Physicists 'teleport' logic operation between separated ions
Experiment completes key step in quantum computing development. Nick Carne reports.
It’s not quite a “beam me up, Scotty” moment, but the successful teleporting of a complete quantum logic operation using ions could be the start of something big.
At very least, say physicists from the National Institute of Standards and Technology (NIST) in the US, their work showcases how quantum computer programs could carry out tasks in future large-scale quantum networks.
Quantum teleportation transfers data from one quantum system to another, even if the two are completely isolated from each other.
It has been demonstrated previously with ions and a variety of other quantum systems, but Yong Wan and colleagues say they are the first to teleport a complete quantum logic operation – a computer circuit instruction – using just ions.
"We verified that our logic operation works on all input states of two quantum bits with 85 to 87% probability – far from perfect, but it is a start," says NIST’s Dietrich Leibfried.
That operation involved teleporting a quantum controlled-NOT (CNOT, in which NOT is not an acronym) logic operation, or logic gate, between two beryllium ion qubits located more than 340 millionths of a metre apart in separate zones of an ion trap, a distance that, they say, ruled out any substantial direct interaction.
The process relied on entanglement, which links the quantum properties of particles even when they are separated. A "messenger" pair of entangled magnesium ions is used to transfer information between the beryllium ions.
"Gate teleportation allows us to perform a quantum logic gate between two ions that are spatially separated and may have never interacted before," Leibfried says.
“The trick is that they each have one ion of another entangled pair by their side, and this entanglement resource, distributed ahead of the gate, allows us to do a quantum trick that has no classical counterpart.”
The entangled messenger pairs, he adds, could be produced in a dedicated part of the computer and “shipped separately to qubits that need to be connected with a logic gate but are in remote locations”.
The research also integrated into a single experiment, for the first time, several operations the team say will be essential for building large-scale quantum computers based on ions, including control of different types of ions, ion transport, and entangling operations on selected subsets of the system.
The potential lies in the ability to scale up quantum computing to the level where it is really useful.
“Quantum computers have the potential to solve problems that are intractable for conventional computers,” the researchers write in the journal Science.
“However, many quantum bits (qubits) are required to out-perform conventional computing capabilities, and scaling quantum computers to be useful in practical applications is difficult.
“As the system size increases, the average distance between qubits grows, making it harder to connect arbitrary qubits.
“Quantum gate teleportation (QGT) is a uniquely quantum solution that enables logical gates between spatially separated qubits, where shared entanglement eliminates the need for a direct quantum coherent interaction.”