Physicists demonstrate a quantum Fredkin gate

March 25, 2016
An artist's rendering of the quantum Fredkin (controlled-SWAP) gate, powered by entanglement, operating on photonic qubits. Credit: Raj Patel and Geoff Pryde, Center for Quantum Dynamics, Griffith University.

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 ."

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 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 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: Dramatic simplification paves the way for building a quantum computer

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

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eachus
5 / 5 (8) Mar 25, 2016
"There are quantum computing algorithms, such as Shor's algorithm for factorising prime numbers, that require the controlled-SWAP operation."

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
4 / 5 (4) Mar 25, 2016
Eachus that is correct, we let that one slip through the net unfortunately.
Da Schneib
5 / 5 (2) Mar 25, 2016
Here's an interesting question: given the existence of quantum logic, would it be possible to emulate a quantum computer on a sufficiently powerful digital computer, using quantum logic to implement it?
antialias_physorg
5 / 5 (4) Mar 25, 2016
would it be possible to emulate a quantum computer on a sufficiently powerful digital computer, using quantum logic to implement it?

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
1 / 5 (1) Mar 26, 2016
Da Schneib

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
3.2 / 5 (5) Mar 26, 2016
Ok, this question is a little off topic so please bear with me. From what I can gather, quantum computing has the potential furnish extreme advances in overall computing power but is dependent on supercooling using liquid nitrogen (liquid nitrogen being generally out of the scope of safe useability for the average consumer). Does this create a tendency toward quantum supercomputing being remanded to the custodial care of governments/corporations while severely limiting its accessability to the general public?
Tektrix
5 / 5 (2) Mar 26, 2016
@DarkSolar: Already the general public routinely takes advantage of computing resources that are far beyond the reach of any one individual. Many of the services we access online are made possible through the use of enormously expensive and highly complex computational infrastructure. When it becomes profitable to use quantum computers to provide new or enhanced services to the general public, you can bet it will be done.
Tektrix
5 / 5 (3) Mar 26, 2016
. . . would it be possible to emulate a quantum computer on a sufficiently powerful digital computer, using quantum logic to implement it?


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
3.3 / 5 (3) Mar 26, 2016
Here's an interesting question: given the existence of quantum logic, would it be possible to emulate a quantum computer on a sufficiently powerful digital computer, using quantum logic to implement it?


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
4 / 5 (4) Mar 26, 2016
... (liquid nitrogen being generally out of the scope of safe useability for the average consumer). Does this create a tendency toward quantum supercomputing being remanded to the custodial care of governments/corporations while severely limiting its accessability to the general public?


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
5 / 5 (1) Mar 26, 2016
would it be possible to emulate a quantum computer on a sufficiently powerful digital computer, using quantum logic to implement it?

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)
Yes, that's an acknowledged limitation. However this also means that quantum computers are equivalent to Turing machines (since digital computers, all of which are reducible to equivalent Turing machines, can emulate them).

Which is an interesting thing to know.
Da Schneib
5 / 5 (2) Mar 26, 2016
Ok, this question is a little off topic so please bear with me. From what I can gather, quantum computing has the potential furnish extreme advances in overall computing power but is dependent on supercooling using liquid nitrogen (liquid nitrogen being generally out of the scope of safe useability for the average consumer). Does this create a tendency toward quantum supercomputing being remanded to the custodial care of governments/corporations while severely limiting its accessability to the general public?
Probably not. These temperatures are accessible inside properly designed chip containments in various ways without using liquified gases, see Peltier cooling of astrophysics imaging CCDs for a good start.
Da Schneib
5 / 5 (2) Mar 26, 2016
"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.
Err, actually I was saying that a program could be written to do quantum logic and that would emulate the operation of a quantum computer.

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
1 / 5 (2) Mar 26, 2016
Can this site sink lower? Is it just a coincidence that retrosurf has posted immediately before or after that damnable spammer every time he has spammed the site?

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
5 / 5 (2) Mar 26, 2016
Shucks! @Eachus, you beat me to it.
NOT ! Good catch that. I wouldn't have given it a second thought.
Phil DePayne
3.7 / 5 (3) Mar 26, 2016
Emulating a classical computer on top of quantum architecture would be a necessity. Realistically programming a quantum computer uses true quantum logic processing only for specific instances of quantum algorithms. You still need an operating system for the human operator. Quantum Turing Machine architecture would be analogous to the Turing Machine architecture of a normal CPU. Quantum analogies of caches, instruction lines, and bus architecture would need to be developed. Quantum logic in the architecture would be specifically accessible by the programmer in the same way as is done today in emulated quantum programming languages.
Da Schneib
3 / 5 (2) Mar 26, 2016
@Phil, or the way that math coprocessors are accessed for floating point operations.
Hyperfuzzy
1 / 5 (1) Mar 31, 2016
Wow, how long until we throw away this s#it. We've got non-quantum computers trying to design a quantum computer. I'm thinking this is a cash cow. No end to the nonsense. Promises, promises! Lucky I'm not advising the guy with the deep pockets.

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