Aug 07, 2020
Physicists have designed a quantum "optical compressor" that can reduce the quantum noise in the incident laser beam by 15%. This is the first system of its kind that works at room temperature, making it suitable for compact portable setups and can be added to high-precision experiments to improve laser measurement.
The core of this“compressor” is an optical cavity with two nano-mechanical mirrors located in a vacuum chamber. One of the mirrors is smaller than the diameter of a human hair, suspended by a spring-like cantilever and can move. The larger mirror stands still.
The shape and appearance of the smaller "nanomechanical" mirrors play a key role in the ability of the system to work at room temperature. When the laser beam enters the chamber, it is reflected between the two mirrors. The force exerted by the light causes the nanomechanical mirror to swing back and forth, enabling researchers to design parameters to give the light special quantum properties.
The laser can leave the system in a compressed state, which can be used for more accurate measurements, such as quantum computing and gravitational wave detection. MIT Marble Professor and Deputy Director of Physics Nergis Mavalvala said: "The importance of the result is that you can engineer these mechanical systems to have quantum mechanics at room temperature. Performance."
Laser contains a large number of photons, these photons flow out in the form of synchronized waves to produce a bright focused beam. However, in this orderly configuration, there is some randomness among the individual photons of the laser, which appear in the form of quantum fluctuations, which is also called "shot noise" in physics.
So far, optomechanical compression has been realized in large-scale devices that need to be housed in cryogenic refrigerators. This is because, even at room temperature, the surrounding thermal energy is sufficient to affect the movable parts of the system, causing "jitter", which cancels out any effects of quantum noise. In order to resist thermal noise, the researchers had to cool the system to approximately 10 K (-263.5 ℃). "When you need cryogenic cooling, you can't have a portable compact extruder," Mahuawala said. "That might be a breakthrough because you can't put the compressor in a large refrigerator and use it for experiments or some equipment used in the field."
The team led by Aggarwal wanted to design an opto-mechanical system where the movable mirror of the system is made of a material that essentially absorbs very little heat energy, so they don’t need to cool the system externally. They finally designed a very small 70-micron wide mirror with alternating layers of gallium arsenide and aluminum gallium arsenide. Both materials are crystals with a very ordered atomic structure that can prevent any incoming heat from escaping. This feature allows the team to identify and thereby reduce the laser's quantum noise by 15%, resulting in more precise "compressed" light. "Very messy materials can easily lose energy because electrons collide and collide and generate thermal motion in many places," Aggarwal said. "The more orderly and pure a material is, the fewer places it loses or dissipates energy."
Mavalvala said, "This shows that we know how to make a room temperature compressor that is independent of wavelength. As we improve our experiments and materials, we will make better compressors."