Tag Archives: coherence

Surviving 39 minutes at room temperature—recordbreaking for quantum materials

There are two news releases about this work which brings quantum computing a step closer to reality. I’ll start with the Nov. 15, 2013 Simon Fraser University (SFU; located in Vancouver, Canada) news release (Note: A link has been removed),,

An international team of physicists led by Simon Fraser University professor Mike Thewalt has overcome a key barrier to building practical quantum computers, taking a significant step to bringing them into the mainstream.

In their record-breaking experiment conducted on SFU’s Burnaby campus, [part of Metro Vancouver] the scientists were able to get fragile quantum states to survive in a solid material at room temperature for 39 minutes. For the average person, it may not seem like a long time, but it’s a veritable eternity to a quantum physicist.

“This opens up the possibility of truly long-term coherent information storage at room temperature,” explains Thewalt.

Quantum computers promise to significantly outperform today’s machines at certain tasks, by exploiting the strange properties of subatomic particles. Conventional computers process data stored as strings of ones or zeroes, but quantum objects are not constrained to the either/or nature of binary bits.

Instead, each quantum bit – or qubit – can be put into a superposition of both one and zero at the same time, enabling them to perform multiple calculations simultaneously. For instance, this ability to multi-task could allow quantum computers to crack seemingly secure encryption codes.

“A powerful universal quantum computer would change technology in ways that we already understand, and doubtless in ways we do not yet envisage,” says Thewalt, whose research was published in Science today.

“It would have a huge impact on security, code breaking and the transmission and storage of secure information. It would be able to solve problems which are impossible to solve on any conceivable normal computer. It would be able to model the behaviour of quantum systems, a task beyond the reach of normal computers, leading, for example, to the development of new drugs by a deeper understanding of molecular interactions.”

However, the problem with attempts to build these extraordinary number-crunchers is that superposition states are delicate structures that can collapse like a soufflé if nudged by a stray particle, such as an air molecule.

To minimize this unwanted process, physicists often cool their qubit systems to almost absolute zero (-273 C) and manipulate them in a vacuum. But such setups are finicky to maintain and, ultimately, it would be advantageous for quantum computers to operate robustly at everyday temperatures and pressures.

“Our research extends the demonstrated coherence time in a solid at room temperature by a factor of 100 – and at liquid helium temperature by a factor of 60 (from three minutes to three hours),” says Thewalt.

“These are large, significant improvements in what is possible.”

The November 15, 2013 University of Oxford news release (also on EurekAlert), features their own researcher and more information (e.g., the previous record for maintaining coherence of a solid state at room temperature),

An international team including Stephanie Simmons of Oxford University report in this week’s Science a test performed as part of a project led by Mike Thewalt of Simon Fraser University, Canada, and colleagues. …

In the experiment, the team raised the temperature of a system, in which information is encoded in the nuclei of phosphorus atoms in silicon, from -269°C to 25°C and demonstrated that the superposition states survived at this balmy temperature for 39 minutes – outside of silicon the previous record for such a state’s survival at room temperature was around two seconds. [emphasis mine] The team even found that they could manipulate the qubits as the temperature of the system rose, and that they were robust enough for this information to survive being ‘refrozen’ (the optical technique used to read the qubits only works at very low temperatures).

‘Thirty-nine minutes may not seem very long but as it only takes one-hundred-thousandth of a second to flip the nuclear spin of a phosphorus ion – the type of operation used to run quantum calculations – in theory over two million operations could be applied in the time it takes for the superposition to naturally decay by 1%. Having such robust, as well as long-lived, qubits could prove very helpful for anyone trying to build a quantum computer,’ said Stephanie Simmons of Oxford University’s Department of Materials, an author of the paper.

The team began with a sliver of silicon doped with small amounts of other elements, including phosphorus. Quantum information was encoded in the nuclei of the phosphorus atoms: each nucleus has an intrinsic quantum property called ‘spin’, which acts like a tiny bar magnet when placed in a magnetic field. Spins can be manipulated to point up (0), down (1), or any angle in between, representing a superposition of the two other states.

The team prepared their sample at just 4°C above absolute zero (-269°C) and placed it in a magnetic field. Additional magnetic field pulses were used to tilt the direction of the nuclear spin and create the superposition states. When the sample was held at this cryogenic temperature, the nuclear spins of about 37% of the ions – a typical benchmark to measure quantum coherence – remained in their superposition state for three hours. The same fraction survived for 39 minutes when the temperature of the system was raised to 25°C.

There is still some work ahead before the team can carry out large-scale quantum computations. The nuclear spins of the 10 billion or so phosphorus ions used in this experiment were all placed in the same quantum state. To run calculations, however, physicists will need to place different qubits in different states. ‘To have them controllably talking to one another – that would address the last big remaining challenge,’ said Simmons.

Even for the uninitiated, going from a record of two seconds to 39 minutes has to raise an eyebrow.

Here’s a link to and a citation for the paper,

Room-Temperature Quantum Bit Storage Exceeding 39 Minutes Using Ionized Donors in Silicon-28.by Kamyar Saeedi, Stephanie Simmons, Jeff Z. Salvail, Phillip Dluhy, Helge Riemann, Nikolai V. Abrosimov, Peter Becker, Hans-Joachim Pohl, John J. L. Morton, & Mike L. W. Thewalt.  Science 15 November 2013: Vol. 342 no. 6160 pp. 830-833 DOI: 10.1126/science.1239584

This paper is behind a paywall.

ETA Nov. 18 ,2013:  The University College of London has also issued a Nov. 15, 2013 news release on EurekAlert about this work. While some of this is repetitive, I think there’s enough new information to make this excerpt worthwhile,

The team even found that they could manipulate the qubits as the temperature of the system rose, and that they were robust enough for this information to survive being ‘refrozen’ (the optical technique used to read the qubits only works at very low temperatures). 39 minutes may not sound particularly long, but since it only takes a tiny fraction of a second to run quantum computations by flipping the spin of phosphorus ions (electrically charged phosphorus atoms), many millions of operations could be carried out before a system like this decays.

“This opens up the possibility of truly long-term coherent information storage at room temperature,” said Mike Thewalt (Simon Fraser University), the lead researcher in this study.

The team began with a sliver of silicon doped with small amounts of other elements, including phosphorus. They then encoded quantum information in the nuclei of the phosphorus atoms: each nucleus has an intrinsic quantum property called ‘spin’, which acts like a tiny bar magnet when placed in a magnetic field. Spins can be manipulated to point up (0), down (1), or any angle in between, representing a superposition of the two other states.

The team prepared their sample at -269 °C, just 4 degrees above absolute zero, and placed it in a magnetic field. They used additional magnetic field pulses to tilt the direction of the nuclear spin and create the superposition states. When the sample was held at this cryogenic temperature, the nuclear spins of about 37 per cent of the ions – a typical benchmark to measure quantum coherence – remained in their superposition state for three hours. The same fraction survived for 39 minutes when the temperature of the system was raised to 25 °C.

 

Rail system and choreography metaphors in a couple of science articles

If you are going to use a metaphor/analogy when you’re writing about a science topic  because you want to reach beyond an audience that’s expert on the topic you’re covering or you want to grab attention from an audience that’s inundated with material, or you want to play (for writers, this can be a form of play [for this writer, anyway]), I think you need to remain true to your metaphor. I realize that’s a lot tougher than it sounds.

I’ve got examples of the use of metaphors/analogies in two recent pieces of science writing.

First, here’s the title for a Jan. 23, 2012 article by Samantha Chan for The Asian Scientist,

Scientists Build DNA Rail System For Nanomotors, Complete With Tracks & Switches

Then, there’s the text where the analogy/metaphor of a railway system with tracks and switchers is developed further and abandoned for origami tiles,

Expanding on previous work with engines traveling on straight tracks, a team of researchers at Kyoto University and the University of Oxford have used DNA building blocks to construct a motor capable of navigating a programmable network of tracks with multiple switches.

In this latest effort, the scientists built a network of tracks and switches atop DNA origami tiles, which made it possible for motor molecules to travel along these rail systems.

Sometimes, the material at hand is the issue. ‘DNA origami tiles’ is a term in this field so Chan can’t change it to ‘DNA origami ties’ which would fit with the railway analogy. By the way, the analogy itself comes from (or was influenced by) the title the scientists chose for their published paper in Nature Nanotechnology (it’s behind a paywall),

A DNA-based molecular motor that can navigate a network of tracks

All in all, this was a skillful attempt to get the most out of a metaphor/analogy.

For my second example, I’m using a Jan. 12, 2012 news release by John Sullivan for Princeton University which was published in Jan. 12, 2012 news item on Nanowerk. Here’s the headline from Princeton,

Ten-second dance of electrons is step toward exotic new computers

This sets up the text for the first few paragraphs (found in both the Princeton news release and the Nanowerk news item),

In the basement of Hoyt Laboratory at Princeton University, Alexei Tyryshkin clicked a computer mouse and sent a burst of microwaves washing across a silicon crystal suspended in a frozen cylinder of stainless steel.

The waves pulsed like distant music across the crystal and deep within its heart, billions of electrons started spinning to their beat.

Reaching into the silicon crystal and choreographing the dance of 100 billion infinitesimal particles is an impressive achievement on its own, but it is also a stride toward developing the technology for powerful machines known as quantum computers.

Sullivan has written some very appealing text for an audience who may or may not know about quantum computers.

Somebody on Nanowerk changed the headline to this,

Choreographing dance of electrons offers promise in pursuit of quantum computers

Here, the title has been skilfully reworded for an audience that knows more quantum computers while retaining the metaphor. Nicely done.

Sullivan’s text goes on to provide a fine explanation of an issue in quantum computing, maintaining coherence, for an audience not expert in quantum computing. The one niggle I do have is a shift in the metaphor,

To understand why it is so hard, imagine circus performers spinning plates on the top of sticks. Now imagine a strong wind blasting across the performance space, upending the plates and sending them crashing to the ground. In the subatomic realm, that wind is magnetism, and much of the effort in the experiment goes to minimizing its effect. By using a magnetically calm material like silicon-28, the researchers are able to keep the electrons spinning together for much longer.

Wasn’t there a way to stay with dance? You could have had dancers spinning props or perhaps the dancers themselves being blown off course and avoided the circus performers. Yes, the circus is more colourful and appealing but, in this instance, I would have worked to maintain the metaphor first introduced, assuming I’d noticed that I’d switched metaphors.

So, I think I can safely say that using metaphors is tougher than it looks.