Charge-noise-insensitive gate operations for always-on, exchange-only   qubits
  We introduce an always-on, exchange-only qubit made up of three localized semiconductor spins that offers a true "sweet spot" to fluctuations of the quantum dot energy levels. Both single- and two-qubit gate operations can be performed using only exchange pulses while maintaining this sweet spot. We show how to interconvert this qubit to other three-spin encoded qubits as a new resource for quantum computation and communication. 
Yun-Pil Shim and Charles Tahan
cond-mat.mes-hall quant-ph