Researchers show off first ever quantum Fredkin gate

Researchers working together from the University of Queensland and Griffith University have demonstrated a key quantum logic operation that is required for quantum computing to move forward. The team demonstrated for the first time a quantum Fredkin gate powered by entanglement that operates on photonic qubits. One of the key challenges to creating a quantum computer has been in the need to minimize the resources needed to implement processing circuits.

Quantum computers will consist of chains of logic gates, just as computers use today, only in quantum computing these gates use quantum phenomena. This experiment has shown how scientists can build larger quantum circuits in a more direct manner without having to use small logic gates. The scientists say that these larger quantum circuits mean fewer logic gates are needed for the circuits to function.

For now small and medium scale quantum computers are impossible to make due to the need for so many integrated logic gates in the circuits, the Fredkin gate or controlled-SWAP gate is an example of one of these circuits. Inside a Fredkin gate, a pair of qubits are swapped depending on the value of a third qubit. Typical Fredkin gates require a circuit with five logic operations.

The researchers on this project were able to use quantum entanglement of photons to perform the controlled-SWAP operation directly. "What is exciting about our scheme is that it is not limited to just controlling whether qubits are swapped, but can be applied to a variety of different operations opening up ways to control larger circuits efficiently," said Professor Geoff Pryde. "This could unleash applications that have so far been out of reach." The quantum Fredkin gate could also be used to compare digital signatures, an essential part of some secure quantum communication protocols.