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Advanced Quantum Technologies

Deterministic Conversion from GHZ State to W State with Rydberg Superatoms

Yingli Liu, Wen‐Xue Cui, Shou Zhang, Hong‐Fu Wang

Published Apr 9, 2025• 3 citations
Publisher

Abstract

Abstract Quantum entanglement is playing an increasingly crucial role in the field of quantum information. The conversion between different types of entangled states, especially for GHZ state and W state, can greatly enhance the efficiency of quantum information processing. Here, a two‐step scheme is proposed to realize the conversion between GHZ state and W state with Rydberg superatoms, in which the collective states of superatom are used to encode quantum information. In the first step, let a single‐photon pulse pass through two cavities that trap superatoms in sequence and detect the state of photon to complete this task. In the second step, shortcuts are employed to adiabaticity based on superadiabatic technique and design appropriate Rabi frequencies for the system. The numerical simulations demonstrate that this scheme possesses a high fidelity and exhibits robustness against detrimental effects such as atomic spontaneous emission, cavity losses, fiber photon leakages and noise. Furthermore, the intricate pulses within this scheme are decomposed into a linear superposition of Gaussian pulses, enhancing experimental feasibility. Finally, the scheme is extended to deal with the scenario of multi‐superatom. This method provides a way to convert other types of entangled states.

DOI
10.1002/qute.202400663

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Abstract Quantum entanglement is playing an increasingly crucial role in the field of quantum information. The conversion between different types of entangled states, especially for GHZ state and W state, can greatly enhance the efficiency of quantum information processing. Here, a two‐step scheme is proposed to realize the conversion between GHZ state and W state with Rydberg superatoms, in which the collective states of superatom are used to encode quantum information. In the first step, let a single‐photon pulse pass through two cavities that trap superatoms in sequence and detect the state of photon to complete this task. In the second step, shortcuts are employed to adiabaticity based on superadiabatic technique and design appropriate Rabi frequencies for the system. The numerical simulations demonstrate that this scheme possesses a high fidelity and exhibits robustness against detrimental effects such as atomic spontaneous emission, cavity losses, fiber photon leakages and noise. Furthermore, the intricate pulses within this scheme are decomposed into a linear superposition of Gaussian pulses, enhancing experimental feasibility. Finally, the scheme is extended to deal with the scenario of multi‐superatom. This method provides a way to convert other types of entangled states.
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.
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.
Abstract Dicke states play an important role in quantum information processing and quantum computing. Here, by virtue of quantum Zeno dynamics and shortcuts to adiabaticity, a scheme for fast conversion of three‐particle symmetric Dicke states to four‐particle symmetric Dicke states () with Rydberg superatoms is proposed. This scheme can be completed within one step through adjusting the Rabi frequencies of classical fields. Moreover, the effect of decoherence induced by atomic spontaneous emission and leakage of the cavity on fidelities are considered. The numerical simulation demonstrates that this scheme has high fidelities and robustness against decoherence.
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 W states play an important role in quantum information processing and quantum computing. Here, it proposes a scheme for preparing W states by designing the evolution operators with Rydberg superatoms. It encodes quantum information on the effective energy level of the superatom, and construct shortcuts to adiabatic passages (STAP) by designing the evolution operators. Combined with Quantum Zeno dynamics and STAP, it can prepare three‐particle W states quickly and efficiently. In addition, the Rabi frequency in this scheme can be described as a linear superposition of Gaussian functions, which reduces the difficulty of practical experiment. The numerical simulation shows that the scheme is robust against decoherence, operational imperfection, and noise. At last, it generalizes this scheme to preparation of N ‐particle W states.
With Rydberg dipole interactions, a mesoscopic atomic ensemble becomes a superatom that behaves like a single atom but couples collectively with photons. It is potentially a strong candidate as a qubit in quantum information science, especially for quantum networks. In this paper, we report a cavity-enhanced single-photon interface for a Rydberg superatom and demonstrate deterministic qubit readout via a photon burst. We make use of a low-finesse ring cavity to enhance the atom–photon interaction and obtain in-fiber single-photon generation efficiency of 44%. Harnessing the dipole interaction between two Rydberg levels, we may create either a sequence of multiple single photons or nothing, conditioned on an initial qubit state. We achieve a measurement fidelity of 93.0% in 4.8 µs. Our work complements the experimental toolbox of harnessing Rydberg superatoms for quantum information applications.