Fast generation of W states of superconducting qubits with multiple Schrödinger dynamics

Superradiant Quantum Phase Transition for an Exactly Solvable Two-Qubit Spin-Boson Model

A spin-boson-like model with two interacting qubits is analysed. The model turns out to be exactly solvable since it is characterized by the exchange symmetry between the two spins. The explicit expressions of eigenstates and eigenenergies make it possible to analytically unveil the occurrence of first-order quantum phase transitions. The latter are physically relevant since they are characterized by abrupt changes in the two-spin subsystem concurrence, in the net spin magnetization and in the mean photon number.

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.

Non-locality Correlation in Two Driven Qubits Inside an Open Coherent Cavity: Trace Norm Distance and Maximum Bell Function

We analytically investigate two separated qubits inside an open cavity field. The cavity is initially prepared in a superposition coherent state. The non-locality correlations [including trace norm measurement induced non-locality, maximal Bell-correlation, and concurrence entanglement] of the two qubits are explored. It is shown that, the generated non-locality correlations crucially depend on the decay and the initial coherence intensity of the cavity field. The enhancement of the initial coherence intensity and its superposition leads to increasing the generated non-locality correlations. The phenomena of sudden birth and death entanglement are found.

Tripartite Entanglement: Foundations and Applications

We review some current ideas of tripartite entanglement. In particular, we consider the case representing the next level of complexity beyond the simplest (though far from trivial) one, namely the bipartite case. This kind of entanglement plays an essential role in understanding the foundations of quantum mechanics. It also allows for implementing several applications in the fields of quantum information processing and quantum computing. In this paper, we review the fundamental aspects of tripartite entanglement focusing on Greenberger–Horne–Zeilinger and W states for discrete variables. We discuss the possibility of using it as a resource to execute quantum protocols and present some examples in detail.

Fast and robust population transfer with a Josephson qutrit via shortcut to adiabaticity

We propose an effective scheme to implement fast and robust population transfer with a Josephson qutrit via shortcut to adiabaticity. Facilitated by the level-transition rule, a Λ-configuration resonant interaction can be realized between microwave drivings and the qutrit with sufficient level anharmonicity, from which we perform the reversible population transfers via invariant-based shortcut. Compared with the detuned drivings, the utilized resonant drivings shorten the transfer times significantly. Further analysis of the dependence of transfer time on Rabi couplings is helpful to experimental investigations. Thanks to the accelerated process, transfer operation is highly insensitive to noise effects. Thus the protocol could provide a promising avenue to experimentally perform fast and robust quantum operations on Josephson artificial atoms.

Shortcut to adiabatic passage in a three-level system via a chosen path and its application in a complicated system

We construct a shortcut to an adiabatic passage in a three-level system by choosing a dressed state acting as an evolutive path. Two designed auxiliary pulses are added into the original pulses to eliminate the couplings between the chosen evolutive-path state and the other two dressed states. The same target state as one gotten by adiabatic passage can be rapidly obtained, and the population of the lossy intermediate state can be controlled by setting proper parameters. Furthermore, as an example, we use this method in the adiabatic-passage scheme [Opt. Express20, 014547 (2012)], a complicated cavity quantum electrodynamics system, to successfully accelerate the generation of the three-dimensional entanglement between a single atom and a Bose-Einstein condensate.

Fusing atomic W states via quantum Zeno dynamics

We propose a scheme for preparation of large-scale entangled W states based on the fusion mechanism via quantum Zeno dynamics. By sending two atoms belonging to an n-atom W state and an m-atom W state, respectively, into a vacuum cavity (or two separate cavities), we may obtain a (n + m - 2)-atom W state via detecting the two-atom state after interaction. The present scheme is robust against both spontaneous emission of atoms and decay of cavity, and the feasibility analysis indicates that it can also be realized in experiment.