Algorithmic cooling of spins using optimal control

Yossi Attiya, M.Sc. Thesis Seminar
Wednesday, 4.1.2012, 13:30
Taub 601
Prof. Tal Mor

Nuclear magnetic resonance (NMR) has proven to be a leading implementation of quantum information processors where each molecule in the sample constitutes a register of quantum bits (qubits). However, at room temperature, the qubits that are realized by nuclear spins (1/2) are in a highly mixed state: noisy or with high entropy. Source coding (compression) can cool some spins (reducing their Shannon entropy) while heating others, yet this closed-system technique is limited by Shannon's entropy conservation. Algorithmic cooling bypasses this bound by utilizing fast-reseting spins and thermalization, an interaction of the qubits with the environment, which is non-reversible. By using GRAPE, an optimal control algorithm, we design efficient and robust radio frequency pulses, and applied multiple rounds of algorithmic cooling to a 3-spin system at the Technion NMR lab. No previous knowledge of nuclear magnetic resonance, quantum computers or data compression is required for the talk.

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