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Physicists Hack Uncertainty to See an Ion Wiggle



In a laboratory in Boulder, Colorado, physicist Daniel Slichter plays an eerie little version of pinball with an individual atom like the ball. He and his colleagues at the National Institute of Standards and Technology have built a chip about the size of a grain of rice that they hold in a small freezer at about -430 degrees Fahrenheit. The chip, a square with gold-plated sapphire with metal wires attached to it, contains a single magnesium ion. Limited by an electric field, the ion floats 30 microns above the surface of the chip. Outside the freezer, Slichter's team hits the keys and turns the button to bathe around with electrical pulses.

However, their game is easier than pinball. All they want to do is find the ion to see the movement of the ball as it jiggles back and forth on the chip.

It is much more challenging than it sounds. Butts work with an object many thousands of times less than a bacterium. His team wants to pinch the location of the moving ion to less than a nanometer, a fraction of the ion's own diameter. At this level of precision, they inevitably stock up against one of nature's unbreakable rules: Heisenberg's uncertainty principle.

The principle of uncertainty basically says that you must not measure or describe an object with absolute precision. This inaccuracy is no fault with the researcher or the measuring apparatus. Nature has innate mystery; its smallest building block is fuzzy and diffuse objects. "The principle of uncertainty means that you cannot at all know everything about a particular system," says Slichter.

The principle doesn't matter much in everyday life because no one needs to bake a cake or even build a car with atomic precision. But it is a great thing for scientists like Slichter working on the quantum scale. They want to study particles like electrons, atoms and molecules, which often causes them to cool to temperatures near absolute zero, lowering them to a more manageable rate. But nature condemns these researchers, always to a level of inaccuracy.

So Slichter can never fully know his magnesium ion. At some point, if he measures a property of the ionic well, it comes at the expense of studying another aspect of the ion. For him, the principle of uncertainty is a mandatory tax that you have to pay to nature. "I think of it as" There is no free lunch, "says Slichter. For example, if he controls the speed of the ion precisely, the particle actually spreads out, making it harder for him to determine his position.

But he can try To play the system In a paper published today Science describes his team how to hide the uncertainty principle to better measure the position of the ion, their method achieves 50 times more precision than the previous best techniques, which also means that they can make measurements 50 times faster than before. Now the narrowing of the particle's position to an atomic size of less than one second.

The key to their method is to accept the noise determined by the uncertainty principle and control where It manifests itself, in order to measure the position of the ion, it basically transfers the uncertainty to its velocity, a value which they happen to care less about. nne method "squeeze" because they somehow "squeeze" uncertainty from one property to another.

To be clear, crushing does not push the principle of uncertainty. Nothing can. It is just the former that physicists could not negotiate which characteristic of the ion would contain the uncertainty at a particular moment. When the ion is left to its own units, fuzziness is evenly distributed over different properties. By squeezing, "you put the noise where it matters," said physicist Nancy Aggarwal of Northwestern University who was not involved in the experiment. Slichters team must still pay the same tax, but now they can tell nature which account is to be charged.

As the ion spins around the chip, they reduce the uncertainty in the ion position by periodically hitting it with an electric field. The reason for this seems complicated, but essentially the temporary electric field limits the range of motion of the ion and correlates the particle into a smaller space. This makes it easier to measure the position. "When the ion moves away from the center [of its trap]this electric field pushes it back," says Slichter. In essence, they push the ion from the trap center to let it jiggle; as it jiggles, they limit the ion short to reduce position uncertainty. Then they release the ion and repeat.

Bending the uncertainty principle has proved necessary since physicists feel subtle phenomena. For example, in its upgrade this year, Laser Interferometer Gravitational Wave Observatory, known as LIGO, has begun to use clamping to improve its detection of gravity waves, says Aggarwal, who helped develop the technique of collaboration. To detect gravitational waves, LIGO tries to detect changes in length in its two 2.5-mile arms. So they radiate a laser down each arm to coat a mirror at the end with photons. If the photons take more or less time to reach the mirror, it may indicate that space is stretched or shrunk. So LIGO has started using clamp for more precise control when photons leave the laser. But in their Heisenberg trade, they have to sacrifice control of the laser's brightness and allow some flicker.

In addition, physicists studying dark material will also use squeezing, said physicist David Allcock of the University of Oregon, one of Slichter's collaborators. Observations of distant galaxies suggest that an invisible dark matter constitutes 85 percent of the universe, but scientists do not know exactly what it is. Some theories indicate that dark matter particles create extremely weak electric fields. These electric fields, whose real, would push a magnesium ion ever so little, so their chip could be further developed to sense these dark matter particles.

Butchers and Allcock will use clamp for engineering quantum technology. They developed their chip as a precursor to a quantum computer. A so-called capture-ion quantum computer will consist of many ions placed in a grid on a chip as theirs, and a potential system of this computer involves encoding information in each ion's motion. For example, they could define a type of ionwiggle as 1

and another type of shimmy as 0. Because ions are electrically charged, a person's movement will interfere with the neighbor's position. If you can move the ions exactly, you can create a kind of quantum beam, and squeezing is a basic step for monitoring and controlling a person's ion movement.

Although their planned technology does not spread, Slichter and his team still have good rights. Their demonstration is close to the edges of what nature permits, hinting at an ultimate limit to what human technology can achieve. "We control the case with a precision beyond what is usually thought to be possible," says Slichter. "And we do this by exploiting the law of quantum mechanics to our advantage." Physicists can never challenge nature's laws, but they find ways to bend them.

Updated 06-20-2019 3: 15:00 ET: The story was updated to correct the name of David Allcock.


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