Deterministic amplification of Schrödinger cat states in circuit quantum electrodynamics

Joo, Jaewoo and Elliott, Matthew and Oi, Daniel K L and Ginossar, Eran and Spiller, Timothy P. (2016) Deterministic amplification of Schrödinger cat states in circuit quantum electrodynamics. New Journal of Physics, 18 (2). 023028. ISSN 1367-2630

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    Perfect deterministic amplification of arbitrary quantum states is prohibited by quantum mechanics, but determinism can be achieved by compromising between fidelity and amplification power. We propose a dynamical scheme for deterministically amplifying photonic Schrödinger cat states, which show great promise as a tool for quantum information processing. Our protocol is designed for strongly coupled circuit quantum electrodynamics and utilizes artificial atomic states and external microwave controls to engineer a set of optimal state transfers and achieve high fidelity amplification. We compare analytical results with full simulations of the open, driven Jaynes-Cummings model, using realistic device parameters for state of the art superconducting circuits. Amplification with a fidelity of 0.9 can be achieved for sizable cat states in the presence of cavity and atomic-level decoherence. This tool could be applied to practical continuous-variable information processing for the purification and stabilization of cat states in the presence of photon losses.