Earlier this year, we celebrated a first in the field of quantum physics: scientists were able to 'teleport' a qutrit, or a piece of quantum information based on three states, opening up a whole host of new possibilities for quantum computing and communication.
Up until then, quantum teleportation had only been managed with qubits, albeit over impressively long distances. This proof-of-concept study suggests future quantum networks will be able to carry much more data and with less interference than we thought.
If you're new to the idea of qutrits, first let's take a step back. Simply put, the small data units we know as bits in classical computing can be in one of two states: a 0 or a 1. But in quantum computing, we have the qubit, which can be both a 0 and 1 at the same time (known as superposition).
Now, the qutrit has the same relationship to the trit, adding superposition to the classical states that can be represented as 0, 1 or 2. A qutrit can be all of these at the same time, making it another jump forward in terms of (for example) computer processing power or the amount of information that can be sent at once.
It also adds a level of complexity for quantum computing researchers.
Now that we have a grasp on qutrits, what's quantum teleportation? Well, it's getting quantum information from one place to another, through a phenomenon known as quantum entanglement, or "spooky action at a distance", as Albert Einstein called it. That's where two quantum particles (or groups of particles) are interlinked, so that one reveals the properties of the other, no matter how far apart they are in physical terms.
It's not actual teleportation in the sci-fi sense, but it is instantly obtaining data from one place based on another reading somewhere else, potentially across a large distance. This quantum information can be beamed via photons of light, and one use we might see in the future is to create unhackable internet networks, protected by the fundamental laws of physics (because any kind of interference would break up the information itself).
By splitting the path of a photon up into three parts very close to each other, via a carefully calibrated setup of lasers, beam splitters and barium borate crystals, the researchers were able to create their qutrit and produce a state of entanglement.
Over a measurement of 12 states or entanglements, the system produced a fidelity of 0.75 – an accurate result three-quarters of the time. While the setup remains slow and inefficient, it's enough to show qutrit teleportation is possible, the researchers say.
The researchers may have been beaten to the line by a separate team though, as Daniel Garisto reports in Scientific American. This second group of scientists only recorded qutrit teleportation across 10 states though, and haven't had their work accepted in a peer-reviewed journal as yet.
Whichever set of scientists can truly claim to have got to this new level of teleportation first, it's a significant moment in the field of quantum communications – even if its practical use is limited for now.
The team also says they should be able to upgrade their system in the future, perhaps even to the dizzying heights of ququarts (qutrits, with an extra bit added).
"Combining previous methods of teleportation of two-particle composite states and multiple degrees of freedom, our work provides a complete toolbox for teleporting a quantum particle intact," write the researchers in their paper.
"We expect that our results will pave the way for quantum technology applications in high dimensions, since teleportation plays a central role in quantum repeaters and quantum networks."
The research has been published in Physical Review Letters.
A version of this article was first published in August 2019.