In a first, scientists create a holographic wormhole and sent a message through it

A collaborative team of researchers in the U.S. created a holographic wormhole and sent a message through it. This is the first known report of a quantum simulation of a holographic wormhole on a quantum processor.

Einstein's theory of general relativity helps us to understand the physical world such as astronomical objects with high energies or matter densities. Quantum mechanics on the other hand, describes matter at atomic and subatomic scales.

However, the two theories are fundamentally incompatible and the holographic principle is a guide that can help us combine the two.

According to this principle, theories that include both quantum mechanics and gravity can be exactly equal to those that include quantum mechanics but not gravity. This is known as a dual and has fewer dimensions than its gravitational counterpart. The researchers used a quantum computer to create a hologram whose dual is a wormhole.

Einstein's view of blackholes

To understand the significance of this research, we need to go back to Einstein's research on black holes in the context of general relativity. With his collaborator, Nathan Rosen, Einstein said that a black hole had an interior region from where nothing could escape as well as an exterior region, from which escape was still possible. The demarcation between the two was called the event horizon.

What Einstein and Rosen realized was that a black hole had not just one but two exterior regions which were connected by a kind of wormhole which is now known as the Einstein-Rosen bridge. However, Einstein did not think that one could travel from one exterior region to another through the wormhole.

Still, if one goes from one external region and crosses the event horizon, it is still feasible to interact (even if very briefly!) with someone who jumped from the other exterior region before meeting their death.

Einstein's work in quantum mechanics also speaks of quantum entanglement where objects in quantum systems are linked in a non-classical pattern, even though they are separated by long distances.

Back in Einstein's time, the concepts of wormholes and quantum entanglement were considered separate, and the latter could not be used to send messages. Research over the years now points towards the two exteriors of the black hole being connected by quantum entanglement and the inability to travel from one exterior to another is considered to be the holographic dual of using quantum entanglement to send messages.

Sending messages through the wormhole

An emergent wormhole in a quantum computer

SpringerNature 

Researchers now posit that if the two exteriors of the black hole could be made to interact, it could also be used to send a message between them. This happens because during the interaction of the exteriors the wormhole opens up and becomes briefly traversable.

To demonstrate this, one could use two halves of a quantum computer in an entangled state such that they are the holographic dual of blackhole exteriors connected by a wormhole and sending a message across.

The research team led by Maria Spiropulu at the California Institute of Technology performed this simulation of a quantum system comprising of nine quantum bits (qubits) and saw that the message they sent through one half appeared at the other unscrambled.

Since the quantum system used in the experiment is rather small, it does not teach us anything that we do not know or compute something that is not possible with the computation power at our disposal these days. Nevertheless, it sets the stage for future work in this direction and would help us test theories of quantum gravity, where both general relativity and quantum mechanics can be studied together.

The research findings were published in the journal Nature today.

Abstract

The holographic principle, theorized to be a property of quantum gravity, postulates that the description of a volume of space can be encoded on a lower-dimensional boundary. The anti-de Sitter (AdS)/conformal field theory correspondence or duality1is the principal example of holography. The Sachdev–Ye–Kitaev (SYK) model of N ≫ 1 Majorana fermions2,3 has features suggesting the existence of a gravitational dual in AdS2, and is a new realization of holography4–6. We invoke the holographic correspondence of the SYK many-body system and gravity to probe the conjectured ER=EPR relation between entanglement and spacetime geometry7,8 through the traversable wormhole mechanism as implemented in the SYK model9,10. A qubit can be used to probe the SYK traversable wormhole dynamics through the corresponding teleportation protocol9. This can be realized as a quantum circuit, equivalent to the gravitational picture in the semiclassical limit of an infinite number of qubits9. Here we use learning techniques to construct a sparsified SYK model that we experimentally realize with 164 two-qubit gates on a nine-qubit circuit and observe the corresponding traversable wormhole dynamics. Despite its approximate nature, the sparsified SYK model preserves key properties of the traversable wormhole physics: perfect size winding11–13, coupling on either side of the wormhole that is consistent with a negative energy shockwave14, a Shapiro time delay15, causal time-order of signals emerging from the wormhole, and scrambling and thermalization dynamics16,17. Our experiment was run on the Google Sycamore processor. By interrogating a two-dimensional gravity dual system, our work represents a step towards a program for studying quantum gravity in the laboratory. Future developments will require improved hardware scalability and performance as well as theoretical developments including higher-dimensional quantum gravity duals18 and other SYK-like models19.