In the field of ultracold quantum gases atom optics has been established as a completely
new discipline in the last years. This led to fundmentally new results in the field of research
of atom optical systems. In modern experiments especially strongly interacting
nonlinear systems are of great interest. Such a strongly correlated system consists of a
cold atomic quantum gas and a light field both embedded into a nonlinear medium.
This thesis documents for the first time that a two-dimensional photonic crystal fiber
can be used as a novel nonlinear medium for atom optical experiments. It shows that
cold atoms can be guided optically through this fiber with high efficiency and density.
In order to study this system a new experiment for creating cold optically guided atoms
has been built up. This complex experimental setup consists of high-stable laser sources,
optics and electronics for generating, manipulating and detecting cold atomic rubidium
ensembles as well as further elements for implementing photonic band gap fibers as
matter wave guides. One focal point of the thesis has been the detailed investigation
of the atomic flux through the fiber. This analysis demonstrates that the experimental
parameters governing the atomic flux are in a good agreement with a self-developed
numerical model as well as with other theoretical predictions.
For applying this system as injector for other quantum gas experiments or for atom
interferometry, a continuous, coherent atomic flux is necessary.
Studies demonstrate that such a regime can be reached by using an additional dipole
trap in front of the fiber. By properly chosen trap parameters this trap can be used
as a reservoir of cold atoms. With this optical setup the atomic flux can be kept up
significantly longer than in a pulsed guiding system.
Further the experimental possibilities of this nearly one-dimensional, cold, dense and
tightly embedded atomic system are of great interest. The analysis shows that because
of the generated atomic density and the energetic distribution of the atoms in the
fiber potential a coherent atom optics is feasible with this system. So this experiment
paves the way towards a novel, coherent matter wave guide. By exploiting the strongly
photonic interaction in the fiber other physical regimes especially in the field of nonlinear
optics can be reached. This includes for example the studies of four-wave-mixing
processes in the photonic band gap fiber. In a recent theoretical paper it has been
suggested to use the tunability of the atom-light-interaction to reach a photonic regime
of extremely strong repulsion. This possibly leads to decelerated or even stopped light
forming a so-called Tonks-Girardeau gas.
In the field of ultracold quantum gases atom optics has been established as a completely
new discipline in the last years. This led to fundmentally new results in the field of research
of atom optical systems. In modern experiments especially strongly interacting
nonlinear systems are of great interest. Such a strongly correlated system consists of a
cold atomic quantum gas and a light field both embedded into a nonlinear medium.
This thesis documents for the first time that a two-dimensional photonic crystal fiber
can be used as a novel nonlinear medium for atom optical experiments. It shows that
cold atoms can be guided optically through this fiber with high efficiency and density.
In order to study this system a new experiment for creating cold optically guided atoms
has been built up. This complex experimental setup consists of high-stable laser sources,
optics and electronics for generating, manipulating and detecting cold atomic rubidium
ensembles as well as further elements for implementing photonic band gap fibers as
matter wave guides. One focal point of the thesis has been the detailed investigation
of the atomic flux through the fiber. This analysis demonstrates that the experimental
parameters governing the atomic flux are in a good agreement with a self-developed
numerical model as well as with other theoretical predictions.
For applying this system as injector for other quantum gas experiments or for atom
interferometry, a continuous, coherent atomic flux is necessary.
Studies demonstrate that such a regime can be reached by using an additional dipole
trap in front of the fiber. By properly chosen trap parameters this trap can be used
as a reservoir of cold atoms. With this optical setup the atomic flux can be kept up
significantly longer than in a pulsed guiding system.
Further the experimental possibilities of this nearly one-dimensional, cold, dense and
tightly embedded atomic system are of great interest. The analysis shows that because
of the generated atomic density and the energetic distribution of the atoms in the
fiber potential a coherent atom optics is feasible with this system. So this experiment
paves the way towards a novel, coherent matter wave guide. By exploiting the strongly
photonic interaction in the fiber other physical regimes especially in the field of nonlinear
optics can be reached. This includes for example the studies of four-wave-mixing
processes in the photonic band gap fiber. In a recent theoretical paper it has been
suggested to use the tunability of the atom-light-interaction to reach a photonic regime
of extremely strong repulsion. This possibly leads to decelerated or even stopped light
forming a so-called Tonks-Girardeau gas.
We have demonstrated that a two-dimensional photonic crystal fiber can be used as a novel nonlinear medium for atom optical experiments. Our results show for the first time that cold atoms can be guided optically through this fiber with high efficiency and especially with a high density. In order to study this system a new experiment for creating cold optically guided atoms has been built up. Our results show that the experimental parameters governing the atomic flux are in a good agreement with a self-developed numerical model as well as with other theoretical predictions.
We demonstrate the first guiding of cold atoms through a 88 mm long piece of photonic band gap fiber. The guiding potential is created by a far-off resonance dipole trap propagating inside the fiber with a hollow core of 12 μm. We load the fiber from a dark spot 85 Rb magneto-optical trap and observe a peak flux of more than 10 5 atoms s −1 at a velocity of 1.5 m s −1 . With an additional reservoir optical dipole trap, a constant atomic flux of 1.5 × 10 4 atoms s −1 is sustained for more than 150 ms. These results open up interesting possibilities to study nonlinear light–matter interaction in a nearly one-dimensional geometry and pave the way for guided matter wave interferometry.
Atom optics has been a highly active field of research with many scientific breakthroughs over the past two decades, largely due to successful advances in laser technology, microfabrication techniques, and the development of laser cooling and trapping of neutral atoms. This dissertation details several atom optics experiments with the motivation to develop tools and techniques for precision atom wave interferometry. It provides background information about atom optics and the fundamentals behind laser cooling and trapping, including basic techniques for cold gas thermometry and absorptive detection of atoms. A brief overview of magnetic trapping and guiding in tight wire-based traps is also provided before the experimental details are presented. ❧ We developed a novel laser source of 780 nm light using frequency-doubled 1560 nm fiber amplifier. This laser system provided up to a Watt of tunable frequency stabilized light for two Rb laser cooling and trapping experiments. One system generates Bose-Einstein condensates in an optical trap while the second is based on atom chip magnetic traps. The atom chip system, detailed in this thesis, was designed and built to develop the tools necessary for transport and loading large numbers of cold atoms and explore the potential for guided atom interferometry. Techniques and results from this experiment are presented, including an efficient magnetic transport and loading method to deliver cold atom to atom chip traps. We also developed a modeling tool for the magnetic fields formed by coiled wire geometries, as well as planar wire patterns. These models helped us design traps and determine adiabatic transportation of cold atoms between macro-scale traps and micro-traps formed on atom chips. Having achieved near unity transfer efficiency, we demonstrated that this approach promises to be a consistent method for loading large numbers of atoms into micro-traps. Furthermore, we discuss an in situ imaging technique to investigate magnetic field contours of the traps and the dynamics of atoms within those confining potentials. We also controlled the propagation along the atom chip guides by accelerating atoms with longitudinal magnetic gradients, and investigated an atom focusing scheme. ❧ While the atom chip wire guides perform a role analogous to optical fibers guiding light waves, ""free space"" cold atoms offer great opportunity for precision interferometry. We describe a second on-going atom optics experiment that measures gravity gradients using a pair of atom fountain interferometers separated by one meter. We have demonstrated Gravity Gradiometer resolution down to 4x10⁻⁹ g/m using a 40 kg test mass. The atomic physics subsystem is described in detail, including the vacuum, cold atom source, optics, magnetic coils and shields, and vibration isolation and compensation. The system is designed to be a compact, robust, transportable instrument, taking strides towards future gravity gradient measurements in the field. In the realm of space applications, there has been interest for micro-gravity science experiments aboard the International Space Station, along with instrument development for gravity mapping of Earth and planetary bodies with satellite-based instruments. Furthermore, there are ground-based applications for gravity imaging of local density distributions, precision measurement of gravity, as well as proposals for redefining the kilogram, detecting gravitational waves and determining the Gravitational constant.
Our goal is to study quantum optical phenomena in a strong nonlinear optical system. For this purpose, we create a hollow-core photonic-crystal (HCPC) fiber-based platform that confines photons and atomic ensembles together. This enables strong light-matter interactions which are crucial for implementing optical nonlinearities at single-photon levels [1]. We use an optical dipole trap at cesium's magic wavelength to guide laser cooled cesium atoms into and inside the fiber core. This approach will allow us to perform experiments with the dipole trap continuously on as opposed to the previously reported fiber-loading systems [2,3] in which the dipole trap was rapidly amplitude-modulated to avoid the effect from the spatially dependent AC Stark shift. In this system, we perform experiments on electromagnetically induced transparency (EIT) and demonstrate slow light and all optical switch. We also aim to observe large cross-phase modulation (XPM) using a three-level ladder scheme [4,5]. Lastly, the approaches to integrate a cavity into HCPCFs to increase light-matter interactions, thus the optical nonlinearities, will be described.
The ability to control light with light at ultralow powers has been a major avenue of research in photonics with applications to optical communications, computation, and signal processing. Such light-by-light scattering is achieved in a medium with a strong light-matter interaction, and for the development of quantum information networks it is important to demonstrate such effects near the single-photon level. Alkali-metal vapors such as rubidium (Rb) enable strong light-matter interactions due to the large cross section per atom and well-defined energy level structure, while the use of optical fibers offers the advantage of possible integration with modern optical communication systems. Hollow-core photonic band-gap fibers (PBGFs) can combine both these technologies such that both the atoms and the optical fields are transversely confined to a region that is a few wavelengths in size, which offers the prospect of exploring few-photon nonlinear interactions. We generate large optical depths in such a Rb-PBGF system, and the tight light confinement, high vapor density and long interaction length allow us to perform nonlinear optics at ultralow power. We demonstrate large signal amplification (>100) and frequency conversion using a four-wave mixing process with only microwatts of pump power. This is, to our knowledge, the largest gain observed at such low power. We perturb the coherence of this four-wave mixing to demonstrate all-optical modulation at unprecedented bandwidths (~300 MHz) for an atomic-vapor system, with an energy density of only tens of pho- tons per atomic cross-section, comparable to that achieved in more elaborate setups based on cold-atomic clouds. We then demonstrate an enhancement of several orders of magnitude in degenerate two-photon absorption in our RbPBGF system over that achieved in bulk vapor cells in a focused beam geometry. This allows us to directly measure two-photon absorption from a beam by detecting its intensity on a photodiode. Further, employing a near-resonant, non-degenerate two-photon transition in Rb, we demonstrate all-optical intensity modulation with just a few photons (<20), or only a few attojoules of energy, at relatively large bandwidths (~50 MHz) for such a sensitive scheme. This result takes us to within an order of magnitude of single-photon switching, and improves upon previous experiments for freely propagating optical fields, including those in cold-atoms. Finally, we produce relatively large cross-phase shifts of a few milliradians on a meter beam with <20 signal photons by tuning slightly away from resonance on the same non-degenerate two-photon transition. This corresponds to a phase shift of 0.3 milliradian per photon, with a fast response time of <5 ns. This represents, to our knowledge, the largest such nonlinear phase shift induced in a single-pass through a room temperature medium. Our Rb-PBGF system can thus potentially be employed to realize weak-nonlinearity based quantum computation and quantum non-demolition measurement of photon number. Through these experiments, we show the potential of a Rb-PBGF system for exploring quantum nonlinear optics at ultralow powers. Moreover, our system is simpler and easier to control and manipulate than setups based on cold atomic clouds and/or high-finesse cavities, and holds promise for integration with fiber-optic communication networks.
We built a new experiment using cold atoms interacting with the light guided by an optical nanofiber. We first developed a nanofiber manufacturing bench. By heating and stretching a commercial optical fiber, a silica cylinder of 400 nm diameter is obtained. The light guided in these nanofibers is strongly focused over the whole length and exhibits strong evanescent fields. We then prepared a vacuum chamber and the laser system necessary for the manipulation of cold atoms. After inserting a nanofiber amid a cloud of cold atoms, we observed the phenomenon of slow light under the conditions of electromagnetically induced transparency: the light guided by the fiber is slowed down to a speed 3000 times smaller than its usual speed. We also stored the light guided by an optical fiber. After several microseconds, the information stored as a collective atomic excitation could be retrieved in the fiber. We have shown that this optical memory works for light pulses containing less than one photon on average. This system may therefore be used as a quantum memory, an essential tool for future quantum communication networks. Finally, we trapped atoms in an array in the vicinity of the nanofiber thanks to the light guided by the latter. Compared to our first set of experiments, the resulting cloud has a longer lifetime (25 ms) and interacts more strongly with the guided light (OD ~ 100). This new system should allow to efficiently implement other quantum optics protocols, such as the generation of single photons, or the entanglement of two remote atomic ensembles.