Between two mirrors, the quantum dot filters the light beams with just one photon per package out of the laser, so that only packages with multiple photons remain. Credit: Leiden Institute of Physics
Leiden physicists have manipulated light with large artificial atoms, ie quantum dots. Before, this has only been accomplished with actual atoms. It is an important step toward light-based quantum technology. When you point a laser pointer at the screen during a presentation, an immense number of light particles races through the air at a billion km/hour. They don’t travel in a continuous flow, but in packages containing varying numbers of particles. Sometimes as many as 4 so-called photons pass by, and other times none at all. You won’t notice this during your presentation, but for light-based quantum technology, it is crucial that scientists have control over the number of photons/ package.
Credit: Leiden Institute of Physics
In theory, you can manipulate photons with real individual atoms, but because of their small size, it is extremely hard to work with them. Larger quantum dots are much easier to handle. In fact, they managed to filter light beams with 1 photon per package out of a laser. “Another big advantage of quantum dots is that the system already works within nanoseconds,” says Henk Snijders. “With atomic systems, you need microseconds, so a thousand times longer. This way, we can manipulate photons much faster.”
(a) Cartoon of the experiment: Polarization preand postselection in a resonant transmission CQED experiment enables tuning of the photon statistics from antibunched to bunched. (b) Theoretical resonant transmission spectra for coherent light with mean photon number 1, with and without the quantum dot, comparing the conventional case (parallel polarizers) to the case of special polarization postselection along θ ∗ out: close to one of the QD resonances, single-photon transmission is perfectly suppressed, despite the finite lifetime and cavity coupling of the QD transition. (c) Second-order correlation function (QD B) for the special polarization angle case, comparing theory and experiment using two different sets of single photon counters (SPCs) with different timing jitter, 50 ps and 500 ps.
The ultimate goal for the research group led by Prof. Dirk Bouwmeester is to entangle many photons using quantum dots. This is essential, for example, in techniques like quantum cryptography. Snijders: “This research shows that we are already able to manipulate individual photons with our system. And the beauty is that in principle, we don’t need large experimental setups. We can just integrate our quantum dots in small microchips.”
https://arxiv.org/pdf/1604.00479.pdf
http://phys.org/news/2016-08-quantum-dots.htmljCp
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