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HL: Fachverband Halbleiterphysik

HL 11: Quantum information systems: mostly quantum dots

HL 11.3: Vortrag

Montag, 11. März 2013, 12:30–12:45, H16

Tomography scheme for two spin qubits in a double quantum dot — •Niklas Rohling and Guido Burkard — Department of Physics, University of Konstanz, D-78457 Konstanz, Germany

We present a set of measurements which allows the reconstruction of the density matrix for the full two-qubit space of two electron spins in a double quantum dot. Our scheme employs non-local quantum gates induced by the exchange interaction between the spins and selective single-spin rotations by electron spin resonance (ESR). Recently, both kinds of gates have been realized experimentally in the same quantum dot [1]. Projection on specific states can be achieved by an adiabatic spin-to-charge conversion after applying the quantum gate. State tomography for a singlet-triplet qubit, i.e. a subspace of the full two-qubit space, has been demonstrated [2]. It turns out that ESR is harder to realize than exchange interaction. Whereas ESR is unnecessary to gain full information of the state of a single singlet-triplet qubit, it is needed for state tomography of the full four-dimensional space of two single-spin qubits. For each of the measurements we suggest, no more than one π/2-rotation of one of the spins needs to be done by ESR. We estimate the precision of our tomography scheme in dependence of the fidelity of the quantum gates.

[1] N. Brunner, Y.-S. Shin, T. Obata, M. Pioro-Ladrière, T. Kubo, T. Taniyama, Y. Tokura, and S. Tarucha, Phys. Rev. Lett. 107, 146801 (2011).

[2] S. Foletti, H. Bluhm, D. Mahalu, V. Umansky, and A. Yacoby, Nature Phys. 5, 903 (2009).