Interlaced Dynamical Decoupling and Coherent Operation of a Singlet-Triplet Qubit

Barthel, Christian; Medford, James; Marcus, C. M.; Hanson, M.; Gossard, A. C.

doi:10.1103/physrevlett.105.266808

Cited by 142 publications

(148 citation statements)

References 29 publications

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“…11 shows the convergence of δJ as the energy cutoff E c approaches its maximal value, as well as full CI results for the two-electron case and frozen-core results for the other cases. It is not guaranteed that our results for the exchange energy are fully converged, especially 6 electrons 10 electrons for larger numbers of electrons, but Fig. 11 demonstrates that the qualitative trends apparent in Fig.…”

Section: Qubit Operationmentioning

confidence: 88%

Screening of charged impurities with multielectron singlet-triplet spin qubits in quantum dots

et al. 2011

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Charged impurities in semiconductor quantum dots comprise one of the main obstacles to achieving scalable fabrication and manipulation of singlet-triplet spin qubits. We theoretically show that using dots that contain several electrons each can help to overcome this problem through the screening of the rough and noisy impurity potential by the excess electrons. We demonstrate how the desired screening properties turn on as the number of electrons is increased, and we characterize the properties of a double quantum dot singlet-triplet qubit for small odd numbers of electrons per dot. We show that the sensitivity of the multi-electron qubit to charge noise may be an order of magnitude smaller than that of the two-electron qubit.One of the most promising paths to scalable quantum computation is to use laterally defined double quantum dots (DQDs) in semiconductor heterostructures. The qubit is formed by the spin states of the two-electron DQD with total spin projection zero along the z axis. 1,2 Such a qubit is insensitive to spatially uniform magnetic field fluctuations, and, most importantly, amenable to fast electrical manipulation. 2,3 Recent experiments have made tremendous advances along these lines, demonstrating single-qubit initialization, arbitrary manipulation, and single-shot readout, all within a fraction of the coherence time of the qubit. 3-7 Preliminary steps toward an entangling two-qubit gate have also been reported. 8 In principle, successful completion of that program leaves the (admittedly enormous) challenge of scaling up to large numbers of qubits as the last remaining hurdle in the fabrication of a practical quantum computer.However, a practical issue has emerged which threatens to be a crippling impediment to continued rapid progress. The semiconductor samples used to create quantum dots invariably contain a number of charge impurity centers, perhaps 10 10 cm −2 in GaAs systems. 9 Even if the charge on these centers can be frozen to avoid switching noise, their presence inhibits access to the oneelectron-per-dot regime since the lowest energy states of the dot may be fragmented due to the roughened potential landscape. [10][11][12][13] This makes it difficult to find samples suitable for spin qubit realization. Furthermore, typically the impurities do introduce some switching noise, [14][15][16][17] so that even in samples in which the impurities are all far enough from the DQD that a two-electron singlettriplet qubit can be accessed, the interdot exchange energy is still subject to random fluctuation, leading to gate errors and decoherence. [18][19][20] This necessitates operating in a parameter regime such that the sensitivity of the exchange energy to the charge noise is minimized, a so-called "sweet spot". 21 In general, the charge noise problem is even more pernicious when performing twoqubit operations directly mediated by the Coulomb interaction, and one must again seek a sweet spot. 22,23 However, in practice, this strategy may not be sufficient since one typically cannot optimize ov...

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Section: Qubit Operationmentioning

confidence: 88%

Screening of charged impurities with multielectron singlet-triplet spin qubits in quantum dots

et al. 2011

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“…However, it appears that non-equidistant sequences perform better only for particular noise spectral densities that increase for higher frequencies and have a strong cutoff. In the more frequent case, where the spectral density decreases smoothly with the frequency, equidistant sequences were predicted [90][91][92] and demonstrated [49,55,56,62,63,65] to be the best option [65].…”

Section: Basics Of Dynamical Decoupling (A) the Systemmentioning

confidence: 99%

Robust dynamical decoupling

Souza

Álvarez

Suter

2012

Phil. Trans. R. Soc. A.

186

194

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Quantum computers, which process information encoded in quantum mechanical systems, hold the potential to solve some of the hardest computational problems. A substantial obstacle for the further development of quantum computers is the fact that the lifetime of quantum information is usually too short to allow practical computation. A promising method for increasing the lifetime, known as dynamical decoupling (DD), consists of applying a periodic series of inversion pulses to the quantum bits. In the present review, we give an overview of this technique and compare different pulse sequences proposed earlier. We show that pulse imperfections, which are always present in experimental implementations, limit the performance of DD. The loss of coherence due to the accumulation of pulse errors can even exceed the perturbation from the environment. This effect can be largely eliminated by a judicious design of pulses and sequences. The corresponding sequences are largely immune to pulse imperfections and provide an increase of the coherence time of the system by several orders of magnitude.

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“…On the other hand when the spectral density of the bath has a soft cutoff (such as a broad Gaussian or Lorentzian), the CPMG sequence was found to outperform the UDD sequence [19][20][21][22][23][24][25]. Suter and co-workers have studied these different regimes and arrived at optimal conditions for the dynamical decoupling [26].…”

Section: Introductionmentioning

confidence: 99%

Storing entanglement of nuclear spins via Uhrig dynamical decoupling

2011

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Stroboscopic spin flips have already been shown to prolong the coherence times of quantum systems under noisy environments. Uhrig's dynamical decoupling scheme provides an optimal sequence for a quantum system interacting with a dephasing bath. Several experimental demonstrations have already verified the efficiency of such dynamical decoupling schemes in preserving single qubit coherences. In this work we describe the experimental study of Uhrig's dynamical decoupling in preserving two-qubit entangled states using an ensemble of spin-1/2 nuclear pairs in solution state. We find that the performance of odd-order Uhrig sequences in preserving entanglement is superior to both even-order Uhrig sequences and periodic spin-flip sequences. We also find that there exists an optimal order of the Uhrig sequence using which a singlet state can be stored at high correlation for about 30 seconds.

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Interlaced Dynamical Decoupling and Coherent Operation of a Singlet-Triplet Qubit

Cited by 142 publications

References 29 publications

Screening of charged impurities with multielectron singlet-triplet spin qubits in quantum dots

Screening of charged impurities with multielectron singlet-triplet spin qubits in quantum dots

Robust dynamical decoupling

Storing entanglement of nuclear spins via Uhrig dynamical decoupling

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