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We report on a detailed characterization of a three-qubit linear optical quantum Toffoli gate. Our experiment utilizes correlated photon pairs generated in the process of spontaneous parametric down-conversion. Two qubits are encoded into polarization and spatial degrees of freedom of a signal photon, and the third qubit is represented by polarization of an idler photon. The linear optical Toffoli gate is implemented by interference of photons on a partially polarizing beam splitter inserted inside a Mach Zehnder interferometer formed by two calcite beam displacers. We have measured 4032 different two-photon coincidences, which allows us to estimate the fidelity of the gate to be 90%. Although these data are not tomographically complete, we show that they are sufficient for a reliable reconstruction of the quantum process matrix of the gate via the recently proposed maximum likelihood-maximum entropy estimation procedure. To probe the entangling capability of the gate, we have investigated generation of three-qubit GHZ states from fully and partially separable input states and we have performed a full tomography of the output states. We compare the reconstructed states with theoretical predictions obtained with the use of the estimated quantum process matrix and obtain a very good agreement. [ABSTRACT FROM AUTHOR]

The excitation of atomic clusters by intense infrared laser pulses leads to the creation of highly charged ions and to the emission of energetic photons. These phenomena, which follow from ionization processes occurring in the cluster, depend significantly on the population of ground states and excited states in the laserproduced nanoplasma. This makes it necessary to account for collisional excitation and deexcitation processes. We investigate the interaction of femtosecond laser pulses with argon clusters by means of a nanoplasma model. Considering laser excitation with single and double pulses, we analyze the role of excitation and deexcitation processes in detail and calculate the yield of highly charged ions and of energetic photons in different wavelength regimes. [ABSTRACT FROM AUTHOR]

The implementation of polarization-based quantum communication is limited by signal loss and decoherence caused by the birefringence of a single-mode fiber. We investigate the Knill dynamical decoupling scheme, implemented using half-wave plates, to minimize decoherence and show that a fidelity greater than 99% can be achieved in the absence of rotation error and a fidelity greater than 96% can be achieved in the presence of rotation error. Such a scheme can be used to preserve any quantum state with high fidelity and has potential application for constructing all optical quantum delay lines, quantum memory, and quantum repeaters. [ABSTRACT FROM AUTHOR]

We present the dipole induced transparency (DIT) of a diamond nitrogen-vacancy center embedded in a photonic crystal cavity coupled to two waveguides, and it is obvious with the robust and flexible reflectance and transmittance difference of circularly polarized lights between the uncoupled and the coupled cavities even in the bad cavity regime (the Purcell regime). With this DIT, we propose two universal hyperparallel hybrid photonic quantum logic gates, including a hybrid hyper-controlled-NOT gate and a hybrid hyper-Toffoli gate, on photon systems in both the polarization and the spatial-mode degrees of freedom (DOFs), which are equal to two identical quantum logic gates operating simultaneously on the systems in one DOF. They can be used to perform more quantum operations with less resources in the quantum information protocols with multiqubit systems in several DOFs, which may depress the resources consumed and the photonic dissipation. Moreover, they are more robust against asymmetric environment noise in the weak-coupling regime, compared with the integration of two cascaded quantum logic gates in one DOF. [ABSTRACT FROM AUTHOR]

Detecting and quantifying quantum entanglement of a given unknown state poses problems that are fundamentally important for quantum information processing. Surprisingly, no direct (i.e., without quantum tomography) universal experimental implementation of a necessary and sufficient test of entanglement has been designed even for a general two-qubit state. Here we propose an experimental method for detecting a collective universal witness, which is a necessary and sufficient test of two-photon polarization entanglement. It allows us to detect entanglement for any two-qubit mixed state and to establish tight upper and lower bounds on its amount. A different element of this method is the sequential character of its main components, which allows us to obtain relatively complicated information about quantum correlations with the help of simple linear-optical elements. As such, this proposal realizes a universal two-qubit entanglement test within the present state of the art of quantum optics. We show the optimality of our setup with respect to the minimal number of measured quantities. [ABSTRACT FROM AUTHOR]

A scheme for the detection of photons generated by vacuum mixing processes is proposed to observe the quantum electrodynamic photon-photon interaction. The strategy consists in the utilization of a high numerical aperture parabolic mirror that tightly focuses two copropagating laser beams with different frequencies. This produces a very-high-intensity region in the vicinity of the focus, where the photon-photon nonlinear interaction can then induce new electromagnetic radiation by wave-mixing processes. These processes are investigated theoretically. The field at the focus is obtained from the Stratton-Chu vector diffraction theory, which can accommodate any configuration of an incoming laser beam. The number of photons generated is evaluated for an incident radially polarized beam. It is demonstrated that using this field configuration, vacuum mixing processes could be detected with envisaged laser technologies. [ABSTRACT FROM AUTHOR]

We report a nonlocal interferometer capable of detecting entanglement and identifying Bell states statistically. This is possible due to the interferometer's unique correlation dependence on the antidiagonal elements of the density matrix, which have distinct bounds for separable states and unique values for the four Bell states. The interferometer consists of two spatially separated balanced Mach-Zehnder or Sagnac interferometers that share a polarization-entangled source. Correlations between these interferometers exhibit nonlocal interference, while single-photon interference is suppressed. This interferometer also allows for a unique version of the Clauser-Horne-Shimony-Holt-Bell test where the local reality is the photon polarization. We present the relevant theory and experimental results. [ABSTRACT FROM AUTHOR]

To probe the nonlinear effects of photon-photon interaction in quantum electrodynamics, we study the generation of circular polarized photons by the collision of two linearly polarized laser beams. In the framework of the Euler-Heisenberg effective Lagrangian and the quantum Boltzmann equation for the time evolution of the density matrix of polarization, we calculate the intensity of circular polarization generated by the collision of two linearly polarized laser beams and estimate the rate of generation that is proportional to a². As a result, we show that the generated circular polarization can be experimentally measured by two head-on colliding optical laser beams of a cross-sectional area ~0.01 cm2 and a laser pulse energy of ≲mJ, which are currently available in laboratories. Our study presents a valuable supplement to other theoretical and experimental frameworks for the study and measurment of the nonlinear effects of photon-photon interaction in quantum electrodynamics. [ABSTRACT FROM AUTHOR]

We report the efficient creation and detection of hybrid entanglement between one photon's polarization and another photon's complex transverse polarization pattern including various polarization singularities. The polarization measurement of the first photon triggers a polarization-sensitive imaging of its partner photon, the vector photon, using a single-photon-sensitive camera. Thereby, the vector photon's complex polarization pattern is reconstructed tomographically dependent on the type of polarization measurement performed on its partner. To evaluate the quality of the observed patterns, we introduce a fidelity-like measure which compares the reconstructed polarization with the theoretically expected one at every transverse spatial position. We find that the measured polarization patterns and the theory overlap by more than 90%. Moreover, we visualize the varying strengths of polarization entanglement for different transverse regions and demonstrate an interesting phenomenon: Each vector photon can be both entangled and not entangled in polarization with its partner photon. We give an intuitive, information-theoretical explanation for our results. Our results pave the way to study quantum properties of the rich field of such complex light modes with the potential to improve various applications in quantum informational tasks [ABSTRACT FROM AUTHOR]

We report polarimetric measurements of geometric phases that are generated by evolving polarized photons along nongeodesic trajectories on the Poincaré sphere. The core of our polarimetric array consists of seven wave plates that are traversed by a single-photon beam. With this array, any SU(2) transformation can be realized. By exploiting the gauge invariance of geometric phases under U(1) local transformations, we nullify the dynamical contribution to the total phase, thereby making the latter coincide with the geometric phase. We demonstrate our arrangement to be insensitive to various sources of noise entering it. This makes the single-beam, polarimetric array a promising, versatile tool for testing robustness of geometric phases against noise. [ABSTRACT FROM AUTHOR]

We show that a Bell inequality test using an optical hybrid state between a polarized single photon and a coherent field can be highly robust against detection inefficiency. The Bell violation occurs until the efficiency becomes as low as 67% even though its degree becomes small as the detection efficiency degrades. We consider on/off and photon number parity measurements, respectively, for the Bell test and they result in similar conditions. If the detection efficiency is higher than 98.68%, parity measurements give larger Bell violations close to Cirel'son's bound, while on/off measurements give larger but moderate violations for realistic values of detector efficiency. Experimental realization of our proposal seems feasible in the near future for the implementation of a loophole-free Bell inequality test. [ABSTRACT FROM AUTHOR]

We propose a scheme to construct the efficient universal quantum circuit for qubit systems with the assistance of possibly available auxiliary Hilbert spaces. An elementary two-ququart gate, termed the controlled-double-NOT gate, is proposed first in ququart (four-level) systems, and its physical implementation is illustrated in the four-dimensional Hilbert spaces built by the path and polarization states of photons. Then an efficient universal quantum circuit for ququart systems is constructed using the gate and the quantum Shannon decomposition method. By introducing auxiliary two-dimensional Hilbert spaces, the universal quantum circuit for qubit systems is finally achieved using the result obtained in ququart systems with the lowest complexity. [ABSTRACT FROM AUTHOR]

We propose a scheme to investigate the time scale of wave-function collapse by using polarization-entangled photon pairs. The setup is similar to those employed to study quantum correlations, but in the present case, synchronization is essential at all stages. We find that it is possible to discriminate between the scenarios of instantaneous collapse and finite-time reduction via a large number of double measurements of polarization. The quantities to be recorded present distinct behaviors in each scenario, the deviations being small but distinguishable from pure statistical fluctuations. The connection between the presented formalism and the theory of weak measurements is discussed as well as the possible consequences for experimental tests of nonlocality. [ABSTRACT FROM AUTHOR]

The question of the representation of quantum stationary partially polarized waves as random superpositions of different polarization ellipses is addressed. To this end, the Bohmian formulation of quantum mechanics is considered and extended to quantum optical polarization. As is shown, this approach properly combines definite time-evolving trajectories with rigorous stationary quantum distributions via the topology displayed by the associated phase field. [ABSTRACT FROM AUTHOR]

An electromagnetic pair-creation cascade seeded by an électron or a photon in an intense plane wave interacts in a complicated way with the external field. Many simulations neglect the vector nature of photons by including, their interaction using unpolarized cross sections. After deriving rates for the tree-level processes of nonlinear Compton scattering and pair creation with an arbitrary linearly polarized photon in a constant crossed field, we present results of numerical simulations that include the photon's vector nature. The simulations of seed electrons in a rotating electric field of optical frequency on the one hand support the approximation of using unpolarized cross sections for tree-level processes, which predicts the same number of created particles when using polarized cross section to within around 5%. On the other hand, these simulations show that when the polarization of the photon can be influenced by its environment, the asymmetry in the polarization distribution could be used to significantly increase the rates of each process. [ABSTRACT FROM AUTHOR]

Based on the theoretical analysis of the radiative recombination of heavy hydrogen-like ions with unpolarized electrons, a scheme is proposed for observing atomic parity nonconservation (PNC). The scheme employs the sensitivity of the polarization properties of recombination photons on the PNC-induced mixing of opposite-parity ionic levels. For the electron capture into the 1s2p³P0 state of helium-like ions, in particular, the PNC leads to a rotation of the photon linear polarization on the angle, directly proportional to the 1s2p³P0-1s2s ¹S0 mixing parameter. Owing to the recent advances in the development of x-ray Polarimeters, the observation of such a rotation angle and, hence, the corresponding parity mixing is likely to become feasible in the future. [ABSTRACT FROM AUTHOR]

In contrast to recent studies [Rabl, Phys. Rev. Lett. 107, 063601 (2011); Nunnenkamp et al., Phys. Rev. Lett. 107, 063602 (2011)] on photon blockade that prevents subsequent photons from resonantly entering the cavity in optomechanical systems, we study the photon-induced tunneling that increases the probability of admitting subsequent photons in those systems. In particular, we analytically and numerically show how two-or three-photon tunneling can occur by avoiding single-photon blockade. Our study provides another way on photon control using a single mechanical resonator in optomechanical systems. [ABSTRACT FROM AUTHOR]

The classical definition of degree of polarization (DOP) is expressed in the quantum domain by replacing intensities through quantum mechanical average values of relevant number operators and is viewed as the first generalization of intensity. This definition assigns inaccurately the unpolarized status to some typical optical fields, e.g., amplitude-coherent phase-randomized and hidden-polarized light, which are not truly unpolarized light. The apparent paradoxical trait is circumvented by proposing a new definition of DOP in quantum optics through the second generalization of intensity. The correspondence of a new DOP to the usual DOP in quantum optics is established. It is seen that the two definitions disagree significantly for intense optical fields but coincide for weak light (thermal light) or for optical fields in which occupancy of photons in the orthogonal mode is very feeble. Our proposed definition of DOP, similar to other proposals in literature, reveals an interesting feature that states of polarization of optical quantum fields depend upon the average photons (intensity) present therein. [ABSTRACT FROM AUTHOR]

Here we propose a feasible experimental setup for implementing optimal probabilistic cloning of two arbitrary nonorthogonal qubit states. This proposal is based on linear optics together with a pair of entangled twin photons generated via spontaneous parametric down-conversion. The states to be cloned are encoded in the polarization degree of freedom of one of the photons while two perfect clones are generated and encoded in the polarization and the spatial degree of freedom of the resting photon. Therefore, the clones are produced nonlocally. The proposed implementation requires the application of recovery unitary operations onto the photon hosting the clones which are conditional on measurements performed on the other photon in a process akin to quantum teleportation. [ABSTRACT FROM AUTHOR]

We report an optical one-way quantum computing experiment with stationary quantum memory involved. First we create a hybrid four-qubit cluster state with two qubits propagating as photons and the other two stationary and stored in a laser-cooled atomic-ensemble quantum memory, and characterize it with entanglement witnesses and quantum state tomography. Then, by making use of this cluster state and fast operations of electro-optic modulators, we realize memory-assisted feedforward operations and demonstrate deterministic single-qubit rotation as an example. [ABSTRACT FROM AUTHOR]

We suggest and demonstrate a scheme for coherent nonlocal compensation of pure phase objects based on two-photon polarization and momentum entangled states. The insertion of a single phase object on one of the beams reduces the purity of the overall detected state and the amount of shared entanglement, whereas the original entanglement can be retrieved by adding a suitable phase object on the other beam. In our setup polarization and momentum entangled states are generated by spontaneous parametric downconversion and then purified using a programmable spatial light modulator, which may be also used to impose arbitrary space-dependent phase functions on the beams. [ABSTRACT FROM AUTHOR]

Generating entanglement by simply cooling a system into a stationary state which is highly entangled has many advantages. Schemes based on this idea are robust against parameter fluctuations, tolerate relatively large spontaneous decay rates, and achieve high fidelities independent of their initial state. A possible implementation of this idea in atom-cavity systems has recently been proposed by Kastoryano et al., [ Kastoryano et al. Phys. Rev. Lett. 106 090502 (2011)]. Here we propose an improved entanglement cooling scheme for two atoms inside an optical cavity which achieves higher fidelities for comparable single-atom cooperativity parameters C. For example, we predict fidelities above 90% even for C as low as 20 without having to detect photons. [ABSTRACT FROM AUTHOR]

We put the pure-state decomposition mathematical property of a mixed state to a physical test. We present a protocol for preparing two known nonorthogonal quantum states with well-defined a priori probabilities. Hence we characterize all the possible decompositions of a rank-two mixed state by means of the complex overlap between the two involved states. The physical test proposes a scheme for quantum state recognition of one of the two linearly independent states that arise from the decomposition. We find that the two states associated with the balanced pure-state decomposition have the smaller overlap modulus and therefore the smallest probability of being discriminated conclusively, while in the nonconclusive process they have the highest probability of having an error. In addition, we design an experimental scheme that allows discriminating conclusively and optimally two nonorthogonal states prepared with different a priori probabilities. Thus we propose a physical implementation for this linearly independent pure-state decomposition and state discrimination test by using twin photons generated in the process of spontaneous parametric down-conversion. The information state is encoded in a one-photon polarization state, whereas the second single photon is used for heralded detection. [ABSTRACT FROM AUTHOR]

An on-demand single-photon source is a fundamental building block in quantum science and technology. We experimentally demonstrate the proof of concept for a scheme to generate on-demand single photons via actively multiplexing several heralded photons probabilistically produced from pulsed spontaneous parametric down- conversions (SPDCs). By utilizing a four-photon-pair source, an active feed-forward technique, and an ultrafast single-photon router, we show a fourfold enhancement of the output photon rate. Simultaneously, we maintain the quality of the output single-photon states, confirmed by correlation measurements. We also experimentally verify, via Hong-Ou-Mandel interference, that the router does not affect the indistinguishability of the single photons. Furthermore, we give numerical simulations, which indicate that photons based on multiplexing of four SPDC sources can outperform the heralding based on highly advanced photon-number-resolving detectors. Our results show a route for on-demand single-photon generation and the practical realization of scalable linear optical quantum-information processing. [ABSTRACT FROM AUTHOR]

We study the deterministic generation of single guided-mode photons from an atom in the vicinity of a nanofiber with two fiber-Bragg-grating (FBG) mirrors. The technique is based on a cavity-enhanced Raman scattering process involving an adiabatic passage. We take into account the scattering of the pump field from the fiber, the multilevel structure of the atom, and the surface-induced van der Waals potential in describing the photon generation process. We find that, due to the confinement of the cavity field in the transverse plane of the fiber and in the space between the FBG mirrors, the probability of the generation of a single guided-mode photon can be close to unity even when the finesse of the nanofiber cavity is moderate. We show the possibilities of saturation and power broadening in the behavior of the number of photons emitted into the nanofiber. [ABSTRACT FROM AUTHOR]

We systematically study the dynamics of a one-dimensional degenerate Fermi gas in an optical-lattice potential coupled to a single-mode cavity field. We derive an effective model to study the nonperturbative effect caused by the cavity field. Our numerical results show that due to the addition of the optical-lattice potential, the system undergoes second-order transition to a bistable density-wave steady state, where the atoms form a density wave and the cavity field is bistable. In addition, the coherent oscillating behavior of the cavity photon number can be observed. We also present a feasible experimental protocol to realize these phenomena, which may be beneficial for future quantum-information applications. [ABSTRACT FROM AUTHOR]

We investigate the formation of a heteronuclear tetramer A3B by an Efimov-resonance-assisted stimulated Raman adiabatic passage scheme, which is considered a viable means of creating the homonuclear tetramer A4 [H. Jing and Y. Jiang, Phys. Rev. A 77, 065601 (2008)]. The atom-molecule dark-state solution for the system is derived, and the adiabatic conversion from atoms to heteronuclear tetramers is studied via the concept of adiabatic fidelity. In addition, the effects of external field parameters (including Rabi pulse strength, width, and single photon detuning) on the conversion are discussed. [ABSTRACT FROM AUTHOR]

Cross sections for single photoionization of Fe3+ Fe5+, and Fe7+ ions were measured at spectral resolutions of 0.04, 0.15, and 0.13 eV, respectively, by merging mass- and charge-selected ion beams with a beam of monochromatized synchrotron undulator radiation. The measurements span photon energy ranges beginning at the ionization thresholds and extending several tens of electron volts to include the most important resonant contributions due to 3p-nd transitions to autoionizing states. The photoion yield spectra are characterized by narrow resonances and also broad features in Fe3+ and Fe5+ that are believed to result from unresolved fast super- Coster-Kronig transitions following 3p-3d excitation. Absolute photoionization cross-section measurements were also performed using ion beams containing undetermined fractions of ions in their ground and metastable states. A Rydberg series attributed to 3p-nd transitions from the ²G1 metastablestatc in Fe3+ was identified. The data are compared with recently published measurements on Fe3+ and Fe5+ using a similar technique at lower spectral resolution. [ABSTRACT FROM AUTHOR]

We demonstrate that high-order harmonic generation (HHG) with both high cutoff frequency and high conversion efficiency can be realized by using a Rydberg atom in a few-cycle laser pulse. This is because a Rydberg state has a large electron orbital radius and small binding energy; therefore an electron in the Rydberg state can be ionized easily and accelerated directly toward the core under the interaction of a few-cycle laser pulse, leading to emission of harmonic photons. In this case, the tunneling process of the electron is not involved and, hence, the conversion efficiency and the cutoff frequency of harmonic generation can be higher than that predicted by the conventional three-step model. [ABSTRACT FROM AUTHOR]

Bound entangled states are the exotic objects in the entangled world. They require entanglement to create them, but once they are formed, it is not possible to locally distill any free entanglement from them. It is only until recently that a few bound entangled states were realized in the laboratory. Motivated by these experiments, we propose schemes for creating various classes of bound entangled states with photon polarization. These include Acín-Bruß-Lewenstein-Sanpara states, Dür's states, Lee-Lee-Kim bound entangled states, and an unextendible-product-basis bound entangled state. [ABSTRACT FROM AUTHOR]

We experimentally study the spatial properties of the field generated by spontaneous parametric down-conversion (SPDC) when the pump laser beam is strongly focused in the nonlinear crystal. Special attention is paid to classical intensity measurements with a CCD camera. We introduce the concept of a classical equivalent source that replicates all the coherence properties of SPDC light and explains all our experimental results. We show that, in contrast with experiments with a well-collimated pump, here both the phase-matching conditions and the position of the focusing plane determine the measured intensity profiles in the image plane of the crystal. The transition from the near-field regime to the far field is investigated. Measurements of two-photon correlations under strong focusing are also presented and the special features thereof are discussed. [ABSTRACT FROM AUTHOR]

We present nonlinear dynamical features of two-photon double-cavity optical bistability exhibited by a three-level ladder system in the mean-field limit at low input light levels. The system exhibits a hump-like feature in the lower branch of the bistable response, wherein a region of instability develops. The system displays a range of dynamical features varying from normal stable switching to periodic self-pulsing and chaos. The inclusion of two competing cooperative atom-field couplings leads to such rich, nonlinear dynamical behavior. We provide a domain map that clearly delineates the various regions of stability, as well as bifurcation diagrams with associated supporting evidence that identifies the period-doubling route to chaos. [ABSTRACT FROM AUTHOR]

In 2003, Leggett introduced his model of crypto-nonlocality based on considerations on the reality of photon polarization [A. J. Leggett, Found. Phys. 33, 1469 (2003)]. In this paper, we prove that, contrary to hints in subsequent literature, crypto-nonlocality does not follow naturally from the postulate that polarization is a realistic variable. More explicitly, consider physical theories where (a) faster-than-light communication is impossible, (b) all physical photon states have a definite polarization, and (c) given two separate photons, if we measure one of them and post-select on the result, the measurement statistics of the remaining system correspond to a photon state. We show that the outcomes of any two-photon polarization experiment in these theories must follow the statistics generated by measuring a separable two-qubit quantum state. Consequently, in such experiments any instance of entanglement detection--and not necessarily a Leggett inequality violation--can be regarded as a refutation of this class of theories. [ABSTRACT FROM AUTHOR]

We have performed an experiment demonstrating that loop state-preparation-and-measurement tomography [Jackson and van Enk, Phys. Rev. A 92, 042312 (2015)] is capable of detecting correlated errors between the preparation and the measurement of a quantum system. Specifically, we have prepared pure and mixed states of single qubits encoded in the polarization of heralded individual photons. By performing measurements using multiple state preparations and multiple measurement device settings we are able to detect if there are any correlated errors between them, and we are also able to determine which state preparations are correlated with which measurements. This is accomplished by going around a "loop" in parameter space, which allows us to check for self-consistency. No assumptions are made concerning either the state preparations or the measurements, other than that the dimensions of the states and the positive-operator-valued measures (POVMs) describing the detector are known. In cases where no correlations are found we are able to perform quantum state tomography of the polarization qubits by using knowledge of the detector POVMs, or quantum detector tomography by using knowledge of the state preparations. Note, however, that the detection of correlated errors does not require estimating any state or measurement parameters. [ABSTRACT FROM AUTHOR]

Relying on weak cross-Kerr nonlinearities, we propose a nearly deterministic generation scheme of the three-photon polarization-entangled perfect W state which can be applied to the perfect teleportation of an unknown single-photon state and has robust entanglement against the loss of one photon of them. Three photons entangle together by virtue of the bus function of the coherent state serving as the intermediate among them. In the scheme, three processes are executed successively and two kinds of modules are inserted into the circuit, where the homodyne measurement and the photon number measurement are aptly performed. By means of classical feedforward techniques, single-photon unitary transformation operations are performed on the corresponding photons based on the obtained measurement outcomes, by which the generation efficiency of the perfect W state aims to nearly unity. Moreover, some currently available optical elements are applied in the generation process, which offer facilities for the practical implementation. [ABSTRACT FROM AUTHOR]

We propose a heralded quantum repeater protocol based on the general interface between the circularly polarized photon and the quantum dot embedded in a double-sided optical microcavity. Our effective time-bin encoding on photons results in the deterministic faithful entanglement distribution with one optical fiber for the transmission of each photon in our protocol, not two or more. Our efficient parity-check detector implemented with only one input-output process of a single photon as a result of cavity quantum electrodynamics makes the entanglement channel extension and entanglement purification in quantum repeater far more efficient than others, and it has the potential application in fault-tolerant quantum computation as well. Meanwhile, the deviation from a collective-noise channel leads to some phase-flip errors on the nonlocal electron spins shared by the parties and these errors can be depressed by our simplified entanglement purification process. Finally, we discuss the performance of our proposal, concluding that it is feasible with current technology. [ABSTRACT FROM AUTHOR]