Modeling the spontaneous emission of a single-photon emitted from a quantum dot is important for several proposed solid-state quantum computers and quantum networks. In this study we seek to model the fully quantized excitation and spontaneous decay of a quantum dot state through the optical emission of a photon in the non-Markovian limit of the photon bath. We propose the use of discretized central-difference approximations of space and time partial derivatives to describe the interaction between single photon and quantum dot states.
Modeling the spontaneous emission of a single-photon emitted from a quantum dot is important for several proposed solid-state quantum computers and quantum networks. In this study we seek to model the fully quantized excitation and spontaneous decay of a quantum dot state through the optical emission of a photon in the non-Markovian limit of the photon bath. We propose the use of discretized central-difference approximations of space and time partial derivatives to describe the interaction between single photon and quantum dot states.
Spontaneous emission of a source, such as an atom, is often thought of as an inherent property of the source, but is a result of the interaction between the radiating source dipole and the vacuum electromagnetic field. Therefore, the radiation emitted from an atom can be altered by suitably modifying the surrounding vacuum field [1] with a cavity. This has been verified by experiments initiated in the 1980s using atoms which are passed through a cavity and show enhanced[2] or inhibited[3] spontaneous emission. This field, called cavity quantum electrodynamics (QED), is currently addressing important issues in semiconductor nanostructures, in particular, high-efficiency light-emitting diodes for communications and single photon sources for quantum cryptography. [4,5] For example, quantum cryptography has emerged as a significant field of study over the last fifteen years, because it offers the promise of private communication whose security is assured by the laws of physics. Most implementations of quantum cryptography so far have used a protocol introduced by Bennet and Brassard, which uses four different states of a quantum system (generally known as BB84) [6 ]. For example, the message can be encoded on the polarization state of single photons, with a random choice between two non-othogonal polarization bases when the photons are sent (by Alice) and recieved (by Bob). Since an eavesdropper (Eve) does not know what bases have been chosen, any measurement she makes will impose a back-action on the states of the transmitted photons, which can be easily detected. Using error correction and privacy amplification, Alice and Bob can distill the transmitted message into a secure key about which Eve knows arbitrarily little.
In the pursuit of developing a quantum information network, photons appear to be the most convenient carriers to interconnect distant ports. The need to get on-demand single photons that is one and only one photon, with a high reliability, is the main driving force for the development of bright solid-state sources. One important parameter is the brightness defined as the probability that one collected pulse contains a single photon. For some applications like quantum information processing or long distance quantum communications, the emitted single photons must be also indistinguishable, so that can make use of their quantum interference to implement effective photon-photon interactions. To reach the ideal source of single and indistinguishable photons, different systems are explored : defects in diamond (NV centers), trapped atoms or ions, single molecules or semiconductor quantum dots.By coupling a semiconductor quantum dot to an optical cavity, the spontaneous emission of the emitter can be modified to obtain bright single-photon sources. An innovative technique was developed by Pr. Pascale Senellart and her team at the Laboratory of Photonics and Nanostructures (LPN) from CNRS that allows making such sources in a very reproducible way.This work explores the performance of single quantum dot coupled to micropillars. Various techniques are used in order to increase the single photon purity and indistinguishability while keeping a high source brightness. First, the cavity was modified using an adiabatic architecture such that a strong acceleration of the spontaneous emission was implemented. Then, a technique to apply an electric bias on the micropillars has been developed. The combination of the electric bias with a resonant optical excitation of the quantum dot allows to generation purely indistinguishable photons with a high brightness.The results developed in this thesis open a vast field of novel applications in quantum technologies, from quantum cryptography, metrology to quantum imaging.
Semiconductor Quantum dots are potentially an attractive source of non-classical light. They can confine bound electron-hole pairs, excitons, in all three spatial dimensions giving them discrete optical emission energies, much like the electronic states in atomic systems. The semiconductor nature of the system allows quantum dots to be integrated into complicated device structures including optical cavities [1] and electrical injection [2]. The radiative exciton emission from a semiconductor quantum dot can provide the simplest form of quantum light, a single photon source [2]. The finite re-excitation time following the radiative decay of an exciton in a quantum dot prevents the dot from emitting more than one photon if excited with a short optical or electronic pulse. In a similar fashion excitation of the biexciton state, consisting of two electrons and holes, in the quantum dot results in the emission of a pair of photons at the energy of the biexciton and exciton transitions. The biexciton state was, in fact, proposed as a possible source of polarisation-entangled photons in 2000 by Benson et al. [3] as it consists of two polarisation-correlated decay paths which could potentially be indistinguishable. The condition of indistinguishability is fundamental to the generation of entangled photons and is, in general, not true of the two decay paths from the biexciton state in a quantum dot; physical anisotropy causes the intermediate exciton states to hybridise and separate in energy providing ‘which-path’ information about the route taken through the biexciton decay. We demonstrate how the splitting between the intermediate exciton states in a single InAs quantum dot can be controlled by growth [4], rapid thermal annealing [5] and the application of an external magnetic field [6]. Each of these three techniques can be used to make the intermediate exciton states degenerate allowing the biexciton decay to produce singe pairs of entangled photons triggered by short laser pulses [7,8]. Entangled photon pair sources are essential for applications such as entanglement based quantum key distribution, and optical quantum computing. For these applications it is important that no more than one entangled photon pair is generated in a cycle, a requirement met by our quantum dot source which is not possible with traditional methods for generating entangled pairs of photons. Entanglement also enables quantum interferometry and metrology, the basis of image resolution beyond that possible with equivalent classical light. Biphoton interferometry using entangled emission from the biexciton decay reveals fringes with half the period of classical light [9], and less that that of the laser. In addition, interferometry suggests that this type of entangled light source is not limited by decoherence, we fine the biphoton is surprising robust against dephasing, in stark contrast to the devastating effect of decoherence upon single photons emitted by similar structures.
From secure communication to blazingly fast computation, quantum technologies promise arevolutionary horizon with transformative potential across many areas. Single photon sources,essential to utilizing the special qualities of quantum mechanics, are at the core of many ofthese developments. Because single photons are discrete quanta of light, they provide quantum systems withunmatched precision and control, opening up new possibilities for security and sensitivity inapplications like quantum cryptography, quantum key distribution, and quantum sensing.These sources are fundamental components of quantum computing, in which complicatedcomputations can be completed tenfold more quickly than with traditional computers thanks toqubits contained in single photons. To fully realize the promise of quantum technologies andtheir widespread application, single-photon source development and optimization mustcontinue. In the field of quantum technologies, increasing the spontaneous emission rate of a singlephoton source is important for multiple reasons. First of all, a higher emission rate results in amore effective production of single photons, which is necessary for applications like quantumkey distribution (QKD) that demand a high photon flux. A greater emission rate in QKDincreases the overall security and efficiency of quantum communication systems byguaranteeing a quicker and more dependable interchange of quantum information. All things considered, increasing the spontaneous emission rate of a single photon source iscritical to realizing the full promise of quantum technologies, facilitating quicker and moreeffective quantum computing, sensing, integrated photonics, and communication, and openingthe door for revolutionary developments across a range of industries. This thesis explores the impact of electromagnetic scattering on solid-state single photonemitters' spontaneous emission behavior. By applying sophisticated computational approachesand conducting a comprehensive literature analysis, the study seeks to confirm and reproduceprevious findings, expanding and solidifying our knowledge of basic principles andcomputational strategies in this field. Two different scatterer geometries, a sphere, and a cylinder, activated by a point dipoleapproximation that is frequently employed in quantum optics simulations are the subject of thiswork. The main goal is to thoroughly evaluate and validate previously published results, not topresent new physics, but to guarantee the stability and dependability of computational modelsin the study of interactions between light and matter.