1. Quantum Information
and Everything

2. From: Robbert Dijkgraaf at the inauguration of Caltech’s Burke Institute.

3. hep-th papers with “entanglement” in the title14

4. From: Robbert Dijkgraaf at the inauguration of Caltech’s Burke Institute.

5. Frontiers of Physics short distance long distance complexity
Higgs boson
Neutrino masses
Supersymmetry
Quantum gravity
String theory
Large scale structure
Cosmic microwave background
Dark matter
Dark energy
Gravitational waves
“More is different”
Many-body entanglement
Phases of quantum matter
Quantum computing
Quantum spacetime

6. ???
Quantum Supremacy!

7. What’s in here? Problems Quantumly Hard Quantumly Easy
Classically Easy
What’s in here?

8. (Maybe. We don’t actually know for sure.)
particle collision
molecular chemistry
entangled electrons
A quantum computer can simulate efficiently any physical process that occurs in Nature.
(Maybe. We don’t actually know for sure.)
superconductor
black hole
early universe

9. What can we do with a small quantum computer?
(~50 physical qubits, without error correction)

10. small quantum computer?
What can we do with a
small quantum computer?
(~ 50 physical qubits, without error correction)
Learn how to make a big quantum computer.
Demonstrate and optimize fault-tolerant protocols.
Quantum repeaters.
Entangled clocks and sensors.
Quantum simulation: dynamics, variational eigensolvers, …
Study quantum chaos.
Approximate optimization algorithms.
Quantum annealing.
Discover new applications.

11. Can quantum annealers speed up solutions to combinatorial problems?

12. Can quantum computers improve approximate solutions to combinatorial optimization problems?

13. Can quantum computers improve approximate solutions to combinatorial optimization problems?
Quantum annealing.
Quantum Approximate Optimization Algorithm (Farhi et al. 2014).

14. What are the applications of the quantum algorithm for solving linear equations?

15. What are the applications of the quantum algorithm for solving linear equations?
Sample solution of Ax = b with exp. speedup (Harrow et al. 2009).
A well-conditioned and easy to simulate, |b easily prepared, …
Maxwell’s equations (Clader et al. 2013).
Effective resistance in electrical network (Wang 2013).
Machine learning, big data (Lloyd et al. 2014).

16. What can we do with a quantum network?

17. What can we do with a quantum network?
Quantum key distribution, and other quantum protocols.
A global clock (Lukin, Ye et al. 2014).
Long-baseline optical interferometry (Gottesman et al. 2012).

18. Can classical public key cryptosystems be resistant to quantum attacks?

19. Can classical public key cryptosystems be resistant to quantum attacks?
Lattice based.
McEliece.
Other.

20. Quantum Error Correction
-- Superconducting qubits are ready for demonstrations of QECC.
-- Microwave resonators for continuous-variable codes and cat codes.
-- Topological protection is becoming a reality.
-- Other approaches to physical protection (e.g. superinductance).
-- QEC in the AdS/CFT bulk-boundary dictionary.

21. Will future quantum computers be topological?

22. Can we build a
quantum hard drive?

23. What can we learn from analog and digital
quantum simulators?

24. What can we learn from analog and digital
quantum simulators?
Analog is noisy, digital can be error corrected.
Atoms, molecules, ions, superconducting circuits, …
Goal: learn about quantum phenomena that are hard to simulate classically.
Robust, universal properties may be accessible through crude quantum simulations.

25. Can quantum computers efficiently simulate all physical phenomena?

26. Can quantum computers efficiently simulate all physical phenomena?
Both YES and NO are interesting answers!
Real time evolution in chemistry and non-equilibrium stat. mech.
Quantum field theory: gauge theories, massless particles, improved scaling of cost with error, tensor network approaches, …
What is String Theory?

27. emerge from quantum entanglement?
Does spacetime
emerge from quantum entanglement?

28. emerge from quantum entanglement?
Does spacetime
emerge from quantum entanglement?
Relation between boundary entanglement entropy and bulk entanglement in AdS spacetime (Ryu and Takayanagi 2006).
Tensor network description of bulk geometry (Swingle 2009).
ER=EPR (entanglement=wormholes) (Van Raamsdonk 2010, MS 2013).
Computational complexity as geometry (Susskind 2014)
Spacetime as a quantum error-correcting code (Harlow et al. 2015)

29. Entanglement
= Wormholes?

30. Is spacetime a quantum error-correcting code?

31. What is the role of computational complexity
in the quantum theory
of gravity?

32. Reality
Anti-de Sitter space (negative vacuum energy, negative curvature) has a boundary.
This makes quantum mechanics in anti-de Sitter space easier. Observables are anchored to the boundary.
De Sitter space (positive vacuum energy, positive curvature) has no boundary.
We live in de Sitter space. That’s too bad …
We’ll need to learn how to do quantum mechanics in de Sitter space eventually. But it’s hard …

33. What can feasible laboratory experiments teach us about quantum gravity?