Double-slit time diffraction at optical frequencies
nature.com
nature.com
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?
The diagram of page 3 of this helped me understand: https://arxiv.org/ftp/arxiv/papers/2206/2206.04362.pdf.
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 was hoping for time travel or, at a minimum, reversible computing, but I guess I'll settle for faster streaming of cat videos
>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.
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.
Later experiments that relied on individual photons could detect them individually [0]
Here's an article on single photon sources [1]
[0](https://en.wikipedia.org/wiki/Double-slit_experiment#/media/...)
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.
So they are red shifting or blue shifting the photons? And sending the red/blue shifted photons with a very small time delay?
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".
Can you elaborate on this or provide more context/reading links.
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.
Isn't coherence needed?
>a pattern similar to the one you'd see with the two openings on the wall
The pattern was in the frequency domain, i.e. the color of the light changed.
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.
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).
This is the best part of science
—Isaac Asimov
So if you hear a STEM person say either, ask what their job is.
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.
This is gold.