A novel device, developed by a team led by University at Buffalo engineers, simply and conveniently traps, detects and manipulates the single spin of an electron, overcoming some major obstacles that have prevented progress toward spintronics and spin-based quantum computing.

Published online this week in Physical Review Letters, the research paper brings closer to reality electronic devices based on the use of single spins and their promise of low-power/high-performance computing.

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“The task of manipulating the spin of single electrons is a hugely daunting technological challenge that has the potential, if overcome, to open up new paradigms of nanoelectronics,” said Jonathan P. Bird, Ph.D., professor of electrical engineering in the UB School of Engineering and Applied Sciences and principal investigator on the project.

“In this paper, we demonstrate a novel approach that allows us to easily trap, manipulate and detect single-electron spins, in a scheme that has the potential to be scaled up in the future into dense, integrated circuits.”

While several groups have recently reported the trapping of a single spin, they all have done so using quantum dots, nanoscale semiconductors that can only demonstrate spin trapping in extremely cold temperatures, below 1 degree Kelvin.

The cooling of devices or computers to that temperature is not routinely achievable, Bird said, and it makes systems far more sensitive to interference.

The UB group, by contrast, has trapped and detected spin at temperatures of about 20 degrees Kelvin, a level that Bird says should allow for the development of a viable technology, based on this approach.

In addition, the system they developed requires relatively few logic gates, the components in semiconductors that control electron flow, making scalability to complex integrated circuits very feasible.

The UB researchers achieved success through their innovative use of quantum point contacts: narrow, nanoscale constrictions that control the flow of electrical charge between two conducting regions of a semiconductor.

“It was recently predicted that it should be possible to use these constrictions to trap single spins,” said Bird. “In this paper, we provide evidence that such trapping can, indeed, be achieved with quantum point contacts and that it may also be manipulated electrically.”

The system they developed steers the electrical current in a semiconductor by selectively applying voltage to metallic gates that are fabricated on its surface.

These gates have a nanoscale gap between them, Bird explained, and it is in this gap where the quantum point contact forms when voltage is applied to them.

By varying the voltage applied to the gates, the width of this constriction can be squeezed continuously, until it eventually closes completely, he said.

“As we increase the charge on the gates, this begins to close that gap,” explained Bird, “allowing fewer and fewer electrons to pass through until eventually they all stop going through. As we squeeze off the channel, just before the gap closes completely, we can detect the trapping of the last electron in the channel and its spin.”

The trapping of spin in that instant is detected as a change in the electrical current flowing through the other half of the device, he explained.

“One region of the device is sensitive to what happens in the other region,” he said.

Now that the UB researchers have trapped and detected single spin, the next step is to work on trapping and detecting two or more spins that can communicate with each other, a prerequisite for spintronics and quantum computing. 

Physicists at the National Institute of Standards and Technology have transferred information between two “artificial atoms” by way of electronic vibrations on a microfabricated aluminum cable, demonstrating a new component for potential ultra-powerful quantum computers of the future. The setup resembles a miniature version of a cable-television transmission line, but with some powerful added features, including superconducting circuits with zero electrical resistance, and multi-tasking data bits that obey the unusual rules of quantum physics.

The resonant cable might someday be used in quantum computers, which would rely on quantum behavior to carry out certain functions, such as code-breaking and database searches, exponentially faster than today’s most powerful computers. Moreover, the superconducting components in the NIST demonstration offer the possibility of being easier to manufacture and scale up to a practical size than many competing candidates, such as individual atoms, for storing and transporting data in quantum computers.

Unlike traditional electronic devices, which store information in the form of digital bits that each possess a value of either 0 or 1, each superconducting circuit acts as a quantum bit, or qubit, which can hold values of 0 and 1 at the same time. Qubits in this “superposition” of both values may allow many more calculations to be performed simultaneously than is possible with traditional digital bits, offering the possibility of faster and more powerful computing devices. The resonant section of cable shuttling the information between the two superconducting circuits is known to engineers as a “quantum bus,” and it could transport data between two or more qubits.

The NIST work is featured on the cover of the Sept. 27 issue of Nature. The scientists encoded information in one qubit, transferred this information as microwave energy to the resonant section of cable for a short storage time of 10 nanoseconds, and then successfully shuttled the information to a second qubit.

“We tested a new element for quantum information systems,” says NIST physicist Ray Simmonds. “It’s really significant because it means we can couple more qubits together and transfer information between them easily using one simple element.”

The NIST work, together with another letter in the same issue of Nature by a Yale University group, is the first demonstration of a superconducting quantum bus. Whereas the NIST scientists used the bus to store and transfer information between independent qubits, the Yale group used it to enable an interaction of two qubits, creating a combined superposition state. These three actions, demonstrated collectively by the two groups, are essential for performing the basic functions needed in a superconductor-based quantum information processor of the future.

In addition to storing and transferring information, NIST’s resonant cable also offers a means of “refreshing” superconducting qubits, which normally can maintain the same delicate quantum state for only half a microsecond. Disturbances such as electric or magnetic noise in the circuit can rapidly destroy a qubit’s superposition state.

With design improvements, the NIST technology might be used to repeatedly refresh the data and extend qubit lifetime more than 100-fold, sufficient to create a viable short-term quantum computer memory, Simmonds says. NIST’s resonant cable might also be used to transfer quantum information between matter and light — microwave energy is a low-frequency form of light — and thus link quantum computers to ultra-secure quantum communications systems.

If they can be built, quantum computers — harnessing the unusual rules of quantum mechanics, the principles governing nature’s smallest particles — might be used for applications such as fast and efficient code breaking, optimizing complex systems such as airline schedules, making counterfeit-proof money, and solving complex mathematical problems. Quantum information technology in general allows for custom-designed systems for fundamental tests of quantum physics and as-yet-unknown futuristic applications.

A superconducting qubit is about the width of a human hair. NIST researchers fabricate two qubits on a sapphire microchip, which sits in a shielded box about 8 cubic millimeters in size. The resonant section of cable is 7 millimeters long, similar to the coaxial wiring used in cable television but much thinner and flatter, zig-zagging around the 1.1 mm space between the two qubits. Like a guitar string, the resonant cable can be stimulated so that it hums or “resonates” at a particular tone or frequency in the microwave range. Quantum information is stored as energy in the form of microwave particles or photons.

When exposed to high voltage, water does some interesting things. From the article, ‘water in two beakers climbs out of the beakers and crosses empty space to meet, forming the water bridge. The liquid bridge, hovering in space, appears to the human eye to defy gravity. Upon investigating the phenomenon, the scientists found that water was being transported from one beaker to another, usually from the anode beaker to the cathode beaker. The cylindrical water bridge, with a diameter of 1-3 mm, could remain intact when the beakers were pulled apart at a distance of up to 25 mm.

The last few weeks have been pretty manic. I have been busy moving in to my new place in Plymouth to study BSc (Hons) Computing at the University of Plymouth.

Everything has gone very smoothly and I’m currently adjusting to city life again.

My housemates are amazing people and our house is the best student house this side of.. erm.. your fat aunts ass.

You will be hearing much more from me now I have settled in!

Since January, I’ve been almost exclusively using Ubuntu. Before that, I knew absolutely nothing about using Linux. I was a Windows/DOS user for 12 years, and even a Microsoft Beta Tester and TBED engineer for 18 months.

At the same time as switching to Ubuntu on my home desktop, I also started a new job, and all the computers at the office are Windows. As a result I’ve spent the last eight months feeling uncomfortable using a computer between the hours 9-5.30 Monday to Friday.

It’s been an interesting opportunity to compare Linux and Windows, with only the last one not being novel to me. The rest of the post addresses making the switch, including a run down of the handiest things I’ve found and the biggest problems I’ve dealt with.

Over the past few years a lot of what I do has been shifted online rather than sitting on my own hard disk. This makes it easier to play with operating systems, because I don’t generate and store so much personal data to backup and be wary of erasing. I’d noticed frequent Windows reinstalls were becoming less of a pain because of this, but that made me less inclined to stick with it because I thought it would be just as easy for other OSes. It is.

I held out with Windows XP for a long time. But all of the “user friendly” obfuscation in XP makes me shout obscenities and bang my fist on the desk. However, after being made a beta tester for Microsoft I have been using Windows Vista ever since the beta stages. During the beta stages I liked Vista, but as features dropped and performance never greatly improved I grew more and more tired with the glass-like OS and craved an alternative altogether; inspiring me to try Ubuntu. I kept a Windows installation as I did not know what to expect.

So I installed Ubuntu, and after two weeks realised I hadn’t booted into Windows once. I liked it a lot, and got Beryl running with functionality and visual effects better than any aero theme. If these terms are baffling you, don’t worry. If you get into Ubuntu you’ll soon learn all about them.

I’m impressed with the security on Linux and Apple OSes. They don’t just accept your initial login as validation to make changes to the system, instead they demand your password every time anything attempts to change system files. Vista does this also, but it feels sluggish and can be turned off which I think defeats the object.

This does feel a lot more secure than Windows, though I’m absolutely sure there would be ways to punch through it. However, another reason I like it is that encourages the separation of system/program files and the data they use. Furthermore, all of this is done via your home directory, with your personal data and application configs all stored there.

There are a few things I’ve carried from my use of Windows into Linux. Because it’s open, I have it functioning somewhat like a hybrid of both, which is making it better than either.

A few months after installing, I formatted and reinstalled my EXT partition with Ubuntu Fiesty, and everything worked a little better. However, there are a bunch of useful things I’ve learned and problems I’ve dealt with, detailed below.

1. Terminal, run program, and force quit:
These are things you’ll likely use all the time if you become a regular Ubuntu user; it’s handy to have them in your panel (like stuff in Windows quicklaunch or the OS-X dock).

You can drag and drop terminal to your panel from Applications > Accessories. You can add run program and force quit by right clicking on a panel and selecting “Add to Panel…”. I also added a drawer and shoved system monitor, synaptic, and lock screen in there.

2. Search is OK:
Search does work properly in Nautilus, it may just seem like it isn’t to a long time Windows user, because it doesn’t immediately cause massive hard disk activity. Search from “file system” rather than “root” if you want to look at a whole drive. Or install Beagle, a fantastic search program.

3. Hide and Find:
CTRL + H unhides all hidden files and folders in a Nautilus window (hidden items begin with a dot, e.g. .icons)

4. Backups:
There’s a proper way to back up data via the terminal rather than moving icons around in Nautilus. See, for example, the procedure for Evolution. I grumbled at this initially, but by the first time I’d done it I realised why it was better: Not only does it preserve all your file permissions, but you can put all of the commands into an executable script and thus make things very easy whenever you backup in future.

5. Windows Flattens GRUB:
It seems by far the easiest way to set up dual boot is to set up partitions, install Windows first, then install Ubuntu, which drops GRUB in, allowing you select from your OSes on boot.

G-Parted is a great way to set up your partitions (I have: 80gig HDD for Ubuntu, 2 gig swap for Ubuntu, a 40gig NTFS hardrive for XP which I’ll probably make much smaller next time I reformat, and a 25gig NTFS partition for games. Partition Magic is what many would choose, but apparently it can’t handle Linux partitions properly.

The reason to install Windows first is that, if you install Ubuntu beforehand, Windows later shits its vile, inconsiderate spoor all over your MBR and gets rid of GRUB. Of course! If someone is installing Windows, they won’t want to use anything else, right? Hah.

To fix it, the best way is to boot from a live CD of Ubuntu and reinstall GRUB. It’s easy. Various instructions are here, there and everywhere.

Also, if you’re using any flavour of Ubuntu, sign up at the forums! They’re an invaluable learning resource, and so might you be if you’re the first to solve a problem.

Ubuntu is open enough and has enough of a culture around it that I can fix things myself, and in so doing learn a hell of a lot about it. OS-X is still better than Windows in terms of security and aesthetics, but even more closed. I can go a lot deeper into Ubuntu, and as a result it feels like my operating system rather than somebody else’s.

For ideological reasons, I’d like to be able to switch to entirely open source software, and I did. I ditched gaming for a while and I am left with a fantastic OS and just a slight craving to play counter strike. In fact, one of the reasons I started a blog was something to do instead of gaming, so it seems linux can help unleash your creative side also Hopefully, as Linux distros become progressively more user friendly there will be more demand for Linux support in terms of games and hardware. I certainly make sure to fire off emails whenever I’m struggling to get something working with Linux, just to let people know that there are Linux users who are trying to use their products or would like to.

The indicators are clear: Just like the browsers, email clients, and media players I switched to in the past few years, Open Source Operating Systems are almost there and steadily getting better.

In contrast, closed source OSes have been getting worse in many respects for a long time, and I suspect not many years hence will have to do quite a bit of backpedaling to become competitive.

Switching to Ubuntu was easy, fairly trouble free and a refreshing experience. Every time I hear of another switch I grin from ear to ear. Because of what I’ve learned and what I can now do, it was well worth it!