Saturday, March 10, 2012

Breakthrough Toward Quantum Computing

U.Va.'s Pfister Accomplishes Breakthrough Toward Quantum Computing


July 15, 2011 — A sort of Holy Grail for physicists and information scientists is the quantum computer.

Such a computer, operating on the highly complex principles of quantum mechanics, would be capable of performing specific calculations with capabilities far beyond even the most advanced modern supercomputers. It could be used for breaking computer security codes as well as for incredibly detailed, data-heavy simulations of quantum systems.

 Breakthrough Toward Quantum Computing
 Breakthrough Toward Quantum Computing

It could be used for applying precise principles of physics to understanding the minute details of the interactions of molecules in biological systems. It could also help physicists unravel some of the biggest mysteries of the workings of the universe by providing a way to possibly test quantum mechanics.

Such a computer exists in theory, but it does not exist in practicality – yet – as it would need to operate with circuitry at the scale of single atoms, which is still a daunting challenge, even to state-of-the-art experimental quantum science. To build a quantum computer, one needs to create and precisely control individual quantum memory units, called qubits, for information processing.

Qubits are similar to the regular memory "bits" in current digital computers, but far more fragile, as they are microscopic constituents of matter and extremely difficult to separate from their environment. The challenge is to increase the number of qubits to a practical-size quantum register. In particular, qubits need to be created into sets with precise, nonlocal physical correlations, called entangled states.

Olivier Pfister, a professor of physics in the University of Virginia's College of Arts & Sciences, has just published findings in the journal Physical Review Letters demonstrating a breakthrough in the creation of massive numbers of entangled qubits, more precisely a multilevel variant thereof called Qmodes.

Entanglement dwells outside our day-to-day experience; imagine that two people, each tossing a coin on their own and keeping a record of the results, compared this data after a few coin tosses and found that they always had identical outcomes, even though each result, heads or tails, would still occur randomly from one toss to the next. Such correlations are now routinely observed between quantum systems in physics labs and form the operating core of a quantum computing processor.

Pfister and researchers in his lab used sophisticated lasers to engineer 15 groups of four entangled Qmodes each, for a total of 60 measurable Qmodes, the most ever created. They believe they may have created as many as 150 groups, or 600 Qmodes, but could measure only 60 with the techniques they used.

Each Qmode is a sharply defined color of the electromagnetic field. In lieu of a coin toss measurement, the Qmode measurement outcomes are the number of quantum particles of light (photons) present in the field. Hundreds to thousands of Qmodes would be needed to create a quantum computer, depending on the task.

"With this result, we hope to move from this multitude of small-size quantum processors to a single, massively entangled quantum processor, a prerequisite for any quantum computer," Pfister said.

Pfister's group used an exotic laser called an optical parametric oscillator, which emitted entangled quantum electromagnetic fields (the Qmodes) over a rainbow of equally spaced colors called an "optical frequency comb."

Ultrastable lasers emitting over an optical frequency comb have revolutionized the science of precision measurements, called metrology, and paved the way to multiple technological breakthroughs. The inventors of the optical frequency comb, physicists John Hall of the National Institute of Standards and Technology and Theodor Hänsch of the Max-Planck Institute for Quantum Optics, were awarded half of the 2005 Nobel Prize in Physics for their achievement. (The other half went to Roy Glauber, one of the founding fathers of quantum optics.)

With their experiments, Pfister's group completed a major step to confirm an earlier theoretical proof by Pfister and his collaborators that the quantum version of the optical frequency comb could be used to create a quantum computer.

"Some mathematical problems, such as factoring integers and solving the Schrödinger equation to model quantum physical systems, can be extremely hard to solve," Pfister said. "In some cases the difficulty is exponential, meaning that computation time doubles for every finite increase of the size of the integer, or of the system."

However, he said, this only holds for classical computing. Quantum computing was discovered to hold the revolutionary promise of exponentially speeding up such tasks, thereby making them easy computations.

"This would have tremendous societal implications, such as making current data encryption methods obsolete, and also major scientific implications, by dramatically opening up the possibilities of first-principle calculations to extremely complex systems such as biological molecules," Pfister said.

Quantum computing can be summarized by qubit processing; computing with single elementary systems, such as atoms or monochromatic light waves, as memory units. Because qubits are inherently quantum systems, they obey the laws of quantum physics, which are more subtle than those of classical physics.

Randomness plays a greater role in quantum evolution than in classical evolution, Pfister said. Randomness is not an obstacle to deterministic predictions and control of quantum systems, but it does limit the way information can be encoded and read from qubits.

"As quantum information became better understood, these limits were circumvented by the use of entanglement, deterministic quantum correlations between systems that behave randomly, individually," he said. "As far as we know, entanglement is actually the 'engine' of the exponential speed up in quantum computing."

News Release Source : https://news.virginia.edu/content/uvas-pfister-accomplishes-breakthrough-toward-quantum-computing 

Monday, March 5, 2012

Advances in Device Performance for Quantum Computing

IBM Research Advances Device Performance for Quantum Computing

- Latest results bring device performance near the minimum requirements for implementation of a practical quantum computer.

- Scaling up to hundreds or thousands of quantum bits becomes a possibility.

YORKTOWN HEIGHTS, N.Y., Feb. 28, 2012 /PRNewswire/ -- Scientists at IBM Research (NYSE: IBM) / (#ibmresearch) have achieved major advances in quantum computing device performance that may accelerate the realization of a practical, full-scale quantum computer. For specific applications, quantum computing, which exploits the underlying quantum mechanical behavior of matter, has the potential to deliver computational power that is unrivaled by any supercomputer today.


IBM Research Advances Device Performance for Quantum Computing
IBM Research Advances Device Performance for Quantum Computing

Using a variety of techniques in the IBM labs, scientists have established three new records for reducing errors in elementary computations and retaining the integrity of quantum mechanical properties in quantum bits (qubits) – the basic units that carry information within quantum computing. IBM has chosen to employ superconducting qubits, which use established microfabrication techniques developed for silicon technology, providing the potential to one day scale up to and manufacture thousands or millions of qubits.

The Possibilities of Quantum Computing

The special properties of qubits will allow quantum computers to work on millions of computations at once, while desktop PCs can typically handle minimal simultaneous computations. For example, a single 250-qubit state contains more bits of information than there are atoms in the universe.

These properties will have wide-spread implications foremost for the field of data encryption where quantum computers could factor very large numbers like those used to decode and encode sensitive information.

"The quantum computing work we are doing shows it is no longer just a brute force physics experiment. It's time to start creating systems based on this science that will take computing to a new frontier," says IBM scientist Matthias Steffen, manager of the IBM Research team that's focused on developing quantum computing systems to a point where it can be applied to real-world problems.

Other potential applications for quantum computing may include searching databases of unstructured information, performing a range of optimization tasks and solving previously unsolvable mathematical problems.

How Quantum Computing Works

The most basic piece of information that a typical computer understands is a bit. Much like a light that can be switched on or off, a bit can have only one of two values: "1" or "0". For qubits, they can hold a value of "1" or "0" as well as both values at the same time. Described as superposition, this is what allows quantum computers to perform millions of calculations at once.

One of the great challenges for scientists seeking to harness the power of quantum computing is controlling or removing quantum decoherence – the creation of errors in calculations caused by interference from factors such as heat, electromagnetic radiation, and materials defects. To deal with this problem, scientists have been experimenting for years to discover ways of reducing the number of errors and of lengthening the time periods over which the qubits retain their quantum mechanical properties. When this time is sufficiently long, error correction schemes become effective making it possible to perform long and complex calculations.

There are many viable systems that can potentially lead to a functional quantum computer. IBM is focusing on using superconducting qubits that will allow a more facile transition to scale up and manufacturing.

IBM has recently been experimenting with a unique "three dimensional" superconducting qubit (3D qubit), an approach that was initiated at Yale University. Among the results, the IBM team has used a 3D qubit to extend the amount of time that the qubits retain their quantum states up to 100 microseconds – an improvement of 2 to 4 times upon previously reported records. This value reaches just past the minimum threshold to enable effective error correction schemes and suggests that scientists can begin to focus on broader engineering aspects for scalability.

In separate experiments, the group at IBM also demonstrated a more traditional "two-dimensional" qubit (2D qubit) device and implemented a two-qubit logic operation – a controlled-NOT (CNOT) operation, which is a fundamental building block of a larger quantum computing system. Their operation showed a 95 percent success rate, enabled in part due to the long coherence time of nearly 10 microseconds. These numbers are on the cusp of effective error correction schemes and greatly facilitate future multi-qubit experiments.

IBM and Quantum Computing Leadership

The implementation of a practical quantum computer poses tremendous scientific and technological challenges, but all results taken together paint an optimistic picture of rapid progress in that direction.

Core device technology and performance metrics at IBM have undergone a series of amazing advancements by a factor of 100 to 1,000 times since the middle of 2009, culminating in the recent results that are very close to the minimum requirements for a full-scale quantum computing system as determined by the world-wide research community. In these advances, IBM stresses the importance and value of the ongoing exchange of information and learning with the quantum computing research community as well as direct university and industrial collaborations.

"The superconducting qubit research led by the IBM team has been progressing in a very focused way on the road to a reliable, scalable quantum computer. The device performance that they have now reported brings them nearly to the tipping point; we can now see the building blocks that will be used to prove that error correction can be effective, and that reliable logical qubits can be realized," observes David DiVincenzo, professor at the Institute of Quantum Information, Aachen University and Forschungszentrum Juelich.

Based on this progress, optimism about superconducting qubits and the possibilities for a future quantum computer are rapidly growing. While most of the work in the field to date has focused on improvements in device performance, efforts in the community now must now include systems integration aspects, such as assessing the classical information processing demands for error correction, I/O issues, feasibility, and costs with scaling.

IBM envisions a practical quantum computing system as including a classical system intimately connected to the quantum computing hardware. Expertise in communications and packaging technology will be essential at and beyond the level presently practiced in the development of today's most sophisticated digital computers.


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SOURCE IBM

News Release Source : http://www.prnewswire.com/news-releases/ibm-research-advances-device-performance-for-quantum-computing-140670433.html