Bare-Excitation Ground State of a Spinless-Fermion-Boson Model and W-State Engineering in an Array of Superconducting Qubits and Resonators

One-Photon Solutions to the Multiqubit Multimode Quantum Rabi Model for Fast W-State Generation

General solutions to the quantum Rabi model involve subspaces with an unbounded number of photons. However, for the multiqubit multimode case, we find special solutions with at most one photon for an arbitrary number of qubits and photon modes. Such solutions exist for arbitrary single qubit-photon coupling strength with constant eigenenergy, while still being qubit-photon entangled states. Taking advantage of their peculiarities and the reach of the ultrastrong coupling regime, we propose an adiabatic scheme for the fast and deterministic generation of a two-qubit Bell state and arbitrary single-photon multimode W states with nonadiabatic error less than 1%. Finally, we propose a superconducting circuit design to catch and release the W states, and shows the experimental feasibility of the multimode multiqubit quantum Rabi model.

Robust entanglement of an asymmetric quantum dot molecular system in a Josephson junction

We demonstrate the generation of robust entanglement of a quantum dot molecular system in a voltage-controlled junction. To improve the quantum information characteristics of this system, we propose an applicable protocol which contains the implementation of asymmetric quantum dots as well as the engineering of reservoirs. Quantum dots can provide asymmetric coupling coefficients due to the tunable energy barriers through the gap voltage changes. To engineer the reservoirs, superconducting leads are used to prepare a voltage-biased Josephson junction. The high-controllability properties of this system give the arbitrary magnitude of entanglement by the arrangement of parameters. Significantly, the perfect entanglement can be achieved for an asymmetric structure in response to the increase of bias voltage, and also it continues saturated with the near-unit amount.