791 research outputs found
Broadband noise decoherence in solid-state complex architectures
Broadband noise represents a severe limitation towards the implementation of
a solid-state quantum information processor. Considering common spectral forms,
we propose a classification of noise sources based on the effects produced
instead of on their microscopic origin. We illustrate a multi-stage approach to
broadband noise which systematically includes only the relevant information on
the environment, out of the huge parametrization needed for a microscopic
description. We apply this technique to a solid-state two-qubit gate in a fixed
coupling implementation scheme.Comment: Proceedings of Nobel Symposium 141: Qubits for Future Quantum
Informatio
Coherent properties of nano-electromechanical systems
We study the properties of a nano-electromechanical system in the coherent
regime, where the electronic and vibrational time scales are of the same order.
Employing a master equation approach, we obtain the stationary reduced density
matrix retaining the coherences between vibrational states. Depending on the
system parameters, two regimes are identified, characterized by either () an
{\em effective} thermal state with a temperature {\em lower} than that of the
environment or () strong coherent effects. A marked cooling of the
vibrational degree of freedom is observed with a suppression of the vibron Fano
factor down to sub-Poissonian values and a reduction of the position and
momentum quadratures.Comment: 12 pages, 11 figure
Decoherence times of universal two-qubit gates in the presence of broad-band noise
The controlled generation of entangled states of two quantum bits is a
fundamental step toward the implementation of a quantum information processor.
In nano-devices this operation is counteracted by the solid-state environment,
characterized by a broadband and non-monotonic power spectrum, often 1/f at low
frequencies. For single-qubit gates, incoherent processes due to fluctuations
acting on different time scales result in peculiar short- and long-time
behavior. Markovian noise gives rise to exponential decay with relaxation and
decoherence times, T1 and T2, simply related to the symmetry of the
qubit-environment coupling Hamiltonian. Noise with the 1/f power spectrum at
low frequencies is instead responsible for defocusing processes and algebraic
short-time behavior. In this paper, we identify the relevant decoherence times
of an entangling operation due to the different decoherence channels
originating from solid-state noise. Entanglement is quantified by concurrence,
which we evaluate in an analytic form employing a multi-stage approach. The
'optimal' operating conditions of reduced sensitivity to noise sources are
identified. We apply this analysis to a superconducting \sqrt{i-SWAP} gate for
experimental noise spectra.Comment: 35 pages, 11 figure
Exact solution for the dynamical decoupling of a qubit with telegraph noise
We study the dissipative dynamics of a qubit that is afflicted by classical
random telegraph noise and it is subject to dynamical decoupling. We derive
exact formulas for the qubit dynamics at arbitrary working points in the limit
of infinitely strong control pulses (bang-bang control) and we investigate in
great detail the efficiency of the dynamical decoupling techniques both for
Gaussian and non-Gaussian (slow) noise at qubit pure dephasing and at optimal
point. We demonstrate that control sequences can be successfully implemented as
diagnostic tools to infer spectral proprieties of a few fluctuators interacting
with the qubit. The analysis is extended in order to include the effect of
noise in the pulses and we give upper bounds on the noise levels that can be
tolerated in the pulses while still achieving efficient dynamical decoupling
performance
Effects of low-frequency noise cross-correlations in coupled superconducting qubits
We study the effects of correlated low frequency noise sources acting on a
two qubit gate in a fixed coupling scheme. A phenomenological model for the
spatial and cross-talk correlations is introduced. The decoherence inside the
SWAP subspace is analysed by combining analytic results based on the adiabatic
approximation and numerical simulations. Results critically depend on amplitude
of the low frequency noise with respect to the qubits coupling strength.
Correlations between noise sources induce qualitative different behaviors
depending on the values of the above parameters. The possibility to reduce
dephasing due to correlated low frequency noise by a recalibration protocol is
discussed.Comment: 18 pages, 7 figure
Superconducting qubit manipulated by fast pulses: experimental observation of distinct decoherence regimes
A particular superconducting quantum interference device (SQUID)qubit,
indicated as double SQUID qubit, can be manipulated by rapidly modifying its
potential with the application of fast flux pulses. In this system we observe
coherent oscillations exhibiting non-exponential decay, indicating a non
trivial decoherence mechanism. Moreover, by tuning the qubit in different
conditions (different oscillation frequencies) by changing the pulse height, we
observe a crossover between two distinct decoherence regimes and the existence
of an "optimal" point where the qubit is only weakly sensitive to intrinsic
noise. We find that this behaviour is in agreement with a model considering the
decoherence caused essentially by low frequency noise contributions, and
discuss the experimental results and possible issues.Comment: 16 pages, 9 figure
Auditory gaydar: perception of sexual orientation based on female voice
We investigated auditory gaydar (i.e., the ability to recognize sexual orientation) in female speakers, addressing three related issues: whether auditory gaydar is (1) accurate, (2) language-dependent (i.e., occurs only in some languages, but not in others), and (3) ingroup-specific (i.e., occurs only when listeners judge speakers of their own language, but not when they judge foreign language speakers). In three experiments, we asked Italian, Portuguese, and German participants (total N = 466) to listen to voices of Italian, Portuguese, and German women, and to rate their sexual orientation. Our results showed that auditory gaydar was not accurate; listeners were not able to identify speakers’ sexual orientation correctly. The same pattern emerged consistently across all three languages and when listeners rated foreign-language speakers.info:eu-repo/semantics/acceptedVersio
Determining biokinetic coefficients for the upflow anaerobic sludge blanket reactor treating sugarcane wastewater in hot climate conditions
Acknowledgements The managing director of Imam Khomeini (pbuh) Agro-Industry in Shushtar and the laboratory expert of Agro-Industry Treatment Plant are highly appreciated for their cooperation in conducting this study.Peer reviewedPostprin
Profile of porcine respiratory disease complex associated with Pasteurella multocida in Minas Gerais state, Brazil.
Projeto/Plano de Ação: 02.10.61600-01
A tutorial on optimal control and reinforcement learning methods for quantum technologies
Quantum Optimal Control is an established field of research which is necessary for the development of Quantum Technologies. In recent years, Machine Learning techniques have been proved useful to tackle a variety of quantum problems. In particular, Reinforcement Learning has been employed to address typical problems of control of quantum systems. In this tutorial we introduce the methods of Quantum Optimal Control and Reinforcement Learning by applying them to the problem of three-level population transfer. The jupyter notebooks to reproduce some of our results are open-sourced and available on github1
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