It was the year that the first “commercial” quantum computer was unveiled, and 2007 also saw a flurry of research into the supersolid state of matter. Astronomers improved our understanding of the cosmos by zeroing in on the origins of ultra-high energy cosmic rays and providing the best-ever map of dark matter in the universe. While the Nobel Prize in Physics – awarded for the discovery of giant magnetoresistance – demonstrated how investing in fundamental research could lead to rapid improvements in technology, the year ended on a sour note with some physicists in the US and UK facing significant cuts in their research funding.
1. January: Map sheds light on dark matter
2. February: International Linear Collider plans are unveiled
3. March: Graphene meets negative refraction
4. April: Rogue neutrino is ruled out
5. May: Physics loses a polymer pioneer
6. June: Large Hadron Collider misses 2007 start up
7. July: The ongoing saga of the supersolid
8. August: The latest schemes for stopping light
9. September: Quantum computers get on the buses
10. October: GMR pioneers scoop Nobel Prize
11. November: Cosmic-ray mystery solved at last
12. December: US and UK physicists face funding cuts
While physicists are fairly certain that the universe is full of dark matter, no-one has managed to make a direct observation of the mysterious stuff. The best astronomers can do is work out where the dark matter is by watching how its considerable gravitational pull bends light from distant galaxies. In January, astronomers from the Cosmic Evolution Survey (COSMOS) unveiled the first large-scale map of the distribution of of dark matter. It reveals a universe permeated by filaments dark matter that intersect at galaxies and other major structures – adding further weight to the theory that the universe owes its structure to the gravitational pull of dark matter.
In February, an international group of particle physicists outlined their design for the proposed International Linear Collider (ILC). The ILC could be built by about 2019 to search for the Higgs boson, exotic “supersymmetric” particles and to study the nature of dark energy and dark matter. The 31 km-long behemoth is the next big facility after the Large Hadron Collider, which is due to switch on at CERN in 2008. The ILC could cost as much as $15 bn to build and international cooperation will be crucial to its success. Sadly, this began to unravel towards the end of 2007, with the UK pulling all its funding from the ILC in December. Things are also not looking good in the US, where particle physics in general looks set to suffer a significant cut in funding.
Graphene and negative refractive-index materials were two of the hottest topics in physics in 2007. So it should not be that surprising that in March a team of researchers came up with a proposal linking these previously unrelated topics. According to calculations done by the physicists, graphene could be used to make a tiny lens to focus electrons through negative refraction. Graphene, which is a sheet of carbon only one atom thick, made the news throughout 2007 – including in September, when physicists resolved the “mystery of the missing pi” and reconciled the measured conductivity of the material with the value predicted by theory.
In April, physicists working on the MiniBooNE experiment at Fermilab in the US ruled out a puzzling result that had threatened to undermine the Standard Model of particle physics. The team confirmed that nature contains just three types of neutrino – not four as suggested by an experiment carried out in 1995 at the Los Alamos National Laboratory in 1995.
Later this year in Italy, the existence of another controversial particle was put into doubt by the very team that had claimed its discovery. In March 2006, physicists at the PVLAS experiment shone a laser beam through a strong magnetic field and saw that the beam’s polarization rotated slightly. At the time many physicists thought that this was due to an ultralight particle coupling with photons in the beam, and so heralded it as the first glimpse of the “axion”. However, in June 2007 the team reported that the apparent rotation was an artefact related to how the experiment had been performed.
Dubbed the “Isaac Newton of our time” by the Nobel-Prize committee, the French physicist Pierre-Gilles de Gennes died at the age of 74 in May. De Gennes was awarded the Nobel Prize in Physics in 1991 for his ground-breaking work on liquid crystals and polymers and also had an interest in many other fields of science including cellular adhesion and brain function. He was also a passionate advocate of physics education and visited over 200 schools after receiving the Nobel prize.
In 2007, the physics community also lost the particle physicist Wolfgang Panofsky, who was founding director of the Stanford Linear Accelerator Center (SLAC) in California, and cosmologist Ralph Alpher, whose pioneering calculations supported the concept of the Big Bang.
The ILC wasn’t the only “big physics” project to suffer setbacks in 2007. In March, scientists performing preliminary tests on quadrupole magnets for the Large Hadron Collider (LHC) at CERN witnessed a serious failure when structures supporting one of the magnets broke. As a result of this failure, CERN announced in June that the €6.3bn LHC would not start up in 2007 as scheduled. Instead, the world’s largest particle physics experiment will skip its “engineering run” and is expected to switch on in either late March or early April 2008 with an aim to start data collection two months later.
The first convincing evidence for the supersolid state of matter came in 2004, when US physicists Moses Chan and Eun-Song Kim noticed that a small fraction of a sample of solid helium-4 started to behave like a fluid at extremely low temperatures. Subsequent experiments questioned the initial explanation that this effect was caused by lattice vacancies in the solid condensing into a superfluid, leading to a flurry of experimental and theoretical work. In July, theorists put forth the latest explanation for supersolidity – atoms flowing along screw dislocations in the solid helium. In June, Chan showed that supersolidity occurs in single crystals, which appeared to rule out the possibility that atoms were flowing along grain boundaries in the solid helium.
Physicists are always up for a challenge, and dreaming up new ways to slow-down or even “stop” light was a popular pastime in 2007. In August, physicists in Israel came up with a way to store 2D images in an atomic gas for up to 9 µs. The team used a laser technique called electromagnetically-induced transparency (EIT), which resulted in a storage time about 1000-times longer than the previous record. In December, Physicists in the US unveiled a simple way to “store” light pulses in a material by converting them into sound waves using just two lasers and a piece of standard optical fibre.
Quantum computers could someday work exponentially faster than their classical counterparts by entangling multiple quantum bits – or qubits. However for this to happen, physicists must work out ways to link qubits without destroying their delicate quantum nature. In September, two independent groups in the US unveiled “buses” for transferring information between two microchip-based qubits. The buses could allow a number of qubits to be joined together to make quantum computers using standard chip manufacturing processes.
While most physicists agree that it will be sometime before practical quantum computers are a reality, in April a small Canadian company called D-Wave said that had built the world’s first commercial quantum computer. However, not everyone was convinced by the firm’s claims.
In October, the Nobel Prize in Physics was awarded jointly to Albert Fert of the Université Paris-Sud in France and Peter Grünberg of the Forschungszentrum Jülich in Germany for their independent discovery of giant magnetoresistance in 1988. Dubbed “the Nobel Prize inside your iPod” by the press, the award recognized that the discovery has led to dramatic rise in the amount of data that can be stored on computer hard-disk drives and is now standard technology found in nearly all computers worldwide and is also used in some digital cameras and MP3 players.
Fert and Grünberg are pioneers in “spintronics”, which could be used in devices that exploit the spin – as well as the charge – of electrons to store and process information more quickly and efficiently than conventional transistors. In August, researchers in the US unveiled the first silicon spin field-effect transistor (spinFET), which uses an applied voltage to control a current of spin-polarized electrons. The component is an an important step towards the first commercial “spintronic” devices.
Ultrahigh-energy cosmic rays were first discovered in the 1960s and the origins of these extremely rare charged particles have been hotly debated ever since. In November, astronomers using the Pierre Auger Observatory produced the best evidence yet that ultrahigh-energy cosmic rays striking the Earth come from black holes lying at the heart of nearby galaxies. Having solved the mystery of where these cosmic rays come from, researchers now hope to get a better understanding of exactly how these charged particles are accelerated to such high energies.
Many physicists in the US and the UK can look forward to a bleak 2008 thanks to major cuts to research funding announced by their respective governments. In the US, particle and fusion physics will bear the brunt of the cuts, with the US slashing its funding of the International Linear Collider and the international ITER fusion experiment. In addition, up to 200 staff at the Fermi National Accelerator Laboratory (Fermilab) could lose their jobs.
Particle physics in the UK will also be hit hard, with the Science and Technology Facilities Council (STFC) pulling its funding of the ILC. The UK will also stop investing in high-energy gamma-ray astronomy, withdraw from the Gemini telescopes, and cease all support for ground-based solar-terrestrial physics facilities.