Phys. Rev. Lett. 106, 013602 (2011)
Jan Kołodyński and Rafał Demkowicz-Dobrzański
Phys. Rev. A 82, 053804 (2010)
http://link.aps.org/doi/10.1103/PhysRevA.82.053804
We find the optimal scheme for quantum phase estimation in the presence of loss when no a priori knowledge on the estimated phase is available. We prove analytically an explicit lower bound on estimation uncertainty, which shows that, as a function of the number of probes, quantum precision enhancement amounts at most to a constant factor improvement over classical strategies.
arXiv:1010.0164v1 [cond-mat.mes-hall]
Two-qubit interactions are at the heart of quantum information processing. For single-spin qubits in semiconductor quantum dots, the exchange gate has always been considered the natural two-qubit gate. The recent integration of magnetic field or g-factor gradients in coupled quantum dot systems allows for a one-step, robust realization of the controlled phase (C-Phase) gate instead.
M. Cramer, M. B. Plenio, and H. Wunderlich
Phys. Rev. Lett. 106, 020401 (2011)
http://link.aps.org/doi/10.1103/PhysRevLett.106.020401
Phys. Rev. Lett. 104, 100503 (2010)
arXiv:1007.2405v1 [quant-ph]
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.
Phys. Rev. Lett. 103, 240501 (2009)
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.
Nature Physics 6, 249-253 (2010)
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.
Science 329 no. 5991 pp. 542-544
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.
Phys. Rev. B 82, 045208 (2010)