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Dynamics of an open quantum system: decoherence processes & encoded control

Dynamics of an open quantum system: decoherence processes & encoded control. University of California, Riverside. Collaborators: Pinaki Sengupta ( LANL ) Greg Quiroz (USC) Sasha Korotkov (UCR) Yunfan Li (UCR). NSF grant No. 0622242 (since 2006). PI: Leonid Pryadko (Physics)

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Dynamics of an open quantum system: decoherence processes & encoded control

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  1. Dynamics of an open quantum system: decoherence processes & encoded control University of California, Riverside Collaborators: Pinaki Sengupta (LANL) Greg Quiroz (USC) Sasha Korotkov (UCR) Yunfan Li (UCR) NSF grant No. 0622242 (since 2006) PI: Leonid Pryadko (Physics) Co-PI: Ilya Dumer (Electrical Engineering) Publications: PRL 95, 037202 (2005) PRB 73, 085321 (2006) arXiv:0704.3806 (2007) PRB in press arXiv:0706.0501 (2007) arXiv:0708.4267 (2007)

  2. Motivation • Useful QC implementation – error free at level of • qubit • group of qubits • … • Multi-stage coherence protection techniques are needed • Resources (bandwidth, ancillas, etc.) to be used frugally • Optimization of algorithms is needed PRYADKO (UCR) "Dynamics of an open quantum system: decoherence processes and encoded control"

  3. Study of performance for combined coherence protection schemes Measurement-induced decoherence in real time LPP & Korotkov (2007) Multi-stage coherence protection QECC Error structure Decoherence & visibility @ dynamical decoupling LPP & Sengupta (2006) Refocusing error structure LPP & Quiroz (2007) Shaped pulses for encoded dynamical recoupling(current) Pulse-based decoherence reshuffling Pulse & sequence design Sengupta & LPP (2005) PRYADKO (UCR) "Dynamics of an open quantum system: decoherence processes and encoded control"

  4. Shaped pulses for encoded dynamical recoupling • Encoded qubits with decoupling and logic sequences run concurrently [Viola, Lloyd & Knill (1999)] • Low-frequency environment is decoupled if • Visibility suffers when fast logic pulses are inserted between decoupling cycles • Additional errors introduced depending on pulse placement and duration PRYADKO (UCR) "Dynamics of an open quantum system: decoherence processes and encoded control"

  5. Adiabaticity condition: spectral representation • Decoupling shifts the spectral weight to higher frequencies • Execution of non-periodical algorithm widens the corresponding peaks • More stringent condition to avoid the overlap with the spectrum of the environmental modes Environment spectral function F(w) system spectrum with decoupling decoupling & logic w W 2W PRYADKO (UCR) "Dynamics of an open quantum system: decoherence processes and encoded control"

  6. Conclusions • There is a hidden correlations build-up in implementation of combined error correction techniques • Shaped pulses is a must for encoded dynamical recoupling • Very good pulse shapes & sequences are ready for use — Experimentalists, please see my poster! PRYADKO (UCR) "Dynamics of an open quantum system: decoherence processes and encoded control"

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