Physics Colloquium with Thomas F. Rosenbaum

3:30–4:30 pm Maria Goeppert-Mayer Lecture Hall

Quantum Annealing and Information Encoding in the Transverse Ising Model
Tom Rosenbaum, CalTech

On condensed matter experiment

Why climb mountains when you can tunnel through them? Harnessing quantum tunneling holds great promise to speed up solutions for a broad range of optimization problems. I will present experiments on the disordered Ising ferromagnet, L(Ho,Y)F4, that quantitatively compare quantum and classical annealing protocols and demonstrate quantum speedup for reasons that can be understood at a microscopic level. This approach follows from Richard Feynman’s concept of a quantum computer and underlies the power of D-Wave machines. In the dilute limit, where there is no long-range ferromagnetic order, the Ho dipoles form clusters of several hundred spins that bind together and can be excited resonantly. By analogy to laser excitation of atoms, we use a pump-probe magnetic technique to drive the system out of the linear regime, and study both the nature of the excitations and the coupling of the excitations to the spin bath. By applying a magnetic field transverse to the Ising axis, we are able to tune the dynamics of the quantum degrees of freedom such that localized clusters (the “qubits”) essentially decouple from their environment.

Event Type

Colloquia and Lectures

Mar 31