Magnetic trapping is a well-established technique for ground state atoms. We seek to extend this concept to Rydberg atoms. Rydberg atoms are important for current visions of quantum simulators that will be used in the near future to simulate and analyse quantum problems. Current efforts in Amsterdam rely on Rydberg atoms to be excited from a BEC in magnetic microtraps and to stay trapped after excitation. Rydberg atoms are atoms excited to high electronic states, with a spatial size comparable to the size of magnetic microtraps. The question is then whether Rydberg atoms are trappable in magnetic traps so tight that the magnetic field varies appreciably on length scales comparable to the atomic rms radius. Our research indicates that some Rydberg atoms will indeed remain trapped and shows how the magnetic trapping potential is affected by the finite size of Rydberg atoms.
Magnetic trapping is a well-established technique for ground state atoms. We seek to extend this concept to Rydberg atoms. Rydberg atoms are important for current visions of quantum simulators that will be used in the near future to simulate and analyse quantum problems. Current efforts in Amsterdam rely on Rydberg atoms to be excited from a BEC in magnetic microtraps and to stay trapped after excitation. Rydberg atoms are atoms excited to high electronic states, with a spatial size comparable to the size of magnetic microtraps. The question is then whether Rydberg atoms are trappable in magnetic traps so tight that the magnetic field varies appreciably on length scales comparable to the atomic rms radius. Our research indicates that some Rydberg atoms will indeed remain trapped and shows how the magnetic trapping potential is affected by the finite size of Rydberg atoms.
We explore the possibility to trap Rydberg atoms in tightly confining magnetic microtraps. The trapping frequencies for Rydberg atoms are expected to be influenced strongly by magnetic-field gradients. We show that there are regimes where Rydberg atoms can be trapped. Moreover, we show that so-called magic trapping conditions can be found for certain states of rubidium, where both Rydberg atoms and ground-state atoms have the same trapping frequencies. Magic trapping is highly beneficial for implementing quantum gate operations that require long operation times.
Cold Rydberg atoms exposed to strong magnetic fields possess unique properties which open the pathway for an intriguing many-body dynamics taking place in Rydberg gases, consisting of either matter or anti-matter systems. We review both the foundations and recent developments of the field in the cold and ultracold regime where trapping and cooling of Rydberg atoms have become possible. Exotic states of moving Rydberg atoms, such as giant dipole states, are discussed in detail, including their formation mechanisms in a strongly magnetized cold plasma. Inhomogeneous field configurations influence the electronic structure of Rydberg atoms, and we describe the utility of corresponding effects for achieving tightly trapped ultracold Rydberg atoms. We review recent work on large, extended cold Rydberg gases in magnetic fields and their formation in strongly magnetized ultracold plasmas through collisional recombination. Implications of these results for current antihydrogen production experiments are pointed out, and techniques for the trapping and cooling of such atoms are investigated.
In this thesis I examine high-magnetic-field Rydberg spectra, with the goal of discerning the viability of using such states as an interaction mechanism for quantum computation processes. In the presence of a strong magnetic field of B0 = 2.6 T, high-lying states of E ~ -55 cm(-1) are non-degenerate and show a wide range of magnetic dipole moments. Near-degenerate pairs of states of the same mJ manifold but of different axial parity Pi_z will strongly interact in the presence of an applied weak parallel electric field F, generating a pair of highly polar states. I show experimental results that, in agreement with theoretical work presented here, illustrate the presence of strong permanent dipole moments p ~ 1500 ea0 under these conditions. Such Rydberg states can also be tuned into resonance through careful control of the magnetic field, and are suitable for developing quantum phase gates and performing Rydberg-Rydberg interaction experiments. In order to perform such high-field Rydberg excitation experiments, a stable, dense and well-controlled cold atom cloud is needed within a high-magnetic-field environment. Toward this end, I present a full characterization of the utilized high-field trapping apparatus, including measurements of the trapped atom sample size, shape, and temperature. Analysis of the loss rate from the high-magnetic-field atom trap, both as a function of the applied magnetic field B0 and transverse confinement are presented. Experimental results for the high-field confinement of 85Rb are presented, as well as the first demonstration of a high-field 87Rb trap. Current trap limitations and possible improvements to the trapping apparatus are discussed. Other applications of the high-magnetic-field trap, such as the investigation of ultracold two-component plasmas and three-body recombination experiments, are also presented.
Summary form only given. Cooling and trapping in atomic systems have ushered in a revolution in the fields of opto-mechanical control, high precision spectroscopy, quantum electrodynamics and quantum information; to date, however, these advances have been restricted almost exclusively to near-ground state atoms. Highly excited atoms, or Rydberg atoms, have been explored for decades as testing grounds for quantum mechanics, quantum chaos, wavepacket manipulation and, more recently, quantum computing. Though the cooling of Rydberg atoms has been proposed and the generation of cold Rydberg atoms from cold ground state atoms has been achieved, the ability to trap cold Rydberg atoms remains an important and unaddressed milestone. We present a method to trap Rydberg atoms in any electronic state based on the weakly-bound nature of the Rydberg electron.
This thesis contributes to the quantum platform based on an atom chip. In our atom chip, atoms are trapped by means of a magnetic field. This magnetic field is created by a very thin layer of a permanently magnetized material, which is etched to create a periodic structure. Together with an applied homogeneous bias field this structure creates a periodic lattice of magnetic field minima. Cold atoms are trapped in these minima (so called microtraps). In our experiment we want to induce interaction between atoms in different lattice sites by exciting them into so-called Rydberg states: atomic states with a very large principal quantum number. These states have some extreme properties: very strong van der Waals interaction, polarizability, and long lifetimes. This makes Rydberg atoms promising candidates to build a quantum platform. In this thesis we investigate different challenges that one encounters on the way to a quantum platform based on an atom chip with Rydberg atoms. In chapter 2 we present our work on a spatial light modulator (SLM). In chapter 3 we present our experimental results on measuring and controlling stray electric fields on our atom chip. In chapter 4 we construct a comprehensive model, describing such mechanisms in order to describe the measured fields as well as its dynamical change. In chapter 5 we present a setup for our new Magchips Nano experiment. Finally, in chapter 6 we present our first steps, taken to bring the new Magchips Nano machine to life.
Subject of this thesis is the investigation of the quantum dynamics of ultracold atoms in the presence of external inhomogeneous magnetic fields. We discuss the behavior of ground state atoms inside typical magnetic field configurations. Such atoms can be approximately treated as neutral point-like particles which carry a certain spin. In particular we analyze the resonance spectrum and the density of states of both fermionic and bosonic atoms. We point out the existence of so-called quasi-bound states whose wave functions can be approximately calculated analytically. Moreover, we focus on studying quantum mechanical states of ultracold but electronically highly excited atoms - so-called Rydberg atoms - inside magnetic traps. In a first step we explore their internal dynamics by employing a fixed-nucleus approximation. The latter assumes the atomic nucleus to be fixed in the magnetic field minimum. Within this framework we analyze spectral properties as well as properties of the electronic spin and calculate electromagnetic transitions. Finally we present an adiabatic approach which allows for a thorough description of the coupled center of mass and electronic dynamics. We highlight ways to magnetically trap highly excited atoms and present novel quantum states in which the center of mass and the electronic wave function are equal in size. This finding shows that Rydberg atoms even in inhomogeneous fields with moderate gradients cannot be considered point-like.