To create a more efficient quantum sensor, a team of JILA researchers has, for the first time, merged two of the most “frightening” aspects of quantum mechanics: the entanglement between atoms and the delocalization of atoms.
Entanglement is the strange effect of quantum mechanics in which what happens to one atom somehow influences another atom elsewhere. A second rather frightening aspect of quantum mechanics is delocalization, the fact that a single atom can be in several places simultaneously.
In this study, researchers combined the frightening nature of entanglement and delocalization to create a matter-wave interferometer capable of detecting accelerations with an accuracy that exceeds the standard quantum limit. Future quantum sensors will be able to provide more precise navigation, search for necessary natural resources, more accurately determine fundamental constants such as fine structure and gravitational constants, more accurately search for dark matter, and perhaps even detect gravitational waves one day. increasing the scary.
The researchers used light bouncing between mirrors, called an optical cavity, for entanglement. This allowed information to jump between atoms and bind them together in an entangled state. Using this special light-based technique, they produced and observed some of the most entangled states ever generated in any system, whether atomic, photonic, or solid state. Using this technique, the group designed two distinct experimental approaches, which they have used in their recent work.
In the first method, also known as non-demolition quantum measurement, they first measure the quantum noise bound to their atoms and then remove that measurement from the equation. The quantum noise of each atom becomes correlated with the quantum noise of all the other atoms by a process known as twisting on an axis in the second method, where light is injected into the cavity. This allows the atoms to work together to become quieter.
JILA and NIST Fellow James K. Thompson said: “Atoms are a bit like children shutting themselves up to be quiet so they can hear about the party the teacher has promised them, but here it’s the entanglement that makes the silence.”
Matter wave interferometer
The Matter-wave interferometer is one of the most accurate and precise quantum sensors to date.
Graduate student Chengyi Luo explained, “The idea is that one uses pulses of light to make the atoms move simultaneously and not move having both absorbed and unabsorbed laser light. This causes the atoms over time to be simultaneously at two different places at once.
“We shine laser beams on the atoms, so we split the quantum wave packet of each atom in half, in other words, the particle exists simultaneously in two separate spaces.”
Subsequent pulses of laser light reverse the process, bringing the quantum wave packets closer together, allowing any changes in the environment, such as accelerations or rotations, to be detected by measurable interference between the two components of the quantum wave packet. atomic waves, a bit like is done with light fields in classical interferometers, but here with de Broglie waves, or waves made of matter.
The research team figured out how to make this work inside an optical cavity with highly reflective mirrors. They were able to measure how far atoms traveled along the vertically oriented cavity due to gravity in a quantum version of Galileo’s gravity experiment by dropping objects from the Leaning Tower of Pisa, but with all the precision and accuracy benefits that come from quantum mechanics.
The group of graduate students led by Chengyi Luo and Graham Greve were then able to use the entanglement created by light-matter interactions to create a matter-wave interferometer inside an optical cavity to detect acceleration due to gravity in a quieter and more precise manner. This is the first time that a matter wave interferometer has been observed at a level of precision that exceeds the typical quantum limit imposed by the quantum noise of non-entangled atoms.
Thompson said, “With improved accuracy, researchers like Luo and Thompson see many future benefits for using entanglement as a resource in quantum sensors. I think one day we can introduce entanglement into matter wave interferometers for detecting gravitational waves in space or for dark matter searches – things that probe fundamental physics, as well as devices that can be used for everyday applications such as navigation or geodesy.
“With this momentous experimental breakthrough, Thompson and his team hope that others will use this new entangled interferometer approach to lead to further advances in physics. By learning to harness and control all the scary elements we already know, we may be able to discover new scary things about the universe that we haven’t even thought of yet!
Journal reference:
- Graham P. Greve et al., High Finesse Cavity Entanglement Enhanced Matter Wave Interferometry, Nature (2022). DOI: 10.1038/s41586-022-05197-9
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