Saturation Intensity of Rare Earth Ions Doped Crystals

Abstract

The thesis is primarily concerned with rare earth ions doped into yttrium ortho silicate crystals, RE:YSO. It is considered to be an ambitious platform for the development of quantum computing schemes. One such scheme requires the detection of single cerium ions. The project was aimed at measuring the saturation intensity of cerium 5d-4f transition which is needed for the single ion detection.

This work contains theoretical simulations as well as measurements of fluorescence from rare earth ions sitting inside of a crystal as a function of excitation power. For practical reasons the measurement could not be carried out on cerium, but praseodymium was used instead.

By measuring the saturation intensity one can derive the homogeneous linewidth that contributes to the detection procedure. The major complication in this type of measurement is the power broadening. Therefore, the measurement was aided by a theoretical simulation.

The data was then fit with simulated theoretical results.
The measurement was inconclusive for several reasons that are discussed at the end. However, this work is a priceless reference for the future cerium saturation intensity measurement or another experiment that needs to consider power broadening effects.

Popular Abstract

Saturation Intensity of of Rare Earch Ions Doped Crystals

The most ambitious advance of computational technology is now in the hands of atomic physicists who have to unravel the atomic properties of a host substance in order to gain the sufficient knowledge needed for quantum control. It is of one such property needed for better understanding of atomic behaviour that is the niche this thesis aiming to fill.
Instead of the decimal system, the classical computer uses a binary form, only 0 and 1's, to code information, perform and control computations. The basic unit of information that can have one of the two values is called a bit. The two-level representation coupled with the advance in underlying electronics technology led to steady progress in computational technology that is well illustrated by the "Moore's law that states that the storage capacity of computer memory chips grows steadily doubling every 18 months. As the size of a transistor is heading towards atomic dimensions, the law is said to be reaching its physical limit. On the atomic scale the performance is hindered by quantum effects and can no longer be controlled by classical methods of information treatment. However, the idea of ‘quantum computer’ introduced by Richard Feynman in 1982 suggested the asserted limit to be technological rather than physical, while rather than being an obstacle the quantum behaviour turned out to provide computational advantage introducing the qubit – the information unit promissing an unprecedent boost in information handling and processing speed.
There are many available test beds for quantum computing each creating problems of its own niche. The development of quantum computing schemes regardless of their physical platform is limited by the scalability problem, i.e. the ability of the system to perform operations on multiple qubits. In case of rare earths based quantum computing one of the solutions to this problem is to use a single ion approach that requires an additional readout ion. In our case we were looking at praesodynium doped yttrium ortho silicate crystals with additional cerium readout ions. However, detecting the fluorescence of a single readout ion is a difficult tast that requires knowing an atomic parameter known as homogeneous linewidth. One of the ways to detemine the parameter is to measure the saturation intensity of the ion by probing its fluorescence. The major complication in this type of measurement is the power broadening. Measuring the saturation intensity of cerium is precisely the task overtaken by this work.
This work contains theoretical simulations that takes the power broadening into account as well as measurements of fluorescence from rare earth ions sitting inside of a crystal as a function of excitation power. Before the measurements were started the experimental setup had to be completed and tested. During the latter phase of the project it turned out that the measurement could not be carried out on cerium. Praseodymium was used instead for the sole reason of testing the validity of the model developed.
In the end the data was fit with simulated theoretical results. The best fit showed the results that were close to the predicted value. Nevertheless, as the fitted fluorescence signal did not scale as predicted by the model, hence the measurement was inconclusive. The cause for this could possibly originate from both the experimental conditions, or a physical phenomenon that was not taken into account when writing the script for the model.

• author: Solovejus, Martynas
• supervisor: Jenny Karlsson; Stefan Kröll
• organization: Department of Physics; Atomic Physics
• alternative title: A step towards quantum computing
• course: FYSM31 20141
• year: 2014
• type: H2 - Master's Degree (Two Years)
• subject: Physics and Astronomy
• keywords: saturation intensity, spectral broadening, spectral effects, rare earths, rare-earths, cerium, Ce, Ce:YSO, Pr:YSO, RE:YSO, quantum information, quantum computing
• report number: LRAP no 491
• language: English
• id: 4584334
• date added to LUP: 2014-10-20 14:14:25
• date last changed: 2014-10-22 09:53:54