Interplay of charge and spin coherence in Landau-Zener-Stückelberg-Majorana interferometry

Ribeiro, Hugo; Petta, J. R.; Burkard, Guido

doi:10.1103/physrevb.87.235318

Cited by 49 publications

(57 citation statements)

References 67 publications

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“…In this case, the pulse remains adiabatic with respect to the S(0, 2)-S(1, 1) anticrossing; it is, however, only quasi-adiabatic with respect to the S-T − anticrossing, enabling use of the Landau-Zener mechanism to initialize a superposition between states S and T − (Fig. 1C, Inset) (22,(26)(27)(28). Because the voltage pulse takes these states to larger detuning, an energy difference arises between the pair of states, and there is a relative phase accumulation between them.…”

Section: Significancementioning

confidence: 99%

Two-axis control of a singlet–triplet qubit with an integrated micromagnet

Wu¹,

Ward²,

Prance

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

172

193

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The qubit is the fundamental building block of a quantum computer. We fabricate a qubit in a silicon double-quantum dot with an integrated micromagnet in which the qubit basis states are the singlet state and the spin-zero triplet state of two electrons. Because of the micromagnet, the magnetic field difference ΔB between the two sides of the double dot is large enough to enable the achievement of coherent rotation of the qubit's Bloch vector around two different axes of the Bloch sphere. By measuring the decay of the quantum oscillations, the inhomogeneous spin coherence time T 2 * is determined. By measuring T 2 * at many different values of the exchange coupling J and at two different values of ΔB, we provide evidence that the micromagnet does not limit decoherence, with the dominant limits on T 2 * arising from charge noise and from coupling to nuclear spins.semiconductor spin qubit | quantum nanoelectronics F abricating qubits composed of electrons in semiconductor quantum dots is a promising approach for the development of a large-scale quantum computer because of the approach's potential for scalability and for integrability with classical electronics. Much recent progress has been made, and spin manipulation has been demonstrated in systems of two (1-5), three (6, 7), and four (8) quantum dots. A great deal of attention has focused on the singlet-triplet qubit in quantum dots (1, 2, 9-18), which consists of the S z = 0 subspace of two electrons, for which the basis can be chosen to be a singlet and a triplet state. Full two-axis control on the Bloch sphere is achieved by electrical gating in the presence of a magnetic field difference ΔB between the two dots. In previous experiments (2, 9-14), ΔB arises from coupling to nuclear spins in the material, and slow fluctuations in these nuclear fields lead to inhomogeneous decoherence times that, without special nuclear state preparation, typically are shorter than the period of the quantum oscillations. In III-V materials, ΔB is large, so fast oscillation periods of order 10 ns are achievable, but the inhomogeneous dephasing time is also ∼10 ns, so that oscillations from ΔB are overdamped, ending before a complete cycle is observed (2). The fluctuations of the nuclear spin bath can be mitigated to some extent (10), but inhomogeneous dephasing times in III-V materials are short enough that high-fidelity control is still very challenging. Coupling to nuclear spins in silicon is substantially weaker, leading to longer coherence times, but also smaller field differences and hence slower quantum oscillations (14,19).Here, we report the operation of a singlet-triplet qubit in which the magnetic field difference ΔB between the dots is imposed by an external micromagnet (20,21). Because the field from the micromagnet is stable in time, a large ΔB can be imposed without creating inhomogeneous dephasing. We present data demonstrating underdamped quantum oscillations, and, by investigating a variety of voltage configurations and two ΔB configurations, we show that the m...

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Section: Significancementioning

confidence: 99%

Two-axis control of a singlet–triplet qubit with an integrated micromagnet

Wu¹,

Ward²,

Prance

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

172

193

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“…2(g) and (h) for convolved pulses and "double hat" pulses. To compare quantitatively the visibility of the coherent oscillations, we have to neglect the final detuning ε s = ε c , which is strongly affected by relaxation mechanisms [28]. We thus find that the visibility for convolved pulses is ∼ 0.17 and the visibility of "double hat" pulses is ∼ 0.5, which corresponds to an improvement of a factor ∼ 2.9.…”

mentioning

confidence: 96%

“…Here, the contrast is also limited due to the superposition of S(2, 0) and S(1, 1) [28]. First, the weighting of S(1, 1) sets the amount of population that can be transferred to T + .…”

Section: (E)]mentioning

confidence: 99%

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Coherent Adiabatic Spin Control in the Presence of Charge Noise Using Tailored Pulses

et al. 2013

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We study finite-time Landau-Zener transitions at a singlet-triplet level crossing in a GaAs double quantum dot, both experimentally and theoretically. Sweeps across the anticrossing in the high driving speed limit result in oscillations with a small visibility. Here we demonstrate how to increase the oscillation visibility while keeping sweep times shorter than T * 2 using a tailored pulse with a detuning dependent level velocity. Our results show an improvement of a factor ∼ 2.9 for the oscillation visibility. In particular, we were able to obtain a visibility of ∼ 0.5 for Stückelberg oscillations, which demonstrates the creation of an equally weighted superposition of the qubit states.

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“…Of recent interest is the formation and manipulation of coherent superpositions of spin states using the LandauZener-Stückelberg (LZS) approach [2][3][4][5][6][7][8][9]. Observation of spin state LZS oscillations within the charge stability diagram of a quantum-dot device involves a projective measurement in the qubit basis states.…”

Section: Introductionmentioning

confidence: 99%

Role of metastable charge states in a quantum-dot spin-qubit readout

et al. 2015

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Access and use of this website and the material on it are subject to the Terms and Conditions set forth at NRC Publications Record / Notice d'Archives des publications de CNRC:http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=rtdoc&an=21276979&lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=rtdoc&an=21276979&lang=fr READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. Questions? Contact the NRC Publications Archive team atPublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information. NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. For the publisher's version, please access the DOI link below./ Pour consulter la version de l'éditeur, utilisez le lien DOI ci-dessous.http://doi.org/10.1103/PhysRevB.92.125434 Review B: Condensed Matter and Materials Physics, 92, 12, 2015-09-15 PHYSICAL REVIEW B 92, 125434 (2015) Role of metastable charge states in a quantum-dot spin-qubit readout Readout of a spin qubit in a lateral gate-defined quantum-dot device typically involves a charge detector and a spin-to-charge conversion technique employing spin blockade. We investigate alternative mechanisms for spin-to-charge conversion involving metastable excited charge states made possible by an asymmetry in the tunneling rates to the leads. This technique is used to observe Landau-Zener-Stückelberg oscillations of the S-T + qubit within the (1,0) ground state region of the charge stability diagram. The oscillations are π phase shifted relative to those detected using the standard technique and display a nonsinusoidal waveform due to the increased relaxation time from the metastable state. Physical

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Interplay of charge and spin coherence in Landau-Zener-Stückelberg-Majorana interferometry

Cited by 49 publications

References 67 publications

Two-axis control of a singlet–triplet qubit with an integrated micromagnet

Two-axis control of a singlet–triplet qubit with an integrated micromagnet

Coherent Adiabatic Spin Control in the Presence of Charge Noise Using Tailored Pulses

Role of metastable charge states in a quantum-dot spin-qubit readout

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