beecee Posted March 6, 2019 Posted March 6, 2019 https://phys.org/news/2019-03-ion-aces-quantum-scrambling.html Can entangled qubits be used to probe black holes? March 6, 2019, University of California - Berkeley Physicists have used a seven-qubit quantum computer to simulate the scrambling of information inside a black hole, heralding a future in which entangled quantum bits might be used to probe the mysterious interiors of these bizarre objects. Scrambling is what happens when matter disappears inside a black hole. The information attached to that matter—the identities of all its constituents, down to the energy and momentum of its most elementary particles—is chaotically mixed with all the other matter and information inside, seemingly making it impossible to retrieve. This leads to a so-called "black hole information paradox," since quantum mechanics says that information is never lost, even when that information disappears inside a black hole. So, while some physicists claim that information falling through the event horizon of a black hole is lost forever, others argue that this information can be reconstructed, but only after waiting an inordinate amount of time—until the black hole has shrunk to nearly half its original size. Black holes shrink because they emit Hawking radiation, which is caused by quantum mechanical fluctuations at the very edge of the black hole and is named after the late physicist Stephen Hawking. Read more at: https://phys.org/news/2019-03-ion-aces-quantum-scrambling.html#jCp the paper: https://www.nature.com/articles/s41586-019-0952-6 Verified quantum information scrambling: Abstract: Quantum scrambling is the dispersal of local information into many-body quantum entanglements and correlations distributed throughout an entire system. This concept accompanies the dynamics of thermalization in closed quantum systems, and has recently emerged as a powerful tool for characterizing chaos in black holes1,2,3,4. However, the direct experimental measurement of quantum scrambling is difficult, owing to the exponential complexity of ergodic many-body entangled states. One way to characterize quantum scrambling is to measure an out-of-time-ordered correlation function (OTOC); however, because scrambling leads to their decay, OTOCs do not generally discriminate between quantum scrambling and ordinary decoherence. Here we implement a quantum circuit that provides a positive test for the scrambling features of a given unitary process5,6. This approach conditionally teleports a quantum state through the circuit, providing an unambiguous test for whether scrambling has occurred, while simultaneously measuring an OTOC. We engineer quantum scrambling processes through a tunable three-qubit unitary operation as part of a seven-qubit circuit on an ion trap quantum computer. Measured teleportation fidelities are typically about 80 per cent, and enable us to experimentally bound the scrambling-induced decay of the corresponding OTOC measurement.
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