Coulomb blockade in an atomically thin quantum dot coupled to a tunable Fermi reservoir

Abstract

Gate-tunable quantum-mechanical tunnelling of particles between a quantum confined state and a nearbyFermi reservoir of delocalized states has underpinned many advances in spintronics and solid-state quantum optics. The prototypical example is a semiconductor quantum dot separated from a gated contact by a tunnel barrier. This enables Coulomb blockade, the phenomenon whereby electrons or holes can be loaded one-by-one into a quantum dot 1,2 . Depending on the tunnel-coupling strength 3,4 , this capability facilitates single spin quantum bits 1,2,5 or coherent many-body interactions between the confined spin and the Fermi reservoir 6,7 . Van der Waals (vdW) heterostructures, in which a wide range of unique atomic layers can easily be combined, offer novel prospects to engineer coherent quantum confined spins 8,9 , tunnel barriers down to the atomic limit 10 or a Fermi reservoir beyond the conventional flat density of states 11 . However, gatecontrol of vdW nanostructures 12-16 at the single particle level is needed to unlock their potential. Here we report Coulomb blockade in a vdW heterostructure consisting of a transition metal dichalcogenide quantum dot coupled to a graphene contact through an atomically thin hexagonal boron nitride (hBN) tunnel barrier. Thanks to a tunable Fermi reservoir, we can deterministically load either a single electron or a single hole into the quantum dot. We observe hybrid excitons, composed of localized quantum dot states and delocalized continuum states, arising from ultra-strong spin-conserving tunnel coupling through the atomically thin tunnel barrier. Probing the charged excitons in applied magnetic fields, we observe large gyromagnetic ratios (∼8). Our results establish a foundation for engineering next-generation devices to investigate either novel regimes of Kondo physics or isolated quantum bits in a vdW heterostructure platform. Supplementary Figure 5. Lineshape evolution of the excitons states as a function of the gate voltage.Photoluminescence spectra of quantum dots A and B for different applied gate voltage values measured at T = 3.8 K. The green and red labels indicate the charged exciton states for quantum dots A and B, respectively. Labels X 1-, X 0 , X 1+ and X H represent the negatively charged, neutral, positively charged and hybrid excitons, respectively. For comparison purposes, some spectra have been multiplied by the corresponding factors indicated at the left part of the figure.

Identifying defect-related quantum emitters in monolayer WSe2

“…It is worth noting that these quantum emitters in our sample mainly result from defects other than strain effect since no intentional strain is introduced. And the emissions are assumed to be neutral excitons which usually appear without applied electric field [22,23]. The defects introduce various trapping energy levels [24,25,28,[49][50][51] within the electronic band gap of the WSe 2 , thus providing possibilities for various transitions.…”

“…Meanwhile, the properties of such a 2D host of quantum emitters have been intensely investigated, including 3D localized trions in heterostuctures [19], manipulation of fine structure splitting (FSS) [20] and photon-phonon interaction [21]. Furthermore, the optical initialization of a single spin-valley in charged WSe 2 quantum dots [22] and the ability to deterministically load either a single electron or single hole into a Van der Waals heterostructure quantum device via a Coulomb blockade [23] have been demonstrated, which enable a new class of quantum-confined spin system to store and process information. However, the origin of the 2D host of quantum emitters is still vague.…”

Dipolar interactions between localized interlayer excitons in van der Waals heterostructures

“…As the expected blueshift is U dd ∼ 1/r 3 ex where r ex is the interexcitonic distance, localized interlayer excitons are a good candidate to observe this effect. Localized excitons in monolayer WSe 2 have been shown to be single photon emitters with sharp linewidths [18,19] and can host a single charge and spin [20,21]. Very recently, localized interlayer excitons with sharp linewidths were reported in vdW heterostructures [22].…”

Atomically-thin quantum dots integrated with lithium niobate photonic chips [Invited]

“…One of the most prominent examples is WSe2 which, at the monolayer level, is a direct band-gap semiconductor featuring bright localized excitons [15] or bi-excitons [16] at cryogenic temperatures. Once exfoliated, the TMD material can be stacked to create layerby-layer van der Waals heterostructures with designer functionality [17], [18] or placed onto arbitrary substrates [19], including complex photonic circuits, using a variety of transfer methods [20]. As quantum emission is embedded in the single atomic layer, optical extraction is not limited by total internal reflection, an enormous challenge for bulk materials such as GaAs, diamond or SiC.…”