By 
Kim Taylor for Quanta Magazine
A collaborative team of researchers in the U.S. made 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 like astronomical objects with more energies or matter densities. Quantum mechanics on the other hand, explains matter at atomic and subatomic scales.
However, the two theories are fundamentally incompatible and the holographic principle is a way that can help us merge the two.
According to this principle, theories that have 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 scientists used a quantum computer to make a hologram whose dual is a wormhole.
Einstein’s Perspective of Blackholes
To understand the value 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 internal area from where nothing could escape as well as an external area, 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 area and crosses the event horizon, it is still feasible to communicate (even if very briefly!) with someone who jumped from the other outer area 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.
Researchers now posit that if the two exteriors of the black hole could be made to interact, it could also be used to convey 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 tell 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.
