Quantum Entanglement Sensors can test quantum gravity

When you ask most physicists what is the most frustrating problem in modern physics, they will say the contradiction between general theory of relativity and quantum mechanics. That contradiction has been a thorn on the part of the physics community for decades.

There have been some advances in potential theories that can modify the two, but there is little experimental evidence to support these theories. That’s where Selim Sharier from Evanston from Northwestern University comes in. He plans to tackle a concept called space-born ultrafast measurement.

Frankly, the experiment is complicated. At the heart of it uses a space-based platform that carries quantum extension sensors and several precise positioning systems. However, to understand why testing quantum gravity is useful, you need to first have some explanation. First, let’s look at one of the most famous doctrines of general theory of relativity: the principle of equivalence.

The equivalent principle states that gravity and acceleration are the same. It is at the heart of the general theory of relativity, which deals with gravity as a curve of space-time, rather than as a fundamental force. However, many quantum gravity theories predict deviations from this equivalence at the small scales that quantum mechanics begin to take over.

To explain its deviation, physicists use a term known as the Eötvös parameter. It explains how closely related the gravity mass and inertia mass are. In general theory of relativity, at least they must be the same. However, as things approach the realm of quantum mechanics, some theories that argue that provide the theory of quantum gravity begin to see divergence between the two, expressed as the non-zero value of the Eötvös parameter.

So far, the values ​​of this parameter have been tested from about 10 to 15 by microscope experiments specially designed to test this theory. The researchers leading the project published a report in 2022, but to date it remains the most accurate measure of the Eötvös parameters.

However, the microscope used traditional accelerometers, which provided an estimate of over 100 times what we could get on Earth, but was not accurate enough to measure up to the 10-18th level.

Enter Dr. Sharier and his team. Their goal is to develop a space-based platform that uses atomic interferometers to limit parameter values ​​to 10-20. At that point, it could prove or disprove the theory of quantum gravity. But to get there, you need to lay a lot of foundations first.

One step in this process is to understand how quantum entanglement can be utilized with these atomic interferometers (AIS). AIS works by using the double nature of atoms (with wave/particle duality similar to light) and using a laser to divide the beam of atoms into separate paths. In Dr. Sharier’s experiments, these will be rubidium atoms. Once they are divided, if they are not observed, they enter a state equivalent to the famous Schrödinger cat experiment in quantum mechanics.

However, no such quantum mechanical state has been created before. This is the next step in Dr. Sharier’s development work. His team developed a “generalized echo aperture protocol.” This, in theory, allows us to maintain a quantum-entangled state for a long period of time. Doing so allows for accurate measurements of discrepancies between the two states when the two states are finally recombined, and those discrepancies can lead to a very accurate measurement of the Eötvös parameters.

The basic technology the team called “Schrodinger’s Cat Atomic Interferometer” (SCAI) in a recent press release can also be used for Earth’s applications. Using their theoretical implementations, if possible, these sensors are thousands of times more accurate than the typical accelerometer or gyroscope already used in a variety of applications such as guidance, navigation systems, and automobiles.

There is still much work to do to prove that theoretical implementation of this technology is possible in the real world. When people start to operate with quantum uncertainty, things tend to become tricky, not just the theoretical cats. But when Dr. Sharier and his team create a functional space-borne SCAI, we finally have a few steps to truly coordinate one of the biggest issues in modern physics.