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H/F PhD candidate at LPENS for Quantum Nanophotonics

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Français - Anglais

Date Limite Candidature : lundi 9 août 2021

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General information

Reference : UMR8023-CHRVOI-001
Workplace : PARIS 05
Date of publication : Monday, July 19, 2021
Scientific Responsible name : Christophe Voisin
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2021
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

Carbon nanotubes as a plateform for quantum photonics : tuning the optical properties using artificial color centers and hBN encapsulation.

In recent years the assets of carbon nanotubes as a new plateform for quantum photonics (quantum communications and quantum information processing) has driven a lot of efforts, including in our group [Jea16,Jea17,He18]. In fact, carbon nanotubes turn out to be one of the very few quantum emitters working in the telecom C bands (near infrared, 1.5µm) required for long range telecommunications. In addition, their structure makes them easily integrable in photonic devices.
A successful approach has been developed using the chemical grafting of color (defect) centers to tune their optical properties and the use of hBN encapsulation to make their features of single quantum emitters more robust. Room temperature single photon emission has been demonstrated showing the effectiveness of the approach against thermal detrapping of the excitons. [He17]

However, relatively scarce information is available about the photophysics of these grafted nanotubes. In particular, the depth of the potential well induced by various organic defects, together with the electronic structure of the confined states (dark vs bright, coupling to phonons…) are key questions that remain to be addressed. In addition, the possibility to couple several of these defects along the same one-dimensional nanotube is especially attractive for quantum logics implementation.

We developed recently a versatile cryogenic micro-photoluminescence setup that is particularly suited to address those questions, at the level of an individual nanotube. In particular we adapted the techniques of super-resolution (such as in biology) to this cryogenic environment in order to obtain a direct spatial mapping of the defects with below 30nm resolution [Ray19]. Quasi resonant excitation spectroscopy complements this approach by providing thorough information about excited confined states. Various color centers are available through our collaborations with chemists in Germany and in the USA.

The first goal of this PhD proposal is to gain a full understanding of the photophysics of these new color centers in carbon nanotubes using these advanced spectroscopic tools. Possible developments include the investigation of the spin state of the ground state of the defects that show similarities with those of the well-known NV centers in diamond, opening a vast playground for fundamental physics (building a spin/photon interface for quantum computing) and applications (nano-magnetometry).

At the same time, we will investigate the coupling of grafted CNTs (possibly coated by a hBN layer) with on-chip quantum photonic circuits. Building on recent advances in semi-conducting quantum dots photonics, we will fabricate our spatially and spectrally tuned resonant structures by using in-situ lithography of polystyrene. This material is indeed the best matrix to nest the nanotubes and obtain their best intrinsic properties (including almost indistinguishable single photons). Nanotubes will be first optically characterized and localized in a flat polystyrene layer using a red excitation laser. In a second step an upper photoresist layer will be exposed by a green laser on the same setup. In the last step the PS is etched to form the desired structure.

The first structure that will be investigated consists in a single grafted CNT coupled to a waveguide, where the two light propagation directions play the role of a beam splitter. Handbury Brown and Twiss experiments (photon antibunching measurements) will be done by directly measuring the cross correlation between the two ouputs of the waveguide.
Next, two emission sites will be coupled through the same optical waveguide. Additional Stark-shift electrodes placed under the PS layer will be used to finely tuned the emission energy, allowing to obtained the spectral matching between the two emitting sites. The coupling between these two sites will be investigated. If the two grafted defects are attached to the same nanotube, we expect an enhanced interaction by the mediation of the nanotube itself, either by the coupling with 1D acoustic phonons, or by the enhanced long range electronic interaction due to the 1D geometry of CNTs.

[Jea16] A. Jeantet et al, PRL 116 247402 (2016)
[Jea17] A. Jeantet et al, Nano Lett. 17 4184 (2017)
[He18] X. He et al, Nat. Mat. 17 663 (2018)
[He17] X. He et al, Nat. Phot. 11 577 (2017).
[Ray19] C. Raynaud et al, Nano Lett 19, 7210 (2019)

Work Context

The work will be carried out in the 01 (Nano-optics) team of LPENS in interaction with all of its permanent or contractual members as well as with the technical and administrative staff of the laboratory.

Constraints and risks

Risks associated with the use of lasers, cryogenic fluids and electrical equipment.

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