Coherent Dark States of Rubidium 87 in a Buffer Gas using Pulsed Laser Light

The coherent dark resonance between the hyperfine levels F=1, m=0 and F=2, m=0 of the rubidium ground state has been observed experimentally with the light of a pulsed mode-locked diode laser operating at the D1 transition frequency. The resonance occurs whenever the pulse repetition frequency matches an integer fraction of the rubidium 87 ground state hyperfine splitting of 6.8 GHz. Spectra have been taken by varying the pulse repetition frequency. Using cells with argon as a buffer gas a linewidth as narrow as 149 Hz was obtained. The rubidium ground state decoherence cross section 1.1*10^(-18) cm^2 for collisions with xenon atoms has been measured for the first time with this method using a pure isotope rubidium vapor cell and xenon as a buffer gas.Comment: 3 pages, 5 figures, 1 misprint correcte

The Creation and Detection of Arbitrary Photon Number States Using Cavity QED

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Untersuchung von Photonenzahlzustaenden mit dem Ein-Atom-Maser

The quantum mechanical description of the radiation field is based on field states that are characterized by the number of quanta of the radiation field, called photons. These states called photon number states or Fock states consist of a fixed, integer number of photons. They are eigenstates of the Hamiltonian of the radiation field and therefore of fundamental importance to the quantum theory of the electromagnetic field. Photon number states are those states of the electromagnetic field that can be considered to be maximally distant from classical field states. They show extreme sub-Poissonian statistics and vanishing intensity noise. Thus due to the uncertainty relation their phase is completely undefined. These properties are called "intensity squeezing". Since the foundation of the theory of quantum electrodynamics, photon number states have been used in many theories as base states of the electromagnetic field. Yet, so far there have been experimental difficulties in the preparation and detection of these states that could not be overcome. In consequence for a long time it has been an unachieved goal of experimental quantum optics to produce, maintain and detect such states. In this thesis the first experimental production and the unambiguous measurement of photon number states of an extremely long lived resonator field are described. Three different methods are discussed, all of them using the one-atom-maser apparatus, which examines the interaction of single atoms of a weak thermal atomic beam with a single mode of a microwave resonator with a quality factor of 4 discussed in this thesis, shows how such a deterministic source for single photons can be realized in a pulsed one-atom-maser experiment making use of the dynamics of trapping states. Following the detailed description of a theoretical model, a first experimental realization of the source is shown. Here we achieve a creation probability of at least 83% for the one-photon Fock state. In addition in this mode the maser can be considered as a source for single atoms in a certain state. An extension of the optics and laser system of the one-atom-maser that is currently under construction will allow for an even higher yield of one-photon Fock states and also for the deterministic production of higher order Fock states. This will allow for many new interesting experiments using the described methods

Generating Photon Number States on Demand via Cavity Quantum Electrodynamics

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Multiple-photon resolving fiber-loop detector

We show first reconstructions of the photon-number distribution obtained with a multi-channel fiber-loop detector. Apart from analyzing the statistics of light pulses this device can serve as a sophisticated postselection device for experiments in quantum optics and quantum information. We quantify its efficiency by means of the Fisher information and compare it to the efficiency of the ideal photodetector.Comment: 5 pages, 6 figure

Photoluminescence of single colour defects in 50 nm diamond nanocrystals

We used optical confocal microscopy to study optical properties of diamond 50 nm nanocrystals first irradiated with an electron beam, then dispersed as a colloidal solution and finally deposited on a silica slide. At room temperature, under CW laser excitation at a wavelength of 514.5 nm we observed perfectly photostable single Nitrogen-Vacancy (NV) colour defects embedded in the nanocrystals. From the zero-phonon line around 575 nm in the spectrum of emitted light, we infer a neutral NV0 type of defect. Such nanoparticle with intrinsic fluorescence are highly promising for applications in biology where long-term emitting fluorescent bio-compatible nanoprobes are still missing.Comment: proceedings of ICDS 23 conference (23rd International Conference on Defects in Semiconductors, July 24 - July 29, 2005, Awaji Island, Hyogo, Japan); to appear in "Physica B

Universal Continuous Variable Quantum Computation in the Micromaser

We present universal continuous variable quantum computation (CVQC) in the micromaser. With a brief history as motivation we present the background theory and define universal CVQC. We then show how to generate a set of operations in the micromaser which can be used to achieve universal CVQC. It then follows that the micromaser is a potential architecture for CVQC but our proof is easily adaptable to other potential physical systems.Comment: 12 pages, 4 figures, accepted for a presentation at the 9th International Conference on Unconventional Computation (UC10) and LNCS proceedings

Deterministic generation of an on-demand Fock state

We theoretically study the deterministic generation of photon Fock states on-demand using a protocol based on a Jaynes Cummings quantum random walk which includes damping. We then show how each of the steps of this protocol can be implemented in a low temperature solid-state quantum system with a Nitrogen-Vacancy centre in a nano-diamond coupled to a nearby high-Q optical cavity. By controlling the coupling duration between the NV and the cavity via the application of a time dependent Stark shift, and by increasing the decay rate of the NV via stimulated emission depletion (STED) a Fock state with high photon number can be generated on-demand. Our setup can be integrated on a chip and can be accurately controlled.Comment: 13 pages, 9 figure

A modern review of the two-level approximation

The paradigm of the two-level atom is revisited and its perturbative analysis is discussed in view of the principle of duality in perturbation theory. The models we consider are a two-level atom and an ensemble of two-level atoms both interacting with a single radiation mode. The aim is to see how the latter can be actually used as an amplifier of quantum fluctuations to the classical level through the thermodynamic limit of a very large ensemble of two-level atoms [M. Frasca, Phys. Lett. A {\bf 283}, 271 (2001)] and how can remove Schr\"odinger cat states. The thermodynamic limit can be very effective for producing both classical states and decoherence on a quantum system that evolves without dissipation. Decoherence without dissipation is indeed an effect of a single two-level atom interacting with an ensemble of two-level atoms, a situation that proves to be useful to understand recent experiments on nanoscale devices showing unexpected disappearance of quantum coherence at very low temperatures.Comment: 20 pages, no figures. Revised version accepted for publication in Annals of Physic

Screening of qubit from zero-temperature reservoir

We suggest an application of dynamical Zeno effect to isolate a qubit in the quantum memory unit against decoherence caused by coupling with the reservoir having zero temperature. The method is based on using an auxiliary casing system that mediate the qubit-reservoir interaction and is simultaneously frequently erased to ground state. This screening procedure can be implemented in the cavity QED experiments to store the atomic and photonic qubit states.Comment: 4 pages, 5 figure