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Sunday, December 9, 2012
For Athletes, Risks From Ibuprofen Use - NYTimes.com
For Athletes, Risks From Ibuprofen Use - NYTimes.com:
'via Blog this'
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Many active people use the painkiller ibuprofen on an almost daily basis. In surveys, up to 70 percent of distance runners and other endurance athletes report that they down the pills before every workout or competition, viewing the drug as a preemptive strike against muscle soreness.
But a valuable new study joins growing evidence that ibuprofen and similar anti-inflammatory painkillers taken before a workout don’t offer any benefit and may be causing disagreeable physical damage instead, particularly to the intestines.
Studies have already shown that strenuous exercise alone commonly results in a small amount of intestinal trauma. A representative experiment published last year found that cyclists who rode hard for an hour immediately developed elevated blood levels of a marker that indicates slight gastrointestinal leakage.
Physiologically, it makes sense that exercise would affect the intestines as it does, since, during prolonged exertion, digestion becomes a luxury, said Dr. Kim van Wijck, currently a surgical resident at Orbis Medical Center in the Netherlands, who led the small study. So the blood that normally would flow to the small intestine is instead diverted to laboring muscles. Starved of blood, some of the cells lining the intestines are traumatized and start to leak.
Thankfully, the damage seems to be short-lived, Dr. van Wijck said. Her research has shown that within an hour after a cyclist finished riding, the stressed intestines returned to normal.
But the most common side-effect of ibuprofen is gastrointestinal damage. And since many athletes take the drug for pain before and after a workout, Dr. van Wijck set out to determine the combined effect of exercise and ibuprofen.
For the new study, published in the December issue of Medicine & Science in Sports & Exercise, researchers at Maastricht University in the Netherlands recruited nine healthy, active men and had them visit the university’s human performance lab four times.
During two of the visits, the men rested languorously for an hour, although before one of the visits, they swallowed 400 milligrams of ibuprofen the night before and also the morning of their trip to the lab. (Four hundred milligrams is the recommended non-prescription dosage for adults using the drug to treat headaches or other minor pain.)
During the remaining visits, the men briskly rode stationary bicycles for that same hour. Before one of those rides, though, they again took 400 milligrams of ibuprofen the night before and the morning of their workout.
At the end of each rest or ride, researchers drew blood to check whether the men’s small intestines were leaking. Dr. van Wijck found that blood levels of a protein indicating intestinal leakage were, in fact, much higher when the men combined bike riding with ibuprofen than during the other experimental conditions when they rode or took ibuprofen alone. Notably, the protein levels remained elevated several hours after exercise and ibuprofen.
The health implications of this finding are not yet clear, although they are worrying, Dr. van Wijck said. It may be that if someone uses ibuprofen before every exercise session for a year or more, she said, “intestinal integrity might be compromised.” In that case, small amounts of bacteria and digestive enzymes could leak regularly into the bloodstream.
More immediately, if less graphically, the absorption of nutrients could be compromised, especially after exercise, Dr. van Wijck said, which could affect the ability of tired muscles to resupply themselves with fuel and regenerate.
The research looks specifically at prophylactic use of ibuprofen and does not address the risks and benefits of ibuprofen after an injury occurs. Short-term use of Ibuprofen for injury is generally considered appropriate.
Meanwhile, the Dutch study is not the first to find damage from combining exercise and ibuprofen. Earlier work has shown that frequent use of the drug before and during workouts also can lead to colonic seepage. In a famous study from a few years ago, researchers found that runners at theWestern States 100-Mile Endurance Run who were regular ibuprofen users had small amounts of colonic bacteria in their bloodstream.
Ironically, this bacterial incursion resulted in “higher levels of systemic inflammation,” said David C. Nieman, a professor of health and exercise science at Appalachian State University who conducted the study and is himself an ultramarathoner. In other words, the ultramarathon racers who frequently used ibuprofen, an anti-inflammatory, wound up with higher overall levels of bodily inflammation. They also reported being just as sore after the race as runners who had not taken ibuprofen.
Animal studies have also shown that ibuprofen hampers the ability of muscles to rebuild themselves after exercise. So why do so many athletes continue enthusiastically to swallow large and frequent doses of ibuprofen and related anti-inflammatory painkillers, including aspirin, before and during exercise?
“The idea is just entrenched in the athletic community that ibuprofen will help you to train better and harder,” Dr. Nieman said. “But that belief is simply not true. There is no scientifically valid reason to use ibuprofen before exercise and many reasons to avoid it.”
Dr. van Wijck agrees. “We do not yet know what the long-term consequences are” of regularly mixing exercise and ibuprofen, she said. But it is clear that “ibuprofen consumption by athletes is not harmless and should be strongly discouraged.”
Saturday, October 20, 2012
Dane’s Wild Tale of Ruse to Find Anwar al-Awlaki - NYTimes.com
Dane’s Wild Tale of Ruse to Find Anwar al-Awlaki - NYTimes.com
A Biker, a Blonde, a Jihadist and Piles of C.I.A. Cash
By SCOTT SHANE
WASHINGTON — The man with the wire-rim glasses and bushy beard, speaking calmly in American-accented English, is familiar from dozens of Web videos urging violent jihad against the United States.
But in one astonishing clip, recorded more than a year before the man, Anwar al-Awlaki, was killed by a C.I.A. drone strike in Yemen, the American-born cleric had a very different mission: to propose marriage to a third wife.
“This message is specifically for Sister Aminah,” Mr. Awlaki says in the video to his future bride, a comely 32-year-old blonde from Croatia who he hoped would join him in his fugitive existence. The woman had expressed fervent admiration for Mr. Awlaki on his Facebook page and later made clear in her own video reply that she shared his radical views, saying, “I am ready for dangerous things.”
Neither Mr. Awlaki nor his prospective wife knew it, but their match was being managed by a Danish double agent as part of an attempt to help the Danish intelligence service and the C.I.A. find the cleric’s hiding place in Yemen. The attempt failed, but the undercover agent, Morten Storm, 36, a former motorcycle gang member who had converted to Islam, continued to communicate with Mr. Awlaki. When Mr. Awlaki was killed in a drone strike on Sept. 30, 2011, Mr. Storm was certain his efforts had been instrumental in it.
But eventually Mr. Storm’s resentment at not getting what he regarded as sufficient credit boiled over. He phoned Jyllands-Posten, the second-largest newspaper in Denmark, and told the bewildered receptionist that he had helped track down one of the world’s most wanted terrorist leaders. The Danish newspaper spent 120 hours interviewing Mr. Storm and verifying his account.
Among the evidence that the burly, red-haired Mr. Storm produced to confirm his wild tale, in addition to the video of Mr. Awlaki and e-mail exchanges with him, were postcards from intelligence agents, an audiotape of a C.I.A agent he knew as Michael and a photograph of $250,000 in $100 bills — money he says the C.I.A. paid him for his role as marriage broker.
As part of that plan, the suitcase carried to Yemen by the bride, identified only as Aminah in her video messages to Mr. Awlaki, was secretly fitted with a tracking device that the C.I.A. hoped would reveal the cleric’s location, Mr. Storm told the Danish reporters. But a wary associate of Mr. Awlaki’s had her discard the suitcase when she arrived in Sana, Yemen’s capital. She traveled on to meet and marry Mr. Awlaki, but the C.I.A. plan was thwarted.
Mr. Storm’s tale shows the lengths to which American intelligence officials went to hunt down Mr. Awlaki, a leader of Al Qaeda’s affiliate in Yemen who some counterterrorism officials believed posed a greater threat to the United States than Osama bin Laden did. Their method was a variation on the traditional so-called honey trap, in which spy services use the lure of sex to ensnare male targets. Mr. Awlaki had been arrested during his years as an imam in the United States for hiring prostitutes; his two Arab wives lived apart from him in 2010, and he had asked Mr. Storm to find him a European woman willing to stay with him in hiding.
His eloquent calls for violence, scattered across the Web, helped radicalize dozens of young, English-speaking Muslims. He was added to the Obama administration’s “kill list” after intelligence officials concluded that he had helped plan the failed bombing of a Detroit-bound airliner on Dec. 25, 2009.
His influence has survived his death. A 21-year-old Bangladeshi man, charged Wednesday with trying to blow up the Federal Reserve Bank of New York in a sting operation by the F.B.I., told an undercover agent that he had formed his jihadist views listening to Mr. Awlaki’s sermons.
The killing of Mr. Awlaki, an American citizen, without a trial and based on secret intelligence, set off a legal and ethical debate in the United States. Now, in Denmark, the articles in Jyllands-Posten have prompted some Danes to ask whether their government was complicit in Mr. Awlaki’s death and, if so, whether that violated Danish law.
Mr. Storm, whose life has been threatened since he went public, is in hiding and could not be reached for comment. The Danish intelligence service said in a statement that it “cannot and will not publicly confirm whether specific individuals have been used as sources.” A spokeswoman for the C.I.A. said the agency had no comment.
In a conversation in October 2011 with Mr. Storm and a Danish intelligence officer, which Mr. Storm recorded on his cellphone and which the Danish newspaper posted online, the purported C.I.A. officer known as Michael praised Mr. Storm’s efforts and even said that President Obama had been briefed on his efforts against Mr. Awlaki.
But he said “other projects” by the agency had located Mr. Awlaki. “We were very, very close,” Michael said on the tape, comparing their position to players in a World Cup soccer championship who might have scored the winning goal but did not. Mr. Storm can be heard on the tape protesting that the C.I.A. officer was playing down his own role and Denmark’s role.
Pierre Collignon, the editor in chief of Jyllands-Posten, said in an interview that the two reporters who met with Mr. Storm over a period of months, Orla Borg and Carsten Ellegaard, corroborated much of what he said about his dealings with Mr. Awlaki, the Danish intelligence service and the C.I.A.
“We were very cautious,” Mr. Collignon said. “We were afraid he might still be a jihadist and might be luring our reporters into a trap, maybe to kidnap them. He was a criminal before becoming a devout Muslim, and it’s difficult to trust him entirely. But we were able to document his story.”
The newspaper has examined paperwork showing regular payments to Mr. Storm from the Danish intelligence service and has confirmed that the snapshot of $250,000 spilling from an attaché case — the purported C.I.A. fee — was taken at his mother’s house. Mr. Collignon said the newspaper was planning to publish more articles based on Mr. Storm’s account of his six years of undercover work if it could confirm the details.
But he said that Jyllands-Posten, which was the target of terrorist threats after it published a dozen cartoons of the Prophet Muhammad in 2005, had decided not to post another video that showed Aminah removing her head covering to prove that she had blond hair, Mr. Collignon said. He said it might be considered provocative and invade the woman’s privacy.
Aminah is hiding with Qaeda militants in Yemen and helping produce Inspire magazine, a slick English-language publication that offers bomb-making advice and taunts against the United States. She last contacted Mr. Storm a month ago, Mr. Collignon said, and told him her dream was to become a suicide bomber.
Saturday, October 13, 2012
Why Netanyahu Retreated on Attacking Iran Soon - NYTimes.com
Why Netanyahu Retreated on Attacking Iran Soon - NYTimes.com
Why Netanyahu Backed Down
By GRAHAM T. ALLISON Jr. and SHAI FELDMAN
Published: October 12, 2012
FOR three years Israel’s prime minister, Benjamin Netanyahu, and his defense minister, Ehud Barak, seemed to be united in urging an early military attack on Iran’s nuclear facilities. But last week that alliance collapsed, with Mr. Netanyahu accusing Mr. Barak of having conspired with the Obama administration, in talks behind his back.
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Rift Grows Between Israeli Leaders Over Relations With U.S. (October 4, 2012)
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The clash came as a surprise in Israel, but in hindsight, there was a prelude — the speech Mr. Netanyahu delivered a week earlier to the United Nations General Assembly. In a memorable cartoonish graphic, Mr. Netanyahu depicted a “red line” that he said Israel would not let Iran cross. But he also acknowledged that Iran would not be able to cross it until next spring or summer. In doing so, he essentially reset the urgency of his warnings and ended speculation that Israel might mount a unilateral attack on Iran before the American presidential election.
The public row with Mr. Barak illustrated the magnitude of Mr. Netanyahu’s retreat and his difficulty in explaining it. He was left with implying that he had been undermined, if not betrayed by, his own defense minister. But that was not the full story of why he had blinked.
In fact, Mr. Netanyahu’s about-face resulted from a long-building revolt by Israel’s professional security establishment against the very idea of an early military attack, particularly one without the approval of the United States.
For months, former and even serving chiefs of Israel’s defense and intelligence communities have vigorously and publicly opposed Mr. Netanyahu’s case for attacking Iran sooner, rather than after all other means have been exhausted. Meir Dagan, the much respected former head of Mossad, did so to an American audience in an interview with Lesley Stahl broadcast last March by CBS’ “60 Minutes.” In Israel earlier, he had been quoted as saying that such an attack was “the stupidest idea I have ever heard.”
In addition, Mr. Netanyahu and Mr. Barak had proved unable to win sufficient support for early military action from other members of the government. Despite months of sustained effort, Mr. Netanyahu was not able to muster a majority even in his nine-member informal inner cabinet, much less Israel’s larger security cabinet, whose agreement he would need before attacking.
And in August, Israel’s president, Shimon Peres, took the occasion of his 89th birthday celebration to decisively reject any unilateral Israeli attack. The country’s pre-eminent elder statesman and the father of Israel’s own nuclear project, he broke with the nonpolitical traditions of Israel’s largely ceremonial presidency to argue that the central issue was the harm that going it alone could do to future American-Israeli relations.
Meanwhile, behind the scenes, the Obama administration was conducting a quiet campaign that would strengthen the view, already circulating among Israeli security professionals, that prematurely attacking Iran would not advance Israel’s interests and would damage Israel’s relationship with America. Instead of holding Israel at bay or threatening punitive action, the administration was upgrading American security assistance to Israel — so much so that earlier this year Mr. Barak described the level of support as greater than ever in Israel’s history.
This increase was manifest at every level: intelligence sharing that resulted in a convergence of assessments about Iran’s nuclear efforts; joint cyberoperations to slowIran’s nuclear program; support of Israel’s development of antimissile defenses; and reaching a common declared strategic approach to Iran’s nuclear program. That approach now focuses the two countries’ efforts on preventing Iran from obtaining nuclear weapons, while also ruling out the option of a retreat to containing and deterring a nuclear-armed Iran.
Equally important, increased American assistance has been accompanied by closer institutional links between the two countries’ defense and intelligence communities, as well as more intimate personal ties between both communities’ top echelons. Through numerous meetings in Tel Aviv, Jerusalem and Washington, the Obama administration has used these connections to convey an unambiguous message: Do not attack before all nonmilitary efforts to roll back Iran’s nuclear program have been exhausted.
Ever deeper American-Israeli defense ties have created what might be labeled a “United States lobby” among Israeli security professionals, who now have a strong interest in continuing the close partnership. It is no accident that the security institutions have become among the most vocal opponents of attacking Iran. No one knows better than they what is at stake if they ignore Washington’s concerns.
And their views have resonated with the Israeli general public: a poll conducted jointly last month by the Truman Institute at Hebrew University and the Palestinian Center for Policy and Survey Research found that 77 percent of Israelis now oppose a military attack on Iran that is not approved by Washington, although 71 percent would support an attack with American consent.
The plain fact is that the Obama administration achieved its objective of persuading Israel to refrain from a premature attack largely without explicit or implied threats. Instead, it has built a closer relationship with Israel’s defense community, and has capitalized on it.
And that should be a model for the future.
Especially when allies are as close as Israel and the United States, the relationship between them should not depend on whether the personal chemistry between their leaders is strong or weak. Instead, it should be based on firm mutual respect for the enduring national interests each side has. On that score, the professional security officials on both sides can be counted on to put domestic politics aside and to try to find a mutual approach to thorny problems, so long as they can talk candidly, and often, with each other.
A related conclusion is that an American administration will be most successful when it speaks, publicly and privately, with one voice — with the same message coming from the White House, the Pentagon and the Joint Chiefs. Then, its interests and priorities will be unmistakable to Israeli leaders, all of whom know how important American largess is to their own country.
These are important lessons not only for the future American-Israeli discourse on Iran, but also in the event that the next American administration, re-elected or new, will attempt to resurrect efforts to achieve Arab-Israeli peace. In that case, too, the United States is most likely to gain Israel’s cooperation by coupling a demonstrable commitment to the country’s security with a clear, unambiguous and sustained articulation of American national interests. And a thick, multilayered conversation between the national security elites in Israel and the United States could ensure that the two countries remain in sync, even when their leaders are not.
Quantum Computing with Ions [Re-Post]: Scientific American
Quantum Computing with Ions [Re-Post]: Scientific American
TRAPPED-ION COMPUTERS could encode and process data with strings of ions that act somewhat like the suspended metal balls in a Newton's cradle (as seen in this artist's conception). The ions interact through oscillatory motions. Researchers can manipulate the particles by training laser beams on them.Image: David Emmite (computer setup); George Retseck (spheres)
Quantum Computing with Ions [Re-Post]
Researchers are taking the first steps toward building ultrapowerful computers that use individual atoms to perform calculations
Tuesday, October 9, 2012 | 18
TRAPPED-ION COMPUTERS could encode and process data with strings of ions that act somewhat like the suspended metal balls in a Newton's cradle (as seen in this artist's conception). The ions interact through oscillatory motions. Researchers can manipulate the particles by training laser beams on them.Image: David Emmite (computer setup); George Retseck (spheres)ADVERTISEMENT
Editor’s note (10/9/2012): We are making the text of this article freely available for 30 days because the article was cited by the Nobel Committee as a further reading in the announcement of the 2012 Nobel Prize in Physics and was also written by one of the prize winners. The full article with images, which appeared in the August 2008 issue, is available for purchase here.
Over the past several decades technological advances have dramatically boosted the speed and reliability of computers. Modern computer chips pack almost a billion transistors in a mere square inch of silicon, and in the future computer elements will shrink even more, approaching the size of individual molecules. At this level and smaller, computers may begin to look fundamentally different because their workings will be governed by quantum mechanics, the physical laws that explain the behavior of atoms and subatomic particles. The great promise of quantum computers is that they may be able to perform certain crucial tasks considerably faster than conventional computers can.
Perhaps the best known of these tasks is factoring a large number that is the product of two primes. Multiplying two primes is a simple job for computers, even if the numbers are hundreds of digits long, but the reverse process—deriving the prime factors—is so extraordinarily difficult that it has become the basis for nearly all forms of data encryption in use today, from Internet commerce to the transmission of state secrets.
In 1994 Peter Shor, then at Bell Laboratories, showed that a quantum computer, in theory, could crack these encryption codes easily because it could factor numbers exponentially faster than any known classical algorithm could. And, in 1997, Lov K. Grover, also at Bell Labs, showed that a quantum computer could significantly increase the speed of searching an unsorted database—say, finding a name in a phone book when you have only the person’s phone number.
Actually building a quantum computer, however, will not be easy. The quantum hardware—the atoms, photons or fabricated microstructures that store the data in quantum bits, or qubits—needs to satisfy conflicting requirements. The qubits must be sufficiently isolated from their surroundings; otherwise stray external interactions will halt their computations. This destructive process, known as decoherence, is the bane of quantum computers. But the qubits also have to interact strongly with one another and must ultimately be measured accurately to display the results of their calculations.
Scientists around the globe are pursuing several approaches to building the first prototype quantum computers. Our own research focuses on processing information with singly charged positive ions, atoms that have been stripped of one electron. We have trapped short strings of ions—confining the particles in a vacuum using electric fields produced by nearby electrodes—so that they can receive input signals from a laser and share data with one another. Our goal is to develop quantum computers that are scalable—that is, systems in which the number of qubits could be increased to the hundreds or thousands. Such systems would fulfill the promise of the technology by accomplishing complex processing tasks that no ordinary computer could match.
Trapping Ions
Quantum mechanics is a theory based on waves. Just as the sound waves from two or more piano strings can merge into a chord, different quantum states can be combined into a superposition. For example, an atom may be simultaneously in two locations or in two different states of excitation. When a quantum particle in a superposition state is measured, the conventional interpretation is that the state collapses to a single result, with the probability of each possible measurement given by the relative proportions of the waves in the superposition. The potential power of a quantum computer derives from these superpositions: unlike a conventional digital bit, which can have a value of either 0 or 1, a qubit can be both 0 and 1 at the same time. A system with two qubits can hold four values simultaneously—00, 01, 10 and 11. In general, a quantum computer with N qubits can simultaneously manipulate 2N numbers; a collection of only 300 atoms, each storing a quantum bit, could hold more values than the number of particles in the universe!
Quantum mechanics is a theory based on waves. Just as the sound waves from two or more piano strings can merge into a chord, different quantum states can be combined into a superposition. For example, an atom may be simultaneously in two locations or in two different states of excitation. When a quantum particle in a superposition state is measured, the conventional interpretation is that the state collapses to a single result, with the probability of each possible measurement given by the relative proportions of the waves in the superposition. The potential power of a quantum computer derives from these superpositions: unlike a conventional digital bit, which can have a value of either 0 or 1, a qubit can be both 0 and 1 at the same time. A system with two qubits can hold four values simultaneously—00, 01, 10 and 11. In general, a quantum computer with N qubits can simultaneously manipulate 2N numbers; a collection of only 300 atoms, each storing a quantum bit, could hold more values than the number of particles in the universe!
These larger quantum superpositions are usually entangled, meaning that the measurements of the individual qubits will be correlated. Quantum entanglement can be thought of as an invisible wiring between particles that cannot be replicated in classical physics, a wiring that Einstein called “spooky action at a distance.” In our trapped-ion experiments, for example, each electrically levitated ion behaves like a microscopic bar magnet; the qubit states of 1 and 0 can correspond to two possible orientations of each atomic magnet (say, up and down). Laser cooling, which drains kinetic energy from atoms by scattering photons, brings the ions almost to rest within the trap. Because the ions reside in a vacuum chamber, they are isolated from the environment, yet the electric repulsion among them provides a strong interaction for producing entanglement. And laser beams thinner than a human hair can be targeted on individual atoms to manipulate and measure the data stored in the qubits.
Over the past few years scientists have performed many of the proof-of-principle experiments in quantum computing with trapped ions. Researchers have produced entangled states of up to eight qubits and have shown that these rudimentary computers can run simple algorithms. It appears straightforward (though technically very challenging) to scale up the trapped-ion approach to much larger numbers of qubits. Taking the lead from classical computers, this effort would involve sequencing a few types of quantum logic gates, each made up of only a few trapped ions. Scientists could adapt conventional error-correction techniques to the quantum world by using multiple ions to encode each qubit. Here the redundant encoding of information allows the system to tolerate errors, as long as they occur at a sufficiently low rate. In the end, a useful trapped-ion quantum computer would most likely entail the storage and manipulation of at least thousands of ions, trapped in complex arrays of electrodes on microscopic chips.
The first requirement for making a “universal” quantum computer—one that can perform all possible computations—is reliable memory. If we put a qubit in a superposition state of 0 and 1, with the ion’s magnetic orientation pointing up and down at the same time, it must remain in that state until the data are processed or measured. Researchers have long known that ions held in electromagnetic traps can act as very good qubit memory registers, with superposition lifetimes (also known as coherence times) exceeding 10 minutes. These relatively long lifetimes result from the extremely weak interaction between an ion and its surroundings.
The second essential ingredient for quantum computing is the ability to manipulate a single qubit. If the qubits are based on the magnetic orientation of a trapped ion, researchers can use oscillating magnetic fields, applied for a specified duration, to flip a qubit (changing it from 0 to 1, and vice versa) or to put it in a superposition state. Given the small distances between the trapped ions—typically a few millionths of a meter—it is difficult to localize the oscillating fields to an individual ion, which is important because we will often want to change one qubit’s orientation without changing that of its neighbors. We can solve this problem, however, by using laser beams that are focused on the particular qubit (or qubits) of interest.
The third basic requirement is the ability to devise at least one type of logic gate between qubits. It can take the same form as classical logic gates—the AND and OR gates that are the building blocks of conventional processors—but it must also act on the superposition states unique to qubits. A popular choice for a two-qubit logic gate is called a controlled not (CNOT) gate. Let us call the qubit inputs Aand B. A is the control bit. If the value of A is 0, the CNOT gate leaves B unchanged; if A is 1, the gate flips B, changing its value from 0 to 1, and vice versa. This gate is also called a conditional logic gate, because the action taken on qubit input B (whether the bit is flipped or not) depends on the condition of qubit input A.
The third basic requirement is the ability to devise at least one type of logic gate between qubits. It can take the same form as classical logic gates—the AND and OR gates that are the building blocks of conventional processors—but it must also act on the superposition states unique to qubits. A popular choice for a two-qubit logic gate is called a controlled not (CNOT) gate. Let us call the qubit inputs Aand B. A is the control bit. If the value of A is 0, the CNOT gate leaves B unchanged; if A is 1, the gate flips B, changing its value from 0 to 1, and vice versa. This gate is also called a conditional logic gate, because the action taken on qubit input B (whether the bit is flipped or not) depends on the condition of qubit input A.
To make a conditional logic gate between two ion qubits, we require a coupling between them—in other words, we need them to talk to each other. Because both qubits are positively charged, their motion is strongly coupled electrically through a phenomenon known as mutual coulomb repulsion. In 1995 Juan Ignacio Cirac and Peter Zoller, both then at the University of Innsbruck in Austria, proposed a way to use this coulomb interaction to couple indirectly the internal states of the two ion qubits and realize a CNOT gate. A brief explanation of a variant on their gate goes as follows.
First, think about two marbles in a bowl. Assume that the marbles are charged and repel each other. Both marbles want to settle at the bottom of the bowl, but the coulomb repulsion causes them to come to rest on opposite sides, each a bit up the slope. In this state, the marbles would tend to move in tandem: they could, for instance, oscillate back and forth in the bowl along their direction of alignment while preserving the separation distance between them. A pair of qubits in an ion trap would also experience this common motion, jiggling back and forth like two pendulum weights connected by a spring. Researchers can excite the common motion by applying photon pressure from a laser beam modulated at the natural oscillation frequency of the trap.
More important, the laser beam can be made to affect the ion only if its magnetic orientation is up, which here corresponds to a qubit value of 1. What is more, these microscopic bar magnets rotate their orientation while they are oscillating in space, and the amount of rotation depends on whether one or both of the ions are in the 1 state. The net result is that if we apply a specific laser force to the ions for a carefully adjusted duration, we can create a CNOT gate. When the qubits are initialized in superposition states, the action of this gate entangles the ions, making it a fundamental operation for the construction of an arbitrary quantum computation among many ions.
Researchers at several laboratories—including groups at the University of Innsbruck, the University of Michigan at Ann Arbor, the National Institute of Standards and Technology (NIST) and the University of Oxford—have demonstrated working CNOT gates. Of course, none of the gates works perfectly, because they are limited by such things as laser-intensity fluctuations and noisy ambient electric fields, which compromise the integrity of the ions’ laser-excited motions. Currently researchers can make a two-qubit gate that operates with a “fidelity” of slightly above 99 percent, meaning that the probability of the gate operating in error is less than 1 percent. But a useful quantum computer may need to achieve a fidelity of about 99.99 percent for error-correction techniques to work properly. One of the main tasks of all trapped-ion research groups is to reduce the background noise enough to reach these goals, and although this effort will be daunting, nothing fundamental stands in the way of its achievement.
Ion Highways
But can researchers really make a full-fledged quantum computer out of trapped ions? Unfortunately, it appears that longer strings of ions—those containing more than about 20 qubits—would be nearly impossible to control because their many collective modes of common motion would interfere with one another. So scientists have begun to explore the idea of dividing the quantum hardware into manageable chunks, performing calculations with short chains of ions that could be shuttled from place to place on the quantum computer chip. Electric forces can move the ion strings without disturbing their internal states, hence preserving the data they carry. And researchers could entangle one string with another to transfer data and perform processing tasks that require the action of many logic gates. The resulting architecture would somewhat resemble the familiar charge-coupled device (CCD) used in digital cameras; just as a CCD can move electric charge across an array of capacitors, a quantum chip could propel strings of individual ions through a grid of linear traps.
But can researchers really make a full-fledged quantum computer out of trapped ions? Unfortunately, it appears that longer strings of ions—those containing more than about 20 qubits—would be nearly impossible to control because their many collective modes of common motion would interfere with one another. So scientists have begun to explore the idea of dividing the quantum hardware into manageable chunks, performing calculations with short chains of ions that could be shuttled from place to place on the quantum computer chip. Electric forces can move the ion strings without disturbing their internal states, hence preserving the data they carry. And researchers could entangle one string with another to transfer data and perform processing tasks that require the action of many logic gates. The resulting architecture would somewhat resemble the familiar charge-coupled device (CCD) used in digital cameras; just as a CCD can move electric charge across an array of capacitors, a quantum chip could propel strings of individual ions through a grid of linear traps.
Many of the trapped-ion experiments at NIST have involved shuttling ions through a multizone linear trap. Extending this idea to much larger systems, however, will require more sophisticated structures with a multitude of electrodes that could guide the ions in any direction. The electrodes would have to be very small—in the range of 10 to 100 millionths of a meter—to confine and control the ion-shuttling procedure precisely. Fortunately, the builders of trapped-ion quantum computers can take advantage of microfabrication techniques, such as microelectromechanical systems (MEMS) and semiconductor lithography, that are already used to construct conventional computer chips.
Over the past year several research groups have demonstrated the first integrated ion traps. Scientists at the University of Michigan and the Laboratory for Physical Sciences at the University of Maryland employed a gallium arsenide semiconductor structure for their quantum chip. Investigators at NIST developed a new ion-trap geometry in which the ions float above a chip’s surface. Groups at Alcatel-Lucent and Sandia National Laboratories have fabricated even fancier ion traps on silicon chips. Much work remains to be done on these chip traps. The atomic noise emanating from nearby surfaces must be reduced, perhaps by cooling the electrodes with liquid nitrogen or liquid helium. And researchers must skillfully choreograph the movement of ions across the chip to avoid heating the particles and disturbing their positions. For example, the shuttling of ions around a simple corner in a T junction requires the careful synchronization of electric forces.
The Photon Connection
Meanwhile other scientists are pursuing an alternative way to build quantum computers from trapped ions, and this approach may circumvent some of the difficulties in controlling the motion of the ions. Instead of coupling the ions through their oscillatory motions, these researchers are using photons to link the qubits. In a scheme based on ideas described in 2001 by Cirac, Zoller and their colleagues Luming Duan of the University of Michigan and Mikhail Lukin of Harvard University, photons are emitted from each trapped ion so that the attributes of the photons—such as polarization or color—become entangled with the internal, magnetic qubit states of the ion emitter. The photons then travel down optical fibers to a beam splitter, a device typically used to split a light beam in two. In this setup, however, the beam splitter works in reverse: the photons approach the device from opposite sides, and if the particles have the same polarization and color, they interfere with each other and can emerge only along the same path. But if the photons have different polarizations or colors—indicating that the trapped ions are in different qubit states—the particles can follow separate paths to a pair of detectors. The important point here is that after the photons are detected, it is not possible to tell which ion has emitted which photon, and this quantum phenomenon produces entanglement between the ions.
Meanwhile other scientists are pursuing an alternative way to build quantum computers from trapped ions, and this approach may circumvent some of the difficulties in controlling the motion of the ions. Instead of coupling the ions through their oscillatory motions, these researchers are using photons to link the qubits. In a scheme based on ideas described in 2001 by Cirac, Zoller and their colleagues Luming Duan of the University of Michigan and Mikhail Lukin of Harvard University, photons are emitted from each trapped ion so that the attributes of the photons—such as polarization or color—become entangled with the internal, magnetic qubit states of the ion emitter. The photons then travel down optical fibers to a beam splitter, a device typically used to split a light beam in two. In this setup, however, the beam splitter works in reverse: the photons approach the device from opposite sides, and if the particles have the same polarization and color, they interfere with each other and can emerge only along the same path. But if the photons have different polarizations or colors—indicating that the trapped ions are in different qubit states—the particles can follow separate paths to a pair of detectors. The important point here is that after the photons are detected, it is not possible to tell which ion has emitted which photon, and this quantum phenomenon produces entanglement between the ions.
The emitted photons, though, are not successfully collected or detected in every attempt. In fact, the vast majority of the time the photons are lost and the ions are not entangled. But it is still possible to recover from this type of error by repeating the process and simply waiting for photons to be simultaneously counted on the detectors. Once this occurs, even though the ions may be widely separated, the manipulation of one of the qubits will affect the other, allowing the construction of a CNOT logic gate.
Scientists at the University of Michigan and the University of Maryland have successfully entangled two trapped-ion qubits, separated by about one meter, using the interference of their emitted photons. The main obstacle in such experiments is the low rate of entanglement generation; the likelihood of capturing these single photons into a fiber is so small that ions are entangled only a few times per minute. That rate could be increased dramatically by surrounding each ion with highly reflective mirrors in a so-called optical cavity, which would greatly improve the coupling of the ion emission with the optical fibers, but this enhancement is currently very difficult to accomplish experimentally. Nevertheless, as long as the interference eventually occurs, researchers can still use the system for quantum information processing. (The procedure is comparable to getting cable TV installed in a new house: although it may take many phone calls to get the service provider to install the system, eventually the cable is hooked up, and you can watch TV.)
Furthermore, investigators can expand the quantum gate operations to large numbers of qubits by connecting additional ion emitters by optical fiber and repeating the procedure until more entangled links are established. It should also be possible to use both photon coupling and the motional coupling discussed earlier to connect several small clusters of trapped ions over remote or even global distances. This is exactly the idea behind a “quantum repeater,” in which small quantum computers are networked at periodic distances to maintain a qubit as it travels over hundreds of kilometers. Without such a system the data would usually be lost forever.
The Quantum Future
Scientists are still far from constructing a quantum computer that can take on the daunting challenges—such as factoring very large numbers—that have stymied conventional machines. Still, some features of quantum information processing are already finding uses in the real world. For example, several of the simple logic operations required for two-qubit gates can be employed in atomic clocks, which keep time based on the frequency of the radiation emitted when atoms transition between quantum states. And researchers can apply the techniques for entangling trapped ions to increase the sensitivity of measurements in spectroscopy, the analysis of the light emitted by excited atoms.
Scientists are still far from constructing a quantum computer that can take on the daunting challenges—such as factoring very large numbers—that have stymied conventional machines. Still, some features of quantum information processing are already finding uses in the real world. For example, several of the simple logic operations required for two-qubit gates can be employed in atomic clocks, which keep time based on the frequency of the radiation emitted when atoms transition between quantum states. And researchers can apply the techniques for entangling trapped ions to increase the sensitivity of measurements in spectroscopy, the analysis of the light emitted by excited atoms.
The field of quantum information science promises to radically change the rules of computing. Collections of trapped ions are at the forefront of this effort because they offer a level of isolation from the environment that is currently unmatched in most other physical systems. At the same time, through the use of lasers, researchers can readily prepare and measure entangled quantum superpositions devised with small numbers of ions. In the coming years, we look forward to a new generation of trapped-ion chips that may pave the way for quantum computers with much larger numbers of qubits. Then scientists may finally realize their dream of creating a quantum machine that can tackle Herculean tasks once thought to be impossible.
Thursday, July 5, 2012
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