# Welcome to the Quantum Photonics Laboratory!

We are an experimental group at RMIT University’s School of Engineering. Our research spans from engineering photonic quantum information and communication technologies to studying quantum effects in biological, chemical and physical systems.

# RECENT NEWS

## Ab-initio prediction of bright NV+ photoluminescence

Our recently published novel method to predict solid-state photoluminescence has discovered a possible bright transition in the positively charged nitrogen vacancy in diamond (NV+).

NV+ has historically been considered a dark state due to absence of experimental photoluminescence. Our work reveals that there is an optically active singlet-singlet transition approximately 16x less bright than the analogous triplet-triplet transition of the NV- charge state.

Our work in NV+ is a step towards unlocking applications such as quantum memory. We demonstrate that the lack of optical signature used for identification is not reliable and we subsequently provide predictions to guide experimental investigation. This will be useful for experimental work with NV defects in diamond as well as a motivation for further theoretical work investigating potential charge dependent quenching mechanisms.

Access the pre-print here

## A novel method to predict the solid-state ab-initio photoluminescence spectrum of defects in crystals has been created

Our method works for defects with the same symmetry in ground and excited state, which could not necessarily be treated by existing methods.

This is accomplished by using a cluster calculation with TD-DFT and applying a low frequency cutoff to recreate the solid-state.

The low frequency cutoff is shown to eliminate vibrational modes unique to the surface of the cluster, and demonstrates a connection between cluster and solid-state.

Furthermore, our cluster calculation demonstrates the first vibrationally resolved ab-initio photoluminescence spectrum of NV- centres in nanodiamonds.

Our method has been recently published in Journal of Applied Physics.

https://aip.scitation.org/doi/full/10.1063/5.0033417

## New paper on quantum topological photonics published in Science Advances

Congratulations to Rob, Jean-Luc and our collaborators!

From the press article by Physicsworld:

Topological insulators are a recently discovered phase of matter that are electrical insulators in the bulk but which can conduct electricity on their surface via special “topologically protected” surface electronic states. These states have remarkable properties, including the fact that they are robust to defects and noise in the surrounding environment. A team of researchers in Australia, Italy and Switzerland have now shown that topological states made from single photons can be used as quantum bits (qubits) to process quantum information in a reliable way. The work could help in the development of more robust quantum computers.

These results have recently been published in Science Advances.