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Quantum phase transition and entanglement in the Rabi model with a squeezed light are investigated. We find a special unitary-transformation method that removes the nonintegrable squeezing and counterrotating-wave interactions when the qubit frequency is close to the field frequency. The analytical ground state agrees well with the numerical solution. We demonstrate that the ground state exhibits a first-order quantum phase transition at a critical point induced linearly by the squeezed light. This quantum phase transition requires neither multiple qubits nor an infinite ratio of qubit frequency to field frequency, which solves a critical problem for the theory and experiment in Rabi model. As the qubit-field coupling strength increases, the ground-state entanglement reaches its maximum value at the critical point.

Quantum key distribution (QKD) provides information theoretically secure key exchange requiring authentication of the classic data processing channel via pre-sharing of symmetric private keys to kick-start the process. In previous studies, the lattice-based post-quantum digital signature algorithm Aigis-Sig, combined with public-key infrastructure (PKI), was used to achieve high-efficiency quantum security authentication of QKD, and we have demonstrated its advantages in simplifying the MAN network structure and new user entry. This experiment further integrates the PQC algorithm into the commercial QKD system, the Jinan field metropolitan QKD network comprised of 14 user nodes and 5 optical switching nodes, and verifies the feasibility, effectiveness and stability of the post-quantum cryptography (PQC) algorithm and advantages of replacing trusted relays with optical switching brought by PQC authentication large-scale metropolitan area QKD network. QKD with PQC authentication has potential in quantum-secure communications, specifically in metropolitan QKD networks.

The optical beam splitter is an essential device used for decoding in quantum key distribution. The impact of optical beam splitters on the security of quantum key distribution was studied, and it was found that the realistic device characteristics closely influence the error rate introduced by the wavelength-dependent attack on optical beam splitters. A countermeasure, combining device selection and error rate over-threshold alarms, is proposed to protect against such attacks. Beam splitters made of mirror coatings are recommended, and the variation of splitting ratio should be restricted to lower than 1 dB at 1260–1700 nm. For the partial attack scenario where the eavesdropper attacks only a portion of the quantum signal, a modified secure key rate formula is proposed to eliminate the revealed information of the attacked portion. Numerical results show that the QKD system adopting this countermeasure exhibits good performance with a secure key rate of over 10 kbps at 100 km and a maximum transmission distance of over 150 km, with only a small difference from the no-attack scenario. Additionally, a countermeasure to monitor the light intensity of different wavelengths is proposed to protect against the wavelength-dependent attack on optical beam splitters.

Nonreciprocal transmission of optical or microwave signals is indispensable in various applications involving sensitive measurements. In this paper, we study optomechanically induced directional amplification and isolation in a generic setup including two cavities and two mechanical oscillators by exclusively using blue-sideband drive tones. The input and output ports defined by the two cavity modes are coupled through coherent and dissipative paths mediated by the two mechanical resonators, respectively. By choosing appropriate transfer phases and strengths of the driving fields, either a directional amplifier or an isolator can be implemented at low thermal temperature, and both of them show bi-directional nonreciprocity working at two mirrored frequencies. The nonreciprocal device can potentially be demonstrated by opto- and electro-mechanical setups in both optical and microwave domains., Comment: 5 pages, 3 figures

The study of entanglement between discrete and continuous variables is an important theoretical and experimental topic in quantum information processing, for which entanglement swapping is one of the interesting elements. Entanglement swapping allows two particles without interacting with each other in any way, to form an entangled state by the action of another pair of entangled particles. In this paper, we propose an experimentally feasible scheme to realize deterministic entanglement swapping in the hybrid system with discrete and continuous variables. The process is achieved by preparing two pairs of entangled states, each is formed by a qubit and two quasi-orthogonal coherent state elements of a cavity, performing a Bell-state analysis through nonlocal operations on the continuous variable states of the two cavities, and projecting the two qubits into a maximally entangled state. The present scheme may be applied to other physical systems sustaining such hybrid discrete and continuous forms, providing a typical paradigm for entanglement manipulation through deterministic swapping operations.

We report an efficient mechanism to generate mechanical entanglement in a two-cascaded cavity optomechanical system with optical parametric amplifiers (OPAs) inside the two coupled cavities. We use the especially tuned OPAs to squeeze the hybrid mode composed of two mechanical modes, leading to strong macroscopic entanglement between the two movable mirrors. The squeezing parameter as well as the effective mechanical damping are both modulated by the OPA gains. The optimal degree of mechanical entanglement therefore depends on the balanced process between coherent hybrid mode squeezing and dissipation engineering. The mechanical entanglement is robust to strong cavity decay, going beyond simply resolved sideband regime, and is resistant to reasonable high thermal noise. The scheme provides an alternative way for generating strong macroscopic entanglement in cascaded optomechanical systems.

We study the quantum phase transition in the Dicke model beyond the thermodynamic limit. With the Kibble–Zurek mechanism and adiabatic dynamics, we find that the residual energy is inversely proportional to the number of qubits, indicating that more qubits can obtain more energies from the oscillator as the number of qubits increases. Finally, we put forward a promising experiment device to realize this system.

Quantum key distribution (QKD) is one of the most practical applications in quantum information processing, which can generate information-theoretical secure keys between remote parties. With the help of the wavelength-division multiplexing technique, QKD has been integrated with the classical optical communication networks. The wavelength-division multiplexing can be further improved by the mode-wavelength dual multiplexing technique with few-mode fiber (FMF), which has additional modal isolation and large effective core area of mode, and particularly is practical in fabrication and splicing technology compared with the multi-core fiber. Here, we present for the first time a QKD implementation coexisting with classical optical communication over weakly-coupled FMF using all-fiber mode-selective couplers. The co-propagation of QKD with one 100 Gbps classical data channel at -2.60 dBm launched power is achieved over 86 km FMF with 1.3 kbps real-time secure key generation. Compared with single-mode fiber using wavelength-division multiplexing, given the same fiber-input power, the Raman noise in FMF using the mode-wavelength dual multiplexing is reduced by 86% in average. Our work implements an important approach to the integration between QKD and classical optical communication and previews the compatibility of quantum communications with the next-generation mode division multiplexing networks.

Quantum key distribution (QKD) provides an information-theoretically secure method to share keys between legitimate users. To achieve large-scale deployment of QKD, it should be easily scalable and cost-effective. The infrastructure construction of quantum access network (QAN) expands network capacity and the integration between QKD and classical optical communications reduces the cost of channel. Here, we present a practical downstream QAN over a 10 Gbit/s Ethernet passive optical network (10G-EPON), which can support up to 64 users. In the full coexistence scheme using the single feeder fiber structure, the co-propagation of QAN and 10G-EPON signals with 9 dB attenuation is achieved over 21 km fiber, and the secure key rate for each of 16 users reaches 1.5 kbps. In the partial coexistence scheme using the dual feeder fiber structure, the combination of QAN and full-power 10G-EPON signals is achieved over 11 km with a network capacity of 64-user. The practical QAN over the 10G-EPON in our work implements an important step towards the achievement of large-scale QKD infrastructure., 9 pages, 4 figures. Accepted for publication in Optics Express

Holonomies, arising from non-Abelian geometric transformations of quantum states in Hilbert space, offer a promising way for quantum computation. These holonomies are not commutable and thus can be used for the realization of a universal set of quantum logic gates, where the global geometric feature may result in some noise-resilient advantages. Here we report the first on-chip realization of a non-Abelian geometric controlled-Not gate in a superconducting circuit, which is a building block for constructing a holonomic quantum computer. The conditional dynamics is achieved in an all-to-all connected architecture involving multiple frequency-tunable superconducting qubits controllably coupled to a resonator; a holonomic gate between any two qubits can be implemented by tuning their frequencies on resonance with the resonator and applying a two-tone drive to one of them. This gate represents an important step towards the all-geometric realization of scalable quantum computation on a superconducting platform., Comment: 13 pages, 11 figures, 2 tables

Entangled coherent states for multiple bosonic modes, also referred to as multimode cat states, not only are of fundamental interest, but also have practical applications. The nonclassical correlation among these modes is well characterized by the violation of the Mermin-Klyshko inequality. We here study Mermin-Klyshko inequality violations for such multi-mode entangled states with rotated quantum-number parity operators. Our results show that the Mermin-Klyshko signal obtained with these operators can approach the maximal value even when the average quantum number in each mode is only 1, and the inequality violation exponentially increases with the number of entangled modes. The correlations among the rotated parities of the entangled bosonic modes are in distinct contrast with those among the displaced parities, with which a nearly maximal Mermin-Klyshko inequality violation requires the size of the cat state to be increased by about 15 times., 6 pages, 3 figures

Entanglement of quasiclassical (coherent) states of two harmonic oscillators leads to striking quantum effects and is useful for quantum technologies. These effects and applications are closely related to nonlocal correlations inherent in these states, manifested by the violation of Bell inequalities. With previous frameworks, this violation is limited by the size of the system, which does not approach the maximum even when the amount of entanglement approaches its maximum. Here we propose a new version of Bell correlation operators, with which a nearly maximal violation can be obtained as long as the associated entanglement approximates to the maximum. Consequently, the revealed nonlocality is significantly stronger than those with previous frameworks for a wide range of the system size. We present a new scheme for realizing the gate necessary for measurement of the nonlocal correlations. In addition to the use in test of quantum nonlocality, this gate is useful for quantum information processing with coherent states, Comment: 5 pages, 3 figures

In this paper, La0.8K0.2MnO3 powder was synthesized by sol–gel method. The phase structure, morphology of the composite have been characterized by X-ray diffraction, field emission scanning electron microscope. Testing of the microwave absorption was carried out by using the network analyzer Agilent HP-8722ES at room temperature. The results show that the La0.8K0.2MnO3 powder has excellent absorbing property. The maximum reflection loss is −33.51 dB at about 12.22 GHz with a thickness of only 1.25 mm. Moreover, the bandwidth with the reflection loss above 10 dB reaches about 2.1 GHz.

We propose a method to improve the stimulated Raman adiabatic passage (STIRAP) via dissipative quantum dynamics, taking into account the dephasing effects. Fast and robust population transfer can be obtained with the scheme by the designed pulses and detuning, even though the initial state of the system is imperfect. With a concrete three-level system as an example, the influences of the imperfect initial state, variations in the control parameters, and various dissipation effects are discussed in detail. The numerical simulation shows that the scheme is insensitive to moderate fluctuations of experimental parameters and the relatively large dissipation effects of the excited state. Furthermore, the dominant dissipative factors, namely, the dephasing effects of the ground states and the imperfect initial state are no longer undesirable, in fact, they are the important resources to the scheme. Therefore, the scheme could provide more choices for the realization of the complete population transfer in the strong dissipative fields, Comment: 8 pages, 10 figures, has been accepted by Optics Express

We propose a scheme for deterministic generation of entanglement embodied by two $\Lambda $ -type atoms distributed in two coupled cavities. We study such a system in the dispersive atom-field interactions, where the dynamics of the system operates through the virtual population of both the atomic excited states and the photonic states in the cavities (plus the fiber). We verify the validity of the dynamics, and moreover, study the influences of the decoherence due to the spontaneous emission and photon leakage. We also apply the dynamics for realizing quantum state transfer and quantum phase gates.

The cross-talk in plastic scintillating fiber array detector with high-energy gamma incident was studied through Monte-Carlo simulation.The relationship between cross-talk and lead layer was also analyzed.Modulate transfer function(MTF),which shows quantity of spatial resolution of imaging detector,was analyzed and compared in order to get the MTF results caused from the difference thickness of lead layer.The results show that there exists severe cross-talk in the detector irradiated by high-energy particles,and the lead layer can reduce the effect.On the other hand,the pixel of detector may become big as the lead layer is introduced,which can reduce the spatial resolution.Through the simulation computation,it is proved that the right thickness of lead layer will reduce cross-talk and increase spatial resolution of imaging detector.

We propose a scheme for realizing conditional quantum phase gates for two atoms that are distributed in two coupled cavities. Due to the resonant interaction in temporal evolution of the entire system, the gate operation time is greatly reduced as compared with that of the nonresonant schemes. We study the influence of imperfections in the interaction and the effect of decoherence and find the gate to be robust. We discuss the issue related to the practical implementation and show that the gate is accessible within the current cavity QED technology.

A new scheme is proposed for preparation of a type of nonclassical state in cavity QED. In the scheme, an atom either flying through or trapped within a cavity, is controlled by the classical Stark effect; this makes it interact alternately with a (resonant) classical field and with the (dispersive) cavity field. The cavity field, which allows an arbitrary displacement operation during the process, after the detection on the atom, finally collapses to the specific superpositions of coherent states, with their weighting factors controllable. The scheme is also applied for preparation of superpositions of motional coherent states for a trapped ion. The scheme is in contrast to all the previous ones, and thus provides a new perspective for quantum state engineering.

We propose a scheme for generating maximally entangled states for multiple atoms trapped in distant cavities connected by fibers. During the operation neither the atomic system nor the fibers are excited, which is important in view of decoherence. Under certain conditions, the probability that the cavities are excited is negligible. The scheme does not include projective measurement and the GHZ state is generated deterministically. Taking advantage of adiabatic passage, the entanglement fidelity is insensitive to fluctuation of experimental parameters.

We propose a scheme for the generation of an arbitrary quantum states for multiple trapped ions in the symmetric Dicke subspace. One can manipulate the collective ion transition in a selective symmetric Dicke subspace via the virtual excitation induced inequidistant energy levels. All the states undergo the same phonon-number-dependent Stark shift and thus the scheme is insensitive to the thermal motion. Furthermore, the scheme does not require individual addressing of the ions.

In this paper, the effects of temperature on laser diode ignition and the resulting consequences were discussed in detail through theoretical analysis, experiments and numerical calculations. The results indicated that the output power of laser diode decreases and the wavelength of laser redshifts with elevated working temperature under a certain condition. The threshold conditions of ignition for powders are easily satisfied with increase in ambient temperature. While the temperature reaches a high enough level, ignition can occur and also the self-combustion or thermal induced explosion can do, even if laser power is very low. Therefore, it is of great importance to carefully control the working temperature of laser diode and the ambient temperature of powder system, and in the meanwhile, to install necessary insurance apparatus in order to ensure the normal and safe operation of the ignition system.

A scheme is discussed for probabilistic teleportation of a special type of two-atom pure state – an arbitrary superposition of symmetric two-atom Dicke states. The scheme follows the previous idea [S.B. Zheng, Phys. Rev. A 69 (2004) 064302], which is proposed for approximate and probabilistic teleportation of an atomic state through only a detection on the sender atom. In principle, the present scheme can achieve faithful teleportation by resorting to a very different model, which depicts the resonant interaction of a Λ -type three-level atom with a two-mode cavity field. The scheme can also be used for teleportation of an arbitrary superposition of symmetric multi-atom Dicke states.

Following a previous work [S.B. Zheng, Phys. Rev. A 69 (2004) 064302], we propose a scheme for probabilistic teleportation of arbitrary superposition of three states of an atom through only a single measurement. The scheme is also generalized for teleportation of arbitrary superposition of more states of an atom. The correlative experimental matter and decoherence are briefly discussed.

We describe a simple position sensitive γ-ray detector configuration and investigate its performance using a Monte Carlo simulation method. The detector is based on the characteristics of Compton scattering of high energy photons by electrons and the leakage of high energy photons from a rod shaped plastic scintillating fiber. Both energy and spatial resolution have been presented with energies in the range of 0.8–7 MeV, about 10% and a few centimeters, respectively. Cross-talk of the configuration has also been considered.

We propose a scheme for realizing the beam-splitter-type coupling between two cavity modes. In the scheme a collection of Λ -type three-level atoms are coupled with the two cavity modes with large detunings. Under certain conditions, the effective Hamiltonian for the cavity modes describes the frequency-up conversion, which is decoupled with the atomic system. The effective coupling strength increases with the number of the atoms, which allows the procedure to be completed in a reasonable time. The atoms have no probability of being populated in the excited states and thus the scheme is insensitive to atomic spontaneous emission.

We propose a scheme to realize strong squeezing for a cavity field with a single three-level atom. In the scheme the atom is sent through the cavity initially filled with a coherent field. The atom dispersively interacts with the cavity field, which is displaced by a microwave resource during the interaction. Then, a selective measurement on the atom collapses the field to a superposition of an even coherent state with a vacuum state, which exhibits strong squeezing. The scheme can also be generalized to the two-mode case.

A scheme is proposed for the implementation of phase-covariant anti-cloning in a single step. In the scheme N atoms dispersively interact with a cavity, with the coupling of the first atom different from that of the other atoms. Throughout the procedure the cavity is only virtually excited and thus the cavity decay is suppressed. The asymmetric nonresonant coupling can also be used to perform a one-step entangling operation.

We investigate the geometric phase for a quantum field driven by an external source and subjected to spontaneous decay from coupling to the reservoir. Starting from a coherent state, we analyze the effect of decoherence when the system undergoes a nonadiabatic cyclic evolution in phase space, and show that the lowest correction to the conventional geometric phase is quadratic in the decaying rate of the quantum field. This is in distinct contrast with the nonadiabatic geometric phase associated with the evolution of a spin system subjected to spontaneous decay, which contains the first-order correction term. We further show that the unconventional geometric phase is also robust to field decay.

We consider a hybrid three-mode optomechanical system where one mechanical oscillator couples to a second one via a Coulomb force and to a cavity mode via an optomechanical interaction. It is shown that stationary cavity-mechanical entanglement can be achieved by effectively cooling a Bogoliubov mode via the intermediate mode acting as an engineered reservoir. The entanglement can be maximized by carefully balancing the two confronting effects of the ratio of the effective couplings. Moreover, we analyze in detail the effects of the nonresonant terms. It is found that while the stability zone of the system shrinks in the parameter plane for large cooperativity, the maximal entanglement is not significantly reduced by the nonresonant terms. We numerically optimize the ratio in the stable region and obtain remarkably strong entanglement in the large cooperativity regime.

We propose a robust scheme for the implementation of two-qubit phase gates with a cavity QED system. After the gate operation the computational basis states are equally damped by the decoherence effect and thus the gate error is suppressed. The scheme is based on resonant atom–cavity interaction and thus the operation speed is high. During the atom–cavity interaction no external laser fields are required and thus the gate errors arising from external sources are suppressed.

A fiber probe-based positioning scan approach was established, whose precision can reach as high as 0.8 μm. And a set of modified microscope system was designed utilizing this approach, in which the scanning probe microscope (SPM) combined with an optical microscope was manipulated. The optical microscope and scanning probe can conveniently be switched through a switch panel. The observation period of samples can significantly be shortened. And more reliable images can be provided using this approach. Our design can effectively solve the inherent disadvantages of SPM technology, which makes SPM scan and image more reliably, conveniently, safely and rapidly.

A scheme is presented for generating entangled states for two atoms in a cavity. In the scheme two atoms simultaneously interact with a cavity mode with a small detuning. The operation time is very short and thus the decoherence can be effectively suppressed. Furthermore, the scheme is valid no matter whether the two atoms have the same coupling strengths or not. The scheme can be used to generate multi-atom W states without the requirement of individual addressing of the atoms, which is also experimentally important. The scheme can also be generalized to produce entangled states in an ion trap without individually addressing the ions.

A scalable scheme is presented for generating W-type entangled states for many atoms. The scheme only requires a single resonant interaction of the atoms with a cavity mode. The time required to complete the process does not increase with the number of atoms. The scheme can also be used to generate the W states for multiple trapped ions with a single interaction.

Summary The fiber micro-probe for near-field scanning optical microscope (NSOM) was fabricated using end-fixed laser-assisted melting and pulling method. The scanning electron microscope (SEM) observation showed that the fiber probes obtained by this method possessed small diameter of tip and large conic angle. The reproducibility came close to 70%. The effects of various fabrication parameters on probes were investigated, including laser power, pulling force, and the diameter of melting zone. The optimal processing conditions were derived based on the experiments and theoretical analysis. This research provides an alternative and advantageous method for fabrication of high-quality fiber probes.

We propose a scheme for the direct measurement of the Wigner function of a cavity field with no more than three photons around the origin. In the scheme the cavity field is first displaced by a small amount. Then a two-level atom is sent through the cavity. After a resonant interaction time the difference between the probabilities of the atom being in the ground and excited states is directly related to the Wigner function for the field state. The scheme can also be used for conditional generation of four-photon and six-photon states using two and three resonant atoms, respectively.

We describe a protocol for establishing multiparticle entanglement among particles belonging to distant users using nonmaximally entangled pairs in a communication network. Each of the users shares nonmaximally entangled pairs with the control centre. A series of controlled-not operations, measurements and a one-qubit rotation are performed at the control centre. Then the particles belonging to the users collapse to a maximally or nonmaximally entangled state. Any user may concentrate the nonmaximally entangled state into a maximally entangled state probabilistically.

Inspired by a recent paper [J. Phys. B47, 055502 (2014)10.1088/0953-4075/47/5/055502JPAPEH0953-4075], we propose a simplified scheme to generate and stabilize a Bell state of two qubits coupled to a resonator. In the scheme only one qubit is needed to be driven by external classical fields, and the entanglement dynamics is independent of the phases of these fields and insensitive to their amplitude fluctuations. This is a distinct advantage as compared with the previous ones that require each qubit to be addressed by well-controlled classical fields. Numerical simulation shows that the steady singlet state with high fidelity can be obtained with currently available techniques in circuit quantum electrodynamics.

We study the electromagnetically induced transparency (EIT) effect with two individually addressed four-level Rydberg atoms subjected to the interatomic van der Waals interaction. We derive an effectively atomic Raman transition model where two ladders of the usual Rydberg-EIT setting terminating at the same upper Rydberg level of long radiative lifetime are turned into a Rydberg-EIT lambda setup via two-photon transitions, leaving the middle levels of each ladder largely detuned from the coupling and probe laser beams. It can hence overcome the limits of applications for EIT with atoms of the ladder-type level configuration involving a strongly decaying intermediate state by inducing coherence between two ground states. By probing one of the atoms, we observe four doublets of absorption induced by the Autler-Townes (AT) splitting and the van der Waals interaction. In particular, we find that the location of the EIT center remains unchanged compared to the interatomic-interaction-free case, which demonstrated that the interference among the multiple transition channels is basically destructive. The EIT with controlled Rydberg-Rydberg interaction among few atoms provides a versatile tool for engineering the propagation dynamics of light., 5 pages, 4 figures

The geometric phase is of fundamental interest and plays an important role in quantum information processing. However, the definition and calculation of this phase for open systems remains a problem due to the lack of agreement on generalizations of the parallel transport condition to mixed state nonunity evolutions. Here we tackle this problem by associating the open system geometric phase with the parallel transport of the joint system-reservoir state. Our approach not only provides a way around the nonunitary evolution obstacle, but also sheds light on the relation between the geometric phase and the system-reservoir entanglement, which has not been investigated. Based on this approach, we calculate the geometric phase of different quantum systems subject to energy decay, showing that it is robust against decoherence, which is in distinct contrast with previous results., 6 pages + Supplementary information

We consider a coupled cavity optomechanical setup driven by a periodically modulated pump. We investigate the asymptotic behaviors of Heisenberg operator mean values and mechanical entanglement. It is shown that the system will acquire the same period of the modulation in the long time limit and, compared to the no modulation case, the mechanical entanglement can be significantly enhanced by periodic driving with more conservative system parameters and a higher permitted bath temperature. The mechanism of entanglement generation is discussed and an approximate optimal modulation frequency for small effective coupling is derived.

We propose a scheme for realizing quantum logic gates between any pair of ions confined in a linear trap with a pair of laser beams tuned to the carrier. The striking feature of the scheme is that the carrier excitation accompanying the spin-motion coupling does not affect the gate dynamics. As a consequence, the gate not only is much more insensitive to motional heating but also can operate at a higher speed compared to the previous schemes. The other important advantages are that the gate speed does not need to be inversely proportional to the number of ions in the chain, and the accompanying carrier drive results in dynamical decoupling, making the gate performance robust against dephasing noises. We show that for the same error sources the gate infidelity can be decreased by about ten times compared with previous schemes.

We propose a scheme for the determination of entangled states for atom-cavity systems and ion traps. Our scheme provides a means of directly measuring the Wigner function matrix, that contains all the information on a composite system. It is useful for studying quantum correlation between an electronic system and a harmonic oscillator and quantum information processing.

We propose a scheme to drive the centre-of-mass vibrational motion of two trapped ions to an arbitrary finite superposition of Fock states from the vacuum state. In order to generate a superposition of N Fock states we need N operations. The scheme does not require differential laser addressing of individual ions.

A scheme is proposed for generating motional pair coherent states of an ion in a two-dimensional anisotropic trap. In the scheme the ion is excited by two laser beams in the x-y plane. Under certain conditions, the system finally reaches the steady state given by the product of the ground electronic state with the motional pair coherent state. The scheme can be generalized to prepare pair cat states and two-mode SU(1,1) intelligent states in a two-dimensional anisotropic trap.

We propose a simple scheme for the generation of multi-atom Greenberger–Horne–Zeilinger (GHZ) states. Three appropriately prepared atoms are sent through a nonresonant cavity filled with a coherent field. The whole system evolves into an entangled state, in which two three-atom maximally entangled states are correlated with coherent field states separated by π in phase space. The field is then driven by a classical current and measured by an atom, which collapses the atomic system onto a GHZ state. The scheme can be easily generalized to prepare n -atom maximally entangled states.

We propose a scheme for generating superpositions of several coherent states of the motion of a trapped ion. In the scheme, an ion is trapped in a two-dimensional anisotropic harmonic potential and driven by several travelling-wave laser fields tuned to the ion transition. After a short interaction time, a conditional measurement of the electronic state may leave the vibrational motion in the X axis in a superposition of several coherent states along a straight line.

A scheme is proposed for testing the symmetrization postulate (SP) for photons in a cavity. In the scheme a two-level atom interacts dispersively with a cavity field initially in a q-deformed coherent state, and is manipulated by two classical fields. The probability that the atom does not flip from one state to the other characterizes the violation of the SP.

A scheme is proposed for preparing superpositions of many equidistant coherent states on a circle for the motion of an ion in an anisotropic two-dimensional trap, in which the ion is tightly bound in the y direction. In the scheme the ion is excited by one laser field in the x direction and then by two laser fields propagating along the x and y directions alternately many times. Then a state-selective measurement on the ion is made, which collapses the vibrational motion to a coherent state superposition.