  We present a novel technique for the manipulation of the energy spectrum of
hard-wall InAs/InP nanowire quantum dots. By using two local gate electrodes,
we induce a strong electric dipole moment on the dot and demonstrate the
controlled modification of its electronic orbitals. Our approach allows us to
dramatically enhance the single-particle energy spacing between the first two
quantum levels in the dot and thus to increment the working temperature of our
InAs/InP single-electron transistors. Our devices display a very robust
modulation of the conductance even at liquid nitrogen temperature, while
allowing an ultimate control of the electron filling down to the last free
carrier. Potential further applications of the technique to time-resolved spin
manipulation are also discussed.
