The dynamics of two entangled qubits exposed to classical noise: role of spatial and temporal noise correlations

Szańkowski, Piotr; Trippenbach, Marek; Cywiński, Łukasz; Band, Yehuda B.

doi:10.1007/s11128-015-1044-7

Cited by 18 publications

(16 citation statements)

References 67 publications

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“…[213,214] for entanglement of QD-based spin qubits, [215] for entanglement of NV centers, and [216,217] for entanglement of superconducting qubits), show that noise spectroscopy with multiple qubits is within experimental reach. It is well known that the multi-qubit decoherence, and consequently entanglement dynamics [218], can depend qualitatively on the presence and degree of correlations between the noises affecting distinct qubits [75,210,[219][220][221][222], and when all the qubits are experiencing the same (common) noise, decoherence-free subspaces, hosting entangled states immune to such noise, appear [223,224]. It is also well understood that dynamical decoupling suppresses decoherence and disentanglement of multi-qubit states [75,[225][226][227][228][229][230], even if the unitary operations are applied to single qubits only [75,[230][231][232].…”

Section: Noise Spectroscopy With Multiple Qubitsmentioning

confidence: 99%

Environmental noise spectroscopy with qubits subjected to dynamical decoupling

Szańkowski

Ramon

Krzywda

et al. 2017

J. Phys.: Condens. Matter

123

184

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A qubit subjected to pure dephasing due to classical Gaussian noise can be turned into a spectrometer of this noise by utilizing its readout under properly chosen dynamical decoupling (DD) sequences to reconstruct the power spectral density of the noise. We review the theory behind this DD-based noise spectroscopy technique, paying special attention to issues that arise when the environmental noise is non-Gaussian and/or it has truly quantum properties. While we focus on the theoretical basis of the method, we connect the discussed concepts with specific experiments, and provide an overview of environmental noise models relevant for solid-state based qubits, including quantum-dot based spin qubits, superconducting qubits, and NV centers in diamond.

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Section: Noise Spectroscopy With Multiple Qubitsmentioning

confidence: 99%

Environmental noise spectroscopy with qubits subjected to dynamical decoupling

Szańkowski

Ramon

Krzywda

et al. 2017

J. Phys.: Condens. Matter

123

184

View full text Add to dashboard Cite

show abstract

“…The entanglement of a mixed state resulting from subjecting an initial Bell state to such an interaction is simply proportional to the single nontrivial coherence present in the two-qubit reduced density matrix. This is a special case of a general result for socalled 'X' states (superpositions and mixtures of Bell states) [3,46,47], i.e. the concurrence [48] that measures the entanglement [49][50][51] of the two-qubit state is given by C = 2 max 0, |ρ 14…”

Section: Decay Of Entanglement Due To Correlated Environmentsmentioning

confidence: 99%

“…Correlations in environmental noise experienced by an entangled pair of qubits strongly affect their decoherence [1][2][3][4][5]. The most well-known example is the fact that |Ψ ± Bell states form a decoherence-free subspace [6] when both qubits are exposed to exactly the same phase noise.…”

Section: Introductionmentioning

confidence: 99%

Decoherence of two entangled spin qubits coupled to an interacting sparse nuclear spin bath: Application to nitrogen vacancy centers

Kwiatkowski

Cywiński

2018

Phys. Rev. B

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We consider pure dephasing of Bell states of electron spin qubits interacting with a sparse bath of nuclear spins. Using the newly developed two-qubit generalization of cluster correlation expansion method, we calculate the spin echo decay of |Ψ and |Φ states for various interqubit distances. Comparing the results with calculations in which dephasing of each qubit is treated independently, we identify signatures of influence of common part of the bath on the two qubits. At large interqubit distances, this common part consists of many nuclei weakly coupled to both qubits, so that decoherence caused by it can be modeled by considering multiple uncorrelated sources of noise (clusters of nuclei), each of them weakly affecting the qubits. Consequently, the resulting genuinely two-qubit contribution to decoherence can be described as being caused by classical Gaussian noise. On the other hand, for small interqubit distances the common part of the environment contains clusters of spins that are strongly coupled to both qubits, and their contribution to two-qubit dephasing has visibly non-Gaussian character. We show that one van easily obtain information about non-Gaussianity of environmental noise affecting the qubits from the comparison of dephasing of |Ψ and |Φ Bell states. Numerical results are obtained for two nitrogen vacancy centers interacting with a bath of 13 C nuclei of natural concentration, for which we obtain that Gaussian description of correlated part of environmental noise starts to hold for centers separated by about 3 nm. arXiv:1806.06845v2 [cond-mat.mes-hall]

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“…A number of works have introduced dynamical noise-suppression techniques, such as the dynamical decoupling and Bayesian estimation methods mentioned above, as well as dynamically corrected gates [38][39][40][41][42][43][44][45][46] , which partially cancel out the effects of noise by applying carefully designed pulse sequences. In addition, several works have studied the decoherence of an initially prepared entangled state of two or more qubits subject to various types of noise [47][48][49][50][51] . There has also been some theoretical work on the dynamics of two coupled electron spins under a constant exchange coupling and applied magnetic field gradient.…”

Section: Introductionmentioning

confidence: 99%

Environmental noise effects on entanglement fidelity of exchange-coupled semiconductor spin qubits

2017

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We investigate the effect of magnetic field and charge noise on the generation of entanglement between two Heisenberg exchange-coupled electron spins in a double quantum dot. We focus on exchange-driven evolution that would ideally take an initial unentangled tensor product state to a maximally-entangled state in the absence of noise. The presence of noise obviously adversely affects the attainment of maximal entanglement, which we study quantitatively and exactly. To quantify the effects of noise, we calculate two-qubit coherence times and entanglement fidelity, both of which can be extracted from simulations or measurements of the return probability as a function of interaction time, i.e., the time period during which the exchange coupling remains effective between the two spins. We perform these calculations for a broad range of noise strengths that includes the regime of recent experiments. We find that the two types of noise reduce the amount of entanglement in qualitatively distinct ways and that, although charge noise generally leads to faster decoherence, the relative importance of the two types of noise in entanglement creation depends sensitively on the strength of the exchange coupling. Our results can be used to determine the level of noise suppression needed to reach quantum error correction thresholds. We provide quantitative guidance for the requisite noise constraints necessary to eventually reach the > 99% fidelity consistent with the quantum error correction threshold.

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The dynamics of two entangled qubits exposed to classical noise: role of spatial and temporal noise correlations

Cited by 18 publications

References 67 publications

Environmental noise spectroscopy with qubits subjected to dynamical decoupling

Environmental noise spectroscopy with qubits subjected to dynamical decoupling

Decoherence of two entangled spin qubits coupled to an interacting sparse nuclear spin bath: Application to nitrogen vacancy centers

Environmental noise effects on entanglement fidelity of exchange-coupled semiconductor spin qubits

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