This thesis presents a new experimental facility that has been developed in the course of the PhD of the author together with the experimental measurements of the dipole moments for transitions between 5P3/2 and nD5/2 states in Rb atoms, where 20 ≤ n ≤ 48. A laser cooling setup for rubidium atoms was designed and built that allows to produce 3 x 10 atoms at temperature of few microkelvins. A laser system for coherent excitation to Rydberg states was realised that exploits a two-photon ladder excitation scheme. Such setup allowed to directly measure transition dipole moments from the first excited state to high n Rydberg states. The electromagnetically induced transparency and Autler-Townes splitting phenomena were exploited in order to obtain the values of the dipole moments, which were found to be in an excellent agreement with the theoretical values calculated using the quasiclassical approach by our collaborators in Novosibirsk. To the author's knowledge, these are the first direct measurements of such dipole moments. The data shown in the thesis proves the reliability of the measurement method. The obtained results are extremely useful to validate theoretical models and gain insight in the physics of the interactions that will be an object of subsequent studies. The methods presented in the dissertation will be used in the future to detect in a non-destructive way Rydberg-Rydberg interactions within mesoscopic samples.
This thesis presents a new experimental facility that has been developed in the course of the PhD of the author together with the experimental measurements of the dipole moments for transitions between 5P3/2 and nD5/2 states in Rb atoms, where 20 ≤ n ≤ 48. A laser cooling setup for rubidium atoms was designed and built that allows to produce 3 x 10 atoms at temperature of few microkelvins. A laser system for coherent excitation to Rydberg states was realised that exploits a two-photon ladder excitation scheme. Such setup allowed to directly measure transition dipole moments from the first excited state to high n Rydberg states. The electromagnetically induced transparency and Autler-Townes splitting phenomena were exploited in order to obtain the values of the dipole moments, which were found to be in an excellent agreement with the theoretical values calculated using the quasiclassical approach by our collaborators in Novosibirsk. To the author's knowledge, these are the first direct measurements of such dipole moments. The data shown in the thesis proves the reliability of the measurement method. The obtained results are extremely useful to validate theoretical models and gain insight in the physics of the interactions that will be an object of subsequent studies. The methods presented in the dissertation will be used in the future to detect in a non-destructive way Rydberg-Rydberg interactions within mesoscopic samples.
During the course of this PhD an experimental set-up has been designed and implemented to confine neutral atoms in microscopic dipole traps and to manipulate their internal states by laser excitation to Rydberg states. A lot of effort was devoted to the stabilization of the laser sources for two-photon excitation to the Rydberg states, using techniques based on modulation transfer spectroscopy and electromagnetically induced transparency (EIT). Taking advantage of the EIT spectroscopy scheme, we have measured for the first time the electric dipole moments for the transitions between the first excited 5P3/2 and Rydberg nDS/2 level of rubidium. These measurements provided benchmarking of existing theoretical models to calculate the reduced matrix elements and have helped us to identify the D'yachkov Pankratov method as a particularly reliable one. Therefore we made use of the existing code to calculate the relative radial matrix elements for bound-bound, bound-free and free-free transitions between arbitrary states of alkali atoms. Our results allowed us to identify many features of interest and several Cooper minima have been revealed for the first time. The preparation of a new apparatus required ultra-high vacuum for efficient laser cooling and trapping experiments. A unique 4-beam magneto-optical trap has been designed and implemented in our new system. The tetrahedral MOT operating at a very acute beams angle has been demonstrated for the first time. The characterisation of the basic properties of our MOT has highlighted. some interesting new cooling mechanisms that do not fully match existing theoretical models and will require further investigation. It has been demonstrated that our tetrahedral MOT is suitable to prepare cold, diluted reservoirs of atoms and therefore efficiently load our microscopic dipole trap.
In this thesis, the development of an experimental system for microscopic dipole trapping of ultracold neutral rubidium atoms is presented. The purpose of this system is to advance towards the experimental realisation of a quantum computational protocol utilising neutral atoms as qubits. It is intended that the quantum gate operations between qubits will be implemented by a scheme using Rydberg blockade, imposing a restriction on the maximum size of the dipole-trapped atom cloud; the spatial extent of the atomic ensemble contained in this trap must be smaller than the blockade radius to ensure that one single collective Rydberg state per qubit can be achieved. Therefore the experiment was designed with the intent of fulfilling these challenging requirements. This project involved the design and construction of an improved ultra-high vacuum chamber containing the optical setup for the experiment, successfully achieving pressures below 5 x 10-10 mbar. A magneto-optical trap was produced to act as a background reservoir of atoms from which to load the dipole trap. Numerous experimental measurements were done to characterise the physical properties of the trapped atoms, including the number, density and temperature of atoms, as well as the lifetime of the trap. The results of these measurements led to the conclusion that a suitable reservoir for loading the dipole trap had been produced. Significant work was carried out to set up and obtain the dipole trap in the laboratory. Measurements of the characteristic properties of the trap and the atoms confined in the trap were carried out to investigate the behaviour of the atoms and to validate our design. Ultimately a trap containing tens of atoms was achieved, with an atom cloud diameter of ~1.2 µm in two dimensions, being well within the estimated Rydberg blockade radius of ~4.4 µm for n ~ 60 as intended. The two-photon excitation laser system for the probing of Rydberg states, for future applications in Rydberg blockade-based quantum gate operations, was also developed during the course of this work. Different Rydberg states were detected experimentally by the observation of Autler-Townes splitting in a three-level atom scheme. Overall, the work presented in this thesis provides a strong groundwork for the advancement towards neutral atom-based quantum gates, including the development of the experimental system and the production of standard procedures to carry out characterisation measurements of the traps efficiently in the future. The main achievements of this work are the establishment of the experimental apparatus, the achievement of a microscopic dipole trap which conforms to the requirements of an atomic qubit, and the significant growth in the knowledge of atom trapping specific to our system.
In this dissertation we report the results of two experimental projects with laser-cooled rubidium atoms: I. Application of Bessel beams for atom optics, and II. Spectroscopic measurements of Rydberg blockade effect. The first part of the thesis is devoted to the development of new elements of atom optics based on blue-detuned high-order Bessel beams. Properties of a 4th order Bessel beam as an atomic guide were investigated for various parameters of the hollow beam, such as the detuning from an atomic resonance, size and the order of the Bessel beam. We extended its application to create more complicated interferometer-type structures by demonstrating a tunnel lock, a novel device that can split an atomic cloud, transport it, delay, and switch its propagation direction between two guides. We reported a first-time demonstration of an atomic beam switch based on the combination of two crossed Bessel beams. We achieved the 30% efficiency of the switch limited by the geometrical overlap between the cloud and the intersection volume of the two tunnels, and investigate the heating processes induced by the switch. We also showed other applications of crossed Bessel beams, such as a 3-D optical trap for atoms confined in the intersection volume of two hollow beams and a splitter of the atomic density. The second part of this dissertation is devoted to the spectroscopic measurements of the Rydberg blockade effect, a conditional suppression of Rydberg excitations depending on the state of a control atom. We assembled a narrow-linewidth, tunable, frequency stabilized laser system at 480 nm to excite laser-cooled rubidium atoms to Rydberg states with a high principal quantum number n ~ 50 through a two-photon transition. We applied the laser system to observe the Autler-Townes splitting of the intermediate 5p state and used the broadening of the resonance features to investigate the enhancement of Rydberg-Rydberg interactions in the presence of an external electric field.
Atoms in highly excited (Rydberg) states have a number of unique properties which make them attractive for applications in quantum information.These are large dipole moments, lifetimes and polarizabilities, as well as strong long-range interactions between Rydberg atoms.Experimental methods of laser cooling and precision spectroscopy enable the trapping and manipulation of single Rydberg atoms and applying them for practical implementation of quantum gates over qubits of a quantum computer based on single neutral atoms in optical traps.In this paper, we give a review of the experimental and theoretical work performed by the authors at the Rzhanov Institute of Semiconductor Physics SB RAS and Novosibirsk State University on laser and microwave spectroscopy of cold Rb Rydberg atoms in a magneto-optical trap and on their possible applications in quantum information.We also give a brief review of studies done by other groups in this area.
Atoms in highly excited (Rydberg) states have a number of unique properties which make them attractive for applications in quantum information. These are large dipole moments, lifetimes and polarizabilities, as well as strong long-range interactions between Rydberg atoms. Experimental methods of laser cooling and precision spectroscopy enable the trapping and manipulation of single Rydberg atoms and applying them for practical implementation of quantum gates over qubits of a quantum computer based on single neutral atoms in optical traps. In this paper, we give a review of the experimental and theoretical work performed by the authors at the Rzhanov Institute of Semiconductor Physics SB RAS and Novosibirsk State University on laser and microwave spectroscopy of cold Rb Rydberg atoms in a magneto-optical trap and on their possible applications in quantum information. We also give a brief review of studies done by other groups in this area.
This thesis focusses on the development of the experimental system used to study the eff ect of Rydberg blockade interactions in clouds of ultracold atoms and quantum degenerate gases. Initial measurements have been performed quantifying these interactions, like the Rydberg blockade radius and its variation\n\n\n\nwith the density of sample, which can be very useful in devising eff cient systems for quantum information processing in quantum gates and/or as probes for detecting impurities in a sample as has been recently proposed [1]. The e ffects of the Rydberg atom interactions are probed via electromagnetically-induced\n\n\n\ntransparency (EIT). The experimental system and apparatus required for the production and detection of ultracold atoms and quantum degenerate gases is developed. Furthermore, the laser systems used for the production of Rydberg atoms via the two-photon transitions are also described. To highlight the density dependent eff ects of the Rydberg atom interactions and the\n\n\n\nunique advantages o ered to us by the Rydberg blockade eff ect, we compare the EIT experiments performed on a Λ-system using Raman lasers and the experiments performed with a ladder system involving the ground state, the fi rst excited state and a Rydberg state of Rb-87. The manifestation of the blockade eff ect with atom number density, with temperature of the atoms and with the principal quantum number of the Rydberg state to which the\n\n\n\natoms are excited, is discussed. The usefulness of the Rydberg blockade interaction as a phenomenon to be exploited in quantum information processing and an outline of the future directions of our experiments concludes the thesis.