What do they mean by time slits? A beam of light twice gated in time... what does this mean?
Is it something like sending pulses of light towards each other separated by some very small amount of time and observing an interference pattern of some kind?
I believe it's like a filter which briefly lets light pass through, twice, although the way they achieve this is weird. In conventional double-slit the 2 splits have different x positions, here they have different t positions.
A rolling shutter doesn't cause changes in frequency of the light itself.
The temporal slit appears to be causing frequency changes in the light beam. These frequency changes then interfere with each other creating a diffraction in the spectral frequency (rather than by physical distance as is with the traditional double slit experiment).
I think the nature author thought the same thing and then added a sentence at the very end, which sums up the rest they did not quite grasp (like me) and sound more like Dr. Who:
>Temporal interference and time reversal could lead to new ways of creating time crystals, which are mind-bending structures that repeat periodically, not in space — as ordinary crystals do — but in time. They could also help researchers build quantum computers based on photons.
This is a slightly off topic question but commenters here might have an answer.
In the original double slit experiment, how do they actually know that they are emitting a just a single photon. The entire experiment depends on this being the case, but how is it done? Especially way back when it was first performed. How could they confidently say that have an apparatus that can reliably only emit a single photon, yet at the same not be clear about whether light was a wave or a particle.
The original experiment did not rely on the emission of individual photons. It just observed an interference pattern that classical particles would not exhibit.
Later experiments that relied on individual photons could detect them individually [0]
Imagine you and your friend are playing with flashlights in a dark room. You shine your flashlights on a wall with two small openings (slits) close to each other. When the light from both flashlights goes through these openings and reaches the other side, you notice a cool pattern on the wall with light and dark lines. This is called an interference pattern, and it happens because light behaves like a wave.
Now, in this experiment, scientists did something similar but instead of using two small openings on a wall, they created two very short moments in time when light could pass through. They called these moments "time slits." They used a special material called Indium-Tin-Oxide and high-power infrared light to create these time slits.
When they looked at how the light changed after going through these time slits, they saw a pattern similar to the one you'd see with the two openings on the wall. But, they were surprised to find that the pattern had more lines than they expected based on the current understanding of how light interacts with the material.
This discovery means that the material changes much faster than previously thought, and it challenges the theories scientists had so far. This experiment also opens the door for creating new materials that can control light in exciting ways, like making it go backward or changing its path. These new materials could be useful in many areas, like making better computers and improving communication technologies.
Well swap the flashlight for a laser pointer and I'm sure saying the color shimmers if you switch it on two times very fast isn't harder to understand than saying it makes patterns on a wall if you shine it through two slits.
No need to be explicitly wrong, even if explaining on a lower level. In fact, the betrayal felt when one later learns a contradictory (not clarifying) truth is bad for learning.
Space and time in general relativity are but inseparable axes of the same spacetime. But, unlike completely interchangeable and real space axes (e.g. "length, width. depth"), the time axis is slightly special: it's counted as imaginary (see Minkowski space: the distance contracts along the time axis). But otherwise it's an axis like width of height or length.
Quantum "particles" are also "waves", that is, they behave a bit like both, but not exactly like your normal grains of sand or water waves. Like particles, they are "separate", so you can count electrons or photons, and can't cut them in half Like waves, they are wavy and fuzzy, without a sharp edge or border, and interact like waves. When one wave's hump meets another wave's trough, they cancel out ("destructive interference"). When two humps meet, they reinforce each other, resulting in a bigger hump ("constructive interference", yes, sounds ironic).
This is easy to imagine in the space domain, with normal waves that go, say, "up" and "down". With experiments with photons the waves represent the strength of the electromagnetic field, and the interference pictures are ring-like.
Now replace one of the dimensions of the ring with time. This will mean that instead of e.g. darker / brighter circles or stripes on the picture, you will detect "bands" or "stripes" of higher / lower intensity spread over time. Intensity changing over time is oscillation. E.g. air pressure oscillating over time is sound. Electromagnetic field oscillating over time is radiation: radio waves, light, x-rays, etc.
So the experiment managed to let two photons through "slits" in time rather than in space, by opening a "hole" for them to pass and then closing it back really quickly, so that two photons would pass the opening really close in time to each other. This is similar to how the typical double-slit experiment puts slits (or holes) really close by in space, so that the photons can't be far away from each other while interacting.
Then they registered the interference picture, which, AFAICT, was a burst of various electromagnetic frequencies (a "spectrum"). Each photon has a very well-defined frequency (or wavelength, or color, for visible light). So seeing a variety of different frequencies ("colors") would be a tell-tale sign that interference happened, producing multiple "stripes" in the time domain, not space domain.
As far as I can understand the abstract (I did not shell out the $29), they register multiple red-shifted and blue-shifted photons, with their frequencies forming the expected stripe-like interference picture. They say: «The separation between time slits determines the period of oscillations in the frequency spectrum», that is, these "stripes" are not separated by space (red and blue circles) but rather by time. That is, the light quickly changes between red / blue shifted, as if we were traveling through the spatial interference picture, not looked at it "from above".
So yes, I think our understanding more or less matches: they likely register red/blue shifted photons with small time delays between the same "colors".
With the classic double slit experiment both space coordinates affect each other. With this time axis double slit experiment one has to ask if t1 affects t2 or if t2 also affects t1. The latter would raise a lot of questions. I don't understand the paper well enough to know which of these cases they are observing but I assume only the t1->t2 case? I'd appreciate if someone with more domain knowledge could enlighten.
Edit: after more thought I guess it would make sense that two slits after each other in time show a change in wavelength if they are brought close enough together.
Essentially the time separated slits act like a space separated double slit experiment wherin the slits are oriented on an axis parallel to the direction of the light path instead of at a perpendicular one. The wave like nature does not just expand in one dimension in space but all three and so there must be interference in the direction of travel. Do I have the right idea with this?
The wave nature of light is revealed by diffraction from physical structures. We report a time-
domain version of the classic Young’s double-slit experiment: a beam of light twice gated in
time produces an interference in the frequency spectrum. The 'time slits', narrow enough to
produce diffraction at optical frequencies, are generated from a thin film of Indium-Tin-Oxide
illuminated with high-power infrared pulses, inducing a fast reflectivity rise, followed by a
slower decay. Separation between the time slits determines the period of oscillations in the
frequency spectrum, while the decay of fringe visibility in frequency reveals the shape of the
time slits. Here we find a surprise: many more oscillations are visible than expected from
existing theory, implying a rise time for the leading edge of around 1-10 fs, approaching an
optical cycle of 4.4 fs. This is over an order of magnitude faster than the width of the pump and
can be inferred from the decay of the frequency oscillations.
...
In conclusion, we report a direct observation of spectral oscillations, at optical frequencies,
resulting from double-slit time diffraction, the temporal analogue of the Young’s slits
experiment. The measurements show a clear inverse proportionality between the oscillation
period and the time slit separation. These oscillations reveal a 1-10 fs temporal dynamics of
the ITO/Au bilayer, much faster than previously thought and beyond the adiabatic and linear
intensity dependence assumed so far in most theoretical models (10)(11),(17), calling for a
new fundamental understanding of such ultrafast non-equilibrium responses. The observation
of temporal Young’s double-slit diffraction paves the way for optical realizations of time-
varying metamaterials, promising enhanced wave functionalities such as nonreciprocity (18),
new forms of gain (19)(20), time reversal (21)(22) and optical Floquet topology (23)(24).
Double-slit time diffraction could be extended to other wave domains, e.g. matter waves (6),
optomechanics (25) and acoustics (26)(27), electronics (28), and spintronics (29), with
applications for pulse shaping, signal processing and neuromorphic computation. Finally, the
visibility of the oscillations can be used to measure the phase coherence of the wave
interacting with it, similarly to matter-wave interferometers (6).
But it doesn’t capture what makes the quantum version of the experiment interesting.
Which is that if you only have one clap, but at two possible times, you will detect (“hear”) the clap at only one location each time.
But the chance you hear the clap at any given position is based on where that position is in the wave you might expect if there had been two classical claps.
I.e. the quantum surprise is single particles interfere with themselves across the alternate paths they could take, not just each other.
Or in this case, interfere with themselves across two alternate times they could take on the same path.
Is it something like sending pulses of light towards each other separated by some very small amount of time and observing an interference pattern of some kind?