A quantum dot coupled to an optical cavity has recently proven to be an excellent source of ondemand single photons. Typically, applications require simultaneous high efficiency of the source and quantum indistinguishability of the extracted photons. While much progress has been made both in suppressing background sources of decoherence and utilizing cavity-quantum electrodynamics to overcome fundamental limitations set by the intrinsic exciton-phonon scattering inherent in the solid-state platform, the role of the excitation pulse has been often neglected. We investigate quantitatively the factors associated with pulsed excitation that can limit simultaneous efficiency and indistinguishability, including excitation of multiple excitons, multi-photons, and pump-induced dephasing, and find for realistic single photon sources that these effects cause degradation of the source figures-of-merit comparable to that of phonon scattering. We also develop rigorous open quantum system polaron master equation models of quantum dot dynamics under a time-dependent drive which incorporate non-Markovian effects of both photon and phonon reservoirs, and explicitly show how coupling to a high Q-factor cavity suppresses multi-photon emission in a way not predicted by commonly employed models. We then use our findings to summarize the criteria that can be used for single photon source optimization.

Quantum emitters coupled to plasmonic resonators are known to allow enhanced broadband Purcell factors, and such systems have been recently suggested as possible candidates for on-demand single photon sources, with fast operation speeds. However, a true single photon source has strict requirements of high efficiency (brightness) and quantum indistinguishability of the emitted photons, which can be quantified through two-photon interference experiments. To help address this problem, we employ and extend a recently developed quantized quasinormal mode approach, which rigorously quantizes arbitrarily lossy open system modes, to compute the key parameters that accurately quantify the figures of merit for plasmon-based single photon sources. We also present a quantized input-output theory to quantify the radiative and nonradiative quantum efficiencies. We exemplify the theory using a nanoplasmonic dimer resonator made up of two gold nanorods, which yields large Purcell factors and good radiative output beta factors. Considering an optically pulsed excitation scheme, we explore the key roles of pulse duration and pure dephasing on the single photon properties, and show that ultrashort pulses (sub-ps) are generally required for such structures, even for low temperature operation. We also quantify the role of the nonradiative beta factor both for single photon and two-photon emission processes. Our general approach can be applied to a wide variety of plasmon systems, including metal-dielectrics, and cavity-waveguide systems, without recourse to phenomenological quantization schemes.

Rigorous and intuitive master equation models are presented to study on‐demand single photon sources from pulse‐excited quantum dots coupled to optical cavities. Three methods of source excitation are considered: resonant pi‐pulse, off‐resonant phonon‐assisted inversion, and two‐photon excitation of a biexciton–exciton cascade, and the effect of the pulse excitation process on the quantum indistinguishability, efficiency, and purity of emitted photons is investigated. By explicitly modelling the time‐dependent pulsed excitation process in a manner which captures non‐Markovian effects associated with coupling to photon and phonon reservoirs, it is found that photons of near‐unity indistinguishability can be emitted with over 90% efficiency for all these schemes, with the off‐resonant schemes not necessarily requiring polarization filtering due to the frequency separation of the excitation pulse, and allowing for very high single photon purities. Furthermore, the off‐resonant methods are shown to be robust over certain parameter regimes, with less stringent requirements on the excitation pulse duration in particular. Also, a semi‐analytical simplification of the master equation is derived for the off‐resonant drive, which gives insight into the important role that exciton–phonon decoupling for a strong drive plays in the off‐resonant phonon‐assisted inversion process.

We study the role of electron-phonon scattering for a pulse-triggered quantum dot single-photon source which utilizes a modified version of stimulated Raman adiabatic passage and cavity-coupling. This on-demand source is coherently pumped with an optical pulse in the presence of a continuous wave laser drive, allowing for efficient generation of indistinguishable single photons with polarizations orthogonal to the applied fields. In contrast to previous studies, we explore the role of electron-phonon scattering on this semiconductor system by using a polaron master equation approach to model the biexciton-exciton cascade and cavity mode coupling. In addition to background zero-phonon-line decoherence processes, electron-acoustic-phonon coupling, which usually degrades the indistinguishability and efficiency of semiconductor photon sources, is rigorously taken into account. We study how cavity and laser detunings affect the device performance, and explore the effects of finite temperature on pure dephasing and intrinsic phonon-coupling. We describe how this biexciton-exciton cascade scheme allows for true single photons to be generated with over 90% quantum indistinguishability and efficiency simultaneously using realistic experimental parameters. We also show how the double-field dressing can be probed through the cavity-emitted spectrum.arXiv:1706.07521v1 [quant-ph]

We present an open-system master equation study of the coherent and incoherent resonance fluorescence spectrum from a two-level quantum system under coherent pulsed excitation. Several pronounced features which differ from the fluorescence under a constant drive are highlighted, including a multi-peak structure and a pronounced off-resonant spectral asymmetry, in stark contrast to the conventional symmetrical Mollow triplet. We also study semiconductor quantum dot systems using a polaron master equation, and show how the key features of dynamic resonance fluorescence change with electron-acoustic-phonon coupling.The theory of resonant scattering of light from a twolevel system (TLS) is a major achievement in quantum optics and provides an experimentally accessible gateway to probing strong-field quantum optics. In recent decades, advances in the ability to coherently manipulate atomic systems with light has allowed for a breadth of technological innovations which harness the quantum mechanical properties of these systems [1]. Furthermore, quantum dots (QDs) -semiconductor materials confined in three dimensions, with excited electron-hole pairs (excitons) mimicking the behaviour of an excited atom, can serve as "artificial atoms", maintaining the physics of the quantized system's interaction with the electromagnetic field, but with tunable properties and potential for scalability [2]. Semiconductor QDs have been the subject of much recent research for their potential as sources of quantum light, particularly single and entangled photons [3]. While constant excitation with a continuous wave (cw) laser drive can be used to create a TLS singlephoton source, often technological proposals require a deterministic source -one that can be triggered on-demand. This is typically done by an optical pulse, which renders resonance fluorescence (RF) of a TLS a genuine timedependent quantum dynamical process.The usual features of the RF spectrum under strong cw excitation manifest as the so-called Mollow triplet [4], where the power spectrum of the scattered field takes on a characteristic three-peak resonance structure due to radiative transitions between eigenstates of the system Hamiltonian, as well as a delta function peak at the (monochromatic) drive frequency corresponding to coherent elastic scattering. However, under excitation by a short pulse, the RF spectrum can take on features which obscure or eliminate this characteristic spectrum, especially under off-resonant excitation. The pulsed RF spectrum has been studied theoretically in atomic systems [5][6][7][8][9][10], and more recently in QD-cavity systems for on-resonance excitation [11], where a dynamic spectrum has been observed in the presence of cavity coupling [12].In this Letter, we describe the unique features of pulsed * c.gustin@queensu.ca RF spectra in depth using a master equation approach, and explore the different effects under time-dependent excitation, which are of interest to emerging experimental studies of pulsed quantum optical systems. In particul...