Ion traps are widely used to contain and study charged particles. In recent years, there has been an effort to utilize trapped particles as quantum detectors or as components of quantum computers. Before trapping a particle inside an ion trap, it needs to be ionised and cooled, which is commonly achieved using fine-tuned semiconductor lasers. The main objective of this thesis is to develop PID regulator capable of stabilising a 423nm photoionising laser, which is a part of the ion trapping experiment in the Ultracold plasma laboratory. The thesis includes a basic insight into the theory of linear regulators, as well as a detailed implementation procedure with thorough description of employed hardware components.
Ion traps are widely used to contain and study charged particles. In recent years, there has been an effort to utilize trapped particles as quantum detectors or as components of quantum computers. Before trapping a particle inside an ion trap, it needs to be ionised and cooled, which is commonly achieved using fine-tuned semiconductor lasers. The main objective of this thesis is to develop PID regulator capable of stabilising a 423nm photoionising laser, which is a part of the ion trapping experiment in the Ultracold plasma laboratory. The thesis includes a basic insight into the theory of linear regulators, as well as a detailed implementation procedure with thorough description of employed hardware components.
This thesis describes experimental work towards developing a trapped ion quantum information processor. An existing ion trap apparatus was capable of trapping and laser-cooling single ions or small ion strings of 40 Ca+, and had been used for studies of quantum jumps and natural lifetime measurements in Ca. This thesis describes improvements in this apparatus, which have allowed the stability and the flexibility of experimental control of the ions to be greatly increased. This enabled experiments to read out the spin state of a single trapped ion, and to load ions with isotope selectivity through photoionization. The optical systems were improved by installation of new lasers, optical reference cavities, and a system of acousto-optic modulators for laser intensity switching and frequency control. The photon counting for fluorescence detection was improved, and a new photon time-of-arrival correlation circuit developed. This has permitted rapid and more sensitive detection of micromotion, and hence cancellation of stray fields in the trap. A study of resonant circuits in the low RF, high voltage (10 MHz, 1 kV) regime was carried out with a view to developing a new RF supply for the Paul trap with reduced noise and increased power. A new supply based on a helical resonator was built and used to trap ions. This technique has reduced noise and will permit higher secular frequencies to be attained in the future. A magnetic field B in the ion trap is used to define a quantization axis, and in one series of experiments was required to be of order 100 G to provide a substantial Zeeman splitting. A set of magnetic field coils to control the size and direction of B is described. The design of these posed some problems owing to an unforseen issue with the vacuum chamber. In short, it is magnetizable and acts to first approximation like a magnetic shield. The field coils had to be sufficiently substantial to produce the desired field at the ion even in the presence of this shielding effect, and dark resonance (and other) spectra with Zeeman splitting were obtained to calibrate the field using the ion as a probe. Finally, the thesis describes the successful loading of the ion trap by laser photoionization from a weak atomic beam. This involved two new lasers at 423 nm and 389 nm. Saturated absorption spectroscopy of neutral calcium is first described, then transverse excitation of an atomic beam in our vacuum chamber is used to identify all the main isotopes of calcium and confirm their abundances in our source (a heated sample of natural calcium). Finally, photoionization is used to load the trap. This has three advantages over electron-impact ionization. By avoiding an electron gun, we avoid charging of insulating patches and subsequent electric field drift as they discharge; the flux in the atomic beam and hence calcium (and other) deposits on the electrodes can be greatly reduced; and most importantly, the photoionization is isotope selective. Evidence is presented which suggests that even with an non-enriched source, the rare isotope 43 Ca can be loaded with reasonable efficiency. This isotope is advantageous for quantum information experiments for several reasons, but chiefly because its ground state hyperfine structure can act as a stable qubit.
EN The laser-cooling of ions to temperatures below 1 millikelvin is a standard technique in quantum computing development, but achieving similar cooling for electrons remains difficult. Discovering an effective method could lead to new qubit architecture possibilities. This thesis presents a potential appro- ach for cooling electrons based on Coulomb interactions with laser-cooled ions, providing the necessary theoretical foundation, surveying the latest li- terature, and detailing an experimental implementation currently underway. It also explores how the ultracold ion and electron system could serve as a quantum detector for radio-frequency waves and microwaves. The core ex- perimental work focuses on developing a technique for fabricating miniature optical cavities from optical fibres, with preliminary results and future di- rections for producing highly integrated optical devices provided. 1
This dissertation focuses on observing and controlling cold atom-ion collisions. Such collisions have numerous applications ranging from providing insight into the formation of the interstellar medium to presenting a potential platform for developing quantum information architectures. The experimental apparatus at the center of this work is a hybrid atom-ion trapping system in which laser-cooled Ca atoms held within a magneto-optical trap are spatially overlapped with ions localized within an ion trap. The ions studied in this work are both laser-cooled atomic ions as well as sympathetically cooled molecular ions. As detailed in the remainder of this thesis, by employing tools such as optical pumping, collision energy control, and mass spectrometry, reactions between these species can not only be studied with high precision but can also be controlled, leading to expanded tools for reaction engineering as well as the creation of exotic chemical species. Finally, this work also includes efforts to use inelastic collisions between room temperature BaCl^+} molecular ions and cold Ca atoms to create ro-vibrational ground state molecules, a precursor for developing a high-fidelity qubit based on rotational levels in polar molecules.
In recent years there has been increasing interest in quantum atom optics, in which the discretenature of atoms plays an important role. As such, the ability to resolve atoms at the singleatom level has become important.This thesis investigates detecting atoms using photoionisation and ion detection. Thismethod is applicable to all atoms in common use in atom optics experiments, enables theirdetection with high e±ciency, allows atom counting with sub-Poissonian resolution (¾N < pN)and is applicable for large atom numbers (up to » 105). Two approaches towards atom detectionvia photoionisation and ion detection are examined, di®ering in the rate of photoionisation. Fastphotoionisation of individual atoms can be used for detecting a series of single atoms, such asmight be produced with an atom laser. Slow ionisation is required for counting large numbersof atoms contained in a single region, due to the necessity of being able to resolve the individualions with the ion detector. The application of these methods to 87Rb is examined, althoughthey can be adapted to other atoms.The scheme for quickly detecting single atoms uses STImulated Raman Adiabatic Passage(STIRAP) to excite 87Rb atoms to the 5D5=2 level followed by ionisation from this level usinga Nd:YAG laser pulse. Simulations and experiments were carried out and used to predict thatexcitation to the 5D5=2 level can be achieved with close to 100% e±ciency, and to show theexperimental parameters required. The photoionisation cross-section of 87Rb in the 5D5=2 stateusing 1064 nm light was measured in order to predict the photoionisation e±ciency that maybe achieved, which was found to approach 100%.The scheme for atom counting uses 2£778 nm photon excitation to raise atoms to the5D5=2 state followed by ionisation from this state using a cw Nd:YAG laser. The statisticsof atom counting are examined and used to ¯nd the counting accuracy as a function of thedetection e±ciency and its uncertainty. For a precisely calibrated detector, sub-Poissoniancounting is possible for detection e±ciencies greater than 50%. The e®ect of losses and the useof the scheme for measuring number squeezing are examined. Achieving low count uncertaintiesrequires measuring the ion detection e±ciency to high accuracy. A method for doing this isproposed and analysed, and experiments were carried out to measure the ion detection e±ciencyof an ion detector in a mock experimental setup. A detailed scheme is proposed and analysed for measuring number di®erence squeezing ina RF induced double well potential using atom counting via photoionisation and ion detection.Simulations of the double well potential were performed to show how even splitting can beachieved and the degree of squeezing expected to occur. A design for an experimental setup isdescribed and analysed in detail, in order to show the accuracy with which number di®erencesqueezing can be measured.
This PhD thesis reports on the development of a wide variety of theoretical and experimental capabilities in the field of quantum information processing using trapped ions. The presentation is organized in two distinct parts. The first part presents a series of published articles containing theoretical results, and their experimental validation, advancing a range of tools and techniques in error-resilient quantum control and robust verification procedures. One of the fundamental challenges in realizing a general purpose quantum computer is the management of error in fragile quantum systems. A familiar aspect of this challenge is decoherence, a process by which the system looses its stored quantum information, rendering it useless for subsequent computation. This collection of works focuses on reducing sources of quantum decoherence and precisely quantifying residual errors in real quantum systems dominated by realistic temporally-correlated noise processes, of central importance in any future architecture for quantum computing. The second part focuses on the design, construction and characterization of a complex experimental system capable of supporting a broad calls of quantum simulation experiments with hundreds of spin qubits using 9Be+ ions in a Penning trap. The trap design is optimized to suppress non-harmonic trapping potentials while providing wide optical access for engineering enhanced spin-motion coupling across large ion crystals. A superconducting magnet, equipped with a fully closed-cycle dual LN2/LHe recondensor, provides the magnetic field for trapping and produces the 55-GHz Zeeman-split qubit states suitable for microwave control. A custom UV laser system for driving the relevant transitions in neutral and ionized beryllium, as well as UV-compatible fibers and in-bore optomechanics for delivering microwave and laser beams to the trap, is presented. The thesis concludes with a brief outlook towards future theoretical and experimental studies, and extensions of the experimental setup
In the experiments involving trapped ions, application of a cooling procedure is required. The optical Doppler scheme is one of the most commonly used methods for slowing down the ions motion. In this paper we present an optical system sufficient for cooling calcium ions in such scheme. The system allows also for optical detection of the trapped ions. Full Text: PDF ReferencesF. Major, V. Gheorghe, and G. Werth, Charged Particle traps, Physics and Techniques of Charged Particle Field Confinement (Springer 2005). DirectLink Ł. Kłosowski, M. Piwiński, and M. Drewsen, "Integral electron impact ionization cross section of molecules through Coulomb crystallization of the product ions", J. Phys. Conf. Ser. 635, 072003 (2015) CrossRef D. J. Wineland and Wayne M. Itano, "Laser cooling of atoms", Phys. Rev. A 20, 1521 (1979) CrossRef R. Drever et al., "Laser phase and frequency stabilization using an optical resonator", Appl. Phys. B 31, 97 (1983) CrossRef P. W. Smith, "Mode-locking of lasers", Proceedings of the IEEE 58, 1342 (1970) CrossRef S. Stenholm, "The semiclassical theory of laser cooling", Rev. Mod. Phys. 58, 699 (1986) CrossRef