41 research outputs found
Numerical modelling of the coupling efficiency of single quantum emitters in photonic-crystal waveguides
Planar photonic nanostructures have recently attracted a great deal of
attention for quantum optics applications. In this article, we carry out full
3D numerical simulations to fully account for all radiation channels and
thereby quantify the coupling efficiency of a quantum emitter embedded in a
photonic-crystal waveguide. We utilize mixed boundary conditions by combining
active Dirichlet boundary conditions for the guided mode and perfectly-matched
layers for the radiation modes. In this way, the leakage from the quantum
emitter to the surrounding environment can be determined and the spectral and
spatial dependence of the coupling to the radiation modes can be quantified.
The spatial maps of the coupling efficiency, the -factor, reveal that
even for moderately slow light, near-unity is achievable that is
remarkably robust to the position of the emitter in the waveguide. Our results
show that photonic-crystal waveguides constitute a suitable platform to achieve
deterministic interfacing of a single photon and a single quantum emitter,
which has a range of applications for photonic quantum technology
Two mechanisms of disorder-induced localization in photonic-crystal waveguides
Unintentional but unavoidable fabrication imperfections in state-of-the-art
photonic-crystal waveguides lead to the spontaneous formation of
Anderson-localized modes thereby limiting slowlight propagation and its
potential applications. On the other hand, disorder-induced cavities offer an
approach to cavity-quantum electrodynamics and random lasing at the nanoscale.
The key statistical parameter governing the disorder effects is the
localization length, which together with the waveguide length determines the
statistical transport of light through the waveguide. In a disordered
photonic-crystal waveguide, the localization length is highly dispersive, and
therefore, by controlling the underlying lattice parameters, it is possible to
tune the localization of the mode. In the present work, we study the
localization length in a disordered photonic-crystal waveguide using numerical
simulations. We demonstrate two different localization regimes in the
dispersion diagram where the localization length is linked to the density of
states and the photon effective mass, respectively. The two different
localization regimes are identified in experiments by recording the
photoluminescence from quantum dots embedded in photonic-crystal waveguides.Comment: Accepted for publication in Physical Review
A diamond-confined open microcavity featuring a high quality-factor and a small mode-volume
With a highly coherent, optically addressable electron spin, the nitrogen-vacancy (NV) center in diamond is a promising candidate for a node in a quantum network. A resonant microcavity can boost the flux of coherent photons emerging from single NV centers. Here, we present an open Fabry–Pérot microcavity geometry containing a single-crystal diamond membrane, which operates in a regime where the vacuum electric field is strongly confined to the diamond membrane. There is a field anti-node at the diamond–air interface. Despite the presence of surface losses, a finesse of ℱ=11500 was observed. The quality
Quantum optics with near lifetime-limited quantum-dot transitions in a nanophotonic waveguide
Establishing a highly efficient photon-emitter interface where the intrinsic
linewidth broadening is limited solely by spontaneous emission is a key step in
quantum optics. It opens a pathway to coherent light-matter interaction for,
e.g., the generation of highly indistinguishable photons, few-photon optical
nonlinearities, and photon-emitter quantum gates. However, residual broadening
mechanisms are ubiquitous and need to be combated. For solid-state emitters
charge and nuclear spin noise is of importance and the influence of photonic
nanostructures on the broadening has not been clarified. We present near
lifetime-limited linewidths for quantum dots embedded in nanophotonic
waveguides through a resonant transmission experiment. It is found that the
scattering of single photons from the quantum dot can be obtained with an
extinction of , which is limited by the coupling of the quantum
dot to the nanostructure rather than the linewidth broadening. This is obtained
by embedding the quantum dot in an electrically-contacted nanophotonic
membrane. A clear pathway to obtaining even larger single-photon extinction is
laid out, i.e., the approach enables a fully deterministic and coherent
photon-emitter interface in the solid state that is operated at optical
frequencies.Comment: 27 pages, 7 figure
Low-Noise GaAs Quantum Dots for Quantum Photonics
Quantum dots are both excellent single-photon sources and hosts for single
spins. This combination enables the deterministic generation of Raman-photons
-- bandwidth-matched to an atomic quantum-memory -- and the generation of
photon cluster states, a resource in quantum communication and
measurement-based quantum computing. GaAs quantum dots in AlGaAs can be matched
in frequency to a rubidium-based photon memory, and have potentially improved
electron spin coherence compared to the widely used InGaAs quantum dots.
However, their charge stability and optical linewidths are typically much worse
than for their InGaAs counterparts. Here, we embed GaAs quantum dots into an
---diode specially designed for low-temperature operation. We
demonstrate ultra-low noise behaviour: charge control via Coulomb blockade,
close-to lifetime-limited linewidths, and no blinking. We observe high-fidelity
optical electron-spin initialisation and long electron-spin lifetimes for these
quantum dots. Our work establishes a materials platform for low-noise quantum
photonics close to the red part of the spectrum.Comment: (19 pages, 12 figures, 1 table
A chiral one-dimensional atom using a quantum dot in an open microcavity
In a chiral one-dimensional atom, a photon propagating in one direction interacts with the atom; a photon propagating in the other direction does not. Chiral quantum optics has applications in creating nanoscopic single-photon routers, circulators, phase-shifters, and two-photon gates. Here, we implement chiral quantum optics using a low-noise quantum dot in an open microcavity. We demonstrate the non-reciprocal absorption of single photons, a single-photon diode. The non-reciprocity, the ratio of the transmission in the forward-direction to the transmission in the reverse direction, is as high as 10.7 dB. This is achieved by tuning the photon-emitter coupling in situ to the optimal operating condition (β = 0.5). Proof that the non-reciprocity arises from a single quantum emitter lies in the photon statistics—ultralow-power laser light propagating in the diode’s reverse direction results in a highly bunched output (g(2)(0) = 101), showing that the single-photon component is largely removed
Photon bound state dynamics from a single artificial atom
The interaction between photons and a single two-level atom constitutes a fundamental paradigm in quantum physics. The nonlinearity provided by the atom leads to a strong dependence of the light–matter interface on the number of photons interacting with the two-level system within its emission lifetime. This nonlinearity unveils strongly correlated quasiparticles known as photon bound states, giving rise to key physical processes such as stimulated emission and soliton propagation. Although signatures consistent with the existence of photon bound states have been measured in strongly interacting Rydberg gases, their hallmark excitation-number-dependent dispersion and propagation velocity have not yet been observed. Here we report the direct observation of a photon-number-dependent time delay in the scattering off a single artificial atom—a semiconductor quantum dot coupled to an optical cavity. By scattering a weak coherent pulse off the cavity–quantum electrodynamics system and measuring the time-dependent output power and correlation functions, we show that single photons and two- and three-photon bound states incur different time delays, becoming shorter for higher photon numbers. This reduced time delay is a fingerprint of stimulated emission, where the arrival of two photons within the lifetime of an emitter causes one photon to stimulate the emission of another