We present a scheme for implementing locally a nonlocal N -target controlled–controlled gate with unit probability of success by harnessing two ( N +1)-qubit Greenberger–Horne–Zeilinger (GHZ) states as quantum channel and N qutrits as catalyser. The quantum network that implements this nonlocal ( N +2)-body gate is built entirely of local single-body and two-body gates, and has only (3 N +2) two-body gates. This result suggests that both the computational depth of quantum network and the quantum resources required to perform this nonlocal gate might be significantly reduced. This scheme can be generalized straightforwardly to implement a nonlocal N -target and M -control qubits gate.
A recent major technological breakthrough in superconducting circuits is the realization of more than 50 qubits arranged on two-dimensional (2D) lattices with tunable nearest-neighbor couplings. We propose a protocol to generate Greenberger-Horne-Zeilinger (GHZ) states on 2D superconducting-qubit lattices by applying multiqubit controlled-
iswap gates in parallel. The multiqubit gate can be naturally implemented based on an effective three-body interaction, which can be synthesized with appropriate detunings and coupling strengths between qubits. We simulate the preparation process of GHZ states with realistic parameters, and show a
37-qubit GHZ state can be generated with a controlled-
iswap depth of
3. Our proposal provides a more promising method of generating GHZ states on the latest 2D superconducting-qubit architectures and will stimulate the preparation of multiqubit entangled states based on multiqubit gates.
We propose a probabilistic quantum cloning scheme using Greenberger-Horne-Zeilinger (GHZ) states, Bell-basis measurements, single-qubit unitary operations, and generalized measurements, all of which are within the reach of current technology. Compared to another possible scheme via Tele-controlled-NOT gate [D. Gottesman and I. L. Chuang, Nature (London) 402, 390 (1999)], the present scheme may be used in experiment to clone the states of one particle to those of two different particles with higher probability and less GHZ resources.