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Physical Review A

Robust generation of entangled fields against inhomogeneous parameters of coupled superconducting resonators and qubits

Sheng-li Ma, Ji-kun Xie, Xinke Li, Fuli Li

Published Apr 10, 2019• 5 citations
Publisher

Abstract

We propose an efficient approach for the generation of a stable entangled state of microwave fields in circuit quantum electrodynamics. The system under consideration consists of two linearly coupled superconducting resonators, each of which is coupled to a superconducting flux qubit. By individually driving the qubits to engineer the desired interactions with the resonators, we show that the energy relaxation of qubits can be exploited to steer the two resonators into the two-mode entangled state via a dissipative dynamical process. Since our protocol is based on quantum reservoir engineering, neither specific initialization nor unitary dynamics is required. Moreover, the distinct advantage of our scheme is that the quantum state preparation is robust in relation to inhomogeneous parameters, i.e., there is no need for identical qubit-field couplings, as well as the same resonance frequencies of the resonators. These features make the present scheme pretty feasible for experimental implementation.

DOI
10.1103/physreva.99.042317

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We propose an efficient approach for the generation of a stable entangled state of microwave fields in circuit quantum electrodynamics. The system under consideration consists of two linearly coupled superconducting resonators, each of which is coupled to a superconducting flux qubit. By individually driving the qubits to engineer the desired interactions with the resonators, we show that the energy relaxation of qubits can be exploited to steer the two resonators into the two-mode entangled state via a dissipative dynamical process. Since our protocol is based on quantum reservoir engineering, neither specific initialization nor unitary dynamics is required. Moreover, the distinct advantage of our scheme is that the quantum state preparation is robust in relation to inhomogeneous parameters, i.e., there is no need for identical qubit-field couplings, as well as the same resonance frequencies of the resonators. These features make the present scheme pretty feasible for experimental implementation.
We propose a quantum reservoir engineering approach for stabilizing Bell states of two superconducting qubits. The system under consideration consists of two linearly coupled superconducting transmission line resonators and two separated flux qubits, one of which is interacted with one resonator. Applying external driving fields to tailor appropriate qubit-resonator interactions, we show that dissipative photons of the resonators can be exploited to autonomously drive and stabilize the two flux qubits into an approximate Bell state at the stationary state. Because of using the dissipative dynamical process, the present approach does not need to well prepare the initial state of the system and exactly monitor the evolution time. Compared with previous schemes, the present one has the remarkable features that the generation of the entangled state is implemented at a single-photon quantum level, and all four Bell states can be generated and stabilized on demand by changing the external driving parameters. Our result may have useful applications for the realization of quantum computation with superconducting quantum circuits.
We propose an efficient method for dissipative preparation of controllable steady-state entanglement of two superconducting qubits coupled to spatially separated transmission line resonators, which are linked by an additional superconducting qubit acting as a tunable coupler. The quantum-state production process is based on a form of reservoir engineering, i.e. , the dissipation of the coupler is utilized to steer the system into the desired state at stationary state. The distinct feature of our scheme is that neither initial state preparation nor unitary dynamics are required. These make the present protocol more feasible in the experimental implementation.
We present an efficient approach for dissipative generation of quantum superposition states in the microwave resonator, which is coupled to a superconducting qubit. We investigate the situation where the inversion symmetry of potential energy of the qubit is broken, and the strong two-photon nonlinear coupling between qubit and resonator can be realized via the transverse and longitudinal couplings. According to the two-photon dissipation and driving process, the dissipation of a qubit can be utilized to steer the microwave field into a quantum superposition of distinct coherent states, i.e., the Schr\"odinger cat state. In addition, we also extend the method to produce an entangled coherent state of two spatially separated resonators. Our scheme is based on quantum reservoir engineering and turns detrimental noise into a resource, which makes it feasible in experimental implementation. The present result may have potential applications in the field of quantum information processing with circuit QED systems.
We study controllable generation of two-mode-entangled states in a circuit QED setup, which consists of two spatially separated superconducting transmission line resonators and a single gap-tunable superconducting qubit. Two sharp coupling sidebands are induced when the artificial atom is suitably driven by a bichromatic microwave field. The two resonators can have squeezing-type interactions with the qubit via the coupling sidebands. If the two resonators are not degenerate, we show that the two resonators can be cooled down into the two-mode squeezed vacuum via dissipation of the qubit. The generation of the two-mode squeezed state is based on a dissipative state-engineering process, which explores the energy relaxation of the qubit as a resource. Moreover, the scheme does not need both the specific preparation of the initial state and the designed special dynamical process of the system. If the resonators are degenerate, we show that entangled coherent states of the resonators can be generated by use of the unitary dynamical evolution process of the system and the state-projection measurement. Moreover, macro entangled coherent states of the resonators with huge photons can in principle be created if the resonators and the qubit have sufficiently long lifetimes. The present scheme has two remarkable features: (1) only a single qubit is used in the generation of the two-mode squeezed state; and (2) the ultrastrong coupling condition and initializing the resonators in coherent states are not required. These make the present scheme more simple and feasible in experimental implementation.
We present a scheme for the dissipative preparation of an entangled steady state of two superconducting qubits in a circuit quantum electrodynamics (QED) setup. Combining resonator photon loss---a dissipative process already present in the setup---with an effective two-photon microwave drive, we engineer an effective decay mechanism which prepares a maximally entangled state of the two qubits. This state is then maintained as the steady state of the driven, dissipative evolution. The performance of the dissipative state preparation protocol is studied analytically and verified numerically. In view of the experimental implementation of the presented scheme we investigate the effects of potential experimental imperfections and show that our scheme is robust to small deviations in the parameters. We find that high fidelities with the target state can be achieved both with state-of-the-art three-dimensional, as well as with the more commonly used two-dimensional transmons. The promising results of our study thus open a route for the demonstration of a highly entangled steady state in circuit QED.
Abstract We propose an experimentally feasible scheme for the dissipative generation of stable entanglement of superconducting qubits via coupling modulation without applying any drives on qubits and resonator. Firstly, we study the circuit of one superconducting transmission line resonator coupled to two separated qubits via two superconducting quantum interference devices (SUQIDs). By modulating the inductance of the SQUIDs via external fluxes, we can tailor an appropriate qubit-resonator coupling with both red- and blue-sideband interactions. Combined with the photon loss of the resonator, the two qubits can be autonomously steered into a long-lived entangled state with high fidelity. Moreover, we extend the model to one resonator coupled to two separated qubit chains, each of which contains N linearly coupled superconducting qubits. We show that the lossy resonator can drive the whole system into a unique dark state, i.e. , a series of N entangled pairs of qubits across the chains can be stabilized at the stationary state. So, the present work enables the preparation of a stable long-range entangled state between the two qubits in the end sites of the chains, which plays an important role for implementing scalable quantum computation and quantum communication.