Circuit quantum electrodynamics with a quadruple quantum dot

In this theoretical work,we describe a mechanism for the coupling between a plane structure consisting of four quantum dots and a resonator.We systematically study the dependence of the quadruple coupling strength and the qubit decoherence rate and point out the optimized operating position of the hybrid system.According to the transmission given by the input-output theory,the signatures in the resonator spectrum are predicted.Furthermore,based on the parameters already achieved in previous works,we prove that the device described in this paper can achieve the strong coupling limit,i.e.,this approach can be used for system extension under the existing technical conditions.Our results show an effective and promotable approach to couple quantum dot structures in plane with the resonator and propose a meaningful extension method.

A scheme for two-photon lasing with two coupled flux qubits in circuit quantum electrodynamics

We theoretically study the system of a superconducting transmission line resonator coupled to two interacting super- conducting flux qubits. It is shown that under certain conditions the resonator mode can be tuned to two-photon resonance between the ground state and the highest excited state while the middle excited states are far-off resonance. Furthermore, we study the steady-state properties of the flux qubits and resonator, such as the photon statistics, the spectrum and squeezing of the resonator, and demonstrate that two-photon laser can be implemented with current experimental technology.

Controllable cross-Kerr interaction between microwave photons in circuit quantum electrodynamics

We propose a scheme to enable a controllable cross-Kerr interaction between microwave photons in a circuit quantum electrodynamics （QED） system. In this scheme we use two transmission-line resonators （TLRs） and one superconducting quantum interference device （SQUID） type charge qubit, which acts as an artificial atom. It is shown that in the dispersive regime of the eircuit-QED system, a controllable cross-Kerr interaction can be obtained by properly preparing the initial state of the qubit, and a large cross-phase shift between two microwave fields in the two TLRs can then be reached. Based on this cross-Kerr interaction, we show how to create a macroscopic entangled state between the two TLRs.

Fast generation of W state via superadiabatic-based shortcut in circuit quantum electrodynamics

We propose a scheme to fast prepare the three-qubit W state via superadiabatic-based shortcuts in a circuit quantumelectrodynamics (circuit QED) system. We derive the effective Hamiltonian to suppress the unwanted transitions betweendifferent eigenstates by counterdiabatic driving, and obtain the W state with high-fidelity based on the superadiabaticpassage. The numerical simulation results demonstrate that the proposed scheme can accelerate the evolution, and is moreefficient than that with the adiabatic passage. In addition, the proposed scheme is robust to the decoherence caused by theresonator decay and qubit relaxation, and does not need additional parameters, which could be feasible in experiment.

Remote entangling gate between a quantum dot spin and a transmon qubit mediated by microwave photons

Spin qubits and superconducting qubits are promising candidates for realizing solid-state quantum information processors.Designing a hybrid architecture that combines the advantages of different qubits on the same chip is a highly desirable but challenging goal.Here we propose a hybrid architecture that utilizes a high-impedance SQUID array resonator as a quantum bus,thereby coherently coupling different solid-state qubits.We employ a resonant exchange spin qubit hosted in a triple quantum dot and a superconducting transmon qubit.Since this hybrid system is highly tunable,it can operate in a dispersive regime,where the interaction between the different qubits is mediated by virtual photons.By utilizing such interactions,entangling gate operations between different qubits can be realized in a short time of 30 ns with a fidelity of up to 96.5%under realistic parameter conditions.Further utilizing this interaction,remote entangled state between different qubits can be prepared and is robust to perturbations of various parameters.These results pave the way for exploring efficient fault-tolerant quantum computation on hybrid quantum architecture platforms.

Preparation of multi-photon Fock states and quantum entanglement properties in circuit QED

We demonstrate the controllable generation of multi-photon Fock states in circuit quantum electrodynamics （circuit QED）. The external bias flux regulated by a counter can effectively adjust the bias time on each superconducting flux qubit so that each flux qubit can pass in turn through the circuit cavity and thereby avoid the effect of decoherence. We further investigate the quantum correlation dynamics of coupling superconducting qubits in a Fock state. The results reveal that the lower the photon number of the light field in the number state, the stronger the interaction between qubits is, then the more beneficial to maintaining entanglement between qubits it will be.

Change-over switch for quantum states transfer with topological channels in a circuit-QED lattice

We propose schemes to realize robust quantum states transfer between distant resonators using the topological edge states of a one-dimensional circuit quantum electrodynamics(QED)lattice.Analyses show that the distribution of edge states can be regulated accordingly with the on-site defects added on the resonators.And we can achieve different types of quantum state transfer without adjusting the number of lattices.Numerical simulations demonstrate that the on-site defects can be used as a change-over switch for high-fidelity single-qubit and two-qubit quantum states transfer.This work provides a viable prospect for flexible quantum state transfer in solid-state topological quantum system.

Realization of the iSWAP-like gate among the superconducting qutrits

High-dimensional quantum systems, such as qutrits(quantum three-level systems), have multiple accessible energy levels beyond the two-level qubits. Therefore, qutrits can offer a larger state space to improve the efficiency of quantum computation. Here, we demonstrate a high-fidelity iSWAP-like gate operation on a frequency-tunable superconducting qutrits system. The superconducting quantum system consists of two qutrits that are coupled via a resonator with fixed qutrit-resonator coupling strengths. Through designing the frequency pulse profile and optimizing the parameter values,the gate error can be suppressed below 1.5 × 10^(-3). To bear out the feasibility of the proposal, we have conducted our study with experimentally accessible parameters. As the resonator can mediate the interaction between the irrelevant qutrits, the presented approach can also be used to couple multiple qutrits together, providing a good platform for quantum information processing.