Quantum Computing? Quantum Bar Magnets in a Transparent Salt

ScienceDaily (June 15, 2012) — Scientists have managed to switch on and off the magnetism of a new material using quantum mechanics, making the material a test bed for future quantum devices.

This image shows the antiferromagnetic arrangement of the spins (colored arrows) in the magnetic salt used by the Swiss-German-US-London team. (Credit: University College London)

The international team of researchers led from the Laboratory for Quantum Magnetism (LQM) in Switzerland and the London Centre for Nanotechnology (LCN), found that the material, a transparent salt, did not suffer from the usual complications of other real magnets, and exploited the fact that its quantum spins -- which are like tiny atomic magnets -- interact according to the rules of large bar magnets. The study is published in Science.

Anybody who has played with toy bar magnets at school will remember that opposite poles attract, lining up parallel to each other when they are placed end to end, and anti-parallel when placed adjacent to each other. As conventional bar magnets are simply too large to reveal any quantum mechanical nature, and most materials are too complex for the spins to interact like true bar magnets, the transparent salt is the perfect material to see what's going on at the quantum level for a dense collection of tiny bar magnets.

The team were able to image all the spins in the special salt, finding that the spins are parallel within pairs of layers, while for adjacent layer pairs, they are antiparallel, as large bar magnets placed adjacent to each other would be. The spin arrangement is called "antiferromagnetic." In contrast, for ferromagnets such as iron, all spins are parallel.

By warming the material to only 0.4 degrees Celsius above the absolute "zero" of temperature where all classical (non-quantum) motion ceases, the team found that the spins lose their order and point in random directions, as iron does when it loses its ferromagnetism when heated to 870 Celsius, much higher than room temperature because of the strong and complex interactions between electron spins in this very common solid.

The team also found that they could achieve the same loss of order by turning on quantum mechanics with an electromagnet containing the salt. Thus, physicists now have a new toy, a collection of tiny bar magnets, which naturally assume an antiferromagnetic configuration and for which they can dial in quantum mechanics at will.

"Understanding and manipulating magnetic properties of more traditional materials such as iron have of course long been key to many familiar technologies, from electric motors to hard drives in digital computers," said Professor Gabriel Aeppli, UCL Director of the LCN.

"While this may seem esoteric, there are deep connections between what has been achieved here and new types of computers, which also rely on the ability to tune quantum mechanics to solve hard problems, like pattern recognition in images."

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IBM takes giant step to faster, quantum computers

IBM researchers presenting the results at this week’s American Physical Society meeting in Boston said that quantum computing “has the potential to deliver computational power that is unrivaled by any supercomputer today.” – Reuters File Photo

WASHINGTON: IBM researchers have taken a leap in computing by using quantum mechanics to harness the power of atoms and molecules, a move likely to lead to vast increases in speed and security of computers and other devices.

IBM researchers presenting the results at this week’s American Physical Society meeting in Boston said that quantum computing “has the potential to deliver computational power that is unrivaled by any supercomputer today.” The new type of computing uses information encoded into quantum bits or qubits, putting into use a theory that scientists have been discussing for decades.

“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,” an IBM statement said.

“For example, a single 250-qubit state contains more bits of information than there are atoms in the universe.” “The quantum computing work we are doing shows it is no longer just a brute force physics experiment,” said IBM scientist Matthias Steffen, manager of the research team that is working on applications for quantum computing systems.

“It’s time to start creating systems based on this science that will take computing to a new frontier.” Quantum computing expands on the most basic piece of information that a typical computer understands — a bit. While a normal bit can have only one of two values: “1” or “0,” qubits 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,” IBM says.

A problem for scientists is that qubits have a short life of several billionths of a second, but IBM has succeeded in developing “three dimensional” superconducting qubits which retain their quantum states up to 100 microseconds – an improvement of two to four times prior records.

“Based on this progress, optimism about superconducting qubits and the possibilities for a future quantum computer are rapidly growing,” says IBM.

To harness the power of quantum computing, scientists have had to work to minimize errors in calculations caused by interference from factors such as heat, electromagnetic radiation, and materials defects.

The use of quantum computing “will have widespread 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,” IBM said.

“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.”

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IBM's New Optochip Transfers One Trillion Bits Per Second

By Alex Knapp, Forbes Staff

The Holey Optochip (Credit: IBM Research)

As Big Data increasingly becomes a part of our economy bandwidth becomes increasingly important. Not just wired or wireless bandwidth, either. When it comes to server racks and supercomputers, the internal bandwidth within a computer also matters a lot more.

IBM has made a big step forward in improving that bandwidth with their announcement today that they’ve developed a parallel optical transceiver – dubbed the “Holey Optochip” – that’s capable of transferring information at the rate of one trillion bits per second. That’s eight times faster than currently available optical components.

“We’re trying to deliver a component that looks like an electrical chip,” IBM researcher Clint Schow told me on the phone yesterday. “But it also had to be dense, compact, and power efficient. We were also focused on delivering it with components available today.”

IBM Paves The Way Towards Scalable Quantum Computing Alex Knapp Forbes Staff

For the prototype optochip, the IBM research team drilled 48 holes in a conventional 90nm CMOS chip, which then allowed for the placement of 24 receiver and 24 transmitter channels within the chip. Because it’s so compact, the chip is incredibly power efficient – it consumes less than five watts. And by using a standard CMOS chip, they’re able to bring the interconnects as close to the processors as possible, which allows for its incredible transfer speeds.

IBM’s next step will be to work with commercial partners to further refine and develop the chip. Even though the current iteration is only a prototype, Schow is confident that the development cycle for commercial applications will be short. That’s because all of the individual components of the chip are readily available, and the modifications can be performed without customized equipment.

“Part of the real advantage of this chip is that we put it together by using small tweaks in clever ways,” he said.

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IBM Scalable Quantum Computing

IBM Scalable Quantum Computing

IBM Paves The Way Towards Scalable Quantum Computing

Alex Knapp, Forbes Staff

Three superconducting qubits. (Credit: IBM Research)

IBM has announced today that it’s achieved a breakthrough in its work to develop scalable quantum computing by developing a superconducting qubit made from microfabricated silicon that maintains coherence long enough for practical computation.

And now that I’ve thrown a ton of information at you in one tiny sentence, let’s break it all down. I had a chance to talk with IBM scientist Matthias Steffen about this new technology, and he broke it down for me. Let’s start with the qubit. Classical computing, as you probably know, is based on the bit. A bit can exist in one of two possible states, which are typically referred to as “0″ or “1″. A qubit is the equivalent of a bit for quantum computing. It can be in three possible states – “0″ or “1″ or both. The “both” state is known as the superposition. Now, the difference may seem subtle, but mathematically, it’s huge. A few hundred qubits can contain more classical bits of information than the the universe has atoms.

IBM Shrinks Computer Memory Into Only Twelve Atoms
  Alex Knapp Forbes Staff
 
What makes quantum computing challenging is the problem of decoherence. When a qubit is moved from the 0 state to either 1 or the superposition, it will decohere to state 0 due to interference from other parts of the computer. In order for quantum computing to be scalable and practical, the qubits have to be coherent for a long enough time that error-correction techniques can be employed to make sure that the decoherence doesn’t prevent accurate computation.

“In 1999, coherence times were about 1 nanosecond,” Steffen told me. “Last year, coherence times were achieved for as long as 1 to 4 microseconds. With these new techniques, we’ve achieved coherence times of 10 to 100 microseconds. We need to improve that by a factor of 10 to 100 before we’re at the threshold we want to be. But considering that in the past ten years we’ve increased coherence times by a factor of 10,000, I’m not scared.”

 

Alex Knapp Forbes Staff
 MIT's Scott Aaronson Explains Quantum Computing

The IBM team has taken two approaches to quantum computing, both of which factor into the breakthroughs announced here. The first approach is building a 3-D qubit made from superconducting, microfabricated silicon. Steffen notes that the benefit of using silicon for these qubits is that the manufacturing equipment and know-how already exists – new techniques don’t have to be developed. 3-D qubits were pioneered by the Schoelkopf Lab at Yale, and Steffen expressed his admiration for that work. Building on the Yale techniques, the IBM team was able to maintain coherence for 95 microseconds. (“But you could round that to 100 for the piece if you want,” Steffen joked.)

How To Make A Cheaper Quantum Computer
  Alex Knapp Forbes Staff

 The second approach involved a traditional 2-D qubit, which IBM’s scientists used to build a “Controlled NOT gate” or CNOT gate, which is a building block of quantum computing. A CNOT gate connects two qubits such that the second qubit will change state if the first qubit changes its state to 1. For example, if qubit A’s state is changed from 0 to 1, and qubit B’s state is 1, it will flip to state 0. But if qubit A’s state is changed from 1 to 0, qubit B is unaffected. That seems simple enough, but when you scale multiple logic gates like this together, you have a very real basis for computation. The CNOT gates were able to maintain coherence times of 10 microseconds, which is long enough to show a 95% accuracy rate. The previous accuracy record for CNOT gates was 81% accuracy, so this is a huge step.  Of course, Steffen was quick to note that there’s still a ways to go before this can be implemented as a computing solution. That makes common sense, since 95% is accurate, but in the long run you need the accuracy to be as close to 100% as possible. 
 

The Inner Workings of a Quantum von Neumann Computer Alex Knapp Forbes Staff

Given the rapid progress that IBM has made, scalable quantum computing is starting to look like a real possibility. As error-correction protocols improve and coherence times lengthen, accurate quantum computing becomes a real possibility. But don’t expect to have a quantum smartphone anytime soon using this technique. In order to get the results the IBM team has seen in either the 2-D or 3-D configuration, the qubits have to be cooled down to less than a degree above absolute zero.

“There’s a growing sense that a quantum computer can’t be a laptop or desktop,” said Steffen. “Quantum computers may well just being housed in a large building somewhere. It’s not going to be something that’s very portable.  In terms of application, I don’t think that’s a huge detriment because they’ll be able to solve problems so much faster than traditional computers.”

The next steps for the team is to improve coherence and error-correction protocols to the point where the accuracy is over 99.9%. That means they’ll have achieved a “logical qubit” – one that, for practical purposes, doesn’t experience decoherence. From that point, the next step is to develop a quantum computing architecture. IBM is considering some possibilities here, including developing some quantum memory architechture. But what encourages Steffen in these endeavors is that these are questions of engineering, not of theory.

“We are very excited about how the quantum computing field has progressed over the past ten years,” he told me. “Our team has grown significantly over past 3 years, and I look forward to seeing that team continue to grow and take quantum computing to the next level.”

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Best of 2011: How To Turn A Laser Into A Tractor Beam?

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Published by MIT

How To Turn A Laser Into A Tractor Beam

Physicists work out how to generate a backward pulling force from a forward propagating beam

A photon has a small momentum which it can impart to anything it hits, as Arthur Compton and Peter Lebedev discovered at the beginning of the last century. We now know that photons can be used to push anything from electrons to solar sails.

Today, Jun Chen from Fudan University in China and a few pals demonstrate the counterintuitive result that photons can pull things too. In other words, they've worked out how to generate a backward pulling force from a forward propagating beam.



Chen and buddies say this is possible when the system meets two conditions. First, it works only for beams in which the momentum in the direction of propagation is small, as is the case for beams that merely glance off an object. Second, the photons must simultaneously excite several multipoles within the particle, which scatter the beam.

If the scattering angle is just right, the total momentum in the direction of propagation can be negative, meaning the particle is pulled back towards the source and the light becomes a tractor beam.

This must not be confused with various "optical tweezer" type mechanisms in which particles trapped in a beam follow the intensity gradient of the light. In this case, the particles always reach some point of equilibrium where the intensity reaches a maximum.

Chen and co's new force works when there is no gradient. Given the chance, their tractor beam will pull a particle all the way back to the source.

That's a handy additional tool in the nanomanipulator's box of tricks. "This may open up new avenues for optical micromanipulation, of which typical examples include transporting a particle backward over a long distance and particle sorting," say Chen and co.

This is a theory paper so there's one piece of the puzzle left to fit. All they have to do now is demonstrate that their tractor beam works.

Ref: arxiv.org/abs/1102.4905: Backward Pulling Force From A Forward Propagating Beam

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