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We propose a scheme utilizing a quantum interference phenomenon, analogous to Electromagnetically Induced Transparency, to switch the transport of atoms in a 1D optical lattice through a site containing an impurity atom with two relevant internal states, thus representing a qubit.
Specifically, the quantum interference phenomenon is achieved by coupling pairs of probe and impurity atoms near-resonantly to a hetero-molecular state by means of a magnetical or optical Feshbach-resonance. In the strong coupling regime the atomic fields get strongly dressed by the molecular fields, yielding several paths for the probe atoms to tunnel through the impurity, which can be made to interfere constructively or destructively by an appropriate detuning of e.g.~the photo-association laser. By this means one achieves the impurity to be in one state completely transparent for the probe atoms, and in the other state to act as a single atom mirror. After considering the detailed scattering processes involved in the transport of a single particle through the impurity, we generalize the latter to interacting many-particle systems including a 1D Tonks gas. For a macroscopic number of atoms passing the impurity, one e.g. obtains a macroscopic superposition of the probe atoms being on the left hand side of the impurity with the qubit in spin up and the probe atoms being on the right hand side of the impurity with the qubit in spin down. Thus the state of impurity gets amplified by the atomic cloud and measuring the current of atoms passing the impurity allows a single-shot quantum non-demolition measurement of the qubit spin. In view of the analogy between state amplification via this type of blocking mechanism and readout with single electron transistors (SET) used in solid state systems, we refer to this setup as a Single Atom Transistor (SAT). |