© Thomas Angus / Imperial College London
The experiment relies on materials that can change their optical properties in fractions of a second, which could be used in new technologies or to explore fundamental questions in physics.
The original double-slit experiment, performed in 1801 by Thomas Young at the Royal Institution, showed that light acts as a wave. Further experiments, however, showed that light actually behaves as both a wave and as particles - revealing its quantum nature.
These experiments had a profound impact on quantum physics, revealing the dual particle and wave nature of not just light, but other 'particles' including electrons, neutrons, and whole atoms.
Now, a team led by Imperial College London physicists has performed the experiment using 'slits' in time rather than space. They achieved this by firing light through a material that changes its properties in femtoseconds (quadrillionths of a second), only allowing light to pass through at specific times in quick succession.
Lead researcher Professor Riccardo Sapienza, from the Department of Physics at Imperial, said: "Our experiment reveals more about the fundamental nature of light while serving as a stepping-stone to creating the ultimate materials that can minutely control light in both space and time."
Details of the experiment are published today in Nature Physics.
Patterns of interference
The original double-slit setup involved directing light at an opaque screen with two thin parallel slits in it. Behind the screen was a detector for the light that passed through.
To travel through the slits as a wave, light splits into two waves that go through each slit. When these waves cross over again on the other side, they 'interfere' with each other. Where peaks of the wave meet, they enhance each other, but where a peak and a trough meet, they cancel each other out. This creates a striped pattern on the detector of regions of more light and less light.
Light can also be parcelled up into 'particles' called photons, which can be recorded hitting the detector one at a time, gradually building up the striped interference pattern. Even when researchers fired just one photon at a time, the interference pattern still emerged, as if the photon split in two and travelled through both slits.
In the classic version of the experiment, light emerging from the physical slits changes its direction, so the interference pattern is written in the angular profile of the light.
Instead, the time slits in the new experiment change the frequency of the light, which alters its colour. This created colours of light that interfere with each other, enhancing and cancelling out certain colours to produce an interference-type pattern.
Metamaterials and time crystals
The material the team used was a thin film of indium-tin-oxide, which forms most mobile phone screens. The material had its reflectance changed by lasers on ultrafast timescales, creating the 'slits' for light. The material responded much quicker than the team expected to the laser control, varying its reflectivity in a few femtoseconds.
The material is a metamaterial - one that is engineered to have properties not found in nature. Such fine control of light is one of the promises of metamaterials, and when coupled with spatial control, could create new technologies and even analogues for studying fundamental physics phenomena like black holes.
Co-author Professor Sir John Pendry said: "The double time slits experiment opens the door to a whole new spectroscopy capable of resolving the temporal structure of a light pulse on the scale of one period of the radiation."
The team next want to explore the phenomenon in a 'time crystal', which is analogous to an atomic crystal, but where the optical properties vary in time.
© Thomas Angus / Imperial College London
Publication:
'Double-slit time diffraction at optical frequencies' by Romain Tirole, Stefano Vezzoli, Emanuele Galiffi, Iain Robertson, Dries Maurice, Benjamin Tilmann, Stefan A. Maier, John B. Pendry and Riccardo Sapienza is published in Nature Physics.
Reader Comments
The analogy they use at first of a VR headset for the game grand theft auto, maps to what Platos Cave allegory revealed long ago.
REALITY IS AN ILLUSION: How To Design Your Dream Life & EXIT THE MATRIX | Donald Hoffman
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As each wave carries energy, the shorter the wave, the more energy is carried over a specific time.
So simple.
But the release of "one at a time" is generally done via excitation by laser on a substance that will release/generate a photon when energy is applied.
The whole "mystery" of the double-slit experiment (which the above article fails to mention at all) is that if you send "one photon at a time" through only "one slit at a time" you end up with no interference pattern. It basically looks like the pattern you would see by firing "tiny bullets" through the slit.
But if BOTH slits are open then you get an interference pattern; even if you only send one photon through at a time.
To date no-one seems to be able to explain the phenomenon.
Quantum theory also includes a measurement principle, where by observing something, you change the expected outcome.
So for me, half the article should have explained how in fact exactly they know that they released only 1 photon, moving at the speed of light.
Personally I think resonance comes into play with light. Sonar luminescence. If sound is a wave and can create light in water, leads me to think there is a sound component to light. The release of energy, creates a wave, such as a shock wave. String theory, also makes me think of this experiment.
Whatever the case, we will never fully know the absolute truth, just absolute approximation is how I see it.
I *do* think science has come to the point where releasing single photons can be done consistently. The experiments generally have a "detector" at the end which would track the release of "more than one."
But, from what I've read, there have been "timed" experiments in the past where the scientists running the experiment were NOT able to know in advance whether the released photon would be going through 1 slit or 2. Even some where the "choice" was (supposedly) made "by the experiment" (without human intervention) after the photon was released. In every case [that I've read] the photon "knows" the setup and acts accordingly; presenting as a particle for "1 slit" and a wave for "2 slits."
For some reason I find this fascinating.
All these experiments focus on releasing photons, a so called particle. Is that the correct assumption to be making in the first place?
I've not heard of any where they assume light is a wave and work it backwards?
Lasers are supposed resonating concentrated wave's of light (photons).
What if we are measuring and assuming it all wrong. Light is a wave, that can act as a single particle and not the other way around.
We know what a molecule of water looks like and a bunch of them together in lake can make a wave. Is this flawed too? Tesla, did not believe in what we've been taught as the structure of an atom or if its really a measurable thing. So many assumptions are made and supposedly proven and then taught, but what if they are all wrong. Wrong becasue of our assumptions and how we look at them. What we have today is a working model of our reality, but it is not a 100% accurate working model and not because we haven't explained everything, but simply because things happen in the working model that can't be explained. This, above is one of them.
Here is another thought experiment. Tell a big lie, repeat often, until people believe it is the truth. So if light is photon and all the math around it proves it, it must be so, but, then we see it as a wave. So does that mean all the math around the photon should remain valid when we know this paradox exists? So as far as I can tell, we have mathematics that validates assumptions enough to mimic the reality perceived by most around us. They just don't account for everything and the oddities we can ignore, as they don't really affect us, or do they?
Fascinating. It's phenomena such as this, that makes me think that all the equations I ever learned are at best a very close assumption to true reality we are taught to believe.
Another "fun tidbit:" If light (at least some of the time) *is* a wave then what is the "medium" that it waves in? I've never heard a good explanation for that one either.