Final Report Summary - SPINTRANSFER (Coherent transport of a single electron spin in semiconducting nanostructures)
The goal of the project is to transfer coherently a single electron spin in between two quantum dots in AlGaAs heterostructures. It is based on the knowledge developed over the last ten years to control a single electron spin in lateral quantum dots. Expertise in this field has been acquired by the researcher Tristan Meunier during his post-doctoral work at TU Delft. The ERG project started when the researcher joined the CNRS-Néel Institute in 2008 and the goal of the first period of the "SPINTRANSFER" project was to develop all the skills needed for this project in Grenoble: nanofabrication of dot-structures in Grenoble clean rooms from AlGaAs heterostructures, RF equipments and test of a dilution fridge, development of home-made electronics needed to control the dot systems. At the end, we reproduce the main results of single electron in a single dot.
The second period was dedicated to the experimental realization of the first milestone towards the ambitious goal: the transfer of a single electron between distant quantum dots. We will describe this point in the main part of this report.
Significant results:
A first important step towards coherent transport of a single electron spin17 has been accomplished during the period of the SPINTRANSFER project. It consists in controlling the displacement of a single electron in a path free of the other electrons of the nanostructures. A picture of the sample is presented in Fig1. Moving quantum dots can be defined in a one-dimensional (1D) electrostatic channel free of electrons between two distant quantum dots by exciting surface acoustic waves (SAW) on top of the AlGaAs heterostructure. The speed of the moving quantum dots is determined by the speed propagation of the SAW and is equal to 3μm/ns. We demonstrated that a single electron, first isolated in a static quantum dot, could be efficiently transferred in one of the moving quantum dots created by exciting the SAW and can be caught back in the second quantum dot. In addition, we were able to trigger the transfer of the electron at nanosecond timescale faster than T2*and to demonstrate the ability to separate two electrons in a singlet state to potentially produce a distant entangled pair of electrons.
This work has been the subject of a publication in Nature (S. Hermelin et al, Nature (London) 447, 435 (2011)). It has been the subject of a number of press releases around the world. We have received several invitations to international conferences to disseminate the results of our work. This work has received attention due to the control of electron transport at the single electron level. This milestone experiment opens new routes towards the investigation of spin coherence and spin dynamic properties during single electron transfer and towards the realization of quantum optics experiments using flying electrons. In the following we will describe point by point the key results of this work.
The single electron source and the single electron detector
To prepare and to detect the electron state, we use the two quantum dots placed at the extremity of the channel (see figure 1). Capacitively coupled to the each quantum dot, a quantum point contact is used to measure the charge state of the quantum dot. It enabled us to check that we can empty each quantum dots and therefore prepare them determistically with one or zero electron (see charge stability diagrams ijn figure 2ab).
In addition, we have the possibility to realize cycles in the charge stability diagram in order to prepare the electron in a metastable state above the Fermi energy well coupled to the 1D channel (position C on fig1a). It was crucial for the realization of the experiment and this possibility is largely due to the tunability of our dot systems. The resulting response of the QPC for the source dot is presented on figure 1C. When a radiofrequency burst is applied to the interdigited transducer (see figure1), the electron is forced to leave the source quantum as
The second period was dedicated to the experimental realization of the first milestone towards the ambitious goal: the transfer of a single electron between distant quantum dots. We will describe this point in the main part of this report.
Significant results:
A first important step towards coherent transport of a single electron spin17 has been accomplished during the period of the SPINTRANSFER project. It consists in controlling the displacement of a single electron in a path free of the other electrons of the nanostructures. A picture of the sample is presented in Fig1. Moving quantum dots can be defined in a one-dimensional (1D) electrostatic channel free of electrons between two distant quantum dots by exciting surface acoustic waves (SAW) on top of the AlGaAs heterostructure. The speed of the moving quantum dots is determined by the speed propagation of the SAW and is equal to 3μm/ns. We demonstrated that a single electron, first isolated in a static quantum dot, could be efficiently transferred in one of the moving quantum dots created by exciting the SAW and can be caught back in the second quantum dot. In addition, we were able to trigger the transfer of the electron at nanosecond timescale faster than T2*and to demonstrate the ability to separate two electrons in a singlet state to potentially produce a distant entangled pair of electrons.
This work has been the subject of a publication in Nature (S. Hermelin et al, Nature (London) 447, 435 (2011)). It has been the subject of a number of press releases around the world. We have received several invitations to international conferences to disseminate the results of our work. This work has received attention due to the control of electron transport at the single electron level. This milestone experiment opens new routes towards the investigation of spin coherence and spin dynamic properties during single electron transfer and towards the realization of quantum optics experiments using flying electrons. In the following we will describe point by point the key results of this work.
The single electron source and the single electron detector
To prepare and to detect the electron state, we use the two quantum dots placed at the extremity of the channel (see figure 1). Capacitively coupled to the each quantum dot, a quantum point contact is used to measure the charge state of the quantum dot. It enabled us to check that we can empty each quantum dots and therefore prepare them determistically with one or zero electron (see charge stability diagrams ijn figure 2ab).
In addition, we have the possibility to realize cycles in the charge stability diagram in order to prepare the electron in a metastable state above the Fermi energy well coupled to the 1D channel (position C on fig1a). It was crucial for the realization of the experiment and this possibility is largely due to the tunability of our dot systems. The resulting response of the QPC for the source dot is presented on figure 1C. When a radiofrequency burst is applied to the interdigited transducer (see figure1), the electron is forced to leave the source quantum as
