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Untersuchung von Photonenzahlzustaenden mit dem Ein-Atom-Maser

S. Brattke

Published Jan 1, 2001• 0 citations
Publisher

Abstract

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.

DOI
10.5282/edoc.212

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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.
The widely discussed applications in quantum information and quantum cryptography require radiation sources capable of producing a fixed number of photons. This paper reviews the work performed in our laboratory using the one-atom maser or micromaser to produce these fields on demand. In order to achieve this goal the maser is operating under the condition of the so-called trapping states. In this situation the field of the micromaser stabilises to a photon number state. Recently, we have also succeeded in determining the Wigner function of a single-photon state. Presently measurements of the phase diffusion of the one-atom maser field are underway, whereby the case will be studied in detail when the field approaches a number state. The measurements will also give information on the decoherence of the maser field.
A wide range of applications in quantum information and quantum cryptography requires radiation sources capable of producing a fixed number of photons. This paper reviews the work performed in our laboratory to produce these fields on demand. Two different methods are discussed. The first is based on the one-atom maser or micromaser operating under the conditions of the so-called trapping states. In this situation, the micromaser field stabilizes to a photon number state. Recently, we also succeeded in determining the Wigner function of a single-photon state. The second device, recently realized in our laboratory, uses a single trapped ion in an optical cavity.
The one atom maser is an archetype experiment of quantum optics, where the interaction is between the basic quantum components of a single atoms and a single mode field, uncluttered by unwanted side effects. Thus the one atom maser is able to examine the most fundamental aspects of the atom light interaction. In this paper we review three of the most recent experiments on the very topical subject of photon Fock state creation. Namely the creation Fock states via trapping states, dynamical Fock state preparation using state reduction of lower state atoms and finally the creation of Fock states on demand. In the two decades since its first operation, the one atom maser continues to operate at the forefront of quantum optics research having produced many first class results. We present some taste of future, as we turn the micromaser to quantum computing and the creation of exotic entangled states.
There are only fistful of systems in physics that can be described by an exact theory from first principles and, at the same time, can be investigated under experimental conditions approaching the idealized theoretical ones. The one-atom-maser or micromaser provides such an example, making a detailed study of the fundamental properties of the atom-field interaction possible. The situation realized in a micromaser is very close to the ideal case of a single two-level atom interacting with a single quantized mode of a cavity field. In the micromaser the atoms have a dual purpose of both pumping the field and also probing it via measurements of the outgoing atoms. Any other means of measuring the field inside the resonator has the detrimental effect of lowering its Q-factor and thereby the photon storage time. The long photon storage time of the resonator allows for the decay of the field to be negligible during the passage of an atom and its interaction with the field. The behavior of atoms in a cavity is governed by the oscillatory exchange of energy between the atoms and the field, which is called Rabi oscillation. For cavity fields in the vacuum and few photon number states (Fock states), Rabi oscillations have been measured in the past. To prevent thermal effects from polluting the pure number states these experiments were performed at low temperatures (below 1 K). However, the observed resolution of the Rabi oscillations measurements was quite disappointing (only about 2% of the predicted theoretical value) and precluded more ambitious experiments like atom-atom correlations or time resolved investigations of the maser field dynamics. The observed contrast of Rabi oscillations can be considered as a figure of merit for the experimental resolution of quantum features of a maser field. Therefore, a high resolution in the measurements of Rabi oscillations is crucial. This thesis describes the methods and improvements applied to enhance the resolution of Rabi oscillations by a factor of 8. The following upgrades and developments proved to be crucial in this work: 1) The base temperature of the cryogenic system was lowered to 0.3 K, i.e. one third of the original value. At the same time, the time during which the system remains at the base temperature was improved by almost of an order of magnitude (to more than 12 h). 2) For the promotion of the atoms to the Rydberg regime new three-step diode laser setup was constructed. The excitation efficiency compared to the old dye laser was increased by two orders. Using top-of-fringe stabilization with new spectroscopic methods, specially designed error detection and feedback schemes as well as state-of-the-art PID regulators the continuous locking of lasers is about 8 h (compared to about 20 min with the old dye laser system). 3) The flexibility of using the three step excitation allows to excite different maser states and for the first time to investigate pure maser transition. 4) Various improvements on the atomic oven and the channeltron detection unit led to the reliable and stable production and detection of the atomic beam. Observed distribution of the atomic beam statistics reaches to within 6% the Poisson limit which is expected in the absence of experimental imperfections. 5) New developed techniques in magnetic field compensation allow to perform such measurements with two orders of magnitude better accuracy compared to the previous experiments. To demonstrate the new capabilities of the apparatus and to apply its improved resolution of quantum fields we performed a previously impossible in-depth analysis of mean photon number and the atomic inversion produced by a micromaser for various detunings between the cavity- and atomic resonance frequency.
The widely discussed applications in quantum information and quantum cryptography require radiation sources capable of producing a fixed number of photons. This paper reviews the work performed in our laboratory to produce these fields on demand. Two different methods are discussed. The first is based on the one-atom maser or micromaser operating under the conditions of the so-called trapping states. In this situation the micromaser stabilises to a photon number state. Recently, we also succeeded in determining the Wigner function of a single-photon state. The second device, recently realised in our laboratory, uses a single trapped ion in an optical cavity. 1
. In this paper experiments performed with the one-atom maser are reviewed. Furthermore, possible experiments to test basic quantum physics are discussed. Introduction, the One-Atom-Maser The most promising avenue to study the generation process of radiation in lasers and masers is to drive a maser consisting of a single mode cavity by single atoms. This system, at first glance, seems to be another example of a Gedanken-experiment treated in the pioneering work of Jaynes and Cummings (1963), but such a one-atom maser (Meschede, Walther and Müller, 1985) really exists and can in addition be used to study the basic principles of radiation-atom interaction. The advantages of the system are: it is the first maser which sustains oscillations with less than one atom on the average in the cavity, this setup allows to study in detail the conditions necessary to obtain nonclassical radiation, especially radiation with sub-Poissonian photon statistics in a maser system directly in a Poissonian pumping process, and it is possible to study a variety of phenomena of a quantum field including the quantum measurement process. What are the tools that make this device work: It was the enormous progress in constructing superconducting cavities together with the laser preparation of highly excited atoms – Rydberg atoms – that have made the realization of such a one-atom maser possible.