Christopher L. Morrison, Markus Rambach, Zhe Xian Koong, Francesco Graffitti, Fiona Thorburn, Ajoy K. Kar, Yong Ma, Suk-In Park, Jin Dong Song, Nick G. Stoltz, Dirk Bouwmeester, Alessandro Fedrizzi, and Brian D. Gerardot, A bright source of telecom single photons based on quantum frequency conversion, https://aip.scitation.org/doi/10.1063/5.0045413


Abstract

On-demand indistinguishable single-photon sources are essential for quantum networking and communication. Semiconductor quantum dots are among the most promising candidates, but their typical emission wavelength renders them unsuitable for use in fiber networks. Here, we present quantum frequency conversion of near-infrared photons from a bright quantum dot to the telecommunication C-band, allowing integration with existing fiber architectures. We use a custom-built, tunable 2400 nm seed laser to convert single photons from 942 nm to 1550 nm in a difference-frequency generation process. We achieve an end-to-end conversion efficiency of ≃35%, demonstrate count rates approaching 1 MHz at 1550 nm with g(2)(0)=0.043(1), and achieve Hong-Ou-Mandel (HOM) visibilities of 60%. We expect this scheme to be preferable to quantum dot sources directly emitting at telecom wavelengths for fiber-based quantum networking.

Samuel Gyger, Julien Zichi, Lucas Schweickert, Ali W Elshaari, Stephan Steinhauer, Saimon F Covre da Silva, Armando Rastelli, Val Zwiller, Klaus D Jöns, Carlos Errando-Herranz, Reconfigurable photonics with on-chip single-photon detectors, https://www.nature.com/articles/s41467-021-21624-3


Abstract

Integrated quantum photonics offers a promising path to scale up quantum optics experiments by miniaturizing and stabilizing complex laboratory setups. Central elements of quantum integrated photonics are quantum emitters, memories, detectors, and reconfigurable photonic circuits. In particular, integrated detectors not only offer optical readout but, when interfaced with reconfigurable circuits, allow feedback and adaptive control, crucial for deterministic quantum teleportation, training of neural networks, and stabilization of complex circuits. However, the heat generated by thermally reconfigurable photonics is incompatible with heat-sensitive superconducting single-photon detectors, and thus their on-chip co-integration remains elusive. Here we show low-power microelectromechanical reconfiguration of integrated photonic circuits interfaced with superconducting single-photon detectors on the same chip. We demonstrate three key functionalities for photonic quantum technologies: 28 dB high-extinction routing of classical and quantum light, 90 dB high-dynamic range single-photon detection, and stabilization of optical excitation over 12 dB power variation. Our platform enables heat-load free reconfigurable linear optics and adaptive control, critical for quantum state preparation and quantum logic in large-scale quantum photonics applications.

 

Hyeonjun Baek, Mauro Brotons-Gisbert, Aidan Campbell, Kenji Watanabe, Takashi Taniguchi, Brian D. Gerardot, Optical read-out of Coulomb staircases in a moiré superlattice via trapped interlayer trions, https://arxiv.org/abs/2102.01358


Abstract

Moiré patterns with a superlattice potential can be formed by vertically stacking two layered materials with a relative twist or lattice constant mismatch. The moiré superlattice can generate flat bands that result in new correlated insulating, superconducting, and topological states. Strong electron correlations, tunable by the fractional filling, have been observed in both graphene and transition metal dichalcogenide (TMD) based systems. In addition, in TMD based systems, the moiré potential landscape can trap interlayer excitons (IX) at specific atomic registries. Here we report that spatially isolated trapped IX in a molybdenum diselenide/tungsten diselenide heterobilayer device provide a sensitive optical probe of carrier filling in their immediate environment. By mapping the spatial positions of individual trapped IX, we are able to spectrally track the emitters as the moiré lattice is filled with excess carriers. Upon initial doping of the heterobilayer, neutral trapped IX form charged IX (IX trions) uniformly with a binding energy of ~7 meV. Upon further doping, the empty superlattice sites sequentially fill, creating a Coulomb staircase: stepwise changes in the IX trion emission energy due to Coulomb interactions with carriers at nearest neighbour moiré sites. This non-invasive, highly local technique can complement transport and non-local optical sensing techniques to characterise Coulomb interaction energies, visualise charge correlated states, or probe local disorder in a moiré superlattice.

Carlos Errando-Herranz, Eva Schöll, Raphaël Picard, Micaela Laini, Samuel Gyger, Ali W. Elshaari, Art Branny, Ulrika Wennberg, Sebastien Barbat, Thibaut Renaud, Marc Sartison, Mauro Brotons-Gisbert, Cristian Bonato, Brian D. Gerardot, Val Zwiller, and Klaus D. Jöns, Resonance Fluorescence from Waveguide-Coupled, Strain-Localized, Two-Dimensional Quantum Emitters, https://pubs.acs.org/doi/full/10.1021/acsphotonics.0c01653 


Abstract

Efficient on-chip integration of single-photon emitters imposes a major bottleneck for applications of photonic integrated circuits in quantum technologies. Resonantly excited solid-state emitters are emerging as near-optimal quantum light sources, if not for the lack of scalability of current devices. Current integration approaches rely on cost-inefficient individual emitter placement in photonic integrated circuits, rendering applications impossible. A promising scalable platform is based on two-dimensional (2D) semiconductors. However, resonant excitation and single-photon emission of waveguide-coupled 2D emitters have proven to be elusive. Here, we show a scalable approach using a silicon nitride photonic waveguide to simultaneously strain-localize single-photon emitters from a tungsten diselenide (WSe2) monolayer and to couple them into a waveguide mode. We demonstrate the guiding of single photons in the photonic circuit by measuring second-order autocorrelation of g(2)(0) = 0.150 ± 0.093 and perform on-chip resonant excitation, yielding a g(2)(0) = 0.377 ± 0.081. Our results are an important step to enable coherent control of quantum states and multiplexing of high-quality single photons in a scalable photonic quantum circuit.

 

Z. X. Koong, E. Scerri, M. Rambach, M. Cygorek, M. Brotons-Gisbert, R. Picard, Y. Ma, S. I. Park, J. D. Song, E. M. Gauger, and B. D. Gerardot, Coherent Dynamics in Quantum Emitters under Dichromatic Excitation, https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.126.047403 

Abstract

We characterize the coherent dynamics of a two-level quantum emitter driven by a pair of symmetrically detuned phase-locked pulses. The promise of dichromatic excitation is to spectrally isolate the excitation laser from the quantum emission, enabling background-free photon extraction from the emitter. While excitation is not possible without spectral overlap between the exciting pulse and the quantum emitter transition for ideal two-level systems due to cancellation of the accumulated pulse area, we find that any additional interactions that interfere with cancellation of the accumulated pulse area may lead to a finite stationary population inversion. Our spectroscopic results of a solid-state two-level system show that, while coupling to lattice vibrations helps to improve the inversion efficiency up to 50% under symmetric driving, coherent population control and a larger amount of inversion are possible using asymmetric dichromatic excitation, which we achieve by adjusting the ratio of the intensities between the red- and blue-detuned pulses. Our measured results, supported by simulations using a real-time path-integral method, offer a new perspective toward realizing efficient, background-free photon generation and extraction.