Interferometer of entangled matter and waves. Now with double the spookiness

Interferometer of entangled matter and waves. Now with double the spookiness

The Interferometer of Entangled Matter and Waves — now with double the spookiness

Display of entangled atoms inside an interferometer. Credit: Steven Burrows, Thompson Group/JILA

A team of JILA researchers and NIST colleague James K. Thompson has for the first time successfully combined two of the “spookiest” features of quantum mechanics to make a better quantum sensor: entanglement between atoms and delocalization of atoms.

Einstein originally mentioned entanglement like creating ghostly action at a distance—a strange effect of quantum mechanics in which what happens to one atom somehow affects another atom somewhere else. Entanglement is at the heart of quantum computers, quantum simulators and the hoped-for quantum sensors.

Another rather spooky aspect of quantum mechanics is delocalization, the fact that a single atom can be in more than one place at the same time. As described in their paper recently published in NatureThompson’s group combined the spookiness of both entanglement and delocalization to realize a matter-wave interferometer that can sense accelerations with precision that exceeds the standard quantum limit (the limit to the accuracy of experimental measurement at the quantum level) for the first time.

By doubling the spookiness, future quantum sensors will be able to provide more precise navigation, explore needed natural resources, more precisely determine fundamental constants such as fine structure and gravitational constants, more precisely search for dark matter, or perhaps even one day detect gravitational waves.

Creating entanglement

In order to entangle two objects, you usually have to bring them close to each other so that they can interact. Thompson’s group learned how to entangle thousands to millions of atoms even when they are separated by millimeters or more. They do this by using light that bounces between mirrors, called an optic cavity, to allow information to jump between atoms and bind them into a entangled state. Using this unique light-based approach, they created and observed some of the most intricate states ever generated in any system, whether atomic, photonic or solid state.

The group devised two different experimental approaches, both of which they used in their recent work. In the first approach, called nondestructive quantum measurement, they make a preliminary measurement of the quantum noise associated with their atoms and simply subtract the quantum noise from the final measurement.

In another approach, light injected into the cavity causes the atoms to undergo uniaxial twisting, a process in which the quantum noise of each atom becomes correlated with the quantum noise of all other atoms so that they can combine to become quieter. . “Atoms are like children who shut each other up to be quiet so they can hear about the fun their teacher promised them, but here it’s the entanglement that rustles,” says Thompson.

Matter and wave interferometer

One of the most accurate and precise quantum sensors today is the matter-wave interferometer. The idea is to use pulses of light to make the atoms move and not move at the same time by absorbing and not absorbing the laser light. This causes the atoms to be in two different places at once over time.

As graduate student Chengyi Luo explains, “We shine laser beams on atoms so that we actually split each atom’s quantum wave packet into two, in other words, the particle actually exists in two separate spaces at the same time.” Later pulses of laser light then reverse the process by putting the quantum wave packets back together so that any changes in the environment such as accelerations or rotations can be sensed by a measurable amount of interference occurring with the two parts of the atomic wave packet, similar to what is done with light fields in normal interferometers, but here with de’Broglie waves, or waves made of matter.

A team of JILA graduate students figured out how to do all of this inside an optical cavity with high-reflection mirrors. They could measure how far atoms fell along a 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 advantages of precision and accuracy that come from quantum mechanics.

Doubling down on the spookiness

By learning how to operate a matter-wave interferometer inside an optical cavity, a team of graduate students led by Chengyi Lu and Graham Greve were then able to take advantage of light-matter interactions to create entanglements between different atoms to make quieter and more precise measurements of acceleration due to gravity . This is the first time anyone has been able to observe a matter-wave interferometer with a precision that exceeds the standard quantum precision limit set by the quantum noise of uncoupled atoms.

Thanks to the improved precision, researchers like Luo and Thompson see many future advantages in using entanglement as a resource in quantum sensors. Thompson says, “I think one day we will be able to introduce entanglement into matter-wave interferometers for detection gravitational waves in space, or for Black matter searches — things that examine fundamental physicsas well as devices that can be used for everyday applications such as navigation or surveying.”

With this significant experimental advance, Thompson and his team hope that others will use this new interferometric approach to lead to other advances in the field of physics. Optimistically, Thompson says, “By learning to harness and control all the spookiness we already know about, we may be able to discover new spooky things about the universe that we haven’t even thought of yet.”

A quantum network of entangled atomic clocks

More information:
Graham P. Greve et al, High-fineness cavity entanglement-enhanced matter-wave interferometry, Nature (2022). DOI: 10.1038/s41586-022-05197-9

Citation: Interferometer of entangled matter and waves. Now with Double Spookiness (2022, October 21) Retrieved October 22, 2022, from

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