Optical control of a single spin-valley in charged WSe$_2$ quantum dots

TL;DR

This paper demonstrates optical control of a single spin-valley state in charged WSe₂ quantum dots, advancing 2D valleytronics towards quantum information applications by manipulating individual charge states.

Contribution

It provides the first evidence of controlling the spin-valley state of localized holes in charged WSe₂ quantum dots using optical helicity and magnetic fields.

Findings

Localized holes with net spin are confirmed in WSe₂ quantum dots.

Spin-valley state control is achieved with laser helicity under magnetic field.

Valley lifetime of a single charge is estimated to be on the order of nanoseconds.

Abstract

Control and manipulation of single charges and their internal degrees of freedom, such as spins, is a fundamental goal of nanoscience with promising technological applications. Recently, atomically thin semiconductors such as WSe$_2$ have emerged as a platform for valleytronics, offering rich possibilities for optical, magnetic and electrical control of the valley index. While progress has been made in controlling valley index of ensemble of charge carriers, valley control of individual charges, crucial for valleytronics, remains unexplored. Here, we provide unambiguous evidence for localized holes with net spin in optically active WSe$_2$ quantum dots (QDs) and control their spin-valley state with the helicity of the excitation laser under small magnetic field. We estimate a lower bound on the valley lifetime of a single charge in QD from recombination time to be $\sim$ nanoseconds. Remarkably, neutral QDs do not exhibit such a control, demonstrating the role of excess charge in prolonging the valley lifetime. Our work extends the field of 2D valleytronics to the level of single spin-valley, relevant for quantum information and sensing applications