The objective of this thesis is to develop the quantum theory of the motional degrees of freedom of a charged particle in a Penning trap. The theory is treated within the formalism of quantum optics, and explores the use of dressed-atom methods by exploiting the threefold SU(N) algebraic structure of the problem. The quantum form of the experimental techniques of sideband coupling and driving to the ultra-elliptical regime are examined in this context, and resulting future applications considered. Interpretation of the quantum dynamics of the separate x and y motions of an electron is discussed, motivated by the desire to modify the trapping potential without changing the basic experimental configuration. A detailed discussion of operator methods which exploit the algebraic structure of the problem is given. This results in a clearer understanding of the physical manifestations of a range of unitary transformations upon a general three-dimensional system, and a novel interpretation of the mapping between canonical angular momentum components of isotropic and anisotropic trapping systems. The results highly promote future use of these methods in Penning trap theory, detailing a robust formulation of unitary operations which can be used to prepare the quantum state of a charged particle. The majority of the results can be applied to any Penning trap, but the theory is based throughout upon the “Geonium Chip" trap at Sussex; the scalability and planar design of this trap promotes it as natural candidate in experimental quantum optics and Gaussian quantum information studies. The work in this thesis aims to provide framework for such future applications.
The objective of this thesis is to develop the quantum theory of the motional degrees of freedom of a charged particle in a Penning trap. The theory is treated within the formalism of quantum optics, and explores the use of dressed-atom methods by exploiting the threefold SU(N) algebraic structure of the problem. The quantum form of the experimental techniques of sideband coupling and driving to the ultra-elliptical regime are examined in this context, and resulting future applications considered. Interpretation of the quantum dynamics of the separate x and y motions of an electron is discussed, motivated by the desire to modify the trapping potential without changing the basic experimental configuration. A detailed discussion of operator methods which exploit the algebraic structure of the problem is given. This results in a clearer understanding of the physical manifestations of a range of unitary transformations upon a general three-dimensional system, and a novel interpretation of the mapping between canonical angular momentum components of isotropic and anisotropic trapping systems. The results highly promote future use of these methods in Penning trap theory, detailing a robust formulation of unitary operations which can be used to prepare the quantum state of a charged particle. The majority of the results can be applied to any Penning trap, but the theory is based throughout upon the “Geonium Chip" trap at Sussex; the scalability and planar design of this trap promotes it as natural candidate in experimental quantum optics and Gaussian quantum information studies. The work in this thesis aims to provide framework for such future applications.
Abstract We present the quantum theory of the elliptical Penning trap, i.e. the general case where the cylindrical symmetry of the electrostatic trapping potential around the trapping magnetic field axis is broken. The theory applies to both slightly and highly elliptical traps, where it is shown that the difference between the quantum states of particles in these traps corresponds to a variation of the degree of squeezing of their motional modes in the xy-plane. In a trap with tunable ellipticity, such as the Geonium Ghip planar Penning trap, it follows that control of the ellipticity via the trapping voltages enables squeezing of the quantum states of the particle. We discuss the adiabatic preparation of such squeezed states, which follows naturally from the appearance of an avoided crossing between the diabatic levels of the coupled motional states of the particle.
In this thesis is presented the realisation of `The Geonium Chip', a novel planar Penning trap. The chip is designed with the goal of building a truly scalable planar Penning trap, while retaining the accuracy of 3D traps. Manufactured with conventional metalon- silicon microfabrication techniques, the chip takes the 5 electrodes of the compensated cylindrical trap and projects them onto a ground-plane surface, thus forming the basis for its layout by reducing the electrode shape to an array of at rectangular surfaces. In this thesis I describe the conception, design and construction of a full cryogenic set-up, including the magnetics, for trapping and observing a single electron in the Geonium Chip Penning trap. The cyclotron mode of the trapped electron lies in the microwave regime, and thus the Geonium Chip has the potential to become a powerful building block for quantum microwave circuits, with coherent coupling to the cyclotron degree of freedom. This will also allow non-destructive measurement and interaction with the spin state of the electron. The development of the experimental process is detailed from scratch including the design, fabrication, and testing of the Geonium Chip, as well as the design, fabrication and testing of the experimental apparatus. The original solutions and space saving designs developed as part of the construction process are detailed, such as the custom on-chip cryogenic vacuum chamber, planar magnetic field source, and the LED-based electron loading system. The vacuum chamber and control systems are also described, and the in-house manufacturing capabilities of the Geonium group are detailed at length, with an emphasis on rapid prototyping high-accuracy components suitable for experimental use. The apparatus built within this PhD is within a few weeks of performing the first loading of electrons into the chip trap.
A novel planar Penning trap is presented, which results from the projection of the well-known three-dimensional cylindrical trap onto the surface of a chip. The introduced trap is also a coplanar-waveguide cavity, similar to those used in circuit quantum electrodynamics experiments with superconducting two-level systems. It opens up the possibility of integrating a single trapped electron, or geonium atom, into quantum circuits. The trap is an elliptical Penning trap, with the magnetic field parallel to the chip's surface. A design procedure is described, which permits the compensation of electric anharmonicities up to sixth order. This should render possible the observation of a single trapped electron and the accurate measurement of its eigenfrequencies, a sine qua non requirement for a useful planar geonium technology.
Laser-cooled trapped ions are one of the main systems used in experiments in the fields of quantum optics and quantum information. There are two commonly-used types of ion trap, the radiofrequency trap and the Penning trap. In general, the RF trap has been more widely used in quantum information experiments, meaning that the set of experimental tools for conducting these types of experiments in a Penning trap is currently less complete. The aim of the work presented in this thesis is to increase this array of tools. Our experiment uses 40Ca+ ions in a Penning trap alongside lasers. Spectroscopy has been performed on single Doppler cooled ions, and on ions that have been prepared close to their ground state of motion using a multiple-stage sideband cooling technique resulting in an average phonon occupation number of $\nzbar = 0.029\pm 0.011$ from an initial $\nzbar \approx 24$. This corresponds to a quantum ground state population of 97%, which is close to the sideband cooling limit in our system. An axial heating rate measurement of $\dot{\bar{n}}_z=\SI{0.56\pm0.52}{\per\second}$ has also been obtained, which is the lowest recorded to date, due in part to the large dimensions of our trap. Additionally improved control of the Penning trap radial motion has been demonstrated and the average phonon occupation number of the modified cyclotron motion has been reduced from $\ncbar\approx150$ after Doppler cooling to $\ncbar=0.6$ after sideband cooling. Some preliminary single-ion coherent operations have also been performed. In the future we hope that this system of ground state cooled ions in a Penning trap can be used to generate highly-entangled states in two or more ions, with a view to performing simple quantum error-correcting codes and eventually an analogue quantum simulation of spin systems.
This thesis presents the development of the Geonium Chip, a planar Penning trap. The Geonium Chip consists of the five electrodes of a cylindrical Penning trap projected onto the surface of a microfabricated chip. Beneath the chip is a planar magnetic field source currently made from coils of niobium titanium wire. Traditionally the magnetic field source is a large superconducting solenoid, replacing this with a planar source makes the setup scalable, portable and economical. The Geonium Chip, with its magnetic field source and detection electronics, need to be placed in a cryostat. In this thesis, I describe the development of the cryogenic setup with particular emphasis on the design and optimisation of the non-destructive detection system. I detail the cryogenic wiring of the cryostat including the thermalisation of high current wires and the noise reduction techniques employed on the detection signal. In addition, I explore the parasitic capacitances of the Geonium Chip using microwave network analysis and describe the testing of the magnetic field source at 4 K. Finally, I discuss the generation of electrons within the trap and the results of our first attempts at trapping a cloud of electrons. Together, the chip and the magnetic field source can be used to trap ions for ultraaccurate mass spectrometry or an electron for single microwave photon detection. A single microwave photon detector is a tool that is currently still missing in quantum technology and is needed for determining the quantum state of microwave radiation fields. This is vital for quantum communication and cryptography. Additionally, using the Geonium Chip as a mass spectrometer has the potential to lead to very accurate mass spectrums without the need for frequent calibration. Finally, eliminating the expensive superconducting solenoid will make accurate mass spectrometry available to a wider market.
The Geonium Chip Penning trap is a planar trap that aims to reduce both the size and the cost of other conventional systems while maintaining the same level of accuracy, making it an ideal candidate for practical quantum technology applications, such as the implementation of the Microwave Quantum Illumination Protocol. This is possible thanks to the possibility of using a single electron trapped in the Geonium Chip as the emitter and receiver of single microwave photons, as well as to facilitate the creation and detection of quantum correlations. The results presented in this thesis consist on the first steps towards the engineering of a scalable and deployable system, adapted to the requirements of the Quantum Illumination Protocol. This thesis has tackled all the aspects associated to this task, such as studies on how to enhance the quantum efficiency of single microwave photons using a trapped electron, the engineering and characterisation of a novel LED-based electron source which will help to reduce the overall size of the experiment and the first steps towards the development of a novel planar magnetic field source made of GdBCO, a high temperature superconductor.