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arXiv:1806.05336 · Physical Review A

Unconventional Rydberg pumping and applications in quantum information processing

Dongxiao Li, Xiao‐Qiang Shao

Published Dec 28, 2018• 66 citations
arXivHTMLPDF

Abstract

We propose a mechanism of unconventional Rydberg pumping (URP) via simultaneously driving each Rydberg atom by two classical fields with different strengths of Rabi frequencies. This mechanism differs from the general Rydberg blockade or Rydberg antiblockade since it is closely related to the ground states of atoms, i.e., two atoms in the same ground state are stable while two atoms in different ground states are resonantly excited. Furthermore, we find the URP can be employed to simplify some special quantum information processing tasks, such as implementation of a three-qubit controlled-phase gate with only a single Rabi oscillation, preparation of two- and three-dimensional steady-state entanglement with two identical atoms, and realization of the autonomous quantum error correction in a Rydberg-atom-cavity system. The feasibility of the above applications is discussed explicitly by the state-of-the-art technology.

DOI
10.1103/physreva.98.062338

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We propose a mechanism of unconventional Rydberg pumping (URP) via simultaneously driving each Rydberg atom by two classical fields with different strengths of Rabi frequencies. This mechanism differs from the general Rydberg blockade or Rydberg antiblockade since it is closely related to the ground states of atoms, i.e., two atoms in the same ground state are stable while two atoms in different ground states are resonantly excited. Furthermore, we find the URP can be employed to simplify some special quantum information processing tasks, such as implementation of a three-qubit controlled-phase gate with only a single Rabi oscillation, preparation of two- and three-dimensional steady-state entanglement with two identical atoms, and realization of the autonomous quantum error correction in a Rydberg-atom-cavity system. The feasibility of the above applications is discussed explicitly by the state-of-the-art technology.
The resonant dipole-dipole interaction between highly excited Rydberg levels dominates the interaction of neutral atoms at short distances scaling as 1/r31/{r}^{3}1/r3. Here we take advantage of the combined effects of strong dipole-dipole interaction and multifrequency driving fields to propose one type of selective Rydberg pumping mechanism. In the computational basis of two atoms ${|00\ensuremath{\rangle},|01\ensuremath{\rangle},|10\ensuremath{\rangle},|11\ensuremath{\rangle}}$, this mechanism allows $|11\ensuremath{\rangle}$ to be resonantly pumped upwards to the single-excited Rydberg states while the transitions of the other three states are suppressed. From the perspective of mathematical form, we achieve an analogous F\"orster resonance for ground states of neutral atoms. The performance of this selective Rydberg pumping is evaluated using the definition of fidelity for a controlled-ZZZ gate, which manifests a characteristic robustness to the deviation of interatomic distance, fluctuation of F\"orster resonance defect, and spontaneous emission of double-excited Rydberg states. As applications of this mechanism, we discuss in detail the preparation of the maximally entangled symmetric state for two atoms via ground-state blockade, and the maximally entangled antisymmetric state via engineered spontaneous emission, within the state-of-the-art experiments, respectively.
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We propose a mechanism of ground-state blockade between two NNN-type Rydberg atoms by virtue of the Rydberg-antiblockade effect and the Raman transition. Inspired by the quantum Zeno effect, the strong Rydberg antiblockade interaction plays a role in frequently measuring one ground state of two, leading to a blockade effect for double occupation of the corresponding quantum state. By encoding the logic qubits into the ground states, we efficiently avoid the spontaneous emission of the excited Rydberg state and maintain the nonlinear Rydberg-Rydberg interaction at the same time. As applications, we discuss in detail the feasibility of preparing two-atom and three-atom entanglement with ground-state blockade in closed and open systems, respectively, which shows that a high fidelity of the entangled state can be obtained with current experimental parameters.
Abstract We study the steady-state quantum correlations arising from the atom–field and interatomic interplays in two-level Rydberg atoms coherently driven by an external laser field. Three kinds of quantum correlations, i.e., atom–atom correlation, atom–field entanglement and photon–photon correlation, are simultaneously examined by considering dipole–dipole interactions (DDI) for pairwise Rydberg atoms. They are shown to be closely linked with single and double Rydberg excitations, which can be modulated to work in the blockade or antiblockade regime depending on the driving field frequency, the DDI strength and the Rydberg decay rate. As a result, we obtain strongly correlated atoms and highly antibunching photons (indispensable resources in applications of quantum information processing) intermediated with robust atom–field entanglement.
Compared with the idea of universal quantum computation, a direct synthesis of a multiqubit logic gate can greatly improve the efficiency of quantum information processing tasks. Here we propose an efficient scheme to implement a three-qubit controlled-not (Toffoli) gate of neutral atoms based on unconventional Rydberg pumping. By adjusting the strengths of Rabi frequencies of driving fields, the Toffoli gate can be achieved within one step, which is also insensitive to the fluctuation of the Rydberg-Rydberg interaction. Considering different atom alignments, we can obtain a high-fidelity Toffoli gate at the same operation time ∼7 μs. In addition, our scheme can be further extended to the four-qubit case without altering the operating time.
Abstract Entangling gates are important for the generation of entanglement in quantum communicational and computational tasks. In this work, we propose an efficient protocol to realize the multi-qubit entangling gates with high fidelity in Rydberg atoms. Particularly, we apply the technique of soft quantum control to design the off-resonant pulses such that the atoms are driven to the ground-state subspace via unconventional Rydberg pumping. Thus, our scheme is insensitive to the decay effect as all atoms are only virtually excited. Moreover, Gaussian temporal modulation is further adopted to improve its robustness against the model uncertainty, such as operating time and environment noise. Finally, we perform numerical simulation to validate the effectiveness of our scheme. Hence, our work has potential applications in quantum information processing based on Rydberg atoms.