Single-photon sources with near-unity efficiency and indistinguishability play a major role in the development of quantum technologies. However, on-demand excitation of the emitter imposes substantial limitations to the source performance. Here, we show that coherent two-color pumping allows for population inversion arbitrarily close to unity in bulk quantum dots thanks to a decoupling effect between the emitter and its phonon bath. Driving a micropillar single-photon source with this scheme, we calculate very high photon emission into the cavity mode (0.95 photons per pulse) together with excellent indistinguishability (0.975) in a realistic configuration, thereby removing the limitations imposed by the excitation scheme on single-photon source engineering.
Single-photon sources with near-unity efficiency and indistinguishability play a major role in the development of quantum technologies. However, on-demand excitation of the emitter imposes substantial limitations to the source performance. Here, we show that coherent two-color pumping allows for population inversion arbitrarily close to unity in bulk quantum dots thanks to a decoupling effect between the emitter and its phonon bath. Driving a micropillar single-photon source with this scheme, we calculate very high photon emission into the cavity mode (0.95 photons per pulse) together with excellent indistinguishability (0.975) in a realistic configuration, thereby removing the limitations imposed by the excitation scheme on single-photon source engineering.
Semiconductor quantum dots (QDs) coupled with optical microcavities provide an excellent platform for generating high-performance single-photon sources. However, the current microcavity structures are difficult to solve the tradeoff between single-photon purity and indistinguishability without additional filtering, due to challenges in suppressing broad phonon sideband spectrum and two-photon emission in the practical experiments. To address these issues, we have developed a novel asymmetric microcavity that supports two nondegenerate polarized modes, both resonant with a single quantum dot. One cavity mode is broadband and is used for excitation to reduce two-photon emission intensity, while the other is narrowband and is used for collection to enhance the indistinguishability of single-photon sources. This asymmetric microcavity also has the ability to overcome at least half of the photon efficiency loss under polarization filtering. Moreover, our model has employed an excitation pulse that resonates with cavity modes eliminating spectral distortion of intracavity fields, and efficiently achieving deterministic population inversion of QDs compared to an elliptical cavity. Our scheme paves the way to develop the excellent performance single-photon sources with higher brightness, near-unity purity, and indistinguishability without any additional filtering in practical experiments.
Scalable photonic quantum technologies require on-demand single-photon sources with simultaneously high levels of purity, indistinguishability, and efficiency. These key features, however, have only been demonstrated separately in previous experiments. Here, by s-shell pulsed resonant excitation of a Purcell-enhanced quantum dot-micropillar system, we deterministically generate resonance fluorescence single photons which, at π pulse excitation, have an extraction efficiency of 66%, single-photon purity of 99.1%, and photon indistinguishability of 98.5%. Such a single-photon source for the first time combines the features of high efficiency and near-perfect levels of purity and indistinguishabilty, and thus opens the way to multiphoton experiments with semiconductor quantum dots.
Long-range, terrestrial quantum networks require high-brightness single-photon sources emitting in the telecom C-band for maximum transmission rates. For solid-state quantum emitters, the underlying pumping process, i.e., coherent or incoherent excitation schemes, impacts several photon properties such as photon indistinguishability, single-photon purity, and photon number coherence. These properties play a major role in quantum communication applications, the latter in particular for quantum cryptography. Here, we present a versatile telecom C-band single-photon source that is operated coherently and incoherently using two complementary pumping schemes. The source is based on a quantum dot coupled to a circular Bragg grating cavity, whereas coherent (incoherent) operation is performed via the novel SUPER scheme (phonon-assisted excitation). In this way, high end-to-end-efficiencies (η end ) of 5.36% (6.09%) are achieved simultaneously with a small multiphoton contribution g (2) (0) of 0.076 ± 0.001 [ g (2) (0) of 0.069 ± 0.001] for coherent (incoherent) operation.
Abstract A major challenge in generating single photons with a single emitter is to excite the emitter while avoiding laser leakage into the collection path. Ideally, any scheme to suppress this leakage should not result in a loss in the efficiency of the single-photon source. Here, we investigate a scheme in which a single emitter, a semiconductor quantum dot, is embedded in a microcavity. The scheme exploits the splitting of the cavity mode into two orthogonally-polarised modes: one mode is used for excitation, the other for collection. By linking the experiment to theory, we show that the best population inversion is achieved with a laser pulse detuned from the quantum emitter. The Rabi oscillations exhibit an unusual dependence on pulse power. Our theory describes them quantitatively, enabling us to determine the absolute population inversion. By comparing the experimental results with our theoretical model, we determine a population inversion of 98 % − 5 % + 1 % for optimal laser detuning. The Rabi oscillations depend on the sign of the laser-pulse detuning, a phenomenon arising from the non-trivial effect of phonons on the exciton dynamics. The exciton–phonon interaction is included in the theory and gives excellent agreement with all the experimental results.
An optimal single-photon source should deterministically deliver one, and only one, photon at a time, with no trade-off between the source's efficiency and the photon indistinguishability. However, all reported solid-state sources of indistinguishable single photons had to rely on polarization filtering, which reduced the efficiency by 50%, fundamentally limiting the scaling of photonic quantum technologies. Here, we overcome this long-standing challenge by coherently driving quantum dots deterministically coupled to polarization-selective Purcell microcavities. We present two examples: narrowband, elliptical micropillars and broadband, elliptical Bragg gratings. A polarization-orthogonal excitation–collection scheme is designed to minimize the polarization filtering loss under resonant excitation. We demonstrate a polarized single-photon efficiency of 0.60 ± 0.02 (0.56 ± 0.02), a single-photon purity of 0.975 ± 0.005 (0.991 ± 0.003) and an indistinguishability of 0.975 ± 0.006 (0.951 ± 0.005) for the micropillar (Bragg grating) device. Our work provides promising solutions for truly optimal single-photon sources combining near-unity indistinguishability and near-unity system efficiency simultaneously. Single-photon sources with a single-photon efficiency of 0.60, a single-photon purity of 0.975 and an indistinguishability of 0.975 are demonstrated. This is achieved by fabricating elliptical resonators around site-registered quantum dots.
Solid-state emitters are excellent candidates for developing integrated sources of single photons. Yet, phonons degrade the photon indistinguishability both through pure dephasing of the zero-phonon line and through phonon-assisted emission. Here, we study theoretically and experimentally the indistinguishability of photons emitted by a semiconductor quantum dot in a microcavity as a function of temperature. We show that a large coupling to a high quality factor cavity can simultaneously reduce the effect of both phonon-induced sources of decoherence. It first limits the effect of pure dephasing on the zero-phonon line with indistinguishabilities above 97% up to 18 K. Moreover, it efficiently redirects the phonon sidebands into the zero-phonon line and brings the indistinguishability of the full emission spectrum from 87% (24%) without cavity effect to more than 99% (76%) at 0K (20K). We provide guidelines for optimal cavity designs that further minimize the phonon-induced decoherence.