Monitoring electron spin decoherence in a quantum dot by weak measurement

Ren‐Bao Liu, Shu Hong Fung, Hok-Kin Fung +2 more

We show in theory that the electron spin decoherence, excluding the inhomogeneous broadening effect, can be seen in the third-order correlation function of sequential weak quantum measurement by Faraday rotation.

Hisashi Aikawa, Kensuke Kobayashi, Akira Sano +2 more

Mateusz Krzykowski, Michał Gawełczyk, Krzysztof Gawarecki +1 more

Alessandro Romito, Yuval Gefen, Yaroslav M. Blanter

We propose a protocol for a controlled experiment to measure a weak value of the electron's spin in a solid state device. The weak value is obtained by a two step procedure--weak measurement followed by a strong one (postselection), where the outcome of the first measurement is kept provided a second postselected outcome occurs. The setup consists of a double quantum dot and a weakly coupled quantum point contact to be used as a detector. Anomalously large values of the spin of a two electron system are predicted, as well as negative values of the total spin. We also show how to incorporate the adverse effect of decoherence into this procedure.

O. W. S. Tedder

Indium gallium arsenide self-assembled quantum dots have attracted a lot of attention due to their ability to trap single electrons and holes whose spin can be manipulated optically. This makes them attractive as qubits and light sources in various quantum computing and communication schemes. However, the spin of electrons and holes rapidly decoheres due to hyper-fine interaction with the atomic nuclei of the dot. The theme of this thesis is to find ways of overcoming this decoherence, in particular to allow generation of photonic cluster states from quantum dots. This was first approached by designing theoretical schemes to measure and compensate for the source of the decoherence, which were experimentally tested. Two new systems were then theoretically designed where the effects of decoherence could be mitigated. It is shown theoretically that exciting a quantum dot with a laser of well-defined polarisation and monitoring the polarisation of emitted photons, it is possible to determine the vector polarisation of the nuclear spin ensemble. It is shown through simulation that this measurement can be performed on and possibly faster than the time-scale of nuclear fluctuations. The fundamental concept behind the measurement procedure is proved in an experiment using coupled quantum dots. Through the course of the experiment anomalous behaviour of the dots was discovered. A second theoretical proposal is made for a system allowing the fast application of an effective field to compensate for the decoherence mechanism. It is then shown by simulation that a coupled dot system with a prepared in-plane nuclear spin polarisation, can allow optical spin rotation and entanglement generation. A different system is then theoretically proposed where the electron spin in quantum dot can be replaced with another qubit, such as embedded manganese atoms. It is shown through simulation that this system also allows the generation of photonic cluster states.

Philosophisch-Naturwissenschaftlichen Fakultät