Double-slit experiment: light waves squeeze through time slits
Physicists have recreated the famous double-slit experiment - but with temporally instead of spatially separated slits. This brought surprising results to light.
Many people will remember the experiment in physics lessons: when light hits two narrow, parallel slits, it is diffracted and creates an interference pattern of dark and light stripes on an observation screen behind it. The double slit experiment was first carried out by Thomas Young in 1802 and was regarded as proof that light behaves like a wave. It was later repeated with electrons, atoms and even entire molecules, demonstrating that particles can also behave like waves. The so-called wave-particle duality of quantum objects is one of the key statements of quantum mechanics.
Now, physicists at Imperial College London have recreated the famous experiment and shown that a similar interference effect can occur when light is channelled through temporally separated slits instead of spatially separated ones: A type of mirror that can be switched on and off extremely quickly causes interference in a laser pulse, just like a double slit, but this causes the pulse to change colour. The team describes the results in the scientific journal "Nature Physics".
The scientists led by Romain Tirole used an infrared laser to bombard a thin layer of indium tin oxide, a semiconducting material that is also used for smartphone screens. Under normal conditions, it is transparent to infrared light, meaning that such light rays simply pass through it unhindered. However, the physicists used a second laser that changed the optical properties of the semiconductor for brief moments: the light that arrives during this time is reflected. When they fired two ultrashort pulses with the second laser a few tens of femtoseconds apart - and thus switched on the mirror twice in quick succession - they noticed that the waveform of the reflected laser light and thus the colour changed. They had sent the light through "time slits".
Source: Wikipedia
In the classic version of the double-slit experiment, two physical phenomena occur: Diffraction and interference. The former is caused because the light is guided through an extremely narrow slit - thus the position of the light particles, which are quantum objects, is fixed. The Heisenberg uncertainty principle requires that the direction of movement cannot be predicted exactly: the light wave fans out behind the slit. The same happens at the neighbouring slit, so that both waves interfere behind the double slit. Like waves on a water surface, the movements strengthen and weaken, the minima and maxima of the interference pattern are distributed on the screen at a certain angle to the light source.
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The diffraction at the "time slit" changes the frequency of the light
The time slits in the new experiment also lead to diffraction and interference - which, however, manifest themselves in slightly different ways. Here, too, a version of Heisenberg's uncertainty applies: if you narrow down a temporal component of a system extremely tightly - as the time slits do - its energy becomes all the more imprecise. The energy of a light wave depends on the frequency: Thus, the "diffraction" at the timeslot changes the frequency of the light. As this is a double time slit, the light wave can interfere with a second one, resulting in another interference pattern, albeit one in the frequency spectrum. Some colours intensify, others cancel each other out.
Riccardo Sapienza, experiment leader and professor of physics at Imperial College, said, according to a statement from the university: "Our experiment sheds light on the fundamental nature of light and also serves as a starting point for the development of new materials that can precisely control light in space and time. "The most impressive and surprising result was also that the interference pattern showed more lines than they had expected based on current theoretical knowledge. The material used had therefore changed its optical properties much faster than previously thought possible - in just one quadrillionth of a second.
Next, the team wants to investigate the phenomenon in a time crystal. This is a quantum system in which the optical properties change over time instead of spatially as in a conventional crystal.
Spectrum of Science
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