Advanced Theoretical methods for emerging 2D materials in Quantum Information Technology Studies



Scientific activities of the various Research Units


WP1: Identify and characterize the defects/impurities/strain (two-level systems) in 2DM for possible use as spin (Task1.1-1.2) and PQ (Task1.3-1.5), Units: (MI, RM2, LNF-CS, LNF)

Task1.1 Explore electronic structure of ADI (vacancies, substitutional magnetic and non-magnetic atoms) in hBN and 2D-TMD using DFT with local and non-local hybrid functionals to identify new systems with in-gap double-level spin-states (Units: MI, LNF-CS, )

Task1.2 In the most promising structures calculate optical transitions and spin nonconserving transitions driven by intersystem crossing, useful for spin initialization and redout (Units: MI, RM2)

Task1.3 Characterize ADI able to create isolated states for PQ and SPE by using Density Functional Theory (DFT). Specific systems of interest are h-BN; MSe2 (M=W,Mo) and newly discovered wide-band gap nitride and oxide 2D materials (Units: MI, LNF)

Task1.4 For the most promising structures carry out a characterization of excitonic properties employing the GW+ BSE and TDDFT approaches (Units involved: RM2, LNF-CS, LNF)

Task1.5 Assess the efficiency in the SPE in real, operational conditions taking into account finite temperature effects, such as the electron-phonon coupling by performing on-the-fly finite-T MD or frozen phonons simulations. Estimate radiative/non radiative exciton lifetimes and QY efficiency and its relation with plasmonic DOF. (Units involved MI, RM2,LNF-CS)

 WP2: Investigate how the excitonic properties of misaligned 2D heterostructures can be tailored by tuning the twisting angle between layers. We aim to identify highly-bound long-living dark excitons in the trapping potential generated by Moiré patterns, that can be exploited to store QI. Exploiting our expertise in dealing with DFT-based and MB perturbation theory approaches we intend to go beyond the state of the art for the description of excitons in twisted 2D-materials which is currently performed with model Hamiltonians with ab initio derived parameters. (Units involved: (MI, RM2, LNF-CS, LNF)

Task 2.1 Characterization, through a completely ab initio approach at DFT level, of structural and electronic properties of heterostructures of twisted 2D layers (2D-BN bilayers,2D-TMD, Ge/Sn heterostructures, ….) varying the twisting angle. Systems with many thousands of atoms (Moiré periodicity ~ tens of nm) will be described in a completely ab initio framework accounting for the full structural relaxation on the electronic properties. (Units: MI, RM2)

Task 2.2 Explore the dependence of the 2D electrostatic confining potential for excitons and of the interlayer coupling on twisting angle in a fully ab initio framework. (Units : MI, LNF-CS,LNF)

Task 2.3 Calculate of the excitonic spectrum with the inclusion of Many-Body effects  (DFT+GW+BSE level) for 2D twisted bilayers with small Moiré periodicity (up to few hundred  atoms) (Units involved : RM2, MI, LNF-CS)

Task 2.4 Exploit a variational scheme with model excitonic Hamiltonian from ab initio results for 2D heterostructure with small twisting angles (several hundreds atoms) (Units: RM2, MI)

WP3: Explore the stability of exotic phases of 2D quantum matter such as equilibrium and Floquet topological excitonic-insulator (EI) [11]. These excitonic superfluids  can provide new concepts for QI technologies, with quantum bits formed either by states with one (state 0) and two (state 1) more excitons (similarly to a qubit in exciton-polaritons condensate) or couples (states 0 and 1) of Floquet topological states at the edge of the sample. Units: (RM2, LNF)

Task 3.1: Identify the equilibrium EI phase by the solution of BSE. Characterize the topological phase by evaluating the Chern number resulting from DFT and GW band structures. We aim at understanding to what extent the topological phase is protected against MB correlations.

Task 3.2: Carry out real-time Green’s function simulations of TMD’s like WSe2 pumped resonantly at the exciton energy using the Yambo code within the Hartree+Screened Exchange (HSEX) approximation. We also plan to perform first-time simulations with a time-dependent RPA screening. We here aim at shedding light on the phase transition (or phase coexistence) from excitonic superfluid to free-carrier plasma as the density of conduction electrons increases.

Task 3.3: Perform real-time Green’s function simulations of systems with dark s-wave exciton and bright p-wave excitons (e.g., biased graphene bilayers) driven by laser pulses. We have recently shown that this class of systems may exhibit  a nonequilibrium (NEQ) EI phase with nontrivial topological character. We will demonstrate the possibility of steering the system toward this phase by suitable laser pulse protocols. We will also characterize the Floquet Majorana states forming at material’s edges and assess their possible use as qubits (see WP5)

Task 3.4. Calculate the NEQ spectral function (SF) resolved in the Bloch quasimomentum and band index. NEQ-SF probes removal energies and its shape depends on the nature of the EI phase. Furthermore, NEQ-SF can be directly compared with available time-resolved and angle-resolved photoemission spectra to assess calculations accuracy. We will study results stability against phonon relaxation/intervalley scattering. This is essential for real device applications, as energy transfer to the lattice is an important source of decoherence (see task 4.2).

 WP4: Identify and characterize QD made with the above-mentioned materials, using tools [12,13] borrowed from quantum metrology and QI theory, which will lead eventually to specific, suitably optimized protocols for QI processing, with applications in metrology, sensing, quantum communication, and, possibly, quantum thermodynamics Units (MI, LNF-CS)

Task 4.1. Time as a resource: a quantum metrology protocol typically consists of three stages: probe preparation, sensing and then readout, where the time required for the first and last stages is usually neglected. We will investigate the use and potential time advantage of spin and photonics qubits in 2D materials as universal sensors.

Task 4.2. Decoherence as a resource: coherence of solid state qubits is usually very fragile and this is often considered an undesired effect for implementation of quantum technologies. On the other hand, fragility implies high sensitivity, a crucial feature to build precise quantum sensors. Of course, decoherence should be too fast, since readout takes time. For this reason, we will exploit sensitivity to decoherence of relatively long living 2D systems, e.g. SQ in graphene.

Task 4.3. We will further explore the possibility to use the QD to perform specific finite time (and finite power) thermodynamic transformations, characterizing their performances in terms of efficiency and entropy production. 


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Next meeting

April, 20-21 2022

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