Coupled multipolar interactions in clusters of nanoparticles with metal shells

Coupled multipolar interactions between spherical nanoparticles coated with metal nanoshells are shown to yield very different optical behaviour to those between all metal nanoparticles in the same configurations. Controlled spectral tuning of absorption bands in metal shell nano-systems is shown to be easier than with all metal particles because strong localised fields between particles and the associated high order multipoles are much weaker. In the touching limit differences in field distributions mean that whereas all metal clusters are far from convergent when 300 pole-terms are included in the calculation, the metal nanoshells give full convergence after less than 10 poles, even for metal volume fractions over 50%. Extinction bands are also far less sensitive to particle spacing in the shell case. © 2002 Elsevier Science B.V. All rights reserved

Room-temperature cavity quantum electrodynamics with strongly coupled Dicke states

Quantum Engineering: ambient solid-state quantum optics Creating practical solid-state, quantum computers that operate at room-temperature is a challenging task. This is because stored information is readily destroyed by thermal noise. A signature of a physical system’s ability to function as a quantum computer is the observation of quantum Rabi oscillations since they represent the possibility of “reading” and “writing” quantum information. Thus far, these have been observed reliably and consistently only at milli-Kelvin temperatures. Jonathan Breeze at Imperial College London and collaborators have used an organic molecular crystal, a dielectric resonator and pulses of laser light to produce pronounced quantum Rabi oscillations at microwave frequencies, lasting up to 10 microseconds at room-temperature. This discovery paves the way for room-temperature quantum information processing devices such as spin memories and quantum-enhanced technologies for metrology, sensing, communications and ultimately – quantum computing

Room-temperature cavity quantum electrodynamics with strongly-coupled Dicke states

The strong coupling regime is essential for efficient transfer of excitations between states in different quantum systems on timescales shorter than their lifetimes. The coupling of single spins to microwave photons is very weak but can be enhanced by increasing the local density of states by reducing the magnetic mode volume of the cavity. In practice, it is difficult to achieve both small cavity mode volume and low cavity decay rate, so superconducting metals are often employed at cryogenic temperatures. For an ensembles of N spins, the spin–photon coupling can be enhanced by N−−√N through collective spin excitations known as Dicke states. For sufficiently large N the collective spin–photon coupling can exceed both the spin decoherence and cavity decay rates, making the strong-coupling regime accessible. Here we demonstrate strong coupling and cavity quantum electrodynamics in a solid-state system at room-temperature. We generate an inverted spin-ensemble with N ~ 1015 by photo-exciting pentacene molecules into spin-triplet states with spin dephasing time T∗2~3T2*~3 μs. When coupled to a 1.45 GHz TE01δ mode supported by a high Purcell factor strontium titanate dielectric cavity (Vm~0.25Vm~0.25 cm3, Q ~ 8,500), we observe Rabi oscillations in the microwave emission from collective Dicke states and a 1.8 MHz normal-mode splitting of the resultant collective spin–photon polariton. We also observe a cavity protection effect at the onset of the strong-coupling regime which decreases the polariton decay rate as the collective coupling increases