1,514 research outputs found
High resolution field imaging with atomic vapor cells
No full textIn this thesis, I report on the development of imaging techniques in atomic vapor cells. This is a relatively unexplored area, despite the ubiquitous use of imaging in experiments with ultracold atoms. Our main focus is in high resolution imaging of microwave near fields, for which there is currently no satisfactory established technique. We detect microwave fields through Rabi oscillations driven by the microwave on atomic hyperfine transitions. The technique can be easily modified to also image dc magnetic fields. In addition, we have developed techniques to image vapor cell processes such as atomic T1 and T2 relaxation. These provide a new window into vapor cell physics, which we have used to obtain spatially resolved information on Rb interactions with the cell walls, and to estimate the Rb relaxation probability in a collision with the cell wall.
As a first application of our imaging techniques, we imaged the dc and microwave magnetic fields inside a state-of-the-art vapor cell atomic clock. This new clock characterisation technique should lead to real improvements in clock performance, and is in the process of being adopted by the atomic clock community.
We have developed a widefield, high resolution imaging setup using a microfabricated vapor cell, which we have used to image microwave and dc magnetic vector fields. With the addition of a 480 nm laser, the setup can be configured to image microwave electric fields. Our camera-based imaging system records 2D images with a 6x6 mm2 field of view at a rate of 10 Hz. It provides up to 50 um spatial resolution, and allows imaging of fields as close as 150 um above structures, through the use of extremely thin external cell walls. This is crucial in allowing us to take practical advantage of the high spatial resolution, as feature sizes in near-fields are on the order of the distance from their source, and represents an order of magnitude improvement in surface-feature resolution compared to previous vapor cell experiments. We demonstrate a microwave magnetic field sensitivity of 1.4 uT/sqrt-Hz per 50x50x140 um3 voxel, at present limited by the speed of our imaging system. Since we image 120x120 voxels in parallel, a single scanned sensor would require a sensitivity of at least 12 nT/sqrt-Hz to produce images with the same sensitivity.
The spatial resolution, distance of approach, and sensitivity of our high resolution setup are sufficient for characterising 6.8 GHz microwave fields above a range of real world devices. However, frequency tunability is essential for wider applications of our imaging technique. Industry is particularly interested in techniques for imaging high frequency microwaves, above 18 GHz, where simulations become increasingly unreliable. I have shown that our technique can be extended to image microwaves of any frequency, in principle from dc to 100s of GHz, by using a large dc magnetic field to Zeeman shift the hyperfine ground state transitions to the desired frequency. I present results from a proof-of-principle setup, where we have used a 0.8 T solenoid to detect and image microwaves from 2.3 GHz to 26.4 GHz
Sympathetic cooling and self-oscillations in a hybrid atom-membrane system
No full textHybrid systems combining mechanical oscillators and ultracold atoms provide novel
opportunities for cooling, detection and quantum control of mechanical motion with
applications in precision sensing, quantum-level signal transduction and for fundamental
tests of quantum mechanics.
In this thesis I present experiments performed with a hybrid atom-membrane
system, in which the vibrations of a Si_3N_4 membrane in an optical cavity are coupled
to the motion of laser-cooled atoms in an optical lattice. The interactions are
mediated by the lattice light over a macroscopic distance and enhanced by the cavity.
Via the coupling to the cold atoms, the fundamental vibrational mode of the
membrane at 2π x 276 kHz is cooled sympathetically from room temperature to
0.4(2) K, even though the mass of the mechanical oscillator exceeds that of the
atomic ensemble by a factor of 4 x 10^10. In other systems, sympathetic cooling
of molecules with cold atoms or ions has been limited to mass ratios of up to 90.
Previous theoretical work has shown that our coupling mechanism is able to cool the
membrane vibration into the ground state and to perform coherent state transfers
between atomic and membrane motion.
Under certain experimental conditions, the atom-membrane system shows self-oscillations,
which arise from an effective delay in the backaction of the atoms onto
the light. This retardation drives the system into limit-cycle oscillations if the coupling
is large. I study the dependence of this instability on several system parameters
and find that a larger atom number and a smaller atom-light detuning make the system
less stable. Further, the stability of the coupled system in presence of a delay is
investigated theoretically and a modified expression for the sympathetic cooling rate
is derived. This model allows to fit the measured atom number dependence with a
delay of τ = 88(1) ns. Moreover, direct measurements of the atomic backaction onto
the lattice light are presented. These show phase lags exceeding 180° in parameter
regimes where the instability is observed, proving that the retardation arises within
the atomic ensemble. Finally, I present the results of numerical simulations, which
show that collective atomic effects within the atomic ensemble in an asymmetric
lattice are able to induce the observed phase lag in the atomic backaction
Sympathetic cooling of a membrane oscillator in a hybrid mechanical-atomic system
No full textThe quantum behaviour of macroscopic mechanical oscillators is currently being investigated using a variety of mechanical systems and techniques such as optomechanical cooling and cold damping. As mechanical systems are also very versatile transducers between different physical systems, it is possible to build hybrid systems that combine the advantages of their constituents. This opens up new possibilities for fundamental studies of quantum physics, precision sensing and quantum information processing. Ultra-cold atoms represent one of the best-controlled systems available, thus making a well-developed toolbox for quantum manipulation available to mechanical oscillators in a hybrid system.
In this thesis, I report on the realization of a hybrid mechanical-atomic system consisting of a Si3N4 membrane inside an optical cavity coupled to an ensemble of atoms. The coupling is mediated by a light field that couples the atomic motion to the membrane motion over a large distance. By laser cooling the atomic motion, the membrane is sympathetically cooled via its interaction with the atoms to a temperature of 0.7 K starting from room temperature, despite the enormous mass ratio of 10^10 between the membrane and the atomic ensemble. Up to now, sympathetic cooling had only been used to cool microscopic particles with much lower masses. The system reported in this thesis is the first hybrid system where the back-action of the atoms onto the mechanical oscillator is sufficiently large for practical applications. It represents a significant improvement over a previous experiment in our laboratory, where the atom’s influence onto the mechanical oscillator was barely detectable. An atom-membrane cooperativity C > 1 is achieved, thus enabling the study of effects such as a mechanical analog of electromagnetically induced transparency in the system, which will be investigated in the future. The quantitative analysis of the coupling mechanism also allows to predict experimental requirements for future ground state cooling of the mechanical oscillator, which are within reach. Interestingly, hybrid systems such as ours can provide ground-state cooling of low-frequency mechanical oscillators in a regime, where neither cavity optomechanical cooling nor cold damping can reach the ground state
Philipp Melanchthon
No full textPhilipp Melanchthon (1497–1560) was, with Martin Luther, the most influential reformer of the church during the 16th century. He was also a reformer of university education, especially theological studies, as well as the school system in Germany. He was responsible for a theological curriculum that included Greek, Hebrew, and philosophy. He, as a professor of Greek at the University of Wittenberg since 1518, was the author of the first generally accepted Protestant confession, known as the Confessio Augustana (1530). He also wrote the first Protestant commentaries on Paul’s letter to the Romans (1519), as well as the first Protestant handbook in systematic theology (1521). He was the main negotiator of the Protestant movement during the diets and religious discussions with the Roman Catholic Church. He is known as the ‘teacher of Germany and Europe’ and is respected as the father of the ecumenical movement. Yet, Melanchthon is not known to South Africans and especially Afrikaans-speaking people who, traditionally, have close links with the reformational tradition. There is not yet one single publication on Melanchthon in Afrikaans or by a South African scholar, making this book, therefore, the first by an Afrikaans-speaking scholar on Melanchthon
On-demand semiconductor source of 780 nm single photons with controlled temporal wave packets
No full textWe report on a fast, bandwidth-tunable single-photon source based on an epitaxial GaAs quantum dot. Exploiting spontaneous spin-flip Raman transitions, single photons at 780 nm are generated on demand with tailored temporal profiles of durations exceeding the intrinsic quantum dot lifetime by up to three orders of magnitude. Second-order correlation measurements show a low multiphoton emission probability [g2(0)∼0.10–0.15] at a generation rate up to 10 MHz. We observe Raman photons with linewidths as low as 200 MHz, which is narrow compared to the 1.1-GHz linewidth measured in resonance fluorescence. The generation of such narrow-band single photons with controlled temporal shapes at the rubidium wavelength is a crucial step towards the development of an optimized hybrid semiconductor-atom interface
#Bitcoin : an analysis of the field of a decentralized virtual currency using twitter data
No full textAuthor Philipp AllerstorferAbstract in englischer SpracheMasterarbeit Universität Linz 201
Matter-wave interference. Nanomechanical answer to Einstein
No full textQuantum mechanical wave interference of massive molecules at an atomically thin grating sheds new light on an old question
Strong light-mediated coupling between a membrane oscillator and an atomic spin ensemble
No full textThis thesis presents theoretical and experimental work on light-mediated coupling between a collective atomic spin and a micromechanical membrane oscillator. With our work we address a fundamental question of quantum optics: Can a beam of light mediate coherent Hamiltonian interactions between two distant quantum systems? This is an intriguing question whose answer is not a priori clear, since the light carries away information about the systems and might be subject to losses, giving rise to intrinsic decoherence channels associated with the coupling. Our answer is affirmative and we derive a particularly simple sufficient condition for the interactions to be Hamiltonian: The light field needs to interact twice with the systems and the second interaction has to be the time reversal of the first. We demonstrate theoretically that, even in the presence of significant optical loss, coherent interactions can be realized and generate substantial amounts of entanglement between the systems.
In our experiments, we employ this approach to strongly couple a spin-polarized atomic ensemble and a micromechanical oscillator via a free-space laser beam across a distance of one meter in a room-temperature environment. The atomic ensemble consists of about ten million laser-cooled Rubidium atoms in an optical dipole trap that interact with the coupling laser via an off-resonant Faraday interaction. The mechanical oscillator is a silicon nitride membrane which is mounted in a single-sided optical cavity and couples to the laser field via radiation-pressure forces. In order to mediate a bidirectional Hamiltonian interaction between spin and membrane, the coupling beam is arranged in a loop such that it couples twice to the spin. This looped geometry enables destructive interference of quantum back-action by the light field on the spin.
Using this setup, we experimentally demonstrate for the first time strong Hamiltonian coupling between remote quantum systems and explore different dynamical regimes of cascaded light-mediated interactions: With the spin initialized in its ground state we observe normal-mode splitting and coherent energy exchange oscillations, both hallmarks of strong coupling. If we invert the spin to its highest energy state, we observe parametric-gain interactions, resulting in two-mode thermal noise squeezing. Furthermore, by shifting the phase of the light field between spin and membrane we can switch to non-Hamiltonian coupled dynamics, allowing us to observe level attraction and exceptional points. This high level of control in a strongly coupled modular system gives access to a unique toolbox for designing hybrid quantum systems and coherent optical feedback loops. Our approach to engineer coherent long-distance interactions with light makes it possible to couple very different systems in a modular way, opening up a range of new opportunities for quantum control
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