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Spooks can ignore fragility of quantum entanglement
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Alaska Stockt/Alamy
SEVERAL volcanoes erupted in 2009 – but only one screamed. The guttural cries from the Redoubt volcano near Anchorage in Alaska may hold clues to the forces that cause volcanoes to blow their tops. Redoubt erupted for two weeks in March 2009. Before many of the explosions, a flurry of tremors of magnitude 0.5 to 1.5 were detected, peaking 1 minute before the explosion at 30 events per second. Researchers dubbed it the “seismic scream” because it built to a crescendo of increasing pitch. It even entered the lowest range of human hearing – sounding like a low hum when the vibrations reached the surface, says Eric Dunham at Stanford University in California. Following each scream, there was about 30 seconds of silence before the volcano exploded. Dunham and colleagues have modelled this seismic activity, and reckon that a rise in friction in the heart of the volcano – for example, between the upwelling magma and the walls – could have created the scream. The magma may slip past the walls in a quickening sequence of judders just before an explosion (Nature Geoscience, doi.org/m7s). The screams could help show how the pressure in the centre of a volcano alters just before an eruption, perhaps explaining why some blasts are so destructive.
Spooks can ignore the fragility of quantum entanglement WHEN it comes to quantum cryptography, we can have our cake and eat it. A cryptography scheme works even after the delicate quantum entanglement behind it has been destroyed, suggesting the idea is more practical than we thought. Entanglement, a quantum link between disparate objects, can enable ultra-secure cryptography, but even a slight jostle can destroy it, so systems that rely on it are not always useful in practice. Or so it seemed. Jeffrey Shapiro of the
Massachusetts Institute of Technology and colleagues devised a cryptography scheme in which one person, Alice, entangles two beams of light. She sends one to Bob, and retains the other as a key. Bob changes phase of the beam he receives to mean “yes”, or leaves it alone to mean “no”, amplifies it and sends it back. Only Alice, who holds the entangled partner, can work out whether Bob made the change, making the system super secure. Crucially, she can do this even if the entanglement itself is gone.
When Shapiro’s team recreated the set-up in the lab, the entanglement was destroyed. However, Alice was still able to use her beam to decode Bob’s message, because of relic correlations between the two beams. Although no longer entangled, photons in the beams are still more likely than chance to share the same state (Physical Review Letters, doi.org/m62). “The quantum state really helps even though we end up with no quantumness at all,” says team member Zheshen Zhang. David White Photography
Volcano screams hold deep secrets
Our sun wags a lucky clover tail LUCKY us! Our solar system has a tail shaped like a four-leaf clover, according to new observations of the plasma bubble that separates us from the rest of the galaxy. Particles blowing out from the sun – the solar wind – keep the plasma bubble inflated. Astronomers have long assumed that the sun’s motion as it orbits the centre of the galaxy squashes the bubble into a bullet shape, with a tail extending to the rear. Using observations from NASA’s Interstellar Boundary Explorer (IBEX) spacecraft, astronomers were able to map this “heliotail” for the first time (Astrophysical Journal, doi.org/ m65). One surprise was that, if we were to look down its length from front to back, we would see particles clustered into four lobes: two on the sun’s polar plane made of fast-moving particles and two on its equatorial plane made of slower-moving ones. The lobes might be a reflection of solar activity, says IBEX principal investigator David McComas. The map is based on data taken when the sun was minimally active and the solar wind had slowed down around the sun’s low to mid-latitudes.
London underground: mind the mould THE Jubilee line is the youngest and smartest of all London Underground lines, but it is mouldier than the much older Central and Bakerloo lines. Daniel Henk, now at the University of Bath, UK, and colleagues collected fungal cells lurking on the platforms at 12 stations across the three lines. They then compared these levels with those in a London hospital and in one of the city’s parks. People travelling on the Jubilee line – which opened in 1979 and was extended in 1999 – breathe in fractionally more fungal cells than those on the Central line, which
opened in 1900. In both cases, it was just over 1 fungal cell per minute. This is twice as much as you would get in the park and, reassuringly, four times as much as in the hospital. On the Bakerloo line, which opened in 1906, people take in 0.75 cells a minute. Strangely, the Jubilee line had the fewest Penicillium cells – from which penicillin is produced – though it is one of the most common fungal species in the outside air. The difference is likely to be down to temperature, humidity and how the stations are connected to the outside (Fungal Ecology, doi.org/m66).
20 July 2013 | NewScientist | 15
Alaska Stockt/Alamy
SEVERAL volcanoes erupted in 2009 – but only one screamed. The guttural cries from the Redoubt volcano near Anchorage in Alaska may hold clues to the forces that cause volcanoes to blow their tops. Redoubt erupted for two weeks in March 2009. Before many of the explosions, a flurry of tremors of magnitude 0.5 to 1.5 were detected, peaking 1 minute before the explosion at 30 events per second. Researchers dubbed it the “seismic scream” because it built to a crescendo of increasing pitch. It even entered the lowest range of human hearing – sounding like a low hum when the vibrations reached the surface, says Eric Dunham at Stanford University in California. Following each scream, there was about 30 seconds of silence before the volcano exploded. Dunham and colleagues have modelled this seismic activity, and reckon that a rise in friction in the heart of the volcano – for example, between the upwelling magma and the walls – could have created the scream. The magma may slip past the walls in a quickening sequence of judders just before an explosion (Nature Geoscience, doi.org/m7s). The screams could help show how the pressure in the centre of a volcano alters just before an eruption, perhaps explaining why some blasts are so destructive.
Spooks can ignore the fragility of quantum entanglement WHEN it comes to quantum cryptography, we can have our cake and eat it. A cryptography scheme works even after the delicate quantum entanglement behind it has been destroyed, suggesting the idea is more practical than we thought. Entanglement, a quantum link between disparate objects, can enable ultra-secure cryptography, but even a slight jostle can destroy it, so systems that rely on it are not always useful in practice. Or so it seemed. Jeffrey Shapiro of the
Massachusetts Institute of Technology and colleagues devised a cryptography scheme in which one person, Alice, entangles two beams of light. She sends one to Bob, and retains the other as a key. Bob changes phase of the beam he receives to mean “yes”, or leaves it alone to mean “no”, amplifies it and sends it back. Only Alice, who holds the entangled partner, can work out whether Bob made the change, making the system super secure. Crucially, she can do this even if the entanglement itself is gone.
When Shapiro’s team recreated the set-up in the lab, the entanglement was destroyed. However, Alice was still able to use her beam to decode Bob’s message, because of relic correlations between the two beams. Although no longer entangled, photons in the beams are still more likely than chance to share the same state (Physical Review Letters, doi.org/m62). “The quantum state really helps even though we end up with no quantumness at all,” says team member Zheshen Zhang. David White Photography
Volcano screams hold deep secrets
Our sun wags a lucky clover tail LUCKY us! Our solar system has a tail shaped like a four-leaf clover, according to new observations of the plasma bubble that separates us from the rest of the galaxy. Particles blowing out from the sun – the solar wind – keep the plasma bubble inflated. Astronomers have long assumed that the sun’s motion as it orbits the centre of the galaxy squashes the bubble into a bullet shape, with a tail extending to the rear. Using observations from NASA’s Interstellar Boundary Explorer (IBEX) spacecraft, astronomers were able to map this “heliotail” for the first time (Astrophysical Journal, doi.org/ m65). One surprise was that, if we were to look down its length from front to back, we would see particles clustered into four lobes: two on the sun’s polar plane made of fast-moving particles and two on its equatorial plane made of slower-moving ones. The lobes might be a reflection of solar activity, says IBEX principal investigator David McComas. The map is based on data taken when the sun was minimally active and the solar wind had slowed down around the sun’s low to mid-latitudes.
London underground: mind the mould THE Jubilee line is the youngest and smartest of all London Underground lines, but it is mouldier than the much older Central and Bakerloo lines. Daniel Henk, now at the University of Bath, UK, and colleagues collected fungal cells lurking on the platforms at 12 stations across the three lines. They then compared these levels with those in a London hospital and in one of the city’s parks. People travelling on the Jubilee line – which opened in 1979 and was extended in 1999 – breathe in fractionally more fungal cells than those on the Central line, which
opened in 1900. In both cases, it was just over 1 fungal cell per minute. This is twice as much as you would get in the park and, reassuringly, four times as much as in the hospital. On the Bakerloo line, which opened in 1906, people take in 0.75 cells a minute. Strangely, the Jubilee line had the fewest Penicillium cells – from which penicillin is produced – though it is one of the most common fungal species in the outside air. The difference is likely to be down to temperature, humidity and how the stations are connected to the outside (Fungal Ecology, doi.org/m66).
20 July 2013 | NewScientist | 15