Modern Physic