|地 震の発生日時： 02月27日15時34分頃
震源地： 南米西部 マグニチュード： 8.6 深さ： 不明
津波警報・注意報 平成２２年 ２月２８日０９時３３分 気象庁発表 ＊＊＊＊＊＊＊＊＊＊＊＊＊＊ 見出し ＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊ 大津波・津波の津波警報を発表しました 東北地方太平洋沿岸、北海道太平洋沿岸、青森県日本海沿岸、関東地方、 伊豆・小笠原諸島、東海地方、近畿四国太平洋沿岸、岡山県、 有明・八代海、九州地方東部、鹿児島県、沖縄県地方 これらの沿岸では、直ちに安全な場所へ避難してください なお、これ以外に津波注意報を発表している沿岸があります ＊＊＊＊＊＊＊＊＊＊＊＊＊＊ 本文 ＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊ 津波警報を発表した沿岸は次のとおりです ＜大津波＞ 青森県太平洋沿岸、岩手県、宮城県 ＜津波＞ 北海道太平洋沿岸東部、北海道太平洋沿岸中部、北海道太平洋沿岸西部、 青森県日本海沿岸、福島県、茨城県、千葉県九十九里・外房、 千葉県内房、東京湾内湾、伊豆諸島、小笠原諸島、相模湾・三浦半島、 静岡県、愛知県外海、伊勢・三河湾、三重県南部、淡路島南部、 和歌山県、岡山県、徳島県、愛媛県宇和海沿岸、高知県、有明・八代海、 大分県瀬戸内海沿岸、大分県豊後水道沿岸、宮崎県、鹿児島県東部、 種子島・屋久島地方、奄美諸島・トカラ列島、鹿児島県西部、 沖縄本島地方、大東島地方、宮古島・八重山地方 これらの沿岸では、直ちに安全な場所へ避難してください 津波注意報を発表した沿岸は次のとおりです ＜津波注意＞ 北海道日本海沿岸南部、オホーツク海沿岸、陸奥湾、大阪府、 兵庫県瀬戸内海沿岸、広島県、香川県、愛媛県瀬戸内海沿岸、 山口県瀬戸内海沿岸、福岡県瀬戸内海沿岸、福岡県日本海沿岸、 長崎県西方、熊本県天草灘沿岸 ＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊ 解説 ＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊ ＜大津波の津波警報＞ 高いところで３ｍ程度以上の津波が予想されますので、厳重に警戒してくだ さい ＜津波の津波警報＞ 高いところで２ｍ程度の津波が予想されますので、警戒してください ＜津波注意報＞ 高いところで０．５ｍ程度の津波が予想されますので、注意してください ＊＊＊＊＊＊＊＊＊＊＊＊ 震源要素の速報 ＊＊＊＊＊＊＊＊＊＊＊＊＊ ［震源、規模］ きのう２７日１５時３４分頃地震がありました 震源地は、南米西部（南緯３６．１度、西経７２．６度）で、地震の規模（ マグニチュード）は８．６と推定されます
(found here – )
World Book at NASA
Earthquake is a shaking of the ground caused by the sudden breaking and shifting of large sections of Earth’s rocky outer shell. Earthquakes are among the most powerful events on earth, and their results can be terrifying. A severe earthquake may release energy 10,000 times as great as that of the first atomic bomb. Rock movements during an earthquake can make rivers change their course. Earthquakes can trigger landslides that cause great damage and loss of life. Large earthquakes beneath the ocean can create a series of huge, destructive waves called tsunamis (tsoo NAH meez)that flood coasts for many miles.
Earthquakes almost never kill people directly. Instead, many deaths and injuries result from falling objects and the collapse of buildings, bridges, and other structures. Fire resulting from broken gas or power lines is another major danger during a quake. Spills of hazardous chemicals are also a concern during an earthquake.
The force of an earthquake depends on how much rock breaks and how far it shifts. Powerful earthquakes can shake firm ground violently for great distances. During minor earthquakes, the vibration may be no greater than the vibration caused by a passing truck.
On average, a powerful earthquake occurs less than once every two years. At least 40 moderate earthquakes cause damage somewhere in the world each year. Scientists estimate that more than 8,000 minor earthquakes occur each day without causing any damage. Of those, only about 1,100 are strong enough to be felt.
This article discusses Earthquake (How an earthquake begins) (How an earthquake spreads) (Damage by earthquakes) (Where and why earthquakes occur) (Studying earthquakes).
How an earthquake begins
Most earthquakes occur along a fault — a fracture in Earth’s rocky outer shell where sections of rock repeatedly slide past each other. Faults occur in weak areas of Earth’s rock. Most faults lie beneath the surface of Earth, but some, like the San Andreas Fault in California, are visible on the surface. Stresses in Earth cause large blocks of rock along a fault to strain, or bend. When the stress on the rock becomes great enough, the rock breaks and snaps into a new position, causing the shaking of an earthquake.
Earthquakes usually begin deep in the ground. The point in Earth where the rocks first break is called the focus, also known as the hypocenter, of the quake. The focus of most earthquakes lies less than 45 miles (72 kilometers) beneath the surface, though the deepest known focuses have been nearly 450 miles (700 kilometers) below the surface. The point on the surface of Earth directly above the focus is known as the epicenter of the quake. The strongest shaking is usually felt near the epicenter.
From the focus, the break travels like a spreading crack along the fault. The speed at which the fracture spreads depends on the type of rock. It may average about 2 miles (3.2 kilometers) per second in granite or other strong rock. At that rate, a fracture may spread more than 350 miles (560 kilometers) in one direction in less than three minutes. As the fracture extends along the fault, blocks of rock on one side of the fault may drop down below the rock on the other side, move up and over the other side, or slide forward past the other.
How an earthquake spreads
When an earthquake occurs, the violent breaking of rock releases energy that travels through Earth in the form of vibrations called seismic waves. Seismic waves move out from the focus of an earthquake in all directions. As the waves travel away from the focus, they grow gradually weaker. For this reason, the ground generally shakes less farther away from the focus.
There are two chief kinds of seismic waves: (1) body waves and (2) surface waves. Body waves, the fastest seismic waves, move through Earth. Slower surface waves travel along the surface of Earth.
Body waves tend to cause the most earthquake damage. There are two kinds of body waves: (1) compressional waves and (2) shear waves. As the waves pass through Earth, they cause particles of rock to move in different ways. Compressional waves push and pull the rock. They cause buildings and other structures to contract and expand. Shear waves make rocks move from side to side, and buildings shake. Compressional waves can travel through solids, liquids, or gases, but shear waves can pass only through solids.
Compressional waves are the fastest seismic waves, and they arrive first at a distant point. For this reason, compressional waves are also called primary (P) waves. Shear waves, which travel slower and arrive later, are called secondary (S) waves.
Body waves travel faster deep within Earth than near the surface. For example, at depths of less than 16 miles (25 kilometers), compressional waves travel at about 4.2 miles (6.8 kilometers) per second, and shear waves travel at 2.4 miles (3.8 kilometers) per second. At a depth of 620 miles (1,000 kilometers), the waves travel more than 11/2 times that speed.
Surface waves are long, slow waves. They produce what people feel as slow rocking sensations and cause little or no damage to buildings.
There are two kinds of surface waves: (1) Love waves and (2) Rayleigh waves. Love waves travel through Earth’s surface horizontally and move the ground from side to side. Rayleigh waves make the surface of Earth roll like waves on the ocean. Typical Love waves travel at about 23/4 miles (4.4 kilometers) per second, and Rayleigh waves, the slowest of the seismic waves, move at about 21/4 miles (3.7 kilometers) per second. The two types of waves were named for two British physicists, Augustus E. H. Love and Lord Rayleigh, who mathematically predicted the existence of the waves in 1911 and 1885, respectively.
Damage by earthquakes
How earthquakes cause damage
Earthquakes can damage buildings, bridges, dams, and other structures, as well as many natural features. Near a fault, both the shifting of large blocks of Earth’s crust, called fault slippage, and the shaking of the ground due to seismic waves cause destruction. Away from the fault, shaking produces most of the damage. Undersea earthquakes may cause huge tsunamis that swamp coastal areas. Other hazards during earthquakes include rockfalls, ground settling, and falling trees or tree branches.
The rock on either side of a fault may shift only slightly during an earthquake or may move several feet or meters. In some cases, only the rock deep in the ground shifts, and no movement occurs at Earth’s surface. In an extremely large earthquake, the ground may suddenly heave 20 feet (6 meters) or more. Any structure that spans a fault may be wrenched apart. The shifting blocks of earth may also loosen the soil and rocks along a slope and trigger a landslide. In addition, fault slippage may break down the banks of rivers, lakes, and other bodies of water, causing flooding.
Ground shaking causes structures to sway from side to side, bounce up and down, and move in other violent ways. Buildings may slide off their foundations, collapse, or be shaken apart.
In areas with soft, wet soils, a process called liquefaction may intensify earthquake damage. Liquefaction occurs when strong ground shaking causes wet soils to behave temporarily like liquids rather than solids. Anything on top of liquefied soil may sink into the soft ground. The liquefied soil may also flow toward lower ground, burying anything in its path.
An earthquake on the ocean floor can give a tremendous push to surrounding seawater and create one or more large, destructive waves called tsunamis, also known as seismic sea waves. Some people call tsunamis tidal waves, but scientists think the term is misleading because the waves are not caused by the tide. Tsunamis may build to heights of more than 100 feet (30 meters) when they reach shallow water near shore. In the open ocean, tsunamis typically move at speeds of 500 to 600 miles (800 to 970 kilometers) per hour. They can travel great distances while diminishing little in size and can flood coastal areas thousands of miles or kilometers from their source.
Structures collapse during a quake when they are too weak or rigid to resist strong, rocking forces. In addition, tall buildings may vibrate wildly during an earthquake and knock into each other. Picture San Francisco earthquake of 1906 A major cause of death and property damage in earthquakes is fire. Fires may start if a quake ruptures gas or power lines. The 1906 San Francisco earthquake ranks as one of the worst disasters in United States history because of a fire that raged for three days after the quake.
Other hazards during an earthquake include spills of toxic chemicals and falling objects, such as tree limbs, bricks, and glass. Sewage lines may break, and sewage may seep into water supplies. Drinking of such impure water may cause cholera, typhoid, dysentery, and other serious diseases.
Loss of power, communication, and transportation after an earthquake may hamper rescue teams and ambulances, increasing deaths and injuries. In addition, businesses and government offices may lose records and supplies, slowing recovery from the disaster.
Reducing earthquake damage
In areas where earthquakes are likely, knowing where to build and how to build can help reduce injury, loss of life, and property damage during a quake. Knowing what to do when a quake strikes can also help prevent injuries and deaths.
Where to build
Earth scientists try to identify areas that would likely suffer great damage during an earthquake. They develop maps that show fault zones, flood plains (areas that get flooded), areas subject to landslides or to soil liquefaction, and the sites of past earthquakes. From these maps, land-use planners develop zoning restrictions that can help prevent construction of unsafe structures in earthquake-prone areas.
How to build
|An earthquake-resistant building includes such structures as shear walls, a shear core, and cross-bracing. Base isolators act as shock absorbers. A moat allows the building to sway. Image credit: World Book illustration by Doug DeWitt|
Engineers have developed a number of ways to build earthquake-resistant structures. Their techniques range from extremely simple to fairly complex. For small- to medium-sized buildings, the simpler reinforcement techniques include bolting buildings to their foundations and providing support walls called shear walls. Shear walls, made of reinforced concrete (concrete with steel rods or bars embedded in it), help strengthen the structure and help resist rocking forces. Shear walls in the center of a building, often around an elevator shaft or stairwell, form what is called a shear core. Walls may also be reinforced with diagonal steel beams in a technique called cross-bracing.
Builders also protect medium-sized buildings with devices that act like shock absorbers between the building and its foundation. These devices, called base isolators, are usually bearings made of alternate layers of steel and an elastic material, such as synthetic rubber. Base isolators absorb some of the sideways motion that would otherwise damage a building.
Skyscrapers need special construction to make them earthquake-resistant. They must be anchored deeply and securely into the ground. They need a reinforced framework with stronger joints than an ordinary skyscraper has. Such a framework makes the skyscraper strong enough and yet flexible enough to withstand an earthquake.
Earthquake-resistant homes, schools, and workplaces have heavy appliances, furniture, and other structures fastened down to prevent them from toppling when the building shakes. Gas and water lines must be specially reinforced with flexible joints to prevent breaking.
Safety precautions are vital during an earthquake. People can protect themselves by standing under a doorframe or crouching under a table or chair until the shaking stops. They should not go outdoors until the shaking has stopped completely. Even then, people should use extreme caution. A large earthquake may be followed by many smaller quakes, called aftershocks. People should stay clear of walls, windows, and damaged structures, which could crash in an aftershock.
People who are outdoors when an earthquake hits should quickly move away from tall trees, steep slopes, buildings, and power lines. If they are near a large body of water, they should move to higher ground. Where and why earthquakes occur
Scientists have developed a theory, called plate tectonics, that explains why most earthquakes occur. According to this theory, Earth’s outer shell consists of about 10 large, rigid plates and about 20 smaller ones. Each plate consists of a section of Earth’s crust and a portion of the mantle, the thick layer of hot rock below the crust. Scientists call this layer of crust and upper mantle the lithosphere. The plates move slowly and continuously on the asthenosphere, a layer of hot, soft rock in the mantle. As the plates move, they collide, move apart, or slide past one another.
The movement of the plates strains the rock at and near plate boundaries and produces zones of faults around these boundaries. Along segments of some faults, the rock becomes locked in place and cannot slide as the plates move. Stress builds up in the rock on both sides of the fault and causes the rock to break and shift in an earthquake.
There are three types of faults: (1) normal faults, (2) reverse faults, and (3) strike-slip faults. In normal and reverse faults, the fracture in the rock slopes downward, and the rock moves up or down along the fracture. In a normal fault, the block of rock on the upper side of the sloping fracture slides down. In a reverse fault, the rock on both sides of the fault is greatly compressed. The compression forces the upper block to slide upward and the lower block to thrust downward. In a strike-slip fault, the fracture extends straight down into the rock, and the blocks of rock along the fault slide past each other horizontally.
Most earthquakes occur in the fault zones at plate boundaries. Such earthquakes are known as interplate earthquakes. Some earthquakes take place within the interior of a plate and are called intraplate earthquakes.
Interplate earthquakes occur along the three types of plate boundaries: (1) mid-ocean spreading ridges, (2) subduction zones, and (3) transform faults.
Mid-ocean spreading ridges are places in the deep ocean basins where the plates move apart. As the plates separate, hot lava from Earth’s mantle rises between them. The lava gradually cools, contracts, and cracks, creating faults. Most of these faults are normal faults. Along the faults, blocks of rock break and slide down away from the ridge, producing earthquakes.
Near the spreading ridges, the plates are thin and weak. The rock has not cooled completely, so it is still somewhat flexible. For these reasons, large strains cannot build, and most earthquakes near spreading ridges are shallow and mild or moderate in severity.
Subduction zones are places where two plates collide, and the edge of one plate pushes beneath the edge of the other in a process called subduction. Because of the compression in these zones, many of the faults there are reverse faults. About 80 per cent of major earthquakes occur in subduction zones encircling the Pacific Ocean. In these areas, the plates under the Pacific Ocean are plunging beneath the plates carrying the continents. The grinding of the colder, brittle ocean plates beneath the continental plates creates huge strains that are released in the world’s largest earthquakes.
The world’s deepest earthquakes occur in subduction zones down to a depth of about 450 miles (700 kilometers). Below that depth, the rock is too warm and soft to break suddenly and cause earthquakes.
Transform faults are places where plates slide past each other horizontally. Strike-slip faults occur there. Earthquakes along transform faults may be large, but not as large or deep as those in subduction zones.
One of the most famous transform faults is the San Andreas Fault. The slippage there is caused by the Pacific Plate moving past the North American Plate. The San Andreas Fault and its associated faults account for most of California’s earthquakes.
Intraplate earthquakes are not as frequent or as large as those along plate boundaries. The largest intraplate earthquakes are about 100 times smaller than the largest interplate earthquakes.
Intraplate earthquakes tend to occur in soft, weak areas of plate interiors. Scientists believe intraplate quakes may be caused by strains put on plate interiors by changes of temperature or pressure in the rock. Or the source of the strain may be a long distance away, at a plate boundary. These strains may produce quakes along normal, reverse, or strike-slip faults.
Recording, measuring, and locating earthquakes
To determine the strength and location of earthquakes, scientists use a recording instrument known as a seismograph. A seismograph is equipped with sensors called seismometers that can detect ground motions caused by seismic waves from both near and distant earthquakes. Some seismometers are capable of detecting ground motion as small as 0.1 nanometer. One nanometer is 1 billionth of a meter or about 39 billionths of an inch. Scientists called seismologists measure seismic ground movements in three directions: (1) up-down, (2) north-south, and (3) east-west. The scientists use a separate sensor to record each direction of movement.
A seismograph produces wavy lines that reflect the size of seismic waves passing beneath it. The record of the wave, called a seismogram, is imprinted on paper, film, or recording tape or is stored and displayed by computers.
Probably the best-known gauge of earthquake intensity is the local Richter magnitude scale, developed in 1935 by United States seismologist Charles F. Richter. This scale, commonly known as the Richter scale, measures the ground motion caused by an earthquake. Every increase of one number in magnitude means the energy release of the quake is about 32 times greater. For example, an earthquake of magnitude 7.0 releases about 32 times as much energy as an earthquake measuring 6.0. An earthquake with a magnitude of less than 2.0 is so slight that usually only a seismometer can detect it. A quake greater than 7.0 may destroy many buildings. The number of earthquakes increases sharply with every decrease in Richter magnitude by one unit. For example, there are 8 times as many quakes with magnitude 4.0 as there are with magnitude 5.0.
Although large earthquakes are customarily reported on the Richter scale, scientists prefer to describe earthquakes greater than 7.0 on the moment magnitude scale. The moment magnitude scale measures more of the ground movements produced by an earthquake. Thus, it describes large earthquakes more accurately than does the Richter scale.
The largest earthquake ever recorded on the moment magnitude scale measured 9.5. It was an interplate earthquake that occurred along the Pacific coast of Chile in South America in 1960. The largest intraplate earthquakes known struck in central Asia and in the Indian Ocean in 1905, 1920, and 1957. These earthquakes had moment magnitudes between about 8.0 and 8.3. The largest intraplate earthquakes in the United States were three quakes that occurred in New Madrid, Missouri, in 1811 and 1812. The earthquakes were so powerful that they changed the course of the Mississippi River. During the largest of them, the ground shook from southern Canada to the Gulf of Mexico and from the Atlantic Coast to the Rocky Mountains. Scientists estimate the earthquakes had moment magnitudes of 7.5.
Scientists locate earthquakes by measuring the time it takes body waves to arrive at seismographs in a minimum of three locations. From these wave arrival times, seismologists can calculate the distance of an earthquake from each seismograph. Once they know an earthquake’s distance from three locations, they can find the quake’s focus at the center of those three locations.
Scientists can make fairly accurate long-term predictions of where earthquakes will occur. They know, for example, that about 80 percent of the world’s major earthquakes happen along a belt encircling the Pacific Ocean. This belt is sometimes called the Ring of Fire because it has many volcanoes, earthquakes, and other geologic activity.
Scientists are working to make accurate forecasts on when earthquakes will strike. Geologists closely monitor certain fault zones where quakes are expected. Along these fault zones, they can sometimes detect small quakes, the tilting of rock, and other events that might signal a large earthquake is about to occur.
Exploring Earth’s interior
Most of what is known about the internal structure of Earth has come from studies of seismic waves. Such studies have shown that rock density increases from the surface of Earth to its center. Knowledge of rock densities within Earth has helped scientists determine the probable composition of Earth’s interior.
Scientists have found that seismic wave speeds and directions change abruptly at certain depths. From such studies, geologists have concluded that Earth is composed of layers of various densities and substances. These layers consist of the crust, mantle, outer core, and inner core. Shear waves do not travel through the outer core. Because shear waves cannot travel through liquids, scientists believe the outer core is liquid. Scientists believe the inner core is solid because of the movement of compressional waves when they reach the inner core.
Contributor: Karen C. McNally, Ph.D., Professor of Earth Sciences, University of California, Santa Cruz.
How to cite this article: To cite this article, World Book recommends the following format: McNally, Karen C. “Earthquake.” World Book Online Reference Center. 2005. World Book, Inc. http://www.worldbookonline.com/wb/Article?id=ar171680
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Chile quake similar to 2004 Indian Ocean temblor
February 27, 2010 By ALICIA CHANG , AP Science Writer
Residents look at a collapsed building in Concepcion, Chile, Saturday Feb. 27, 2010 after an 8.8-magnitude struck central Chile. The epicenter was 70 miles (115 kilometers) from Concepcion, Chile’s second-largest city. (AP Photo
(AP) — Scientists say the major earthquake that struck off the coast of Chile was a “megathrust” – similar to the 2004 Indian Ocean temblor that spawned a catastrophic tsunami.
Megathrust earthquakes occur in subduction zones where plates of the Earth’s crust grind and dive. Saturday’s jolt occurred when the Nazca plate dove beneath the South American plate, releasing tremendous energy.
The U.S. Geological Survey says 13 temblors of magnitude-7 or larger have hit coastal Chile since 1973.
The latest quake occurred about 140 miles north of the largest earthquake ever recorded. The magnitude-9.5 struck southern Chile in 1960, killing some 1,600 people and generating a tsunami that killed another 200 people in Japan, Hawaii and the Philippines.
2010 The Associated Press
My Note –
The difference is that the earthquake in Chile yesterday morning at 23 hours ago, was much deeper – 35 kilometers down. Now, there are 300 people listed as killed during the earthquake.
1.5M homes damaged in Chile quake—official
First Posted 07:54:00 02/28/2010
SANTIAGO, Chile—Some 1.5 million homes were damaged by the powerful earthquake that struck central Chile, Housing Minister Patricia Poblete said Saturday.
The figure includes half a million homes “with severe damage” that will “probably not be able to be lived in again,” Poblete told reporters.
The huge 8.8-magnitude earthquake that rocked Chile in the pre-dawn hours of Saturday left a trail of twisted buildings, destroyed bridges, and closed down the Santiago International Airport
The city of Concepcion, some 440 kilometers (273 miles) southwest of Santiago, and its surrounding area was especially hard-hit.
The Liquiñe-Ofqui Fault marked with red.
The Liquiñe-Ofqui Fault is major geological fault that runs a length of roughly 1000 km in a north-south direction and exhibits current seismicity . It is located in the Chilean northern patagonean Andes.
As the name implies it runs from the Liquiñe hot springs in the north to the Ofqui Isthmus in the south, where the Antarctic Plate meets the Nazca Plate and the South American Plate in Chile Triple Junction. A large parth of the fault runs along the Moraleda Channel. North of Liquiñe the fault is gradually converted into a compression area. At Quetrupillán volcano the fault is crossed by the Gastre Fault Zone. It may be classified as a dextral intra-arc transform fault.
The 1960 eruption of Cordón Caulle soon after the Great Chilean Earthquake was triggered by movements in the fault. The Aysén Fjord earthquake in 2007 and the eruption of Chaitén Volcano in 2008 are belivied to have been caused by movements in the fault.
My Note – as I was looking for information about the earthquake fault zones in Chile and other info about the tsunami earlier today, I also found a few other good things including these which were interesting – cricketdiane
magnetic polarity reversal. A change of the earth’s magnetic field to the opposite polarity that has occurred at irregular intervals during geologic time. Polarity reversals can be preserved in sequences of magnetized rocks and compared with standard polarity-change time scales to estimate geologic ages of the rocks. Rocks created along the oceanic spreading ridges commonly preserve this pattern of polarity reversals as they cool, and this pattern can be used to determine the rate of ocean ridge spreading. The reversal patterns recorded in the rocks are termed sea-floor magnetic lineaments.
Quantum measurement precision approaches Heisenberg limit
February 26, 2010 By Lisa Zyga
This illustration shows an adaptive feedback scheme being used to measure an unknown phase difference between the two red arms in the interferometer. A photon (qubit) is sent through the interferometer, and detected by either c1 or c0, depending on which arm it traveled through. Feedback is sent to the processing unit, which controls the phase shifter in one arm so that, when the next photon is sent, the device can more precisely measure the unknown phase in the other arm, and calculate a precise phase difference. Image credit: Hentschel and Sanders.
(PhysOrg.com) — In the classical world, scientists can make measurements with a degree of accuracy that is restricted only by technical limitations. At the fundamental level, however, measurement precision is limited by Heisenberg’s uncertainty principle. But even reaching a precision close to the Heisenberg limit is far beyond existing technology due to source and detector limitations.
Now, using techniques from machine learning, physicists Alexander Hentschel and Barry Sanders from the University of Calgary have recently shown how to generate measurement procedures that can outperform the best previous strategy in achieving highly precise quantum measurements. The new level of precision approaches the Heisenberg limit, which is an important goal of quantum measurement. Such quantum-enhanced measurements are useful in several areas, such as atomic clocks, gravitational wave detection, and measuring the optical properties of materials.
“The precision that any measurement can possibly achieve is limited by the so-called Heisenberg limit, which results from Heisenberg’s uncertainty principle,” Hentschel told PhysOrg.com. “However, classical measurements cannot achieve a precision close to the Heisenberg limit. Only quantum measurements that use quantum correlations can approach the Heisenberg limit. Yet, devising quantum measurement procedures is highly challenging.”
Heisenberg’s uncertainty principle ultimately limits the achievable precision depending on how many quantum resources are used for the measurement. For example, gravitational waves are detected with laser interferometers, whose precision is limited by the number of photons available to the interferometer within the duration of the gravitational wave pulse.
In their study, Hentschel and Sanders used a computer simulation of a two-channel interferometer with a random phase difference between the two arms. Their goal was to estimate the relative phase difference between the two channels. In the simulated system, photons were sent into the interferometer one at a time. Which input port the photon entered was unknown, so that the photon (serving as a qubit) was in a superposition of two states, corresponding to the two channels. When exiting the interferometer, the photon was detected as leaving one of the two output ports, or not detected at all if it was lost. Since photons were fed into the interferometer one at a time, no more than one bit of information could be extracted at once. In this scenario, the achievable precision is limited by the number of photons used for the measurement.
As previous research has shown, the most effective quantum measurement schemes are those that incorporate adaptive feedback. These schemes accumulate information from measurements and then exploit it to maximize the information gain in subsequent measurements. In an interferometer with feedback, a sequence of photons is successively sent through the interferometer in order to measure the unknown phase difference. Detectors at the two output ports measure which way each of the photons exits, and then transmit this information to a processing unit. The processing unit adapts the value of a controllable phase shifter after each photon according to a given policy.
However, devising an optimal policy is difficult, and usually requires guesswork. In their study, Hentschel and Sanders adapted a technique from the field of artificial intelligence. Their algorithm autonomously learns an optimal policy based on trial and error – replacing guesswork by a logical, fully automatic, and programmable procedure.
Specifically, the new method uses a machine learning algorithm called particle swarm optimization (PSO). PSO is a “collective intelligence” optimization strategy inspired by the social behavior of birds flocking or fish schooling to locate feeding sites. In this case, the physicists show that a PSO algorithm can also autonomously learn a policy for adjusting the controllable phase shift.
As Hentschel and Sanders show, after a sequence of input qubits have been sent through the interferometer, the measurement procedure learned by the PSO algorithm delivers a measurement of the unknown phase shift that scales closely to the Heisenberg limit, setting a new precedent for quantum measurement precision. The new high level of precision could have important implications for the gravitational wave detection.
“Einstein’s theory of General Relativity predicts gravitational waves,” Hentschel said. “However, a direct detection of gravitational waves has not been achieved. Gravitational wave detection will open up a new field of astronomy that augments electromagnetic wave and neutrino observations. For example, gravitational wave detectors can spot merging black holes or binary star systems composed of two neutron stars, which are mostly hidden to conventional telescopes.”
More information: Alexander Hentschel and Barry C. Sanders. “Machine Learning for Precise Quantum Measurement.” Physical Review Letters 104, 063603 (2010). DOI:10.1103/PhysRevLett.104.063603
Physicists detect entanglement of one photon shared among four locations
May 08, 2009 | not rated yet | 0
Evidence of a new phase in liquid hydrogen
February 25, 2010 By Miranda Marquit
Protium, the most common isotope of hydrogen. Image: Wikipedia.
(PhysOrg.com) — We like to think that we’ve got hydrogen, one of the most basic of elements, figured out. However, hydrogen can still surprise, especially once scientists start probing its properties on the most fundamental levels. “We ran simulations in order to provide a quantitative map of the molecular to atomic transition in liquid hydrogen,” Isaac Tamblyn tells PhysOrg.com. “Some of what we found was surprising, and could change the basic equations of state used in models involving hydrogen.”
Tamblyn is a scientist at Dalhousie University in Halifax, Canada. He worked with Stanimir A. Bonev to simulate the transition in liquid hydrogen, offering evidence for an unreported liquid phase, and noting some interesting structural characteristics of liquid hydrogen. Information on the simulation efforts, as well as results and conclusions, are presented in Physical Review Letters: “Structure and Phase Boundaries of Compressed Liquid Hydrogen.”
“We used first principles molecular dynamics simulations to model the liquid,” Tamblyn explains. “Forces between atoms were obtained using the Schrödinger equation. Velocities of the atoms were then updated, and the system was evolved through time.”
“We ran simulations to determine what would happen under different thermodynamic conditions, like density and temperature, and monitored the stability of molecules as the simulations progressed,” Tamblyn continues. “Our transition line is based on molecular stability. The chances of a molecule surviving are greater in a molecular liquid than in an atomic one, so this is a natural way to describe the transition.”
After running the simulations, Tamblyn and Bonev then had to analyze them. “We discovered an ordering in the liquid that accounts for some of the interesting characteristics of hydrogen, such as the fact that under certain conditions, liquid hydrogen is more dense than the solid. We also found that highly ordered packing explains properties related to dissociation that were previously not well understood.”
The pair found that the simulations suggest criteria for the existence of a first-order phase transition in liquid hydrogen. “The existence of this has been debated,” Tamblyn explains, “and we provide some evidence for its possibility.”
One of the most significant things Tamblyn and Bonev discovered through their simulations, from an astrophysics standpoint, is that equations describing the properties of hydrogen might need to be updated. “This should change the modeling going forward,” Tamblyn insists. “What we found in the liquid suggests what the solid might look like, and that can help determine some of its thermal and electronic properties.”
There is a good chance that planetary models might be changed using the new information on hydrogen structure discovered through these simulations. “Some previous calculations may need to be revised,” Tamblyn predicts. He also says that the simulations hint at some of the potential effects of mixtures involving hydrogen. “We’re especially interested in the implication for hydrogen and helium mixtures.”
Going forward, Tamblyn believes there is room to expand upon the work. “We are looking at the metallization of hydrogen, following the transition into a liquid metal. We are also looking at simulating hydrogen mixtures, especially with helium, to see if our findings hold true.”
More information: Isaac Tamblyn and Stanimir A. Bonev, “Structure and Phase Boundaries of Compressed Liquid Hydrogen,” Physical Review Letters (2010). Available online: http://link.aps.org/doi/10.1103/PhysRevLett.104.065702