Hyperfine interaction induced dephasing of coupled spin qubits in semiconductor double quantum dots

Hung, Jo-Tzu; Cywiński, Łukasz; Hu, Xuedong; Sarma, S. Das

doi:10.1103/physrevb.88.085314

Cited by 24 publications

(34 citation statements)

References 91 publications

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“…Specifically, we consider the case where the typical frequencies of the system are larger compared to those of the environment, so that the system dynamics can be described as a pure dephasing [24,[32][33][34][35][36]. Dephasing induced by classical noise has been studied previously [5,37], and it is known to induce a monotonic decay of entanglement, including the phenomenon of sudden death [38] (ESD) i.e.…”

Section: Introductionmentioning

confidence: 99%

Engineering decoherence for two-qubit systems interacting with a classical environment

Rossi

Benedetti

Paris

2014

Int. J. Quantum Inform.

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We address the dynamics of a two-qubit system interacting with a classical dephasing environment driven by a Gaussian stochastic process. Upon introducing the concept of entanglement-preserving time, we compare the degrading effects of different environments, e.g. those described by Ornstein-Uhlenbeck or fractional noise. In particular, we consider pure Bell states and mixtures of Bell states and study the typical values of the entanglement-preserving time for both independent and common environments. We found that engineering environments towards fractional Gaussian noise is useful to preserve entanglement as well as to improve its robustness against noise. We also address entanglement sudden death by studying the entanglement-survival time as a function of the initial negativity. We found that: i) the survival time is bounded from below by an increasing function of the initial negativity, ii) the survival time depends only slightly on the process used to describe the environment and exhibits typicality. Overall, our results show that engineering the environment has only a slight influence over the entanglement-survival time, i.e. the occurence of entanglement sudden-death, while it represents a valuable resource to increase the entanglement-preserving time, i.e. to maintain entanglement closer to the initial level for a longer interaction time.

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Section: Introductionmentioning

confidence: 99%

Engineering decoherence for two-qubit systems interacting with a classical environment

Rossi

Benedetti

Paris

2014

Int. J. Quantum Inform.

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“…We next account for contributions to dephasing from fluctuations in the hyperfine field gradient, Γ n , determined independently from measured dephasing time T * 2,n in a diabatic singlet-separation measurement, following the analysis in Ref. [26] (see supplement). The formula we use for Γ n is valid for J 1/T * 2,n .…”

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confidence: 99%

Coherent Operations and Screening in Multielectron Spin Qubits

Higginbotham

Kuemmeth²,

Hanson

et al. 2014

Phys. Rev. Lett.

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The performance of multi-electron spin qubits is examined by comparing exchange oscillations in coupled single-electron and multi-electron quantum dots in the same device. Fast (> 1 GHz) exchange oscillations with a quality factor Q > 15 are found for the multi-electron case, compared to Q ∼ 2 for the single-electron case, the latter consistent with previous experiments. A model of dephasing that includes voltage and hyperfine noise is developed that is in good agreement with both single-and multi-electron data, though in both cases additional exchange-independent dephasing is needed to obtain quantitative agreement across a broad parameter range.Spin-1/2 quantum dots with controlled exchange coupling form a potentially powerful platform for manipulating quantum information [1]. Single electrons confined by electrostatic gates in semiconductors are a well-developed realization of this system, and meet many of the basic requirements of quantum information processing, including reliable preparation and manipulation [2], long decoherence time [3], single-shot readout [4,5], and two-qubit entanglement [6]. However, producing large numbers of single-electron quantum dots places severe demands on materials and device design, which may ultimately limit scaling. Moving from single confined electrons to multi-electron qubits can relax these requirements, and, as shown here, can also improve performance.Requirements for conventional spin qubits include a spin-1/2 ground state, and a gap to excited states larger than temperature and the energy scales associated with control and coupling. In quantum dots formed from GaAs heterostructures, interactions are relatively weak, typically (though not always) resulting in a spin-1/2 ground state for odd occupancy [7,8]. Higher spin ground states appear near degeneracies [9] or at very low densities, but can be avoided in practice.Previous experimental work on multi-electron quantum dots has demonstrated Pauli blockade [10][11][12][13][14][15][16] and coherent operation [17]. In single-electron dots, both nuclear [18,19] and electrical [20,21] dephasing have been characterized, with electrical noise modeled as a fluctuating detuning between double-dot levels. Multi-electron quantum dots have also received theoretical attention due to ease of realization as well as possibly improved performance [7,9,[22][23][24].In this Letter, we investigate coherent exchange oscillations in coupled multi-electron GaAs quantum dots-this operation was specifically chosen to be sensitive to electrical noiseand compare results to oscillations in the same device operated with single-electron dots. We find significantly improved coherence in the multi-electron case, consistent with expectations of screening by core electrons [7,22]. By analyzing the dephasing during the exchange-gate operation, we characterize the electrical noise environment for each occupancy. For both single and multiple occupancies, voltage noise affecting the detuning between dots dominates dephasing for large exchange, and fluctuat...

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“…Since T ∇ 2,e is independent of b, z gradients do not contribute; in order for a longitudinal gradient to contribute to dephasing, nonsecular terms in the hyperfine interaction would need to be included. 41 As in recent calculations for hole-spin echo dynamics, 32 for large b, a motional-averaging regime can be reached in Hahn echo. Indeed, when b b x , we have ω k s γ s b and then Eq.…”

Section: B Hahn Echomentioning

confidence: 80%

Enhanced hyperfine-induced spin dephasing in a magnetic-field gradient

Beaudoin

Coish

2013

Phys. Rev. B

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Magnetic-field gradients are important for single-site addressability and electric-dipole spin resonance of spin qubits in semiconductor devices. We show that these advantages are offset by a potential reduction in coherence time due to the non-uniformity of the magnetic field experienced by a nuclear-spin bath interacting with the spin qubit. We theoretically study spins confined to quantum dots or at single donor impurities, considering both free-induction and spin-echo decay. For quantum dots in GaAs, we find that, in a realistic setting, a magnetic-field gradient can reduce the Hahn-echo coherence time by almost an order of magnitude. This problem can, however, be resolved by applying a moderate external magnetic field to enter a motional averaging regime. For quantum dots in silicon, we predict a cross-over from non-Markovian to Markovian behavior that is unique to these devices. Finally, for very small systems such as single phosphorus donors in silicon, we predict a breakdown of the common Gaussian approximation due to finite-size effects.Comment: 16 pages, 5 figure

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Hyperfine interaction induced dephasing of coupled spin qubits in semiconductor double quantum dots

Cited by 24 publications

References 91 publications

Engineering decoherence for two-qubit systems interacting with a classical environment

Engineering decoherence for two-qubit systems interacting with a classical environment

Coherent Operations and Screening in Multielectron Spin Qubits

Enhanced hyperfine-induced spin dephasing in a magnetic-field gradient

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