Quantum teleportation is poised to change the world.
It sounds like science fiction – that the quantum state of one system can be transferred, or 'teleported', to another system a great distance away at close to the speed of light.
It's real, and it has been proven – at relatively small scales. But if quantum computers are ever going to communicate across large networks, they're going to need a way to send a lot of quantum information at once – which means scaling it up.
A new breakthrough represents the next step on the quantum bandwidth journey: A team of physicists led by Jietai Jing of East China Normal University has achieved quantum teleportation across 100 simultaneous channels, demonstrated by successfully teleporting the quantum information encoded in a 100-pixel image.
"As far as we know, it is indeed the largest number of independently addressable quantum teleportation channels ever demonstrated simultaneously," Jing told ScienceAlert.
"In principle, this architecture could provide a flexible high-capacity interface for future quantum communication networks."
Quantum teleportation was first proposed in 1993, and experimentally demonstrated just a few years later.
Despite its name, it doesn't involve matter disappearing from one location and reappearing in another. Instead, quantum teleportation transfers one system's quantum state to another using a shared entangled state and classical communication.
Since those first experiments, scientists have teleported quantum states using photons, atoms, and solid-state qubits, and across distances of more than 100 kilometers – even from the ground to a satellite.
But distance is only one way quantum teleportation needs to scale. Capacity is another.
Most quantum teleportation experiments have involved a single channel, or a relatively small number of multiplexed channels. A large-scale quantum network, however, would need to juggle many quantum states in parallel.
That's tricky to do because each additional channel needs a corresponding entangled resource, precisely matched to the quantum information being teleported.
Conventional approaches can also require separate detection, electronic processing, and modulation for each channel. The more channels you add, the more complicated the apparatus becomes.
Jing and his colleagues approached the problem by arranging 100 spatially separated modes of light into a 10-by-10 grid. Each mode could be independently controlled, effectively giving the researchers 100 separate quantum teleportation channels.
They then created a matching grid of entangled light and developed an all-optical system that could process all 100 channels in parallel, rather than requiring separate electronic feedforward for each one.
"By overcoming these two challenges, we implement quantum teleportation of 100 spatial modes with fidelities beating their corresponding classical limits," Jing said.
The next step was putting the system to the test, and this is where the 'image' comes in – although it should not be understood as a picture disappearing from one location and appearing in another, Jing explained.
"In our experiment, the image is encoded into a 10 × 10 array of spatial optical modes. Each mode can be regarded as one pixel," he said.
"More precisely, the information transferred by quantum teleportation is the continuous-variable quantum state of the optical field in each spatial mode, characterized by its amplitude and phase quadratures.
"The intensity pattern formed by all of these modes collectively represented the letter 'Q'."
In other words, each of the 100 modes of light acted somewhat like a pixel, carrying part of the information needed to make the Q. The team teleported the quantum state encoded in each mode in parallel and reconstructed the pattern at the receiving end.
But reproducing the Q was not the only signature that quantum teleportation had taken place.
The researchers also measured how closely the quantum states at the receiving end matched the states at the input. This is measured using a quantity known as fidelity, which ranges from 0 to 1, with higher values indicating a closer match.
Across the image, the researchers achieved an average fidelity of 0.60. That may not sound particularly impressive – until you compare it with the corresponding classical limit – the 0.52 average fidelity possible without the help of quantum entanglement.
The fidelity of the quantum teleportation exceeded the classical limit across all 100 spatial modes, the researchers showed.
It's a finding that suggests that quantum teleportation doesn't have to become vastly more cumbersome as more channels are added.
"Instead of implementing a separate teleportation system for each channel, our architecture enables parallel operation across the entire array of spatial optical modes," Jing said.
"As the capacity and complexity of quantum networks grow, this distinction may become increasingly important."
Ultimately, the approach could give quantum networks something they sorely need: bandwidth, allowing different quantum information to travel across multiple channels in parallel.
Related: Quantum Teleportation Achieved Over Internet For The First Time
For now, though, the system has room to grow.
The researchers say the size of their 10-by-10 array was limited largely by the roughly one watt of laser power available to pump the experiment. More powerful lasers could allow many more spatial modes – and therefore more teleportation channels – to be added.
"Our results establish an excellent paradigm for achieving scalable and flexible quantum communication," the researchers write in their paper.
Today, a Q. Tomorrow… Cats?
The findings have been published in Physical Review Letters.