Condensed Matter - Mesoscale and Nanoscale Physics Quantum Physics 2013-06-17 Nature The stochastic evolution of quantum systems during measurement is arguably the most enigmatic feature of quantum mechanics. Measuring a quantum system typically steers it towards a classical state, destroying any initial quantum superposition and any entanglement with other quantum systems. Remarkably, the measurement of a shared property between non-interacting quantum systems can generate entanglement starting from an uncorrelated state. Of special interest in quantum computing is the parity measurement, which projects a register of quantum bits (qubits) to a state with an even or odd total number of excitations. Crucially, a parity meter must discern the two parities with high fidelity while preserving coherence between same-parity states. Despite numerous proposals for atomic, semiconducting, and superconducting qubits, realizing a parity meter creating entanglement for both even and odd measurement results has remained an outstanding challenge. We realize a time-resolved, continuous parity measurement of two superconducting qubits using the cavity in a 3D circuit quantum electrodynamics (cQED) architecture and phase-sensitive parametric amplification. Using postselection, we produce entanglement by parity measurement reaching 77% concurrence. Incorporating the parity meter in a feedback-control loop, we transform the entanglement generation from probabilistic to fully deterministic, achieving 66% fidelity to a target Bell state on demand. These realizations of a parity meter and a feedback-enabled deterministic measurement protocol provide key ingredients for active quantum error correction in the solid state. Nature 10.1038/nature12513 oai:arXiv.org:1306.4002 10.1038/nature12513 oai:arXiv.org:1306.4002 true false 0.9 dedup-similarity-result ec_fp7_ict__::d260bb33b4396ab7415ba37172c08704 8 Schouten R.N. ec_fp7_ict__::4a4df312b07d439f20baa8c5e3c3478f 7 Lehnert K.W. ec_fp7_ict__::23a2062a2c28b3b186662cf162ba57c0 3 Watson C.A. ec_fp7_ict__::4603a400f566d1317692b8fcd13bfd17 5 Tiggelman M.J. ec_fp7_ict__::38ee4e36c87f2cd9432d268afb723b1a 6 Blanter Y.M. ec_fp7_ict__::10e6bdd3667f90c78e09fd3e7dc2665b 9 Dicarlo L. ec_fp7_ict__::9a489d691c64a29509b7738261cbf0ac 1 Riste D. ec_fp7_ict__::09006f86d1d852616b0a452f37172007 2 Dukalski M. dedup_wf_001::6fa66a4f131635e842e977a88255242f 4 Lange G corda_______::227ed4d9a31899e1fccdc6cddbc0df40 600927 SCALEQIT ec__________::EC::FP7 ec__________::EC::FP7::SP1 ec__________::EC::FP7::SP1::ICT 2013-06-17 http://dx.doi.org/10.1038/nature12513 http://arxiv.org/abs/1306.4002 [1] Castellanos-Beltran, M. A., Irwin, K. D., Hilton, G. C., Vale, L. R. & Lehnert, K. W. 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