Sometimes they even behave like particles and waves at the same time.
Sometimes, scientists needed to assume that the quantum objects were waves to get the correct result.
Other times, they needed to assume that the objects were, in fact, particles.
Sometimes either approach would work.
Instead, the result is lots of little blocks of light, arranged in a characteristic order.
Placing a double slit in a stream of water would result in the same pattern a little further down.
Hence, this experiment led to the conclusion that light is a wave.
Then, in 1881, Heinrich Hertzmade a funny discovery.
When he took two electrodes and applied a high enough voltage between them, sparks resulted.
So far, so good.
But when Hertz shone a light on those electrodes, the sparking voltage changed.
The explanation was that the light knocked electrons out of the electrode material.
This result should have been impossible if wave theory was true.
In 1905, Albert Einstein had the solution: Light was, in fact, a particle.
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Scientists prefer one theory that is always right to two theories that are sometimes right.
But that was exactly the problem with this discovery.
They knew that some things trigger wave-like behavior, such as the edges of slits.
But they didnt have a clear explanation why that is the case, or when to use which theory.
This conundrum, called wave-particle duality, persists to this day.
But new research might be clearing things up a bit.
Or so are the hopes.
Each of these beams hits a crystal, which, in turn, produces two photons.
This produces four photons in total, two from each crystal.
The scientists sent one photon from each crystal into an interferometer.
This unit merges two sources of light and creates an interference pattern.
Such a pattern was first observed by Thomas Young in his aforementioned double-slit experiment.
In other words, the interferometer detects the wave nature of light.
The paths of the other two photons were used to detect their particle characters.
For example, one can shoot the photon through gas, which then lights up where the photon went.
By focusing on the trajectory rather than the end destination, the photon cant be a wave.
This is one of the many examples inquantum physicswhere the measurement actively influences the outcome of said measurement.
The researchers thus revealed how a photon could be a particle.
Because both photons of one crystal are produced together, they form a single quantum state.
This means that one can find a mathematical formula that describes both of these photons at the same time.
Indeed, the researchers managed just that.
They measured how wavy the photon was by checking the visibility of the interference pattern.
When the visibility was high, the photon was very wavelike.
When the pattern was barely visible, they concluded that the photon must be very particle-like.
And this visibility wasnt random.
It was highest when both crystals got an equal intensity of the laser beam.
This result is exciting because most experiments only measure light as either waves or as particles.
Few experiments to date have measured both at the same time.
Doing so means its easier to determine how much of each property a light source has.
Theoretical physicists are excited
This result matchesthe predictionthat theorists made earlier.
A quantum object is wavelike if an interference pattern is visible or if the quantity V is not zero.
Also, it is particle-like if a path is distinguishable or if P is not zero.
The scientists who conducted the experiment showed this mathematically in their paper.
Faster quantum computers?
The connection between a quantum objects entanglement and its particleness and waviness is particularly exciting.
Quantum devices, which might one day power thequantum internet, rely on entanglement.
The quantum internet is the quantum analogy to what the internet is for classical computers.
In addition, quantum computers themselvesmight get betterusing particle-wave duality.
This would create more possible quantum states, which in turn enhances the power of the shot computer.
So, although this is very fundamental research, possible applications are already on the horizon.
The research is solid, but its also very fundamental.
As usual in science and technology, its a long way from fundamental research to real-life applications.
One of the first use cases might happen in quantum computing.
Quantum entanglement and wave-particle duality are linked, as scientists have shown.
Instead of entanglement, one could therefore measure the quantities of waviness and particleness.
This could help the scientists who are working on developing the quantum internet.
Or, one could use the duality to enhance quantum computers and make them even faster.
Either way, it seems that exciting quantum times are soon to be upon us.
This article was originally published on Built In.
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