Exploiting quench dynamics in spin chains for distant entanglement and quantum communication

摘要

We suggest a method of entangling significantly the distant ends of a one-dimensional lattice of spins using minimal control. Tins long-distance en-tanglement is brought about solely by exploiting the dynamics of an initial state with Neel order if the lattice features nearest-neighbor X X Z interaction. In par-ticular, there is no need for any control of single subsystems or repeated switchings or pulsings. The method only requires an initial non-adiabatic switching between two appropriately tailored Hamiltonians followed by evolution under a permanent Hamiltonian. The scheme could potentially be implemented in various experimen-tal setups, ranging from ultracold atoms in an optical lattice to Josephson junction arrays. In our scheme, first the lattice of strongly interacting spins is cooled to its ground state. Then, upon instantly changing a global parameter in its Hamiltonian (i.e., performing a quench (Sengupta et al., Phys. Rev. A, 69 (2004) 053616), the pair of edge spins evolve to a highly entangled mixed state. For this state, entan-glement purification methods are known (Bennett et al., Phys. Rev. A, 54 (1996) 3824), which two remote parties (Alice and Bob) can use to convert, only by local actions, a few (say n) copies of the state to m < n pure maximally entangled states (EPR pairs). This pure entanglement could then be used to teleport (Bennett et al., Phys. Rev. Lett. 70 (1993) 1895) any state from Alice to Bob. Details on this work can be found in Wichterich et al., arXiv:/quant-ph/0806.4568 (submitted to Phys. Rev. Lett.).