Driving a Strongly Interacting Superfluid out of Equilibrium

A new field of research, which gained interest in the past years, is the field of non- equilibrium physics of strongly interacting fermionic systems. In this thesis we present a novel apparatus to study an ultracold strongly interacting superfluid Fermi gas driven out of equilibrium. In more detail, we study the excitation of a collective mode, the Higgs mode, and the dynamics occurring after a rapid quench of the interaction strength. Ultracold gases are ideal candidates to explore the physics of strongly interacting Fermi gases due to their purity and the possibility to continuously change many different system parameters, such as the interaction strength. The novel apparatus enabling the experiments outlined below is built from scratch. The setup is described and characterized in detail. We produce a fermionic superfluid of 4 × 10^6 6Li atoms at a temperature of T/T_F = 0.07 ± 0.02, where T_F is the Fermi temperature. This is achieved within 23 s by a combination of laser cooling, radio frequency evaporation of 23Na and simultaneous sympathetic cooling of 6Li in an optical plugged magnetic trap and subsequent evaporative cooling of 6Li in a dipole trap. In this thesis we provide the first experimental evidence of the Higgs mode in a strongly interacting Fermi gas in the crossover from a BCS superfluid to a molecular Bose-Einstein condensate. We develop a novel excitation method, which directly couples to the amplitude of the order parameter. This is achieved by continuously changing the population of one spin component by driving a radio frequency transition to a previously unoccupied third hyperfine state. This effectively modulates the interaction strength and the amplitude of the order parameter. We spectroscopically observe a resonance behavior at twice the gap frequency. For strong coupling, the peak width broadens and eventually the Higgs mode disappears when the Cooper pairs turn into tightly bound dimers signaling the instability of the Higgs mode. It has been suggested that the Higgs mode frequency is a precise measure of the superconducting gap in the BEC-BCS crossover, where the exact value of the gap is yet unknown and numerical calculations are challenging. Hence, our novel method provides a unique technique to determine the superconducting gap. Moreover, we perform rapid variations of the interaction parameter and vary both the initial interaction strength and the amplitude of the quench. The rapid quenches are performed by rapidly transferring one spin component of a two-component spin mixture into a third state with a different interaction strength by using a radio frequency transition. Using this novel method, we can perform the quenches in half the Fermi time, which is experimentally very close to a sudden change and to date faster than any other research group performing interaction quenches with ultra cold gases. In the experiment, we observe a fast relaxation to a zero order parameter for large quenches, whereas for small quenches we observe, after a sudden drop, a revival of the order parameter and equilibration to a long-term superfluid steady state. Our measurement provides the first evidence of the collapse and subsequent revival of order in a strongly interacting fermionic system

Dithio- and Diselenophosphinate Thorium(IV) and Uranium(IV) complexes:molecular and electronic structure, spectroscopy, and transmetalation reactivity

We report a comparison of the molecular and electronic structures of dithio- and diselenophosphinate, (E2PR2)1– (E = S, Se; R = iPr, tBu), with thorium(IV) and uranium(IV) complexes. For the thorium dithiophosphinate complexes, reaction of ThCl4(DME)2 with 4 equiv of KS2PR2 (R = iPr, tBu) produced the homoleptic complexes, Th(S2PiPr2)4 (1S-Th-iPr) and Th(S2PtBu2)4 (2S-Th-tBu). The diselenophosphinate complexes were synthesized in a similar manner using KSe2PR2 to produce Th(Se2PiPr2)4 (1Se-Th-iPr) and Th(Se2PtBu2)4 (2Se-Th-tBu). U(S2PiPr2)4, 1S-U-iPr, could be made directly from UCl4 and 4 equiv of KS2PiPr2. With (Se2PiPr2)1–, using UCl4 and 3 or 4 equiv of KSe2PiPr2 yielded the monochloride product U(Se2PiPr2)3Cl (3Se-UiPr-Cl), but using UI4(1,4-dioxane)2 produced the homoleptic U(Se2PiPr2)4 (1Se-U-iPr). Similarly, the reaction of UCl4 with 4 equiv of KS2PtBu2 yielded U(S2PtBu2)4 (2S-U-tBu), whereas the reaction with KSe2PtBu2 resulted in the formation of U(Se2PtBu2)3Cl (4Se-UtBu-Cl). Using UI4(1,4-dioxane)2 and 4 equiv of KSe2PtBu2 with UCl4 in acetonitrile yielded U(Se2PtBu2)4 (2Se-U-tBu). Transmetalation reactions were investigated with complex 2Se-U-tBu and various CuX (X = Br, I) salts to yield U(Se2PtBu2)3X (6Se-UtBu-Br and 7Se-UtBu-I) and 0.25 equiv of [Cu(Se2PtBu2)]4 (8Se-Cu-tBu). Additionally, 2Se-U-tBu underwent transmetalation reactions with Hg2F2 and ZnCl2 to yield U(Se2PtBu2)3F (6) and U(Se2PtBu2)3Cl (4Se-UtBu-Cl), respectively. The molecular structures were analyzed using 1H, 13C, 31P, and 77Se NMR and IR spectroscopy and structurally characterized using X-ray crystallography. Using the QTAIM approach, the electronic structure of all homoleptic complexes was probed, showing slightly more covalent bonding character in actinide–selenium bonds over actinide–sulfur bonds

Circuit quantum acoustodynamics with surface acoustic waves

The experimental investigation of quantum devices incorporating mechanical resonators has opened up new frontiers in the study of quantum mechanics at a macroscopic level$^{1,2}$. Superconducting microwave circuits have proven to be a powerful platform for the realisation of such quantum devices, both in cavity optomechanics$^{3,4}$, and circuit quantum electro-dynamics (QED)$^{5,6}$. While most experiments to date have involved localised nanomechanical resonators, it has recently been shown that propagating surface acoustic waves (SAWs) can be piezoelectrically coupled to superconducting qubits$^{7,8}$, and confined in high-quality Fabry-Perot cavities up to microwave frequencies in the quantum regime$^{9}$, indicating the possibility of realising coherent exchange of quantum information between the two systems. Here we present measurements of a device in which a superconducting qubit is embedded in, and interacts with, the acoustic field of a Fabry-Perot SAW cavity on quartz, realising a surface acoustic version of cavity quantum electrodynamics. This quantum acoustodynamics (QAD) architecture may be used to develop new quantum acoustic devices in which quantum information is stored in trapped on-chip surface acoustic wavepackets, and manipulated in ways that are impossible with purely electromagnetic signals, due to the $10^{5}$ times slower speed of travel of the mechanical waves.Comment: 12 pages, 9 figures, 1 tabl

Desert and Economic Interdependence

Outside of philosophy, the idea that workers deserve to be paid according to their productive contributions is very popular. But political philosophers have given it relatively little attention. In this paper, I argue against the attempt to use this idea about desert and contribution to vindicate significant income inequality. I claim that reward according to contribution fails on its own terms when the following condition holds: the size of each worker's contribution depends on what others only together do. When workers only together make another more productive, that is not reflected in the sum of their own contributions. Thus reward according to contribution recognizes individual accomplishments without recognizing their dependence on collectives, dependence that is, in complex economies, ubiquitous

Double-sided coaxial circuit QED with out-of-plane wiring

Superconducting circuits are well established as a strong candidate platform for the development of quantum computing. In order to advance to a practically useful level, architectures are needed which combine arrays of many qubits with selective qubit control and readout, without compromising on coherence. Here we present a coaxial circuit QED architecture in which qubit and resonator are fabricated on opposing sides of a single chip, and control and readout wiring are provided by coaxial wiring running perpendicular to the chip plane. We present characterisation measurements of a fabricated device in good agreement with simulated parameters and demonstrating energy relaxation and dephasing times of $T_1 = 4.1\,\mu$s and $T_2 = 5.7\,\mu$s respectively. The architecture allows for scaling to large arrays of selectively controlled and measured qubits with the advantage of all wiring being out of the plane.Comment: 4 pages, 3 figures, 1 tabl

On the Challenges of Reaching Pupils With Spacetech-Related Extracurricular Activities

Today\u27s rapid progress in space exploration leads to a high impact on our society. Especially young people are highly affected by this fascination. Despite this large pool of curious pupils, it remains challenging to find entry points into space and aeronautic-related careers for them. Often, these topics seem to be out of reach for most pupils. Educational programs like AstroPi (offered by ESA) or High School Aerospace Scholars (offered by NASA) target this issue. However, those projects never get into contact with actual outer space and remain mostly theoretical. The goal of the mission SpaceTeamSat1 and the CubeSat with the same name, is to provide an entry point to pupils, by giving them the opportunity to participate in a space mission. With SpaceTeamSat1, the TU Wien Space Team develops a 1U CubeSat platform from scratch and operates it in low earth orbit at an approximate altitude of 500 km. It shall allow pupils of secondary schools, aged between 15 and 19 to run their own code on a Raspberry Pi payload in space. The mentioned payload offers a variety of sensors and cameras, which allows the execution of a broad range of experiments. Participating pupils and teams formed from them will be supervised by their teachers on a regular basis. In order to teach common industry practices and maximize the chances of a successful mission, the TU Wien Space Team will offer additional guidance in the form of documentation, reviews, and get-togethers. The highlight of the mission will be a coding challenge, where teams of pupils will compete against each other over the most successful in-orbit experiment according to inventiveness, project management, and code quality. These tasks are divided into different levels, beginning at entry-level tasks, such as calculating the rotation rate or investigating the thermal behavior of the CubeSat. More advanced tasks may include taking pictures of the Earth or Moon. At the moment, SpaceTeamSat1 is in its prototyping phase and is planned to be launched in 2024. Complementary to that, a preliminary school outreach has begun, and a hand-selected group of secondary-level schools has been accepted to join as pilot participants. This allows for fine-tuning of the offered educational program and reveals drawbacks that can be targeted before the official start of the CubeSat mission. Additionally, the educational mission is evaluated and developed in cooperation with ESERO Austria. To our knowledge, the TU Wien Space Team is the only organization that offers such a mission so far. Since the know-how and technology that is produced in the course of the SpaceTeamSat1 mission is supposed to be open source, we are able to share insights on the difficulties that have been faced – or are expected – when proposing extracurricular activities to schools and pupils

Structure and properties of [(4,6-tBu2C6H2O)2Se]2An(THF)2, An = U, Np, and their reaction with p-benzoquinone.

The synthesis and characterization of U(iv) and Np(iv) selenium bis(phenolate) complexes are reported. The reaction of two equivalents of the U(iv) complex with p-benzoquinone results in the formation of a U(v)-U(v) species with a bridging reduced quinone. This represents a rare example of high-valent uranium chemistry as well as a rare example of a neptunium aryloxide complex