Enhanced indistinguishability of in-plane single photons by resonance fluorescence on an integrated quantum dot

Integrated quantum light sources in photonic circuits are envisaged as the building blocks of future on-chip architectures for quantum logic operations. While semiconductor quantum dots have been proven to be the highly efficient emitters of quantum light, their interaction with the host material induces spectral decoherence, which decreases the indistinguishability of the emitted photons and limits their functionality. Here, we show that the indistinguishability of in-plane photons can be greatly enhanced by performing resonance fluorescence on a quantum dot coupled to a photonic crystal waveguide. We find that the resonant optical excitation of an exciton state induces an increase in the emitted single-photon coherence by a factor of 15. Two-photon interference experiments reveal a visibility of 0.80 ± 0.03, which is in good agreement with our theoretical model. Combined with the high in-plane light-injection efficiency of photonic crystal waveguides, our results pave the way for the use of this system for the on-chip generation and transmission of highly indistinguishable photons

Controllable Photonic Time-Bin Qubits from a Quantum Dot

Photonic time bin qubits are well suited to transmission via optical fibres and waveguide circuits. The states take the form $\frac{1}{\sqrt{2}}(\alpha \ket{0} + e^{i\phi}\beta \ket{1})$, with $\ket{0}$ and $\ket{1}$ referring to the early and late time bin respectively. By controlling the phase of a laser driving a spin-flip Raman transition in a single-hole-charged InAs quantum dot we demonstrate complete control over the phase, $\phi$. We show that this photon generation process can be performed deterministically, with only a moderate loss in coherence. Finally, we encode different qubits in different energies of the Raman scattered light, demonstrating wavelength division multiplexing at the single photon level

High Purcell factor generation of indistinguishable on-chip single photons

On-chip single-photon sources are key components for integrated photonic quantum technologies. Semiconductor quantum dots can exhibit near-ideal single-photon emission, but this can be significantly degraded in on-chip geometries owing to nearby etched surfaces. A long-proposed solution to improve the indistinguishablility is to use the Purcell effect to reduce the radiative lifetime. However, until now only modest Purcell enhancements have been observed. Here we use pulsed resonant excitation to eliminate slow relaxation paths, revealing a highly Purcell-shortened radiative lifetime (22.7 ps) in a waveguide-coupled quantum dot–photonic crystal cavity system. This leads to near-lifetime-limited single-photon emission that retains high indistinguishablility (93.9%) on a timescale in which 20 photons may be emitted. Nearly background-free pulsed resonance fluorescence is achieved under π-pulse excitation, enabling demonstration of an on-chip, on-demand single-photon source with very high potential repetition rates

On-chip transmission of non-classical light from an integrated quantum emitter

We report the on-chip transmission of single photons emitted by a semiconductor quantum dot coupled to a photonic crystal waveguide. Autocorrelation measurements show strong multiphoton suppression. The device efficiency is 24% under optical pumping. © 2012 OSA

On-chip single photon emission from an integrated semiconductor quantum dot into a photonic crystal waveguide

We demonstrate the in-plane emission of highly polarized single photons from an InAs quantum dot embedded into a photonic crystal waveguide. The spontaneous emission rates are Purcell-enhanced by the coupling of the quantum dot to a slow-light mode of the waveguide. Photon-correlation measurements confirm the sub-Poissonian statistics of the in-plane emission. Under optical pulse excitation, single photon emission rates of up to 19 MHz into the guided mode are demonstrated, which corresponds to a device efficiency of 24. These results herald the monolithic integration of sources in photonic quantum circuits. © 2011 American Institute of Physics

On-chip generation and transmission of single photons

We discuss the highly-efficient on-chip transmission of quantum light from an integrated source. Under optical excitation, single photons emitted from a semiconductor quantum dot are injected into the propagating mode of a coupled photonic crystal waveguide. In such a system, slow-light effects induce Purcell enhancement of the coupled emitter increasing significantly the single-photon emission rates. Our system exhibits a single-photon emission rate into the propagating mode of 19 MHz with 23% efficiency. The high emission rates together with the coherence properties of the emitted single photons demonstrate the suitability of these systems for on-chip quantum information processing using quantum optical circuits. © 2013 Copyright SPIE

Observation and modeling of the time-dependent descreening of internal electric field in a wurtzite GaN/Al0.15Ga0.85N quantum well after high photoexcitation

We use the intense, 5-ns-long, excitation pulses provided by the fourth harmonic of a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser to induce a strong high-energy shift of the photoluminescence of a 7.8-nm-wide GaN/Al0.15Ga0.85N single quantum well. We follow the complex relaxation dynamics of the energy and of the intensity of this emission, by using a time-resolved photoluminescence setup. We obtain excellent agreement between our experimental results and those of our finite-element modeling of the time-dependent energy and oscillator strength. The model, based on a self-consistent solution of the Schrodinger and Poisson equations, accounts for the three important sources of energy shifts: (1) the screening of the electric field present along the growth axis of the well, by accumulation of electron-hole dipoles, (2) the band-gap renormalization induced by many-body interactions, and (3) the filling of the conduction and valence bands

In-plane single-photon emission from a L3 cavity coupled to a photonic crystal waveguide

We report on the design and experimental demonstration of a system based on an L3 cavity coupled to a photonic crystal waveguide for in-plane single-photon emission. A theoretical and experimental investigation for all the cavity modes within the photonic bandgap is presented for stand-alone L3 cavity structures. We provide a detailed discussion supported by finite-difference time-domain calculations of the evanescent coupling of an L3 cavity to a photonic crystal waveguide for onchip single-photon transmission. Such a system is demonstrated experimentally by the in-plane transmission of quantum light from an InAs quantum dot coupled to the L3 cavity mode. © 2012 Optical Society of America

Large size dependence of exciton-longitudinal-optical-phonon coupling in nitride-based quantum wells and quantum boxes

We present an experimental and theoretical study of the size dependence of the coupling between electron-hole pairs and longitudinal-optical phonons in Ga1-xInxN/GaN-based quantum wells and quantum boxes. We found that the Huang-Rhys factor S, which determines the distribution of luminescence intensities between the phonon replicas and the zero-phonon peak, increases significantly when the vertical size of the boxes or the thickness of quantum well increases. We assign this variation to (1) the strong electric field present along the growth axis of the system, due to spontaneous and piezoelectric polarizations in these wurtzite materials, and (2) the localization on separate sites of electrons and holes in the plane of the wells or boxes, due to potential fluctuations in the ternary alloy. Indeed, envelope-function calculations for free or localized excitons, with electron-hole distance only controlled by Coulomb interaction, do not account quantitatively for the measured behavior of the S factor. In fact, the latter is rather similar to what is obtained for donor-acceptor pairs, with a statistical distribution of distances between localization centers for electrons and holes. (C) 2002 American Institute of Physics