Scientists have built a functional 'hybrid' logic gate for use in quantum computers

Scientists have built a functional 'hybrid' logic gate for use in quantum computers Logic Gate, Moore's Law, Quantum Computing, U of Oxford, NIST, U of Washington, Calcium,

An ion trap used in NIST quantum computing experiments. Credit: Blakestad/NIST

Here's how to solve the problem of quantum memory.

As conventional computers draw ever closer to their theoretical limit, the race is on to build a machine that can truly harness the unprecedented processing power of quantum computing. And now two research teams have independently demonstrated how entangling atoms from different elements can address the problem of quantum memory errors while functioning within a logic gate framework, and also pass the all-important test of true entanglement. 

"Hybrid quantum computers allow the unique advantages of different types of quantum systems to be exploited together in a single platform," said lead author Ting Rei Tan. "Each ion species is unique, and certain ones are better suited for certain tasks such as memory storage, while others are more suited to provide interconnects for data transfer between remote systems."

In the computers we use today, data is processed and stored as binary bits, with each individual bit taking on a state of either 0 or 1. Because these states are set, there’s a finite amount of information that can ultimately be processed, and we’re quickly approaching the point where this isn’t going to be enough.

Quantum computers, on the other hand, store data as qubits, which can be in the state of 0 or 1, or can take on another state called superposition, which allows them to be both 0 and 1 at the same time. If we can figure out how to build a machine that integrates this phenomenon with data-processing capabilities, we’re looking at computers that are hundreds of millions of times faster than the super computers of today.

The qubits used in this set-up are actually atomic ions (atoms with an electron removed), and their states are determined by their spin - spin up is 1, spin down is 0. Each atomic ion is paired off, and if the control ion takes on the state of superposition, it will become entangled with its partner, so anything you do to one ion will affect the other.

This can pose problems, particularly when it comes to memory, and there’s no point storing and processing information if you can’t reliably retain it. If you’ve got an entire system built on pairs of the same atomic ions, you leave yourself open to constant errors, because if one ion is affected by a malfunction, this will also affect its partner. At the same time, using the same atomic ions in a pair makes it very difficult for them to perform separate functions.

So researchers from the University of Oxford in the UK, and a second team from the National Institute of Standards and Technology (NIST) and the University of Washington, have figured out which combinations of different elements can function together as pairs in a quantum set-up.

"Each trapped ion is used to represent one ‘quantum bit’ of information. The quantum states of the ions are controlled with laser pulses of precise frequency and duration," says one of the researchers, David Lucas from the University of Oxford. "Two different species of ion are needed in the computer: 

• one to store information, a 'memory qubit', and 
• one to link different parts of the computer together via photons, an 'interface qubit'."

While the Oxford team achieved this using two different isotopes of calcium (the abundant isotope calcium-40 and the rare isotope calcium-43), the second team went even further by pairing up entirely different atoms - magnesium and beryllium. Each one is sensitive to a different wavelength of light, which means zapping one with a laser pulse to control its function won’t affect its partner.

The teams them went on to demonstrate for the first time that these pairs could have their 0,1, or superposition states controlled by two different types of logic gates, called the CNOT gate and the SWAP gate. Logic gates are crucial components of any digital circuit, because they’re able to record two input values and provide a new output based on programmed logic. 

"A CNOT gate flips the second (target) qubit if the first (control) qubit is a 1; if it is a 0, the target bit is unchanged," the NIST press release explains. "If the control qubit is in a superposition, the ions become entangled. A SWAP gate interchanges the qubit states, including superpositions."

The Oxford team demonstrated ion pairing in this set-up for about 60 seconds, while the NIST/Washington team managed to keep theirs entangled for 1.5 seconds. That doesn’t sound like much, but that's relatively stable when it comes to qubits.

"Both teams confirm that their two atoms are entangled with a very high probability; 0.998 for one, 0.979 for the other (of a maximum of one)," John Timmer reports for Ars Technica. "The NIST team even showed that it could track the beryllium atom as it changed state by observing the state of the magnesium atom."

Further, both teams were able to successfully perform a Bell test by using the logic gate to entangle the pairs of different-species ions, and then manipulating and measuring them independently.

"[W]e show that quantum logic gates between different isotopic species are possible, can be driven by a relatively simple laser system, and can work with precision beyond the so-called 'fault-tolerant threshold' precision of approximately 99 percent - the precision necessary to implement the techniques of quantum error correction, without which a quantum computer of useful size cannot be built," said Lucas in an Oxford press release.

Of course, we don't have proper quantum computers to actually test these components in the context of a functioning system - that will have to be the next step, and international teams of scientists and engineers are racing to get us there. We can't wait to see it when they do.

The papers have been published in Nature here and here.

ORIGINAL: ScienceAlert

BEC CREW

18 DEC 2015

IBM Announces Computer Chips More Powerful Than Any in Existence

A wafer made up of seven-nanometer chips. IBM said it made the advance by using silicon-germanium instead of pure silicon. CreditDarryl Bautista/IBM

IBM said on Thursday that it had made working versions of ultradense computer chips, with roughly four times the capacity of today’s most powerful chips.

The announcement, made on behalf of an international consortium led by IBM, the giant computer company, is part of an effort to manufacture the most advanced computer chips in New York’s Hudson Valley, where IBM is investing $3 billion in a private-public partnership with New York State, GlobalFoundries, Samsung and equipment vendors.

The development lifts a bit of the cloud that has fallen over the semiconductor industry, which has struggled to maintain its legendary pace of doubling transistor density every two years.

Intel, which for decades has been the industry leader, has faced technical challenges in recent years. Moreover, technologists have begun to question whether the longstanding pace of chip improvement, known as Moore’s Law, would continue past the current 14-nanometer generation of chips.

Each generation of chip technology is defined by the minimum size of fundamental components that switch current at nanosecond intervals. Today the industry is making the commercial transition from what the industry generally describes as 14-nanometer manufacturing to 10-nanometer manufacturing.

Michael Liehr of the SUNY College of Nanoscale Science and Engineering, left, and Bala Haranand of IBM examine a wafer comprised of the new chips. They are not yet ready for commercial manufacturing. CreditDarryl Bautista/IBM

Each generation brings roughly a 50 percent reduction in the area required by a given amount of circuitry. IBM’s new chips, though still in a research phase, suggest that semiconductor technology will continue to shrink at least through 2018.

The company said on Thursday that it had working samples of chips with seven-nanometer transistors. It made the research advance by using silicon-germanium instead of pure silicon in key regions of the molecular-size switches.

The new material makes possible faster transistor switching and lower power requirements. The tiny size of these transistors suggests that further advances will require new materials and new manufacturing techniques.

As points of comparison to the size of the seven-nanometer transistors, a strand of DNA is about 2.5 nanometers in diameter and a red blood cell is roughly 7,500 nanometers in diameter. IBM said that would make it possible to build microprocessors with more than 20 billion transistors.

“I’m not surprised, because this is exactly what the road map predicted, but this is fantastic,” said Subhashish Mitra, director of the Robust Systems Group in the Electrical Engineering Department at Stanford University.

Even though IBM has shed much of its computer and semiconductor manufacturing capacity, the announcement indicates that the company remains interested in supporting the nation’s high technology manufacturing base.

“This puts IBM in the position of being a gentleman gambler as opposed to being a horse owner,” said Richard Doherty, president of Envisioneering, a Seaford, N.Y., consulting firm, referring to the fact that IBM’s chip manufacturing facility was acquired by GlobalFoundries effective last week.

IBM's seven-nanometer node transistors. A strand of DNA is about 2.5 nanometers in diameter and a red blood cell is roughly 7,500 nanometers in diameter. CreditIBM Research

“They still want to be in the race,” he added.

IBM now licenses the technology it is developing to a number of manufacturers and GlobalFoundries, owned by the Emirate of Abu Dhabi, to make chips for companies including Broadcom, Qualcomm and Advanced Micro Devices.

The semiconductor industry must now decide if IBM’s bet on silicon-germanium is the best way forward.

It must also grapple with the shift to using extreme ultraviolet, or EUV, light to etch patterns on chips at a resolution that approaches the diameter of individual atoms. In the past, Intel said it could see its way toward seven-nanometer manufacturing. But it has not said when that generation of chip making might arrive.

IBM also declined to speculate on when it might begin commercial manufacturing of this technology generation. This year, Taiwan Semiconductor Manufacturing Company said that it planned to begin pilot product of seven-nanometer chips in 2017. Unlike IBM, however, it has not demonstrated working chips to meet that goal.

It is uncertain whether the longer exposure times required by the new generation of EUV photolithographic stepper machines would make high-speed manufacturing operations impossible. Even the slightest vibration can undermine the precision of the optics necessary to etch lines of molecular thicknesses, and the semiconductor industry has been forced to build specialized stabilized buildings to try to isolate equipment from vibration.

An IBM official said that the consortium now sees a way to use EUV light in commercial manufacturing operations.

“EUV is another game changer,” said Mukesh Khare, vice president for semiconductor research at IBM. To date, he noted, the demonstration has taken place in a research lab, not in a manufacturing plant. Ultimately the goal is to create circuits that have been reduced in area by another 50 percent over the industry’s 10-nanometer technology generation scheduled to be introduced next year.

ORIGINAL: NYTimes

By JOHN MARKOFF

JULY 9, 2015