An artist's rendering of a quantum Fredkin (controlled-SWAP) gate, powered by entanglement, operating on photonic qubits. Raj Patel, Geoff Pryde/Center for Quantum Dynamics/Griffith University

In a major breakthrough in quantum computing, scientists from Griffith University and the University of Queensland in Australia announced Monday that they had found a way to simplify a complicated logic operation by creating a quantum “Fredkin gate” for the first time ever. The development, detailed in the journal Science Advances, could bring fully functional quantum computers closer to reality.

“Much like our everyday computer, the brains of a quantum computer consist of chains of logic gates, although quantum logic gates harness quantum phenomena,” Raj Patel, from the Griffith University’s Centre for Quantum Dynamics, said in a statement. “Similar to building a huge wall out lots of small bricks, large quantum circuits require very many logic gates to function. However, if larger bricks are used the same wall could be built with far fewer bricks.”

Patel and his team carried out their experiment using a particular type of quantum logic gate known as the Fredkin gate, where two “qubits” — the quantum computing equivalent of bits — are swapped depending on the value of the third.

The experiment demonstrated how to build larger quantum circuits in a more direct way, using photons, without using small logic gates.

“The quantum Fredkin gate can also be used to perform a direct comparison of two sets of qubits to determine whether they are the same or not,” co-author Timothy Ralph from the University of Queensland, said in the statement. “This is not only useful in computing but is an essential feature of some secure quantum communication protocols where the goal is to verify that two strings, or digital signatures, are the same.”

The development of quantum computers capable of performing operations many orders of magnitude faster than conventional computers has been a goal of computer scientists and physicists ever since the idea was first floated in the early 1980s. However, given the inherently unstable nature of qubits, the goal has remained out of reach.

Quantum computers utilize two basic properties these qubits possess — superposition and entanglement. Unlike conventional bits, which can exist in one of the two states, 0 and 1, qubits can exist in superposition, allowing them to have both states at the same time. This superposition of qubits, coupled with quantum entanglement — wherein they are physically separate but act as if they are connected — is what gives quantum computers a significant advantage over conventional computers.

“The allure of quantum computers is the unparalleled processing power that they provide compared to current technology,” Patel said in the statement.