19,463 research outputs found
High fidelity one-qubit operations under random telegraph noise
We address the problem of implementing high fidelity one-qubit operations
subject to time dependent noise in the qubit energy splitting. We show with
explicit numerical results that high fidelity bit flips and one-qubit NOT gates
may be generated by imposing bounded control fields. For noise correlation
times shorter than the time for a pi-pulse, the time optimal pi-pulse yields
the highest fidelity. For very long correlation times, fidelity loss is
approximately due to systematic error, which is efficiently tackled by
compensation for off-resonance with a pulse sequence (CORPSE). For intermediate
ranges of the noise correlation time we find that short CORPSE, which is less
accurate than CORPSE in correcting systematic errors, yields higher fidelities.
Numerical optimization of the pulse sequences using gradient ascent pulse
engineering results in noticeable improvement of the fidelities for the bit
flip and marginal improvement for the NOT gate.Comment: 7 pages, 6 figure
Correlation-powered Information Engines and the Thermodynamics of Self-Correction
Information engines can use structured environments as a resource to generate
work by randomizing ordered inputs and leveraging the increased Shannon entropy
to transfer energy from a thermal reservoir to a work reservoir. We give a
broadly applicable expression for the work production of an information engine,
generally modeled as a memoryful channel that communicates inputs to outputs as
it interacts with an evolving environment. The expression establishes that an
information engine must have more than one memory state in order to leverage
input environment correlations. To emphasize this functioning, we designed an
information engine powered solely by temporal correlations and not by
statistical biases, as employed by previous engines. Key to this is the
engine's ability to synchronize---the engine automatically returns to a desired
dynamical phase when thrown into an unwanted, dissipative phase by corruptions
in the input---that is, by unanticipated environmental fluctuations. This
self-correcting mechanism is robust up to a critical level of corruption,
beyond which the system fails to act as an engine. We give explicit analytical
expressions for both work and critical corruption level and summarize engine
performance via a thermodynamic-function phase diagram over engine control
parameters. The results reveal a new thermodynamic mechanism based on
nonergodicity that underlies error correction as it operates to support
resilient engineered and biological systems.Comment: 22 pages, 13 figures;
http://csc.ucdavis.edu/~cmg/compmech/pubs/tos.ht
Robustness of composite pulses to time-dependent control noise
We study the performance of composite pulses in the presence of time-varying
control noise on a single qubit. These protocols, originally devised only to
correct for static, systematic errors, are shown to be robust to time-dependent
non-Markovian noise in the control field up to frequencies as high as ~10% of
the Rabi frequency. Our study combines a generalized filter-function approach
with asymptotic dc-limit calculations to give a simple analytic framework for
error analysis applied to a number of composite-pulse sequences relevant to
nuclear magnetic resonance as well as quantum information experiments. Results
include examination of recently introduced concatenated composite pulses and
dynamically corrected gates, demonstrating equivalent first-order suppression
of time-dependent fluctuations in amplitude and/or detuning, as appropriate for
the sequence in question. Our analytic results agree well with numerical
simulations for realistic noise spectra with a roll-off to ,
providing independent validation of our theoretical insights.Comment: 11 pages, 4 figures, text and figures updated to published versio
- …