The researchers from the University of Queensland and Griffith University say that by simplifying a complex quantum logic operation through a Fredkin gate, they've removed one of the key obstacles on the road to creating true quantum computing power.
A Fredkin (or controlled-SWAP) gate swaps three inputs into three outputs, changing the value of two qubits, from 1 to 0 or vice versa depending on the value of the third.
Professor Tim Ralph from the University of Queensland said: “The quantum Fredkin gate can also be used to perform a direct comparison of two sets of qubits (quantum bits) to determine whether they are the same or not. 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.”
Usually, the Fredkin gate requires the integration of five logic operations, but the researchers were able to use the quantum entanglement of photons to implement the same operation directly. This means small- and medium-scale quantum computers are now more feasible than ever.
Dr Raj Patel from Griffith's Centre for Quantum Dynamics, said: "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."
In the researchers’ experiments they have demonstrated how to build larger quantum circuits in a more direct way without using small logic gates.
Geoff Pryde, the project's chief investigator, added: "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. This could unleash applications that have so far been out of reach."
