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Why climb mountains when you can tunnel through them? Harnessing quantum tunnelingholds great promise to speed up solutions for a broad range of optimization problems. I willpresent experiments on the disordered Ising ferromagnet, L(Ho,Y)F4, that quantitativelycompare quantum and classical annealing protocols, and demonstrate quantum speedup forreasons that can be understood at a microscopic level. This approach follows from RichardFeynman’s concept of a quantum computer and underlies the power of D-Wave machines. Inthe dilute limit, where there is no long-range ferromagnetic order, the Ho dipoles form clustersof several hundred spins that bind together and can be excited resonantly. By analogy to laserexcitation of atoms, we use a pump-probe magnetic technique to drive the system out of thelinear regime, and study both the nature of the excitations and the coupling of the excitationsto the spin bath. By applying a magnetic field transverse to the Ising axis, we are able to tunethe dynamics of the quantum degrees of freedom such that localized clusters (the “qubits”)essentially decouple from their environment.
Thomas Rosenbaum is the Sonja and William Davidow Presidential Chair, a Professor of Physics, and the President of the California Institute of Technology.
Physics Colloquium: Tom Rosenbaum, CalTech
Meeting ID: 962 9210 8492Password: 329448