Berlin 2015 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 64: Quantum Information Systems: Mostly Concepts (jointly with HL)

TT 64.7: Talk

Wednesday, March 18, 2015, 12:30–12:45, EW 202

Electrically controlled echo sequences for the exchange-only qubit — •Niklas Rohling and Guido Burkard — Department of Physics, University of Konstanz, Germany

We consider a model of an exchange-only qubit [1] in a triple quantum dot under the influence of the surrounding nuclear spin bath, which we describe by an inhomogeneous Overhauser field. This field can lead to decoherence and leakage out of the logical qubit space. When a strong external magnetic field is applied, the spin in each of the quantum dots precess effectively about the same axis. In this case, only one leakage state has to be taken into account [2]. For this situation, we present a purely exchange-based pulse sequence that corrects decoherence as well as leakage as long as the Overhauser field varies slowly compared to the pulse times. As the pulses rely on the exchange interaction, they can be electrically tuned similarly to the quantum gates of the qubit [1]. For the case of a well-known initial state, we further refine the sequence to allow for first-order correction of errors in the applied pulses in analogy to the Carr-Purcell-Meiboom-Gill sequence known from spin resonance techniques.

[1] D. P. DiVincenzo, D. Bacon, J. Kempe, G. Burkard, and K. B. Whaley, Nature 408, 339 (2000)

[2] J.-T. Hung, J. Fei, M. Friesen, and X. Hu, Phys. Rev. B 90, 045308 (2014)