Search

This Perspective presents an overview on the epitaxial growth and optical properties of GaAs quantum dots obtained with the droplet etching method as high-quality sources of quantum light. We illustrate recent achievements regarding the generation of single photons and polarization entangled photon pairs and the use of these sources in applications of central importance in quantum communication such as entanglement swapping and quantum key distribution. [ABSTRACT FROM AUTHOR]

Photonic structures capable of enhancing the light‐outcoupling efficiency of embedded epitaxial quantum dots (QDs) in a broad spectral range are attractive for the realization of bright sources of single photons and entangled photon pairs. In this work, a planar‐multilayer antenna is experimentally demonstrated for GaAs QDs embedded in AlGaAs membranes. The antenna consists of a metal (Au or Ag) reflector and a semi‐transparent metal (Ag) director, with a thin oxide layer (hafnium dioxide (HfO2) or aluminium oxide (Al2O3)) between metal and semiconductor layers. Simulations using the 3D finite‐difference time‐domain (FDTD) method indicate a maximal efficiency of 43% (for collection optics with a numerical aperture (NA) of 0.85), a wavelength‐dependent Purcell factor ranging from ≈0.7 to ≈1.45, strong directional emission characteristics, as well as a broad bandwidth of ≈30 nm. In the experiment, we find a Purcell factor compatible with the simulation results, a maximum collection efficiency as high as ≈19% and an ultralow multiphoton emission probability of 0.006 ± 0.005. The planar geometry, its compatibility with post‐growth tuning methods, facile fabrication, broad spectral bandwidth, and achieved performance make the presented structure competitive for solid‐state sources of quantum light. [ABSTRACT FROM AUTHOR]

The generation and long-haul transmission of highly entangled photon pairs is a cornerstone of emerging photonic quantum technologies with key applications such as quantum key distribution and distributed quantum computing. However, a natural limit for the maximum transmission distance is inevitably set by attenuation in the medium. A network of quantum repeaters containing multiple sources of entangled photons would allow overcoming this limit. For this purpose, the requirements on the source's brightness and the photon pairs' degree of entanglement and indistinguishability are stringent. Despite the impressive progress made so far, a definitive scalable photon source fulfilling such requirements is still being sought after. Semiconductor quantum dots excel in this context as sub-Poissonian sources of polarization entangled photon pairs. In this work, we present the state-of-the-art set by GaAs based quantum dots and use them as a benchmark to discuss the challenges toward the realization of practical quantum networks. [ABSTRACT FROM AUTHOR]

The article discusses the research on designing a quantum teleportation protocol using solid-state quantum emitters. According to the author entangled photon pairs generated on-demand by the quantum emitter were used to develop the protocol. Topics include fabrication of gallium quantum dot system, light sources of photons, and measurement of photon emission rate.

• Broadening of single GaAs quantum dot photoluminescence (PL) linewidth. • Treatment of the surface by sulphur passivation and oxide encapsulation. • Partial revival of the linewidth and PL intensity by above surface treatment. • Estimation of the random Gaussian fluctuation strength related to line broadening. Epitaxial GaAs quantum dots grown by droplet etching have recently shown excellent properties as sources of single photons as well as entangled photon pairs. Integration in some nanophotonic structures requires surface-to-dot distances of less than 100 nm. This demands a surface passivation scheme, which could be useful to lower the density of surface states. To address this issue, sulphur passivation with dielectric overlayer as an encapsulation is used for surface to QD distances of ≲40 nm, which results in the partial recovery of emission linewidths to bulk values as well as in the increase of the photoluminescence intensity. [ABSTRACT FROM AUTHOR]

We report on the observation of nearly maximally entangled photon pairs from semiconductor quantum dots, without resorting to postselection techniques. We use GaAs quantum dots integrated on a patterned piezoelectric actuator capable of suppressing the exciton fine structure splitting. By using a resonant two-photon excitation, we coherently drive the biexciton state and demonstrate experimentally that our device generates polarization-entangled photons with a fidelity of 0.978(5) and a concurrence of 0.97(1) taking into account the nonidealities stemming from the experimental setup. By combining fine-structure-dependent fidelity measurements and a theoretical model, we identify an exciton spin-scattering process as a possible residual decoherence mechanism. We suggest that this imperfection may be overcome using a modest Purcell enhancement so as to achieve fidelities >0.99, thus making quantum dots evenly matched with the best probabilistic entangled photon sources. [ABSTRACT FROM AUTHOR]