# Unraveling the Mysteries of Black Holes with Quantum Computing
Written on
Exploring Black Holes Through Quantum Entanglement
Recent research has unveiled an intriguing connection between cosmology and quantum computing, proposing that entangled qubits could be utilized to explore the enigmatic interiors of black holes. Physicists have successfully employed a seven-qubit quantum computer to simulate the chaotic information scrambling that occurs within a black hole, paving the way for potential future investigations into these cosmic phenomena.
When matter crosses into a black hole, it becomes scrambled—its associated information, including the characteristics of its particles, energy, and momentum, is mixed into the singularity at the black hole's core. This chaotic blending renders the retrieval of that information impossible. According to quantum mechanics, information is never truly lost, even when it seems to vanish within a black hole, which leads to what is known as the "black hole information paradox."
Some physicists argue that the information that crosses a black hole's event horizon is irretrievably lost. In contrast, others contend that while it may be reconstructible, this process could take an extraordinarily long time—potentially until the black hole has reduced to nearly half its original size. This shrinkage may occur due to the emission of Hawking radiation, a phenomenon caused by quantum fluctuations at the edge of the black hole, named in honor of the renowned physicist Stephen Hawking.
As Hawking theorized, larger black holes emit Hawking radiation at a slower rate, suggesting that a black hole with a mass equivalent to our Sun would take far longer than the universe's current age to evaporate, while microscopic black holes could dissipate in mere fractions of a second. However, there’s a possibility that the infalling information could be retrieved much sooner by measuring the delicate entanglements between the black hole and the emitted Hawking radiation.
Understanding Quantum Entanglement
Two pieces of information, such as quantum bits or qubits, are said to be entangled when their quantum states are so interlinked that the state of one instantly determines the state of the other, regardless of the distance separating them. Einstein famously described this phenomenon as "spooky action at a distance," but it’s more accurately a characteristic of the mathematical framework that defines quantum systems. The measurement of entangled qubits can facilitate "teleportation," enabling the instantaneous transfer of quantum information between qubits.
Norman Yao, an assistant professor of physics at UC Berkeley, states: “One can recover the information that fell into the black hole by conducting a complex quantum calculation on the outgoing Hawking photons. While this is expected to be extremely challenging, it should theoretically be possible if quantum mechanics holds true. That’s exactly what we are attempting here, albeit with a small three-qubit ‘black hole’ situated within a seven-qubit quantum computer.”
By introducing an entangled qubit into a black hole and analyzing the resultant Hawking radiation, one could, in theory, ascertain the state of a qubit inside the black hole, thereby offering a glimpse into the abyss.
Yao, alongside colleagues from the University of Maryland and the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada, plans to present their findings in the March 6 issue of Nature.
Innovative Approaches to Quantum Scrambling
Yao learned from his colleague Beni Yoshida at the Perimeter Institute that it is possible to recover quantum information that falls into a black hole if the information is scrambled rapidly within it. The more extensively it is mixed, the more reliably it can be retrieved through teleportation. Based on this insight, Yoshida and Yao proposed an experiment last year designed to demonstrate scrambling within a quantum computer.
Yao explains: “With our method, if you measure a sufficiently high teleportation fidelity, you can confirm that scrambling has occurred within the quantum circuit.” Yao collaborated with Chris Monroe, a physicist at the University of Maryland who leads one of the top trapped-ion quantum information groups. Monroe’s team implemented the protocol proposed by Yoshida and Yao and effectively measured an out-of-time-ordered correlation function.
These unique correlation functions, termed OTOCs, arise from comparing two quantum states that differ in the timing of applied perturbations. The crucial aspect is the ability to evolve a quantum state both forward and backward in time to analyze how the second perturbation affects the first.
Monroe's group developed a scrambling quantum circuit using three qubits within a seven-qubit trapped-ion quantum computer and characterized the decay of the OTOC. While a declining OTOC typically suggests that scrambling has occurred, they needed to demonstrate that this decay wasn’t merely due to decoherence—meaning it wasn’t just a result of inadequate shielding from environmental noise that causes quantum states to deteriorate.
Yao and Yoshida established that the more precisely they could recover the entangled or teleported information, the more rigorously they could impose a lower limit on the extent of scrambling that took place in the OTOC. Monroe and his team achieved a teleportation fidelity of about 80%, indicating that roughly half of the quantum state was scrambled, while the other half succumbed to decoherence. Nonetheless, this result was sufficient to confirm that authentic scrambling had indeed occurred in the three-qubit quantum circuit.
Yao elaborates on the significance of their work: “One potential application for our approach lies in benchmarking quantum computers, where this technique could be used to diagnose more complex forms of noise and decoherence in quantum processors.” Yao is also collaborating with a UC Berkeley team led by Irfan Siddiqi to demonstrate scrambling within a different quantum system: superconducting qutrits—quantum bits capable of existing in three states instead of two.
Siddiqi, a professor of physics at UC Berkeley, leads an effort at Lawrence Berkeley National Laboratory to construct a state-of-the-art quantum computing testbed, and he notes: “At its essence, this is an experiment involving qubits or qutrits, but its connection to cosmology arises from our belief that the dynamics of quantum information are universal.”
The United States is launching a billion-dollar quantum initiative, and understanding the dynamics of quantum information links various fields within this initiative: quantum circuits and computing, high-energy physics, black hole dynamics, condensed matter physics, and atomic, molecular, and optical physics. The terminology of quantum information has become integral to our comprehension of these diverse systems.
Originally published at Scisco Media