A team based at Princeton University in the US has demonstrated that two quantum computing components, known as silicon “spin” qubits, can interact even when spaced relatively far apart on a computer chip.
“The ability to transmit messages across this distance on a silicon chip unlocks new capabilities for our quantum hardware,” said leader of the study Jason Petta.
“The eventual goal is to have multiple quantum bits arranged in a two-dimensional grid that can perform even more complex calculations. The study should help in the long term to improve communication of qubits on a chip as well as from one chip to another,” Petta said.
Quantum computers have the potential to tackle challenges beyond the capabilities of everyday computers, such as factoring large numbers.
A quantum bit, or qubit, can process far more information than an everyday computer bit because, whereas each classical computer bit can have a value of 0 or 1, a quantum bit can represent a range of values between 0 and 1 simultaneously.
To realise quantum computing’s promise, these futuristic computers will require tens of thousands of qubits that can communicate with each other.
Today’s prototype quantum computers from Google, IBM and other companies contain tens of qubits made from a technology involving superconducting circuits, but many technologists view silicon-based qubits as more promising in the long run.
Silicon spin qubits have several advantages over superconducting qubits. The silicon spin qubits retain their quantum state longer than competing qubit technologies.
The widespread use of silicon for everyday computers means that silicon-based qubits could be manufactured at low cost.
The challenge stems in part from the fact that silicon spin qubits are made from single electrons and are extremely small.
“The wiring or ‘interconnects’ between multiple qubits is the biggest challenge towards a large scale quantum computer,” said James Clarke, director of quantum hardware at Intel, whose team is building silicon qubits using Intel’s advanced manufacturing line.
“Jason Petta’s team has done great work toward proving that spin qubits can be coupled at long distances,” said Clarke who was not involved in the study.
To accomplish this, the Princeton team connected the qubits via a “wire” that carries light in a manner analogous to the fibre optic wires that deliver Internet signals to homes.
In this case, however, the wire is actually a narrow cavity containing a single particle of light, or photon, that picks up the message from one qubit and transmits it to the next qubit.
The study was published in the journal Nature.
“Demonstration of long-range interactions between qubits is crucial for further development of quantum technologies such as modular quantum computers and quantum networks,” said Jelena Vuckovic, Professor at Stanford University who was not involved in the study.