Doppler sensitivity and optimization of Rydberg atom-based antennas

Radio frequency antennas based on Rydberg atoms can in principle reach sensitivities beyond those of any conventional wire antenna, especially at lower frequencies where very long wires are needed to accommodate the growing wavelength. This paper presents a detailed theoretical investigation of Rydberg antenna sensitivity, elucidating parameter regimes that could cumulatively lead to 2--3 orders of magnitude sensitivity increase. Of special interest are three-laser setups proposed to compensate for atom motion-induced Doppler spreading. Such setups are in indeed shown to be advantageous, but only because they restore sensitivity to the \emph{expected} Doppler-limited value, removing significant additional off-resonance reductions.Comment: 5 pages, 6 figure

Study, Development and Optimization of Laser Resonant Photo-Ionization processes applied to species of interest for the Isolpharm-SPES project

The principle of resonance laser photo-ionization is used to selectively ionize elements of interest in isotope separation online (ISOL) facilities. The work presents the study of two-step resonance photo-ionization of silver atoms in the context of selective production of exotic species (SPES) at INFN-LNL. Using a hot ablation plume of silver atoms in a time of flight mass spectrometer (TOF-MS), Doppler-suppressed and Doppler-broadened resonance frequency profile of the transition steps. It is shown that a Doppler-suppressed resonance profile can be achieved in a two-step resonant transition by introducing an angular separation as low as 8.5° between the two resonant laser beams. In the case of collinear injection of these laser beams, Doppler broadening is observed and the effect of the laser linewidth in a Doppler-broadened resonance profile is also studied. A silver hollow cathode lamp has also been used to study the same resonant transitions. Two kinds of opto-galvanic signals i.e. slow signal and fast signal are used to detect the resonance in this case. Using the hollow cathode lamp, strong evidence of high-lying Rydberg states of silver around the energy value of 7.56 eV (60945.32 cm$^{-1}$). First-time characterization of the SPES laser ion source (LIS) at ISOLDE Offline 2 is also presented. The SPES-LIS is a hot tubular tantalum cavity inside which laser beams with frequencies tuned to the electronic transitions of particular elements are made to interact with the vapor of the element. Important parameters such as thermal stability of the ion source, time structure of the ion beam, laser enhancement of the ion yield, and resonance laser ionization efficiency have been measured in relation to the production of the gallium ion beam. The effect of the electrostatic axial field on the movement of the ions along the length of the ion source is discussed. The dependence of the laser enhancement of the ion yield on the ion source temperature and the total ion current has been studied too. At a high ion source temperature of 2200°C, the laser enhancement of the ion yield at different total ion currents is found relatively stable compared to lower ion source temperatures. A new TOF-MS has been designed and assembled in the online laser lab at the SPES facility. Two independent sources of atomic beam viz. an effusion cell and an ablation target system, are employed in the system. This new TOF-MS should aid in scheme developments for the photo-ionization of several elements and also provide the geometry for high-resolution laser resonant spectrometry

Entwicklung und Aufbau hybrider Quantensysteme für Quantencomputing und Metrologie

Die Verknüpfung von Qubits gehört zu den aktuellen Herausforderungen der Quantentechnologie. Dies betrifft einerseits Systeme, die weit voneinander entfernt sind, als auch hybride Systeme, in denen unterschiedliche Realisierungen der Qubits ihre individuellen Stärken ausspielen und anschließend den Quantenzustand auf einen anderen Typ übertragen sollen. In dieser Arbeit wird ein Mischcryostat vorgestellt, der Supraleiter auf Temperaturen unterhalb hundert Millikelvin abkühlen kann und zugleich eine Apparatur zur Präparation von ultrakalten Atomen enthält. Es konnte gezeigt werden, dass es möglich ist, ultrakalte Atomwolken in dieser Umgebung zu präparieren und zu manipulieren. Im nächsten Schritt müssen die Atomwolken in die Millikelvin-Umgebung transportiert und an einen Chip mit funktionalen supraleitenden Elementen herangeführt werden. Zwar steht die Demonstration des Austausches von Quanteninformation noch aus, dennoch stellt dies einen bedeutenden Schritt in Richtung eines hybriden Quantensystems dar. Es ist von zentraler Bedeutung, den Wärmeeintrag in die Millikelvinumgebung zu minimieren. Gleichzeitig erfordern die typischen magnetischen Fallenpotentiale Ströme im Bereich einiger Ampere. Konventionelle Spulen aus supraleitenden Drähten erzeugen zwar keine Heizleistung, allerdings verbleibt ein Wärmeeintrag durch Wärmeleitung. Einen Ausweg bieten geschlossene supraleitende Schleifen, die von einem permanenten Strom durchflossen werden. In dieser Arbeit wurde die Idee der Baseball-Falle aufgegriffen, die mit einem einzelnen Strompfad eine vollständige Falle realisiert. Dies wurde in einem zweiten System mit einer supraleitenden Schleife umgesetzt. Eine zusätzlich angebrachte konventionelle Spule koppelt magnetischen Fluss in die Schleife ein, wodurch der permanente Strom moduliert werden kann. Diese Spule kann sich an einer anderen Temperaturstufe des Cryostaten befinden, so dass auch die Wärmeleitung unterbunden wird. Als Vermittler zwischen unterschiedlichen Qubits können Rydberg-Atome eine Schlüsselrolle einnehmen, da ihr Anregungsspektrum einen weiten Frequenzbereich überdeckt. Ihre Sensitivität gegenüber elektrischen Feldern erfordert allerdings eine sorgfältige Betrachtung der Umgebung und ggf. eine Abschirmung oder Kompensation der Störfelder. In der vorliegenden Arbeit wurde ein Referenzsystem aufgebaut, an dem die absoluten Übergangsfrequenzen mit verbesserter Genauigkeit ermittelt und der Einfluss externer Felder untersucht wurden. Auf dieser Basis können nun die Korrekturen vorgenommen werden. Als Referenz für die Frequenzmessungen dient bislang ein Mikrowellenübergang. Verwendet man stattdessen einen optischen Übergang, so wird die Zeit in kleinere Abschnitte unterteilt und somit die Unsicherheit reduziert. Diese optischen Uhren aus neutralen Atomen haben bislang den Nachteil, dass die Messung destruktiv erfolgt. Durch die erneute Präparation steht die Uhr nur einen Bruchteil der Zeit zur Verfügung. Hier wurde ein Konzept erarbeitet, das den Betrieb einer kontinuierlichen optischen Uhr ermöglichen soll. Die erste Stufe der Präparation eines Ensembles ultrakalter Atome konnte bereits demonstriert werden. Im weiteren Verlauf ist eine zweite Präparationsstufe, sowie eine Spektroskopie erforderlich. Letztendlich ist die Anbindung des bestehenden Frequenzkamms geplant, um die erhöhte Genauigkeit auch auf andere Frequenzbereiche zu übertragen. Die erzielten Erkenntnisse tragen zur Weiterentwicklung der Quantentechnologien bei. Einerseits bieten sie die Perspektive Quanteninformationsverarbeitung mit hybriden Systemen aus Supraleitern und ultrakalten Atomen durchzuführen. Dabei kann die optische Schnittstelle mehrere derartige Systeme auch über große Entfernungen miteinander verknüpfen und so die Vision eines Quanten-Internets wahr werden lassen. Optische Uhren werden in absehbarer Zeit die Cäsium-Uhren zur Definition der Sekunde ablösen. Ihre hohe Sensitivität lässt neue Anwendungen in der Metrologie, Geodäsie oder auch Astronomie erwarten

Excited state spatial distributions in a cold strontium gas

This thesis describes the development of a new technique for measuring the spatial distribution of Rydberg atoms in a cold strontium gas. Strontium atoms are cooled and trapped in a magneto-optical trap and coherently excited to Rydberg states in a two-photon, three-level ladder scheme. Several methods of stabilizing the frequency to the cooling transition are discussed and characterized. A frequency stabilization scheme based on electromagnetically-induced transparency for the second laser required for Rydberg excitation is also explained. The Rydberg population dynamics are studied experimentally and modeled using an optical Bloch equation simulation. The divalent nature of strontium allows doubly excited “autoionizing” states to be accessed using resonant optical excitation. These states ionize in subnanosecond timescales, with the ions recorded on a micro-channel plate being proportional to the amount of Rydberg atoms. Translation of an autoionizing laser focused to a waist of 10 μm gives a spatially resolved Rydberg signal. A two-dimensional map of the Rydberg spatial distribution has been made using this autoionizing microscopy technique

Dynamics in a Fermi lattice gas

We use 40K atoms trapped in a cubic optical lattice to simulate the Fermi-Hubbard model. The work in this thesis focuses on investigating dynamics in the Fermi-Hubbard model and developing techniques for engineering Hamiltonians beyond the minimal Hubbard model. We discussed three experiments. In the first, we investigated the transport properties of a Fermi lattice gas by directly measuring the transport lifetime at various interaction strengths and temperatures. The resistivity is inferred from the measured transport lifetime. We observe anomalous transport behavior, which is analogous to bad-metal behavior in strongly correlated electronic materials. The second experiment presents the first realization of correlated, density-dependent tunneling in a Fermi-Hubbard optical lattice model by applied Raman laser fields. This correlated tunneling involves spin-flips and the generation of doublons, which have been observed experimentally. We also confirmed that the amplitude of correlated tunneling is suppressed when neighboring lattice sites are unoccupied. The last experiment explores the possibility to introduce long-range interactions for fermions trapped in optical lattices via Rydberg-dressed states. We developed a novel velocity-selective spectroscopy method to measure the transition between the 5P_1/2 and Rydberg states via electromagnetically induced transparency. This measurement is a first step toward inducing Rydberg-dressed interactions in optical lattices

Spectroscopic Studies on Aluminum Monofluoride

This thesis reports on optical and radio frequency (rf) spectroscopic investigation on the molecule aluminum monofluoride (AlF). The experiments are carried out on a jet-cooled, seeded pulsed molecular beam. The molecules are produced in a laser ablation process. Pulsed dye lasers and excimer lasers are used for optical excitation and ionization. A linear Time-of-flight mass spectrometer is used for ion detection. A detailed characterization of the electronic ground state (X1Σ+) and energetically excited triplet states (a3Π, b3Σ+ and c3Σ+) of AlF is given using Molecular orbital theory. The lifetimes of the b3Σ+ and c3Σ+ states are measured using multiphoton ionization. Rotationally resolved spectra are recorded for the a3Π1 ← X1Σ+, b3Σ+ ← a3Π1 and c3Σ+ ← a3Π1 bands using multiple resonance excitation schemes. Hyperfine resolved spectra are recorded for the b3Σ+, J = 1 ← a3Π1, J = 2 transition. All the spectroscopic studies are carried out between the vibrational ground states of the involved electronic states. Supplementary spectra on vibrational higher states are reported incidentally. A lineshape model, an excitation scheme and a modification of the experimental setup is worked out that enables spectroscopic measurements between the hyperfine levels of the a3Π1,J = 1 state of AlF. The setup includes a self designed and manufactured parallel plates transmission line for the rf-transition. Experiments are carried out with different carrier gases. In the end, a draft for an experimental setup that enables the measurement of spectral lines with sub-natural linewidths is presented.Diese Thesis berichtet über die experminetelle Erforschung des Moleküls Aluminium Monofluorid (AlF) mittels optischer und Hochfrequenz-Spektroskopie. Die Experimente werden an einem gepulsten Molekularstrahl durchgeführt, der durch eine Überschallexpansion erzeugt wird. Die Moleküle werden durch Laserablation hergestellt und optisch mittels Farbstofflasern und Excimer-Lasern angeregt. Der elektronische Grundzustand (X1Σ+) sowie die ersten angeregten Triplettzustände (a3Π, b3Σ+ und c3Σ+) von AlF werden auf der Basis von Molekülorbitaltheorie charakterisiert. Die Lebensdauern der beiden Triplettzustände b3Σ+ und c3Σ+ werden gemessen. Rotationsaufgelöste Spektren der a3Π1 ← X1Σ+, b3Σ+ ← a3Π1 und c3Σ+ ← a3Π1 Banden werden mittels resonanzverstärkter Mehrphotonenionisation aufgenommen. Die Hyperfeinstruktur des b3Σ+, J = 1 ← a3Π1, J = 2 Energeniveaus wird bestimmt. Ein Modell zur Beschreibung der Linienform für einen Übergang innerhalb der Hyperfeinstruktur des a3Π1,J = 1 Energieniveaus wird hergeleitet. Eine Übertragungsleitung wird in den experimentellen Aufbau integriert um mittels Hochfrequenzen einen molekularen Übergang zwischen hyperfeinen Energieniveaus anzuregen. Die Experimente werden mit verschiedenen Gaskompositionen durchgeführt. Zum Schluss wird ein experimenteller Aufbau entwickelt, der die Messung von Absorptionslinen die schmaler sind als die natürliche Linienbreite ermöglicht

Experiments with Frequency Converted Photons from a Trapped Atomic Ion

Trapped atomic ions excel as local quantum information processing nodes, given their long qubit coherence times combined with high fidelity single-qubit and multi-qubit gate operations. Trapped ion systems also readily emit photons as flying qubits, making efforts towards construction of large-scale and long-distance trapped-ion-based quantum networks very appealing. Two-node trapped-ion quantum networks have demonstrated a desirable combination of high-rate and high-fidelity remote entanglement generation, but these networks have been limited to only a few meters in length. This limitation is primarily due to large fiber-optic propagation losses experienced by the ultraviolet and visible photons typically emitted by trapped ions. These wavelengths are also incompatible with existing telecommunications technology and infrastructure, as well as being incompatible with many other emerging quantum technologies designed for useful tasks such as single photon storage, measurement, and routing, limiting the scalability of ion-based networks. In this thesis, I discuss a series of experiments where we introduce quantum frequency conversion to convert single photons at 493 nm, produced by and entangled with a single trapped $^{138}$Ba$^+$ ion, to near infrared wavelengths for reduced network transmission losses and improved quantum networking capabilities. This work is the first-ever to frequency convert Ba$^+$ photons, being one of three nearly concurrent demonstrations of frequency converted photons from any trapped ion. After discussing our experimental techniques and laboratory setup, I first showcase our quantum frequency converters that convert ion-produced single photons to both 780 nm and 1534 nm for improved quantum networking range, whilst preserving the photons' quantum properties. Following this, I present two hybrid quantum networking experiments where we interact converted ion-photons near 780 nm with neutral $^{87}$Rb systems. In the initial experiment, we observe, for the first time, interactions between converted ion-photons and neutral Rb vapor via slow light. The following experiment is a multi-laboratory project where we observe Hong-Ou-Mandel interference between converted ion-photons and photons produced by an ensemble of neutral Rb atoms, where notably these sources are located in different buildings and are connected and synchronized via optical fiber. Finally, I describe an experiment in which we verify entanglement between a $^{138}$Ba$^+$ ion and converted photons near 780 nm. These results are critical steps towards producing remote entanglement between trapped ion and neutral atom quantum networking nodes. Motivated by these experimental results, I conclude by presenting a theoretical hybrid-networking architecture where neutral-atomic based nondestructive single photon measurement and storage can be integrated into a long-distance trapped-ion based quantum network to potentially improve remote entanglement rates