11 October 2019

from 09:30

Specialized seminar by Prof. John Preskill.

#### Address / Location

MPI of Quantum Optics | B.032

Hans-Kopfermann-Straße 1

85748

Garching

Germany

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As
MCQST Distinguished Lecturer
, Prof. John Preskill is giving a series of talks targeted to varied audiences. The seminar entiteled **"The ghost in the radiation: Robust encodings of the black hole interior"** is the third and last talk of the series. This specialized seminar is designed for researchers working in the same field.

**Abstract**

We reconsider the black hole firewall puzzle, emphasizing that quantum error correction, computational complexity, and pseudorandomness are crucial concepts for understanding the black hole interior. We assume that the Hawking radiation emitted by an old black hole is pseudorandom, meaning that it cannot be distinguished from a perfectly thermal state by any efficient quantum computation acting on the radiation alone. We then infer the existence of a subsystem of the radiation which we interpret as an encoding of the black hole interior. This encoded interior is entangled with the late outgoing Hawking quanta emitted by the old black hole, and is effectively invisible to computationally bounded observers who are outside the black hole. Specifically, efficient operations acting on the radiation, those with quantum computational complexity polynomial in the entropy of the remaining black hole, commute with logical operators acting on the encoded interior, up to corrections which are exponentially small in the entropy. Thus, under our pseudorandomness assumption, the black hole interior is well protected from exterior observers as long as the remaining black hole is macroscopic. On the other hand, if the radiation is not pseudorandom, an exterior observer can create a firewall.

**About John Preskill**

**John Preskill** is the Richard P. Feynman Professor of Theoretical Physics at the California Institute of Technology, and Director of the Institute for Quantum Information and Matter at Caltech. Preskill received his Ph.D. in physics in 1980 from Harvard, and joined the Caltech faculty in 1983. Preskill began his career in particle physics and cosmology, but in the 1990s he got excited about the possibility of solving otherwise intractable computational problems by exploiting quantum physics; he is especially intrigued by the ways our deepening understanding of quantum information and quantum computing can be applied to other fundamental issues in physics, such as the quantum structure of space and time.

You can follow him on Twitter @preskill.

**The seminar is intended for a highly specialized audience, but is open to everyone interested in the topic. **