Researchers from Griffith University and the University of Queensland have overcome one of the key challenges to quantum computing by simplifying a complex quantum logic operation. They demonstrated this by experimentally realising a challenging circuit—the quantum Fredkin gate—for the first time.

"The allure of quantum computers is the unparalleled processing power that they provide compared to current technology," said Dr Raj Patel from Griffith's Centre for Quantum Dynamics.

"Much like our everyday computer, the brains of a quantum computer consist of chains of logic gates, although quantum logic gates harness quantum phenomena."

The main stumbling block to actually creating a quantum computer has been in minimising the number of resources needed to efficiently implement processing circuits.

"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," said Dr Patel.

"We demonstrate in our experiment how one can build larger quantum circuits in a more direct way without using small logic gates."

At present, even small and medium scale quantum computer circuits cannot be produced because of the requirement to integrate so many of these gates into the circuits. One example is the Fredkin (controlled- SWAP) gate. This is a gate where two qubits are swapped depending on the value of the third.

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.

"There are quantum computing algorithms, such as Shor's algorithm for finding prime numbers, that require the controlled-SWAP operation.

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," said Professor Tim Ralph from the University of Queensland.

Professor Geoff Pryde, from Griffith's Centre for Quantum Dynamics, is the project's chief investigator.

"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 Pryde.

"This could unleash applications that have so far been out of reach."

The research has been published as 'A quantum Fredkin gate' in *Science Advances*.

**Explore further:**
Semiconductor-inspired superconducting quantum computing devices

**More information:**
A quantum Fredkin gate, *Science Advances*, dx.doi.org/10.1126/sciadv.1501531

## eachus

I can factor prime numbers very quickly. Their factors are 1 and the number itself. ;-)

Shor's algorithm is for factoring non-prime numbers into their prime factors.

## Baggio4378

## Da Schneib

## antialias_physorg

Yes, but for some implementations (like the mentioned Shors algorithm) such a 'regular' computer would quickly reach limits (e.g. exceeding the atoms in the universe to construct it given a sufficiently large number to process within a given time - which MUCH smaller quantum computer could handle in the same timeframe)

## Spaced out Engineer

Is emulated classical computation of quantum computation is the same?

That depends. Probably, but it is contingent on the existence of time closed loop curves. Then again without these, mathematics itself maybe philosophically existential and with them the possibly Godelian axiomatic over flow becomes interesting.

Using high fidelity we can observed truths we can not get to with given origins. And so there must be a meta truths to aggregate what once was taken as high fidelity. It becomes some sort of continuously updating network from the dimensionality with varying in factors decidability, completeness and consistency. Knot and loop transforms conditioned on vantage.

Most opt for decidability first, but we'll see.

## Dark_Solar

## Tektrix

## Tektrix

It is possible to emulate quantum logic with binary logic, just like it's possible to water an entire soccer pitch by applying a single drop to each blade of grass with an eyedropper . . . however, watering them all at once with a large sprinkler is ever so much faster and efficient.

## retrosurf

Of course you can emulate a quantum computer on a sufficiently power digital computer. Your emulation, however, will not display the speed-ups that make quantum computing attractive. The emulation of a quantum Fourier transform, for example, will have a big O complexity that is no less than that of the best conventional discrete Fourier transform.

"using quantum logic to emulate it" is a non-starter. There is no "quantum logic" in the hardware of your emulating computer. There is no trick for achieving quantum computer performance with conventional hardware. Further, decidability is unaffected by the computing platform that you use. What is undecidable in conventional computation is still undecidable in quantum computing.

## retrosurf

It's worse than that. Most quantum computing runs at liquid helium temperatures.

There was once a time when all computers were under control of governments and corporations. Now you have one in your pocket.

I think we have more to worry about from conventional AI in the hands of corporations than we do from quantum computing in the hands of governments or corporations.

## Da Schneib

Which is an interesting thing to know.

## Da Schneib

## Da Schneib

Your note that it would not provide the speedups a real quantum processor would is well taken, but I was merely talking about whether they're equivalent, not whether they're the same. It's a computer science argument, not a performance tuning argument.

## antigoresockpuppet

That tells you how the site is regarded. Someone that's actually serious about the content...and then thinks, "Shit, there's no moderation or accountability at all here. Might as well ream them up the butthole with some spam!" Pitiful.

## Jayman

NOT ! Good catch that. I wouldn't have given it a second thought.

## Phil DePayne

## Da Schneib

## Hyperfuzzy