The first complete 'quantum computer'

For decades physicists have dreamed of building a quantum computer that could solve certain problems faster than a conventional counterpart. Actually building such a thing has proven extremely difficult, but in August Jonathan Home and colleagues at NIST unveiled the first small-scale device that could be described as a "quantum computer". The chip can perform a complete set of quantum logic operations without significant amounts of information being lost in transit.

Over the past few years, Home's team has used ultracold ions to demonstrate separately all of the steps needed for quantum computation. But in 2009, the group made the crucial breakthrough of combining all these stages on a single device, which was, in our view, such a significant piece of work that we felt compelled to pick it as our "breakthrough of the year".

The device even looks a bit like an early computer chip – but don't expect it to be running a quantum version of Windows any time soon. Its overall accuracy of 94% is impressive for a quantum device, but this must be boosted to 99.99% before it could be used in a large-scale quantum computer comprising many such processors.

What do the quantum computing experts have to say? "A great step forward and most impressive," said Hans Bachor, at the Australian National University. "A tour-de-force," said Boris Blinov of the University of Washington.

Home was back in the news in November, when he teamed up with David Hanneke and others at NIST to create a quantum computer from two trapped ions. The device can perform at least 160 different quantum-computing operations.

Much more work must be done before quantum computers become a commercial reality – but real progress was made in 2009.

The best of the rest for 2009

Top results from Tevatron
The Large Hadron Collider may have been hogging the limelight in 2009, but physicists on Fermilab's Tevatron kept churning out a tremendous number of results. Indeed, it seemed that every week, at least one or two papers from Tevatron's two main experiments (CDF and D0) were published in Physical Review Letters. While it's tough to pick out the most important result, our favourite is the double act in March when CDF and D0 experiments independently reported unambiguous evidence that top quarks, the heaviest of the six known quark flavours, can be produced individually rather than in pairs as had been observed until now.

Spins spotted in room-temperature silicon
For several decades, physicists have promised smaller, faster and more efficient electronic devices that use electron spin to store and process information. But with the exception of giant magnetoresistance read heads in hard drives, physicists have struggled to create practical 'spintronic' devices. In November, Ron Jansen and colleagues at the University of Twente in the Netherlands made an important move in this direction by showing that spin-polarized electrons can be injected into silicon at room temperature. The spins endured long enough to suggest that spintronics circuits could include silicon features that are nanometres in size and operate at frequencies of 10–100 GHz – just like today's integrated circuits.

Graphane makes its debut

The "wonder material" graphene burst onto the scene five years ago – and the sheet of carbon just one atom thick continues to wow physicists with its growing list of remarkable properties. In January, a team including the UK-based research group that discovered graphene announced a new material called graphane, made by adding hydrogen atoms to their original discovery. As well as being an insulator that could prove useful for creating graphene-based electronic devices, graphane might also find use as a hydrogen-storage medium that could help hydrogen-powered vehicles travel further before refuelling.

Magnetic monopoles spotted in spin ices
Ever since magnetic monopoles were first predicted by Paul Dirac in 1931, physicists have looked in vain for these elusive entities. In September, two independent research groups claimed to have caught sight of monopoles – essentially magnets with only one pole – in magnetic materials called spin ices. The spin-ice monopoles have very different origins from those predicted by Dirac, and therefore are unlikely to help physicists develop grand unified theories of particle physics or string theories. But because the monopoles occur in magnetic materials, understanding their properties could help with the development of magnetic memories and other spintronic devices.

Water on the Moon

We can see the surface of the Moon with the naked eye and some people have even driven on its surface – but until September we weren't sure how much water is on our nearest neighbour. That's when scientists working on the Indian space mission Chandrayaan-1 revealed a wealth of data suggesting that there is much more water than previously thought. And then a week or so later, NASA's LCROSS probe smashed into a crater at near the lunar south pole, throwing up about 100 kg of water. The presence of water makes the long-term colonization of the Moon a little bit easier and such a colony could be a proving ground for a station on Mars – which we know has lots of water. I'm sure we will hear more in 2010 from NASA, ESA and other space agencies about future manned space missions.

Atoms teleport information over long distance
Once the stuff of science fiction, teleportation is now part of the physics lexicon. In January, Christopher Monroe and colleagues in Maryland and Michigan told us how to teleport quantum information between two atoms separated by a significant distance – an advance that could be a significant milestone in the quest for a workable quantum computer. The ions were one metre apart and until this work, teleportation had only been achieved between photons, and between two nearby atoms through the intermediary action of a third. Quantum teleportation is a 'spooky' form of transport whereby quantum information such as the spin of a particle or the polarization of a photon can be transferred between particles without the movement of the particles or the transmission of information.

Black-hole analogue traps sound

Is there anything that can't be simulated using ultracold atoms? In June, Jeff Steinhauer and colleagues at Technion University in Israel added black hole to that growing list. The team's black-hole analogue can trap sound in the same way that an astrophysical black hole can trap light. But instead of a collapsed star, it involves a Bose–Einstein condensate – a collection of atoms so cold that they move coherently in the same quantum state. The next step is to see if the analogue emits something resembling Hawking radiation – particles that are created near to black holes and manage to escape, but have yet to be observed.

Dark matter spotted in Minnesota?
The physics community is still digesting this week's news that the CDMS-II collaboration has come tantalizingly close to detecting dark matter. The team has found two events that fit a dark-matter constituent known as a weakly interacting massive particle, or WIMP. The probability that these could be radioactive decays or cosmic rays is 23% so much more work needs to be done. Will CDMS-II or perhaps another experiment make a stronger case for dark-matter detection in 2010?

And finally, a big bang at the LHC
No list would be complete with out a mention of the 2.36 TeV proton collisions earlier this month at the LHC – the highest energy ever. You can read about that and lots more in our look ahead to all the exciting physics that could be done in 2010.