Spin Relaxation in Ge/Si Core-Shell Nanowire Qubits

Controlling decoherence is the most challenging task in realizing quantum information hardware. Single electron spins in gallium arsenide are a leading candidate among solid- state implementations, however strong coupling to nuclear spins in the substrate hinders this approach. To realize spin qubits in a nuclear-spin-free system, intensive studies based on group-IV semiconductor are being pursued. In this case, the challenge is primarily control of materials and interfaces, and device nanofabrication. We report important steps toward implementing spin qubits in a predominantly nuclear-spin-free system by demonstrating state preparation, pulsed gate control, and charge-sensing spin readout of confined hole spins in a one-dimensional Ge/Si nanowire. With fast gating, we measure T1 spin relaxation times in coupled quantum dots approaching 1 ms, increasing with lower magnetic field, consistent with a spin-orbit mechanism that is usually masked by hyperfine contributions

Spin blockade and exchange in Coulomb-confined silicon double quantum dots

Electron spins confined to phosphorus donors in silicon are promising candidates as qubits(1) because of their long coherence times, exceeding seconds in isotopically purified bulk silicon(2). With the recent demonstrations of initialization, readout(3) and coherent manipulation(4) of individual donor electron spins, the next challenge towards the realization of a Si:P donor-based quantum computer is the demonstration of exchange coupling(1,5,6) in two tunnel-coupled phosphorus donors. Spin-to-charge conversion(3,7) via Pauli spin blockade(8,9), an essential ingredient for reading out individual spin states, is challenging in donor-based systems due to the inherently large donor charging energies (similar to 45 meV), requiring large electric fields (\u3e1 MV m(-1)) to transfer both electron spins onto the same donor(10). Here, in a carefully characterized double donor-dot device, we directly observe spin blockade of the first few electrons and measure the effective exchange interaction between electron spins in coupled Coulomb-confined systems

Alginate hydrogels allow for bioactive and sustained release of VEGF-C and VEGF-D for lymphangiogenic therapeutic applications

Lymphatic dysfunction is associated with the progression of many cardiovascular disorders due to their role in maintaining tissue fluid homeostasis. Promoting new lymphatic vessels (lymphangiogenesis) is a promising strategy to reverse these cardiovascular disorders via restoring lymphatic function. Vascular endothelial growth factor (VEGF) members VEGF-C and VEGF-D are both potent candidates for stimulating lymphangiogenesis, though maintaining spatial and temporal control of these factors represents a challenge to developing efficient therapeutic lymphangiogenic applications. Injectable alginate hydrogels have been useful for the controlled delivery of many angiogenic factors, including VEGF-A, to stimulate new blood vasculature. However, the utility of these tunable hydrogels for delivering lymphangiogenic factors has never been closely examined. Thus, the objective of this study was to utilize ionically cross-linked alginate hydrogels to deliver VEGF-C and VEGF-D for potential lymphangiogenic applications. We demonstrated that lymphatic endothelial cells (LECs) are sensitive to temporal presentation of VEGF-C and VEGF-D but with different responses between the factors. The greatest LEC mitogenic and sprouting response was observed for constant concentrations of VEGF-C and a high initial concentration that gradually decreased over time for VEGF-D. Additionally, alginate hydrogels provided sustained release of radiolabeled VEGF-C and VEGF-D. Finally, VEGF-C and VEGF-D released from these hydrogels promoted a similar number of LEC sprouts as exogenously added growth factors and new vasculature in vivo via a chick chorioallantoic membrane (CAM) assay. Overall, these findings demonstrate that alginate hydrogels can provide sustained and bioactive release of VEGF-C and VEGF-D which could have applications for therapeutic lymphangiogenesis