The research will focus on the application of ab initio calculation, using the Quantum Espresso (QE) package at DFT level, to simulate properties of interest for quantum materials, specifically for quantum computing purposes. We will thus consider materials like transition metals dichalcogenides (TMDs) investigating in depth the peculiar properties of defects in these systems. The overall goal is comparing different types of materials against each other to find the most suitable one for a future material that can be used as a quantum processing unit (QPU). TMDs have attracted the researchers attention for over a decade. They exhibit a plethora of different properties and have potential use in various fields including electronic, optoelectronic, sensing and energy storage. Moreover is an ideal 2D host for quantum defects. These defects can be engineered on demand at atomic size level precision, which holds a promise for a scalable and addressable quantum unit. However no coherent control of single spins have been reported. The inherit SOC and excitonic effects provides long coherence time and electric controlled spin-valley coupling. Recent investigation realized the creation of a carbon defect in tungsten diselenide through STM tip with atomic precision, in which carbon replaces sulfur, that could isolate a single defect with a doublet spin state [1]. We will thus analyze electronic, structural and spin properties of these materials in order to gain insight into their potential as qubits. Thus determining whether a material can be used as a QPU or not based on the fact that to have a successful initialization and read-out of the system we need to have at least a three level system. This three level system is composed of a lower energy state in which the initialization occurs and a higher energy state in which we can read-out the state. More specifically, we shall focus on defected materials, since they provide a localized structure of electronic levels that may be the basis for building a qubit. In particular, in the literature [2] there are proposals on the energy ladder arrangements and electronic properties that these levels should have to be used as qubit. In this project, we shall screen by DFT several defects to identify the most promising ones for further refinements via more accurate approaches (DFT+U or GW) in a subsequent project. This project will provide helpful insight in the electronic properties that govern these systems and we convey a new perspective in selecting the best materials for application like quantum computing and sensing. We expect to see a clear difference between the properties of each material. Moreover each type of defect can have a huge impact in the electronic structure of TMDs, specifically from the starting material molybdenum disulfide. We we will indeed sample a combination of different defects. First we will replace one S atom with Se and Te (2 structures). Then we will substitute Mo with W and Re (2 structures) and we will consider also the combination with the S replacements (4 structures). Moreover the S will be replaced by C, N, P (3 structures). Finally we will add a vacancy within the structures of Mo, W and Re (3 structures), leading to 14 structures to analyze, which could possibly galvanize the attention of experimentalists to synthesize such compounds and verify the applicability of our conclusions. [1] Li, Song, et al. Nat. comm., 2022, 13: 1. [2] Kielpinski, D. Front. Phys. China, 2008, 3: 365.
La ricerca verterà sull'applicazione di metodi ab initio, utilizzando la suite Quantum Espresso a livello DFT , per simulare proprietà di interesse per i materiali quantistici, nello specifico per applicazioni nell'ambito dei computer quantistici. Considereremo quindi materiali quali i dicalcogenuri di metalli di transizione (TMD), analizzando le peculiari proprietà di sistemi difettati. In questo lavoro compareremo tipi diversi di difetti per trovare un futuro materiale che potrà essere utilizzato come Quantum Processing Unit (QPU). I TMD hanno attratto l'attenzione dei ricercatori per oltre un decennio. Esibiscono infatti una pletora di proprietà differenti e hanno le potenzialità per essere utilizzati in vari campi quali l'elettronica, optoelettronica, sensing etc. Inoltre sono host ideali per dei difetti localizzati. Questi in particolare possono essere ingegnerizzati a livelli di precisione atomica, e quindi posseggono buone probabilità di scaling e di controllo. Purtroppo non sono ancora stati riportati casi di controllo di singolo spin. Lo SOC intrinseco e gli effetti eccitonici di questi materiali permettono tempi di coerenza lunghi ed un controllo elettronico di accoppiamento spin-valley. Recenti studi hanno portato alla generazione di difetti al carbonio in disolfuro di tungsteno grazie ad una punta STM nel quale il carbonio rimpiazza un solfuro nella struttura che isola un singolo difetto con uno stato di doppietto [1]. Analizzeremo quindi proprietà elettroniche, strutturali e di spin di questi materiali per avere degli indizzi sulla potenzialità di utilizzo come quibit. Questo basato sull' assuzione che per avere una buona inizializzazzione ed un read-out del sistema ci debba essere un sistema a tre livelli isolato. Questo sistema a tre livelli è composto da uno a energia minore su cui avviene l'inizializzazione ed uno ad energia maggiore su cui avviene il read-out dello stato. Più nello specifico ci concentremo su materiali con difetti, dato che generano naturalmente nel sistema una struttura di livelli localizzati possibilmente utilizzabili come qubit. In particolare, in letteratura[2] ci sono proposte sull’arrangiamento dei livelli energetici, e le proprietà elettroniche che questi livelli dovrebbero avere, per essere utilizzati come qubit. In questo progetto indagheremo e confronteremo vari difetti e selezioneremo quelli più promettenti per sottoporli ad analisi con approcci più accurati (DFT+U o GW) in futuro. Questo progetto quindi provvederà a dare una nuova prospettiva alle proprietà che governano questi sistemi e suggeriremo un nuovo punto di vista per selezionare materiali per applicazioni quali quantum computing, sensing, etc. Ci aspettiamo una demarcata differenza tra le proprietà di questi materiali. Inoltre ogni difetto avrà un grande impatto sulla strttura elettronica del materiale di partenza, il Disolfuro di Molibdeno. Analizzeremo quindi una combinazione di differenti difetti. In prima istanza rimpiazzeremo uno Zolfo con Selenio e Tellurio. Poi il Molibdeno sarà sostituito con Tungsteno e Renio, considereremo inoltre la combinazione delle sostituizioni di Zolfo con quelle del Molibdeno. Successivamente sostituiremo lo Zolfo con Carbonio, Azoto e Fosforo. Infine introdurremo una vacanza nelle struttre di Molibdeno, Tungsteno e Renio, portandoci quindi ad uno studio ad ampio spettro che possa attrarre l’attenzione di ricercatori sperimentali per sintetizzare tali composti e verificare l’applicabilità delle nostre conclusioni. [1] Li, Song, et al. Nat. comm., 2022, 13: 1. [2] Kielpinski, D. Front. Phys. China, 2008, 3: 365.
Analisi computazionale di difetti in dicalcogenuri di metalli di transizione per i computer quantistici
BELLO, ALESSANDRO
2022/2023
Abstract
The research will focus on the application of ab initio calculation, using the Quantum Espresso (QE) package at DFT level, to simulate properties of interest for quantum materials, specifically for quantum computing purposes. We will thus consider materials like transition metals dichalcogenides (TMDs) investigating in depth the peculiar properties of defects in these systems. The overall goal is comparing different types of materials against each other to find the most suitable one for a future material that can be used as a quantum processing unit (QPU). TMDs have attracted the researchers attention for over a decade. They exhibit a plethora of different properties and have potential use in various fields including electronic, optoelectronic, sensing and energy storage. Moreover is an ideal 2D host for quantum defects. These defects can be engineered on demand at atomic size level precision, which holds a promise for a scalable and addressable quantum unit. However no coherent control of single spins have been reported. The inherit SOC and excitonic effects provides long coherence time and electric controlled spin-valley coupling. Recent investigation realized the creation of a carbon defect in tungsten diselenide through STM tip with atomic precision, in which carbon replaces sulfur, that could isolate a single defect with a doublet spin state [1]. We will thus analyze electronic, structural and spin properties of these materials in order to gain insight into their potential as qubits. Thus determining whether a material can be used as a QPU or not based on the fact that to have a successful initialization and read-out of the system we need to have at least a three level system. This three level system is composed of a lower energy state in which the initialization occurs and a higher energy state in which we can read-out the state. More specifically, we shall focus on defected materials, since they provide a localized structure of electronic levels that may be the basis for building a qubit. In particular, in the literature [2] there are proposals on the energy ladder arrangements and electronic properties that these levels should have to be used as qubit. In this project, we shall screen by DFT several defects to identify the most promising ones for further refinements via more accurate approaches (DFT+U or GW) in a subsequent project. This project will provide helpful insight in the electronic properties that govern these systems and we convey a new perspective in selecting the best materials for application like quantum computing and sensing. We expect to see a clear difference between the properties of each material. Moreover each type of defect can have a huge impact in the electronic structure of TMDs, specifically from the starting material molybdenum disulfide. We we will indeed sample a combination of different defects. First we will replace one S atom with Se and Te (2 structures). Then we will substitute Mo with W and Re (2 structures) and we will consider also the combination with the S replacements (4 structures). Moreover the S will be replaced by C, N, P (3 structures). Finally we will add a vacancy within the structures of Mo, W and Re (3 structures), leading to 14 structures to analyze, which could possibly galvanize the attention of experimentalists to synthesize such compounds and verify the applicability of our conclusions. [1] Li, Song, et al. Nat. comm., 2022, 13: 1. [2] Kielpinski, D. Front. Phys. China, 2008, 3: 365.File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.12608/47461