Quantum Computing

Quantum computing breakthrough: Qubits made from standard silicon transistors

Australian researchers have managed to create a CNOT quantum logic gate, the basic building block of a quantum computer, by modifying a standard silicon transistor
Australian researchers have managed to create a CNOT quantum logic gate, the basic building block of a quantum computer, by modifying a standard silicon transistor
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The researchers turned standard silicon transistors into single-electron transistors, using the spin of the electron as the qubit
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The researchers turned standard silicon transistors into single-electron transistors, using the spin of the electron as the qubit
Australian researchers have managed to create a CNOT quantum logic gate, the basic building block of a quantum computer, by modifying a standard silicon transistor
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Australian researchers have managed to create a CNOT quantum logic gate, the basic building block of a quantum computer, by modifying a standard silicon transistor
The gate is controlled through an external voltage and microwave radiation
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The gate is controlled through an external voltage and microwave radiation
The technique could scale up to hold thousands, even millions of qubits on a single chip
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The technique could scale up to hold thousands, even millions of qubits on a single chip
Quantum leap: Lead researchers Menno Veldhorst and Andrew Dzurak
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Quantum leap: Lead researchers Menno Veldhorst and Andrew Dzurak
Researchers at UNSW are focusing on the potentially revolutionary approach of building quantum computers out of silicon
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Researchers at UNSW are focusing on the potentially revolutionary approach of building quantum computers out of silicon

In what is likely a major breakthrough for quantum computing, researchers from the University of New South Wales (UNSW) in Australia have managed for the first time to build the fundamental blocks of a quantum computer in silicon. The device was created using standard manufacturing techniques, by modifying current-generation silicon transistors, and the technology could scale up to include thousands, even millions of entangled quantum bits on a single chip. Gizmag spoke to the lead researchers to find out more.

What are quantum computers for?

Quantum computers are a peculiar beast. Though the machines we've been building since the 50s have been aiming to be as deterministic and reliable as possible so a certain input will always result in the same output in a quantum computer, this dynamic is turned on its head, and predictability is sacrificed for (sometimes) incredible speedups.

A quantum bit, or qubit, has two awesome and confusing properties. First, it can set itself to both 0 and 1 at the same time. And second, it can commune (or entangle) with other qubits to compound this ability. This means five entangled qubits can store and process as much information as 32 (two to the power of five) classical bits; 10 qubits can do as much as 1,000 classical bits; and 300 fully entangled qubits can manipulate as many classical bits of information as there are atoms in the Universe.

You might think this would lead to much faster number-crunching over a regular computer – and you'd be right, to a point. A quantum computer can perform any operation a classical computer can, but its exponential speedups only take effect when a quantum algorithm can process data in a massively parallel fashion, such as searching through a very large database, virtually designing a new drug by choosing among quadrillions of possible combinations, or simulating the behavior of every single atom in your right toe. However, if the bulk of operations has to be performed in a sequential order, flowchart-style, then no real quantum speedups are possible.

The downside to these significant speedups is that due to quantum effects, the results returned by a quantum algorithm are not deterministic. That is, even in the best of cases, a quantum computer is never guaranteed to return the correct result.

This usually means that a quantum algorithm must be run several times in succession to confirm that the solution is correct. So, in practice, classical computers will probably be faster and more practical than quantum computers for day-to-day operations, and quantum computers will only come in useful where massive parallelism is involved. When they are let loose, though, their speed will be spectacular.

Quantum CMOS

Most of the prototype quantum computers developed so far feature a limited number of entangled qubits made from exotic and expensive materials like cesium or diamonds and which, in order to reduce external interference, need to be nearly frozen at temperatures just a few thousandths of a degree above absolute zero.

Researchers at UNSW are focusing on the potentially revolutionary approach of building quantum computers out of silicon
Researchers at UNSW are focusing on the potentially revolutionary approach of building quantum computers out of silicon

However, researchers at UNSW are focusing on the potentially revolutionary approach of building quantum computers out of silicon, a material that is cheap, well-known by the industry, and which could ultimately pave the way for quantum computers with not 300 but thousands, even millions of fully entangled qubits.

Last year, UNSW scientists were able to create single "CMOS type" qubits that leveraged current transistor technology and silicon-28, a very common isotope of silicon, to achieve a very high fidelity of 99.6 percent for quantum operations. Now, the researchers have built on this to create what's known as a CNOT quantum logic gate. Together with a single controllable qubit, this is the basic building block of a quantum computer, and paves the way to quantum chips that can perform just about any operation.

The gate is controlled through an external voltage and microwave radiation
The gate is controlled through an external voltage and microwave radiation

The scientists built this logic gate by taking two standard transistors, next to each other, and reconfiguring them so they would only hold a single electron each. The spin of the electron sets a code of 0 or 1, and an external current and microwave field control the qubits and make them interact as needed.

"A CNOT gate is a [...] two-qubit gate [that] flips the state of the target qubit depending on the state of the control qubit," lead author of the paper Menno Veldhorst told Gizmag. "In our case, the target qubit flips its spin if the control qubit is pointing down. If the control qubit is pointing up, the target qubit will remain in the same state.

"This two-qubit gate is most essential for a quantum computer and together with single qubit operations, which we have already demonstrated with very high fidelity, provides what is called a universal gate set. This means that any gate set can be constructed out of [it]."

Although their quantum computers wouldn't work at room temperature, this approach lets the researchers operate their device at approximately 1 Kelvin (-272° C, -458° F). That may not seem like much of an improvement over previous designs, but, the researchers told us, recent advances in cooling technology have resulted in fridges that can easily be operated at these temperatures.

Applications

The technique could scale up to hold thousands, even millions of qubits on a single chip
The technique could scale up to hold thousands, even millions of qubits on a single chip

The real power of this breakthrough is not in a slightly higher operational temperature, but in the fact that these basic building blocks of quantum computers were built by doing simple modifications to current-generation silicon transistors. The researchers say they have worked out a way to extend this technique to a much larger number of qubits, even numbering in the thousands of millions, all reported to be fully entangled.

"Our team is looking for industrial partners to construct a chip that would contain between tens and hundreds of qubits, and which uses the silicon-CMOS technology used today for most computer processor chips," lead researcher Andrew Dzurak told us. "This prototype manufacture would be done in a Si-CMOS foundry with wafer-scale manufacture, so that we can demonstrate a manufacturing process that can be scaled up to the thousands or millions of qubits.

"I believe that a Si-CMOS qubit prototype containing between tens and hundreds of qubits could be made within five years, provided we have the right level of investment and the right industry partners. Our main aim is to develop a prototype that can demonstrate that it is possible to go all the way with 'Quantum CMOS' and make a full-scale quantum processor. That final stage is likely to take 10-20 years."

Such a powerful quantum computer would have major implications for the finance, data security, and health industry. But perhaps one of the most interesting applications of all, and the one advanced by Richard Feynman decades ago as he first proposed the idea of a quantum computer, would be to conduct virtual experiments simulating the behavior of atoms and particles in unusual conditions, such as at the very high energies we can only recreate in the Large Hadron Collider, without actually performing the experiment.

The advance was published today in the journal Nature. Dzurak and Veldhorst further comment on the implications of this breakthrough in the video below.

Source: UNSW

Crucial hurdle overcome for quantum computing

7 comments
Joseph Mertens
Imagination for machines if they can achive multipul answers that may or may not be correct then linked to standard computing it would be like the two hemosphers of the human brain thinking about it is just WOW!
gizmagister
Contrary to the hype given in the article, it apparently would not be possible with this 0.996 level of fidelity to do useful work with a QPU (Quantum Processing Unit) having more than 172 qubits, because 0.996^172 is just over 50% ... 0.50188730306658538551266787020621 and thus, that QPU could process up to 2^172 = 5.9863107065073783529622930748059e+51 possibilities in a single operation, but with a very low confidence in the results. To be confident that it would be correct 2/3 of the time, the number of qubits per QPU would have to be reduced to 101: 0.996^101 = 0.66710344098755554808103067686113 which then means it could handle "only" 2^101 = 2.535301200456458802993406410752e+30 possibilities in a single operation. Very impressive, but even the old 128-bit encryption would still be secure until/unless that fidelity factor can be raised.
DonGateley
So much for cryptography as we know it. Only quantum encryption methods can evade the power of this and that's not suitable for home use. Yet.
Jayna Sheats
While this sort of research is very much at the pinnacle of value and right where academia should be, don't expect to see it in common use in your lifetime. The 1K operating temperature is not even the biggest culprit: how exactly did they "reconfigure" the transistors "so they would only hold a single electron each"? The electrodes have to be of the order of 3 nm with a 1 nm separation. Certainly doable in the lab; not so easy on the "millions and millions" scale. It will happen, but multiply the time estimates by at least 2. (and with all due respect to the author, don't expect to keep track of all the atoms in your toe...) But I agree with Joseph Mertens comment above (or below?) mine: the future of computing is in using analog (neural network-type) processes to get approximate answers to complex optimization problems, and then using digital (von Neumann-type) computers to finish the job.
quax
@DonGateley Your calculation assume no EEC but this wouldn't make sense, quantum error correction is key for any gate based quantum chip. https://en.wikipedia.org/wiki/Quantum_error_correction Literally thousands of papers have been published on this topic. For instance for another architecture the surface code error correction scheme only requires 99% gate fidelity to allow for scale out: http://www.nature.com/nature/journal/v508/n7497/full/nature13171.html As to the temp the D-Wave machines already operate on this level.
charizzardd
pretty mind-blowing piece. The advancements just keep on coming- though I don't think anyone's mind could even comprehend what sort of problems we would be solving with 2^1000 or 2^1000000000 or more entangled qubits. That amount of parallel processing is literally unimaginable. @Jayna_Sheats I think it is worth noting that current mass wafer production lithography is down to about 10nm I believe. MY brother works on the machines and I am pretty sure they are getting close to single digit layers- though this is nearing the limit of current technology- I think 1-3nm is very possible within the 10 years or so discussed in the article.
MichaelCharlton
Lego Star Wars would rock on a quantum computer!