My watch list


Controlled coupling of light and matter

Heiko Groß

Artistic representation of a plasmonic nano-resonator realized by a narrow slit in a gold layer. Upon approaching the quantum dot (red) to the slit opening the coupling strength increases.

07-Mar-2018: Researchers from Würzburg and London have built the foundations for a new field of nano-optics: they have succeeded in controlling the coupling of light and matter at room temperature.

Publishing in a journal like Science Advances usually heralds a particularly exciting innovation. Now, physicists from the Julius-Maximilians-Universität Würzburg (JMU) in Germany and Imperial College London in the UK are reporting controlled coupling of light and matter at room temperature.

This achievement is particularly significant as it builds the foundations for a realization of practical photonic quantum technologies. Indeed, while many demonstrations of optical quantum processes require cryogenic temperatures to protect the quantum states, the present work elevates the quantum processes to room temperature and introduces controllability – both vital elements of quantum technologies such as quantum computers, which to a certain extent "calculate with light" and are conceivably many times more powerful than existing computers.

Emitted photons are trapped and re-absorbed

A light particle (photon) is generated when, for example, an exited molecule or a quantum dot returns to its low-energy ground state. This process is generally known as spontaneous emission and is usually irreversible, i.e. an emitted photon will not simply return to the emitter to be absorbed again.

But if the emitter is intimately coupled to something like a storage element for light, a so-called optical resonator, then the emitted photon remains in the vicinity of the emitter for a sufficiently long period of time, considerably boosting its chance to be reabsorbed. "Such a reversal of spontaneous emission is of highest importance for quantum technologies and information processing, not least as it facilitates exchange of quantum information between matter and light while preserving the quantum properties of both," says Professor Ortwin Hess of Imperial College.

It’s showtime for plasmonic nano-resonators

Such an exchange of quantum information is, however, usually only possible at very low temperatures, which renders spectral lines of emitters spectrally very sharp and therefore increases the probability of absorption. The teams of professors Bert Hecht and Ortwin Hess are now among the pioneering groups in the world who have succeeded in achieving the state of strong coupling of light and a single quantum emitter (quantum dot) at room temperature.

To achieve the re-absorption of a photon even at room temperature, the researchers use a plasmonic nanoresonator, which has the form of an extremely narrow slit in a thin gold layer. "This resonator allows us to spatially concentrate the electromagnetic energy of a stored photon to an area which is not much larger than the quantum dot itself," explains Professor Hecht’s co-worker Heiko Groß. As a result, the stored photon is re-absorbed with high probability by the emitter.

Precise control of the coupling between emitter and resonator

While similar ideas have already been implemented by other researchers in systems such as single molecules, in the work published now the researchers from London and Würzburg have managed to also control the coupling between the resonator and the quantum emitter by implementing a method that allows them to continuously change the coupling and, in particular, to switch it on and off in a precise manner. The team achieved this by attaching the nano-resonator to the tip of an atomic force microscope. This way they are able to move it with nanometer precision within the immediate vicinity of the emitter - in this case a quantum dot.

Ultrafast exchange of energy between emitter and resonator

Building on their accomplishment, the researchers now hope to be able to controllably manipulate the coupling of the quantum dot and the resonator not only by changing their distance but also through external stimuli - possibly even by single photons. This would result in unprecedented new possibilities in the challenging route towards a realization of optical quantum computers.

"It is clearly a most useful feature that the exchange of energy between the quantum dot and the resonator here happens extremely fast," says Groß. This solves a challenge of a low-temperature set-up: At very low temperatures, the oscillation of energy between light and matter is significantly slowed down by the long storage times of the resonator.

Original publication:
Heiko Groß, Joachim M. Hamm, Tommaso Tufarelli, Ortwin Hess, Bert Hecht; "Near-field strong coupling of single quantum dots"; Science Advances; 2018; 4: eaar4906. March 2018

Facts, background information, dossiers

  • quantum computers
  • resonators
  • photons

More about Uni Würzburg

  • News

    Stagediving with biomolecules improves optical microscopy

    Physicists from Dresden and Würzburg have developed a novel method for optical microscopy. Using biological motors and single quantum dots, they acquire ultra-high-resolution images. The resolution of conventional optical microscopy is limited by the fundamental physical principle of diffr ... more

    Stable biradicals adding a new attraction to chemistry

    Researchers at the University of Würzburg in Germany have succeeded in twisting molecules so much that their double bonds have been completely destroyed. The result: unusually stable biradicals. Boron has a range of uses throughout everyday life, from laundry bleaches to heat-proof glass a ... more

    Newly designed molecule binds nitrogen

    Chemists from the University of Würzburg have developed a boron-based molecule capable of binding nitrogen without assistance from a transition metal. This might be the first step towards the energy-saving production of fertilisers. Whether wheat, millet or maize: They all need nitrogen to ... more

  • q&more articles

    High-tech in the beehive

    Healthy honeybee colonies are crucial to maintaining the natural diversity of flowering plants and the global production of plant-derived foodstuffs. As much as 35 % of this production depends on insect-based pollination, in which the honeybee (Apis mellifera) plays a leading role. For fund ... more

  • Authors

    Prof. Dr. Jürgen Tautz

    studied biology, geography and physics at the University of Konstanz before receiving his doctorate from the University on an ecology-related subject. Work in insect, fish and frog bio-acoustics was followed by his foundation of the BEEgroup at the University of Würzburg in 1994, a group th ... more

  • Videos

    High-tech in the beehive


q&more – the networking platform for quality excellence in lab and process

The q&more concept is to increase the visibility of recent research and innovative solutions, and support the exchange of knowledge. In the broad spectrum of subjects covered, the focus is on achieving maximum quality in highly innovative sectors. As a modern knowledge platform, q&more offers market participants one-of-a-kind networking opportunities. Cutting-edge research is presented by authors of international repute. Attractively presented in a high-quality context, and published in German and English, the original articles introduce new concepts and highlight unconventional solution strategies.

> more about q&more

q&more is supported by:

Your browser is not current. Microsoft Internet Explorer 6.0 does not support some functions on Chemie.DE