Papers by Lara Torralbo-Campo
Physical Review A, 2016
We present our experimental investigation of an optical Raman transition between the magnetic clo... more We present our experimental investigation of an optical Raman transition between the magnetic clock states of 87 Rb in an atom chip magnetic trap. The transfer of atomic population is induced by a pair of diode lasers which couple the two clock states off-resonantly to an intermediate state manifold. This transition is subject to destructive interference of two excitation paths, which leads to a reduction of the effective two-photon Rabi frequency. Furthermore, we find that the transition frequency is highly sensitive to the intensity ratio of the diode lasers. Our results are well described in terms of light shifts in the multilevel structure of 87 Rb. The differential light shifts vanish at an optimal intensity ratio, which we observe as a narrowing of the transition linewidth. We also observe the temporal dynamics of the population transfer and find good agreement with a model based on the system's master equation and a Gaussian laser beam profile. Finally, we identify several sources of decoherence in our system, and discuss possible improvements.
New Journal of Physics
This tutorial aims to provide details on the underlying principles and methodologies of atom-base... more This tutorial aims to provide details on the underlying principles and methodologies of atom-based terahertz imaging techniques. Terahertz imaging is a growing field of research which can provide complementary information to techniques using other regions of the electromagnetic spectrum. Unlike infrared, visible and ultraviolet radiation, terahertz passes through many everyday materials, such as plastics, cloth and card. Compared with images formed using lower frequencies, terahertz images have superior spatial resolution due to the shorter wavelength, while compared to x-rays and gamma rays, terahertz radiation is non-ionising and safe to use. The tutorial begins with the basic principles of terahertz to optical conversion in alkali atoms before discussing how to construct a model to predict the fluorescent spectra of the atoms, on which the imaging method depends. We discuss the practical aspects of constructing an imaging system, including the subsystem specifications. We then re...
Cornell University - arXiv, Sep 26, 2022
This tutorial aims to provide details on the underlying principles and methodologies of atom-base... more This tutorial aims to provide details on the underlying principles and methodologies of atom-based terahertz imaging techniques. Terahertz imaging is a growing field of research which can provide complementary information to techniques using other regions of the electromagnetic spectrum. Unlike infrared, visible and ultraviolet radiation, terahertz passes through many everyday materials, such as plastics, cloth and card. Compared with images formed using lower frequencies, terahertz images have superior spatial resolution due to the shorter wavelength, while compared to x-rays and gamma rays, terahertz radiation is non-ionising and safe to use. The tutorial begins with the basic principles of terahertz to optical conversion in alkali atoms before discussing how to construct a model to predict the fluorescent spectra of the atoms, on which the imaging method depends. We discuss the practical aspects of constructing an imaging system, including the subsystem specifications. We then review the typical characteristics of the imaging system including spatial resolution, sensitivity and bandwidth. We conclude with a brief discussion of some potential applications. 1. Introduction. 1.1. Using Atoms as Sensors Atoms in dilute vapour can make very effective sensors [1, 2]. Atoms have no moving parts to wear out, they are relatively unperturbed by inter-atomic interactions, their energy levels are sensitive to applied fields, and crucially, each atom of the same isotope is identical. This final point means that atomic sensors are in effect pre-calibrated and measurements made using them are reproducible and should be, at least in principle, traceable to the SI system of measurements. Atomic systems already provide a platform for precision clocks [3, 4], gyroscopes [5, 6], magnetometers [7, 8], gravimeters [9, 10] and gradiometers [11]. Many atom-based sensors achieve optimal performance by using laser-cooling techniques to create very cold atomic samples [12], and although efforts are ongoing to simplify and miniaturise such apparatus [13, 14], laser cooling inevitably introduces significant experimental complexity and cost to the setup. In contrast, for atomic sensors where inhomogeneous Doppler broadening is not a problem, setups using
Optical Sensors and Sensing Congress 2022 (AIS, LACSEA, Sensors, ES)
We report the ongoing development of a Rydberg atom-based detector for sensing terahertz radiatio... more We report the ongoing development of a Rydberg atom-based detector for sensing terahertz radiation. It will be used to characterize the emission properties of a superconducting terahertz emitter and a terahertz quantum-cascade laser.
We use a phase-only spatial light modulator to generate light distributions in which the intensit... more We use a phase-only spatial light modulator to generate light distributions in which the intensity decays as a power law from a central maximum, with order ranging from 2 (parabolic) to 0.5. We suggest that a sequence of these can be used as a time-dependent optical dipole trap for all-optical production of Bose-Einstein condensates in two stages: efficient evaporative cooling in a trap with adjustable strength and depth, followed by an adiabatic transformation of the trap order to cross the BEC transition in a reversible way. Realistic experimental parameters are used to verify the capability of this approach in producing larger Bose-Einstein condensates than by evaporative cooling alone.
Physical Review A, 2017
We report on the observation of the motional Stark effect of highly excited 87 Rb Rydberg atoms m... more We report on the observation of the motional Stark effect of highly excited 87 Rb Rydberg atoms moving in the presence of a weak homogeneous magnetic field in a vapor cell. Employing electromagnetically induced transparency for spectroscopy of an atomic vapor, we observe the velocity-, quantum state-and magnetic field-dependent transition frequencies between the ground and Rydberg excited states. For atoms moving at velocities around 400 m/s, the principal quantum number n = 100 of the valence electron, and a magnetic field of B = 100 G, we measure a motional Stark shift of ∼10 MHz. Our experimental results are supported by numerical calculations based on a diagonalization of the effective Hamiltonian governing the valence electron of 87 Rb in the presence of crossed electric and magnetic fields.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2016
Trapping a Rydberg atom close to a surface is an important step towards the realisation of many p... more Trapping a Rydberg atom close to a surface is an important step towards the realisation of many proposals of quantum information or hybrid quantum systems. One of the challenges in these experiments is to overcome the electric field emanating from contaminations on the surface. Here we report on measurements of an electric field created by 87 Rb atoms absorbed on a 25 nm thick layer of SiO 2 , covering a 90 nm layer of Au. The electric field is measured using a two-photon transition to the 23D 5/2 and 25S 1/2 state. The electric field value that we measure is higher than typical values measured above metal surfaces, but is consistent with other measurements above SiO 2 surfaces. In addition, we measure the temporal behaviour of the field and observe that we can reduce it in a single experimental cycle, using UV light or by mildly heating the surface, whereas the buildup of the field takes thousands of cycles. We explain these results by a change in the ad-atoms distribution on the surface. These results indicate that the stray electric field can be reduced, opening new possibilities for experiments with trapped Rydberg atoms near surfaces.
Scientific reports, Jan 13, 2015
In recent years, light-induced atomic desorption (LIAD) of alkali atoms from the inner surface of... more In recent years, light-induced atomic desorption (LIAD) of alkali atoms from the inner surface of a vacuum chamber has been employed in cold atom experiments for the purpose of modulating the alkali background vapour. This is beneficial because larger trapped atom samples can be loaded from vapour at higher pressure, after which the pressure is reduced to increase the lifetime of the sample. We present an analysis, based on the case of rubidium atoms adsorbed on pyrex, of various aspects of LIAD that are useful for this application. Firstly, we study the intensity dependence of LIAD by fitting the experimental data with a rate-equation model, from which we extract a correct prediction for the increase in trapped atom number. Following this, we quantify a figure of merit for the utility of LIAD in cold atom experiments and we show how it can be optimised for realistic experimental parameters.
Review of Scientific Instruments, 2015
The lifetime of an atom trap is often limited by the presence of residual background gases in the... more The lifetime of an atom trap is often limited by the presence of residual background gases in the vacuum chamber. This leads to the lifetime being inversely proportional to the pressure. Here, we use this dependence to estimate the pressure and to obtain pressure rate-of-rise curves, which are commonly used in vacuum science to evaluate the performance of a system. We observe different rates of pressure increase in response to different levels of outgassing in our system. Therefore, we suggest that this is a sensitive method which will find useful applications in cold atom systems, in particular, where the inclusion of a standard vacuum gauge is impractical.
Research in Optical Sciences, 2014
ABSTRACT We present our first experimental observations of ultracold atoms in lattices of square ... more ABSTRACT We present our first experimental observations of ultracold atoms in lattices of square and hexagonal geometry with a lattice constant of 10 µm, suitable for experiments in quantum information processing employing the interaction between atoms in highly-excited Rydberg energy levels as qubits.
Review of Scientific Instruments, 2014
We describe the fabrication and construction of a setup for creating lattices of magnetic microtr... more We describe the fabrication and construction of a setup for creating lattices of magnetic microtraps for ultracold atoms on an atom chip. The lattice is defined by lithographic patterning of a permanent magnetic film. Patterned magnetic-film atom chips enable a large variety of trapping geometries over a wide range of length scales. We demonstrate an atom chip with a lattice constant of 10 µm, suitable for experiments in quantum information science employing the interaction between atoms in highly-excited Rydberg energy levels. The active trapping region contains lattice regions with square and hexagonal symmetry, with the two regions joined at an interface. A structure of macroscopic wires, cut out of a silver foil, was mounted under the atom chip in order to load ultracold 87 Rb atoms into the microtraps. We demonstrate loading of atoms into the square and hexagonal lattice sections simultaneously and show resolved imaging of individual lattice sites. Magnetic-film lattices on atom chips provide a versatile platform for experiments with ultracold atoms, in particular for quantum information science and quantum simulation.
The following is an agreed request by candidate and supervisor regarding the electronic publicati... more The following is an agreed request by candidate and supervisor regarding the electronic publication of this thesis: Access to Printed copy and electronic publication of thesis through the University of St Andrews.
Research in Optical Sciences, 2014
ABSTRACT We present our first experimental observations of ultracold atoms in lattices of square ... more ABSTRACT We present our first experimental observations of ultracold atoms in lattices of square and hexagonal geometry with a lattice constant of 10 µm, suitable for experiments in quantum information processing employing the interaction between atoms in highly-excited Rydberg energy levels as qubits.
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Papers by Lara Torralbo-Campo