Interaction between site-controlled quantum dot systems and photonic cavity structures

The goal of this thesis was to investigate light-matter interaction in nanophotonic devices based on site-controlled pyramidal quantum dots (QD) in photonic crystal (PhC) cavities. These QDs provide position and spectral control, which is hardly achievable by the widely exploited self-assembled QD-based systems, thus allowing almost ideal cloning of differently designed devices in thousands of copies on the same chip. Thus, we conducted statistical studies of the optical properties of a large variety of photonic structures without concerns about significant deviations from the targeted layout. In particular, we addressed the influence of the QD position with respect to the electrical field pattern of the cavity mode (CM) on the optical properties of the QD excitonic transitions. We integrated a single pyramidal QD in a linear PhC membrane cavity with three missing holes (L3 PhC cavity) at a set of well-defined positions, among which were points corresponding to the first and the second CM lobes as well as a CM node. Taking advantage of the high reproducibility of the fabricated devices, we aimed at providing statistical evidence of the impact of the positioning of a single dipole on the CM-induced Purcell enhancement. Interestingly, we observed a clear Fano-like resonance in the QD emission component co-polarized with a CM that vanished for devices with a QD at the CM node. Further developing pyramidal QD-based QD-PhC cavity integration technology, we successfully implemented the integration of up to 4 QDs with an L7 PhC cavity. For several such structures we identified the optical transitions of each QD by means of spatial scanning micro-photoluminescence, accompanied with correlations in spectral wandering traces. We demonstrated phonon-assisted weak coupling of 4 different QD excitons with the same CM. Using a combination of temperature- and water condensation- induced exciton-CM tuning allowed probing the coupling of the 4 QDs to different CMs, thereby probing the modal spatial profiles. In parallel, we explored spectral diffusion and spectral wandering processes of QD excitons. As a tool, we developed a correlation technique based on the observation of transitions between different excitonic energy levels induced by the quantum confined Stark effect (QCSE). This technique allowed us to study the nature of charged centers in the vicinity of the QD, leading to spectral jumps between discrete emission energies of the QD excitons. Relating the QD exciton energy to the amplitude of the electric field inducing the QCSE allowed observing unusual spectral response of the QD upon increasing the charge density in its vicinity. Additionally, it allowed probing the ratio between the dipole moments of different excitonic complexes. Scanning spectrally a CM with a single QD exciton tuned by the fluctuations of the built-in electric field, we observed emission intensity enhancement associated with the CM-induced Purcell effect. We also observed an irreversible QCSE-induced giant exciton spectral shift accompanied by the intensity intermittency. Finally, we evidenced a strong dependence of the observed spectral wandering and emission intermittency effects on the sample light exposure history, clearly exhibiting a photon-activated charge trapping in the QD vicinity

Theory of Fano effect in cavity quantum electrodynamics

We propose a Markovian quantum master equation that can describe the Fano effect directly, by assuming a standard cavity quantum electrodynamics system. The framework allows us to generalize the Fano formula, applicable over the weak and strong coupling regimes with pure dephasing. A formulation of its emission spectrum is also given in a consistent manner. We then find that the interference responsible for the Fano effect is robust against pure dephasing. This is counterintuitive because the impact of interference is, in general, severely reduced by decoherence processes. Our approach thus provides a basis for theoretical treatments of the Fano effect and new insights into the quantum interference in open quantum systems

Sub-megahertz homogeneous linewidth for Er in Si via in situ single photon detection

We studied the optical properties of a resonantly excited trivalent Er ensemble in Si accessed via in situ single photon detection. A novel approach which avoids nanofabrication on the sample is introduced, resulting in a highly efficient detection of 70 excitation frequencies, of which 63 resonances have not been observed in literature. The center frequencies and optical lifetimes of all resonances have been extracted, showing that 5% of the resonances are within 1 GHz of our electrically detected resonances and that the optical lifetimes range from 0.5 ms up to 1.5 ms. We observed inhomogeneous broadening of less than 400 MHz and an upper bound on the homogeneous linewidth of 1.4 MHz and 0.75 MHz for two separate resonances, which is a reduction of more than an order of magnitude observed to date. These narrow optical transition properties show that Er in Si is an excellent candidate for future quantum information and communication applications.Comment: 12 pages, 13 figure

Site-controlled quantum dots coupled to photonic crystal waveguides

We demonstrate selective optical coupling of multiple, site controlled semiconductor quantum dots (QDs) to photonic crystal waveguide structures. The impact of the exact position and emission spectrum of the QDs on the coupling efficiency is elucidated. The influence of optical disorder and end-reflections on photon transport in these systems are discussed

Millisecond electron spin coherence time for erbium ions in silicon

Spins in silicon that are accessible via a telecom-compatible optical transition are a versatile platform for quantum information processing that can leverage the well-established silicon nanofabrication industry. Key to these applications are long coherence times on the optical and spin transitions to provide a robust system for interfacing photonic and spin qubits. Here, we report telecom-compatible Er3+ sites with long optical and electron spin coherence times, measured within a nuclear spin-free silicon crystal (<0.01% 29Si) using optical detection. We investigate two sites and find 0.1 GHz optical inhomogeneous linewidths and homogeneous linewidths below 70 kHz for both sites. We measure the electron spin coherence time of both sites using optically detected magnetic resonance and observe Hahn echo decay constants of 0.8 ms and 1.2 ms at around 11 mT. These optical and spin properties of Er3+:Si are an important milestone towards using optically accessible spins in silicon for a broad range of quantum information processing applications.Comment: 14 pages, 6 figure

Time-resolved physical spectrum in cavity quantum electrodynamics

The time-resolved physical spectrum of luminescence is theoretically studied for a standard cavity quantum electrodynamics system. In contrast to the power spectrum for the steady state, the correlation functions up to the present time are crucial for the construction of the time-resolved spectrum, while the correlations with future quantities are inaccessible because of the causality, i.e., the future quantities cannot be measured until the future comes. We find that this causality plays a key role in understanding the time-resolved spectrum, in which the Rabi doublet can never be seen during the time of the first peak of the Rabi oscillation. Furthermore, the causality can influence the transient magnitude of the Rabi doublet in some situations. We also study the dynamics of the Fano antiresonance, where the difference from the Rabi doublet can be highlighted

Remote excitation between quantum emitters mediated by an optical Fano resonance

Remote coupling between quantum emitters is of great importance for constructing quantum networks. Conventionally, this can be achieved via photon exchange by incorporating the quantum emitters in a waveguide or a large cavity. However, such photonic structures suffer from low quality-factors or large mode volumes, limiting the efficiency of light-matter interaction. Here, we demonstrate remote coupling between two site-controlled semiconductor quantum dot emitters mediated by an optical Fano resonance induced by coupling cavity modes via a continuum waveguide state. Unlike ordinary coupled modes, the Fano mode offers both a spatially extended field and a high local density of optical states at the emitters, enhancing light-matter interaction. This coupling scheme allows the demonstration of mutual excitation between two quantum dots separated in space by >17 wavelengths. Our approach holds promise for achieving long-distance interaction without compromising interaction efficiency, which is essential for scaling up on-chip integration of quantum networks based on solid-state quantum emitters. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen

Optical and Zeeman spectroscopy of individual Er ion pairs in silicon

We make the first study the optical energy level structure and interactions of pairs of single rare earth ions using a hybrid electro-optical detection method applied to Er-implanted silicon. Two examples of Er3+ pairs were identified in the optical spectrum by their characteristic energy level splitting patterns, and linear Zeeman spectra were used to characterise the sites. One pair is positively identified as two identical Er3+ ions in sites of at least C2 symmetry coupled via a large, 200 GHz Ising-like spin interaction and 1.5 GHz resonant optical interaction. Small non-Ising contributions to the spin interaction are attributed to distortion of the site measurable because of the high resolution of the single-ion measurement. The interactions are compared to previous measurements made using rare earth ensemble systems, and the application of this type of strongly coupled ion array to quantum computing is discussed.Comment: 11 pages, 5 figure