K. W. Murch, U. Vool, D. Zhou, S. J. Weber, S. M. Girvin, I. Siddiqi
In practice, quantum systems are never completely isolated, but instead interact with degrees of freedom in the surrounding environment, eventually leading to decoherence of some states of the system. Precision measurement techniques such as nuclear magnetic resonance and interferometry, as well as envisioned quantum schemes for computation, simulation, and data encryption, rely on the ability to prepare and preserve delicate quantum superpositions and entanglement. The conventional route to long-lived quantum coherence involves minimizing coupling to a dissipative bath. Paradoxically, it is possible to instead engineer specific couplings to a quantum environment that allow dissipation to actually preserve coherence. We demonstrate such quantum bath engineering for a superconducting artificial atom coupled to a microwave frequency cavity. Cavity-assisted cooling of the atom is tailored to produce any arbitrary superposition of ground and excited states on demand with high fidelity.
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http://arxiv.org/abs/1207.0053
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