M. Kremser, M. Brotons-Gisbert, J. Knörzer, J. Gückelhorn, M. Meyer, M. Barbone, A. V. Stier, B. D. Gerardot, K. Müller, and J. J. Finley, Discrete interactions between a few interlayer excitons trapped at a MoSe2–WSe2 heterointerface, https://www.nature.com/articles/s41699-020-0141-3 


Abstract

Inter-layer excitons (IXs) in hetero-bilayers of transition metal dichalcogenides (TMDs) represent an exciting emergent class of long-lived dipolar composite bosons in an atomically thin, near-ideal two-dimensional (2D) system. The long-range interactions that arise from the spatial separation of electrons and holes can give rise to novel quantum, as well as classical multi-particle correlation effects. Indeed, first indications of exciton condensation have been reported recently. In order to acquire a detailed understanding of the possible many-body effects, the fundamental interactions between individual IXs have to be studied. Here, we trap a tunable number of dipolar IXs (NIX ~ 1–5) within a nanoscale confinement potential induced by placing a MoSe2–WSe2 hetero-bilayer (HBL) onto an array of SiO2 nanopillars. We control the mean occupation of the IX trap via the optical excitation level and observe discrete sharp-line emission from different configurations of interacting IXs. The intensities of these features exhibit characteristic near linear, quadratic, cubic, quartic and quintic power dependencies, which allows us to identify them as different multiparticle configurations with NIX ~ 1–5. We directly measure the hierarchy of dipolar and exchange interactions as NIX increases. The interlayer biexciton (NIX = 2) is found to be an emission doublet that is blue-shifted from the single exciton by ΔE = (8.4 ± 0.6) meV and split by 2J = (1.2 ± 0.5) meV. The blueshift is even more pronounced for triexcitons ((12.4 ± 0.4) meV), quadexcitons ((15.5 ± 0.6) meV) and quintexcitons ((18.2 ± 0.8) meV). These values are shown to be mutually consistent with numerical modelling of dipolar excitons confined to a harmonic trapping potential having a confinement lengthscale in the range 3ℓ≈3 nm. Our results contribute to the understanding of interactions between IXs in TMD hetero-bilayers at the discrete limit of only a few excitations and represent a key step towards exploring quantum correlations between IXs in TMD hetero-bilayers.

Carlos Errando-Herranz, Eva Schöll, Raphaël Picard, Micaela Laini, Samuel Gyger, Ali W. Elshaari, Art Branny, Ulrika Wennberg, Sebastien Barbat, Thibaut Renaud, 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://arxiv.org/abs/2002.07657


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 1 arXiv:2002.07657v3 [physics.app-ph] 15 May 2020 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.

 

 

Zhe-Xian KoongGuillem Ballesteros-GarciaRaphaël ProuxDan DalacuPhilip J. PooleBrian D. Gerardot , Multiplexed Single Photons from Deterministically Positioned Nanowire Quantum Dots,  https://arxiv.org/abs/2005.05361


Abstract

Solid-state quantum emitters are excellent sources of on-demand indistinguishable or entangled photons and can host long-lived spin memories, crucial resources for photonic quantum information applications. However, their scalability remains an outstanding challenge. Here we present a scalable technique to multiplex streams of photons from multiple independent quantum dots, on-chip, into a fiber network for use off-chip. Multiplexing is achieved by incorporating a multi-core fiber into a confocal microscope and spatially matching the multiple foci, seven in this case, to quantum dots in an array of deterministically positioned nanowires. First, we report the coherent control of the emission of biexciton-exciton cascade from a single nanowire quantum dot under resonant two-photon excitation. Then, as a proof-of-principle demonstration, we perform parallel spectroscopy on the nanowire array to identify two nearly identical quantum dots at different positions which are subsequently tuned into resonance with an external magnetic field. Multiplexing of background-free single photons from these two quantum dots is then achieved. Our approach, applicable to all types of quantum emitters, can readily be scaled up to multiplex > 100  quantum light sources, providing a breakthrough in hardware for photonic based quantum technologies. Immediate applications include quantum communication, quantum simulation, and quantum computation.

Mauro Brotons-Gisbert, Hyeonjun Baek, Alejandro Molina-Sánchez, Aidan Campbell, Eleanor Scerri, Daniel White, Kenji Watanabe, Takashi Taniguchi, Cristian Bonato and Brian D. Gerardot  Spin - layer locking of interlayer excitons trapped in moiré potentials,  https: / / www.nature.com/articles/s41563-020-0687-7 


Abstract

Van der Waals heterostructures offer attractive opportunities to design quantum materials. For instance, transition metal dichalcogenides (TMDs) possess three quantum degrees of freedom: spin, valley index and layer index. Furthermore, twisted TMD heterobilayers can form moiré patterns that modulate the electronic band structure according to the atomic registry, leading to spatial confinement of interlayer excitons (IXs). Here we report the observation of spin - layer locking of IXs trapped in moiré potentials formed in a heterostructure of bilayer 2H-MoSe2 and monolayer WSe2. The phenomenon of locked electron spin and layer index leads to two quantum-confined IX species with distinct spin - layer - valley configurations. Furthermore,we observe that the atomic registries of the moiré trapping sites in the three layers are intrinsically locked together due to the 2H-type stacking characteristic of bilayer TMDs. These results identify the layer index as a useful degree of freedom to engineer tunable few-level quantum systems in two-dimensional heterostructures. 

 

 

 

H. Baek, M. Brotons-Gisbert, ZX Koong, A. Campbell, M. Rambach, K. Watanabe, T. Takashi, and BD Gerardot,  Highly tunable quantum light from moiré trapped excitons,  https://arxiv.org/ abs / 2001.04305 .