Researchers have suggested a different approach over the years. We don't have to start from the bulk of our universe and search for the quantum entanglement pattern which could produce it. Instead, we can look the other way. Maybe experimenters can build systems with intriguing entanglements such as the CFT on the top and then search for analogues of space-time geometry or gravity.
This is easier said than done. It is not possible to create a system that looks like the gravitational duals of any of the strongly interconnected quantum systems. Theorists only have mapped out a fraction of the possible systems. Many others are too complicated to be studied theoretically using existing mathematical tools. It is possible to construct these systems in the laboratory and test if they have a gravitational dual. Maldacena said that these experimental constructions could help us find such systems. Maldacena said that there might be simpler systems than we currently know. Therefore, quantum gravity theorists have turned towards Schleier-Smith and her group of experts in controlling and building entanglement within quantum systems.
Quantum Gravity Meets Cold Atoms
Schleier-Smith said that there is something so beautiful about quantum mechanics. You'll find cables everywhere in the lab. There are also vacuum systems, messy hardware and other electronics that we built. You can still make a system that is neat and controlled so that it maps onto the elegant theory you can write on paper.
Since her graduation at Massachusetts Institute of Technology in 1995, Schleier-Smiths' work has been marked by this messy elegance. She used light to condense atoms into entangled states using light and showed how to use these systems to create more precise atomic clocks. After MIT she spent a few more years at the Max Planck Institute of Quantum Optics, Garching, Germany before landing at Stanford in 2013. Brian Swingle (a theoretical physicist at Stanford, working on string theory and quantum gravity, approached her with an unusual question a few years later. Swingle replied that I had sent her an email asking, "Can you reverse the time in your lab?" She said yes. So we began to talk.
Swingle wanted time to be reversed in order to study black hole phenomena and the quantum phenomenon called scrambling. Quantum scrambling is where information about quantum systems' states is quickly dispersed over a larger system. This makes it difficult to recover the original information. Swingle said that black holes are excellent at hiding information. Black holes are excellent at hiding information. Since the 1970s, theoretical physics has focused on the role of black holes in hiding information about objects that fall into them. This is also a key question for theoretical physics.
A black hole in the bulk is a dense web at the surface of entanglement that scrambles information very rapidly. This corresponds to the AdS/CFT correspondence. Swingle was curious to see how a fast-scrambling quantum systems would look in the laboratory. He realized that researchers needed to closely control the system to verify scrambling was occurring as quickly as possible. They also had to be able to reverse all interactions. Swingle stated that the only way to achieve this was to be able to fast-forward and reverse the system. Swingle said that this is not possible in everyday experiments. However, he knew Schleier Smiths lab could control the entanglement betweenatoms so they can reverse all their interactions. It was as if time were going backwards. He said that if you have this well-engineered, isolated quantum many-body system with high engineering, you might have a chance.
Swingle reached out and told Schleier-Smith what he wanted. Schleier-Smith explained to him that the process of scrambling has a fundamental speed limit. He also suggested that you could create a quantum system at Stanford that can scramble at that fundamental speed limit.
Schleier-Smith was left thinking about other quantum gravitational issues that her lab could explore after this work. She said that this made her think that these platforms might be a good way to create models of quantum gravity using toy methods. She began to think about a system where pairs of atoms were entangled together and each pair would then be entangled with another, creating a kind of tree. Although it seemed impossible to do, I could at least imagine how one would create a system that allows for this, she said. She wasn't certain if it corresponded with any quantum gravity model.
