Quantum Nanophotonics

Light-matter strong coupling in nanoplasmonics

Angela Demetriadou, Rohit Chikkaraddy

Light has the ability to drive the free electrons in metals, such that the electrons are concentrated at metal-dielectric interfaces. This accumulation of electrons induces strong field enhancements, referred to as plasmons. For metallic nano-structures, light collectively oscillates the electrons in the nano-structure, creating localized plasmons. By specifically designing the shape and arrangement of metallic nano-structures, one has the ability to manipulate plasmons and even concentrate light at small enough volumes that enclose just one molecule.

Photo-excited molecules absorb a photon to excite an electron to a higher energy state, and emit a photon when the electron relaxes to the molecule’s ground state When such photo-excited molecules are placed in plasmonic devices, then the plasmon causes the electron excitations in molecules, but also emissions from the molecule excite the plasmons. Hence, light (plasmon) and matter (molecule) blend together, forming a hybrid system with unique properties. This behaviour allows us to access and manipulate the quantum state of molecules and has the potential to bring and develop quantum technologies at room temperatures. Our focus in this theme is on providing a theoretical framework, numerical modelling and experimental validation of these strongly-coupled systems, aiming to understand and utilize their properties for future applications.

The theoretical and numerical strands of this theme is facilitated by our workstations and University of Birmingham supercomputer BlueBEAR running electromagnetic software, while the experimental strand is primarily supported by a confocal Raman microscope (Renishaw), a Mai Tai ultrafast Ti:Sapphire laser with Inspire OPO fs laser (Spectra-Physics) and a closed-cycle cryostat integrated into optical table (attocube).

Nano-antennas/cavities for sensing and nonlinear optics

Rohit Chikkaraddy, Angela Demetriadou, Miguel Navarro-Cía, Andre Kaplan

Antennas are widely used at radio and microwave frequencies to couple/radiate energy from a source to free space efficiently. Due to reciprocity, they also collect radiation efficiently. These functionalities are performed via the manipulation of enhanced fields in subdiffraction volumes. With the advent of nanotechnology, antennas operating at optics, nanoantennas, have become accessible. This opens the possibility to bring the microwave engineering toolbox to enhance processes and applications mediated by light-matter interaction like electromagnetic sensing and nonlinear optics.

The group focuses on the use of nanoantennas to boost the upconversion of challenging to detect low-energy (FIR, MIR and NIR) photons to high-energy visible photons to push detection limits down to single-photon and single-molecule regimes. It also researches on utilising nanoantennas to enhance the local probing field of spectroscopy techniques, something that can be seen as surface-enhanced spectroscopy 2.0 (with 1.0 being standard surface-enhanced techniques based on unstructured metal plates).

The design and numerical strand of this theme is underpinned by the group's expertise in microwave engineering and is facilitated by our workstations and University of Birmingham supercomputer BlueBEAR running electromagnetic software. The experimental strand is primarily supported by a confocal Raman microscope (Renishaw), a Mai Tai ultrafast Ti:Sapphire laser with Inspire OPO fs laser (Spectra-Physics), a fourier transform infrared spectrometer (Bruker), and bespoke ultrafast spectroscopy setups, including a pump-probe time-resolved Z-scan, run with a commercial laser system (Coherent Ltd).