Spin-based electronics or spintronics relies on the ability to store, transport and manipulate electron spin polarization with great precision. In its ultimate limit, information is stored in the spin state of a single electron, at which point quantum information processing also becomes a possibility. Here, we demonstrate the manipulation, transport and readout of individual electron spins in a linear array of three semiconductor quantum dots. First, we demonstrate single-shot readout of three spins with fidelities of 97% on average, using an approach analogous to the operation of a charge-coupled device (CCD). Next, we perform site-selective control of the three spins, thereby writing the content of each pixel of this 'single-spin charge-coupled device'. Finally, we show that shuttling an electron back and forth in the array hundreds of times, covering a cumulative distance of 80 μm, has negligible influence on its spin projection. Extrapolating these results to the case of much larger arrays points at a diverse range of potential applications, from quantum information to imaging and sensing.

Transition voltage spectroscopy (TVS) has been proposed as a tool to analyze charge transport through molecular junctions. We extend TVS to Au-vacuum-Au junctions and study the distance dependence of the transition voltage V(t)(d) for clean electrodes in cryogenic vacuum. On the one hand, this allows us to provide an important reference for V(t)(d) measurements on molecular junctions. On the other hand, we show that TVS forms a simple and powerful test for vacuum tunneling models.

We report on the fabrication and measurement of nanoscale devices that permit electrostatic confinement in bilayer graphene on a substrate. The graphene bilayer is sandwiched between hexagonal boron nitride bottom and top gate dielectrics. Top gates are patterned such that constrictions and islands can be electrostatically induced. The high quality of the devices becomes apparent from the smooth pinch-off characteristics of the constrictions at low temperature with features indicative of conductance quantization. The islands exhibit clear Coulomb blockade and single-electron transport.

We demonstrate a coherent spin shuttle through a GaAs/AlGaAs quadruple-quantum-dot array. Starting with two electrons in a spin-singlet state in the first dot, we shuttle one electron over to either the second, third, or fourth dot. We observe that the separated spin-singlet evolves periodically into the m = 0 spin-triplet and back before it dephases due to nuclear spin noise. We attribute the time evolution to differences in the local Zeeman splitting between the respective dots. With the help of numerical simulations, we analyze and discuss the visibility of the singlet-triplet oscillations and connect it to the requirements for coherent spin shuttling in terms of the inter-dot tunnel coupling strength and rise time of the pulses. The distribution of entangled spin pairs through tunnel coupled structures may be of great utility for connecting distant qubit registers on a chip. 13 However, there are practical limitations to the size of tunnel-coupled quantum dot arrays in one or two dimensions. Integrating larger numbers of qubits can be achieved by coherently connecting distant qubit registers on a chip.14-17 Such coherent links could also serve to connect different functions such as memory and processor units.2 As an alternative to coherent spin-spin coupling at a distance, the physical transfer of electrons across the chip while preserving the spin information can serve as an interface between separated quantum dot arrays. 2,18 This is similar in spirit to experiments with trapped ions that were shuttled around through segmented ion traps. 19,20 To our knowledge, there are no demonstrations of the transfer of single electron spins coherently through arrays of three or more coupled quantum dots. (A closely related work appeared subsequent to our submission. H. Flentje et al., Coherent long-distance displacement of individual electron spins. arXiv:1701.01279) Various physical mechanisms have been proposed to controllably transfer single charges through confined structures, including Thouless pumps, 21, 22 charge pumps 23 , and surface acoustic waves, 24 and several of these approaches have been experimentally demonstrated with quantum dot devices. 12,25,26 Furthermore, charge transfer with preservation of spin projection was shown using surface acoustic waves 27 and charge pumps.