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Current Month (May '08)

 

:: Mon 5/5, 4:15pm in 36-428 (QIP seminar)

Barbara Terhal (IBM)
Simulation of Many-Body Hamiltonians using Perturbation Theory with Bounded-Strength Interactions

We show how to map a given n-qubit target Hamiltonian with bounded-strength k-body interactions onto a simulator Hamiltonian with two-body interactions, such that the ground-state energy of the target and the simulator Hamiltonians are the same up to an extensive error O(epsilon n) for arbitrary small epsilon. The strength of interactions in the simulator Hamiltonian depends on epsilon and k but does not depend on n. We accomplish this reduction using a new way of deriving an effective low-energy Hamiltonian which relies on the Schrieffer-Wolff transformation of many-body physics.


:: Mon 5/12, 4:15pm in 36-428 (QIP seminar)

Carlos Mochon (Perimeter Institute)
Quantum weak coin flipping with arbitrarily small bias

Coin flipping by telephone (Blum '81) is one of the most basic cryptographic tasks of two-party secure computation. In a quantum setting, it is possible to realize (weak) coin flipping with information theoretic security.

Quantum coin flipping has been a longstanding open problem, and its solution uses an innovative formalism developed by Alexei Kitaev for mapping quantum games into convex optimization problems. The optimizations are carried out over duals to the cone of operator monotone functions, though the mapped problem can also be described in a very simple language that involves moving points in the plane.

Time permitting, I will discuss both Kitaev's formalism, and the solution that leads to quantum weak coin flipping with arbitrarily small bias.


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