Sub-Natural Linewidth Single Photons from a Quantum Dot

The observation of quantum dot resonance fluorescence enabled a new solid-state approach to generating single photons with a bandwidth almost as narrow as the natural linewidth of a quantum dot transition. Here, we operate in the Heitler regime of resonance fluorescence to generate sub-natural linewidth and high-coherence quantum light from a single quantum dot. The measured single-photon bandwidth exhibits a 30-fold reduction with respect to the radiative linewidth of the QD transition and the single photons exhibit coherence properties inherited from the excitation laser. In contrast, intensity-correlation measurements reveal that this photon source maintains a high degree of antibunching behaviour on the order of the transition lifetime with vanishing two-photon scattering probability. This light source will find immediate applications in quantum cryptography, measurement-based quantum computing and, in particular, deterministic generation of high-fidelity distributed entanglement among independent and even disparate quantum systems

Interplay of trapped species and absence of electron capture in Moir\'{e} heterobilayers

Moir\'e heterobilayers host interlayer excitons in a natural, periodic array of trapping potentials. Recent work has elucidated the structure of the trapped interlayer excitons and the nature of photoluminescence (PL) from trapped and itinerant charged complexes such as interlayer trions in these structures. In this paper, our results serve to add to the understanding of the nature of PL emission and explain its characteristic blueshift with increasing carrier density, along with demonstrating a significant difference between the interlayer exciton-trion conversion efficiency as compared to both localized and itinerant intra-layer species in conventional monolayers. Our results show the absence of optical generation of trions in these materials, which we suggest arises from the highly localized, near sub-nm confinement of trapped species in these Moir\'e potentials.Comment: 3 figures, Supplementary information available on reques

Flatland nanophotonics: A study of quantum-confined excitons in 2D materials

Thesis (Ph. D.)--University of Rochester. Department of Mechanical Engineering, Materials Science Program, 2018.Semiconducting two-dimensional materials have gained increasing scientific interest within the last decade. Their electronic band gap in the visible range of the electromagnetic spectra, intriguing properties associated with spin and valley pseudospin of carriers and strongly bound excitons make them an excellent platform for both fundamental research, and technology tailored towards applications in nanophotonics and optoelectronics. Recently, 3D localized excitons in 2D materials have emerged as a novel source of single photon emitters, thus, unlocking the potential of these flatland materials in quantum optics and quantum information technology. The discovery of these localized excitons and the advances made in the study of quantum emitters in 2D materials are the major contributions of this thesis. In this thesis, we study quantum-confined excitons in monolayer transition metal dichalcogenides (TMDCs), a semiconducting class of 2D material. The effects of 3D confinement of excitons in the host monolayer TMDCs are investigated by optical spectroscopy. Low-temperature photoluminescence emission from the localized excitons exhibits narrow linewidths ranging from 100 fineV - 500 fineV with peak energies that are red-shifted from the delocalized excitons. Photon antibunching in intensity autocorrelation measurement confirms their single-photon nature. Magneto-optical studies reveal an exciton g-factor of fi10. Next, electric- field tunable devices based on van derWaals heterostructure are built around these localized emitters hosted by monolayer TMDC to study the quantum-confined Stark effect and demonstrate the electrical modulation of their photophysical properties such as emission energy, intensity, linewidth and fine structure splitting. We also investigate fully localized trions embedded in a charge-tunable van der Waals heterostructure. In such a device, direct electrostatic doping results in the formation of quantum confined trions with reduced electron-hole exchange interactions manifested by a reduction in the fine structure splitting and enhanced degree of circular polarization. This fosters the possibility of fabricating optically controlled spin-valley qubits with 2D materials. Lastly, we present various integrated devices based on 2D materials that are coupled with nanostructures such as metallic nano-antenna, nanowire-based waveguide and planar optical cavity based on distributed Bragg reflectors. These devices not only serve as a platform for solid-state quantum optics research but also provide building blocks for future nanophotonic and optoelectronic circuits

Nanophotonics with two-dimensional semiconductors.

Thesis (Ph. D.)--University of Rochester. Institute of Optics, 2017.The silicon-based transistor has been one of the driving forces for electronics for over half of a century. However, as they are continuously made smaller, the physical size limits for these transistors are being approached, necessitating methods or materials that can compliment silicon and allow for continued improvements in size and speed of devices. One recent area of interest has been layered two-dimensional materials. The transition metal dichalcogenides (TMDCs), such as molybdenum disulfide (MoS2), have gained much interest due to their change from indirect band gap semiconductors to direct band gap when thinned down to a single layer and accompanying increase in photoluminescence. This thesis explores the usage of the TMDCs for nanophotonics and nano-optoelectronic applications by means of scanning fluorescence and photocurrent microscopy as well as low-temperature spectroscopy. First, the interaction of optical plasmons supported by a single silver nanowire with electrons in a monolayer of MoS2 is analyzed. Various mechanisms of coupling far-field photons, surface plasmon polaritons, and free electrons were characterized in this architecture. This nano-optics study led to the development of an on-chip electrical plasmon detector. This detector had a maximum measured plasmon responsivity of 255 mA/W in the near-field and demonstrated appreciable responsivity across a bandwidth of ~90 nanometers. Another type of detector studied combined low-dimensional materials with different band gaps to lay groundwork for devices with larger spectral response. Structures of colloidal quantum dots and molybdenum diselenide, separated by flakes of hexagonal boron nitride (h-BN), were studied to demonstrate a reduction in the quenching efficiency as a function of distance between the semiconducting materials. Finally, devices consisting of heterostructures of multiple two-dimensional materials are explored. Tungsten diselenide (WSe2), which can host defects that emit single photons, was sandwiched by thick h-BN insulating barriers, which was further sandwiched by conductive few-layer graphene flakes to control defect emission via the quantum-confined Stark effect (QCSE). A MoSe2/WSe2 heterostructure, which has spectrally-resolved interlayer exciton emission and potential for a polarization-sensitive photodetector, was also studied. The work in this thesis provides the realization of potential applications of two-dimensional materials for photodetection and next-generation opto-electronic devices

Optomechanics with levitated nanodiamonds

Thesis (Ph. D.)--University of Rochester. Department of Physics and Astronomy, 2015.Free-space optical levitation of massive objects marries the physics and experimental techniques from the mature field of optical tweezers, with the relatively new and expanding field of optomechanics. This thesis details the design, construction, and characterization of an apparatus which can optically levitate and manipulate the dynamics of dielectric nanoparticles in a vacuum environment. It further describes work toward the development of a versatile spin-optomechanics platform based on optically levitated nanodiamonds. The apparatus relies on the optical gradient force imparted to the particle by a single, tightly-focused Gaussian laser beam which confines the particle in three dimensions. Near the laser focus, the optical potential well is approximately parabolic, giving rise to harmonic motion in vacuum. A parametric feedback signal generated from real-time measurements of the particle position modulates the trapping laser intensity. This allows optomechanical damping or excitation of the motion. We characterize the optomechanical cooling performance, and directly compare it to a similar, previously reported system. Finally, we use the apparatus to conduct preliminary optomechanics experiments with nanodiamonds which contain either individual, or ensembles of, optically addressable spins in the form of nitrogen-vacancy defect centers. We observe fluorescence from the defects in nanodiamonds levitated at atmospheric pressure and in low vacuum. In vacuum, we demonstrate the ability to optomechanically modulate the fluorescence rates, and resonantly drive spin transitions. This proof-of-principle work suggests levitated nanodiamonds to be suitable platforms for future spin-optomechanical work