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Quantum weirdness helps design better accelerometers

“BUILD A BETTER Accelerometers and the world pave the way for your door. Probably not as snappy as Ralph Waldo Emerson’s first maxim about mousetrap. But that’s the hope of Graham Malcolm, a physicist at the University of Strathclyde in Glasgow. Dr. Malcolm specializes in high-purity lasers. These can be used to make highly accurate equipment. You can then use them to build devices that can detect the smallest forces, such as the gravitational pull of a heavy truck passing through.

Laser light is famously pure. The way the laser works means that the beam coming out of the laser is monochromatic. But there is purity, then there is purity. With a truly monochromatic beam, all light has exactly the same frequency. In reality, this never happens. Small temperature changes and vibrations, and wobbling caused by defects in the mirror cavity where the beam is generated and amplified, mean that there is no completely pure laser beam. Light from cheap laser pointers can have a frequency range of 500 MHz (called the line width).MHz), the line width of a special scientific laser will be close to 1.MHz. In contrast, Dr. Malcolm’s latest product has a line width of only 20Hz.

This device, called SolsTiS, has a cavity containing titanium-dipped sapphire. Although this is a common material for lasers, SolsTiS cavities promote single-frequency emission and dissipate waste heat quickly by precision engineering and locking of components in place after calibration. It is shaped like.

The resulting beam purity can do something extraordinary for those who are accustomed to dealing with the world of classical mechanics rather than quantum mechanics (that is, most humans). This is to temporarily split an atom in two, using a trick that takes advantage of the fact that virtually every particle is clearly substantive, but in fact it is also a wave. ..

To perform this trick, the output from SolsTiS is split into multiple beams. The atom in question is the diffuse gas of rubidium in a cell that is refrigerated within 1/10 million of absolute zero. This extreme cold is achieved by using six of these beams to slow down the atoms in a process called Doppler cooling.

Place, place, place

In such a quiet atomic state, hit by a pulse of light of the correct frequency (SolsTiS laser tuned), it is split into two quanta waves moving apart (see figure). The second pulse reverses this and undoes the two waves, the third pulse allows them to interfere with each other, a characteristic interference that depends on the acceleration received when the waves are separated. Create a pattern. In addition, laser pulses can be used to detect different interference patterns of different atoms in a cell. That information reveals the amount of acceleration the atom has received. To take advantage of this phenomenon, Dr. Malcolm founded a company called M Squared. The plan is to use this atomic interference to create an accelerometer that is at least 100 times more accurate than the existing version.

Miniature accelerometers are already common (for example, most mobile phones include one), but these are mechanical devices rather than laser-based devices. Their job is inertial navigation, which divides the acceleration by time to calculate the speed and direction of movement, and thus the position. Once in the tunnel, inertial navigation will track your location. GPS Satellite signal.

However, such devices drift rapidly. Small errors are quickly amplified, resulting in a large miscalculation of position. Your cell phone will not go into orbit for more than a few minutes, and even the best military-grade inertial navigation systems that use lasers but no atomic interference will drift a few kilometers per day. In contrast, atomic interferometers drift only 2km a month.

First of all, this reliability is expensive and requires a fairly large kit. Therefore, it is primarily of interest for military applications, and one or two other specialized applications such as mining where satellite-based navigation is not possible. However, the equipment needed will eventually shrink to chip size, and costs should go down accordingly. This allows it to be incorporated into vehicles, phones and other mobile electronics. This could be useful in the world of unmanned vehicles, drone delivery, and self-driving taxis.

Atomic interference accelerometers have other uses as well. If you point one vertically, it becomes a gravimeter. It is a device that measures gravity, and its intensity varies slightly from place to place depending on the geology of the area. Oil and mineral explorers have adopted gravimeters since the 1930s. Atomic interference gravimeters are promised to be 1000 times more sensitive than current devices. Dr. Malcolm says the company is testing a prototype that can detect heavy trucks passing underneath under the gravitational pull of gravity when placed on a barge passing through a waterway. Such sensitive equipment helps to better understand the geology of the area before expensive drilling begins.

The first laser was a lab curiosity with little practicality, but it has changed a lot over the years. Lasers are now the basis for several excellent mousetraps, from broadband fiber networks to barcode scanners. Using them to manipulate the quantum properties of atoms in this way promises more such mousetraps in the future.

This article was published in the Science and Technology section of the printed version under the heading “Cool Thinking”.

Quantum weirdness helps design better accelerometers Source link Quantum weirdness helps design better accelerometers

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