Fig. 1
Basic operating principles of our nanoplasmonic quantum logic gate. a Simplest square-root-of-swap gate. Two photons are sent in the two ports of a 50:50 beamsplitter. If the photons are distinguishable, half of the times the photons exit from different ports and a square-root-of-swap gate is achieved. The other half of the times the two photons exit through the same port and the gate fails. If the photons are indistinguishable, they bunch and always exit from the same port, so the gate always fails. b Electronic band structure of graphene with a non-zero Fermi energy EF. Two photons can produce an interband transition and be absorbed, whereas single-photon absorption is forbidden for photon energies below 2EF. c Ratios between the two-plasmon absorption rate, γ(2) (at the plasmon resonance frequency), and the intrinsic damping rate, γ = 500 fs−1, for a range of nanoribbon widths, W, and Fermi energies, EF. The blue areas are regions in which two-plasmon absorption is two to six orders of magnitude faster than linear absorption, providing a strong \(\gamma ^{(2)} \gg \gamma\) condition that leads to extremely high success probabilities for the gate
