# Browsing by Subject "Quantum optics"

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Item Coherent control and decoherence of single semiconductor quantum dots in a microcavity(2008-08) Flagg, Edward Bradstreet, 1979-; Shih, Chih-kangShow more Semiconductor quantum dots tightly confine excited electron-hole pairs, called excitons, resulting in discrete energy levels similar to those of single atoms. Transition energies in the visible or near-infrared make quantum dots suitable for many applications in quantum optics and quantum information science, but to take advantage of all the properties of quantum dot emission, it is necessary to excite them coherently which has been a great challenge due to background scattering of the excitation laser. This dissertation presents the first coherent control of a single quantum dot with observation of its resonance fluorescence and decoherence phenomena. Strong continuous-wave excitation causes the dot to undergo several Rabi oscillations before emitting. These are visible as oscillations in the first- and second-order correlation functions of the emission, and the quantum dot states are "dressed", resulting in a Mollow triplet in the emission spectrum. Some resonantly excited dots, in addition to resonance fluorescence, also emit light from excited states several meV higher in energy. Such up-conversion fits existing theories of decoherence but has never been directly observed before. The up-conversion intensity is shown to be described well by a fairly simple three-level model with single-phonon absorption. The coherent phenomena of resonance fluorescence and the decoherence due to up-conversion paint a dual picture of single quantum dots wherein they can sometimes be treated as an ideal two-level system, but their interactions with the host crystal can lead to many complex behaviors.Show more Item Dynamic tunneling and chaos in atom optical systems(2004) Luter, Robert Raymond; Reichl, L. E.Show more Dynamical tunneling has been observed in atom optics experiments by two groups, one in Texas using Cesium atoms and the other at NIST using a Bose–Einstein condensate. This tunneling is classically forbidden due to the isolation of the atoms in momentum space. The experimental results are extremely well described by time-periodic Hamiltonians with momentum quantized in units of the atomic recoil. The oscillations observed in these experiments are due to a few Floquet states that were excited by the initial conditions in the experiment. The observed tunneling has a well defined period when only two Floquet states dominate the dynamics. Beat frequencies are observed when three Floquet states dominate. Frequencies which are calculted theoretically match those observed by both experiments. The dynamical origin of the dominant Floquet states is identified as resulting from states which are excited by the initial conditions of the experiment.Show more Item Dynamics of ultracold atoms in optical potentials(2005) Dudarev, Artem; Niu, Qian; Raizen, Mark G.Show more In this dissertation, we discuss the manipulation of ultracold atoms with optical fields. We show how a one-way barrier for ground state atoms may be constructed. Its use for phase space compression is analyzed. Using several ideas from solid-state physics, we reveal a number of novel phenomena in quantum transport of ultracold atoms in two-dimensional optical lattices. These include Berry phase, self-rotation, spin-orbit coupling, and discrete solitons. Finally, we analyze in detail an approach to extract a small and deterministic number of atoms from a trapped Bose condensed gas by the introduction of an optical quantum dot. We show how small numbers of atoms in microtraps can be used for quantum state engineering.Show more Item Entangled optical state creation and characterization(2022-08-11) Ko, Gabriel D. J.; Kunz, Paul D.; La Cour, Brian R.Show more We describe a typical type-I phasematched Spontaneous Parametric Down Conversion (SPDC) crystal setup and characterize the quality of the source as a function of state fidelity and strength of Bell's inequality violation. Experimental results show a Bell statistic of 2.23 with a fidelity of 0.745 with the theoretical φ+ Bell state through 5m of single-mode (SM) fiber.Show more Item The micromaser theory and comparison to experiment(2003) Johnson, David Brian; Schieve, W. C.Show more The one-atom maser or micromaser is a quantum optics system that allows the observation of single two-level atoms interacting with a single-mode field. The microscopic nature of the micromaser system and the absence of significant amounts of stochasticity and noise, allows for the observation of behavior that is drastically different from that of macroscopic masers. This dissertation describes theoretical studies of the micromaser system and extensions of the previous micromaser theory to improve its agreement with experimental observations.Show more Item Optical resonators and quantum dots: and excursion into quantum optics, quantum information and photonics(2007-08) Bianucci, Pablo, 1975-; Shih, Chih-KangShow more Modern communications technology has encouraged an intimate connection between Semiconductor Physics and Optics, and this connection shows best in the combination of electron-confining structures with light-confining structures. Semiconductor quantum dots are systems engineered to trap electrons in a mesoscopic scale (the are composed of [approximately] 10000 atoms), resulting in a behavior resembling that of atoms, but much richer. Optical microrseonators are engineered to confine light, increasing its intensity and enabling a much stronger interaction with matter. Their combination opens a myriad of new directions, both in fundamental Physics and in possible applications. This dissertation explores both semiconductor quantum dots and microresonators, through experimental work done with semiconductor quantum dots and microsphere resonators spanning the fields of Quantum Optics, Quantum Information and Photonics; from quantum algorithms to polarization converters. Quantum Optics leads the way, allowing us to understand how to manipulate and measure quantum dots with light and to elucidate the interactions between them and microresonators. In the Quantum Information area, we present a detailed study of the feasibility of excitons in quantum dots to perform quantum computations, including an experimental demonstration of the single-qubit Deutsch-Jozsa algorithm performed in a single semiconductor quantum dot. Our studies in Photonics involve applications of microsphere resonators, which we have learned to fabricate and characterize. We present an elaborate description of the experimental techniques needed to study microspheres, including studies and proof of concept experiments on both ultra-sensitive microsphere sensors and whispering gallery mode polarization converters.Show more Item Resonance fluorescence and cavity quantum electrodynamics with quantum dots(2007-05) Muller, Andreas, 1978-; Shih, Chih-KangShow more Next-generation information technology is expected to rely on discrete two-state quantum systems that can deterministically emit single photons. Quantum dots are mesoscopic (~10,000 atoms large) semiconductor islands grown in a host crystal of larger band-gap that make well-defined two-level quantum systems and are very attractive due to stability, record coherence times, and the possibility of integrating them into larger structures, such as optical microcavities. This work presents experimental progress towards understanding the coherent optical processes that occur in single quantum dots, particularly such phenomena that might be one day utilized for quantum communication applications. High resolution low temperature optical spectroscopy is used in conjunction with first order (amplitude) and second-order (intensity) correlation measurements of the emitted field. A novel technique is introduced that is capable of harvesting the fluorescence of single dots at the same frequency as the laser, previously impossible due to insurmountable scattering. This technique enables the observation, for the first time, of single quantum dot resonance fluorescence, in both the weak and strong excitation regimes, which forms the basis for deterministic generation of single photons. Guided by the rich theoretical description available from quantum optics with atoms we obtain insight into the complex dynamics of this driven system. Quantum dots confined to novel optical microcavities were further investigated using micro photoluminescence. An optical microcavity properly coupled to a two-level system can profoundly modify its emission characteristics via quantum electrodynamical effects, which are highly attractive for single photon sources. The all-epitaxial structures we probe are distinguished by a bulk morphology that overcomes the fragility problems of existing approaches, and provides high quality factors as well as small mode volumes. Lasing is obtained with larger strucutres. Additionally, isolation of individual dots is further realized in smaller cavities and the Purcell effect observed in time-resolved photon counting experiments.Show more Item Studies on quantum coherence phenomena of self-assembled quantum dots(2001-12) Htoon, Han, 1967-; Shih, Chih-KangShow more This work explores the quantum coherence phenomena in self-assembled assembled quantum dots as an initial step toward the realization of novel technological applications such as single photon turnstile devices, single quantum dots lasers and solid state quantum logic gates. We performed extensive studies on quantum decoherenece processes of excitons trapped in the various excited states of SAQDs. Energy level structure and dephasing times of excited states were first determined by conducting photoluminescence excitation spectroscopy and wave-packet interferometry on a large number of individual SAQDs. This large statistical basis allows us to extract the correlation between the energy level structure and dephasing times. The major decohernce mechanisms and their viii active regime were identified from this correlation. A significant suppression of decoherence was also observed in some of the energetically isolated excited states, providing an experimental evidence for the theoretical prediction, known as “phonon bottleneck effect”. Furthermore, we observed the direct experimental evidence of Rabi oscillation in these excited states with long decoherence times. In addition, a new type of quantum interference phenomenon was discovered in the wavepacket interferometry experiments performed in the strong excitation regime where the non-linear effects of Rabi oscillation become important. Detailed theoretical investigations attribute this phenomenon to the coherent dynamics resulting from the interplay of Rabi oscillation and quantum interference.Show more Item The theory of non-Markovian open quantum systems(2008-05) Rodriguez, Cesar Alberto, 1979-; Sudarshan, E. C. G.Show more We study the role of correlations with the environment as the source of non-Markovian quantum evolutions. We first focus on the impact that correlations with the environment can have on the dynamical map that evolve the system. We expand the set of initial states of a system and its environment that are known to guarantee completely positive reduced dynamics for the system when the combined state evolves unitarily. We characterize the correlations in the initial state in terms of its quantum discord. The induced maps can be not completely positive when quantum correlations including, but not limited to, entanglement are present. We discuss the implications and limitations of the Markov approximation necessary to derive the Kossakowski-Lindblad master equation. A generalized non-Markovian master equation is derived from the dynamical map of systems correlated with their environment. The physical meaning of not completely positive maps is studied to obtain a consistent theory of non-Markovian quantum dynamics. These are associated to inverse maps necessary to establish correlations and they give rise to a canonical embedding map that is local in time. This master equation goes beyond the Kossakowski-Lindblad master equation. Non-equilibrium quantum thermodynamics can be be studied within this theory. Through out this discussion, the general dynamics of two interacting qubits is used as an example for illustrations.Show more