Search query: Electrostatic trap excitons single-photon

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abstract: Single photon sources are basic building blocks for quantum communications, processing, and metrology. Solid state quantum emitters in semiconductors have the potential for robust and reliable generation of photons, and atomically thin transition metal dichalcogenides, such as MoS2, MoSe2, WS2, and WSe2, are a promising new class of two dimensional semiconductors with a direct optical bandgap in the visible or near IR. Here, we observe bright and stable single photon emission from localized excitons in a monolayer of tungsten diselenide (WSe2) The emitters appear at the edges of the flakes and are linearly polarized. The spectral width of their emission is below 120 meV in a freestanding WSe2 monolayer. Photoluminescence excitation spectroscopy reveals the excitonic nature of the emitters and provides evidence that these single excitons originate from free excitons trapped in local potential wells at the edges of the atomically thin flakes. We find that the emitters can also be deterministically created by scratching the WSe2 monolayer. Their excellent spectral stability implies that these localized single photon emitters could find application in optoelectronics. Our results light the way to single exciton physics and quantum optics with atomically thin semiconductors.
author_names: Philipp Tonndorf

Robert Schmidt

Robert J Schneider

Johannes Kern

Michele Buscema

Gary A Steele

Andres Castellanos-Gomez

Herre S J van der Zant

S Michaelis de Vasconcellos

Rudolf Bratschitsch
title: Single photon emission from localized excitons in an atomically thin semiconductor
year: 2015

abstract: The demonstration of stable quantum emitters in semiconductor transition metal dichalcogenides (TMDs) [1] and insulating hexagonal boron nitride (hBN) [2] has begun to impact the field of integrated quantum optics due to the promising properties of two dimensional materials, such room temperature operation, stretchability, heterogeneous device assembly and straightforward integration with photonic circuits. Nevertheless, major questions remain. Single photon emitters (SPEs) in hBN are associated with atom like defects that confine electronic levels deep within the wide band gap. As recently reported, hBN can host several different families of emitters with emission energy that spans over a large spectral band [3] On the other hand, quantum emission in TMDs is attributed to individual excitons bound to defects or impurities of the crystal structure. Recently, it has been shown that strain pockets can create potential traps able to confine single excitons producing SPEs with high spatial control [4,5] Nevertheless, the relation between strain and emission energy is still not fully clear. The lack of a clear understanding of the nature of these defects [6] brings along the challenge of controlling the emission energy and of the deterministic creation of such emitters. These crucial aspects present central problems for developing identical single photon sources and for integration with photonic platforms. We developed a material processing based on ion irradiation and high temperature annealing of exfoliated hBN that sharply improves the single photon purity with g(2)(0) 0.08, and brightness with emission rate exceeding 10^7 counts/sec at room temperature. We also showed that the emitters persist material transfer process allowing to integrate them onto different platforms. To investigate the wide span of the emission energy we applied external compressive and tensile strain. Emitters in hBN show different tuning coefficients up to 6 meV per strain unit [7] Furthermore, we performed photoluminescence excitation experiments at cryogenic temperature on different families of emitters. Our experimental results allow to identify the excited states of these atom like systems and shine light on the characteristic level structures of the different families of emitters in hBN and can potentially help to reduce the spectral wandering with more efficient resonant excitation. Recently, new methods to develop quantum emitters in monolayer TMDs have been reported [4,5] They rely on the strain induced by nanostructures in the substrate. This technique allows to create emitters with high spatial resolution. Unfortunately, it is still not possible to engineer the single photon energy with strain since the relation between strain and the emission energy of the localized excitons in TMDs is still not fully understood. To answer this question, we transferred CVD grown WSe2 on a pre patterned Si3N4 substrate with pillars of 200 nm in diameter. We combined hyperspectral measurements, which allow to locate a single energy emission peak with a spatial resolution of around 10 nm, with strain measurements. Strain is measured optically by resolving in polarization the intensity of the second harmonic signal. This method allows to measure the photoelastic tensor of TMD monolayers and to retrieve the magnitude of biaxial strain with a spatial resolution of 200 nm [8] The combination of these techniques opens a new way to investigate the correspondence between the strain magnitude created by a nanopatterned substrate and the emission energy of the single photon emitted due to exciton localization in the nanostructures. [1] Perebeinos, V. Nat. Nano. 10, 485 (2015) [2] Tran, T. T. et al. Nat. Nano. 11, 37 (2016) [3] Tran, T. T. et al. ACS Nano 10, 7331 (2016) [4] Branny, A. et al. Nature Comm. 8, 15053 (2017) [5] Palacios Berraquero, C. et al. Nature Comm. 8, 15093 (2017) [6] Tawfik, S.A. et al. Nanoscale 9, 13575 (2017) [7] Grosso, G. Moon, H, et al. Nature Comm. 8, 705 (2017) [8] L. Mennel, et al. Nature Comm. 9, 516 (2018)
author_names: Gabriele Grosso

Hyowon Moon

D Englund
title: Spectroscopy of single photon emitters based on 2D materials (Conference Presentation)
venue: 2D Photonic Materials and Devices II
year: 2019

abstract: Deterministic Single Photon Sources in 2 D Semiconductors Two dimensional semiconductors present a new potential solid state host for single photon sources. A notable characteristic of these systems compared with traditional single photon sources, such as InGaAs quantum dots or color centers in diamond, is the ability to trap single excitons at a surface. This asset could unlock the potential for developing highly effi cient photon extraction mechanisms and for coupling confi ned excitons to photonic structures and other quantum systems. Since 2015, single photon emitt ing sites of unknow n origin have been reported to appear at random locations in monolayer fl akes of WSe2, WS2 and MoSe2. This year, we were able to deterministically engineer such sources at precise locations with a 96 percent yield, in unlimited numbers, in a scalable manner and with bett er optical properties than their randomly occurring counterparts.3 We accomplished this deterministic source by deforming the material locally at the nanoscale, using patt erned substrates. We fi rst exfoliated monolayer fl akes of WSe2 and WS2 from bulk crystals. Then, we transferred the fl akes onto silica substrates patt erned with square arrays of nanopillars, spaced 4 mm apart and ranging from 100 to 200 nm in height and with a 90 nm apex diameter. Atomicforce microscopy scans show that the fl akes tent over each nanopillar and att ach by Van der Waals forces to the fl at areas of the substrate in between. Low temperature photoluminescence (PL) measurements showed a brightening of PL and narrow spectral lines from the pillar locations. Photon correlation measurements on these narrow lines confi rmed the single photon nature of the emission, and high resolution spectral measurements revealed a fi ne structure in the majority of dots. The parameters measured are very similar to those measured for the randomly appearing single photon emitt ing sites in the same materials, which suggests a common origin. Characterization of the quantum emission with increasing pillar height also yielded interesting results: the number of narrow lines per site decreases and the spectral wandering improves by an order of magnitude compared with the random emission sites. We believe that this work paves the way for a true singlephoton emitt er that can be easily scaled up and integrated with other photonic components. In addition, as a new platform for deterministic quantum light matt er interaction between single excitons and photons, it allows researchers to explore the potential for optical single spin control toward quantum information applications. OPN
author_names: Duhee Yoon

Anna K Ott

Andrea C Ferrari
title: Deterministic Single Photon Sources in 2 D Semiconductors
year: 2017

abstract: We observe stable and narrowband single photon emission from localized quantum emitters in a WSe 2 monolayer. Photoluminescence excitation spectroscopy reveals that the emission originates from single excitons trapped in a local potential well.
author_names: Philipp Tonndorf

Robert Schmidt

Johannes Kern

Michele Buscema

Gary A Steele

Andres Castellanos-Gomez

Herre S J van der Zant

S Michaelis de Vasconcellos

Rudolf Bratschitsch
title: Single photon emission from localized excitons in monolayer WSe 2
venue: CLEO 2015
year: 2015

abstract: We observe stable and narrowband single photon emission from localized quantum emitters in a WSe2 monolayer. Photoluminescence excitation spectroscopy reveals that the emission originates from single excitons trapped in a local potential well.
author_names: Philipp Tonndorf

Robert Schmidt

Johannes Kern

Michele Buscema

Gary A Steele

Andres Castellanos-Gomez

Herre S J van der Zant

Steffen Michaelis de Vasconcellos

Rudolf Bratschitsch
title: Single photon emission from localized excitons in monolayer WSe2
venue: 2015 Conference on Lasers and Electro Optics (CLEO)
year: 2015

abstract: We report on the principle and realization of a new trap for excitons the diamond electrostatic trap which uses a single electrode to create a confining potential for excitons. We also create elevated diamond traps which permit evaporative cooling of the exciton gas. We observe the collection of excitons towards the trap center with increasing exciton density. This effect is due to screening of disorder in the trap by the excitons. As a result, the diamond trap behaves as a smooth parabolic potential which realizes a cold and dense exciton gas at the trap center.
author_names: Alexander A High

A K Thomas

Gabriele Grosso

Mikas Remeika

Aaron Tynes Hammack

Andrew Meyertholen

Michael M Fogler

L V Butov

Micah P Hanson

Arthur C Gossard
title: Trapping indirect excitons in a GaAs quantum well structure with a diamond shaped electrostatic trap.
venue: Physical review letters
year: 2009

abstract: Voltage tunable quantum traps confining individual spatially indirect and long living excitons are realized by providing a coupled double quantum well with nanoscale gates. This enables us to study the transition from confined multiexcitons down to a single, electrostatically trapped indirect exciton. In the few exciton regime, we observe discrete emission lines identified as resulting from a single dipolar exciton, a biexciton, and a triexciton, respectively. Their energetic splitting is well described by Wigner like molecular structures reflecting the interplay of dipolar interexcitonic repulsion and spatial quantization.
author_names: G J Schinner

Jens Repp

Enrico Schubert

Ashish K Rai

Dirk Reuter

Andreas Dirk Wieck

Alexander O Govorov

Alexander W Holleitner

Jorg P Kotthaus
title: Confinement and interaction of single indirect excitons in a voltage controlled trap formed inside double InGaAs quantum Wells.
venue: Physical review letters
year: 2013

abstract: Measuring fluorescence photon statistics of single chains of a conjugated polymer we determine the lifetime of the metastable dark state, the triplet exciton. The single molecule emits single photons one at a time, giving rise to photon antibunching. These photons appear bunched in time over longer timescales because of excursions to the triplet dark state. Remarkably, this triplet intermittency in the fluorescence is spontaneously suppressed over timescales of seconds, implying that either triplet formation is inhibited; or that triplets are selectively quenched without the singlet fluorescence being affected. Such discrete switching in the strength of photon bunching is only seen in highly ordered and rigid chains of a ladder type conjugated polymer. It does not occur in single dye molecules. We propose that trapped photogenerated charges on the chain selectively quench triplets but not singlets, presumably because the effective diffusion length of triplets is longer along the highly rigid ladder type backbone.
author_names: Jakob Schedlbauer

Ullrich Scherf

Jan Vogelsang

John M Lupton
title: Dynamic Quenching of Triplet Excitons in Single Conjugated Polymer Chains.
venue: The journal of physical chemistry letters
year: 2020

abstract: The temperature of Bose Einstein condensation and the fraction of particles in a condensate for a system of spatially indirect dipole excitons in an electrostatic ring trap have been found. If only levels of the radial motion close to the bottom of the potential well of the trap are populated considerably, the oscillatory model of the single particle spectrum is applicable. In this case, even the strong exciton exciton interaction can be taken into account.
author_names: Alexander V Chaplik
title: Bose Einstei condensation of dipolar excitons in a ring trap
year: 2016

abstract: We report on the principle and realization of a new trap for excitons the diamond electrostatic trap which uses a single electrode to create a confining potential for excitons. We also create elevated diamond traps which permit evaporative cooling of the exciton gas. We observe collection of excitons towards the trap center with increasing exciton density. This effect is due to screening of disorder in the trap by the excitons. As a result, the diamond trap behaves as a smooth parabolic potential which realizes a cold and dense exciton gas at the trap center.
author_names: Alexander A High

A K Thomas

Gabriele Grosso

Mikas Remeika

Aaron Tynes Hammack

Andrew Meyertholen

Michael M Fogler

L V Butov

Micah P Hanson

Arthur C Gossard
title: Collection of indirect excitons in a diamond shaped electrostatic trap
year: 2009