We extend the recent result of bipartite Bell singlet [Carr and Saffman, Phys. Rev. Lett. 111, (2013)] to a stationary three-dimensional entanglement between two-individual neutral Rydberg atoms. This proposal makes full use of the coherent dynamics provided by Rydberg mediated interaction and the dissipative factor originating from the spontaneous emission of Rydberg state. The numerical simulation of the master equation reveals that both the target state negativity N (ρ∞) and fidelity F(ρ∞) can exceed 99.90%. Furthermore, a steady three-atom singlet state |S3 is also achievable based on the same mechanism.

We propose a simplified parity meter for photonic qubits with cross-Kerr nonlinearities, homodyne measurement, and some optical elements. Our scheme has lower error probability than the protocol proposed in Nemoto and Munro [Phys. Rev. Lett. 93, 250502 (2004)]. Based on the present parity meter, we achieve cluster-state preparation, a complete Bell-state analyzer, and quantum teleportation. All of these schemes are nearly deterministic in the regime with little noise and include less optical elements, which makes our schemes more meaningful for large-scale quantum computing.

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We propose a mechanism of ground-state blockade between two N -type Rydberg atoms in virtue of Rydbergantiblockade effect and 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 RydbergRydberg 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 system and open system, respectively, which shows that a high fidelity of entangled state can be obtained with current experimental parameters.

We have investigated theoretically a deterministic method for preparing arbitrary multi-atom symmetric Dicke states in cavity quantum electrodynamics (QED) via combining quantum Zeno dynamics with adiabatic passage. By quantitatively discussing the case of N = 4, we show that all these states are robust against both the loss of cavity and atomic spontaneous emission, since no cavity-photon or excited level of atom is populated during the whole operation. Meanwhile, the interaction time does not change with the variation of excitation number l of |D (l) 4 (l = 1, 2, 3). Furthermore, the operating time for creating arbitrary N -atom symmetric Dicke states |D (m) N is just the same as the one for preparing |D (l) 4 . This particular feature would reduce the complexity for achieving Dicke states in experimental operation.

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A novel scheme is proposed for dissipative generation of maximally entanglement between two Rydberg atoms in the context of cavity QED. The spontaneous emission of atoms combined with quantum Zeno dynamics and Rydberg antiblockade guarantees a unique steady solution of the master equation of system, which just corresponds to the antisymmetric Bell state |S . The convergence rate is accelerated by the ground-state blockade mechanism of Rydberg atoms. Meanwhile the effect of cavity decay is suppressed by the Zeno requirement, leading to a steady-state fidelity about 90% as the single-atom cooperativity parameter C ≡ g 2 /(κγ) = 10, and this restriction is further relaxed to C = 5.2 once the quantum-jump-based feedback control is exploited.PACS numbers: 03.67. Bg,32.80.Ee,42.50.Dv,42.50.Pq The quantum dissipation arising from weak coupling between a quantum system and its surrounding reservoirs, is usually indicated by a Lindblad generator in Markovian quantum master equations for open quantum systems. Compared with unitary dynamics, the dissipative dynamics does provide a more accurate image for characterizing the evolution of quantum states in a realistic situation. It has always been regarded that the quantum dissipation plays a negative role in quantum information processing (QIP) tasks, since it causes decoherent effect on investigated quantum system. Nevertheless, the study in recent decades has changed people's view of dissipation, and the environment can be used as a resource in QIP experimentally [1][2][3][4][5][6][7].Quantum entanglement, as one of the most striking features in quantum theory, is defined to describe a strongly correlated system constituted by pairs or groups of particles, and a measurement made on either of the particles collapses the state of the system instantaneously. Thus it is an interesting question how can one prepare this kind of strongly 'coherent' system using the 'decoherent' factors. Currently, there are several representative schemes creating steady bipartite entanglement of high quality by dissipation [8][9][10][11][12][13][14][15][16][17]. For instance, in the context of cavity QED, the cavity decay was exploited to drive the system into a maximally entangled stationary state, making the spontaneous emission of atom be the solely detrimental element [9]. In neutral atom systems, two groups independently prepared high-fidelity steady-state entanglement between a pair of Rydberg atoms with dissipative Rydberg pumping [12,13]. More recently, a highly entangled state with fidelity above 99% was achieved in ion traps, and the fidelity was further enhanced by detection of photons spontaneous emission emitted in to the environment [17]. However, it is challenging to detect atomic decay event in experiment.In this work, we suggest an alternative scheme in the context of cavity QED for dissipatively preparing a maximally entangled state by capitalizing the advantages of above protocols. We combine the spontaneous emission of atom with quantum Zeno dynamics and Rydberg antiblockad...