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Two particles are said to be entangled when one cannot be perfectly described without information about the other being included. Shutterstock/ezphoto
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"Quantum entanglement" is one of the storey techniques used in contemporary science fiction films. For example, fans of Marvel superhero films will be familiar with the concept of separate time lines merging and overlapping, or individuals' destiny becoming entangled by seemingly miraculous ways.
Quantum
entanglement, on the other hand, isn't just a sci-fi jargon. It's a true,
confusing, and beneficial phenomenon. Quantum mechanics is a theory that
describes the behaviour of nature at the atomic, and even subatomic, level.
"Entanglement" is one facet of a larger collection of theories in
physics known as quantum mechanics.
Many
cutting-edge technologies rely on understanding and utilising entanglement.
Quantum computers, which can handle certain problems significantly more quickly
than ordinary computers, and quantum communication devices, which would allow
humans to speak with one another without the risk of an eavesdropper listening
in, are two examples.
But what
is quantum entanglement, exactly? When one of two particles in quantum
mechanics cannot be properly described without providing all of the information
about the other, they are said to be entangled: the particles are
"linked" in such a way that they are not independent of one another.
While this concept appears to make sense at first glance, it is a tough concept
to grasp — and physicists are still learning about it.
Quantum
dice
Assume I
give each of you and your friend, Thandi, a small, opaque black box. Each box
includes a standard six-sided die. To confuse the dice, you're both advised to
lightly shake your boxes. After that, you split ways. Thandi returns to a South
African metropolis, Cape Town, while you return to Durban. During the process,
you don't communicate with each other. You each open your box when you arrive home
and examine the upward-facing number on your die.
There
would normally be no link between the numbers you and Thandi view. She, like
you, would be as likely to see any number between 1 and 6; more crucially, the
number she sees on her die has no influence on the number you see on yours.
This isn't
shocking; after all, it's how the world works. If we could make this example
"quantum," though, it might act quite differently. Assume I now
instruct Thandi and you to lightly tap your boxes together before shaking them
individually and going your separate ways.
In a
quantum mechanics example, tapping the boxes against each other would enchant
the dice and link – or entangle – them in a mysterious way: whenever you both
get home and open your boxes and look at the numbers, your number and Thandi's
will be assured to be exactly correlated. If you see a '4' in Durban, you can
be sure Thandi in Cape Town will measure a '4' on her die as well; if you see a
'6', she will as well.
In this
analogy, the dice represent individual particles (such as atoms or light
particles known as photons), and the physical act of tapping the boxes together
entangles them, allowing us to measure one die and learn about the other.
Making better entanglement
On our human, macroscopic size, there is no magical box-tapping action to enchant a pair of dice or other objects, as far as we know (if there were, we would be able to experience quantum mechanics in our everyday life and it would probably not be such a foreign, perplexing concept). For the time being, scientists must make do with objects on the microscopic level, where quantum effects are much easier to observe, such as charged atoms known as ions or unique superconducting gadgets known as transmons.
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