Fiber-optic realization of anisotropic depolarizing quantum channels

Karpiński, Michał; Radzewicz, Czesław; Banaszek, Konrad

doi:10.1364/josab.25.000668

Cited by 26 publications

(24 citation statements)

References 28 publications

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“…Maximizing f N (ϕ) yields N opt = −1/ ln λ ⊥ N opt (rounded to the nearest integer and using natural logarithm). This approximation to the optimal "sampling time" N opt only depends on λ ⊥ , which is experimentally accessible through process tomography [40].…”

Section: B Optimal "Sampling Time"mentioning

confidence: 99%

Practical quantum metrology in noisy environments

et al. 2016

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The problem of estimating an unknown phase ϕ using two-level probes in the presence of unital phase-covariant noise and using finite resources is investigated. We introduce a simple model in which the phase-imprinting operation on the probes is realized by a unitary transformation with a randomly sampled generator. We determine the optimal phase sensitivity in a sequential estimation protocol and derive a general (tight-fitting) lower bound. The sensitivity grows quadratically with the number of applications N of the phase-imprinting operation, then attains a maximum at some N opt , and eventually decays to zero. We provide an estimate of N opt in terms of accessible geometric properties of the noise and illustrate its usefulness as a guideline for optimizing the estimation protocol. The use of passive ancillas and of entangled probes in parallel to improve the phase sensitivity is also considered. We find that multiprobe entanglement may offer no practical advantage over single-probe coherence if the interrogation at the output is restricted to measuring local observables.

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Section: B Optimal "Sampling Time"mentioning

confidence: 99%

Practical quantum metrology in noisy environments

et al. 2016

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“…We note that QST is an established experimental tool-in particular in quantum information-inspired setups. It has been used to characterize quantum states in a large number of different platforms- [4][5][6][7][8][9][10][11][12] are an incomplete list.…”

Section: Introductionmentioning

confidence: 99%

Error regions in quantum state tomography: computational complexity caused by geometry of quantum states

Suess¹,

Rudnicki²,

Maciel³

et al. 2017

New J. Phys.

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The outcomes of quantum mechanical measurements are inherently random. It is therefore necessary to develop stringent methods for quantifying the degree of statistical uncertainty about the results of quantum experiments. For the particularly relevant task of quantum state tomography, it has been shown that a significant reduction in uncertainty can be achieved by taking the positivity of quantum states into account. However-the large number of partial results and heuristics notwithstandingno efficient general algorithm is known that produces an optimal uncertainty region from experimental data, while making use of the prior constraint of positivity. Here, we provide a precise formulation of this problem and show that the general case is NP-hard. Our result leaves room for the existence of efficient approximate solutions, and therefore does not in itself imply that the practical task of quantum uncertainty quantification is intractable. However, it does show that there exists a non-trivial trade-off between optimality and computational efficiency for error regions. We prove two versions of the result: one for frequentist and one for Bayesian statistics.

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“…2. The requirement that the process matrix should have eigenvalues between 0 and 1, that sum up to 1, dictates that physically possible radii can not reside in the dark green zones [9,15]. By examining the parameter space of θ 1 and θ 2 it can be shown that our configuration can create any channel within the yellow zone.…”

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confidence: 99%

“…In order to study the effect of noise on quantum information channels, there is a need for a physical realization of controlled depolarization processes. Previously, photonic noisy channels which partially depolarize light were implemented in several ways [6][7][8][9][10][11]. Here, we report on the implementation of a simple controllable isotropic depolarizer, which depolarizes to the same extent light of any initial polarization, to any required final degree of polarization.…”

mentioning

confidence: 99%