Characterization of decoherence from an environmental perspective

Helm, Julius; Strunz, Walter T.; Rietzler, Stephan; Würflinger, Lars Erik

doi:10.1103/physreva.83.042103

Cited by 34 publications

(38 citation statements)

References 25 publications

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“…Recall that pure dephasing of an open quantum system in the basis {|n } implies a controlled-unitary form U tot (t) = e −iHtott/ = n |n n| ⊗ U n (t) of the total propagator [44]. Here, U n (t) = e −iHnt/ with H n = n|H tot |n are system-state-dependent propagators for the environment (see also [45]).…”

Section: Random Unitary Representationsmentioning

confidence: 99%

System–environment correlations and non-Markovian dynamics

Pernice

Helm

Strunz

2012

J. Phys. B: At. Mol. Opt. Phys.

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We determine the total state dynamics of a dephasing open quantum system using the standard environment of harmonic oscillators. Of particular interest are random unitary approaches to the same reduced dynamics and system-environment correlations in the full model. Concentrating on a model with an at times negative dephasing rate, the issue of "non-Markovianity" will also be addressed. Crucially, given the quantum environment, the appearance of non-Markovian dynamics turns out to be accompanied by a loss of system-environment correlations. Depending on the initial purity of the qubit state, these system-environment correlations may be purely classical over the whole relevant time scale, or there may be intervals of genuine system-environment entanglement. In the latter case, we see no obvious relation between the build-up or decay of these quantum correlations and "Non-Markovianity".

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Section: Random Unitary Representationsmentioning

confidence: 99%

System–environment correlations and non-Markovian dynamics

Pernice

Helm

Strunz

2012

J. Phys. B: At. Mol. Opt. Phys.

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“…On the other hand, when the environment is instead described as a collection of several fluctuators, the QFI is has two local maxima, whose positions drift towards the boundaries of the interval [0. 5,2] as N is increased. The largest quantum signal-to-noise ratio is obtained for brown noise, i.e.…”

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

“…In particular, in the case of phase damping, i.e. pure dephasing, it has been shown that the interaction of a quantum system with a quantum bath can be written in terms of a random unitary evolution driven by a classical stochastic process [4,5].The characterization of classical noise is often performed by collecting a series of measurements to estimate the autocorrelation function and the spectral properties [6][7][8][9][10][11]. This procedure is generally time consuming and may require the control of a complex system.…”

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confidence: 99%

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Quantum probes for the spectral properties of a classical environment

Benedetti

Buscemi

Bordone³

et al. 2014

Phys. Rev. A

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We address the use of simple quantum probes for the spectral characterization of classical noisy environments. In our scheme a qubit interacts with a classical stochastic field describing environmental noise and is then measured after a given interaction time in order to estimate the characteristic parameters of the noise. In particular, we address estimation of the spectral parameters of two relevant kinds of non-Gaussian noise: random telegraph noise with Lorentzian spectrum and colored noise with 1/f α spectrum. We analyze in details the estimation precision achievable by quantum probes and prove that population measurement on the qubit is optimal for noise estimation in both cases. We also evaluate the optimal interaction times for the quantum probe, i.e. the values maximizing the quantum Fisher information (QFI) and the quantum signal-to-noise ratio. For random telegraph noise the QFI is inversely proportional to the square of the switching rate, meaning that the quantum signal-to-noise ratio is constant and thus the switching rate may be uniformly estimated with the same precision in its whole range of variation. For colored noise, the precision achievable in the estimation of "color", i.e. of the exponent α, strongly depends on the structure of the environment, i.e. on the number of fluctuators describing the classical environment. For an environment modeled by a single random fluctuator estimation is more precise for pink noise, i.e. for α = 1, whereas by increasing the number of fluctuators, the quantum signal-to-noise ratio has two local maxima, with the largest one drifting towards α = 2, i.e. brown noise. In any communication channel or measurement scheme, the interaction of the information carriers with the external environment introduces noise in the system, thus degrading the overall performances. The precise characterization of the noise is thus a crucial ingredient for the design of highprecision measurements and reliable communication protocols. In many physical situations, the main source of noise is associated to the fluctuations of bistable quantities. In these cases, a suitable description of the noise is given in terms of classical stochastic processes [1][2][3]. In particular, in the case of phase damping, i.e. pure dephasing, it has been shown that the interaction of a quantum system with a quantum bath can be written in terms of a random unitary evolution driven by a classical stochastic process [4,5].The characterization of classical noise is often performed by collecting a series of measurements to estimate the autocorrelation function and the spectral properties [6][7][8][9][10][11]. This procedure is generally time consuming and may require the control of a complex system. A question thus arises on whether more effective techniques may be developed. To this purpose, we address the use of quantum probes to estimate the parameters of classical noise. We assume to have a quantum system interacting with the classical fluctuating field generating the noise and explore the performances of...

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“…Helm et al developed a geometrical measurement by using the Bloch sphere picture to determine the non-RU channels [7,8]. In this paper a new method is presented using expansion of considerable state based on Hamiltonian's eigenvalues to investigate the non-RU dynamics.…”

Section: Introductionmentioning

confidence: 99%

Investigation of a Two-Qubit Decoherence by Using Bloch Vectors

Ahmadi¹,

Jami²

2014

Acta Phys. Pol. A

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The loss of the coherence happens due to the interaction between the desired system and its surroundings. Addressing decoherence is one of the main concepts in the study of quantum channels to access their potential for various scale. In this process the information of the system is penetrated into the environment. Therefore, the measurement of the environment could be used as the error correction method. Phase damping channels principally belong to random unitary channels and can be corrected by classical information. This paper presents a method to generate non-random unitary phase damping channels based on the Bloch vectors in two qubits systems. A phase damping channel which consisted of a two qubits system and a single qubit environment was investigated. The results demonstrated that the phase damping channels belong to random unitary dynamics if the three-dimensional tetrahedron volume spanned by the Bloch vectors in R 3 is not zero, or, the same hyperplane in R 3 was not pointed by the Bloch vectors. It is found that the Bell state belongs to random unitary class and can be corrected based on classical information obtained from environmental measurements.

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Characterization of decoherence from an environmental perspective

Cited by 34 publications

References 25 publications

System–environment correlations and non-Markovian dynamics

System–environment correlations and non-Markovian dynamics

Quantum probes for the spectral properties of a classical environment

Investigation of a Two-Qubit Decoherence by Using Bloch Vectors

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