Splitting Atoms & Putting Them Back Together

Posted on June 17, 2012 by marcia

Franken-Physics: Atoms Split in Two & Put Back Together

Jesse Emspak, LiveScience Contributor

Date: 13 June 2012

University of Bonn physicists split atoms and put them back together.

A team of scientists was able to “split” an atom into its two possible spin states, up and down, and measure the difference between them even after the atom resumed the properties of a single state.
CREDIT: University of Bonn

Physicists have just upped their ante: Not only have they split atoms but, even trickier, they’ve put them back together.

Their secret? Quantum physics. A team of scientists was able to “split” an atom into its two possible spin states, up and down, and measure the difference between them even after the atom resumed the properties of a single state.

The research wasn’t just playtime for quantum physicists: It could be a steppingstone toward the development of a quantum computer, a way to simulate quantum systems (as plant photosynthesis and other natural processes appear to be) that would help solve complex problems far more efficiently than present-day computers can.

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Physicists have just upped their ante: Not only have they split atoms but, even trickier, they’ve put them back together.

The team at the University of Bonn in Germany did a variation on the famous double-slit experiment, which shows how ostensibly solid particles (atoms, electrons and the like) can behave like waves. The researchers found that they could send an atom to two places at once, separated by 10 micrometers (a hundredth of a millimeter — a huge distance for an atom).

Double slits

In the classic double-slit experiment, atoms are fired at a wall with two breaks in it, and they pass through to the other side, where they hit a detector, creating the kind of interference pattern expected from a wave. If atoms behaved the way we intuitively expect particles to behave, they should emerge out of one slit or the other, with no interference pattern. As more and more atoms passed through the slits, there should be a cluster of them around the two points behind the slits.

Since this is quantum mechanics, that’s not what happens.

Instead, there’s an interference pattern that shows peaks and valleys. The atoms behave like light waves. The atom is in two places at once.

But if you try to see the atom in one or both places, it “collapses” into one, as the act of observing it determines its fate; hence, the interference pattern disappears.

Atomic twins

In the experiment at Bonn, the researchers fired two lasers in sequence at a single atom of cesium, moving it to the left or right. The lasers allowed the researchers to control the movement of the atom precisely, in a way that the old-fashioned double slit would not. (Before firing the lasers, the researchers cooled the atom to within a hair of absolute zero, eliminating most of its own movement.)

Each atom has a spin state, which is either up or down. By moving the atom in two directions at once (using both lasers), the scientists were able to make it “split.” Unlike splitting an atom into its constituent subatomic particles, as happens in radioactive decay, in this case the atom was essentially splitting into a set of twins. It was in two states at once — up and down.

It’s not possible to see both states at once. If one were to try to measure the state of the atom, it would “collapse” into a single state. But when one looks at the atom at the end of its journey, the combination of the two states can be measured.

Since atoms — and other quantum particles — behave like waves, they have phases, just as waves do. (The phase is the particular point in the cycle of a wave, and is measured by degrees. Two waves that are the same shape and 180 degrees out of phase with each other will cancel each other out as one’s trough aligns with the other’s crest. Waves in phase with each other will add up as one crest aligns with the other crest).

The laser distorts the wave phase when it moves the atom to the left or right. So there is now a difference in the phases of the two spin states when the atom arrives at its destination and is no longer “split.” Even though it’s not possible to see both states at once, when one looks at the atom at the end of its journey, the combination of the two states can be measured.

Controlling qubits

In addition to measuring that phase difference, the researchers also saw “delocalization” — the double path through space the atom takes — at a greater distance than ever before, on the scale of micrometers as opposed to nanometers.

It’s this dual nature, called a superposed state, of atoms that would make quantum computers so powerful. The bits (known as “qubits”) could be in more than one state at once, allowing for calculations that would take ordinary computers an extremely long time. It also means that quantum computers could be useful for simulating other quantum systems.

Physicist Andrea Alberti, one of the paper’s co-authors, said that’s why in the future the researchers want to experiment with more atoms. “With two atoms, you have four different trajectories, but only one is where they are ‘meeting,'” he said. By controlling the phase of more atoms, you have more bits. One could think of it as two bits in all four possible states at once.

It isn’t clear, he said, what minimum number of bits would be needed to make a working quantum computer. But the fact that scientists can control the phase states of a single atom means it should be possible to do the same thing with more than one.

The point, Alberti said, is to build a way of simulating quantum systems. Right now that is difficult because the calculations are so complex. But a quantum computing system lends itself to such calculations better than a classical computer does.

from: http://www.livescience.com/20926-quantum-physics-atoms-split.html

Quantum Physics & Biology

Posted on June 7, 2012 by marcia

Weird World of Quantum Physics May Govern Life

Clara Moskowitz, LiveScience Senior Writer

Date: 05 June 2012

The bizarre rules of quantum mechanics may in fact enable many of life’s fundamental processes, scientists say.
CREDIT: agsandrew | Shutterstock

NEW YORK — The bizarre rules of quantum physics are often thought to be restricted to the microworld, but scientists now suspect they may play an important role in the biology of life.

Evidence is growing for the involvement of quantum mechanics in a wide range of biological processes, including photosynthesis, bird migration, the sense of smell, and possibly even the origin of life.

These and other mysteries were the topic of a panel lecture June 1 held here at the Kaye Playhouse at Hunter College, part of the fifth annual World Science Festival.

uantum mechanics refers to the strange set of rules that governs the behavior of subatomic particles, which can travel through walls, behave like waves and stay connected over vast distances. [Stunning Photos of the Very Small]

“Quantum mechanics is weird, that’s its defining characteristic. It’s funky and strange,” said MIT mechanical engineer Seth Lloyd.

These oddities generally don’t affect everyday macroscopic objects, which are thought to be too hot and wet for delicate quantum states to withstand. But it seems nature may have found ways to harness quantum mechanics to power some of its most complex and vital systems.

“Life is made out of atoms and atoms behave quantum mechanically,” said cosmologist Paul Davies of Arizona State University. “Life has been around for a long time — 3.5 billion years on this planet at least — and there’s plenty of time to learn some quantum trickery if it confers an advantage.”

Bird brains

One area where clues are implicating quantum mechanics is the internal compasses of birds and other migratory animals. Many bird species migrate thousands of miles every year to return not just to the same region, but to the exact same breeding spot.

For ages, scientists have puzzled how birds could achieve such a feat of navigation, assuming they possess some ability to sense direction based on Earth’s magnetic field.

“We see clearly they can detect the magnetic field,” said University of California, Irvine, biophysicist Thorsten Ritz. “What we cannot do is say, ‘This is the magnetic organ.'”

Mounting evidence now suggests birds may be relying on quantum entanglement — the strange ability of particles to share properties even when separated, so that if an action is performed on one, the other feels its consequences.

Scientists think the process is made possible by a protein inside birds’ eye cells called cryptochrome.

When green light passes into the bird’s eye, it hits cryptochrome, which gives an energy boost to one of the electrons of an entangled pair, separating it from its partner. In its new location, the electron experiences a slightly different magnitude of Earth’s magnetic field, and this alters the electron’s spin. Birds can use this information to build an internal map of Earth’s magnetic field to figure out their position and direction.

“It’s certainly very plausible,” Lloyd said. “It sounded kind of crazy when I first heard it. We don’t have direct experimental evidence, but it does make sense.”

The theory gained support from a recent experiment with fruit flies, which also contain cryptochrome. When this light-detecting protein was extracted from the fruit flies, they lost their magnetic sensitivity and became discombobulated.

Sniffing scents

Another case where quantum mechanics may come to the rescue is the sense of smell. At first, biologists thought they understood smell through a simple model: Odor molecules waft into the nose, and receptor molecules there bind to these molecules and identify them based on their particular shape.

But scientists realized that some odor molecules that have identical shapes have completely different smells, due to a minute chemical change, such as a single hydrogen atom in the molecule being replaced by a heavier version of hydrogen called deuterium. While this affects the weight of the molecule, it doesn’t change its shape, so it still fits into the receptor molecule in exactly the same way.

How, then, can olfactory systems sense the difference? The answer may lie in quantum particles’ ability to act like waves.

“The theory is that even if the shape of the molecule is the same, because it’s got this slight difference, it vibrates in a different fashion,” Lloyd said. “And this kind of wavelike nature, which is a purely quantum kind of effect, somehow this receptor is able to sense this vibrational difference.”

Missing pieces

Physicists are probing more and more unsolved mysteries of biology, hoping that quantum mechanics may provide the missing piece of the puzzle. They even have hope that it could shed light on one of the most intractable questions in all of biology: How did life get started?

“We want to know ‘How did non-life turn into life?'” Davies said. “Life is clearly a distinctive state of matter. What we would like to know is if that distinctiveness is fundamentally quantum mechanical.”

But in their excitement to try the quantum key in the locks of biology, some scientists are wary of overreaching.

“Quantum mechanics is strange and mysterious,” Lloyd said. “The origins of life are strange and mysterious. That doesn’t mean that they’re all the same thing. I think one should be careful saying that all strange and mysterious things have the same origin.”

from: http://www.livescience.com/20753-quantum-physics-biology-life.html

Uncertain about the Uncertainty Principle — Read On

Posted on February 22, 2012 by marcia

Wacky Physics: New Uncertainty About the Uncertainty Principle

Clara Moskowitz, LiveScience Senior Writer

Date: 21 February 2012 Time: 10:34 AM ET

An atom consists of a nucleus of protons and neutrons, with electrons orbiting around.

The uncertainty principle posits, for instance, that if you make a measurement to find out the exact position of an electron around an atom, you will only be able to get a hazy idea of how fast it’s moving.
CREDIT: Dreamstime

One of the most often quoted, yet least understood, tenets of physics is the uncertainty principle.

Formulated by German physicist Werner Heisenberg in 1927, the rule states that the more precisely you measure a particle’s position, the less precisely you will be able to determine its momentum, and vice versa.

The principle is often invoked outside the realm of physics to describe how the act of observing something changes the thing being observed, or to point out that there’s a limit to how well we can ever really understand the universe.

While the subtleties of the uncertainty principle are often lost on nonphysicists, it turns out the idea is frequently misunderstood by experts, too. But a recent experiment shed new light on the maxim and led to a novel formula describing how the uncertainty principle really works.

Perplexing logic

The uncertainty principle only applies in the quantum mechanical realm of the very small, on scales of subatomic particles. Its logic is perplexing to the human mind, which is acclimated to the macroscopic world, where measurements are only limited by the quality of our instruments.

But in the microscopic world, there truly is a limit to how much information we can ever glean about an object.

For example, if you make a measurement to find out exactly where an electron is, you will only be able to get a hazy idea of how fast it’s moving. Or you might choose to determine an electron’s momentum fairly precisely, but then you will have only a vague idea of its location.

Heisenberg originally explained the limitation using a thought experiment. Imagine shining light at a moving electron. When a photon, or particle of light, hits the electron, it will bounce back and record its position, yet in the process of doing so, it has given the electron a kick, thereby changing its speed.

The wavelength of the light determines how precisely the measurement can be made. The smallest wavelength of light, called gamma-ray light, can make the most precise measurements, but it also carries the most energy, so an impacting gamma-ray photon will deliver a stronger kick to the electron, thereby disturbing its momentum the most.

Though not imparting as much disruption to the electron’s momentum, a longer wavelength of light wouldn’t allow as precise a measurement.

Marbles and billiard balls

“In the early days of quantum mechanics, people interpreted the uncertainty relation in terms of such back-reactions of the measurement process,” said physicist Georg Sulyok of the Institute of Atomic and Subatomic Physics in Austria. “But this explanation is not 100 percent correct.”

Sulyok worked with a research team, led by physicists Masanao Ozawa of Japan’s Nagoya University and Yuji Hasegawa of Vienna University of Technology in Austria, to calculate and experimentally demonstrate how much of the uncertainty principle is due to the effects of measurement, and how much is simply due to the basic quantum uncertainty of all particles.

In quantum mechanics, particles can’t be thought of as marbles or billiard balls — tiny, physically distinct objects that travel along a straight course from point A to point B. Instead, particles can behave like waves, and can only be described in terms of the probability that they are at point A or point B or somewhere in between.

This is also true of a particle’s other properties, such as its momentum, energy and spin.

This probabilistic nature of particles means there will always be imprecision in any quantum measurement, no matter how little that measurement disturbs the system it is measuring.

“This has nothing to do with error or disturbances due to a measurement process, but is a basic fundamental property that every quantum mechanical particle has,” Sulyok told LiveScience. “In order to describe the basic uncertainty together with measurement errors and disturbances, both particle and measurement device in a successive measurement have to be treated in the framework of quantum theory.”

Calculating the uncertainty

To test how much this fundamental property contributes to the overall uncertainty, the researchers devised an experimental setup to measure the spin of a neutron in two perpendicular directions. These quantities are related, just as position and momentum are, so that the more precise a measurement is made of one, the less precise a measurement can be made of the other.

The physicists used magnetic fields to manipulate and measure the neutrons’ spin, and conducted a series of measurements where they systematically changed the parameters of the measuring device.

“You have this basic uncertainty, and then by measuring you add an additional uncertainty,” Sulyok said. “But with an apparatus performing two successive measurements, you can identify the different contributions.”

Using their data, the physicists were able to calculate just how the different types of uncertainty add together and influence each other. Their new formula doesn’t change the conclusion of the Heisenberg uncertainty principle, but it does tweak the reasoning behind it.

“The explanation that Heisenberg gave is very intuitive,” Sulyok said. “On a popular science level it is hardly ever distinguished at all, and sometimes it’s even not correctly explained in university textbooks. The quantum-mechanically correct calculation reinforced by our experimental data is a valuable step in achieving a more consistent view on the uncertainty principle.”

The results of the study were published in January 2012 in the journal Nature Physics.

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