Physics Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2800
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Item Raman coherence effects in a superconducting Jaynes-Cummings system(2015) Novikov, Sergey; Wellstood, Frederick C; Palmer, Benjamin S; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation describes a study of Raman coherence effects using superconducting quantum circuits. Raman coherence can occur in a three-level system driven by two coherent electromagnetic fields. In a suitable system with a metastable state, the effect is typically manifest as coherent population trapping (CPT) and electromagnetically induced transparency (EIT). I derive the theoretical framework and show experimentally that in the case of a cascade three-level system based on transmon superconducting qubit states, an effect known as the Autler-Townes doublet (ATD), rather than CPT or EIT, occurs. I propose, model, and implement a quasi- system made of combined transmon-cavity levels, which has a meta-stable state required for CPT and EIT. I measure CPT, and demonstrate coherence of the dark state in the time domain. Instead of EIT, I observe a new phenomenon – electromagnetically suppressed transmission (EST). The large negative dispersion accompanying EST leads to superluminal pulse propagation in the system. My results suggest that quantum superconducting circuits provide a viable platform for studying quantum optics of multi-level systems.Item Timing the State of Light with Anomalous Dispersion and a Gradient Echo Memory(2013) Clark, Jeremy; Rolston, Steven L; Lett, Paul D; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We study the effects of anomalous dispersion on the continuous-variable entanglement of EPR states (generated using four-wave mixing in 85Rb) by sending one part of the state through a fast-light medium and measuring the state's quantum mutual information. We observe an advance in the maximum of the quantum mutual information between modes. In contrast, due to uncorrelated noise added by a small phase-insensitive gain, we do not observe any statistically significant advance in the leading edge of the mutual information. We also study the storage and retrieval of multiplexed optical signals in a Gradient Echo Memory (GEM) at relevant four-wave mixing frequencies in 85Rb. Temporal multiplexing capabilities are demonstrated by storing multiple classical images in the memory simultaneously and observing the expected first-in last-out order of recall without obvious cross-talk. We also develop a technique wherein selected portions of an image written into the memory can be spatially targeted for readout and erasure on demand. The effect of diffusion on the quality of the recalled images is characterized. Our results indicate that Raman-based atomic memories may serve as a flexible platform for the storage and retrieval of multiplexed optical signals.Item The Optical Response of Strongly Coupled Quantum Dot- Metal Nanoparticle Hybrid Systems(2012) Artuso, Ryan Domenick; Bryant, Garnett W; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this thesis, we study, theoretically, hybrid systems composed of semiconducting quantum dots (SQDs) and metallic nanoparticles (MNPs) which are coupled by means of an applied optical field. Systems composed of SQDs and MNPs have recently been a very active area of research. Such structures are considered to be viable candidates for use in nanodevices in quantum information and nanoscale excitation transfer. The goal of this thesis is to investigate the interactions of the constituent particles and predict the hybrid response of SQD/MNP systems. We first study a single SQD coupled to a spherical MNP, and explore the relationship between the size of the constituents and the response of the system. We identify four distinct regimes of behavior in the strong field limit that each exhibit novel properties, namely, the Fano regime, exciton induced transparency, suppression and bistability. In chapter 3, we will explore these four regimes in detail and set bounds on each. In chapter 4, we then show that the response of the system can be tailored by engineering metal nanoparticle shape and the exciton resonance of SQDs to control the local-fields that couple the MNPs and SQDs. We identify regimes where dark modes and higher order multipolar modes can influence hybrid response. External fields do not directly drive MNP dark modes, so SQD/MNP coupling is dominated by the local induced coupling, providing a situation in which the induced self-interaction could be probed using near field techniques. Finally, we consider a system of two SQDs coupled to a MNP. In particular, we identify and address issues in modeling the system using a semiclassical approach, which can lead to unstable and chaotic behavior in a strong SQD-SQD coupling regime. When we model the system using a more quantum mechanical approach, this chaotic regime is absent. Finally, we compare the two models on a system with a strong plasmon-mediated interaction between the SQDs and a weak direct interaction between them.Item Experiments in Two-Mode Cavity QED(2011) Norris, David Glenn; Orozco, Luis A.; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Cavity quantum electrodynamics (QED) allows the study of light-matter interactions at the most basic level, through precise identification of the coherent and incoherent (dissipative) parts of the system evolution. We present measurements of light from a cavity QED system consisting of a high-finesse optical resonator coupled to a beam of cold Rb atoms. The novelty of the design lies in the interplay of two degenerate and orthogonal polarization modes. One mode (driven) behaves as the canonical cavity mode of the Jaynes-Cummings Hamiltonian, coherently exciting the atoms with a modest coupling strength; the other mode (undriven) collects a small fraction of spontaneously emitted light and provides a probe of the dissipative processes. We first demonstrate the ability to detect individual atoms passing through the cavity modes in real time by coincidence detection of photons from the undriven mode. Calculation of statistics and correlation functions from the complete photon detection record allows the determination of detection probabilities and the reconstruction of atomic trajectories. We next present evidence of quantum coherence that is created, modied, and measured in the excitation-spontaneous emission cycle. The coherence appears as a long-lived quantum beat at the ground-state Larmor frequency, visible in the intensity autocorrelation function of the undriven mode. Quantum jumps of the atomic state, occurring in between the detections of photons from the cavity, result in substantial changes in the frequency and spectral width of the beats. We present the results of a full quantum Monte Carlo calculation in order to quantitatively explain the measurements.