We use the approach of "transitionless quantum driving" proposed by Berry to construct shortcuts to the population transfer and the creation of maximal entanglement between two Λ-type atoms based on the cavity quantum electronic dynamics (CQED) system. An effective Hamiltonian is designed by resorting to an auxiliary excited level, a classical driving field and an extra cavity field mode to supplement or substitute the original reference Hamiltonian, and steer the system evolution along its instantaneous eigenstates in an arbitrarily short time, speeding up the rate of population transfer and creation of maximal entanglement between the two atoms inside a cavity. Numerical simulation demonstrates that our shortcuts' performance is robust against the decoherences caused by atomic spontaneous emission and cavity photon leakage.

We propose a scheme for the generation of entangled states for two atoms trapped in separate cavities coupled to each other. The scheme is based on the competition between the unitary dynamics induced by the classical fields and the collective decays induced by the dissipation of two delocalized field modes. Under certain conditions, the symmetric or asymmetric entangled state is produced in the steady state. The analytical result shows that the distributed steady entanglement can be achieved with high fidelity independent of the initial state, and is robust against parameter fluctuations. We also find out that the linear scaling of entanglement fidelity has a quadratic improvement compared to distributed entangled state preparation protocols based on unitary dynamics.There have been various practical applications for quantum entangled states, ranging from quantum teleportation [1, 2] to universal quantum computation [3,4]. The main obstacle in preserving entanglement is decoherence induced by the environment. Recently, dissipative state preparation has become a focus in quantum computation and entanglement engineering [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], which uses decoherence as a powerful resource without destroying the quantum entanglement. These schemes are robust against parameter fluctuations, obtain high fidelity entanglement with arbitrarily initial states, and do not need accurate control of the evolution time. Particularly, Kastoryano and Reiter et al. [5,6] proposed a novel scheme for dissipative preparation of entanglement for two atoms in an optical cavity which gets a qualitative improvement in the scaling of the fidelity with optimal cavity parameters as compared to any state preparation protocol with coherent unitary dynamics. However, most of the previous theoretical schemes and experiments [21] concentrate on the case in which two atoms are trapped in a single cavity.For distributed quantum information processing, it is a basic requirement to perform state transfer and quantum gate operation between separate nodes of a quantum network. To overcome the difficulty of individual addressability existing in a single cavity, efforts have been devoted to the coupled-cavity models both theoretically [22][23][24][25][26][27][28] and experimentally [29]. Most works on the coupled-cavity system focused on the traditional coherent unitary dynamics, requiring precise timing and special initial states. Clark et al. [30] proposed a scheme to entangle the internal states of atoms in separate optical cavities using technique of quantum reservoir engineering, however the scheme requires a complex atomic level configuration. Furthermore, the evolution towards the steady state slows down as the entanglement of the desired state increases.In this paper, we generalize the idea of Refs. [5, 6] * sbzheng@pub5.fz.fj.cn and propose a scheme for producing distributed entanglement for two atoms trapped in coupled cavities. Due to the coherent photon hopping between the two cavities, the system is m...

A quantum system can behave as a wave or as a particle, depending on the experimental arrangement. When, for example, measuring a photon using a Mach-Zehnder interferometer, the photon acts as a wave if the second beam splitter is inserted, but as a particle if this beam splitter is omitted. The decision of whether or not to insert this beam splitter can be made after the photon has entered the interferometer, as in Wheeler's famous delayed-choice thought experiment. In recent quantum versions of this experiment, this decision is controlled by a quantum ancilla, while the beam splitter is itself still a classical object. Here, we propose and realize a variant of the quantum delayed-choice experiment. We configure a superconducting quantum circuit as a Ramsey interferometer, where the element that acts as the first beam splitter can be put in a quantum superposition of its active and inactive states, as verified by the negative values of its Wigner function. We show that this enables the wave and particle aspects of the system to be observed with a single setup, without involving an ancilla that is not itself a part of the interferometer. We also study the transition of this quantum beam splitter from a quantum to a classical object due to decoherence, as observed by monitoring the interferometer output. The wave-particle duality is one of the fundamental mysteries that lie at the heart of quantum mechanics. However, these two incompatible aspects cannot be observed simultaneously, as captured by Bohr's principle of complementarity [1-5]: Particlelike versus wavelike outcomes are selected by experimental arrangements that are mutually exclusive. This is well illustrated by the Mach-Zehnder interferometer, as shown in Fig. 1(a). Split by the first beam splitter (BS 1 ), a photon travels along two paths, 0 and 1. The relative phase θ between the quantum states associated with these paths is tunable. In the presence of the second beam splitter (BS 2 ), the two paths are recombined and the probability for detecting the photon in the detector D 0 or D 1 is a sinusoidal function of θ exhibiting wavelike interference fringes. On the other hand, in the absence of BS 2 , the experiment reveals which path the photon followed, and the photon is detected in one or the other detector with equal probability 1=2, thus behaving as a particle.One can argue that the behavior of the photon is predetermined by the experimental arrangement, where the presence or absence of the second beam splitter affects the photon prior to its entering the interferometer. The possibility of such a causal link is precluded in Wheeler's delayed-choice experiment [6][7][8], in which the observer randomly chooses whether to insert BS 2 , and thus whether to perform an interference or a which-path experiment, after the photon has passed through BS 1 . Therefore, the photon could not "know" in advance which behavior it should exhibit. Wheeler's delayed-choice experiment has been demonstrated previously [9][10][11][12][13], where the spacelike separation ...

We propose a scheme for dissipative preparation of W-type entangled steady states of three atoms trapped in an optical cavity. The scheme is based on the competition between the decay processes into and out of the target state. By suitable choice of system parameters, we resolve the whole evolution process and employ the effective operator formalism to engineer four independent decay processes so that the target state becomes the stationary state of the quantum system. The scheme requires neither the preparation of definite initial states nor precise control of system parameters and preparation time.

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