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Strong electrically tunable exciton g-factors in an individual quantum dots due to hole orbital angular momentum quenching

Mon, 2011-02-14 19:52 - Daniel Rudolph

Date:

2010-08-31

Author(s):

V. Jovanov, T. Eissfeller, S. Kapfinger, E. C. Clark, F. Klotz, G. Abstreiter, J. J. Finley

Reference:

arXiv:1008.3354v3 [cond-mat.mes-hall]

URL:

http://arxiv.org/abs/1008.3354v3

Strong electrically tunable exciton g-factors are observed in individual (Ga)InAs self-assembled quantum dots and the microscopic origin of the effect is explained. Realistic eight band k.p simulations quantitatively account for our observations, simultaneously reproducing the exciton transition energy, DC Stark shift, diamagnetic shift and g-factor tunability for model dots with the measured size and a comparatively low In-composition of x(In)~35% near the dot apex. We show that the observed g-factor tunability is dominated by the hole, the electron contributing only weakly.

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Electrical control of the exciton-biexciton splitting in a single self-assembled InGaAs quantum dots

Mon, 2011-02-14 19:50 - Daniel Rudolph

Date:

2010-09-10

Author(s):

M. Kaniber, M. F. Huck, K. Müller, E. C. Clark, F. Troiani, M. Bichler, H. J. Krenner, J. J. Finley

Reference:

arXiv:1009.1989v1 [cond-mat.mes-hall]

URL:

http://arxiv.org/abs/1009.1989v1

We report on single InGaAs quantum dots embedded in a lateral electric field device. By applying a voltage we tune the neutral exciton transition into resonance with the biexciton using the quantum confined Stark effect. The results are compared to theoretical calculations of the relative energies of exciton and biexciton. Cascaded decay from the manifold of single exciton-biexciton states has been predicted to be a new concept to generate entangled photon pairs on demand without the need to suppress the fine structures splitting of the neutral exciton.

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Robustness and Errors in Quantum Optimal Control

Mon, 2011-02-14 19:43 - Daniel Rudolph

Date:

2010-07-14

Author(s):

Antonio Negretti, Rosario Fazio, Tommaso Calarco

Reference:

arXiv:1007.2405v1 [quant-ph]

URL:

http://arxiv.org/abs/1007.2405v1

We introduce a new approach to quantify the robustness of optimal control of closed quantum systems. Our theory allows to assess the degree of distortion that can be applied to a set of known optimal control parameters, which are solutions of an optimal control problem. The formalism is applied to an exactly solvable model and to the Landau-Zener model, whose optimal control problem is solvable only numerically. The presented method is of importance for any application where a high degree of controllability of the quantum system dynamics is required.

Blockade and Counterflow Supercurrent in Exciton-Condensate Josephson Junctions

Mon, 2011-02-14 19:42 - Daniel Rudolph

Date:

2010-01-14

Author(s):

Fabrizio Dolcini, Diego Rainis, Fabio Taddei, Marco Polini, Rosario Fazio, and A. H. MacDonald

Reference:

Phys. Rev. Lett. 104, 027004 (2010)

URL:

http://link.aps.org/doi/10.1103/PhysRevLett.104.027004

We demonstrate that perfect conversion between charged supercurrents in superconductors and neutral supercurrents in electron-hole pair condensates is possible via a new Andreev-like scattering mechanism. As a result, when two superconducting circuits are coupled through a bilayer exciton condensate, the superflow in both layers is drastically modified. Depending on the phase biases the supercurrents can be completely blocked or exhibit perfect drag.

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Optimal Control at the Quantum Speed Limit

Mon, 2011-02-14 19:40 - Daniel Rudolph

Date:

2009-12-07

Author(s):

T. Caneva, M. Murphy, T. Calarco, R. Fazio, S. Montangero, V. Giovannetti, and G. E. Santoro

Reference:

Phys. Rev. Lett. 103, 240501 (2009)

URL:

http://link.aps.org/doi/10.1103/PhysRevLett.103.240501

Optimal control theory is a promising candidate for a drastic improvement of the performance of quantum information tasks. We explore its ultimate limit in paradigmatic cases, and demonstrate that it coincides with the maximum speed limit allowed by quantum evolution.

Quantum register based on coupled electron spins in a room-temperature solid

Mon, 2011-02-14 19:37 - Daniel Rudolph

Date:

2010-02-28

Author(s):

P. Neumann, R. Kolesov, B. Naydenov, J. Beck1, F. Rempp, M. Steiner, V. Jacques, G. Balasubramanian, M. L. Markham, D. J. Twitchen, S. Pezzagna, J. Meijer, J. Twamley, F. Jelezko & J. Wrachtrup

Reference:

Nature Physics 6, 249-253 (2010)

URL:

http://www.nature.com/nphys/journal/vaop/ncurrent/abs/nphys1536.html

Devices that harness the laws of quantum physics hold the promise for information processing that outperforms their classical counterparts, and for unconditionally secure communication. However, in particular, implementations based on condensed-matter systems face the challenge of short coherence times. Carbon materials, particularly diamond, however, are suitable for hosting robust solid-state quantum registers, owing to their spin-free lattice and weak spin–orbit coupling.

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Single-Shot Readout of a Single Nuclear Spin

Mon, 2011-02-14 19:33 - Daniel Rudolph

Date:

2010-07-01

Author(s):

Philipp Neumann, Johannes Beck, Matthias Steiner, Florian Rempp, Helmut Fedder, Philip R. Hemmer, Jörg Wrachtrup and Fedor Jelezko

Reference:

Science 329 no. 5991 pp. 542-544

URL:

http://www.sciencemag.org/content/329/5991/542.abstract

Projective measurement of single electron and nuclear spins has evolved from a gedanken experiment to a problem relevant for applications in atomic-scale technologies like quantum computing. Although several approaches allow for detection of a spin of single atoms and molecules, multiple repetitions of the experiment that are usually required for achieving a detectable signal obscure the intrinsic quantum nature of the spin’s behavior.