RESEARCHERS at Griffith University have overcome one of the key challenges to quantum computing by simplifying a complex quantum logic operation.
The researcher, led by Dr Raj Patel from Griffith’s Centre for Quantum Dynamics, experimentally realised the quantum Fredkin gate for the first time.
Quantum computers consist of chains of logic gates in a way similar to conventional computers, except these logic gates harness quantum phenomena. One of the biggest obstacles to creating a working quantum computer has been in minimising the number of resources needed to efficiently implement processing circuits.
According to Dr Patel, large quantum circuits require many basic logic gates to function. This makes them difficult to build. However, the development of more capable logic gates with more complex functionality, but with simpler, more direct structures, would reduce the number of logic gates needed in a given quantum circuit.
Researchers from Griffith University and the University of Queensland demonstrated how to build larger quantum circuits in a more direct way without using small logic gates.
The experiments involved the Fredkin (controlled-SWAP) gate, where two qubits are swapped depending on the value of the third. This is a building block of quantum computing algorithms, such as Shor’s algorithm for finding prime factors.
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 implementing a circuit of five logic operations. The research team used the quantum entanglement of photons – particles of light – to implement the controlled-SWAP operation directly.
The breakthrough applies not just to controlling the swapping of qubits, but can be applied to a variety of different operations, opening up ways to build and control larger quantum circuits efficiently.