1. Dynamics of an open quantum system: decoherence processes & encoded control
PI: Leonid Pryadko (Physics)
Co-PI: Ilya Dumer (Electrical Engineering)
University of California, Riverside
Collaborators:
Pinaki Sengupta (LANL)
Greg Quiroz (USC)
Sasha Korotkov (UCR)
Yunfan Li (UCR)
NSF grant No
(since 2006)
Publications:
PRL 95, (2005)
PRB 73, (2006)
arXiv: (2007) PRB in press
arXiv: (2007)
arXiv: (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 & 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
Advantage similar to lock-in measurement W 2W w
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"