Avoided Level Crossing (Entangled State) Engineering in the 4coupled Qubits System

Ahmad Salmaogli

Peng ZHANG, Yang YU

Superconducting qubits are artificial solid state quantum systems which present quantized energy level at low temperature and low dissipation. The energy difference between levels can be tuned by external driving electro-magnetic field, leading to avoided level crossings under certain conditions. Recent research has shown Landau-Zener-Stückelberg(LZS) interference can be realized in solid state qubits with such avoided level crossings. This provides a new method for the measurement of energy spectroscopy, the characterization of coupling between quantum system and environment, as well as the realization of quantum logic gates and quantum entanglement.

Ahmad Salmanogli

David B. Kaplan, Natalie Klco, Alessandro Roggero

A new method is proposed for determining the ground state wave function of a quantum many-body system on a quantum computer, without requiring an initial trial wave function that has good overlap with the true ground state. The technique of Spectral Combing involves entangling an arbitrary initial wave function with a set of auxiliary qubits governed by a time dependent Hamiltonian, resonantly transferring energy out of the initial state through a plethora of avoided level crossings into the auxiliary system. The number of avoided level crossings grows exponentially with the number of qubits required to represent the Hamiltonian, so that the efficiency of the algorithm does not rely on any particular energy gap being large. We give an explicit construction of the quantum gates required for the realization of this procedure and explore the results of classical simulations of the algorithm on a small quantum computer with up to 8 qubits. We show that for certain systems and comparable results, Spectral Combing requires fewer quantum gates to realize than the Quantum Adiabatic Algorithm.

W L Yang, Wan-Lu Song, Jun‐Hong An +3 more

It remains challenging to preserve entanglement between distant solid-state qubits with high-fidelity, such as nitrogen vacancy centers (NVCs). We propose a Floquet engineering strategy to protect the maximal entanglement between two weakly interacting NVCs separated in long spatial distance by locally applying periodic strong driving on the NVCs. It is found that entanglement of the Floquet states of the NVCs resonantly reaches its maximum during the whole driving period at certain values of the driving parameters. Our analysis reveals that it is the occurrence of the avoided level crossing in the Floquet quasienergy spectrum which results in such entanglement resonance. The dissipation effect on the generated entanglement has also been analyzed. Our results may be of both theoretical and experimental interests in exploring the long-lasting entanglement between weakly interacting spins to long distances in realistic environments.

János K. Asbóth, Петер Адам, Mátyás Koniorczyk +1 more