Optical control of TMDCs valley pseudospin qubits

Linked project

• This project is conducted by the same people as 👉 Control over the atomic spins within certain molecules by NMR technique

Group members

• XU ZIZHOU
  • Matric Number: A0229645W
  • Email: zizhou_xu@u.nus.edu
• CHU WENHAO

Description

• The strategies and materials for building universal quantum computers are being actively researched, and various platforms for holding qubits have been proposed and tested. Within all the options such as superconducting qubits and ion trap qubits, solid-state qubits have illustrated great benefits of the compatibility with the existing semiconductor technology, which attracts lots of attention to this platform. Moreover, because of the direct band gap and strong spin-orbit coupling discovered in the monolayer transition metal dichalcogenides (TMDCs), especially some semiconductor monolayers possess a sizeable direct bandgap of ≈1.5–2 eV in the optical range allowing electrostatic confinement and optical manipulation of carriers, chances are TMDCs materials have the potential to become the promising platform for fabricating qubits. There are four main types of TMDCs that have been suggested as advantageous in acting qubits, ${\text{WS}}_2$ , ${\text{WSe}}_2$ , ${\text{MoS}}_2$ and ${\text{MoSe}}_2$ . Kormányos et al used DFT calculations to confirm that ${\text{WS}}_2$ and ${\text{WSe}}_2$ , are better than ${\text{MoS}}_2$ and ${\text{MoSe}}_2$ in terms of the spin-valley coupling, which is really important since spin-valley coupling is regarded as a key factor that can improve the coherence lifetime of spin-valley states.

• After people took a deeper look at the properties of TMDCs, some interesting features have been found. Such as the extra degree of freedom offered by valley magnetic moment, which can realise bit 0 and bit 1 to form a qubit in momentum space. In addition, these valleys are independently addressable by an optical signal, and optical controlling technique is currently under research by many groups both theoretically and experimentally. As a result, as inspired by the idea from one of the theoretical work, we intend to build a quantum simulator and investigate optical control of the spin-valley qubits.

Q & A

What are K & K' points?

K & K' points

• K-points are sampling points of Brillouin zone in reciprocal lattice
• The monolayer TMDs have a unique band structure with the conduction and valence band edges both at the degenerate K and K‘ valleys at the corners of the hexagonal Brillouin zone. The direct-gap optical transitions have a selection rule: left- (right-) handed circular polarized photons couple to the interband transitions in the K (K’) valley only

Choose monolayer TMDCs materials or 2D heterostructure?

• There are four main carrier properties that optimal Opto-valleytronics should possess.
  1. long carrier lifetime
  2. long valley lifetime
  3. high valley polarization
  4. long valley coherence time
• By adopting 2D heterostructure TMDCs materials, we can create these conditions for building promising quantum platform. (eg. Due to the type II band alignment and weak hybridization of van der Waals heterostructure, the electron–hole layer separation, the electron–hole exchange interaction is greatly reduced, resulting in a long cryogenic lifetime (ns to $\mu$s)and valley lifetime (~ 10 ns) of the interlayer exciton)

Method

Experimental setup

Quantum simulator

• We intend to use WSe2 2D heterostructure encapsulated in hexagonal boron nitride (h-BN) as the physical platform, and ...