Quantum mechanics
the time it was sent and the time it was received to find the distance as it travels at the speed of light. This comes with a problem as GPS satellites are around 20,200 km from Earth and the speed of light is 300 million ms-1 so the time it takes to reach Earth is very small. This means that very accurate times are required to reduce error and determine accurate locations which is why atomic clocks must be utilized, making GPS depend on quantum mechanics. Some other uses of atomic clocks include in the military where precise time measurements are needed and in scientific research and experiments where precise measurements are needed, for example when determining physical constants to a high degree of accuracy.
MRI
Possibly the most impactful application of quantum mechanics is in MRI (magnetic resonance imaging). The underlying principle of MRI imaging is deeply rooted in the quantum mechanics of the hydrogen atom in the water which makes up 60% of the human body. Quantum mechanics dictates that these hydrogen atoms have an innate property called spin allowing the MRI scanner to behave like a magnet, and the probability of the direction of its magnetic field is random, meaning the combined magnetic field of a large amount of hydrogen atoms normally cancels out. However, the external magnetic field created by the MRI causes all the magnetic fields of the hydrogen atoms to align with it. From there the machine produces a magnetic radio frequency pulse by applying an alternating current at a specific frequency misaligns the hydrogen atoms' magnetic fields towards the pulse for a moment before they realign with the machine's magnetic field, but as it does it decays with a changing magnetic field, inducing a current which is read as a signal by the MRI machine. The stronger the magnet the more hydrogen atoms will align with the magnetic field, causing a larger current, increasing the strength of the signal received and improving the quality of the image formed. This was revolutionary for medicine as before the only tools available were harmful X-rays and ultrasounds which produced low-quality 2-D images and pale in
Image from https://www.youtube.com/watch? v=NlYXqRG7lus
comparison to the detailed 3-D images provided by MRI.
Quantum cryptography (1980s)
Another unique application of quantum mechanics is in cryptography, the aim being to increase the security of encrypted data which only becomes more important as we move more of our lives and information online. It uses the properties of quantum mechanics to both send information and determine if it has been read. Photons are sent through a polarizer which randomly polarizes them in four directions, vertical, horizontal, 45 degrees right and 45 degrees left. They then travel through one of two beam splitters, either a horizontal or vertical and a diagonal which determines the polarization.
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