Thursday, July 18, 2013

Spintronics Approach Enables New Quantum Technologies

Spintronics Approach Enables New Quantum Technologies

by Liyan

A team of researchers including members of the University of Chicago's Institute for Molecular Engineering highlight the power of emerging quantum technologies in two recent papers published in the Proceedings of the National Academy of Sciences (PNAS). These technologies exploit quantum mechanics, the physics that dominates the atomic world, to perform disparate tasks such as nanoscale temperature measurement and processing quantum information with lasers.

[caption id="attachment_174" align="aligncenter" width="450"]Spintronics Approach Enables New Quantum Technologies Spintronics Approach Enables New Quantum Technologies[/caption]

The two papers are both based on the manipulation of the same material, an atomic-scale defect in diamond known as the nitrogen vacancy center. Both works also leverage the intrinsic "spin" of this defect for the applications in temperature measurement and information processing. This spintronics approach involves understanding and manipulating the spin of electronics for technological advancement.

"These studies build on research efforts undertaken over the last 20 years to isolate and control single electronic spins in the solid state," said David Awschalom, a principle investigator on both papers and a Liew Family Professor in Molecular Engineering at UChicago. "Much of the initial motivation for working in this field was driven by the desire to make new computing technologies based on the principles of quantum physics. In recent years the research focus has broadened as we've come to appreciate that these same principles could enable a new generation of nanoscale sensors."

Controlling qubits with light

In one PNAS paper posted April 22 and published in the May 7 print edition, Awschalom and six co-authors at the University of California, Santa Barbara and the University of Konstanz describe a technique that offers new routes toward the eventual creation of quantum computers, which would possess far more capability than modern classical computers.

In this application, Awschalom's team has developed protocols to fully control the quantum state of the defect with light instead of electronics. The quantum state of interest in this defect is its electronic spin, which acts as quantum bit, or qubit, the basic unit of a quantum computer. In classical computers, bits of information exist in one of only two states: zero or one. In the quantum mechanical realm, objects can exist in multiple states at once, enabling more complex processing.

This all-optical scheme for controlling qubits in semiconductors "obviates the need to have microwave circuits or electronic networks," Awschalom said. "Instead, everything can be done solely with photons, with light."

As a fully optical method, it shows promise as a more scalable approach to qubit control. In addition, this scheme is more versatile than conventional methods and could be used to explore quantum systems in a broad range of materials that might otherwise be difficult to develop as quantum devices.

Single spin thermometers

The quantum thermometer application, reported in a PNAS contribution posted online May 6 and published in the May 21 print edition, represents a new direction for the manipulation of quantum states, which is more commonly linked to computing, communications, and encryption. In recent years, defect spins had also emerged as promising candidates for nanoscale sensing of magnetic and electric fields at room temperature. With thermometry now added to the list, Awschalom foresees the possibility of developing a multifunctional probe based on quantum physics.

"With the same sensor you could measure magnetic fields, electric fields and now temperature, all with the same probe in the same place at approximately the same time," he said. "Perhaps most importantly, since the sensor is an atomic-scale defect that could be contained within nanometer-scale particles of diamond, you can imagine using this system as a thermometer in challenging environments such as living cells or microfluidic circuits."

The key aspect of this innovation is the development of control techniques for manipulating the spin that make it a much more sensitive probe of temperature shifts. "We've been exploring the potential of defect spins for thermometry for the past few years," said David Toyli, a graduate student in physics at UCSB and lead author of the temperature sensing work.

"This latest work is exciting because we've succeeded in adapting techniques used for stabilizing quantum information to measuring temperature-dependent changes in the quantum states. These techniques minimize the effects of environmental noise and allow us to make much more sensitive temperature measurements."

The team of researchers, also including Slava Dobrovitski of the Department of Energy's Ames Laboratory in Iowa, conducted experiments to determine the temperature range over which the spins could operate as a useful thermometer. It turns out that the particle spins can operate quite well at a wide temperature range, from room temperature to 500 degrees Kelvin (approximately 70 to 400 degrees Fahrenheit).

The chemical properties of a diamond-based thermometer also support the idea that this system could be useful for measuring temperature gradients in biological systems, such as the interior of living cells, Awschalom said. But the initial studies suggest the method is so flexible that it probably lends itself to uses yet to be imagined. "Like any new technology development, the exciting thing is what people will do with this now."

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Monday, July 15, 2013

USC Study Validates Large-Scale Quantum Chip

USC (University of Southern California) Study Validates Large-Scale Quantum Chip   

by Softboook

In a newly published study, researchers from USC confirmed that quantum effects are indeed at play in the first commercial quantum optimization processor.

Scientists demonstrated that the D-Wave processor housed at the USC-Lockheed Martin Quantum Computing Center behaves in a manner that indicates that quantum mechanics has a functional role in the way it works. The demonstration involved a small subset of the chip's 128 qubits.

[caption id="attachment_170" align="aligncenter" width="450"]USC Study Validates Large-Scale Quantum Chip USC Study Validates Large-Scale Quantum Chip[/caption]

In other words, the device appears to be operating as a quantum processor - something that scientists had hoped for but have needed extensive testing to verify.

The quantum processor was purchased from Canadian manufacturer D-Wave nearly two years ago by Lockheed Martin and housed at the Information Sciences Institute (ISI) based at the USC Viterbi School of Engineering. As the first of its kind, the task for scientists putting it through its paces was to determine whether the quantum computer was operating as hoped.

"Using a specific test problem involving eight qubits, we have verified that the D-Wave processor performs optimization calculations [that is, finds lowest-energy solutions] using a procedure that is consistent with quantum annealing and is inconsistent with the predictions of classical annealing," said Daniel Lidar, scientific director of the Quantum Computing Center and one of the researchers on the team. Lidar holds joint appointments at USC Viterbi and the USC Dornsife College of Letters, Arts and Sciences.
Quantum annealing is a method of solving optimization problems using quantum mechanics - at a large enough scale, potentially much faster than a traditional processor can.

Research institutions throughout the world build and use quantum processors but most only have a few quantum bits, or qubits.

Qubits have the capability of encoding the two digits of one and zero at the same time, as opposed to traditional bits, which can encode distinctly either a one or a zero. This property, called superposition, along with the ability of quantum states to "tunnel" through energy barriers, are hoped to play a role in helping future generations of the D-Wave processor to ultimately perform optimization calculations much faster than traditional processors.

With 108 functional qubits, the D-Wave processor at USC inspired hopes for a significant advance in the field of quantum computing when it was installed in October 2011 - provided it worked as a quantum information processor. Quantum processors can fall victim to a phenomenon called decoherence, which stifles their ability to behave in a quantum fashion.

The USC team's research showed that the chip, in fact, performed largely as hoped, demonstrating the potential for quantum optimization on a larger-than-ever scale.

"Our work seems to show that, from a purely physical point of view, quantum effects play a functional role in information processing in the D-Wave processor," said Sergio Boixo, first author of the research paper, who conducted the research while he was a computer scientist at ISI and research assistant professor at USC Viterbi.

Boixo and Lidar collaborated with Tameem Albash, postdoctoral research associate in physics at USC Dornsife; Federico Spedalieri, computer scientist at ISI; and Nicholas Chancellor, a recent physics graduate at USC Dornsife

The news comes just two months after the Quantum Computing Center's original D-Wave processor - known commercially as the Rainier chip - was upgraded to a new 512-qubit Vesuvius chip. The computing center, which includes a magnetically shielded box that is kept frigid (near absolute zero) to protect the computer against decoherence, was designed to be upgradable to keep up with the latest developments in the field.

The new Vesuvius chip at USC is currently the only one in operation outside of D-Wave. A second such chip, owned by Google and housed at NASA's Ames Research Center in Moffett Field, Calif., is expected to become operational later this year.

Next, the USC team will take the Vesuvius chip for a test drive, putting it through the same paces as the Rainier chip.

The research was supported by the Lockheed Martin Corp., the U.S. Army Research Office (grant number W911NF-12-1-0523), the National Science Foundation (grant number CHM-1037992), and the Army Research Office Multidisciplinary University Research Initiative

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Friday, July 12, 2013

Rubidium Atoms Clouds use for Create Quantum Computer Memory

Studying Clouds of Rubidium Atoms Aims to Create Memory for Quantum Computers   

by Ivy

Talk about storing data in the cloud. Scientists at the Joint Quantum Institute (JQI) of the National Institute of Standards and Technology (NIST) and the University of Maryland have taken this to a whole new level by demonstrating that they can store visual images within quite an ethereal memory device - a thin vapor of rubidium atoms. The effort may prove helpful in creating memory for quantum computers.

[caption id="attachment_165" align="aligncenter" width="450"]Rubidium Atoms Clouds use for Create Quantum Computer Memory Rubidium Atoms Clouds use for Create Quantum Computer Memory[/caption]

Their work builds on an approach developed at the Australian National University, where scientists showed that a rubidium vapor could be manipulated in interesting ways using magnetic fields and lasers. The vapor is contained in a small tube and magnetized, and a laser pulse made up of multiple light frequencies is fired through the tube. The energy level of each rubidium atom changes depending on which frequency strikes it, and these changes within the vapor become a sort of fingerprint of the pulse's characteristics. If the field's orientation is flipped, a second pulse fired through the vapor takes on the exact characteristics of the first pulse - in essence, a readout of the fingerprint.

"With our paper, we've taken this same idea and applied it to storing an image - basically moving up from storing a single 'pixel' of light information to about a hundred," says Paul Lett, a physicist with JQI and NIST's Quantum Measurement Division. "By modifying their technique, we have been able to store a simple image in the vapor and extract pieces of it at different times."

It's a dramatic increase in the amount of information that can be stored and manipulated with this approach. But because atoms in a vapor are always in motion, the image can only be stored for about 10 milliseconds, and in any case the modifications the team made to the original technique introduce too much noise into the laser signal to make the improvements practically useful. So, should the term vaporware be applied here after all? Not quite, says Lett - because the whole point of the effort was not to build a device for market, but to learn more about how to create memory for next-generation quantum computers.

"What we've done here is store an image using classical physics. However, the ultimate goal is to store quantum information, which a quantum computer will need," he says. "Measuring what the rubidium atoms do as we manipulate them is teaching us how we might use them as quantum bits and what problems those bits might present. This way, when someone builds a solid-state system for a finished computer, we'll know how to handle them more effectively."

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Sunday, July 7, 2013

Small step for quantum computing, giant leap for qubits

Sci-tech information: Small step for quantum computing, giant leap for qubits

by Lynn@ghq

Australian researchers have taken the next step in an incremental journey to developing the first large-scale quantum computer.

The world's potentially fastest computer system will be made up of tricky little building blocks called quantum bits, or qubits -- consisting of a single electron bound to a phosphorus atom.

[caption id="attachment_159" align="aligncenter" width="443"]Small step for quantum computing, giant leap for qubits Small step for quantum computing, giant leap for qubits[/caption]

Information is stored in the spin of each qubit electron, which can be moving in two directions at once. The qubits need to be placed with atomic precision, only a few nanometres apart, for the system to work.

Scientists have previously encountered difficulties in making qubits, placing them so close together, distinguishing individual qubits from their neighbours, and controlling their spin independently.

University of New South Wales (UNSW) researchers, who prefer to work with qubits in a silicon chip, have proposed a solution to each of these challenges, working with Sandia National Laboratories in New Mexico.

"It is a daunting challenge to rotate the spin of each qubit individually," said Holger Bch, lead author of the new study.

"But if each electron is hosted by a different number of phosphorus atoms, then the qubits will respond to different electromagnetic fields -- and each qubit can be distinguished from the others around it," he said.

The researchers say they are now one step closer to realising a practical, large-scale quantum computer -- the supercomputer of the future.

"This first demonstration that we can maintain long spin lifetimes of electrons on multi-donor systems is very powerful. It offers a new method for addressing individual qubits," said Michelle Simmons, UNSW Australian Centre of Excellence for Quantum Computation and Communication Technology director.

"This is an elegant and satisfying piece of work," she said.

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Monday, July 1, 2013

Scientists Found a New Technique to Store Quantum States

Scientists Found a New Technique to Store Quantum States

by Ivy

Researchers at the University of Sydney and Dartmouth College have developed a new way to design quantum memory, bringing quantum computers a step closer to reality. The results appear in the journal Nature Communications.

[caption id="attachment_150" align="aligncenter" width="450"]Scientists Found a New Technique to Store Quantum States Scientists Found a New Technique to Store Quantum States[/caption]

Quantum computing may revolutionize information processing, by providing a means to solve problems too complex for traditional computers, with applications in code breaking, materials science and physics. But figuring out how to engineer such a machine, including vital subsystems like quantum memory, remains elusive.

In the worldwide drive to build a useful quantum computer, the simple-sounding task of effectively preserving quantum information in a quantum memory is a major challenge. The same physics that makes quantum computers potentially powerful also makes them likely to experience errors, even when quantum information is just being stored idly in memory. Keeping quantum information alive  for long periods, while remaining accessible to the computer, is a key problem.

The Sydney-Dartmouth team  results demonstrate a path to what is considered a holy grail in the research community: storing quantum states with high fidelity for exceptionally long times, even hours according to their calculations. Today, most quantum states survive for tiny fractions of a second.

"Our new approach allows us to simultaneously achieve very low error rates and very long storage times, said co-senior author Dr. Michael J. Biercuk,  director of the Quantum Control Laboratory in the University of Sydney  School of Physics and ARC Center for Engineered Quantum Systems. But our work also addresses a vital practical issue - providing small access latencies, enabling on-demand retrieval with only a short time lag to extract stored information.

The team  new method is based on techniques to build in error resilience at the level of the quantum memory hardware, said Dartmouth Physics Professor Lorenza Viola, a co-senior author who is leading the quantum control theory effort and the Quantum Information Initiative at Dartmouth.

"Weve now developed the quantum firmware  appropriate to control a practically useful quantum memory, added Biercuk. But vitally, we've shown that with our approach a user may guarantee that error never grows beyond a certain level even after very long times, so long as certain constraints are met. The conditions we establish for the memory to function as advertised then inform system engineers how they can construct an efficient and effective quantum memory. Our method even incorporates a wide variety of realistic experimental imperfections.

The study was supported by the U.S. Army Research Office, National Science Foundation, Intelligence Advanced Research Projects Activity, and ARC Centre for Engineered Quantum Systems.

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