Entangled states are of significant importance in the realms of quantum communication and quantum information processing. Fusion technology has been proven as a viable method to prepare large-size entangled states from two or more small-size entangled states in a quantum electrodynamics (QED) system. However, most fusion schemes in QED systems require precise control over the evolution time, thereby amplifying the difficulty in the experiment. Therefore, it is of great importance to find a scheme to fuse entangled states in a QED system without requiring precise control over the evolution time. In this study, we propose a fusion scheme to efficiently prepare large-scale entangled states by transitionless quantum driving (TQD) with Rydberg superatoms. We position an ultracold ensemble of n individual ladder-type Rydberg atoms within the blockade sphere, thereby forming a superatom. Subsequently, we encode quantum information onto the collective state of the Rydberg superatoms. Through the combined use of quantum Zeno dynamics and TQD, the scheme enables the fast fusion of an m -qubits W (GHZ) state and an n -qubits W (GHZ) state into a ( m + n −2)-qubits W (GHZ) state without the requirement for precise control over the evolution time. Moreover, the impact of decoherence factors, operational imperfection, and noise on fidelity is taken into account. Numerical simulations suggest that the proposed method demonstrates high fidelity.
Entangled states are of significant importance in the realms of quantum communication and quantum information processing. Fusion technology has been proven as a viable method to prepare large-size entangled states from two or more small-size entangled states in a quantum electrodynamics (QED) system. However, most fusion schemes in QED systems require precise control over the evolution time, thereby amplifying the difficulty in the experiment. Therefore, it is of great importance to find a scheme to fuse entangled states in a QED system without requiring precise control over the evolution time. In this study, we propose a fusion scheme to efficiently prepare large-scale entangled states by transitionless quantum driving (TQD) with Rydberg superatoms. We position an ultracold ensemble of n individual ladder-type Rydberg atoms within the blockade sphere, thereby forming a superatom. Subsequently, we encode quantum information onto the collective state of the Rydberg superatoms. Through the combined use of quantum Zeno dynamics and TQD, the scheme enables the fast fusion of an m -qubits W (GHZ) state and an n -qubits W (GHZ) state into a ( m + n −2)-qubits W (GHZ) state without the requirement for precise control over the evolution time. Moreover, the impact of decoherence factors, operational imperfection, and noise on fidelity is taken into account. Numerical simulations suggest that the proposed method demonstrates high fidelity.
The W state, as a robust multipartite entangled state, plays an important role in quantum information processing, quantum network construction and quantum computing. In this paper, a three-level ladder-type Rydberg atomic system is placed into a Rydberg blocking sphere to form a superatom. Each superatom has many collective states including just one Rydberg excitation constrained by the Rydberg blockade effect. In the weak cavity field limit, at most one atom can be pumped into excited state, then we can describe the superatom by using a three-level ladder-type system. Afterwards we encode quantum information about the effective energy levels of Rydberg superatoms and propose a fast scheme for preparing the Rydberg superatom W state based on the superadiabatic iterative technique and quantum Zeno dynamics.This scheme can be achieved in only one step by controlling the laser pulses. In this scheme, the superatoms are trapped in spatially separated cavities connected by optical fibers, thereby greatly improving the feasibility of experimental manipulation. A remarkable feature is that it does not need to accurately control experimental parameters and interaction time. Meanwhile, the form of counterdiabatic Hamiltonian is the same as that of the effective Hamiltonian. Through numerical simulations, the fidelity of this scheme can reach 99.94%. Even considering decoherence effects, including atomic spontaneous emission and photon leakage, the fidelity can still exceed 97.5%, thereby further demonstrating the strong robustness of the solution. In addition, the Rabi frequency can be characterized as a linear superposition of Gaussian functions, and this representation significantly alleviates the complexity encountered in practical experiments. Futhermore, we also analyze the influence of parameter fluctuations on the fidelity, and the results show that this scheme is robust against parameter fluctuations. Finally, the present scheme is extended to the case of N Rydberg superatoms, which shows the scalability of our scheme.
Quantum entanglement is a basic resource of quantum information processing and quantum computation. The simple and efficient generation of entangled states is always one of the hot research topics. As one of the ideal carriers of quantum information encoding, neutral Rydberg atom occupies a place in the field of generation of entangled state with its unique advantages. For example, Rydberg atom has a large volume and is easily ionized by an external electric field, so it is very sensitive to the change in the external electric field. Therefore, the interaction strength between Rydberg atoms can be changed by altering the external electric field. Rydberg state is a highly excited state, but its radiation attenuation is very small: the radiation lifetime can reach a millisecond level or even longer. The distance between the atomic kernel and the outermost electron is relatively long, and the electric dipole moment is very large. In this paper, the four-level inverted “Y”-type Rydberg atomic system is introduced into the Rydberg blocking ball to form a superatom, and the quantum information is encoded on the effective energy level of the superatom under the condition of weak cavity field. We construct shortcuts to adiabatic passage in a three-superatom system. Combined with quantum Zeno dynamics and shortcuts to adiabatic passage, the three-particle singlet state is simply and effectively generated. In addition, the influence of decoherence factors (including cavity decay and spontaneous emission of superatoms) on the fidelity is considered in this scheme. Numerical simulation results show that the proposed scheme can obtain high fidelity without precisely controlling the evolution time, and the fidelity of singlet state is robust to decoherence factors, since no cavity-photon population is involved in the whole process because of the quantum Zeno dynamics.
A scheme for preparing a three-dimensional entangled state of two atoms is proposed. In the present scheme, two atoms are placed in two cavities that are spatially separated and connected by a fiber. With the help of quantum Zeno dynamics, the shortcuts to adiabaticity can be constructed through transitionless quantum driving to fast achieve the preparation of a three-dimensional entangled state. During this process, we consider the influence of fluctuations about system parameters and various decoherence factors on the fidelity. Numerical simulation results demonstrate that this scheme can not only realize the preparation of a three-dimensional entangled state with a high fidelity, but is also insensitive to parameter fluctuations. Moreover, our scheme can be extended to realize the N-dimensional entanglement of two atoms.
Abstract Quantum entanglement is the basic resource of quantum information processing and quantum computation, especially multi-partite entanglement. The simple and efficient generation of multi-partite entanglement has always been one of the hot topics of scholars. In this paper, we propose a qubit-loss-free fusion scheme for generation of large-scale entangled W states with Rydberg superatom. By sending two superatoms belonging to a k -atom W states and a l -atom W states, respectively, into a cavity, we may obtain a ( k + l )-atom W states via detecting the cavity state after interaction. The numerical simulation analysis shows that the fidelity is robust against both spontaneous emission of superatoms and decay of the cavity. In addition, the feasibility analysis indicates this scheme can also be realized in experiment.
ABSTRACT Bell state and W state are not just common entangled states, they are foundational resources in the field of quantum information. In this scheme, a Rydberg atomic ensemble with a four‐level “”‐shaped structure is confined within a Rydberg blockade sphere to form a superatom. Exploiting the unique advantages of the weak cavity field limit, the quantum information can be encoded with reliability on the superatom's effective energy levels. By integrating the methods of quantum Zeno dynamics (QZD) and Lewis‐Riesenfeld (LR) invariants, the Bell state, three‐qubit W state, and ‐qubit W state are prepared rapidly. Furthermore, the influences exerted by decoherence factors are also factored in. Numerical simulations confirm that the present scheme not only achieves high fidelities but also exhibits robustness against these decoherence factors. Finally, we further investigate the influences of parameter fluctuations on fidelities, and the results demonstrate that the fidelities of the proposed scheme remain robust against parameter fluctuations.
Multiparticle entanglement has important applications in quantum information and quantum computing. Here, we propose two schemes to fuse large-scale entangled W states and GHZ states. In the first fusion scheme, we send two Rydberg superatoms that belong to an n particle W state and an m particle W state, respectively, into a vacuum cavity; an ( n + m −2) particle W state can be obtained by detecting the state of the superatoms after the interaction. In the second fusion scheme, we send two Rydberg superatoms into two separate cavities; with the assistance of a circularly polarized photon, we can obtain a ( k + l ) particle GHZ state after detecting the state of the photon. The numerical simulation analysis shows that both schemes are robust against the spontaneous emission of superatoms and the decay of the cavity. The feasibility analysis indicates that these two schemes can be realized in experiments.