9 research outputs found
Transfer of a quantum state from a photonic qubit to a gate-defined quantum dot
Interconnecting well-functioning, scalable stationary qubits and photonic
qubits could substantially advance quantum communication applications and serve
to link future quantum processors. Here, we present two protocols for
transferring the state of a photonic qubit to a single-spin and to a two-spin
qubit hosted in gate-defined quantum dots (GDQD). Both protocols are based on
using a localized exciton as intermediary between the photonic and the spin
qubit. We use effective Hamiltonian models to describe the hybrid systems
formed by the the exciton and the GDQDs and apply simple but realistic noise
models to analyze the viability of the proposed protocols. Using realistic
parameters, we find that the protocols can be completed with a success
probability ranging between 85-97%
Engineering of Neutral Excitons and Exciton Complexes in Transition Metal Dichalcogenide Monolayers through External Dielectric Screening
In order to fully exploit the potential of transition metal dichalcogenide
monolayers (TMD-MLs), the well-controlled creation of atomically sharp lateral
heterojunctions within these materials is highly desirable. A promising
approach to create such heterojunctions is the local modulation of the
electronic structure of an intrinsic TMD-ML via dielectric screening induced by
its surrounding materials. For the realization of this non-invasive approach,
an in-depth understanding of such dielectric effects is required. We report on
the modulations of excitonic transitions in TMD-MLs through the effect of
dielectric environments including low-k and high-k dielectric materials. We
present absolute tuning ranges as large as 37 meV for the optical band gaps of
WSe 2 and MoSe 2 MLs and relative tuning ranges on the order of 30% for the
binding energies of neutral excitons in WSe 2 MLs. The findings suggest the
possibility to reduce the electronic band gap of WSe 2 MLs by 120 meV, paving
the way towards dielectrically defined lateral heterojunctions.Comment: 11 pages + 6 pages supporting informatio
Excitons in InGaAs Quantum Dots without Electron Wetting Layer States
The Stranski-Krastanov (SK) growth-mode facilitates the self-assembly of
quantum dots (QDs) using lattice-mismatched semiconductors, for instance InAs
and GaAs. SK QDs are defect-free and can be embedded in heterostructures and
nano-engineered devices. InAs QDs are excellent photon emitters: QD-excitons,
electron-hole bound pairs, are exploited as emitters of high quality single
photons for quantum communication. One significant drawback of the SK-mode is
the wetting layer (WL). The WL results in a continuum rather close in energy to
the QD-confined-states. The WL-states lead to unwanted scattering and dephasing
processes of QD-excitons. Here, we report that a slight modification to the
SK-growth-protocol of InAs on GaAs -- we add a monolayer of AlAs following InAs
QD formation -- results in a radical change to the QD-excitons. Extensive
characterisation demonstrates that this additional layer eliminates the
WL-continuum for electrons enabling the creation of highly charged excitons
where up to six electrons occupy the same QD. Single QDs grown with this
protocol exhibit optical linewidths matching those of the very best SK QDs
making them an attractive alternative to standard InGaAs QDs
Effect of gallium termination on InGaAs wetting layer properties in droplet epitaxy InGaAs quantum dots
Self-assembled quantum dots based on III-V semiconductors have excellent
properties for applications in quantum optics. However, the presence of a 2D
wetting layer which forms during the Stranski-Krastanov growth of quantum dots
can limit their performance. Here, we investigate wetting layer formation
during quantum dot growth by the alternative droplet epitaxy technique. We use
a combination of photoluminescence excitation spectroscopy, lifetime
measurements, and transmission electron microscopy to identify the presence of
an InGaAs wetting layer in these droplet epitaxy quantum dots, even in the
absence of distinguishable wetting layer photoluminescence. We observe that
increasing the amount of Ga deposited on a GaAs (100) surface prior to the
growth of InGaAs quantum dots leads to a significant reduction in the emission
wavelength of the wetting layer to the point where it can no longer be
distinguished from the GaAs acceptor peak emission in photoluminescence
measurements
Semiconductor membranes for electrostatic exciton trapping in optically addressable quantum transport devices
Combining the capabilities of gate defined quantum transport devices in
GaAs-based heterostructures and of optically addressed self-assembled quantum
dots could open broad perspectives for new devices and functionalities. For
example, interfacing stationary solid-state qubits with photonic quantum states
would open a new pathway towards the realization of a quantum network with
extended quantum processing capacity in each node. While gated devices allow
very flexible confinement of electrons or holes, the confinement of excitons
without some element of self-assembly is much harder. To address this
limitation, we introduce a technique to realize exciton traps in quantum wells
via local electric fields by thinning a heterostructure down to a 220 nm thick
membrane. We show that mobilities over
cmVs can be retained and that quantum point contacts and
Coulomb oscillations can be observed on this structure, which implies that the
thinning does not compromise the heterostructure quality. Furthermore, the
local lowering of the exciton energy via the quantum-confined Stark effect is
confirmed, thus forming exciton traps. These results lay the technological
foundations for devices like single photon sources, spin photon interfaces and
eventually quantum network nodes in GaAs quantum wells, realized entirely with
a top-down fabrication process.Comment: v2: added missing acknowledgement. v3: fixed typos in acknolwedgemen
Optical properties of MoSe monolayer implanted with ultra-low energy Cr ions
The paper explores the optical properties of an exfoliated MoSe monolayer
implanted with Cr ions, accelerated to 25 eV. Photoluminescence of the
implanted MoSe reveals an emission line from Cr-related defects that is
present only under weak electron doping. Unlike band-to-band transition, the
Cr-introduced emission is characterised by non-zero activation energy, long
lifetimes, and weak response to the magnetic field. To rationalise the
experimental results and get insights into the atomic structure of the defects,
we modelled the Cr-ion irradiation process using ab-initio molecular dynamics
simulations followed by the electronic structure calculations of the system
with defects. The experimental and theoretical results suggest that the
recombination of electrons on the acceptors, which could be introduced by the
Cr implantation-induced defects, with the valence band holes is the most likely
origin of the low energy emission. Our results demonstrate the potential of
low-energy ion implantation as a tool to tailor the properties of 2D materials
by doping
Vapor transport growth of MoS nuceated on SiO patterns and graphene flakes
Vapor transport growth of atomically thin MoS2 layers on patterned substrates is investigated, as it is a step towards the self-aligned growth and formation of heterojunctions, which could be useful in future applications. Enhanced formation of MoS2 flakes at the pattern edges is observed on both the substrates examined, namely, patterned thermal SiO2 on Si(100) and graphene flakes on SiO2. The diffusion driven growth leads to the formation of MoS2 monolayers (MLs) with sizes of tens of micrometers around the edges of SiO2 patterns. The growth mode and the optical quality of the MoS2 flakes can be controlled by varying the substrate temperature. Besides the lateral growth, 3R-type pyramids are obtained on prolonging the growth. Lateral MoS2-graphene heterostructures are obtained by using graphene flakes on SiO2 as a substrate
Effect of Zinc Incorporation on the Performance of Red Light Emitting InP Core Nanocrystals
This report presents a systematic study on the effect of zinc (Zn) carboxylate precursor on the structural and optical properties of red light emitting InP nanocrystals (NCs). NC cores were assessed using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), energy-dispersive X-ray spectroscopy (EDX), and high-resolution transmission electron microscopy (HRTEM). When moderate Zn:In ratios in the reaction pot were used, the incorporation of Zn in InP was insufficient to change the crystal structure or band gap of the NCs, but photoluminescence quantum yield (PLQY) increased dramatically compared with pure InP NCs. Zn was found to incorporate mostly in the phosphate layer on the NCs. PL, PLQY, and time-resolved PL (TRPL) show that Zn carboxylates added to the precursors during NC cores facilitate the synthesis of high-quality InP NCs by suppressing nonradiative and sub-band-gap recombination, and the effect is visible also after a ZnS shell is grown on the cores