Leggett–Garg inequality
Imagine you have a toy that can either be red or blue, and you want to know what color it is. You ask your friend to check the color every hour to see if it changes. After three hours, your friend tells you that the toy was red every time.
Now, let’s say you have a machine that can measure the color of the toy. You decide to use it to check the color every minute. After 180 minutes, the machine tells you that the toy was blue for the first 60 minutes, then red for the next 60 minutes, and then blue for the final 60 minutes. However, when you asked your friend to check the color, they told you it was always red.
The Leggett-Garg inequality is a way to determine if the toy follows the same rules as classical physics or quantum mechanics. In classical physics, the color of the toy should not change during the time it is being observed, so your friend’s measurements should match the machine’s measurements. However, in quantum mechanics, the toy can exist in two different states at the same time, so your friend’s measurements may not match the machine’s measurements.
The Leggett-Garg inequality compares the results of measurements taken at different times to see if they follow the rules of classical physics or quantum mechanics. If the measurements violate the Leggett-Garg inequality, it means the toy is following the rules of quantum mechanics and can exist in two different states at the same time.
Now, let’s say you have a machine that can measure the color of the toy. You decide to use it to check the color every minute. After 180 minutes, the machine tells you that the toy was blue for the first 60 minutes, then red for the next 60 minutes, and then blue for the final 60 minutes. However, when you asked your friend to check the color, they told you it was always red.
The Leggett-Garg inequality is a way to determine if the toy follows the same rules as classical physics or quantum mechanics. In classical physics, the color of the toy should not change during the time it is being observed, so your friend’s measurements should match the machine’s measurements. However, in quantum mechanics, the toy can exist in two different states at the same time, so your friend’s measurements may not match the machine’s measurements.
The Leggett-Garg inequality compares the results of measurements taken at different times to see if they follow the rules of classical physics or quantum mechanics. If the measurements violate the Leggett-Garg inequality, it means the toy is following the rules of quantum mechanics and can exist in two different states at the same time.