When Heroes (now streaming on Peacock!) hit the airwaves in
September of 2006, few characters were as immediately beloved as the
appropriately named Hiro Nakamura. Granted the ability to manipulate
space-time, Hiro could not only slow down, speed up, and stop time, he could
also teleport from one place to another. That’s a useful skill if you need to
get to a specific point in time and space to fight an evil brain surgeon or
prevent the end of the world. It’s also useful if you want to build the quantum
internet.
Researchers at QuTech — a collaboration between Delft
University of Technology and the Netherlands Organization for Applied
Scientific Research — recently took a big step toward making that a reality.
For the first time, they succeeded in sending quantum information between
non-adjacent qubits on a rudimentary network. Their findings were published in the journal Nature.
While modern computers use bits, zeroes, and ones, to encode
information, quantum computers us quantum bits or qubits. A qubit works in much
the same way as a bit, except it’s able to hold both a 0 and a 1 at the same
time, allowing for faster and more powerful computation. The trouble begins
when you want to transmit that information to another location. Quantum
computing has a communications problem.
Today, if you want to send information to another computer
on a network, that’s largely accomplished using light through fiber optic
cables. The information from qubits can be transmitted the same way but only
reliably over short distances. Fiber optic networks have a relatively high rate
of loss and rely on cloning bits and boosting their signal in order to transmit
over significant distances. Qubits, however, can’t be copied or boosted. That
means that when and if information is lost, it’s lost for good, and the longer
the journey the more likely that is to happen.
That’s where Hiro Nakamura comes in, or at least his quantum
counterpart. In order to reliably transmit quantum data, scientists use quantum
teleportation, a phenomenon that relies on entanglement or what Einstein called
"spooky action at a distance."
As with all things quantum, understanding entanglement isn’t
the easiest endeavor but, for our purposes, we’ll simplify. When two particles
are entangled, they share a connection, regardless of the physical distance
between them. By knowing the state of one entangled particle, you can instantly
know the state of the other even if its out of view. It’s sort of like making
two people share a single pair of shoes. If you know the first person is in
possession of the right shoe, then you know the second person has the left.
Using that spooky connection, scientists can transmit
information between the two particles and that information appears at one
particle and vanishes at the other instantly. That’s where the analogy to
teleportation comes in. First, it’s here, then it’s there, without the need for
a journey along cables. Importantly, only information is transferred, not any
physical matter. Our teleportation technologies aren’t at BrundleFly levels
just yet.
Quantum teleportation isn’t exactly new. It’s been done
before, but always between two directly connected entangled particles. In
communications parlance, it’s the quantum equivalent of talking to your friend
in the next room using two cans connected by a string. In order to create a
true quantum network, we need to be able to transmit data between non-adjacent
nodes using intermediaries.
In this case, researchers wanted to transfer information
between nodes named Alice and Charlie, using Bob as a go-between. To make that
happen Bob created an entangled state with Alice and stored his portion of the
entanglement in a bit of quantum memory. Next, Bob repeats that process with
Charlie. Then, using what researchers at QuTech describe as “quantum mechanical
sleight of hand,” Bob completes a measurement and passes on the entanglement
between Alice and Charlie.
Once that’s done, Charlie prepares the information he wants
to send and completes a complicated measurement between his message and his
half of the entanglement with Alice. Quantum mechanics goes to work, and the
information vanishes on Charlie’s end and appears on Alice’s.
This has some important implications for the future of
communication. First, using quantum teleportation networks avoids the threat of
packet loss over fiber optic cables. Second, it effectively encrypts the
information at Alice’s end. In order to decode the information, you need to
know the result of the calculation Charlie performed. The third thing builds
upon the first; despite the immediate transfer of quantum information, we are
still bound by the speed of light. As you know, the cosmic speed limit isn’t
just a suggestion, it’s the law. Sending the calculation information to Alice
in order to decode the information relies on more traditional communications
bound by light speed. No getting around it.
While this is an important step toward a quantum internet,
in order to build the sorts of networks we’ll need for everyday use, we’re
going to need a lot more nodes. But, hey, even today’s global communications
network started with a single telephone.
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