A cavity leads to a strong interaction between light and matter


A tiny cavity of 2 extremely reflective mirrors is utilized to enable a confined synthetic atom (referred to as a quantum dot) to connect with a single photon. A photon is released and reabsorbed up to 10 times by the quantum dot prior to it is lost. The quantum dot is electrically managed within a semiconductor chip. Credit: University of Basel, Department of Physics

Researchers have actually been successful in developing an effective quantum-mechanical light-matter user interface utilizing a tiny cavity. Within this cavity, a single photon is released and taken in up to 10 times by a synthetic atom. This opens brand-new potential customers for quantum technology, report physicists at the University of Basel and Ruhr-University Bochum in the journal Nature.


Quantum physics explains photons as light particles. Attaining an interaction between a single photon and a single atom is a substantial obstacle due to the small size of the atom. Nevertheless, sending out the photon past the atom a number of times by methods of mirrors substantially increases the likelihood of an interaction.

In order to create photons, the scientists utilize synthetic atoms, referred to as quantum dots. These semiconductor structures include a build-up of 10s of countless atoms, however act just like a single atom: when they are optically delighted, their energy state modifications and they produce a photon. “However, they have the technological advantage that they can be embedded in a semiconductor chip,” states Dr. Daniel Najer, who performed the experiment at the Department of Physics at the University of Basel.

System of quantum dot and microcavity

Normally, these light particles fly off in all instructions like a light bulb. For their experiment, nevertheless, the scientists placed the quantum dot in a cavity with reflective walls. The curved mirrors show the released photon back and forth up to 10,000 times, triggering an interaction between light and matter.

Measurements reveal that a single photon is released and taken in up to 10 times by the quantum dot. At the quantum level, the photon is changed into a greater energy state of the synthetic atom, at which point a brand-new photon is produced. And this takes place extremely rapidly, which is extremely preferable in regards to quantum technological applications: one cycle lasts simply 200 picoseconds.

The conversion of an energy quantum from a quantum dot to a photon and back once again is in theory well supported, however “nobody has ever observed these oscillations so clearly before,” states Professor Richard J. Warburton from the Department of Physics at the University of Basel.

Serial interaction of light and matter

The effective experiment is especially substantial since there are no direct photon-photon interactions in nature. Nevertheless, a managed interaction is needed for usage in quantum details processing.

By changing light into matter according to the laws of quantum physics, an interaction between private photons ends up being indirectly possible—particularly, through the detour of an entanglement between a photon and a single electron spin caught in the quantum dot. If a number of such photons are included, quantum gates can be produced through knotted photons. This is a important action in the generation of photonic qubits, which can keep details by methods of the quantum state of light particles and transfer them over cross countries.

International cooperation

The experiment happens in the optical frequency variety and positions high technical needs on the size of the cavity, which need to be adjusted to the wavelength, and the reflectivity of the mirrors, so that the photon stays in the cavity for as long as possible.


Generation of light in a photon-number quantum superposition


More details:
Nature (2019). DOI: 10.1038/s41586-019-1709-y

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University of Basel

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