title: Coherent spin-exchange via a quantum mediator.
abstract: Coherent interactions at a distance provide a powerful tool for quantum simulation and computation. The most common approach to realize an effective long-distance coupling 'on-chip' is to use a quantum mediator, as has been demonstrated for superconducting qubits and trapped ions. For quantum dot arrays, which combine a high degree of tunability with extremely long coherence times, the experimental demonstration of the time evolution of coherent spin-spin coupling via an intermediary system remains an important outstanding goal. Here, we use a linear triple-quantum-dot array to demonstrate a coherent time evolution of two interacting distant spins via a quantum mediator. The two outer dots are occupied with a single electron spin each, and the spins experience a superexchange interaction through the empty middle dot, which acts as mediator. Using single-shot spin readout, we measure the coherent time evolution of the spin states on the outer dots and observe a characteristic dependence of the exchange frequency as a function of the detuning between the middle and outer dots. This approach may provide a new route for scaling up spin qubit circuits using quantum dots, and aid in the simulation of materials and molecules with non-nearest-neighbour couplings such as MnO (ref. 27), high-temperature superconductors and DNA. The same superexchange concept can also be applied in cold atom experiments.
authors.affiliation: QuTech and Kavli Institute of Nanoscience, TU Delft, 2600 GA Delft, The Netherlands.
authors.forename: Timothy Alexander
authors.initials: TA
authors.lastname: Baart
authors.affiliation: QuTech and Kavli Institute of Nanoscience, TU Delft, 2600 GA Delft, The Netherlands.
authors.forename: Takafumi
authors.initials: T
authors.lastname: Fujita
authors.affiliation: Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Reichl
authors.affiliation: Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland.
authors.forename: Werner
authors.initials: W
authors.lastname: Wegscheider
authors.affiliation: QuTech and Kavli Institute of Nanoscience, TU Delft, 2600 GA Delft, The Netherlands.
authors.forename: Lieven Mark Koenraad
authors.initials: LM
authors.lastname: Vandersypen
mesh_terms: D046228:Microarray Analysis / Q000295:instrumentation / Q000379:methods*; D045663:Quantum Dots / Q000737:chemistry*