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Super-fast quantum computers are now a step closer to becoming a reality, thanks to a breakthrough by scientists.

Edinburgh and Manchester University researchers have created a molecular device which could act as a building block for super-fast computers.

They have created components that could be used to develop quantum computers, which can make intricate calculations faster than conventional machines.

The academics used molecular scale technology instead of silicon chips.

They achieved the breakthrough by combining tiny magnets with molecular machines that can shuttle between two locations without the use of external force.

The manoeuvrable magnets could one day be used as the basic component in quantum computers.

‘Major challenges’

Conventional computers work by storing information in the form of bits, which can represent information in binary code – either as zero or one.

Quantum computers will use quantum binary digits, or qubits, which are far more sophisticated as they are capable of representing not only zero and one, but a range of values simultaneously.

Their complexity will enable quantum computers to perform more quickly than conventional machines.

Professor David Leigh, of Edinburgh University’s school of chemistry, said: “This development brings super-fast, non-silicon based computing a step closer.

“The major challenges we face now are to bring many of these qubits together to build a device that could perform calculations, and to discover how to communicate between them.”

The study, by Edinburgh and Manchester university scientists and published in the journal Nature, was funded by the European Commission.

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The ability to exploit the extraordinary properties of quantum mechanics in novel applications, such as a new generation of super-fast computers, has come closer following recent progress with some of the remaining underlying mathematical problems. In particular, the operator theory used to describe interactions between particles at atomic scales or smaller where quantum mechanical properties are significant needs to be enhanced to deal with systems where digital information is processed or transmitted. In essence, the theory involves mathematical analysis based on Hilbert Spaces, which are extensions of the conventional three dimensional Euclidean geometry to cope with additional dimensions, as are required to describe quantum systems.

These challenges in mathematical analysis and prospects for imminent progress were discussed at a recent conference on operator theory and analysis organised by the European Science Foundation (ESF) in collaboration with the European Mathematical Society and the Mathematical Research and Conference Center in Bedlewo, Poland. The conference brought together some of the world’s leading mathematical physicists and quantum mechanics specialists to tackle the key fields relating to spectral theory, according to the conference’s co-chair Pavel Kurasov from the Lund Institute of Technology in Sweden. Among the participants were Uzy Smilansky, one of the leading authorities on quantum chaos, from the Weizmann Institute of Technology in Israel, and Vladimir Peller, specialist in pure mathematical analysis at Michigan State University in the US.

As Kurasov pointed out, a big challenge lies in extending current operator theory to describe and analyse quantum transport in wires, as will be needed for a new generation of quantum computers. Such computers will allow some calculations to be executed much more quickly in parallel by exploiting quantum coherence, whereby a processing element can represent digital bits in multiple states at once. There is also the prospect of exploiting another quantum mechanical property, quantum entanglement, for quantum cryptography where encryption key information can be transmitted with the ability to detect any attempt at tampering or eavesdropping, facilitating totally secure communication. In fact quantum cryptography has already been demonstrated over real telecommunications links and will be one of the first commercial applications based exclusively on quantum mechanics.

The operator theory required for quantum information processing and transmission is already well developed for what are known as self-adjoint operators, which are used to describe the different quantum states of an ideal system, but cannot be used for systems like a communications network where dissipation occurs. “So far only self-adjoint models have been considered, but in order to describe systems with dissipation even non-self-adjoint operators should be used,” said Kurasov. The aim set out at the ESF conference was to extend the theory to non self-adjoint operators, which can be used to analyse real systems. “These operators may be used to describe quantum transport in wires and waveguides and therefore will be used in design of the new generation of computers,” said Kurasov.”Physicists are doing experiments with such structures, but the theory is not developed yet.  An important question here is fitting of the parameters so that models will describe effects that may be observed in experiments.” This question was discussed during inspiring lecture by Boris Pavlov from Auckland University, New Zealand – world leading specialist in mathematical analysis who became interested in physical applications.

Intriguingly Kurasov hinted that a breakthrough was likely before the next ESF conference on the subject in two years time, on the problem of reconstructing the so called quantum graphs used to represent states and interactions of quantum systems from actual observations. This will play a vital role in constructing the intermediate components of a quantum computer needed to monitor its own state and provide output.

Kurasov noted that this ESF conference was one in a series on the operator analysis field organized every second year, with proceedings published regularly in a book series Operator Theory: Advances and Applications.

The ESF conference Operator Theory, Analysis and Mathematical Physics was held at the Mathematical Research and Conference Center, Będlewo in Poland in June 2008

For more information please click here.

From European Science Foundation

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BY DAN STOBER from Stanford Report

The promise of quantum computing is that it will dramatically outshine traditional computers in tackling certain key problems: searching large databases, factoring large numbers, creating uncrackable codes and simulating the atomic structure of materials.

A quantum step in that direction, if you’ll pardon the pun, has been taken by Stanford researchers who announced their success in a paper published in the journal Nature. Working in the Ginzton Laboratory, they’ve employed ultrafast lasers to set a new speed record for the time it takes to rotate the spin of an individual electron and confirm the spin’s new position.

Why does that matter? Existing computers, from laptops to supercomputers, see data as bits of information. Each bit can be either a zero or a one. But a quantum bit can be both zero and one at the same time, a situation known as a superposition state. This allows quantum computers to act like a massively parallel computer in some circumstances, solving problems that are almost impossible for classic computers to handle.

Quantum computing can be accomplished using a property of electrons known as “spin.” A single unit of quantum information is the qubit, and can be constructed from a single electron spin, which in this experiment was confined within a nano-sized semiconductor known as a quantum dot.

An electron spin may be described as up or down (a variation of the usual zero and one) and may be manipulated from one state to another. The faster these electrons can be switched, the more quickly numbers can be crunched in a quantum fashion, with its intrinsic advantages over traditional computing designs.

The qubit in the Stanford experiment was manipulated and measured about 100 times faster than with previous techniques, said one of the researchers, David Press, a graduate student in applied physics.

The experiments were conducted at a temperature of almost absolute zero, inside a strong magnetic field produced by a superconducting magnet. The researchers first hit the qubit with laser light of specific frequencies to define and measure the electron spin, all within a few nanoseconds. Then they rotated the spin with polarized light pulses in a few tens of picoseconds (a picosecond is one trillionth of a second). Finally, the spin state was read out with yet another optical pulse.

Similar experiments have been done before, but with radio-frequency pulses, which are slower than laser-light pulses. “The optics were quite tricky,” Press said. The researchers had to find a single, specific photon emitted from the qubit in order confirm the spin state of the electron. That photon, however, was clouded in a sea of scattered photons from the lasers themselves.

“The big benefit is to make quantum computing faster,” Press said. The experiment “pushed quantum dots up to speed with other qubit candidate systems to ultimately build a quantum computer.”

Quantum computers are still years away. In the shorter term, Press said, researchers would like to build a system of tens or hundreds of qubits to simulate the operation of a larger quantum system.

The other authors of the Nature paper were Bingyang Zhang of the Ginzton Lab, and Thaddeus Ladd and Yoshihisa Yamamoto of the Ginzton Lab and the National Institute of Informatics in Tokyo.

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Spectroscopy, with amplitude

Gregory P. Hamill, MIT Lincoln Laboratory
September 3, 2008

MIT researchers may have found a way to overcome a key barrier to the advent of super-fast quantum computers, which could be powerful tools for applications such as code breaking.

Ever since Nobel Prize-winning physicist Richard Feynman first proposed the theory of quantum computing more than two decades ago, researchers have been working to build such a device.

One approach involves superconducting devices that, when cooled to temperatures of nearly absolute zero (-459 degrees F, -273 degrees C), can be made to behave like artificial atoms — nanometer-scale “boxes” in which the electrons are forced to exist at specific, discrete energy levels (picture an elevator that can stop at the floors of a building but not in between). But traditional scientific techniques for characterizing — and therefore better understanding – atoms and molecules do not necessarily translate easily to artificial atoms, said William Oliver of MIT Lincoln Laboratory’s Analog Device Technology Group and MIT’s Research Laboratory for Electronics (RLE).

In the Sept. 4 issue of Nature, Oliver and colleagues have reported a technique that could fill that gap. Oliver’s co-authors are lead author David Berns, a graduate student in physics and RLE; Mark Rudner, also a graduate student in physics; Sergio Valenzuela, a research affiliate at MIT’s Francis Bitter Magnet Laboratory; Karl Berggren, the Emanuel E. Landsman Career Development Associate Professor in the Department of Electrical Engineering and Computer Science (EECS); Professor Leonid Levitov of physics; and EECS Professor Terry Orlando. The work is a hallmark of the increased collaboration between researchers on the MIT campus and at Lincoln Laboratory.

Characterizing energy levels is fundamental to the understanding and engineering of any atomic-scale device. Ever since Isaac Newton showed that sunlight could be dispersed into a continuous color spectrum, each color representing a different energy, this has been done through analysis of how an atom responds to different frequencies of light and other electromagnetic radiation — a technique known generally as spectroscopy.

But artificial atoms have energy levels that correspond to a very wide swath of frequencies, ranging from tens to hundreds of gigahertz. That makes standard spectroscopy costly and difficult to apply. “The application of frequency spectroscopy over a broad band is not universally straightforward,” Oliver said.

The MIT team developed a complementary approach called amplitude spectroscopy that provides a way to characterize quantum entities over extraordinarily broad frequency ranges. This procedure is “particularly relevant for studying the properties of artificial atoms,” Oliver said.

Better knowledge of these superconducting structures could hasten the development of a quantum computer. Each artificial atom could function as a “qubit,” or quantum bit, which can be in multiple energy states at once. That means it would not be simply a one or a zero (like the electronic switches in a conventional computer) but rather in a sort of hazy combination of both states (it’s akin to the famous paradox of Schroedinger’s quantum cat, which is considered to be both alive and dead at the same time until an observation is made, simultaneously creating and revealing its true condition). This odd behavior, inherent to the quantum nature of materials at the atomic level, is what gives quantum computing such promise as a paradigm-busting advance.

Amplitude spectroscopy gleans information about a superconducting artificial atom by probing its response to a single, fixed frequency that is strategically chosen to be, as Oliver puts it, “benign.” This probe pushes the atom through its energy-state transitions. In fact, the atoms can be made to jump between energy bands at practically unlimited rates by adjusting the amplitude of the fixed-frequency source.

The radiation emitted by the artificial atom in response to this probe exhibits interference patterns. These patterns, which Oliver calls “spectroscopy diamonds” because of their striking geometric regularity, serve as fingerprints of the artificial atom’s energy spectrum.

This work was funded by the Air Force Office of Scientific Research, the Laboratory for Physical Sciences, the Department of Defense, and the US government.

A version of this article appeared in MIT Tech Talk on September 10, 2008 (download PDF).

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Yale University scientists have accomplished two major steps toward achieving true quantum computing–sending a photon signal on demand from a qubit onto wires and transmitting the signal to a second, distant qubit. Applied physics professor Robert Schoelkopf and physics professor Steven Girvin have spent several years exploring the use of solid-state devices resembling microchips for use in a quantum computer. Their breakthrough means that quantum computing has moved past simply “having information” to “communicating information.” Previously, information in quantum systems was only able to move from qubit to qubit. Schoelkopf and Girvin have engineered a superconducting communication “bus” to store and transfer information between distant quantum bits, the first step to making the fundamentals of quantum computing useful, according to Schoelkopf. The first breakthrough is the ability to produce and control single, discrete microwave photons as the carriers of encoded quantum information. “In this work we demonstrate only the first half of quantum communication on a chip–quantum information efficiently transferred from a stationary quantum bit to a photon or ‘flying qubit,’” says Schoelkopf. “However, for on-chip quantum communication to become a reality, we need to be able to transfer information from the photon back to a qubit.” The researchers accomplished that in their second breakthrough by adding a second qubit and using the photon to transfer a quantum state from one qubit to another.
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