Around 20 years ago, two computer scientists proposed a technique for teleporting a special quantum operation between two locations with the goal of making quantum computers more reliable.
Now a team of researchers from Yale University have successfully turned their idea into reality, demonstrating a practical approach to making this incredibly delicate form of technology scalable.
These physicists have developed a practical method for teleporting a quantum operation – or gate – across a distance and measuring its effect. While this feat has been done before, it's never been done in real time. This paves the way for developing a process that can make quantum computing modular, and therefore more reliable.
Unlike regular computers, which perform their calculations with states of reality called bits (on or off, 1 or 0), quantum computers operate with qubits – a strange state of reality we can't wrap our heads around, but which taps into some incredibly useful mathematics.
In classical computers, bits interact with operations called logic gates. Like the world's smallest gladiatorial arena, two bits enter, one bit leaves. Gates come in different forms, selecting a winner depending on their particular rule.
These bits, channelled through gates, form the basis of just about any calculation you can think of, as far as classical computers are concerned.
But qubits offer an alternative unit to base algorithms on. More than just a 1 or a 0, they also provide a special blend of the two states. It's like a coin held in a hand before you see whether it's heads or tails.
In conjunction with a quantum version of a logic gate, qubits can do what classical bits can't. There's just one problem – that indeterminate state of 1 and 0 turns into a definite 1 or 0 when it becomes part of a measured system.
Worse still, it doesn't take much to collapse the qubit's maybe into a definitely, which means a quantum computer can become an expensive paperweight if those delicate components aren't adequately hidden from their noisy environment.
Right now, quantum computer engineers are super excited by devices that can wrangle just over 70 qubits - which is impressive, but quantum computers will really only earn their keep as they stock up on hundreds, if not thousands of qubits all hovering on the brink of reality at the same time.
To make this kind of scaling a reality, scientists need additional tricks. One option would be to make the technology as modular as possible, networking smaller quantum systems into a bigger one in order to offset errors.
But for that to work, quantum gates – those special operations that deal with the heavy lifting of qubits – also need to be shared.
Teleporting information, such as a quantum gate, sounds pretty sci-fi. But we're obviously not talking about Star Trek transport systems here.
In reality it simply refers to the fact that objects can have their history entangled so that when one is measured, the other immediately collapses into a related state, no matter how far away it is.
This has technically been demonstrated experimentally already, but, until now, the process hasn't been reliably performed and measured in real time, which is crucial if it's to become part of a practical computer.
"Our work is the first time that this protocol has been demonstrated where the classical communication occurs in real-time, allowing us to implement a 'deterministic' operation that performs the desired operation every time," says lead author Kevin Chou.
The researchers used qubits in sapphire chips inside a cutting-edge setup to teleport a type of quantum operation called a controlled-NOT gate. Importantly, by applying error-correctable coding, the process was 79 percent reliable.
"It is a milestone toward quantum information processing using error-correctable qubits," says principal investigator Robert Schoelkopf.
It's a baby step on the road to making quantum modules, but this proof-of-concept shows modules could still be the way to go in growing quantum computers to the scale we need.
This research was published in Nature.