Scattering of entangled two-photon states.
Schotland, John C; Cazé, A; Norris, Theodore B
2016-02-01
We consider the scattering of entangled two-photon states from collections of small particles. We also study the related Mie problem of scattering from a sphere. In both cases, we calculate the entropy of entanglement and investigate the influence of the entanglement of the incident field on the entanglement of the scattered field. PMID:26907393
Entangled photon-added coherent states
NASA Astrophysics Data System (ADS)
Domínguez-Serna, Francisco A.; Mendieta-Jimenez, Francisco J.; Rojas, Fernando
2016-08-01
We study the degree of entanglement of arbitrary superpositions of m, n photon-added coherent states (PACS) {|{ψ }rangle } ∝ u {|{{α },m}rangle }{|{{β },n }rangle }+ v {|{{β },n}rangle }{|{{α },m}rangle } using the concurrence and obtain the general conditions for maximal entanglement. We show that photon addition process can be identified as an entanglement enhancer operation for superpositions of coherent states (SCS). Specifically for the known bipartite positive SCS: {|{ψ }rangle } ∝ {|{α }rangle }_a{|{-α }rangle }_b + {|{-α }rangle }_a{|{α }rangle }_b whose entanglement tends to zero for α → 0, can be maximal if al least one photon is added in a subsystem. A full family of maximally entangled PACS is also presented. We also analyzed the decoherence effects in the entangled PACS induced by a simple depolarizing channel . We find that robustness against depolarization is increased by adding photons to the coherent states of the superposition. We obtain the dependence of the critical depolarization p_{ {crit}} for null entanglement as a function of m,n, α and β.
Entangled photon-added coherent states
NASA Astrophysics Data System (ADS)
Domínguez-Serna, Francisco A.; Mendieta-Jimenez, Francisco J.; Rojas, Fernando
2016-05-01
We study the degree of entanglement of arbitrary superpositions of m, n photon-added coherent states (PACS) {|{ψ }rangle } ∝ u {|{{α },m}rangle }{|{{β },n }rangle }+ v {|{{β },n}rangle }{|{{α },m}rangle } using the concurrence and obtain the general conditions for maximal entanglement. We show that photon addition process can be identified as an entanglement enhancer operation for superpositions of coherent states (SCS). Specifically for the known bipartite positive SCS: {|{ψ }rangle } ∝ {|{α }rangle }_a{|{-α }rangle }_b + {|{-α }rangle }_a{|{α }rangle }_b whose entanglement tends to zero for α → 0 , can be maximal if al least one photon is added in a subsystem. A full family of maximally entangled PACS is also presented. We also analyzed the decoherence effects in the entangled PACS induced by a simple depolarizing channel . We find that robustness against depolarization is increased by adding photons to the coherent states of the superposition. We obtain the dependence of the critical depolarization p_{crit} for null entanglement as a function of m,n, α and β.
Operational multipartite entanglement classes for symmetric photonic qubit states
Kiesel, N.; Wieczorek, W.; Weinfurter, H.; Krins, S.; Bastin, T.; Solano, E.
2010-03-15
We present experimental schemes that allow us to study the entanglement classes of all symmetric states in multiqubit photonic systems. We compare the efficiency of the proposed schemes and highlight the relation between the entanglement properties of symmetric Dicke states and a recently proposed entanglement scheme for atoms. In analogy to the latter, we obtain a one-to-one correspondence between well-defined sets of experimental parameters and multiqubit entanglement classes inside the symmetric subspace of the photonic system.
Polarization and entanglement of photon-added coherent states
NASA Astrophysics Data System (ADS)
Nogueira, K.; Silva, J. B. R.; Gonçalves, J. R.; Vasconcelos, H. M.
2013-04-01
Polarization of light has been used extensively in quantum information processing, and quantum entanglement is essential to many areas of research, including quantum computing. Here we investigate the degree of polarization and the entanglement of a family of quantum states known as photon-added entangled coherent states. Such states could serve as means of entanglement distribution and quantum key distribution. Using the quantum Stokes parameters and the Q function, we demonstrate that, in general, the degree of polarization of two two-mode photon-added coherent states increases significantly with the number of added photons. And using the concurrence, we show that the amount of entanglement in this kind of superposition presents a behavior that is dependent on whether or not the number of added photons in each mode is the same.
Interference and complementarity for two-photon hybrid entangled states
Nogueira, W. A. T.; Santibanez, M.; Delgado, A.; Saavedra, C.; Neves, L.; Lima, G.; Padua, S.
2010-10-15
In this work we generate two-photon hybrid entangled states (HESs), where the polarization of one photon is entangled with the transverse spatial degree of freedom of the second photon. The photon pair is created by parametric down-conversion in a polarization-entangled state. A birefringent double-slit couples the polarization and spatial degrees of freedom of these photons, and finally, suitable spatial and polarization projections generate the HES. We investigate some interesting aspects of the two-photon hybrid interference and present this study in the context of the complementarity relation that exists between the visibility of the one-photon and that of the two-photon interference patterns.
NASA Astrophysics Data System (ADS)
Wang, Meiyu; Yan, Fengli; Xu, Jingzhou
2016-08-01
We show how to concentrate an arbitrary four-photon polarization entangled state into a maximally entangled state based on some quantum nondemolition detectors. The entanglement concentration protocol (ECP) resorts to an ancillary single-photon resource and the conventional projection measurement on photons to assist the concentration, which makes it more economical. Our ECP involves weak cross-Kerr nonlinearities, X homodyne measurement and basic linear-optical elements, which make it feasible in the current experimental technology. Moreover, the ECP considers cyclic utilization to enhance a higher success probability. Thus, our scheme is meaningful in practical applications in quantum communication.
NASA Astrophysics Data System (ADS)
A, Karimi; M, K. Tavassoly
2016-04-01
In this paper, after a brief review on the entangled squeezed states, we produce a new class of the continuous-variable-type entangled states, namely, deformed photon-added entangled squeezed states. These states are obtained via the iterated action of the f-deformed creation operator A = f (n)a † on the entangled squeezed states. In the continuation, by studying the criteria such as the degree of entanglement, quantum polarization as well as sub-Poissonian photon statistics, the two-mode correlation function, one-mode and two-mode squeezing, we investigate the nonclassical behaviors of the introduced states in detail by choosing a particular f-deformation function. It is revealed that the above-mentioned physical properties can be affected and so may be tuned by justifying the excitation number, after choosing a nonlinearity function. Finally, to generate the introduced states, we propose a theoretical scheme using the nonlinear Jaynes–Cummings model.
Experimental perfect state transfer of an entangled photonic qubit
NASA Astrophysics Data System (ADS)
Chapman, Robert J.; Santandrea, Matteo; Huang, Zixin; Corrielli, Giacomo; Crespi, Andrea; Yung, Man-Hong; Osellame, Roberto; Peruzzo, Alberto
2016-04-01
The transfer of data is a fundamental task in information systems. Microprocessors contain dedicated data buses that transmit bits across different locations and implement sophisticated routing protocols. Transferring quantum information with high fidelity is a challenging task, due to the intrinsic fragility of quantum states. Here we report on the implementation of the perfect state transfer protocol applied to a photonic qubit entangled with another qubit at a different location. On a single device we perform three routing procedures on entangled states, preserving the encoded quantum state with an average fidelity of 97.1%, measuring in the coincidence basis. Our protocol extends the regular perfect state transfer by maintaining quantum information encoded in the polarization state of the photonic qubit. Our results demonstrate the key principle of perfect state transfer, opening a route towards data transfer for quantum computing systems.
Experimental perfect state transfer of an entangled photonic qubit.
Chapman, Robert J; Santandrea, Matteo; Huang, Zixin; Corrielli, Giacomo; Crespi, Andrea; Yung, Man-Hong; Osellame, Roberto; Peruzzo, Alberto
2016-01-01
The transfer of data is a fundamental task in information systems. Microprocessors contain dedicated data buses that transmit bits across different locations and implement sophisticated routing protocols. Transferring quantum information with high fidelity is a challenging task, due to the intrinsic fragility of quantum states. Here we report on the implementation of the perfect state transfer protocol applied to a photonic qubit entangled with another qubit at a different location. On a single device we perform three routing procedures on entangled states, preserving the encoded quantum state with an average fidelity of 97.1%, measuring in the coincidence basis. Our protocol extends the regular perfect state transfer by maintaining quantum information encoded in the polarization state of the photonic qubit. Our results demonstrate the key principle of perfect state transfer, opening a route towards data transfer for quantum computing systems. PMID:27088483
Experimental perfect state transfer of an entangled photonic qubit
Chapman, Robert J.; Santandrea, Matteo; Huang, Zixin; Corrielli, Giacomo; Crespi, Andrea; Yung, Man-Hong; Osellame, Roberto; Peruzzo, Alberto
2016-01-01
The transfer of data is a fundamental task in information systems. Microprocessors contain dedicated data buses that transmit bits across different locations and implement sophisticated routing protocols. Transferring quantum information with high fidelity is a challenging task, due to the intrinsic fragility of quantum states. Here we report on the implementation of the perfect state transfer protocol applied to a photonic qubit entangled with another qubit at a different location. On a single device we perform three routing procedures on entangled states, preserving the encoded quantum state with an average fidelity of 97.1%, measuring in the coincidence basis. Our protocol extends the regular perfect state transfer by maintaining quantum information encoded in the polarization state of the photonic qubit. Our results demonstrate the key principle of perfect state transfer, opening a route towards data transfer for quantum computing systems. PMID:27088483
Simultaneous generation of two spin-wave-photon entangled states in an atomic ensemble
NASA Astrophysics Data System (ADS)
Wu, Yuelong; Tian, Long; Xu, Zhongxiao; Ge, Wei; Chen, Lirong; Li, Shujing; Yuan, Haoxiang; Wen, Yafei; Wang, Hai; Xie, Changde; Peng, Kunchi
2016-05-01
Spontaneous Raman scattering (SRS) in atomic ensembles provides a promising method to generate spin-wave-photon entangled states. In the past experiments, a spin-wave-photon entangled state was produced via SRS from an atomic ensemble. Here, we report a scheme of simultaneously generating two spin-wave-photon (atom-photon) entangled states in a cold Rb ensemble via SRS. Based on joint Bell-state measurements on the two photons coming from the two atom-photon entangled sources, respectively, we projected the two stored spin waves into a Bell state and then mapped the quantum memory into a polarization-entangled photon pair. Such a polarization-entangled photon pair can be released on demand and thus the presented scheme has potential application in the preparation of large-size photonic entangled states.
Entangled mixed-state generation by twin-photon scattering
Puentes, G.; Aiello, A.; Woerdman, J. P.; Voigt, D.
2007-03-15
We report experimental results on mixed-state generation by multiple scattering of polarization-entangled photon pairs created from parametric down-conversion. By using a large variety of scattering optical systems we have experimentally obtained entangled mixed states that lie upon and below the Werner curve in the linear entropy-tangle plane. We have also introduced a simple phenomenological model built on the analogy between classical polarization optics and quantum maps. Theoretical predictions from such a model are in full agreement with our experimental findings.
Photon-number entangled states generated in Kerr media with optical parametric pumping
Kowalewska-Kudlaszyk, A.; Leonski, W.; Perina, Jan Jr.
2011-05-15
Two nonlinear Kerr oscillators mutually coupled by parametric pumping are studied as a source of states entangled in photon numbers. Temporal evolution of entanglement quantified by negativity shows the effects of sudden death and birth of entanglement. Entanglement is preserved even in asymptotic states under certain conditions. The role of reservoirs at finite temperature in entanglement evolution is elucidated. Relation between generation of entangled states and violation of Cauchy-Schwartz inequality for oscillator intensities is found.
NASA Astrophysics Data System (ADS)
Lan, Zhou; Yu-Bo, Sheng
2016-02-01
We put forward two efficient entanglement concentration protocols (ECPs) for arbitrary less-entangled NOON state. Both ECPs only require one pair of less-entangled NOON state and an auxiliary photon. In the first ECP, the auxiliary photon is shared by two parties, while in the second ECP, the auxiliary photon is only possessed by one party, which can increase the practical success probability by avoiding the transmission loss and simplify the operations. Moreover, both ECPs can be used repeatedly to get a high success probability. Based on the above features, our two ECPs, especially the second one, may be useful in the quantum information processing. Project supported by the National Natural Science Foundation of China (Grant Nos. 11474168 and 61401222), the Qing Lan Project of Jiangsu Province of China, the Natural Science Foundation of Jiangsu Province of China (Grant No. BK20151502), and the Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.
Entangled coherent states versus entangled photon pairs for practical quantum-information processing
Park, Kimin; Jeong, Hyunseok
2010-12-15
We compare effects of decoherence and detection inefficiency on entangled coherent states (ECSs) and entangled photon pairs (EPPs), both of which are known to be particularly useful for quantum-information processing (QIP). When decoherence effects caused by photon losses are heavy, the ECSs outperform the EPPs as quantum channels for teleportation both in fidelities and in success probabilities. On the other hand, when inefficient detectors are used, the teleportation scheme using the ECSs suffers undetected errors that result in the degradation of fidelity, while this is not the case for the teleportation scheme using the EPPs. Our study reveals the merits and demerits of the two types of entangled states in realizing practical QIP under realistic conditions.
Realizing quantum advantage without entanglement in single-photon states
NASA Astrophysics Data System (ADS)
Maldonado Trapp, Alejandra; Solano, Pablo; Hu, Anzi; Clark, Charles W.
2016-05-01
Quantum discord expresses quantum correlations beyond those associated with entanglement. Although it has been extensively studied theoretically, quantum discord has yet to become a standard tool in experimental studies of correlation. We propose a class of experiments in which quantum correlations are present in the absence of entanglement, and are best understood in terms of quantum discord.. These utilize X-states of two qubits, which correspond to the polarization and the optical path of a single photon within a Mach-Zehnder interferometer. We show how to produce states with diverse measures of discord and entanglement, including the case of discord without entanglement. With these states we show how a classical random variable K can be encoded by Alice and decoded by Bob. Using our previous results we analytically study the correlations between the spin and path qubits and its relation with the information about K that can be decoded by Bob using local measurements with or without two-qubit gate operations.
NASA Astrophysics Data System (ADS)
Wang, Zhen; Li, Heng-Mei; Yuan, Hong-Chun
2016-06-01
We theoretically introduce a kind of non-Gaussian entangled states, i.e., photon-subtracted two-mode squeezed coherent states (PSTMSCS), by successively subtracting photons from each mode of the two-mode squeezed coherent states. The normalization factor which is related to bivariate Hermite polynomials is obtained by virtue of the two-mode squeezing operator in entangled-states representation. The sub-Poissonian photon statistics, antibunching effects, and partial negative Wigner function, respectively, are observed numerically, which fully reflect the nonclassicality of the resultant states. Finally, employing the SV criteria and the EPR correlation, respectively, the entangled property of PSTMSCS is analyzed. It is shown that the photon subtraction operation can effectively enhance the inseparability between the two modes.
Barium Qubit State Detection and Ba Ion-Photon Entanglement
NASA Astrophysics Data System (ADS)
Sosnova, Ksenia; Inlek, Ismail Volkan; Crocker, Clayton; Lichtman, Martin; Monroe, Christopher
2016-05-01
A modular ion-trap network is a promising framework for scalable quantum-computational devices. In this architecture, different ion-trap modules are connected via photonic buses while within one module ions interact locally via phonons. To eliminate cross-talk between photonic-link qubits and memory qubits, we use different atomic species for quantum information storage (171 Yb+) and intermodular communication (138 Ba+). Conventional deterministic Zeeman-qubit state detection schemes require additional stabilized narrow-linewidth lasers. Instead, we perform fast probabilistic state detection utilizing efficient detectors and high-NA lenses to detect emitted photons from circularly polarized 493 nm laser excitation. Our method is not susceptible to intensity and frequency noise, and we show single-shot detection efficiency of ~ 2%, meaning that we can discriminate between the two qubits states with 99% confidence after as little as 50 ms of averaging. Using this measurement technique, we report entanglement between a single 138 Ba+ ion and its emitted photon with 86% fidelity. This work is supported by the ARO with funding from the IARPA MQCO program, the DARPA Quiness program, the AFOSR MURI on Quantum Transduction, and the ARL Center for Distributed Quantum Information.
Realizing quantum advantage without entanglement in single-photon states
NASA Astrophysics Data System (ADS)
Maldonado-Trapp, Alejandra; Solano, Pablo; Hu, Anzi; Clark, Charles W.
Correlations allow us to measure, and quantitatively study, the properties of physical systems, their evolution and their interactions. Quantum discord expresses quantum correlations beyond those associated with entanglement. However, discord has not yet been adopted as a standard subject of study by the experimental community. Here we propose a feasible optical setup to generate symmetric two-qubit X-states with controllable coherences, where the two qubits correspond to the spin and path of a photon. With these states we show how a classical random variable K can be encoded by Alice and decoded by Bob. Using our previous results we study the correlations between the spin and path qubits and its relation with the information about K that can be decoded by Bob using local measurements with or without two-qubit gate operations. Discord is the mutual information contained in the coherences of the system, and it is possible to exploit it for quantum advantage even in the absence of entanglement.
Teleportation of entangled states without Bell-state measurement via a two-photon process
NASA Astrophysics Data System (ADS)
dSouza, A. D.; Cardoso, W. B.; Avelar, A. T.; Baseia, B.
2011-02-01
In this letter we propose a scheme using a two-photon process to teleport an entangled field state of a bimodal cavity to another one without Bell-state measurement. The quantum information is stored in a zero- and two-photon entangled state. This scheme requires two three-level atoms in a ladder configuration, two bimodal cavities, and selective atomic detectors. The fidelity and success probability do not depend on the coefficients of the state to be teleported. For convenient choices of interaction times, the teleportation occurs with fidelity close to the unity.
NASA Astrophysics Data System (ADS)
Yuan, Hong-Chun; Wang, Zhen; Chen, Qin-Miao; Dou, Xiao-Ming
2015-07-01
In this paper, using Wigner function (WF) method in phase space, we re-investigate micro-macro entanglement of a single-photon entangled state after one-sided amplification and de-amplification proposed by Simon’s group, and discuss the effects of the amplification and the loss. For the input-output process, we first build the relation between the input WF and the output WF. Next, the analytical expression of the output WF is derived related to the factors of the amplification and the loss. Finally, based on the above results, using the trace rule we also obtain the exact expressions of the detected probability and concurrence to quantify micro-macro entanglement, and analyze numerically the results. The results show that it is possible to detect micro-macro photon-number entanglement for reasonable values of photon loss.
Practical single-photon-assisted remote state preparation with non-maximally entanglement
NASA Astrophysics Data System (ADS)
Wang, Dong; Huang, Ai-Jun; Sun, Wen-Yang; Shi, Jia-Dong; Ye, Liu
2016-08-01
Remote state preparation (RSP) and joint remote state preparation (JRSP) protocols for single-photon states are investigated via linear optical elements with partially entangled states. In our scheme, by choosing two-mode instances from a polarizing beam splitter, only the sender in the communication protocol needs to prepare an ancillary single-photon and operate the entanglement preparation process in order to retrieve an arbitrary single-photon state from a photon pair in partially entangled state. In the case of JRSP, i.e., a canonical model of RSP with multi-party, we consider that the information of the desired state is split into many subsets and in prior maintained by spatially separate parties. Specifically, with the assistance of a single-photon state and a three-photon entangled state, it turns out that an arbitrary single-photon state can be jointly and remotely prepared with certain probability, which is characterized by the coefficients of both the employed entangled state and the target state. Remarkably, our protocol is readily to extend to the case for RSP and JRSP of mixed states with the all optical means. Therefore, our protocol is promising for communicating among optics-based multi-node quantum networks.
Practical single-photon-assisted remote state preparation with non-maximally entanglement
NASA Astrophysics Data System (ADS)
Wang, Dong; Huang, Ai-Jun; Sun, Wen-Yang; Shi, Jia-Dong; Ye, Liu
2016-05-01
Remote state preparation (RSP) and joint remote state preparation (JRSP) protocols for single-photon states are investigated via linear optical elements with partially entangled states. In our scheme, by choosing two-mode instances from a polarizing beam splitter, only the sender in the communication protocol needs to prepare an ancillary single-photon and operate the entanglement preparation process in order to retrieve an arbitrary single-photon state from a photon pair in partially entangled state. In the case of JRSP, i.e., a canonical model of RSP with multi-party, we consider that the information of the desired state is split into many subsets and in prior maintained by spatially separate parties. Specifically, with the assistance of a single-photon state and a three-photon entangled state, it turns out that an arbitrary single-photon state can be jointly and remotely prepared with certain probability, which is characterized by the coefficients of both the employed entangled state and the target state. Remarkably, our protocol is readily to extend to the case for RSP and JRSP of mixed states with the all optical means. Therefore, our protocol is promising for communicating among optics-based multi-node quantum networks.
Six-photon entangled Dicke state enabled by a UV enhancement cavity as novel SPDC photon source
NASA Astrophysics Data System (ADS)
Wieczorek, Witlef; Krischek, Roland; Ozawa, Akira; Tóth, Géza; Kiesel, Nikolai; Michelberger, Patrick; Udem, Thomas; Weinfurter, Harald
2010-06-01
Photon sources for multi-photon entanglement experiments are commonly based on the process of spontaneous parametric down conversion. Due to the probabilistic photon production, such experiments suffer from low multiphoton count rates. To increase this count rate, we present a novel SPDC pump source based on a femtosecond UV enhancement cavity that increases the available pump power while maintaining a high repetition rate of 80MHz. We apply the cavity as photon source for realizing symmetric, multi-partite entangled Dicke states, which are observed with a high rate and high fidelity. We characterize the observed Dicke states of up to six photons using efficient tools exploiting the state's symmetries.
Podoshvedov, S. A.
2008-03-15
We study a teleportation protocol of an unknown macroscopic qubit by means of a quantum channel composed of the displaced vacuum and single-photon states. The scheme is based on linear optical devices such as a beam splitter and photon number resolving detectors. A method based on conditional measurement is used to generate both the macroscopic qubit and entangled state composed from displaced vacuum and single-photon states. We show that such a qubit has both macroscopic and microscopic properties. In particular, we investigate a quantum teleportation protocol from a macroscopic object to a microscopic state.
Distillation of mixed-state continuous-variable entanglement by photon subtraction
Zhang Shengli; Loock, Peter van
2010-12-15
We present a detailed theoretical analysis for the distillation of one copy of a mixed two-mode continuous-variable entangled state using beam splitters and coherent photon-detection techniques, including conventional on-off detectors and photon-number-resolving detectors. The initial Gaussian mixed-entangled states are generated by transmitting a two-mode squeezed state through a lossy bosonic channel, corresponding to the primary source of errors in current approaches to optical quantum communication. We provide explicit formulas to calculate the entanglement in terms of logarithmic negativity before and after distillation, including losses in the channel and the photon detection, and show that one-copy distillation is still possible even for losses near the typical fiber channel attenuation length. A lower bound for the transmission coefficient of the photon-subtraction beam splitter is derived, representing the minimal value that still allows to enhance the entanglement.
Carving Complex Many-Atom Entangled States by Single-Photon Detection.
Chen, Wenlan; Hu, Jiazhong; Duan, Yiheng; Braverman, Boris; Zhang, Hao; Vuletić, Vladan
2015-12-18
We propose a versatile and efficient method to generate a broad class of complex entangled states of many atoms via the detection of a single photon. For an atomic ensemble contained in a strongly coupled optical cavity illuminated by weak single- or multifrequency light, the atom-light interaction entangles the frequency spectrum of a transmitted photon with the collective spin of the atomic ensemble. Simple time-resolved detection of the transmitted photon then projects the atomic ensemble into a desired pure entangled state. This method can be implemented with existing technology, yields high success probability per trial, and can generate complex entangled states such as mesoscopic superposition states of coherent spin states with high fidelity. PMID:26722909
Carving Complex Many-Atom Entangled States by Single-Photon Detection
NASA Astrophysics Data System (ADS)
Chen, Wenlan; Hu, Jiazhong; Duan, Yiheng; Braverman, Boris; Zhang, Hao; Vuletic, Vladan
2016-05-01
We propose a versatile and efficient method to generate a broad class of complex entangled states of many atoms via the detection of a single photon. For an atomic ensemble contained in a strongly coupled optical cavity illuminated by weak single- or multifrequency light, the atom-light interaction entangles the frequency spectrum of a transmitted photon with the collective spin of the atomic ensemble. Simple time-resolved detection of the transmitted photon then projects the atomic ensemble into a desired pure entangled state. This method can be implemented with existing technology, yields high success probability per trial, and can generate complex entangled states such as mesoscopic superposition states of coherent spin states with high fidelity.
Carving Complex Many-Atom Entangled States by Single-Photon Detection
NASA Astrophysics Data System (ADS)
Chen, Wenlan; Hu, Jiazhong; Duan, Yiheng; Braverman, Boris; Zhang, Hao; Vuletić, Vladan
2015-12-01
We propose a versatile and efficient method to generate a broad class of complex entangled states of many atoms via the detection of a single photon. For an atomic ensemble contained in a strongly coupled optical cavity illuminated by weak single- or multifrequency light, the atom-light interaction entangles the frequency spectrum of a transmitted photon with the collective spin of the atomic ensemble. Simple time-resolved detection of the transmitted photon then projects the atomic ensemble into a desired pure entangled state. This method can be implemented with existing technology, yields high success probability per trial, and can generate complex entangled states such as mesoscopic superposition states of coherent spin states with high fidelity.
Generation of three-photon polarization-entangled decoherence-free states
NASA Astrophysics Data System (ADS)
Dong, Li; Lin, Yan-Fang; Li, Qing-Yang; Dong, Hai-Kuan; Xiu, Xiao-Ming; Gao, Ya-Jun
2016-08-01
We present a generation proposal of three-photon polarization-entangled decoherence-free states, which are immune to the collective decoherence. Based on weak cross-Kerr nonlinearities, the polarization and spacial entanglement gates are realized, and thus three-photon polarization-entangled decoherence-free states can be produced. According to the outcomes of Homodyne measurement performed in the spacial entanglement gate, one Swap gate is inserted into two paths of the photon 1 to swap its spacial modes, by means of classical feed forward. In addition, in the process for realizing two entanglement gates, unitary transformation operations are performed on the appropriate photons conditioned on the different phase shifts occurred on the coherent states, aiming to obtain the same state under two scenarios of the different path compositions of photons. At the output ports of the circuit, three-photon polarization-entangled decoherence-free states which can be utilized to represent two logical qubits, |0>L and |1>L are achieved. Apart from Kerr media, only simple linear optical elements and the classical feed forward techniques are necessary in this proposal, facilitating its practical implementation.
Quantum correlation of path-entangled two-photon states in waveguide arrays with defects
Dou, Yiling; Xu, Lei; Han, Bin; Bo, Fang; Xu, Jingjun; Zhang, Guoquan
2014-04-15
We study the quantum correlation of path-entangled states of two photons in coupled one-dimensional waveguide arrays with lattice defects. Both off-diagonal and diagonal defects are considered, which show different effects on the quantum correlation of path-entangled two-photon states. Two-photon bunching or anti-bunching effects can be observed and controlled. The two photons are found to have a tendency to bunch at the side lobes with a repulsive off-diagonal defect, and the path-entanglement of the input two-photon state can be preserved during the propagation. We also found that defect modes may play an important role on the two-photon correlation of path-entangled states in the waveguide arrays. Due to the quantum interference effect, intriguing evolution dynamics of the two-photon correlation matrix elements with oscillation frequencies being either twice of or the same as that of a classical light wave, depending on the position of the correlation matrix element, is observed. Our results show that it is possible to manipulate the two-photon correlation properties of path-entangled states in waveguide arrays with lattice defects.
Carving complex many-atom entangled states by single-photon detection
NASA Astrophysics Data System (ADS)
Hu, Jiazhong; Chen, Wenlan; Duan, Yiheng; Braverman, Boris; Zhang, Hao; Vuletic, Vladan
We propose a versatile and efficient method to generate a broad class of complex entangled states of many atoms via the detection of a single photon. For an atomic ensemble contained in a strongly coupled optical cavity illuminated by weak single- or multi-frequency light, the atom-light interaction entangles the frequency spectrum of a transmitted photon with the collective spin of the atomic ensemble. Simple time-resolved detection of the transmitted photon then projects the atomic ensemble into a desired pure entangled state. This method can be implemented with existing technology, yields high success probability per trials, and can generate complex entangled states such as multicomponent Schrödinger cat states with high fidelity.
Enhanced two-photon absorption using entangled states and small mode volumes
You Hao; Hendrickson, S. M.; Franson, J. D.
2009-10-15
We calculate the rate of two-photon absorption for frequency-entangled photons in a tapered optical fiber whose diameter is comparable to the wavelength of the light. The confinement of the electric field in the transverse direction increases the intensity associated with a single photon, while the two-photon absorption rate is further enhanced by the fact that the sum of the frequencies of the two photons is on resonance with the upper atomic state, even though each photon has a relatively broad linewidth. As a result, the photons are effectively confined in all three dimensions and the two-photon absorption rate for frequency-entangled photons in a tapered fiber was found to be comparable to that for unentangled photons in a microcavity with a small mode volume.
Photon-number superselection and the entangled coherent-state representation
Sanders, Barry C.; Bartlett, Stephen D.; Rudolph, Terry; Knight, Peter L.
2003-10-01
We introduce the entangled coherent-state representation, which provides a powerful technique for efficiently and elegantly describing and analyzing quantum optics sources and detectors while respecting the photon-number superselection rule that is satisfied by all known quantum optics experiments. We apply the entangled coherent-state representation to elucidate and resolve the long-standing puzzles of the coherence of a laser output field, interference between two number states, and dichotomous interpretations of quantum teleportation of coherent states.
Demonstration of a programmable source of two-photon multiqubit entangled states
Cialdi, Simone; Brivio, Davide; Paris, Matteo G. A.
2010-04-15
We suggest and demonstrate a novel source of two-photon multipartite entangled states which exploits the transverse spatial structure of spontaneous parametric down-conversion together with a programmable spatial light modulator (SLM). The one-dimensional SLM is used to perform polarization entanglement purification and to realize arbitrary phase gates between polarization and momentum degrees of freedom of photons. We experimentally demonstrate our scheme by generating two-photon three-qubit linear cluster states with high fidelity using a diode laser pump with a limited coherence time and power on the crystal as low as {approx}2.5 mW.
Total teleportation of zero- and one-photon entangled states in running waves
NASA Astrophysics Data System (ADS)
Cardoso B., W.; Avelar T., A.; Baseia, B.; Almeida G. de, N.
2008-01-01
Inspired by a recent paper [2002 J. Opt. B 4 316] we present an alternative scheme to teleport an entanglement of zero- and one-photon states of a running-wave field. The scheme employs only linear optical elements plus single-photon sources and detectors.
Distillation of arbitrary single-photon entanglement assisted with polarized Bell states
NASA Astrophysics Data System (ADS)
Feng, Zhao-Feng; Ou-Yang, Yang; Zhou, Lan; Sheng, Yu-Bo
2015-10-01
Single-photon entanglement (SPE) is a promising resource in quantum communication. However, it will suffer from the photon loss. In this paper, we will present an efficient approach to protect the two-mode SPE. This protocol not only can distill the SPE from the mixed state, but also can faithfully protect the information encoded in the polarization degree of freedom. Moreover, different from the previous protocols, if the SPE becomes a less-entangled state, we can also distill it to the maximally entangled state. During the whole protocol, we exploit the polarized Bell states to complete the task. This protocol can also be extended to protect the single-photon multi-mode W state. This protocol is feasible in current technology, for it only requires linear optical elements.
Slow Images and Entangled Photons
Swordy, Simon
2007-06-20
I will discuss some recent experiments using slow light and entangled photons. We recently showed that it was possible to map a two dimensional image onto very low light level signals, slow them down in a hot atomic vapor while preserving the amplitude and phase of the images. If time remains, I will discuss some of our recent work with time-energy entangled photons for quantum cryptography. We were able to show that we could have a measurable state space of over 1000 states for a single pair of entangled photons in fiber.
Remote preparation of single-photon "hybrid" entangled and vector-polarization States.
Barreiro, Julio T; Wei, Tzu-Chieh; Kwiat, Paul G
2010-07-16
Quantum teleportation faces increasingly demanding requirements for transmitting large or even entangled systems. However, knowledge of the state to be transmitted eases its reconstruction, resulting in a protocol known as remote state preparation. A number of experimental demonstrations to date have been restricted to single-qubit systems. We report the remote preparation of two-qubit "hybrid" entangled states, including a family of vector-polarization beams. Our single-photon states are encoded in the photon spin and orbital angular momentum. We reconstruct the states by spin-orbit state tomography and transverse polarization tomography. The high fidelities achieved for the vector-polarization states opens the door to optimal coupling of down-converted photons to other physical systems, such as an atom, as required for scalable quantum networks, or plasmons in photonic nanostructures. PMID:20867752
Generating arbitrary photon-number entangled states for continuous-variable quantum informatics.
Lee, Su-Yong; Park, Jiyong; Lee, Hai-Woong; Nha, Hyunchul
2012-06-18
We propose two experimental schemes that can produce an arbitrary photon-number entangled state (PNES) in a finite dimension. This class of entangled states naturally includes non-Gaussian continuous-variable (CV) states that may provide some practical advantages over the Gaussian counterparts (two-mode squeezed states). We particularly compare the entanglement characteristics of the Gaussian and the non-Gaussian states in view of the degree of entanglement and the Einstein-Podolsky-Rosen correlation, and further discuss their applications to the CV teleportation and the nonlocality test. The experimental imperfection due to the on-off photodetectors with nonideal efficiency is also considered in our analysis to show the feasibility of our schemes within existing technologies. PMID:22714485
Tomography of a high-fidelity spin-photon entangled state
NASA Astrophysics Data System (ADS)
McMahon, Peter; de Greve, Kristiaan; Yu, Leo; Pelc, Jason; Natarajan, Chandra; Kim, Na Young; Abe, Eisuke; Maier, Sebastian; Schneider, Christian; Kamp, Martin; Hoefling, Sven; Hadfield, Robert; Forchel, Alfred; Fejer, M. M.; Yamamoto, Yoshihisa
2013-03-01
The generation of entanglement between a quantum memory and a flying qubit is an important step towards building a quantum repeater node. Entanglement between a photon and a matter qubit has been demonstrated in several systems, including neutral atoms, trapped ions, NV centers and quantum dots. Quantum dots have a natural advantage that their radiative lifetimes are short, and therefore the rate of entanglement generation can be much faster than in other systems. We have recently demonstrated entanglement between an electron spin in a quantum dot, and the polarization of an emitted photon. In addition, the photon is converted to the low-loss 1550 nm band, which is important for implementing long-distance quantum communication systems. In this talk, I will present the reconstruction of the full density matrix of the entangled spin-photon state that we produce. We calculate the fidelity of the state from the density matrix, and conclude that it is > 90 % . This work was supported by the JSPS through its FIRST programme, NICT, NSF CCR-08 29694, NIST 60NANB9D9170, Special Coordination Funds for Promoting Science and Technology, and the State of Bavaria.
NASA Astrophysics Data System (ADS)
Liang, Bian-Bian; Hu, Shi; Cui, Wen-Xue; An, Cheng-Shou; Xing, Yan; Hu, Jing-Si; Sun, Guo-Qing; Jiang, Xin-Xin; Wang, Hong-Fu
2014-11-01
Assisted by a quantum dot-microcavity coupled system, we propose an entanglement concentration scheme for concentrating two unknown partially entangled three-photon W states into a maximally entangled three-photon W state based on spin selective photon reflection from the cavity and the interference of polarized photons. In the scheme, three parties, say Alice, Bob, and Charlie in different distant locations can successfully share the maximally entangled three-photon W state with a high probability of success by local operations performed by Alice and classical communication. We calculate the probability of success of the scheme and the fidelity of the obtained three-photon W state under practical conditions, whose results show that the scheme can work in both weak coupling and strong coupling regimes.
Preparation of entangled states of two photons in several spatial modes
Lemr, Karel; Fiurasek, Jaromir
2008-02-15
We describe a protocol capable of preparing an arbitrary state of two photons in several spatial modes using pairs of photons generated by spontaneous parametric down conversion, linear optical elements, and single-photon detectors or postselection. The protocol involves unitary and nonunitary transformations realizable by beam splitters and phase shifters. Nonunitary transformations are implemented by attenuation filters. The protocol contains several optimization capabilities with the goal of improving overall probability of its success. We also show how entangled two-photon states required for quantum computing with linear optics can be prepared using a very simple and feasible scheme.
Laser-driven parametric instability and generation of entangled photon-plasmon states in graphene
NASA Astrophysics Data System (ADS)
Tokman, Mikhail; Wang, Yongrui; Oladyshkin, Ivan; Kutayiah, A. Ryan; Belyanin, Alexey
2016-06-01
We show that a strong infrared laser beam obliquely incident on graphene can experience a parametric instability with respect to decay into lower-frequency (idler) photons and THz surface plasmons. The instability is due to a strong in-plane second-order nonlinear response of graphene which originates from its spatial dispersion. The parametric decay leads to efficient generation of THz plasmons and gives rise to quantum entanglement of idler photons and surface plasmon states.
Remote preparation of N photon GHZ polarization entangled states within a network
NASA Astrophysics Data System (ADS)
Xia, Y.; Song, J.; Ning, Y.; Lu, P.-M.; Song, H.-S.
2010-02-01
We propose a new linear optical protocol for remote state preparation (RSP) between two parties under control of a number of controllers in terms of optical elements. The proposed setup involves simple linear optical elements, a N-photon polarization entangled state, and photon de tectors, witch have been widely used in experiment. The realization of this protocol is appealing due to the fact that quantum state of light is robust against the decoherence and photons are ideal carriers for transmitting quantum information over long distances.
Multi-photon entanglement in high dimensions
NASA Astrophysics Data System (ADS)
Malik, Mehul; Erhard, Manuel; Huber, Marcus; Krenn, Mario; Fickler, Robert; Zeilinger, Anton
2016-04-01
Forming the backbone of quantum technologies today, entanglement has been demonstrated in physical systems as diverse as photons, ions and superconducting circuits. Although steadily pushing the boundary of the number of particles entangled, these experiments have remained in a two-dimensional space for each particle. Here we show the experimental generation of the first multi-photon entangled state where both the number of particles and dimensions are greater than two. Two photons in our state reside in a three-dimensional space, whereas the third lives in two dimensions. This asymmetric entanglement structure only appears in multiparticle entangled states with d > 2. Our method relies on combining two pairs of photons, high-dimensionally entangled in their orbital angular momentum. In addition, we show how this state enables a new type of ‘layered’ quantum communication protocol. Entangled states such as these serve as a manifestation of the complex dance of correlations that can exist within quantum mechanics.
Tomography of the quantum state of photons entangled in high dimensions
Agnew, Megan; Leach, Jonathan; McLaren, Melanie; Roux, F. Stef; Boyd, Robert W.
2011-12-15
Systems entangled in high dimensions have recently been proposed as important tools for various quantum information protocols, such as multibit quantum key distribution and loophole-free tests of nonlocality. It is therefore important to have precise knowledge of the nature of such entangled quantum states. We tomographically reconstruct the quantum state of the two photons produced by parametric downconversion that are entangled in a d-dimensional orbital angular momentum basis. We determine exactly the density matrix of the entangled two-qudit state with d ranging from 2 to 8. The recording of higher-dimensional states is limited only by the number of data points required and therefore the length of time needed to complete the measurements. We find all the measured states to have fidelities and linear entropies that satisfy the criteria required for a violation of the appropriate high-dimensional Bell inequality. Our results therefore precisely characterize the nature of the entanglement, thus establishing the suitability of such states for applications in quantum information science.
Quantum Authencryption with Two-Photon Entangled States for Off-Line Communicants
NASA Astrophysics Data System (ADS)
Ye, Tian-Yu
2016-02-01
In this paper, a quantum authencryption protocol is proposed by using the two-photon entangled states as the quantum resource. Two communicants Alice and Bob share two private keys in advance, which determine the generation of two-photon entangled states. The sender Alice sends the two-photon entangled state sequence encoded with her classical bits to the receiver Bob in the manner of one-step quantum transmission. Upon receiving the encoded quantum state sequence, Bob decodes out Alice's classical bits with the two-photon joint measurements and authenticates the integrity of Alice's secret with the help of one-way hash function. The proposed protocol only uses the one-step quantum transmission and needs neither a public discussion nor a trusted third party. As a result, the proposed protocol can be adapted to the case where the receiver is off-line, such as the quantum E-mail systems. Moreover, the proposed protocol provides the message authentication to one bit level with the help of one-way hash function and has an information-theoretical efficiency equal to 100 %.
Is There Really AN Entangled State for Far Away Twin Photons?
NASA Astrophysics Data System (ADS)
Valqui, Holger G.
2006-04-01
A certain school of physicists based on the following assumptions: (i) Photons acquire a polarization state only after they have passed through a polarizer (which some claim to be a stipulation of one of the postulates of the Copenhagen Interpretation of Quantum Mechanics), (ii) The states of twin photons are correctly represented by \\chi(1,2) = √ {2}(u ⊗ v + v ⊗ u), where u is an arbitrary state (of polarization) and v is orthogonal to u, and (iii) Numerous experiments directly or indirectly confirm the theoretical predictions., concludes that there exists an extraordinary entangled state of both photons, which permits that each of the photons somehow be sensible to the interaction which affects the other one, notwithstanding the great distance which might exist between them. In the present exposition I show that: (i) There are experimental reasons to maintain that photons have a definite polarization state before and after having passed through a polarizer, (ii) According to the principles of Quantum Mechanics the "official" representation \\chi(1,2) = √ {2}(u ⊗ v + v ⊗ u) can not be right., and (iii)Significant doubts exist concerning the accuracy of the critical measurements and their interpretation. At the last I conclude that the alleged extraordinary entanglement of well separated photons might be a delusion. Finally, to settle the matter, I propose a crucial experiment.
NASA Astrophysics Data System (ADS)
Dong, Li; Wang, Jun-Xi; Li, Qing-Yang; Dong, Hai-Kuan; Xiu, Xiao-Ming; Gao, Ya-Jun
2016-07-01
Employing a polarization-entangled χ state, which is a four-photon genuine entangled state, we propose a protocol teleporting a general two-photon polarization state. Firstly, the sender needs to perform one Controlled-NOT gate, one Hadamard gate, and one Controlled-NOT gate on the state to be teleported in succession. Secondly, the sender performs local nondemolition parity analyses based on cross-Kerr nonlinearities and publicizes the achieved outcomes. Finally, conditioned on the sender's analysis outcomes, the receiver executes the single-photon unitary transformation operations on his own photons to obtain the state originally sit in the sender's location. Due to the employment of nondemolition parity analyses rather than four-qubit joint measurement, it can be realized more feasible with currently available technologies. Moreover, the resources of Bell states can be achieved because the nondestructive measurement is exploited, which facilitates other potential tasks of quantum information processing.
NASA Astrophysics Data System (ADS)
Dong, Li; Wang, Jun-Xi; Li, Qing-Yang; Dong, Hai-Kuan; Xiu, Xiao-Ming; Gao, Ya-Jun
2016-03-01
Employing a polarization-entangled χ state, which is a four-photon genuine entangled state, we propose a protocol teleporting a general two-photon polarization state. Firstly, the sender needs to perform one Controlled-NOT gate, one Hadamard gate, and one Controlled-NOT gate on the state to be teleported in succession. Secondly, the sender performs local nondemolition parity analyses based on cross-Kerr nonlinearities and publicizes the achieved outcomes. Finally, conditioned on the sender's analysis outcomes, the receiver executes the single-photon unitary transformation operations on his own photons to obtain the state originally sit in the sender's location. Due to the employment of nondemolition parity analyses rather than four-qubit joint measurement, it can be realized more feasible with currently available technologies. Moreover, the resources of Bell states can be achieved because the nondestructive measurement is exploited, which facilitates other potential tasks of quantum information processing.
Frozen multipartite entanglement in photonic crystals
NASA Astrophysics Data System (ADS)
Wu, Wei; Xu, Jing-Bo
2016-06-01
We investigate the multipartite entanglement dynamics of a many-body system consisting of N identical two-level atoms locally embedded in their own band-gap photonic crystals. It is shown that the tripartite entanglement of this photonic-crystal system can be frozen in a stationary state. We also find that a double-sudden-change phenomenon of four-partite entanglement occurs in this photonic-crystal system during the decoherence process under certain suitable conditions.
A revised controlled deterministic secure quantum communication with five-photon entangled state
NASA Astrophysics Data System (ADS)
Xiu, Xiao-Ming; Dong, Li; Gao, Ya-Jun; Chi, Feng; Ren, Yuan-Peng; Liu, Hui-Wei
2010-01-01
A revised controlled deterministic secure quantum communication protocol using five-photon entangled state is proposed. It amends the security loopholes pointed by Qin et al. in [S.J. Qin, Q.Y. Wen, L.M. Meng, F.C. Zhu, Opt. Commun. 282 (2009) 2656] in the original protocol proposed by Xiu et al. in [X.M. Xiu, L. Dong, Y.J. Gao, F. Chi, Opt. Commun. 282 (2009) 333]. The security loopholes are solved by using order rearrangement of transmission photons and two-step security test.
NASA Astrophysics Data System (ADS)
Zhao, Yan-Jun; Wang, Changqing; Zhu, Xiaobo; Liu, Yu-Xi
2016-04-01
It has been shown that there are not only transverse but also longitudinal couplings between microwave fields and a superconducting qubit with broken inversion symmetry of the potential energy. Using multiphoton processes induced by longitudinal coupling fields and frequency matching conditions, we design a universal algorithm to produce arbitrary superpositions of two-mode photon states of microwave fields in two separated transmission line resonators, which are coupled to a superconducting qubit. Based on our algorithm, we analyze the generation of evenly-populated states and NOON states. Compared to other proposals with only single-photon process, we provide an efficient way to produce entangled microwave photon states when the interactions between superconducting qubits and microwave fields are in the strong and ultrastrong regime.
Zhao, Yan-Jun; Wang, Changqing; Zhu, Xiaobo; Liu, Yu-xi
2016-01-01
It has been shown that there are not only transverse but also longitudinal couplings between microwave fields and a superconducting qubit with broken inversion symmetry of the potential energy. Using multiphoton processes induced by longitudinal coupling fields and frequency matching conditions, we design a universal algorithm to produce arbitrary superpositions of two-mode photon states of microwave fields in two separated transmission line resonators, which are coupled to a superconducting qubit. Based on our algorithm, we analyze the generation of evenly-populated states and NOON states. Compared to other proposals with only single-photon process, we provide an efficient way to produce entangled microwave photon states when the interactions between superconducting qubits and microwave fields are in the strong and ultrastrong regime. PMID:27033558
Photon-Mediated Interactions: A Scalable Tool to Create and Sustain Entangled States of N Atoms
NASA Astrophysics Data System (ADS)
Aron, Camille; Kulkarni, Manas; Türeci, Hakan E.
2016-01-01
We propose and study the use of photon-mediated interactions for the generation of long-range steady-state entanglement between N atoms. Through the judicious use of coherent drives and the placement of the atoms in a network of cavity QED systems, a balance between their unitary and dissipative dynamics can be precisely engineered to stabilize a long-range correlated state of qubits in the steady state. We discuss the general theory behind such a scheme and present an example of how it can be used to drive a register of N atoms to a generalized W state and how the entanglement can be sustained indefinitely. The achievable steady-state fidelities for entanglement and its scaling with the number of qubits are discussed for presently existing superconducting quantum circuits. While the protocol is primarily discussed for a superconducting circuit architecture, it is ideally realized in any cavity QED platform that permits controllable delivery of coherent electromagnetic radiation to specified locations.
Photon-mediated interactions: a scalable tool to create and sustain entangled states of N atoms
NASA Astrophysics Data System (ADS)
Aron, Camille; Kulkarni, Manas; Tureci, Hakan
We propose and study the use of photon-mediated interactions for the generation of steady-state entanglement between N atoms that are separated by arbitrary distances. Through the judicious use of coherent drives and the placement of the atoms in a network of Cavity QED systems, a balance between their unitary and dissipative dynamics can be precisely engineered to stabilize a long-range correlated state of qubits in the steady state. We discuss the general theory behind such a scheme, and present an example of how it can be used to drive a register of N atoms to a generalized W-state, and the entanglement sustained indefinitely. The achievable steady-state fidelities for entanglement and its scaling with the number of qubits are discussed for presently existing superconducting quantum circuits. While the protocol is primarily discussed for a superconducting circuit architecture, it is ideally realized in any Cavity QED platform that permits controllable delivery of coherent electromagnetic radiation to specified locations.
Kuang Leman; Zhou Lan
2003-10-01
In this paper, we present a method to generate continuous-variable-type entangled states between photons and atoms in atomic Bose-Einstein condensate (BEC). The proposed method involves an atomic BEC with three internal states, a weak quantized probe laser, and a strong classical coupling laser, which form a three-level {lambda}-shaped BEC system. We consider a situation where the BEC is in electromagnetically induced transparency with the coupling laser being much stronger than the probe laser. In this case, the upper and intermediate levels are unpopulated, so that their adiabatic elimination enables an effective two-mode model involving only the atomic field at the lowest internal level and the quantized probe laser field. Atom-photon quantum entanglement is created through laser-atom and interatomic interactions, and two-photon detuning. We show how to generate atom-photon entangled coherent states and entangled states between photon (atom) coherent states and atom-(photon-) macroscopic quantum superposition (MQS) states, and between photon-MQS and atom-MQS states.
Plasmon-assisted transmission of entangled photons.
Altewischer, E; van Exter, M P; Woerdman, J P
2002-07-18
The state of a two-particle system is said to be entangled when its quantum-mechanical wavefunction cannot be factorized into two single-particle wavefunctions. This leads to one of the strongest counter-intuitive features of quantum mechanics, namely non-locality. Experimental realization of quantum entanglement is relatively easy for photons; a starting photon can spontaneously split into a pair of entangled photons inside a nonlinear crystal. Here we investigate the effects of nanostructured metal optical elements on the properties of entangled photons. To this end, we place optically thick metal films perforated with a periodic array of subwavelength holes in the paths of the two entangled photons. Such arrays convert photons into surface-plasmon waves--optically excited compressive charge density waves--which tunnel through the holes before reradiating as photons at the far side. We address the question of whether the entanglement survives such a conversion process. Our coincidence counting measurements show that it does, so demonstrating that the surface plasmons have a true quantum nature. Focusing one of the photon beams on its array reduces the quality of the entanglement. The propagation of the surface plasmons makes the array effectively act as a 'which way' detector. PMID:12124618
Energy-Tunable Sources of Entangled Photons: A Viable Concept for Solid-State-Based Quantum Relays
NASA Astrophysics Data System (ADS)
Trotta, Rinaldo; Martín-Sánchez, Javier; Daruka, Istvan; Ortix, Carmine; Rastelli, Armando
2015-04-01
We propose a new method of generating triggered entangled photon pairs with wavelength on demand. The method uses a microstructured semiconductor-piezoelectric device capable of dynamically reshaping the electronic properties of self-assembled quantum dots (QDs) via anisotropic strain engineering. Theoretical models based on k .p theory in combination with finite-element calculations show that the energy of the polarization-entangled photons emitted by QDs can be tuned in a range larger than 100 meV without affecting the degree of entanglement of the quantum source. These results pave the way towards the deterministic implementation of QD entanglement resources in all-electrically-controlled solid-state-based quantum relays.
Reconstructing high-dimensional two-photon entangled states via compressive sensing
Tonolini, Francesco; Chan, Susan; Agnew, Megan; Lindsay, Alan; Leach, Jonathan
2014-01-01
Accurately establishing the state of large-scale quantum systems is an important tool in quantum information science; however, the large number of unknown parameters hinders the rapid characterisation of such states, and reconstruction procedures can become prohibitively time-consuming. Compressive sensing, a procedure for solving inverse problems by incorporating prior knowledge about the form of the solution, provides an attractive alternative to the problem of high-dimensional quantum state characterisation. Using a modified version of compressive sensing that incorporates the principles of singular value thresholding, we reconstruct the density matrix of a high-dimensional two-photon entangled system. The dimension of each photon is equal to d = 17, corresponding to a system of 83521 unknown real parameters. Accurate reconstruction is achieved with approximately 2500 measurements, only 3% of the total number of unknown parameters in the state. The algorithm we develop is fast, computationally inexpensive, and applicable to a wide range of quantum states, thus demonstrating compressive sensing as an effective technique for measuring the state of large-scale quantum systems. PMID:25306850
Dong Li; Xiu Xiaoming; Gao Yajun; Yi, X. X.
2011-10-15
Using three-photon polarization-entangled GHZ states or W states, we propose controlled quantum key distribution protocols for circumventing two main types of collective noise, collective dephasing noise, or collective rotation noise. Irrespective of the number of controllers, a three-photon state can generate a one-bit secret key. The storage technique of quantum states is dispensable for the controller and the receiver, and it therefore allows performing the process in a more convenient mode. If the photon cost in a security check is disregarded, then the efficiency theoretically approaches unity.
Spin-orbit hybrid entanglement of photons and quantum contextuality
Karimi, Ebrahim; Slussarenko, Sergei; Leach, Jonathan; Franke-Arnold, Sonja; Padgett, Miles J.; Piccirillo, Bruno; Santamato, Enrico; Marrucci, Lorenzo; Chen Lixiang; She Weilong
2010-08-15
We demonstrate electromagnetic quantum states of single photons and of correlated photon pairs exhibiting ''hybrid'' entanglement between spin and orbital angular momentum. These states are obtained from entangled photon pairs emitted by spontaneous parametric down conversion by employing a q plate for coupling the spin and orbital degrees of freedom of a photon. Entanglement and contextual quantum behavior (that is also nonlocal, in the case of photon pairs) is demonstrated by the reported violation of the Clauser-Horne-Shimony-Holt inequality. In addition, a classical analog of the hybrid spin-orbit photonic entanglement is reported and discussed.
Ultrabright source of entangled photon pairs.
Dousse, Adrien; Suffczyński, Jan; Beveratos, Alexios; Krebs, Olivier; Lemaître, Aristide; Sagnes, Isabelle; Bloch, Jacqueline; Voisin, Paul; Senellart, Pascale
2010-07-01
A source of triggered entangled photon pairs is a key component in quantum information science; it is needed to implement functions such as linear quantum computation, entanglement swapping and quantum teleportation. Generation of polarization entangled photon pairs can be obtained through parametric conversion in nonlinear optical media or by making use of the radiative decay of two electron-hole pairs trapped in a semiconductor quantum dot. Today, these sources operate at a very low rate, below 0.01 photon pairs per excitation pulse, which strongly limits their applications. For systems based on parametric conversion, this low rate is intrinsically due to the Poissonian statistics of the source. Conversely, a quantum dot can emit a single pair of entangled photons with a probability near unity but suffers from a naturally very low extraction efficiency. Here we show that this drawback can be overcome by coupling an optical cavity in the form of a 'photonic molecule' to a single quantum dot. Two coupled identical pillars-the photonic molecule-were etched in a semiconductor planar microcavity, using an optical lithography method that ensures a deterministic coupling to the biexciton and exciton energy states of a pre-selected quantum dot. The Purcell effect ensures that most entangled photon pairs are emitted into two cavity modes, while improving the indistinguishability of the two optical recombination paths. A polarization entangled photon pair rate of 0.12 per excitation pulse (with a concurrence of 0.34) is collected in the first lens. Our results open the way towards the fabrication of solid state triggered sources of entangled photon pairs, with an overall (creation and collection) efficiency of 80%. PMID:20613838
Enhancing and expanding remote photonic entanglement via local filtering operations
NASA Astrophysics Data System (ADS)
Xing, Hai-Bo; Yang, Ming; Dong, Ping; Fang, Shu-Dong; Cao, Zhuo-Liang
2014-06-01
We present an entanglement distillation scheme for enhancing remote two-photon polarization entanglement of mixed states. Although the main idea of the current scheme is based on Gisin's work (Phys. Lett. A 210 (1996) 151 [21]), there are new advantages in our new scheme, which are guaranteed by the nondemolition measurement of photonic state and the re-distillation of the garbage states. This entanglement distillation scheme not only can enhance the remote entanglement of mixed states, but also can expand two-photon entangled states to four-photon entangled states. So this scheme is an apparently feasible way for preparing multi-photon entangled states. The main idea is based on the principle of the cross-Kerr nonlinearity and the parity-check measurements (a nondemolition measurement) on photonic states. Two distant users Alice and Bob first start with one shared but less entangled photon pair, and with the help of local auxiliary photons, parity-check measurements and classical communication they can get a four-photon highly entangled states with a high success probability. For the fail result, although the garbage state is less entangled than the initial one, there is still entanglement in it. So these garbage states can be re-collected and distilled again instead of being discarded. In this sense, we can see that this protocol has a high yield, and the fidelity (with respect to the Bell state) of the initial state is not required to be bigger than 1/2 (a common threshold of the standard entanglement purification theory). In addition, post-selection measurements on the entangled photons are not needed here because of the nondemolition measurement. The nondemolition character of the measurement allows further processing of the resulting states. These advantages make the current scheme more feasible within the current technology.
Frequency-bin entangled photons
Olislager, L.; Emplit, P.; Nguyen, A. T.; Massar, S.; Merolla, J.-M.; Huy, K. Phan
2010-07-15
A monochromatic laser pumping a parametric down-conversion crystal generates frequency-entangled photon pairs. We study this experimentally by addressing such frequency-entangled photons at telecommunication wavelengths (around 1550 nm) with fiber-optics components such as electro-optic phase modulators and narrow-band frequency filters. The theory underlying our approach uses the notion of frequency-bin entanglement. Our results show that the phase modulators address coherently up to eleven frequency bins, leading to an interference pattern which can violate by more than five standard deviations a Bell inequality adapted to our setup.
Efficient single-photon entanglement concentration for quantum communications
NASA Astrophysics Data System (ADS)
Zhou, Lan; Sheng, Yu-Bo
2014-02-01
We present two entanglement concentration protocols for single-photon entanglement. The first protocol is implemented with linear optics. With the help of the 50:50 beam splitter, variable beam splitter and an auxiliary photon, a less-entangled single-photon state can be concentrated into a maximally single-photon entangled state with some probability. The second protocol is implemented with the cross-Kerr nonlinearity. With the help of the cross-Kerr nonlinearity, the sophisticated single photon detector is not required. Moreover, the second protocol can be reused to get higher success probability. All these advantages may make the protocols useful in the long-distance quantum communication.
Photonic module: An on-demand resource for photonic entanglement
Devitt, Simon J.; Greentree, Andrew D.; Hollenberg, Lloyd C. L.; Ionicioiu, Radu; O'Brien, Jeremy L.; Munro, William J.
2007-11-15
Photonic entanglement has a wide range of applications in quantum computation and communication. Here we introduce a device: the photonic module, which allows for the rapid, deterministic preparation of a large class of entangled photon states. The module is an application independent, ''plug and play'' device, with sufficient flexibility to prepare entanglement for all major quantum computation and communication applications in a completely deterministic fashion without number-discriminated photon detection. We present two alternative constructions for the module, one using free-space components and one in a photonic band-gap structure. The natural operation of the module is to generate states within the stabilizer formalism and we present an analysis on the cavity requirements to experimentally realize this device.
Quantum key distribution with entangled photon sources
NASA Astrophysics Data System (ADS)
Ma, Xiongfeng; Fung, Chi-Hang Fred; Lo, Hoi-Kwong
2007-07-01
A parametric down-conversion (PDC) source can be used as either a triggered single-photon source or an entangled-photon source in quantum key distribution (QKD). The triggering PDC QKD has already been studied in the literature. On the other hand, a model and a post-processing protocol for the entanglement PDC QKD are still missing. We fill in this important gap by proposing such a model and a post-processing protocol for the entanglement PDC QKD. Although the PDC model is proposed to study the entanglement-based QKD, we emphasize that our generic model may also be useful for other non-QKD experiments involving a PDC source. Since an entangled PDC source is a basis-independent source, we apply Koashi and Preskill’s security analysis to the entanglement PDC QKD. We also investigate the entanglement PDC QKD with two-way classical communications. We find that the recurrence scheme increases the key rate and the Gottesman-Lo protocol helps tolerate higher channel losses. By simulating a recent 144-km open-air PDC experiment, we compare three implementations: entanglement PDC QKD, triggering PDC QKD, and coherent-state QKD. The simulation result suggests that the entanglement PDC QKD can tolerate higher channel losses than the coherent-state QKD. The coherent-state QKD with decoy states is able to achieve highest key rate in the low- and medium-loss regions. By applying the Gottesman-Lo two-way post-processing protocol, the entanglement PDC QKD can tolerate up to 70dB combined channel losses ( 35dB for each channel) provided that the PDC source is placed in between Alice and Bob. After considering statistical fluctuations, the PDC setup can tolerate up to 53dB channel losses.
Photon statistics on the extreme entanglement
Zhang, Yang; Zhang, Jun; Yu, Chang-shui
2016-01-01
The effects of photon bunching and antibunching correspond to the classical and quantum features of the electromagnetic field, respectively. No direct evidence suggests whether these effects can be potentially related to quantum entanglement. Here we design a cavity quantum electrodynamics model with two atoms trapped in to demonstrate the connections between the steady-state photon statistics and the two-atom entanglement. It is found that within the weak dissipations and to some good approximation, the local maximal two-atom entanglements perfectly correspond to not only the quantum feature of the electromagnetic field—the optimal photon antibunching, but also the classical feature—the optimal photon bunching. We also analyze the influence of strong dissipations and pure dephasing. An intuitive physical understanding is also given finally. PMID:27053368
Photon statistics on the extreme entanglement
NASA Astrophysics Data System (ADS)
Zhang, Yang; Zhang, Jun; Yu, Chang-Shui
2016-04-01
The effects of photon bunching and antibunching correspond to the classical and quantum features of the electromagnetic field, respectively. No direct evidence suggests whether these effects can be potentially related to quantum entanglement. Here we design a cavity quantum electrodynamics model with two atoms trapped in to demonstrate the connections between the steady-state photon statistics and the two-atom entanglement. It is found that within the weak dissipations and to some good approximation, the local maximal two-atom entanglements perfectly correspond to not only the quantum feature of the electromagnetic field—the optimal photon antibunching, but also the classical feature—the optimal photon bunching. We also analyze the influence of strong dissipations and pure dephasing. An intuitive physical understanding is also given finally.
Photon statistics on the extreme entanglement.
Zhang, Yang; Zhang, Jun; Yu, Chang-shui
2016-01-01
The effects of photon bunching and antibunching correspond to the classical and quantum features of the electromagnetic field, respectively. No direct evidence suggests whether these effects can be potentially related to quantum entanglement. Here we design a cavity quantum electrodynamics model with two atoms trapped in to demonstrate the connections between the steady-state photon statistics and the two-atom entanglement. It is found that within the weak dissipations and to some good approximation, the local maximal two-atom entanglements perfectly correspond to not only the quantum feature of the electromagnetic field-the optimal photon antibunching, but also the classical feature-the optimal photon bunching. We also analyze the influence of strong dissipations and pure dephasing. An intuitive physical understanding is also given finally. PMID:27053368
Two-photon spectral amplitude of entangled states resolved in separable Schmidt modes
NASA Astrophysics Data System (ADS)
Avella, A.; Brida, G.; Chekhova, M.; Gramegna, M.; Shurupov, A.; Genovese, M.
2015-10-01
The ability to access high dimensionality in Hilbert spaces represents a demanding key-stone for state-of-the-art quantum information. The manipulation of entangled states in continuous variables, wavevector as well frequency, represents a powerful resource in this sense. The number of dimensions of the Hilbert space that can be used in practical information protocols can be determined by the number of Schmidt modes that it is possible to address one by one. In the case of wavevector variables, the Schmidt modes can be losslessly selected using single-mode fibre and a spatial light modulator, but no similar procedure exists for the frequency space. The aim of this work is to present a technique to engineer the spectral properties of biphoton light, emitted via ultrafast spontaneous parametric down conversion, in such a way that the two-photon spectral amplitude (TPSA) contains several non-overlapping Schmidt modes, each of which can be filtered losslessly in frequency variables. Such TPSA manipulation is operated by a fine balancing of parameters like the pump frequency, the shaping of pump pulse spectrum, the dispersion dependence of spontaneous parametric down-conversion crystals as well as their length. Measurements have been performed exploiting the group velocity dispersion induced by the passage of optical fields through dispersive media, operating a frequency-to-time two-dimensional Fourier transform of the TPSA. Exploiting this kind of measurement we experimentally demonstrate the ability to control the Schmidt modes structure in TPSA through the pump spectrum manipulation.
NASA Astrophysics Data System (ADS)
Jeong, Hyunseok; Bae, Seunglee; Choi, Seongjeon
2016-02-01
We study quantum teleportation between two different types of optical qubits using hybrid entanglement as a quantum channel under decoherence effects. One type of qubit employs the vacuum and single-photon states for the basis, called a single-rail single-photon qubit, and the other utilizes coherent states of opposite phases. We find that teleportation from a single-rail single-photon qubit to a coherent-state qubit is better than the opposite direction in terms of fidelity and success probability. We compare our results with those using a different type of hybrid entanglement between a polarized single-photon qubit and a coherent state.
Witnessing trustworthy single-photon entanglement with local homodyne measurements.
Morin, Olivier; Bancal, Jean-Daniel; Ho, Melvyn; Sekatski, Pavel; D'Auria, Virginia; Gisin, Nicolas; Laurat, Julien; Sangouard, Nicolas
2013-03-29
Single-photon entangled states, i.e., states describing two optical paths sharing a single photon, constitute the simplest form of entanglement. Yet they provide a valuable resource in quantum information science. Specifically, they lie at the heart of quantum networks, as they can be used for quantum teleportation, swapped, and purified with linear optics. The main drawback of such entanglement is the difficulty in measuring it. Here, we present and experimentally test an entanglement witness allowing one to say whether a given state is path entangled and also that entanglement lies in the subspace, where the optical paths are each filled with one photon at most, i.e., refers to single-photon entanglement. It uses local homodyning only and relies on no assumption about the Hilbert space dimension of the measured system. Our work provides a simple and trustworthy method for verifying the proper functioning of future quantum networks. PMID:23581297
Coherent state quantum key distribution based on entanglement sudden death
NASA Astrophysics Data System (ADS)
Jaeger, Gregg; Simon, David; Sergienko, Alexander V.
2016-03-01
A method for quantum key distribution (QKD) using entangled coherent states is discussed which is designed to provide key distribution rates and transmission distances surpassing those of traditional entangled photon pair QKD by exploiting entanglement sudden death. The method uses entangled electromagnetic signal states of `macroscopic' average photon numbers rather than single photon or entangled photon pairs, which have inherently limited rate and distance performance as bearers of quantum key data. Accordingly, rather than relying specifically on Bell inequalities as do entangled photon pair-based methods, the security of this method is based on entanglement witnesses and related functions.
Quantum-entangled photon interferometry
NASA Astrophysics Data System (ADS)
Richards, Roger K.
2004-08-01
A two-color quantum-entangled photon source is used to produce fourth-order interference. Because the period of the interference is produced by the frequency difference of the entangled photons, problems associated with counting fringes can be avoided. This also permits measurements at a virtual wavelength, which can prevent problems associated with transmission or absorption when such a longer wavelength may be needed. The interference wavelength can be varied with a geometry change in the beam path without any change in the source wavelength. The entangled photons are produced using an argon ion laser at 351 nanometers and a type I BBO crystal. The interference is detected in coincidence using four photomultiplier tubes.
Jeong, Hyunseok; Nguyen Ba An
2006-08-15
We study Greenberger-Horne-Zeilinger-type (GHZ-type) and W-type three-mode entangled coherent states. Both types of entangled coherent states violate Mermin's version of the Bell inequality with threshold photon detection (i.e., without photon counting). Such an experiment can be performed using linear optics elements and threshold detectors with significant Bell violations for GHZ-type entangled coherent states. However, to demonstrate Bell-type inequality violations for W-type entangled coherent states, additional nonlinear interactions are needed. We also propose an optical scheme to generate W-type entangled coherent states in free-traveling optical fields. The required resources for the generation are a single-photon source, a coherent state source, beam splitters, phase shifters, photodetectors, and Kerr nonlinearities. Our scheme does not necessarily require strong Kerr nonlinear interactions; i.e., weak nonlinearities can be used for the generation of the W-type entangled coherent states. Furthermore, it is also robust against inefficiencies of the single-photon source and the photon detectors.
Generating two-photon entangled states in a driven two-atom system
Almutairi, Khulud; Tanas, Ryszard; Ficek, Zbigniew
2011-07-15
We describe a mechanism for a controlled generation of a pure Bell state with correlated atoms that involve two or zero excitations. The mechanism inhibits transitions into singly excited collective states of a two-atom system by shifting them from their unperturbed energies. The shift is accomplished by the dipole-dipole interaction between the atoms. The creation of the Bell state is found to be dependent on the relaxation of the atomic excitation. When the relaxation is not present or can be ignored, the state of the system evolves harmonically between a separable to the maximally entangled state. We follow the temporal evolution of the state and find that the concurrence can be different from zero only in the presence of the dipole-dipole interaction. Furthermore, in the limit of a large dipole-dipole interaction, the concurrence reduces to that predicted for an X state of the system. A general inequality is found which shows that the concurrence of an X-state system is a lower bound for the concurrence of the two-atom system. With the relaxation present, the general state of the system is a mixed state that under a strong dipole-dipole interaction reduces the system to an X-state form. We find that mixed states admit of lower level of entanglement, and the entanglement may occur over a finite range of time. A simple analytical expression is obtained for the steady-state concurrence which shows that there is a threshold value for the dipole-dipole interaction relative to the Rabi frequency of the driving field above which the atoms can be entangled over the entire time of the evolution.
Lu, Huai-Xin; Cao, Lian-Zhen; Zhao, Jia-Qiang; Li, Ying-De; Wang, Xiao-Qin
2014-01-01
The highest qubit Ardehali inequality violation with 203 standard deviations is first experimentally demonstrated using the hyper-entangled four-photon-eight-qubit Greenberger-Horne-Zeilinger (GHZ) state. Moreover, we experimentally investigate the robustness of the Ardehali inequality for the four-, six-, and eight-qubit GHZ states in a rotary noisy environment systematically. Our results first validate the Ardehali' theoretical statement of relation between violation of Ardehali inequality and particle number, and proved that Ardehali inequality is more robust against noise in larger number qubit GHZ states, and provided an experimental benchmark for us to estimate the safety of quantum channel in the noisy environment. PMID:24667345
Measuring protein concentration with entangled photons
NASA Astrophysics Data System (ADS)
Crespi, Andrea; Lobino, Mirko; Matthews, Jonathan C. F.; Politi, Alberto; Neal, Chris R.; Ramponi, Roberta; Osellame, Roberto; O'Brien, Jeremy L.
2012-06-01
Optical interferometry is amongst the most sensitive techniques for precision measurement. By increasing the light intensity, a more precise measurement can usually be made. However, if the sample is light sensitive entangled states can achieve the same precision with less exposure. This concept has been demonstrated in measurements of known optical components. Here, we use two-photon entangled states to measure the concentration of a blood protein in an aqueous buffer solution. We use an opto-fluidic device that couples a waveguide interferometer with a microfluidic channel. These results point the way to practical applications of quantum metrology to light-sensitive samples.
Lithography system using quantum entangled photons
NASA Technical Reports Server (NTRS)
Williams, Colin (Inventor); Dowling, Jonathan (Inventor); della Rossa, Giovanni (Inventor)
2002-01-01
A system of etching using quantum entangled particles to get shorter interference fringes. An interferometer is used to obtain an interference fringe. N entangled photons are input to the interferometer. This reduces the distance between interference fringes by n, where again n is the number of entangled photons.
Purification of single-photon entanglement.
Salart, D; Landry, O; Sangouard, N; Gisin, N; Herrmann, H; Sanguinetti, B; Simon, C; Sohler, W; Thew, R T; Thomas, A; Zbinden, H
2010-05-01
Single-photon entanglement is a simple form of entanglement that exists between two spatial modes sharing a single photon. Despite its elementary form, it provides a resource as useful as polarization-entangled photons and it can be used for quantum teleportation and entanglement swapping operations. Here, we report the first experiment where single-photon entanglement is purified with a simple linear-optics based protocol. In addition to its conceptual interest, this result might find applications in long distance quantum communication based on quantum repeaters. PMID:20482160
Use of maximally entangled N-photon states for practical quantum interferometry
Gilbert, Gerald; Hamrick, Michael; Weinstein, Yaakov S.
2008-08-15
The phase estimation performance of photonic N00N states propagating in an attenuating medium is analyzed. It is shown that the Heisenberg limit is never achieved and that an attenuated separable state of N photons will actually produce a better phase estimate than an equally attenuated N00N state unless the transmittance of the medium is sufficiently high. Thus, for most practical applications with realistic attenuation, N00N-state-based phase estimation actually performs worse than the standard quantum limit. This performance deficit becomes more pronounced as the number of photons in the signal increases.
Nonlocal hyperconcentration on entangled photons using photonic module system
NASA Astrophysics Data System (ADS)
Cao, Cong; Wang, Tie-Jun; Mi, Si-Chen; Zhang, Ru; Wang, Chuan
2016-06-01
Entanglement distribution will inevitably be affected by the channel and environment noise. Thus distillation of maximal entanglement nonlocally becomes a crucial goal in quantum information. Here we illustrate that maximal hyperentanglement on nonlocal photons could be distilled using the photonic module and cavity quantum electrodynamics, where the photons are simultaneously entangled in polarization and spatial-mode degrees of freedom. The construction of the photonic module in a photonic band-gap structure is presented, and the operation of the module is utilized to implement the photonic nondestructive parity checks on the two degrees of freedom. We first propose a hyperconcentration protocol using two identical partially hyperentangled initial states with unknown coefficients to distill a maximally hyperentangled state probabilistically, and further propose a protocol by the assistance of an ancillary single photon prepared according to the known coefficients of the initial state. In the two protocols, the total success probability can be improved greatly by introducing the iteration mechanism, and only one of the remote parties is required to perform the parity checks in each round of iteration. Estimates on the system requirements and recent experimental results indicate that our proposal is realizable with existing or near-further technologies.
Complementarity reveals bound entanglement of two twisted photons
NASA Astrophysics Data System (ADS)
Hiesmayr, Beatrix C.; Löffler, Wolfgang
2013-08-01
We demonstrate the detection of bipartite bound entanglement as predicted by the Horodecki's in 1998. Bound entangled states, being heavily mixed entangled quantum states, can be produced by incoherent addition of pure entangled states. Until 1998 it was thought that such mixing could always be reversed by entanglement distillation; however, this turned out to be impossible for bound entangled states. The purest form of bound entanglement is that of only two particles, which requires higher-dimensional (d > 2) quantum systems. We realize this using photon qutrit (d = 3) pairs produced by spontaneous parametric downconversion, that are entangled in the orbital angular momentum degrees of freedom, which is scalable to high dimensions. Entanglement of the photons is confirmed via a ‘maximum complementarity protocol’. This conceptually simple protocol requires only maximized complementary of measurement bases; we show that it can also detect bound entanglement. We explore the bipartite qutrit space and find that, also experimentally, a significant portion of the entangled states are actually bound entangled.
Quantum random number generator using photon-number path entanglement.
Kwon, Osung; Cho, Young-Wook; Kim, Yoon-Ho
2009-03-20
We report a quantum random number generator based on the photon-number-path entangled state that is prepared by means of two-photon quantum interference at a beam splitter. The randomness in our scheme is truly quantum mechanical in origin since it results from the projection measurement of the entangled two-photon state. The generated bit sequences satisfy the standard randomness test. PMID:19305476
Exciton absorption of entangled photons in semiconductor quantum wells
NASA Astrophysics Data System (ADS)
Rodriguez, Ferney; Guzman, David; Salazar, Luis; Quiroga, Luis; Condensed Matter Physics Group Team
2013-03-01
The dependence of the excitonic two-photon absorption on the quantum correlations (entanglement) of exciting biphotons by a semiconductor quantum well is studied. We show that entangled photon absorption can display very unusual features depending on space-time-polarization biphoton parameters and absorber density of states for both bound exciton states as well as for unbound electron-hole pairs. We report on the connection between biphoton entanglement, as quantified by the Schmidt number, and absorption by a semiconductor quantum well. Comparison between frequency-anti-correlated, unentangled and frequency-correlated biphoton absorption is addressed. We found that exciton oscillator strengths are highly increased when photons arrive almost simultaneously in an entangled state. Two-photon-absorption becomes a highly sensitive probe of photon quantum correlations when narrow semiconductor quantum wells are used as two-photon absorbers. Research funds from Facultad de Ciencias, Universidad de los Andes
Generation of entangled squeezed states: their entanglement and quantum polarization
NASA Astrophysics Data System (ADS)
Karimi, A.; Tavassoly, M. K.
2015-11-01
In this paper, based on the well-known one-mode and two-mode squeezed states, we introduce the two-mode and four-mode entangled squeezed states. Next, in order to generate the introduced entangled states, we present two theoretical schemes based on the resonant atom-field interaction. In the proposed schemes, a Λ -type three-level atom interacts with the two-mode and four-mode quantized field in the presence of two strong classical fields in which two-photon atomic transitions are allowed. In the continuation, we study entanglement dynamics of the generated entangled states (using the von Neumann entropy) as well as the quantum polarization (using the Stokes operators). It is demonstrated that entanglement and polarization can be achieved for the produced states by adjusting the evolved parameters.
Coherent dynamics of a telecom-wavelength entangled photon source
NASA Astrophysics Data System (ADS)
Ward, M. B.; Dean, M. C.; Stevenson, R. M.; Bennett, A. J.; Ellis, D. J. P.; Cooper, K.; Farrer, I.; Nicoll, C. A.; Ritchie, D. A.; Shields, A. J.
2014-02-01
Quantum networks can interconnect remote quantum information processors, allowing interaction between different architectures and increasing net computational power. Fibre-optic telecommunications technology offers a practical platform for routing weakly interacting photonic qubits, allowing quantum correlations and entanglement to be established between distant nodes. Although entangled photons have been produced at telecommunications wavelengths using spontaneous parametric downconversion in nonlinear media, as system complexity increases their inherent excess photon generation will become limiting. Here we demonstrate entangled photon pair generation from a semiconductor quantum dot at a telecommunications wavelength. Emitted photons are intrinsically anti-bunched and violate Bell’s inequality by 17 standard deviations High-visibility oscillations of the biphoton polarization reveal the time evolution of the emitted state with exceptional clarity, exposing long coherence times. Furthermore, we introduce a method to evaluate the fidelity to a time-evolving Bell state, revealing entanglement between photons emitted up to 5 ns apart, exceeding the exciton lifetime.
System and method for clock synchronization and position determination using entangled photon pairs
NASA Technical Reports Server (NTRS)
Shih, Yanhua (Inventor)
2010-01-01
A system and method for clock synchronization and position determination using entangled photon pairs is provided. The present invention relies on the measurement of the second order correlation function of entangled states. Photons from an entangled photon source travel one-way to the clocks to be synchronized. By analyzing photon registration time histories generated at each clock location, the entangled states allow for high accuracy clock synchronization as well as high accuracy position determination.
Efficient Generation of Frequency-Multiplexed Entangled Single Photons
NASA Astrophysics Data System (ADS)
Qiu, Tian-Hui; Xie, Min
2016-08-01
We present two schemes to generate frequency-multiplexed entangled (FME) single photons by coherently mapping photonic entanglement into and out of a quantum memory based on Raman interactions. By splitting a single photon and performing subsequent state transfer, we separate the generation of entanglement and its frequency conversion, and find that the both progresses have the characteristic of inherent determinacy. Our theory can reproduce the prominent features of observed results including pulse shapes and the condition for deterministically generating the FME single photons. The schemes are suitable for the entangled photon pairs with a wider frequency range, and could be immune to the photon loss originating from cavity-mode damping, spontaneous emission, and the dephasing due to atomic thermal motion. The sources might have significant applications in wavelength-division-multiplexing quantum key distribution.
Speckle statistics of entangled photons
NASA Astrophysics Data System (ADS)
Klein, Avraham; Agam, Oded; Spivak, Boris
2016-07-01
We consider the propagation of several entangled photons through an elastically scattering medium and study statistical properties of their speckle patterns. We find the spatial correlations of multiphoton speckles and their sensitivity to changes of system parameters. Our analysis covers both the directed-wave regime, where rays propagate almost ballistically while experiencing small-angle diffusion, and the real-space diffusive regime. We demonstrate that long-range correlations of the speckle patterns dominate experimental signatures for large-aperture photon detectors. We also show that speckle sensitivity depends strongly on the number of photons N in the incoming beam, increasing as √{N } in the directed-wave regime and as N in the diffusive regime.
Measurement, entanglement, and collapse, in atom-photon scattering
NASA Astrophysics Data System (ADS)
Ozeri, Roee; Glickman, Yinnon; Kotler, Shlomi; Akerman, Nitzan
2013-05-01
Photon scattering is a common tool in atomic physics experiments. We show how, entanglement, measurement and decoherence are intertwined in the process of photon scattering by a single trapped ion. We preform quantum process tomography on the spin of a single trapped 88Sr+ ion, undergoing resonant photon scattering. We observe that, following the scattering and detection of a single photon, a spin measurement basis emerges. The measurement basis is aligned with the scattered photon direction and its state are invariant under photon scattering. We also find that, while the measurement basis states themselves are classically correlated with the scattered photon polarization, superpositions of these basis state become entangled with the scattered photon. Quantum feedback, based on photon polarization measurement, can be used to reverse photon scattering decoherence.
Enhancing quantum entanglement by photon addition and subtraction
NASA Astrophysics Data System (ADS)
Navarrete-Benlloch, Carlos; García-Patrón, Raúl; Shapiro, Jeffrey H.; Cerf, Nicolas J.
2012-07-01
The non-Gaussian operations effected by adding or subtracting a photon on entangled optical beams emerging from a parametric down-conversion process have been suggested to enhance entanglement. Heralded photon addition or subtraction is, as a matter of fact, at the heart of continuous-variable entanglement distillation. The use of such processes has recently been experimentally demonstrated in the context of the generation of optical coherent-state superpositions or the verification of canonical commutation relations. Here, we carry out a systematic study of the effect of local photon additions and subtractions on a two-mode squeezed vacuum state, showing that the entanglement generally increases with the number of such operations. This is analytically proven when additions or subtractions are restricted to one mode only, while we observe that the highest entanglement is achieved when these operations are equally shared between the two modes. We also note that adding photons typically provides a stronger entanglement enhancement than subtracting photons, while photon subtraction performs better in terms of energy efficiency. Furthermore, we analyze the interplay between entanglement and non-Gaussianity, showing that it is more subtle than previously expected.
Scalable spatial superresolution using entangled photons.
Rozema, Lee A; Bateman, James D; Mahler, Dylan H; Okamoto, Ryo; Feizpour, Amir; Hayat, Alex; Steinberg, Aephraim M
2014-06-01
N00N states-maximally path-entangled states of N photons-exhibit spatial interference patterns sharper than any classical interference pattern. This is known as superresolution. However, even given perfectly efficient number-resolving detectors, the detection efficiency of all previous measurements of such interference would decrease exponentially with the number of photons in the N00N state, often leading to the conclusion that N00N states are unsuitable for spatial measurements. A technique known as the "optical centroid measurement" has been proposed to solve this and has been experimentally verified for photon pairs; here we present the first extension beyond two photons, measuring the superresolution fringes of two-, three-, and four-photon N00N states. Moreover, we compare the N00N-state interference to the corresponding classical superresolution interference. Although both provide the same increase in spatial frequency, the visibility of the classical fringes decreases exponentially with the number of detected photons. Our work represents an essential step forward for quantum-enhanced measurements, overcoming what was believed to be a fundamental challenge to quantum metrology. PMID:24949765
Quantum states prepared by realistic entanglement swapping
Scherer, Artur; Howard, Regina B.; Sanders, Barry C.; Tittel, Wolfgang
2009-12-15
Entanglement swapping between photon pairs is a fundamental building block in schemes using quantum relays or quantum repeaters to overcome the range limits of long-distance quantum key distribution. We develop a closed-form solution for the actual quantum states prepared by realistic entanglement swapping, which takes into account experimental deficiencies due to inefficient detectors, detector dark counts, and multiphoton-pair contributions of parametric down-conversion sources. We investigate how the entanglement present in the final state of the remaining modes is affected by the real-world imperfections. To test the predictions of our theory, comparison with previously published experimental entanglement swapping is provided.
Observation of Four-Photon Orbital Angular Momentum Entanglement.
Hiesmayr, B C; de Dood, M J A; Löffler, W
2016-02-19
We demonstrate genuine multipartite quantum entanglement of four photons in their orbital angular momentum degrees of freedom, where a high-dimensional discrete Hilbert space is attached to each photon. This can encode more quantum information compared to the qubit case, but it is a long-standing problem to entangle more than two such photons. In our experiment we use pulsed spontaneous parametric down-conversion to produce the photon quadruplets, which allows us to detect about one four-photon event per second. By means of quantum state reconstruction and a suitable witness operator we find that the photon quadruplets form a genuine multipartite entangled symmetric Dicke state. This opens a new tool for addressing foundational questions in quantum mechanics, and for exploration of novel high-dimensional multiparty quantum information applications such as secret sharing. PMID:26943533
Observation of Four-Photon Orbital Angular Momentum Entanglement
NASA Astrophysics Data System (ADS)
Hiesmayr, B. C.; de Dood, M. J. A.; Löffler, W.
2016-02-01
We demonstrate genuine multipartite quantum entanglement of four photons in their orbital angular momentum degrees of freedom, where a high-dimensional discrete Hilbert space is attached to each photon. This can encode more quantum information compared to the qubit case, but it is a long-standing problem to entangle more than two such photons. In our experiment we use pulsed spontaneous parametric down-conversion to produce the photon quadruplets, which allows us to detect about one four-photon event per second. By means of quantum state reconstruction and a suitable witness operator we find that the photon quadruplets form a genuine multipartite entangled symmetric Dicke state. This opens a new tool for addressing foundational questions in quantum mechanics, and for exploration of novel high-dimensional multiparty quantum information applications such as secret sharing.
NASA Astrophysics Data System (ADS)
Belyanin, Alexey; Wang, Yongrui; Oladyshkin, Ivan; Tokman, Mikhail
Massless Dirac electrons in graphene and on the surface of topological insulators such as Bi2Se3 demonstrate strong nonlinear optical response and support tightly confined surface plasmon modes. Although both systems constitute an isotropic medium for low-energy in-plane electron excitations, their second-order nonlinear susceptibility becomes non-zero when its spatial dispersion is taken into account. In this case the anisotropy is induced by in-plane wave vectors of obliquely incident or in-plane propagating electromagnetic waves. In this work we show that a strong (0.1-1 MW/cm2) near-infrared or mid-infrared laser beam obliquely incident on graphene can experience a parametric instability with respect to decay into lower-frequency (idler) photons and THz surface plasmons. The parametric gain leads to efficient generation of THz plasmons. Furthermore, the parametric decay process gives rise to quantum entanglement of idler photon and surface plasmon states. This enables diagnostics and control of surface plasmons by detecting idler photons. A similar parametric process can be implemented in topological insulator thin films. This work has been supported in part by the Air Force Office for Scientific Research through Grant FA9550-15-1-0153.
The generation of entangled states from independent particle sources
NASA Technical Reports Server (NTRS)
Rubin, Morton H.; Shih, Yan-Hua
1994-01-01
The generation of entangled states of two systems from product states is discussed for the case in which the paths of the two systems do not overlap. A particular method of measuring allows one to project out the nonlocal entangled state. An application to the production of four photon entangled states is outlined.
Two-photon spectroscopy of excitons with entangled photons
Schlawin, Frank; Mukamel, Shaul
2013-12-28
The utility of quantum light as a spectroscopic tool is demonstrated for frequency-dispersed pump-probe, integrated pump-probe, and two-photon fluorescence signals which show Ramsey fringes. Simulations of the frequency-dispersed transmission of a broadband pulse of entangled photons interacting with a three-level model of matter reveal how the non-classical time-bandwidth properties of entangled photons can be used to disentangle congested spectra, and reveal otherwise unresolved features. Quantum light effects are most pronounced at weak intensities when entangled photon pairs are well separated, and are gradually diminished at higher intensities when different photon pairs overlap.
Complete Analysis of Four-Photon χ-Type Entangled State via Cross-Kerr Nonlinearity
NASA Astrophysics Data System (ADS)
Zeng, Zhi; Li, Xi-Han; Wang, Chun; Wang, Li-Li; Liu, Zhen-Zhen; Wei, Hua
2015-09-01
We propose an efficient method to construct an optical four-photon |χ> state analyzer via the cross-Kerr nonlinearity combined with linear optical elements. In this protocol, two four-qubit parity-check gates and two controlled phase gates are employed. We show that all the 16 orthogonal four-qubit |χ> states can be completely discriminated with our apparatus. The scheme is feasible and realizable with current technology. It may have useful potential applications in quantum information processing which based on |χ> state. Supported by the National Natural Science Foundation of China under Grant No. 11004258, and Fundamental Research Funds for the Central Universities Project under Grant No. CQDXWL-2012-014, the Natural Science Foundation Project of CQ CSTC 2011jjA90017
Ion Photon Entanglement with Barium
NASA Astrophysics Data System (ADS)
Noel, Thomas William
Entanglement between a single trapped 138Ba+ and a single spontaneously emitted photon is demonstrated. The system is used to measure a CHSH Bell signal of 2.303(36), verifying the violation of the CHSH inequality by over eight standard deviations. The feasibility of using the system to perform a loophole free measurement of the violation of the Bell inequality is considered. A pair of side projects are discussed. First, the robustness of adiabatic rapid passage in the presence of noise in the driving field is investigated. And second, a ppm measurement of the Landé g factor of the 5 D5/2 level of 138Ba+ is reported. The new ion trap that made all this work possible is introduced.
Fiber transport of spatially entangled photons
NASA Astrophysics Data System (ADS)
Löffler, W.; Eliel, E. R.; Woerdman, J. P.; Euser, T. G.; Scharrer, M.; Russell, P.
2012-03-01
High-dimensional entangled photons pairs are interesting for quantum information and cryptography: Compared to the well-known 2D polarization case, the stronger non-local quantum correlations could improve noise resistance or security, and the larger amount of information per photon increases the available bandwidth. One implementation is to use entanglement in the spatial degree of freedom of twin photons created by spontaneous parametric down-conversion, which is equivalent to orbital angular momentum entanglement, this has been proven to be an excellent model system. The use of optical fiber technology for distribution of such photons has only very recently been practically demonstrated and is of fundamental and applied interest. It poses a big challenge compared to the established time and frequency domain methods: For spatially entangled photons, fiber transport requires the use of multimode fibers, and mode coupling and intermodal dispersion therein must be minimized not to destroy the spatial quantum correlations. We demonstrate that these shortcomings of conventional multimode fibers can be overcome by using a hollow-core photonic crystal fiber, which follows the paradigm to mimic free-space transport as good as possible, and are able to confirm entanglement of the fiber-transported photons. Fiber transport of spatially entangled photons is largely unexplored yet, therefore we discuss the main complications, the interplay of intermodal dispersion and mode mixing, the influence of external stress and core deformations, and consider the pros and cons of various fiber types.
NASA Astrophysics Data System (ADS)
Kuang, Hongyan; Guo, Ying
2015-01-01
We present two deterministic entanglement purification protocols for distilling W state in polarization entanglement in a one-step fashion. The three parties can obtain a maximally entangled W polarization state with success probability 100 % from the hyper-entangled W state in multiple degrees of freedom (DOFs), and they do not require the quantum system to be entangled in polarization DOF but in spatial DOF. The former protocol is implemented with the passive linear optics, which is feasible with current experiments. The later one is implemented with cross-Kerr-nonlinearities, which can achieve higher efficiency of the entanglement transformation among different DOFs since it does not require the sophisticated single-photon detector. The present protocols are both suitable for polarization entanglement purification of multi-photon-entangled W state in quantum computation network because they need less operations and classical communications in the practical implementation.
Extremal extensions of entanglement witnesses: Finding new bound entangled states
Sengupta, R.; Arvind
2011-09-15
In this paper, we discuss extremal extensions of entanglement witnesses based on Choi's map. The constructions are based on a generalization of the Choi map, from which we construct entanglement witnesses. These extremal extensions are powerful in terms of their capacity to detect entanglement of positive under partial transpose (PPT) entangled states and lead to unearthing of entanglement of new PPT states. We also use the Cholesky-like decomposition to construct entangled states which are revealed by these extremal entanglement witnesses.
High-efficient entanglement distillation from photon loss and decoherence.
Wang, Tie-Jun; Wang, Chuan
2015-11-30
We illustrate an entanglement distillation protocol (EDP) for a mixed photon-ensemble which composed of four kinds of entangled states and vacuum states. Exploiting the linear optics and local entanglement resource (four-qubit entangled GHZ state), we design the nondemolition parity-checking and qubit amplifying (PCQA) setup for photonic polarization degree of freedom which are the key device of our scheme. With the PCQA setup, a high-fidelity entangled photon-pair system can be achieved against the transmission losses and the decoherence in noisy channels. And in the available purification range for our EDP, the fidelity of this ensemble can be improved to the maximal value through iterated operations. Compared to the conventional entanglement purification schemes, our scheme largely reduces the initialization requirement of the distilled mixed quantum system, and overcomes the difficulties posed by inherent channel losses during photon transmission. All these advantages make this scheme more useful in the practical applications of long-distance quantum communication. PMID:26698778
Distillation of photon entanglement using a plasmonic metamaterial
Asano, Motoki; Bechu, Muriel; Tame, Mark; Kaya Özdemir, Şahin; Ikuta, Rikizo; Güney, Durdu Ö.; Yamamoto, Takashi; Yang, Lan; Wegener, Martin; Imoto, Nobuyuki
2015-01-01
Plasmonics is a rapidly emerging platform for quantum state engineering with the potential for building ultra-compact and hybrid optoelectronic devices. Recent experiments have shown that despite the presence of decoherence and loss, photon statistics and entanglement can be preserved in single plasmonic systems. This preserving ability should carry over to plasmonic metamaterials, whose properties are the result of many individual plasmonic systems acting collectively, and can be used to engineer optical states of light. Here, we report an experimental demonstration of quantum state filtering, also known as entanglement distillation, using a metamaterial. We show that the metamaterial can be used to distill highly entangled states from less entangled states. As the metamaterial can be integrated with other optical components this work opens up the intriguing possibility of incorporating plasmonic metamaterials in on-chip quantum state engineering tasks. PMID:26670790
Distillation of photon entanglement using a plasmonic metamaterial.
Asano, Motoki; Bechu, Muriel; Tame, Mark; Kaya Özdemir, Şahin; Ikuta, Rikizo; Güney, Durdu Ö; Yamamoto, Takashi; Yang, Lan; Wegener, Martin; Imoto, Nobuyuki
2015-01-01
Plasmonics is a rapidly emerging platform for quantum state engineering with the potential for building ultra-compact and hybrid optoelectronic devices. Recent experiments have shown that despite the presence of decoherence and loss, photon statistics and entanglement can be preserved in single plasmonic systems. This preserving ability should carry over to plasmonic metamaterials, whose properties are the result of many individual plasmonic systems acting collectively, and can be used to engineer optical states of light. Here, we report an experimental demonstration of quantum state filtering, also known as entanglement distillation, using a metamaterial. We show that the metamaterial can be used to distill highly entangled states from less entangled states. As the metamaterial can be integrated with other optical components this work opens up the intriguing possibility of incorporating plasmonic metamaterials in on-chip quantum state engineering tasks. PMID:26670790
Cloning entangled photons to scales one can see
NASA Astrophysics Data System (ADS)
Sekatski, Pavel; Sanguinetti, Bruno; Pomarico, Enrico; Gisin, Nicolas; Simon, Christoph
2010-11-01
By amplifying photonic qubits it is possible to produce states that contain enough photons to be seen with the human eye, potentially bringing quantum effects to macroscopic scales [P. Sekatski, N. Brunner, C. Branciard, N. Gisin, and C. Simon, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.103.113601 103, 113601 (2009)]. In this paper we theoretically study quantum states obtained by amplifying one side of an entangled photon pair with different types of optical cloning machines for photonic qubits. We propose a detection scheme that involves lossy threshold detectors (such as the human eye) on the amplified side and conventional photon detectors on the other side. We show that correlations obtained with such coarse-grained measurements prove the entanglement of the initial photon pair and do not prove the entanglement of the amplified state. We emphasize the importance of the detection loophole in Bell violation experiments by giving a simple preparation technique for separable states that violate a Bell inequality without closing this loophole. Finally, we analyze the genuine entanglement of the amplified states and its robustness to losses before, during, and after amplification.
Cloning entangled photons to scales one can see
Sekatski, Pavel; Sanguinetti, Bruno; Pomarico, Enrico; Gisin, Nicolas; Simon, Christoph
2010-11-15
By amplifying photonic qubits it is possible to produce states that contain enough photons to be seen with the human eye, potentially bringing quantum effects to macroscopic scales [P. Sekatski, N. Brunner, C. Branciard, N. Gisin, and C. Simon, Phys. Rev. Lett. 103, 113601 (2009)]. In this paper we theoretically study quantum states obtained by amplifying one side of an entangled photon pair with different types of optical cloning machines for photonic qubits. We propose a detection scheme that involves lossy threshold detectors (such as the human eye) on the amplified side and conventional photon detectors on the other side. We show that correlations obtained with such coarse-grained measurements prove the entanglement of the initial photon pair and do not prove the entanglement of the amplified state. We emphasize the importance of the detection loophole in Bell violation experiments by giving a simple preparation technique for separable states that violate a Bell inequality without closing this loophole. Finally, we analyze the genuine entanglement of the amplified states and its robustness to losses before, during, and after amplification.
A heralded two-qutrit entangled state
NASA Astrophysics Data System (ADS)
Joo, Jaewoo; Rudolph, Terry; Sanders, Barry C.
2009-06-01
We propose a scheme for building a heralded two-qutrit entangled state from polarized photons. An optical circuit is presented to build the maximally entangled two-qutrit state from two heralded Bell pairs and ideal threshold detectors. Several schemes are discussed for constructing the two Bell pairs. We also show how one can produce an unbalanced two-qutrit state that could be of general purpose use in some protocols. In terms of the applications of the maximally entangled qutrit state, we mainly focus on how to use the state to demonstrate a violation of the Collins-Gisin-Linden-Massar-Popescu inequality under the restriction of measurements which can be performed using linear optical elements and photon counting. Other possible applications of the state, such as for higher dimensional quantum cryptography, teleportation and generation of heralded two-qudit states, are also briefly discussed.
Entanglement of 3000 atoms by detecting one photon
NASA Astrophysics Data System (ADS)
Vuletic, Vladan
2016-05-01
Quantum-mechanically correlated (entangled) states of many particles are of interest in quantum information, quantum computing and quantum metrology. In particular, entangled states of many particles can be used to overcome limits on measurements performed with ensembles of independent atoms (standard quantum limit). Metrologically useful entangled states of large atomic ensembles (spin squeezed states) have been experimentally realized. These states display Gaussian spin distribution functions with a non-negative Wigner quasiprobability distribution function. We report the generation of entanglement in a large atomic ensemble via an interaction with a very weak laser pulse; remarkably, the detection of a single photon prepares several thousand atoms in an entangled state. We reconstruct a negative-valued Wigner function, and verify an entanglement depth (the minimum number of mutually entangled atoms) that comprises 90% of the atomic ensemble containing 3100 atoms. Further technical improvement should allow the generation of more complex Schrödinger cat states, and of states the overcome the standard quantum limit.
Entangled absorption of a single photon with a single spin in diamond.
Kosaka, Hideo; Niikura, Naeko
2015-02-01
Quantum entanglement, a key resource for quantum information science, is inherent in a solid. It has been recently shown that entanglement between a single optical photon and a single spin qubit in a solid is generated via spontaneous emission. However, entanglement generation by measurement is rather essential for quantum operations. We here show that the physics behind the entangled emission can be time reversed to demonstrate entangled absorption mediated by an inherent spin-orbit entanglement in a single nitrogen vacancy center in diamond. Optical arbitrary spin state preparation and complete spin state tomography reveal the fidelity of the entangled absorption to be 95%. With the entangled emission and absorption of a photon, materials can be spontaneously entangled or swap their quantum state based on the quantum teleportation scheme. PMID:25699440
Single pairs of time-bin-entangled photons
NASA Astrophysics Data System (ADS)
Versteegh, Marijn A. M.; Reimer, Michael E.; van den Berg, Aafke A.; Juska, Gediminas; Dimastrodonato, Valeria; Gocalinska, Agnieszka; Pelucchi, Emanuele; Zwiller, Val
2015-09-01
Time-bin-entangled photons are ideal for long-distance quantum communication via optical fibers. Here we present a source where, even at high creation rates, each excitation pulse generates, at most, one time-bin-entangled pair. This is important for the accuracy and security of quantum communication. Our site-controlled quantum dot generates single polarization-entangled photon pairs, which are then converted, without loss of entanglement strength, into single time-bin-entangled photon pairs.
Multi-Particle Interferometry Based on Double Entangled States
NASA Technical Reports Server (NTRS)
Pittman, Todd B.; Shih, Y. H.; Strekalov, D. V.; Sergienko, A. V.; Rubin, M. H.
1996-01-01
A method for producing a 4-photon entangled state based on the use of two independent pair sources is discussed. Of particular interest is that each of the pair sources produces a two-photon state which is simultaneously entangled in both polarization and space-time variables. Performing certain measurements which exploit this double entanglement provides an opportunity for verifying the recent demonstration of nonlocality by Greenberger, Horne, and Zeilinger.
Increasing the orbital angular momentum bandwidth of entangled photons
NASA Astrophysics Data System (ADS)
Romero, Jacquiline; Giovannini, Daniele; Franke-Arnold, Sonja; Barnett, Stephen M.; Padgett, Miles J.
2012-09-01
The bandwidth of any communication system, classical or quantum, is limited by the number of orthogonal states in which the information can be encoded. Quantum key distribution systems available commercially rely on the two-dimensional polarisation state of photons. Quantum computation has also been largely designed on the basis of qubits. However, a photon is endowed with other degrees of freedom, such as orbital angular momentum (OAM). OAM is an attractive basis to be used for quantum information because it is discrete and theoretically infinite-dimensional. This promises a higher information capacity per photon which can lead to more complex quantum computation protocols and more security and robustness for quantum cryptography. Entanglement of OAM naturally arises from spontaneous parametric down-conversion (SPDC). However, any practical experiment utilising the innately high-dimensional entanglement of the orbital angular momentum (OAM) state space of photons is subject to the modal capacity of the detection system. Only a finite subset of this space is accessible experimentally. Given such a constraint, we show that the number of measured, entangled OAM modes in photon pairs generated by SPDC can be increased by tuning the phase-matching conditions in the SPDC process. We achieve this by tuning the orientation angle of the nonlinear crystal generating the entangled photons.
Spectroscopy by frequency-entangled photon pairs
Yabushita, Atsushi; Kobayashi, Takayoshi
2004-01-01
Quantum spectroscopy was performed using the frequency-entangled broadband photon pairs generated by spontaneous parametric down-conversion. An absorptive sample was placed in front of the idler photon detector, and the frequency of signal photons was resolved by a diffraction grating. The absorption spectrum of the sample was measured by counting the coincidences, and the result is in agreement with the one measured by a conventional spectrophotometer with a classical light source.
Entanglement dynamics of photon pairs emitted from quantum dots
Zou, Yang; Gong, Ming; Li, Chuan-Feng; Chen, Geng; Tang, Jian-Shun; Guo, Guang-Can
2010-06-15
We present a model that describes states of photon pairs, which have been generated by biexciton cascade decays of self-assembled quantum dots, the use of which yields a finding that agrees well with the experimental result. Furthermore, we calculate the concurrence and determine the temperature behavior associated with the so-called entanglement sudden death that prevents quantum dots emitting entangled photon pairs at raised temperatures. The relationship between the fine-structure splitting and the sudden death temperature is also provided.
Towards long-distance atom-photon entanglement.
Rosenfeld, W; Hocke, F; Henkel, F; Krug, M; Volz, J; Weber, M; Weinfurter, H
2008-12-31
We report the observation of entanglement between a single trapped atom and a single photon at remote locations. The degree of coherence of the entangled atom-photon pair is verified via appropriate local correlation measurements, after communicating the photon via an optical fiber link of 300 m length to a receiver 3.5 m apart. In addition, we measured the temporal evolution of the atomic density matrix after projecting the atom via a state measurement of the photon onto several well-defined spin states. We find that the state of the single atom dephases on a time scale of 150 micros, which represents an important step towards long-distance quantum networking with individual neutral atoms. PMID:19437626
Towards Long-Distance Atom-Photon Entanglement
Rosenfeld, W.; Hocke, F.; Henkel, F.; Krug, M.; Volz, J.; Weber, M.; Weinfurter, H.
2008-12-31
We report the observation of entanglement between a single trapped atom and a single photon at remote locations. The degree of coherence of the entangled atom-photon pair is verified via appropriate local correlation measurements, after communicating the photon via an optical fiber link of 300 m length to a receiver 3.5 m apart. In addition, we measured the temporal evolution of the atomic density matrix after projecting the atom via a state measurement of the photon onto several well-defined spin states. We find that the state of the single atom dephases on a time scale of 150 {mu}s, which represents an important step towards long-distance quantum networking with individual neutral atoms.
Quantum Discord and Entanglement of Quasi-Werner States Based on Bipartite Entangled Coherent States
NASA Astrophysics Data System (ADS)
Mishra, Manoj K.; Maurya, Ajay K.; Prakash, Hari
2016-06-01
Present work is an attempt to compare quantum discord and quantum entanglement of quasi-Werner states formed with the four bipartite entangled coherent states (ECS) used recently for quantum teleportation of a qubit encoded in superposed coherent state. Out of these, the quasi-Werner states based on maximally ECS due to its invariant nature under local operation is independent of measurement basis and mean photon numbers, while for quasi-Werner states based on non-maximally ECS, it depends upon measurement basis as well as on mean photon number. However, for large mean photon numbers since non-maximally ECS becomes almost maximally entangled therefore dependence of quantum discord for non-maximally ECS based quasi-Werner states on the measurement basis disappears.
Teleportation of entangled states without Bell-state measurement
Cardoso, Wesley B.; Baseia, B.; Avelar, A.T.; Almeida, N.G. de
2005-10-15
In a recent paper [Phys. Rev. A 70, 025803 (2004)] we presented a scheme to teleport an entanglement of zero- and one-photon states from a bimodal cavity to another one, with 100% success probability. Here, inspired by recent results in the literature, we have modified our previous proposal to teleport the same entangled state without using Bell-state measurements. For comparison, the time spent, the fidelity, and the success probability for this teleportation are considered.
Topologically robust transport of entangled photons in a 2D photonic system.
Mittal, Sunil; Orre, Venkata Vikram; Hafezi, Mohammad
2016-07-11
We theoretically study the transport of time-bin entangled photon pairs in a two-dimensional topological photonic system of coupled ring resonators. This system implements the integer quantum Hall model using a synthetic gauge field and exhibits topologically robust edge states. We show that the transport through edge states preserves temporal correlations of entangled photons whereas bulk transport does not preserve these correlations and can lead to significant unwanted temporal bunching or anti-bunching of photons. We study the effect of disorder on the quantum transport properties; while the edge transport remains robust, bulk transport is very susceptible, and in the limit of strong disorder, bulk states become localized. We show that this localization is manifested as an enhanced bunching/anti-bunching of photons. This topologically robust transport of correlations through edge states could enable robust on-chip quantum communication channels and delay lines for information encoded in temporal correlations of photons. PMID:27410836
Entangled-photon compressive ghost imaging
Zerom, Petros; Chan, Kam Wai Clifford; Howell, John C.; Boyd, Robert W.
2011-12-15
We have experimentally demonstrated high-resolution compressive ghost imaging at the single-photon level using entangled photons produced by a spontaneous parametric down-conversion source and using single-pixel detectors. For a given mean-squared error, the number of photons needed to reconstruct a two-dimensional image is found to be much smaller than that in quantum ghost imaging experiments employing a raster scan. This procedure not only shortens the data acquisition time, but also suggests a more economical use of photons for low-light-level and quantum image formation.
NASA Astrophysics Data System (ADS)
Chandra, N.; Ghosh, R.
2004-12-01
In this Rapid Communication, we show that a simple process of two-step double ionization taking place in an atom A , following the absorption of a single photon, produces a spin-entangled state of two electrons. The degree of entanglement of this state can be tuned to the desired value by selecting appropriate total spin quantum numbers of the electronic states of each of the three atomic species (i.e., A, A+ , A2+ ) participating in the process in Russell-Saunders coupling. These entangled states are readily characterized by measuring only energies of two emitted electrons, without requiring the entanglement witness, or any other such protocol.
Entanglement swapping of two arbitrarily degraded entangled states
NASA Astrophysics Data System (ADS)
Kirby, Brian T.; Santra, Siddhartha; Malinovsky, Vladimir S.; Brodsky, Michael
2016-07-01
We consider entanglement swapping, a key component of quantum network operations and entanglement distribution. Pure entangled states, which are the desired input to the swapping protocol, are typically mixed by environmental interactions, causing a reduction in their degree of entanglement. Thus an understanding of entanglement swapping with partially mixed states is of importance. Here we present a general analytical solution for entanglement swapping of arbitrary two-qubit states. Our result provides a comprehensive method for analyzing entanglement swapping in quantum networks. First, we show that the concurrence of a partially mixed state is conserved when this state is swapped with a Bell state. Then, we find upper and lower bounds on the concurrence of the state resulting from entanglement swapping for various classes of input states. Finally, we determine a general relationship between the ranks of the initial states and the rank of the final state after swapping.
NASA Astrophysics Data System (ADS)
Gupta, Manish K.; You, Chenglong; Lee, Hwang; Dowling, Jonathan P.
We study the dynamics of decoherence in an optical fiber for the case of entangled photons. Such a study will allow us to increase the physical length of fiber for the transmission of entangled photon from the sources such as SPDC. We analytically derive the model for decoherence of entangled state photons in a single-mode fiber. We also show that entanglement lifetime can be increased with open loop control technique called dynamical decoupling.
Improving entanglement concentration of Gaussian states by local displacements
Fiurasek, Jaromir
2011-07-15
We investigate entanglement concentration of continuous-variable Gaussian states by local single-photon subtractions combined with local Gaussian operations. We first analyze the local squeezing-enhanced entanglement-concentration protocol proposed very recently by Zhang and van Loock [arXiv:1103.4500] and discuss the mechanism by which local squeezing before photon subtraction helps to increase the entanglement of the output state of the protocol. We next show that a similar entanglement improvement can be achieved by using local coherent displacements instead of single-mode squeezing.
Entanglement under restricted operations: Analogy to mixed-state entanglement
Bartlett, Stephen D.; Doherty, Andrew C.; Spekkens, Robert W.; Wiseman, H. M.
2006-02-15
We show that the classification of bipartite pure entangled states when local quantum operations are restricted yields a structure that is analogous in many respects to that of mixed-state entanglement. Specifically, we develop this analogy by restricting operations through local superselection rules, and show that such exotic phenomena as bound entanglement and activation arise using pure states in this setting. This analogy aids in resolving several conceptual puzzles in the study of entanglement under restricted operations. In particular, we demonstrate that several types of quantum optical states that possess confusing entanglement properties are analogous to bound entangled states. Also, the classification of pure-state entanglement under restricted operations can be much simpler than for mixed-state entanglement. For instance, in the case of local Abelian superselection rules all questions concerning distillability can be resolved.
Momentum entanglement and disentanglement between an atom and a photon
Guo Rui; Guo Hong
2007-07-15
With the quantum interference between two transition pathways, we demonstrate a scheme to coherently control the momentum entanglement between a single atom and a single photon. The unavoidable disentanglement is also studied from the first principle, which indicates that the stably entangled atom-photon system with superhigh degree of entanglement may be realized with this scheme under certain conditions.
Are all maximally entangled states pure?
NASA Astrophysics Data System (ADS)
Cavalcanti, D.; Brandão, F. G. S. L.; Terra Cunha, M. O.
2005-10-01
We study if all maximally entangled states are pure through several entanglement monotones. In the bipartite case, we find that the same conditions which lead to the uniqueness of the entropy of entanglement as a measure of entanglement exclude the existence of maximally mixed entangled states. In the multipartite scenario, our conclusions allow us to generalize the idea of the monogamy of entanglement: we establish the polygamy of entanglement, expressing that if a general state is maximally entangled with respect to some kind of multipartite entanglement, then it is necessarily factorized of any other system.
Are all maximally entangled states pure?
Cavalcanti, D.; Brandao, F.G.S.L.; Terra Cunha, M.O.
2005-10-15
We study if all maximally entangled states are pure through several entanglement monotones. In the bipartite case, we find that the same conditions which lead to the uniqueness of the entropy of entanglement as a measure of entanglement exclude the existence of maximally mixed entangled states. In the multipartite scenario, our conclusions allow us to generalize the idea of the monogamy of entanglement: we establish the polygamy of entanglement, expressing that if a general state is maximally entangled with respect to some kind of multipartite entanglement, then it is necessarily factorized of any other system.
Local cloning of entangled states
Gheorghiu, Vlad; Yu Li; Cohen, Scott M.
2010-08-15
We investigate the conditions under which a set S of pure bipartite quantum states on a DxD system can be locally cloned deterministically by separable operations, when at least one of the states is full Schmidt rank. We allow for the possibility of cloning using a resource state that is less than maximally entangled. Our results include that: (i) all states in S must be full Schmidt rank and equally entangled under the G-concurrence measure, and (ii) the set S can be extended to a larger clonable set generated by a finite group G of order |G|=N, the number of states in the larger set. It is then shown that any local cloning apparatus is capable of cloning a number of states that divides D exactly. We provide a complete solution for two central problems in local cloning, giving necessary and sufficient conditions for (i) when a set of maximally entangled states can be locally cloned, valid for all D; and (ii) local cloning of entangled qubit states with nonvanishing entanglement. In both of these cases, we show that a maximally entangled resource is necessary and sufficient, and the states must be related to each other by local unitary 'shift' operations. These shifts are determined by the group structure, so need not be simple cyclic permutations. Assuming this shifted form and partially entangled states, then in D=3 we show that a maximally entangled resource is again necessary and sufficient, while for higher-dimensional systems, we find that the resource state must be strictly more entangled than the states in S. All of our necessary conditions for separable operations are also necessary conditions for local operations and classical communication (LOCC), since the latter is a proper subset of the former. In fact, all our results hold for LOCC, as our sufficient conditions are demonstrated for LOCC, directly.
Entanglement for All Quantum States
ERIC Educational Resources Information Center
de la Torre, A. C.; Goyeneche, D.; Leitao, L.
2010-01-01
It is shown that a state that is factorizable in the Hilbert space corresponding to some choice of degrees of freedom becomes entangled for a different choice of degrees of freedom. Therefore, entanglement is not a special case but is ubiquitous in quantum systems. Simple examples are calculated and a general proof is provided. The physical…
Wang, Chuan; Zhang, Yong; Zhang, Ru
2011-12-01
We theoretically investigate an entanglement purification protocol with photon and electron hybrid entangled state resorting to quantum-dot spin and microcavity coupled system. The present system is used to construct the parity check gate which allows a quantum non-demolition measurement on the spin parity. The cavity-spin coupled system provides a novel experimental platform of quantum information processing with photon and solid qubit. PMID:22273961
NASA Astrophysics Data System (ADS)
Chen, Hui-Na; Liu, Jin-Ming
2009-10-01
We present an optical scheme to almost completely teleport a bipartite entangled coherent state using a four-partite cluster-type entangled coherent state as quantum channel. The scheme is based on optical elements such as beam splitters, phase shifters, and photon detectors. We also obtain the average fidelity of the teleportation process. It is shown that the average fidelity is quite close to unity if the mean photon number of the coherent state is not too small.
Observation of Entanglement of a Single Photon with a Trapped Atom
Volz, Juergen; Weber, Markus; Schlenk, Daniel; Rosenfeld, Wenjamin; Vrana, Johannes; Saucke, Karen; Kurtsiefer, Christian; Weinfurter, Harald
2006-01-27
We report the observation of entanglement between a single trapped atom and a single photon at a wavelength suitable for low-loss communication over large distances, thereby achieving a crucial step towards long range quantum networks. To verify the entanglement, we introduce a single atom state analysis. This technique is used for full state tomography of the atom-photon qubit pair. The detection efficiency and the entanglement fidelity are high enough to allow in a next step the generation of entangled atoms at large distances, ready for a final loophole-free Bell experiment.
Entanglement manipulation by atomic position in photonic crystals
NASA Astrophysics Data System (ADS)
Wu, Yunan; Wang, Jing; Mo, Minglun; Zhang, Hanzhuang
2015-12-01
We consider two entangled atoms, each of which is embedded in a coherent photonic-band-gap (PBG) reservoir. The effect of the atomic embedded position on the entanglement of the two-atom system is studied. We find that the embedded position of the atom plays an important role in the dynamics of entanglement. The variation of the atomic position can lead to the shift between entanglement sudden death and the entanglement trapping. We also consider the entanglement transfer between different subsystems. Our results could be applied to manipulation of entanglement in nanostructured materials.
Superiority of photon subtraction to addition for entanglement in a multimode squeezed vacuum
NASA Astrophysics Data System (ADS)
Das, Tamoghna; Prabhu, R.; SenDe, Aditi; Sen, Ujjwal
2016-05-01
We investigate the entanglement patterns of photon-added and photon-subtracted four-mode squeezed vacuum states. Entanglements in different scenarios are analyzed by varying the number of photons added or subtracted in certain modes, which are referred to as the "player" modes, the others being "spectators." We find that the photon-subtracted state can give us higher entanglement than the photon-added state which is in contrast to the two-mode situation. We also study the logarithmic negativity of the two-mode reduced density matrix obtained from the four-mode state which again shows that the state after photon subtraction can possess higher entanglement than that of the photon-added state, and we then compare it to that of the two-mode squeezed vacuum state. Moreover, we examine the non-Gaussianity of the photon-added and photon-subtracted states to find that the rich features provided by entanglement cannot be captured by the measure of nonclassicality.
Entanglement and quantum teleportation via decohered tripartite entangled states
Metwally, N.
2014-12-15
The entanglement behavior of two classes of multi-qubit system, GHZ and GHZ like states passing through a generalized amplitude damping channel is discussed. Despite this channel causes degradation of the entangled properties and consequently their abilities to perform quantum teleportation, one can always improve the lower values of the entanglement and the fidelity of the teleported state by controlling on Bell measurements, analyzer angle and channel’s strength. Using GHZ-like state within a generalized amplitude damping channel is much better than using the normal GHZ-state, where the decay rate of entanglement and the fidelity of the teleported states are smaller than those depicted for GHZ state.
Entangled states in quantum mechanics
NASA Astrophysics Data System (ADS)
Ruža, Jānis
2010-01-01
In some circles of quantum physicists, a view is maintained that the nonseparability of quantum systems-i.e., the entanglement-is a characteristic feature of quantum mechanics. According to this view, the entanglement plays a crucial role in the solution of quantum measurement problem, the origin of the “classicality” from the quantum physics, the explanation of the EPR paradox by a nonlocal character of the quantum world. Besides, the entanglement is regarded as a cornerstone of such modern disciplines as quantum computation, quantum cryptography, quantum information, etc. At the same time, entangled states are well known and widely used in various physics areas. In particular, this notion is widely used in nuclear, atomic, molecular, solid state physics, in scattering and decay theories as well as in other disciplines, where one has to deal with many-body quantum systems. One of the methods, how to construct the basis states of a composite many-body quantum system, is the so-called genealogical decomposition method. Genealogical decomposition allows one to construct recurrently by particle number the basis states of a composite quantum system from the basis states of its forming subsystems. These coupled states have a structure typical for entangled states. If a composite system is stable, the internal structure of its forming basis states does not manifest itself in measurements. However, if a composite system is unstable and decays onto its forming subsystems, then the measurables are the quantum numbers, associated with these subsystems. In such a case, the entangled state has a dynamical origin, determined by the Hamiltonian of the corresponding decay process. Possible correlations between the quantum numbers of resulting subsystems are determined by the symmetries-conservation laws of corresponding dynamical variables, and not by the quantum entanglement feature.
Entanglement for all quantum states
NASA Astrophysics Data System (ADS)
de la Torre, A. C.; Goyeneche, D.; Leitao, L.
2010-03-01
It is shown that a state that is factorizable in the Hilbert space corresponding to some choice of degrees of freedom becomes entangled for a different choice of degrees of freedom. Therefore, entanglement is not a special case but is ubiquitous in quantum systems. Simple examples are calculated and a general proof is provided. The physical relevance of the change of tensor product structure is mentioned.
Mixtures of maximally entangled pure states
NASA Astrophysics Data System (ADS)
Flores, M. M.; Galapon, E. A.
2016-09-01
We study the conditions when mixtures of maximally entangled pure states remain entangled. We found that the resulting mixed state remains entangled when the number of entangled pure states to be mixed is less than or equal to the dimension of the pure states. For the latter case of mixing a number of pure states equal to their dimension, we found that the mixed state is entangled provided that the entangled pure states to be mixed are not equally weighted. We also found that one can restrict the set of pure states that one can mix from in order to ensure that the resulting mixed state is genuinely entangled. Also, we demonstrate how these results could be applied as a way to detect entanglement in mixtures of the entangled pure states with noise.
Two-photon entanglement in multiqubit bidirectional-waveguide QED
NASA Astrophysics Data System (ADS)
Mirza, Imran M.; Schotland, John C.
2016-07-01
We study entanglement generation and control in bidirectional-waveguide QED driven by a two-photon Gaussian wave packet. In particular, we focus on how increasing the number of qubits affects the overall average pairwise entanglement in the system. We also investigate how the presence of a second photon can introduce nonlinearities, thereby manipulating the generated entanglement. In addition, we show that, through the introduction of chirality and small decay rates, entanglement can be stored and enhanced up to factors of 2 and 3, respectively. Finally, we analyze the influence of finite detunings and time-delays on the generated entanglement.
Maximally entangled mixed-state generation via local operations
Aiello, A.; Puentes, G.; Voigt, D.; Woerdman, J. P.
2007-06-15
We present a general theoretical method to generate maximally entangled mixed states of a pair of photons initially prepared in the singlet polarization state. This method requires only local operations upon a single photon of the pair and exploits spatial degrees of freedom to induce decoherence. We report also experimental confirmation of these theoretical results.
Inseparability of photon-added Gaussian states
Li Hongrong; Li Fuli; Zhu Shiyao
2007-06-15
The inseparability of photon-added Gaussian states which are generated from two-mode Gaussian states by adding photons is investigated. According to the established inseparability conditions [New J. Phys. 7, 211 (2005); Phys. Rev. Lett. 96, 050503 (2006)], we find that even if a two-mode Gaussian state is separable, the photon-added Gaussian state becomes entangled when the purity of the Gaussian state is larger than a certain value. The lower bound of entanglement of symmetric photon-added Gaussian states is derived. The result shows that entanglement of the photon-added Gaussian states is involved with high-order moment correlations. We find that fidelity of teleporting coherent states cannot be raised by employing the photon-added Gaussian states as a quantum channel of teleportation.
Entangled Terahertz photon pair emitting diode with a HgTe quantum dot
NASA Astrophysics Data System (ADS)
Shi, Li-Kun; Chang, Kai; Sun, Chang-Pu
We propose an experimentally feasible scheme for generating entangled terahertz photons in topological insulator quantum dots (TIQDs). We demonstrate theoretically that in TIQDs with disorders and irregular shapes: 1) the fine structure splitting, which is the obstacle to produce entangled photons in conventional semiconductor quantum dots, is inherently absent for one-dimensional massless excitons due to the time-reversal symmetry; 2) the selection rules obey winding number conservation instead of the conventional angular momentum conservation between edge states with a linear dispersion. With these two advantages, the entanglement of the emitted photons during the cascade in our scheme is robust against unavoidable disorders and morphology fluctuations of the TIQD.
Entanglement of a scattered single photon with an atom
Guo Rui; Guo Hong
2006-01-15
A single photon which is initially uncorrelated with an atom will evolve to be entangled with the atom on their continuous kinetic variables in the process of resonant scattering. We find the relations between the entanglement and their physical control parameters, which indicates that high entanglement can be reached by broadening the scale of the atomic wave or squeezing the linewidth of the incident single-photon pulse.
Deterministic Polarization Entanglement Purification of Cluster State in Multiple Degrees of Freedom
NASA Astrophysics Data System (ADS)
Zhao, Zhisheng; Guo, Ying; Shi, Ronghua; Huang, Dazu
2015-04-01
We propose a deterministic polarization entanglement purification protocol (EPP) towards four-photon Cluster state, resorting to linear optic technology and multiple degrees of freedom (DOF). All of the participants can jointedly distill the maximally entangled states from the mixed states after transmission through a noisy channel with success probability 100 % in principle. The proposed protocol can be employed for the purification of any other multi-partite maximally entangled states, such as the Greenberger-Horne-Zeilinger (GHZ) state and W state, which is actually an universally feasible entanglement purification scheme towards multi-photon entanglement system.
Position-momentum-entangled photon pairs in nonlinear waveguides and transmission lines
NASA Astrophysics Data System (ADS)
Sherkunov, Y.; Whittaker, David M.; Fal'ko, Vladimir
2016-04-01
We analyze the correlation properties of light in nonlinear waveguides and transmission lines, predict the position-momentum realization of the Einstein-Podolsky-Rosen paradox for photon pairs in Kerr-type nonlinear photonic circuits, and we show how two-photon entangled states can be generated and detected.
Entanglement and Squeezing in Solid State Circuits
Wen Yihuo; Gui Lulong
2008-11-07
We investigate the dynamics of a system consisting of a Cooper-pair box and two superconducting transmission line resonators. There exist both linear and nonlinear interactions in such a system. We show that single-photon entanglement state can be generated in a simple way in the linear interaction regime. In nonlinear interaction regime, we derive the Hamiltonian of degenerate three-wave mixing and propose a scheme for generating squeezed state of microwave using the three-wave mixing in solid state circuits. In the following, we design a system for generating squeezed states of nanamechanical resonator.
CW-pumped telecom band polarization entangled photon pair generation in a Sagnac interferometer
NASA Astrophysics Data System (ADS)
Li, Yan; Zhou, Zhi-Yuan; Ding, Dong-Sheng; Shi, Bao-Sen
2015-11-01
A polarization entangled photon pair source is widely used in many quantum information processing applications such as teleportation, quantum swapping, quantum computation and high precision quantum metrology. Here, we report on the generation of a continuous-wave pumped degenerated 1550 nm polarization entangled photon pair source at telecom wavelength using a type-II phase-matched periodically poled KTiOPO4 crystal in a Sagnac interferometer. Hong-Ou-Mandel-type interference measurement shows the photon bandwidth of 2.4 nm. High quality of entanglement is verified by various kinds of measurements, for example two-photon interference fringes, Bell inequality and quantum states tomography. The wavelength of photons can be tuned over a broad range by changing the temperature of crystal or pump power without losing the quality of entanglement. This source will be useful for building up long-distance quantum networks.
NASA Astrophysics Data System (ADS)
Gupta, Manish Kumar; You, Chenglong; Dowling, Jonathan P.; Lee, Hwang
2016-05-01
We study the dynamics of decoherence in an optical fiber for the case of entangled photons. Such a study will allow us to increase the physical length of fiber for transmission of entangled photon from the sources such as SPDC. We analytically derive the model for Decoherence of entangled state photons in a single-mode fiber. We also show that entanglement lifetime can be increased for Bell state and Werner state with open loop control technique called Dynamical decoupling. The authors would like to acknowledge support from the Air Force Office of Scientific Research, the Army Research Office, the National Science Foundation and the Northrop Grumman Corporation.
Generation of energy-entangled W states via parametric fluorescence in integrated devices
NASA Astrophysics Data System (ADS)
Menotti, M.; Maccone, L.; Sipe, J. E.; Liscidini, M.
2016-07-01
Tripartite entangled states, such as Greenberger-Horne-Zeilinger and W states, are typically generated by manipulating two pairs of polarization-entangled photons in bulk optics. Here we propose a scheme to generate W states that are entangled in the energy degree of freedom in an integrated optical circuit. Our approach employs photon pairs generated by spontaneous four-wave mixing in a microring resonator. We also present a feasible procedure for demonstrating the generation of such a state, and we compare polarization-entangled and energy-entangled schemes for the preparation of W states.
Highly entangled states with almost no secrecy.
Christandl, Matthias; Schuch, Norbert; Winter, Andreas
2010-06-18
In this Letter we illuminate the relation between entanglement and secrecy by providing the first example of a quantum state that is highly entangled, but from which, nevertheless, almost no secrecy can be extracted. More precisely, we provide two bounds on the bipartite entanglement of the totally antisymmetric state in dimension d×d. First, we show that the amount of secrecy that can be extracted from the state is low; to be precise it is bounded by O(1/d). Second, we show that the state is highly entangled in the sense that we need a large amount of singlets to create the state: entanglement cost is larger than a constant, independent of d. In order to obtain our results we use representation theory, linear programming, and the entanglement measure known as squashed entanglement. Our findings also clarify the relation between the squashed entanglement and the relative entropy of entanglement. PMID:20867285
Projection of two biphoton qutrits onto a maximally entangled state.
Halevy, A; Megidish, E; Shacham, T; Dovrat, L; Eisenberg, H S
2011-04-01
Bell state measurements, in which two quantum bits are projected onto a maximally entangled state, are an essential component of quantum information science. We propose and experimentally demonstrate the projection of two quantum systems with three states (qutrits) onto a generalized maximally entangled state. Each qutrit is represented by the polarization of a pair of indistinguishable photons-a biphoton. The projection is a joint measurement on both biphotons using standard linear optics elements. This demonstration enables the realization of quantum information protocols with qutrits, such as teleportation and entanglement swapping. PMID:21517363
A new optical scheme for teleportation of entangled coherent state
NASA Astrophysics Data System (ADS)
Liao, Jie-Qiao; Kuang, Le-Man
2006-10-01
We propose a nearly perfect optical scheme for the quantum teleportation of entangled coherent states using optical devices such as nonlinear Kerr media, beam splitters, phase shifters, and photon detectors. Different from those previous schemes, our scheme needs only ``yes'' or `no' measurements of the photon number of the related modes, i.e. nonzero- and zero-photon measurements, while in previous schemes one has to exactly identify the even or odd parity character of the photon numbers detected by detectors.
Twisted photon entanglement through turbulent air across Vienna
Krenn, Mario; Handsteiner, Johannes; Fink, Matthias; Fickler, Robert; Zeilinger, Anton
2015-01-01
Photons with a twisted phase front can carry a discrete, in principle, unbounded amount of orbital angular momentum (OAM). The large state space allows for complex types of entanglement, interesting both for quantum communication and for fundamental tests of quantum theory. However, the distribution of such entangled states over large distances was thought to be infeasible due to influence of atmospheric turbulence, indicating a serious limitation on their usefulness. Here we show that it is possible to distribute quantum entanglement encoded in OAM over a turbulent intracity link of 3 km. We confirm quantum entanglement of the first two higher-order levels (with OAM=± 1ℏ and ± 2ℏ). They correspond to four additional quantum channels orthogonal to all that have been used in long-distance quantum experiments so far. Therefore, a promising application would be quantum communication with a large alphabet. We also demonstrate that our link allows access to up to 11 quantum channels of OAM. The restrictive factors toward higher numbers are technical limitations that can be circumvented with readily available technologies. PMID:26578763
Twisted photon entanglement through turbulent air across Vienna.
Krenn, Mario; Handsteiner, Johannes; Fink, Matthias; Fickler, Robert; Zeilinger, Anton
2015-11-17
Photons with a twisted phase front can carry a discrete, in principle, unbounded amount of orbital angular momentum (OAM). The large state space allows for complex types of entanglement, interesting both for quantum communication and for fundamental tests of quantum theory. However, the distribution of such entangled states over large distances was thought to be infeasible due to influence of atmospheric turbulence, indicating a serious limitation on their usefulness. Here we show that it is possible to distribute quantum entanglement encoded in OAM over a turbulent intracity link of 3 km. We confirm quantum entanglement of the first two higher-order levels (with OAM=± 1ħ and ± 2ħ). They correspond to four additional quantum channels orthogonal to all that have been used in long-distance quantum experiments so far. Therefore, a promising application would be quantum communication with a large alphabet. We also demonstrate that our link allows access to up to 11 quantum channels of OAM. The restrictive factors toward higher numbers are technical limitations that can be circumvented with readily available technologies. PMID:26578763
Remote macroscopic entanglement on a photonic crystal architecture
NASA Astrophysics Data System (ADS)
Flayac, H.; Minkov, M.; Savona, V.
2015-10-01
The outstanding progress in nanostructure fabrication and cooling technologies allows what was unthinkable a few decades ago: bringing single-mode mechanical vibrations to the quantum regime. The coupling between photon and phonon excitations is a natural source of nonclassical states of light and mechanical vibrations, and its study within the field of cavity optomechanics is developing lightning fast. Photonic crystal cavities are highly integrable architectures that have demonstrated the strongest optomechanical coupling to date and should therefore play a central role for such hybrid quantum-state engineering. In this context, we propose a realistic heralding protocol for the on-chip preparation of remotely entangled mechanical states, relying on the state-of-the-art optomechanical parameters of a silicon-based nanobeam structure. Pulsed sideband excitation of a Stokes process, combined with single-photon detection, allows the writing of a delocalized mechanical Bell state in the system, signatures of which can then be read out in the optical field. A measure of entanglement in this protocol is provided by the visibility of a characteristic quantum interference pattern in the emitted light.
Position-momentum Bell nonlocality with entangled photon pairs
NASA Astrophysics Data System (ADS)
Schneeloch, James; Knarr, Samuel H.; Lum, Daniel J.; Howell, John C.
2016-01-01
Witnessing continuous-variable Bell nonlocality is a challenging endeavor, but Bell himself showed how one might demonstrate this nonlocality. Although Bell nearly showed a violation using the Clauser-Horne-Shimony-Holt (CHSH) inequality with sign-binned position-momentum statistics of entangled pairs of particles measured at different times, his demonstration is subject to approximations not realizable in a laboratory setting. Moreover, he does not give a quantitative estimation of the maximum achievable violation for the wave function he considers. In this article, we show how his strategy can be reimagined using the transverse positions and momenta of entangled photon pairs measured at different propagation distances, and we find that the maximum achievable violation for the state he considers is actually very small relative to the upper limit of 2 √{2 } . Although Bell's wave function does not produce a large violation of the CHSH inequality, other states may yet do so.
Efficient and pure femtosecond-pulse-length source of polarization-entangled photons.
Weston, Morgan M; Chrzanowski, Helen M; Wollmann, Sabine; Boston, Allen; Ho, Joseph; Shalm, Lynden K; Verma, Varun B; Allman, Michael S; Nam, Sae Woo; Patel, Raj B; Slussarenko, Sergei; Pryde, Geoff J
2016-05-16
We present a source of polarization entangled photon pairs based on spontaneous parametric downconversion engineered for frequency uncorrelated telecom photon generation. Our source provides photon pairs that display, simultaneously, the key properties for high-performance quantum information and fundamental quantum science tasks. Specifically, the source provides for high heralding efficiency, high quantum state purity and high entangled state fidelity at the same time. Among different tests we apply to our source we observe almost perfect non-classical interference between photons from independent sources with a visibility of (100 ± 5)%. PMID:27409907
Entanglement transfer from electrons to photons in quantum dots: an open quantum system approach.
Budich, Jan C; Trauzettel, Björn
2010-07-01
We investigate entanglement transfer from a system of two spin-entangled electron-hole pairs, each placed in a separate single mode cavity, to the photons emitted due to cavity leakage. Dipole selection rules and a splitting between the light hole and the heavy hole subbands are the crucial ingredients establishing a one-to-one correspondence between electron spins and circular photon polarizations. To account for the measurement of the photons as well as dephasing effects, we choose a stochastic Schrödinger equation and a conditional master equation approach, respectively. The influence of interactions with the environment as well as asymmetries in the coherent couplings on the photon entanglement is analysed for two concrete measurement schemes. The first one is designed to violate the Clauser-Horne-Shimony-Holt (CHSH) inequality, while the second one employs the visibility of interference fringes to prove the entanglement of the photons. Because of the spatial separation of the entangled electronic system over two quantum dots, a successful verification of entangled photons emitted by this system would imply the detection of nonlocal spin entanglement of massive particles in a solid state structure. PMID:20571188
Generation of entangled coherent-squeezed states: their entanglement and nonclassical properties
NASA Astrophysics Data System (ADS)
Karimi, A.; Tavassoly, M. K.
2016-04-01
In this paper, after a brief review on the coherent states and squeezed states, we introduce two classes of entangled coherent-squeezed states. Next, in order to generate the introduced entangled states, we present a theoretical scheme based on the resonant atom-field interaction. In the proposed model, a \\varLambda -type three-level atom interacts with a two-mode quantized field in the presence of two strong classical fields. Then, we study the amount of entanglement of the generated entangled states using the concurrence and linear entropy. Moreover, we evaluate a few of their nonclassical properties such as photon statistics, second-order correlation function, and quadrature squeezing and establish their nonclassicality features.
Enhanced Type-I Polarization-Entangled Photons Using CW-Diode Laser
NASA Astrophysics Data System (ADS)
Hegazi, Salem; Mansour, Mohy S.; El Nadi, Lotfia
2013-03-01
We used two type-I BBO crystals pumped by violet cw-diode laser of relatively wide bandwidth to produce entangled photons of considerable degree of purity. While diode laser serves the mobility and the low-cost of the entangled photons source, suitable temporal compensation is required in this case to recover the purity of the state. We studied also effect of tilting the two-crystal set on overlapping of the SPDC cones.
Two-Photon Entanglement and EPR Experiments Using Type-2 Spontaneous Parametric Down Conversion
NASA Technical Reports Server (NTRS)
Sergienko, A. V.; Shih, Y. H.; Pittman, T. B.; Rubin, M. H.
1996-01-01
Simultaneous entanglement in spin and space-time of a two-photon quantum state generated in type-2 spontaneous parametric down-conversion is demonstrated by the observation of quantum interference with 98% visibility in a simple beam-splitter (Hanburry Brown-Twiss) anticorrelation experiment. The nonlocal cancellation of two-photon probability amplitudes as a result of this double entanglement allows us to demonstrate two different types of Bell's inequality violations in one experimental setup.
Exploration of multiphoton entangled states by using weak nonlinearities
NASA Astrophysics Data System (ADS)
He, Ying-Qiu; Ding, Dong; Yan, Feng-Li; Gao, Ting
2016-01-01
We propose a fruitful scheme for exploring multiphoton entangled states based on linear optics and weak nonlinearities. Compared with the previous schemes the present method is more feasible because there are only small phase shifts instead of a series of related functions of photon numbers in the process of interaction with Kerr nonlinearities. In the absence of decoherence we analyze the error probabilities induced by homodyne measurement and show that the maximal error probability can be made small enough even when the number of photons is large. This implies that the present scheme is quite tractable and it is possible to produce entangled states involving a large number of photons.
Exploration of multiphoton entangled states by using weak nonlinearities
He, Ying-Qiu; Ding, Dong; Yan, Feng-Li; Gao, Ting
2016-01-01
We propose a fruitful scheme for exploring multiphoton entangled states based on linear optics and weak nonlinearities. Compared with the previous schemes the present method is more feasible because there are only small phase shifts instead of a series of related functions of photon numbers in the process of interaction with Kerr nonlinearities. In the absence of decoherence we analyze the error probabilities induced by homodyne measurement and show that the maximal error probability can be made small enough even when the number of photons is large. This implies that the present scheme is quite tractable and it is possible to produce entangled states involving a large number of photons. PMID:26751044
Experimental position-time entanglement with degenerate single photons
Bennett, A. J.; Gevaux, D. G.; Yuan, Z. L.; Shields, A. J.; Atkinson, P.; Ritchie, D. A.
2008-02-15
We report an experiment in which two-photon interference occurs between degenerate single photons that never meet. The two photons travel in opposite directions through our fiber-optic interferometer and interference occurs when the photons reach two different, spatially separated, two-by-two couplers at the same time. We show that this experiment is analogous to the conventional Franson-type entanglement experiment where the photons are entangled in position and time. We measure wave-function overlaps for the two photons as high as 94{+-}3%.
Ikuta, Rikizo; Kato, Hiroshi; Kusaka, Yoshiaki; Yamamoto, Takashi; Imoto, Nobuyuki; Miki, Shigehito; Yamashita, Taro; Terai, Hirotaka; Wang, Zhen; Fujiwara, Mikio; Sasaki, Masahide; Koashi, Masato
2014-12-04
We experimentally demonstrate a high-fidelity visible-to-telecommunicationwavelength conversion of a photon by using a solid-state-based difference frequency generation. In the experiment, one half of a pico-second visible entangled photon pair at 780 nm is converted to a 1522-nm photon. Using superconducting single-photon detectors with low dark count rates and small timing jitters, we observed a fidelity of 0.93±0.04 after the wavelength conversion.
Distillation and purification of symmetric entangled Gaussian states
Fiurasek, Jaromir
2010-10-15
We propose an entanglement distillation and purification scheme for symmetric two-mode entangled Gaussian states that allows to asymptotically extract a pure entangled Gaussian state from any input entangled symmetric Gaussian state. The proposed scheme is a modified and extended version of the entanglement distillation protocol originally developed by Browne et al. [Phys. Rev. A 67, 062320 (2003)]. A key feature of the present protocol is that it utilizes a two-copy degaussification procedure that involves a Mach-Zehnder interferometer with single-mode non-Gaussian filters inserted in its two arms. The required non-Gaussian filtering operations can be implemented by coherently combining two sequences of single-photon addition and subtraction operations.
Entanglement with negative Wigner function of three thousand atoms heralded by one photon
NASA Astrophysics Data System (ADS)
McConnell, Robert; Zhang, Hao; Hu, Jiazhong; Ćuk, Senka; Vuletić, Vladan
2016-06-01
Quantum-mechanically correlated (entangled) states of many particles are of interest in quantum information, quantum computing and quantum metrology. Metrologically useful entangled states of large atomic ensembles have been experimentally realized [1, 2, 3, 4, 5, 6, 7, 8, 9, 10], but these states display Gaussian spin distribution functions with a non-negative Wigner function. Non-Gaussian entangled states have been produced in small ensembles of ions [11, 12], and very recently in large atomic ensembles [13, 14, 15]. Here, we generate entanglement in a large atomic ensemble via the interaction with a very weak laser pulse; remarkably, the detection of a single photon prepares several thousand atoms in an entangled state. We reconstruct a negative-valued Wigner function, an important hallmark of nonclassicality, and verify an entanglement depth (minimum number of mutually entangled atoms) of 2910 ± 190 out of 3100 atoms. Attaining such a negative Wigner function and the mutual entanglement of virtually all atoms is unprecedented for an ensemble containing more than a few particles. While the achieved purity of the state is slightly below the threshold for entanglement-induced metrological gain, further technical improvement should allow the generation of states that surpass this threshold, and of more complex Schrödinger cat states for quantum metrology and information processing.
Direct measurement of nonlocal entanglement of two-qubit spin quantum states.
Cheng, Liu-Yong; Yang, Guo-Hui; Guo, Qi; Wang, Hong-Fu; Zhang, Shou
2016-01-01
We propose efficient schemes of direct concurrence measurement for two-qubit spin and photon-polarization entangled states via the interaction between single-photon pulses and nitrogen-vacancy (NV) centers in diamond embedded in optical microcavities. For different entangled-state types, diversified quantum devices and operations are designed accordingly. The initial unknown entangled states are possessed by two spatially separated participants, and nonlocal spin (polarization) entanglement can be measured with the aid of detection probabilities of photon (NV center) states. This non-demolition entanglement measurement manner makes initial entangled particle-pair avoid complete annihilation but evolve into corresponding maximally entangled states. Moreover, joint inter-qubit operation or global qubit readout is not required for the presented schemes and the final analyses inform favorable performance under the current parameters conditions in laboratory. The unique advantages of spin qubits assure our schemes wide potential applications in spin-based solid quantum information and computation. PMID:26778340
Direct measurement of nonlocal entanglement of two-qubit spin quantum states
NASA Astrophysics Data System (ADS)
Cheng, Liu-Yong; Yang, Guo-Hui; Guo, Qi; Wang, Hong-Fu; Zhang, Shou
2016-01-01
We propose efficient schemes of direct concurrence measurement for two-qubit spin and photon-polarization entangled states via the interaction between single-photon pulses and nitrogen-vacancy (NV) centers in diamond embedded in optical microcavities. For different entangled-state types, diversified quantum devices and operations are designed accordingly. The initial unknown entangled states are possessed by two spatially separated participants, and nonlocal spin (polarization) entanglement can be measured with the aid of detection probabilities of photon (NV center) states. This non-demolition entanglement measurement manner makes initial entangled particle-pair avoid complete annihilation but evolve into corresponding maximally entangled states. Moreover, joint inter-qubit operation or global qubit readout is not required for the presented schemes and the final analyses inform favorable performance under the current parameters conditions in laboratory. The unique advantages of spin qubits assure our schemes wide potential applications in spin-based solid quantum information and computation.
Direct measurement of nonlocal entanglement of two-qubit spin quantum states
Cheng, Liu-Yong; Yang, Guo-Hui; Guo, Qi; Wang, Hong-Fu; Zhang, Shou
2016-01-01
We propose efficient schemes of direct concurrence measurement for two-qubit spin and photon-polarization entangled states via the interaction between single-photon pulses and nitrogen-vacancy (NV) centers in diamond embedded in optical microcavities. For different entangled-state types, diversified quantum devices and operations are designed accordingly. The initial unknown entangled states are possessed by two spatially separated participants, and nonlocal spin (polarization) entanglement can be measured with the aid of detection probabilities of photon (NV center) states. This non-demolition entanglement measurement manner makes initial entangled particle-pair avoid complete annihilation but evolve into corresponding maximally entangled states. Moreover, joint inter-qubit operation or global qubit readout is not required for the presented schemes and the final analyses inform favorable performance under the current parameters conditions in laboratory. The unique advantages of spin qubits assure our schemes wide potential applications in spin-based solid quantum information and computation. PMID:26778340
Dynamical generation of maximally entangled states in two identical cavities
Alexanian, Moorad
2011-11-15
The generation of entanglement between two identical coupled cavities, each containing a single three-level atom, is studied when the cavities exchange two coherent photons and are in the N=2,4 manifolds, where N represents the maximum number of photons possible in either cavity. The atom-photon state of each cavity is described by a qutrit for N=2 and a five-dimensional qudit for N=4. However, the conservation of the total value of N for the interacting two-cavity system limits the total number of states to only 4 states for N=2 and 8 states for N=4, rather than the usual 9 for two qutrits and 25 for two five-dimensional qudits. In the N=2 manifold, two-qutrit states dynamically generate four maximally entangled Bell states from initially unentangled states. In the N=4 manifold, two-qudit states dynamically generate maximally entangled states involving three or four states. The generation of these maximally entangled states occurs rather rapidly for large hopping strengths. The cavities function as a storage of periodically generated maximally entangled states.
Qubit entanglement between ring-resonator photon-pair sources on a silicon chip.
Silverstone, J W; Santagati, R; Bonneau, D; Strain, M J; Sorel, M; O'Brien, J L; Thompson, M G
2015-01-01
Entanglement--one of the most delicate phenomena in nature--is an essential resource for quantum information applications. Scalable photonic quantum devices must generate and control qubit entanglement on-chip, where quantum information is naturally encoded in photon path. Here we report a silicon photonic chip that uses resonant-enhanced photon-pair sources, spectral demultiplexers and reconfigurable optics to generate a path-entangled two-qubit state and analyse its entanglement. We show that ring-resonator-based spontaneous four-wave mixing photon-pair sources can be made highly indistinguishable and that their spectral correlations are small. We use on-chip frequency demultiplexers and reconfigurable optics to perform both quantum state tomography and the strict Bell-CHSH test, both of which confirm a high level of on-chip entanglement. This work demonstrates the integration of high-performance components that will be essential for building quantum devices and systems to harness photonic entanglement on the large scale. PMID:26245267
Optimizing the output-photon entanglement in multimode optomechanical systems
NASA Astrophysics Data System (ADS)
Deng, Zhi Jiao; Yan, Xiao-Bo; Wang, Ying-Dan; Wu, Chun-Wang
2016-03-01
Entangled light beams are important resources for quantum information processing. For some applications like teleportation, only the entanglement between two wave packets (two harmonic oscillators) is needed. So the calculation of output-photon entanglement involves projecting continuous output modes onto wave-packet modes by filter functions, thus resulting in a strong dependence of entanglement on the filter functions. In this paper, we aim at optimizing the filter functions to obtain a large entanglement in a relatively short time, which is important for utilizing the entangled light beams more efficiently in real experiments. We outline the general optimization procedures based on our previous schemes of generating entangled beams in a multimode optomechanical system. Moreover, we give analytic insights into as well as physical explanations of the wave-packet optimization, which are helpful for experimental estimations.
Sensitivity of entangled photon holes to loss and amplification
Franson, J. D.
2011-10-15
Energy-time entangled photon holes are shown to be relatively insensitive to photon loss due to absorption by atoms whose coherence times are longer than the time delays typically employed in nonlocal interferometry (a fraction of a nanosecond). Roughly speaking, the excited atoms do not retain any significant ''which-path'' information regarding the time at which a photon was absorbed. High-intensity entangled photon holes can also be amplified under similar conditions. Decoherence does occur from losses at beam splitters, and these results show that photon loss cannot always be adequately modeled using a sequence of beam splitters. These properties of entangled photon holes may be useful in quantum communications systems where the range of the system is limited by photon loss.
Measurement of entangled states via atomic beam deflection in Bragg's regime
Khosa, Ashfaq H.; Ikram, Manzoor; Zubairy, M. Suhail
2004-11-01
We propose a scheme for the measurement of joint photon statistics and Wigner function of the entangled field states between two separate cavities. The scheme utilizes the momentum state of the two-level atoms in Bragg's regime. The probability of finding the atom in any one of the momentum states is the product of joint photon statistics and an oscillatory function. The argument of the function contains the information of the joint photon numbers in two cavities. We use the method of state reduction to a single set of joint photon numbers, which is a consequence of the measuring sequence. The repeated measurement of the set of photon numbers gives the joint photon statistics of the entangled field state. The complete entangled state can be reconstructed as a Wigner function from the knowledge of photon statistics of the coherently displaced entangled state.
NASA Astrophysics Data System (ADS)
Guerreiro, T.; Monteiro, F.; Martin, A.; Brask, J. B.; Vértesi, T.; Korzh, B.; Caloz, M.; Bussières, F.; Verma, V. B.; Lita, A. E.; Mirin, R. P.; Nam, S. W.; Marsilli, F.; Shaw, M. D.; Gisin, N.; Brunner, N.; Zbinden, H.; Thew, R. T.
2016-08-01
We demonstrate the violation of an Einstein-Podolsky-Rosen steering inequality developed for single-photon path entanglement with displacement-based detection. We use a high-rate source of heralded single-photon path-entangled states, combined with high-efficiency superconducting-based detectors, in a scheme that is free of any postselection and thus immune to the detection loophole. This result conclusively demonstrates single-photon entanglement in a one-sided device-independent scenario, and opens the way towards implementations of device-independent quantum technologies within the paradigm of path entanglement.
Guerreiro, T; Monteiro, F; Martin, A; Brask, J B; Vértesi, T; Korzh, B; Caloz, M; Bussières, F; Verma, V B; Lita, A E; Mirin, R P; Nam, S W; Marsilli, F; Shaw, M D; Gisin, N; Brunner, N; Zbinden, H; Thew, R T
2016-08-12
We demonstrate the violation of an Einstein-Podolsky-Rosen steering inequality developed for single-photon path entanglement with displacement-based detection. We use a high-rate source of heralded single-photon path-entangled states, combined with high-efficiency superconducting-based detectors, in a scheme that is free of any postselection and thus immune to the detection loophole. This result conclusively demonstrates single-photon entanglement in a one-sided device-independent scenario, and opens the way towards implementations of device-independent quantum technologies within the paradigm of path entanglement. PMID:27563941
Theory of two-photon interactions with broadband down-converted light and entangled photons
Dayan, Barak
2007-10-15
When two-photon interactions are induced by down-converted light with a bandwidth that exceeds the pump bandwidth, they can obtain a behavior that is pulselike temporally, yet spectrally narrow. At low photon fluxes this behavior reflects the time and energy entanglement between the down-converted photons. However, two-photon interactions such as two-photon absorption (TPA) and sum-frequency generation (SFG) can exhibit such a behavior even at high power levels, as long as the final state (i.e., the atomic level in TPA, or the generated light in SFG) is narrow-band enough. This behavior does not depend on the squeezing properties of the light, is insensitive to linear losses, and has potential applications. In this paper we describe analytically this behavior for traveling-wave down conversion with continuous or pulsed pumping, both for high- and low-power regimes. For this we derive a quantum-mechanical expression for the down-converted amplitude generated by an arbitrary pump, and formulate operators that represent various two-photon interactions induced by broadband light. This model is in excellent agreement with experimental results of TPA and SFG with high-power down-converted light and with entangled photons [Dayan et al., Phys. Rev. Lett. 93, 023005 (2004); 94, 043602 (2005); Pe'er et al., ibid. 94, 073601 (2005)].
Influence of detector motion in entanglement measurements with photons
Landulfo, Andre G. S.; Matsas, George E. A.; Torres, Adriano C.
2010-04-15
We investigate how the polarization correlations of entangled photons described by wave packets are modified when measured by moving detectors. For this purpose, we analyze the Clauser-Horne-Shimony-Holt Bell inequality as a function of the apparatus velocity. Our analysis is motivated by future experiments with entangled photons designed to use satellites. This is a first step toward the implementation of quantum information protocols in a global scale.
Sensing intruders using entanglement: a photonic quantum fence
Humble, Travis S; Bennink, Ryan S; Grice, Warren P; Owens, Israel J
2009-01-01
We describe the use of quantum-mechanically entangled photons for sensing intrusions across a physical perimeter. Our approach to intrusion detection uses the no-cloning principle of quantum information science as protection against an intruder s ability to spoof a sensor receiver using a classical intercept-resend attack. Moreover, we employ the correlated measurement outcomes from polarization-entangled photons to protect against quantum intercept-resend attacks, i.e., attacks using quantum teleportation. We explore the bounds on detection using quantum detection and estimation theory, and we experimentally demonstrate the underlying principle of entanglement-based detection using the visibility derived from polarization-correlation measurements.
Wavelength-tunable entangled photons from silicon-integrated III–V quantum dots
Chen, Yan; Zhang, Jiaxiang; Zopf, Michael; Jung, Kyubong; Zhang, Yang; Keil, Robert; Ding, Fei; Schmidt, Oliver G.
2016-01-01
Many of the quantum information applications rely on indistinguishable sources of polarization-entangled photons. Semiconductor quantum dots are among the leading candidates for a deterministic entangled photon source; however, due to their random growth nature, it is impossible to find different quantum dots emitting entangled photons with identical wavelengths. The wavelength tunability has therefore become a fundamental requirement for a number of envisioned applications, for example, nesting different dots via the entanglement swapping and interfacing dots with cavities/atoms. Here we report the generation of wavelength-tunable entangled photons from on-chip integrated InAs/GaAs quantum dots. With a novel anisotropic strain engineering technique based on PMN-PT/silicon micro-electromechanical system, we can recover the quantum dot electronic symmetry at different exciton emission wavelengths. Together with a footprint of several hundred microns, our device facilitates the scalable integration of indistinguishable entangled photon sources on-chip, and therefore removes a major stumbling block to the quantum-dot-based solid-state quantum information platforms. PMID:26813326
Wavelength-tunable entangled photons from silicon-integrated III-V quantum dots
NASA Astrophysics Data System (ADS)
Chen, Yan; Zhang, Jiaxiang; Zopf, Michael; Jung, Kyubong; Zhang, Yang; Keil, Robert; Ding, Fei; Schmidt, Oliver G.
2016-01-01
Many of the quantum information applications rely on indistinguishable sources of polarization-entangled photons. Semiconductor quantum dots are among the leading candidates for a deterministic entangled photon source; however, due to their random growth nature, it is impossible to find different quantum dots emitting entangled photons with identical wavelengths. The wavelength tunability has therefore become a fundamental requirement for a number of envisioned applications, for example, nesting different dots via the entanglement swapping and interfacing dots with cavities/atoms. Here we report the generation of wavelength-tunable entangled photons from on-chip integrated InAs/GaAs quantum dots. With a novel anisotropic strain engineering technique based on PMN-PT/silicon micro-electromechanical system, we can recover the quantum dot electronic symmetry at different exciton emission wavelengths. Together with a footprint of several hundred microns, our device facilitates the scalable integration of indistinguishable entangled photon sources on-chip, and therefore removes a major stumbling block to the quantum-dot-based solid-state quantum information platforms.
Wavelength-tunable entangled photons from silicon-integrated III-V quantum dots.
Chen, Yan; Zhang, Jiaxiang; Zopf, Michael; Jung, Kyubong; Zhang, Yang; Keil, Robert; Ding, Fei; Schmidt, Oliver G
2016-01-01
Many of the quantum information applications rely on indistinguishable sources of polarization-entangled photons. Semiconductor quantum dots are among the leading candidates for a deterministic entangled photon source; however, due to their random growth nature, it is impossible to find different quantum dots emitting entangled photons with identical wavelengths. The wavelength tunability has therefore become a fundamental requirement for a number of envisioned applications, for example, nesting different dots via the entanglement swapping and interfacing dots with cavities/atoms. Here we report the generation of wavelength-tunable entangled photons from on-chip integrated InAs/GaAs quantum dots. With a novel anisotropic strain engineering technique based on PMN-PT/silicon micro-electromechanical system, we can recover the quantum dot electronic symmetry at different exciton emission wavelengths. Together with a footprint of several hundred microns, our device facilitates the scalable integration of indistinguishable entangled photon sources on-chip, and therefore removes a major stumbling block to the quantum-dot-based solid-state quantum information platforms. PMID:26813326
Qubit entanglement between ring-resonator photon-pair sources on a silicon chip
Silverstone, J. W.; Santagati, R.; Bonneau, D.; Strain, M. J.; Sorel, M.; O'Brien, J. L.; Thompson, M. G.
2015-01-01
Entanglement—one of the most delicate phenomena in nature—is an essential resource for quantum information applications. Scalable photonic quantum devices must generate and control qubit entanglement on-chip, where quantum information is naturally encoded in photon path. Here we report a silicon photonic chip that uses resonant-enhanced photon-pair sources, spectral demultiplexers and reconfigurable optics to generate a path-entangled two-qubit state and analyse its entanglement. We show that ring-resonator-based spontaneous four-wave mixing photon-pair sources can be made highly indistinguishable and that their spectral correlations are small. We use on-chip frequency demultiplexers and reconfigurable optics to perform both quantum state tomography and the strict Bell-CHSH test, both of which confirm a high level of on-chip entanglement. This work demonstrates the integration of high-performance components that will be essential for building quantum devices and systems to harness photonic entanglement on the large scale. PMID:26245267
Complete analysis of measurement-induced entanglement localization on a three-photon system
Gavenda, Miroslav; Filip, Radim; Nagali, Eleonora; Sciarrino, Fabio; Martini, Francesco De
2010-02-15
We discuss both theoretically and experimentally elementary two-photon polarization entanglement localization after break of entanglement caused by linear coupling of environmental photon with one of the system photons. The localization of entanglement is based on simple polarization measurement of the surrounding photon after the coupling. We demonstrate that nonzero entanglement can be localized back irrespectively to the distinguishability of coupled photons. Further, it can be increased by local single-copy polarization filters up to an amount violating Bell inequalities. The present technique allows restoration of entanglement in those cases, when the entanglement distillation produces no entanglement from the coupling.
Gaussian maximally multipartite-entangled states
Facchi, Paolo; Florio, Giuseppe; Pascazio, Saverio; Lupo, Cosmo; Mancini, Stefano
2009-12-15
We study maximally multipartite-entangled states in the context of Gaussian continuous variable quantum systems. By considering multimode Gaussian states with constrained energy, we show that perfect maximally multipartite-entangled states, which exhibit the maximum amount of bipartite entanglement for all bipartitions, only exist for systems containing n=2 or 3 modes. We further numerically investigate the structure of these states and their frustration for n<=7.
Ring-shaped spectra of parametric downconversion and entangled photons that never meet
NASA Astrophysics Data System (ADS)
Spasibko, Kirill Yu.; Kopylov, Denis A.; Murzina, Tatiana V.; Leuchs, Gerd; Chekhova, Maria V.
2016-06-01
We report on the observation of an unusual type of parametric down-conversion. In the regime where collinear degenerate emission is in the anomalous range of group-velocity dispersion, its spectrum is restricted in both angle and wavelength. Detuning from exact collinear-degenerate phasematching leads to a ring shape of the wavelength-angular spectrum, suggesting a new type of spatiotemporal coherence and entanglement of photon pairs. By imposing a phase varying in a specific way in both angle and wavelength, one can obtain an interesting state of an entangled photon pair, with the two photons being never at the same point at the same time.
Ring-shaped spectra of parametric downconversion and entangled photons that never meet.
Spasibko, Kirill Yu; Kopylov, Denis A; Murzina, Tatiana V; Leuchs, Gerd; Chekhova, Maria V
2016-06-15
We report on the observation of an unusual type of parametric downconversion. In the regime where collinear degenerate emission is in the anomalous range of group-velocity dispersion, its spectrum is restricted in both angle and wavelength. Detuning from exact collinear-degenerate phase-matching leads to a ring shape of the wavelength-angular spectrum, suggesting a new type of spatiotemporal coherence and entanglement of photon pairs. By imposing a phase varying in a specific way in both angle and wavelength, one can obtain an interesting state of an entangled photon pair, with the two photons being never at the same point at the same time. PMID:27304299
Minimum-error discrimination of entangled quantum states
Lu, Y.; Coish, N.; Kaltenbaek, R.; Hamel, D. R.; Resch, K. J.; Croke, S.
2010-10-15
Strategies to optimally discriminate between quantum states are critical in quantum technologies. We present an experimental demonstration of minimum-error discrimination between entangled states, encoded in the polarization of pairs of photons. Although the optimal measurement involves projection onto entangled states, we use a result of J. Walgate et al. [Phys. Rev. Lett. 85, 4972 (2000)] to design an optical implementation employing only local polarization measurements and feed-forward, which performs at the Helstrom bound. Our scheme can achieve perfect discrimination of orthogonal states and minimum-error discrimination of nonorthogonal states. Our experimental results show a definite advantage over schemes not using feed-forward.
Lim, Hyang-Tag; Hong, Kang-Hee; Kim, Yoon-Ho
2016-01-01
An inexpensive and compact frequency multi-mode diode laser enables a compact two-photon polarization entanglement source via the continuous wave broadband pumped spontaneous parametric down-conversion (SPDC) process. Entanglement degradation caused by polarization mode dispersion (PMD) is one of the critical issues in optical fiber-based polarization entanglement distribution. We theoretically and experimentally investigate how the initial entanglement is degraded when the two-photon polarization entangled state undergoes PMD. We report an effect of PMD unique to broadband pumped SPDC, equally applicable to pulsed pumping as well as cw broadband pumping, which is that the amount of the entanglement degradation is asymmetrical to the PMD introduced to each quantum channel. We believe that our results have important applications in long-distance distribution of polarization entanglement via optical fiber channels. PMID:27174100
Lim, Hyang-Tag; Hong, Kang-Hee; Kim, Yoon-Ho
2016-01-01
An inexpensive and compact frequency multi-mode diode laser enables a compact two-photon polarization entanglement source via the continuous wave broadband pumped spontaneous parametric down-conversion (SPDC) process. Entanglement degradation caused by polarization mode dispersion (PMD) is one of the critical issues in optical fiber-based polarization entanglement distribution. We theoretically and experimentally investigate how the initial entanglement is degraded when the two-photon polarization entangled state undergoes PMD. We report an effect of PMD unique to broadband pumped SPDC, equally applicable to pulsed pumping as well as cw broadband pumping, which is that the amount of the entanglement degradation is asymmetrical to the PMD introduced to each quantum channel. We believe that our results have important applications in long-distance distribution of polarization entanglement via optical fiber channels. PMID:27174100
NASA Astrophysics Data System (ADS)
Lim, Hyang-Tag; Hong, Kang-Hee; Kim, Yoon-Ho
2016-05-01
An inexpensive and compact frequency multi-mode diode laser enables a compact two-photon polarization entanglement source via the continuous wave broadband pumped spontaneous parametric down-conversion (SPDC) process. Entanglement degradation caused by polarization mode dispersion (PMD) is one of the critical issues in optical fiber-based polarization entanglement distribution. We theoretically and experimentally investigate how the initial entanglement is degraded when the two-photon polarization entangled state undergoes PMD. We report an effect of PMD unique to broadband pumped SPDC, equally applicable to pulsed pumping as well as cw broadband pumping, which is that the amount of the entanglement degradation is asymmetrical to the PMD introduced to each quantum channel. We believe that our results have important applications in long-distance distribution of polarization entanglement via optical fiber channels.
Geometric phase and entanglement of Raman photon pairs in the presence of photonic band gap
Berrada, K.; Ooi, C. H. Raymond; Abdel-Khalek, S.
2015-03-28
Robustness of the geometric phase (GP) with respect to different noise effects is a basic condition for an effective quantum computation. Here, we propose a useful quantum system with real physical parameters by studying the GP of a pair of Stokes and anti-Stokes photons, involving Raman emission processes with and without photonic band gap (PBG) effect. We show that the properties of GP are very sensitive to the change of the Rabi frequency and time, exhibiting collapse phenomenon as the time becomes significantly large. The system allows us to obtain a state which remains with zero GP for longer times. This result plays a significant role to enhance the stabilization and control of the system dynamics. Finally, we investigate the nonlocal correlation (entanglement) between the pair photons by taking into account the effect of different parameters. An interesting correlation between the GP and entanglement is observed showing that the PBG stabilizes the fluctuations in the system and makes the entanglement more robust against the change of time and frequency.
Physical realization of quantum teleportation for a nonmaximal entangled state
Tanaka, Yoshiharu; Asano, Masanari; Ohya, Masanori
2010-08-15
Recently, Kossakowski and Ohya (K-O) proposed a new teleportation scheme which enables perfect teleportation even for a nonmaximal entangled state [A. Kossakowski and M. Ohya, Infinite Dimensional Analysis Quantum Probability and Related Topics 10, 411 (2007)]. To discuss a physical realization of the K-O scheme, we propose a model based on quantum optics. In our model, we take a superposition of Schroedinger's cat states as an input state being sent from Alice to Bob, and their entangled state is generated by a photon number state through a beam splitter. When the average photon number for our input states is equal to half the number of photons into the beam splitter, our model has high fidelity.
Fang, B; Liscidini, M; Sipe, J E; Lorenz, V O
2016-05-01
Using stimulated emission tomography, we characterize an entangled photon-pair source in the energy and polarization degrees of freedom, with a precision far exceeding what could be obtained by quantum state tomography. Through this multidimensional tomography we find that energy-polarization correlations are a cause of polarization-entanglement degradation, demonstrating that this technique provides useful information for source engineering and can accelerate the development of quantum information processing systems dependent on many degrees of freedom. PMID:27137611
Partially entangled states bridge in quantum teleportation
NASA Astrophysics Data System (ADS)
Cai, Xiao-Fei; Yu, Xu-Tao; Shi, Li-Hui; Zhang, Zai-Chen
2014-10-01
The traditional method for information transfer in a quantum communication system using partially entangled state resource is quantum distillation or direct teleportation. In order to reduce the waiting time cost in hop-by-hop transmission and execute independently in each node, we propose a quantum bridging method with partially entangled states to teleport quantum states from source node to destination node. We also prove that the designed specific quantum bridging circuit is feasible for partially entangled states teleportation across multiple intermediate nodes. Compared to two traditional ways, our partially entanglement quantum bridging method uses simpler logic gates, has better security, and can be used in less quantum resource situation.
Quantum phase estimation using path-symmetric entangled states
Lee, Su-Yong; Lee, Chang-Woo; Lee, Jaehak; Nha, Hyunchul
2016-01-01
We study the sensitivity of phase estimation using a generic class of path-symmetric entangled states |φ〉|0〉 + |0〉|φ〉, where an arbitrary state |φ〉 occupies one of two modes in quantum superposition. With this generalization, we identify the fundamental limit of phase estimation under energy constraint that is characterized by the photon statistics of the component state |φ〉. We show that quantum Cramer-Rao bound (QCRB) can be indefinitely lowered with super-Poissonianity of the state |φ〉. For possible measurement schemes, we demonstrate that a full photon-counting employing the path-symmetric entangled states achieves the QCRB over the entire range [0, 2π] of unknown phase shift ϕ whereas a parity measurement does so in a certain confined range of ϕ. By introducing a component state of the form , we particularly show that an arbitrarily small QCRB can be achieved even with a finite energy in an ideal situation. This component state also provides the most robust resource against photon loss among considered entangled states over the range of the average input energy Nav > 1. Finally we propose experimental schemes to generate these path-symmetric entangled states for phase estimation. PMID:27457267
Quantum phase estimation using path-symmetric entangled states
NASA Astrophysics Data System (ADS)
Lee, Su-Yong; Lee, Chang-Woo; Lee, Jaehak; Nha, Hyunchul
2016-07-01
We study the sensitivity of phase estimation using a generic class of path-symmetric entangled states |φ>|0> + |0>|φ>, where an arbitrary state |φ> occupies one of two modes in quantum superposition. With this generalization, we identify the fundamental limit of phase estimation under energy constraint that is characterized by the photon statistics of the component state |φ>. We show that quantum Cramer-Rao bound (QCRB) can be indefinitely lowered with super-Poissonianity of the state |φ>. For possible measurement schemes, we demonstrate that a full photon-counting employing the path-symmetric entangled states achieves the QCRB over the entire range [0, 2π] of unknown phase shift ϕ whereas a parity measurement does so in a certain confined range of ϕ. By introducing a component state of the form , we particularly show that an arbitrarily small QCRB can be achieved even with a finite energy in an ideal situation. This component state also provides the most robust resource against photon loss among considered entangled states over the range of the average input energy Nav > 1. Finally we propose experimental schemes to generate these path-symmetric entangled states for phase estimation.
Quantum phase estimation using path-symmetric entangled states.
Lee, Su-Yong; Lee, Chang-Woo; Lee, Jaehak; Nha, Hyunchul
2016-01-01
We study the sensitivity of phase estimation using a generic class of path-symmetric entangled states |φ〉|0〉 + |0〉|φ〉, where an arbitrary state |φ〉 occupies one of two modes in quantum superposition. With this generalization, we identify the fundamental limit of phase estimation under energy constraint that is characterized by the photon statistics of the component state |φ〉. We show that quantum Cramer-Rao bound (QCRB) can be indefinitely lowered with super-Poissonianity of the state |φ〉. For possible measurement schemes, we demonstrate that a full photon-counting employing the path-symmetric entangled states achieves the QCRB over the entire range [0, 2π] of unknown phase shift ϕ whereas a parity measurement does so in a certain confined range of ϕ. By introducing a component state of the form , we particularly show that an arbitrarily small QCRB can be achieved even with a finite energy in an ideal situation. This component state also provides the most robust resource against photon loss among considered entangled states over the range of the average input energy Nav > 1. Finally we propose experimental schemes to generate these path-symmetric entangled states for phase estimation. PMID:27457267
Influence of Stark Shift on Entanglement of Two Qubits in the Two-Photon Tavis-Cummings Model
NASA Astrophysics Data System (ADS)
Mastyugin, M. S.; Bashkirov, E. K.
2015-09-01
Considering two-atom degenerate two-photon Tavis-Cummings model, we investigate the entanglement between two atoms prepared initially in the coherent disentangled states and cavity field prepared in few-photon Fock state, and study the effect of the Stark shift on entanglement. The results show that the atom-atom negativity evolve periodically with time and the periods are affected by the Stark shift and initial coherent atomic state and that the atom-atom entanglement can be greatly enhanced due to the presence of Stark shift. We also have shown that entanglement sudden death effect vanishes for some parameters of the considered system due to the presence of Stark shift. In addition, the entanglement sudden death effect vanishes due to the presence of Stark shift. We have derived that the dynamic Stark shift can be used to control entanglement between two initially disentangled atoms.
Tailoring photonic entanglement in high-dimensional Hilbert spaces
Riedmatten, Hugues de; Marcikic, Ivan; Scarani, Valerio; Tittel, Wolfgang; Zbinden, Hugo; Gisin, Nicolas
2004-05-01
We present an experiment where two photonic systems of arbitrary dimensions can be entangled. The method is based on spontaneous parametric down-conversion with trains of d pump pulses with a fixed phase relation, generated by a mode-locked laser. This leads to a photon pair created in a coherent superposition of d discrete emission times, given by the successive laser pulses. Entanglement is shown by performing a two-photon interference experiment and by observing the visibility of the interference fringes increasing as a function of the dimension d. Factors limiting the visibility, such as the presence of multiple pairs in one train, are discussed.
A periodic probabilistic photonic cluster state generator
NASA Astrophysics Data System (ADS)
Fanto, Michael L.; Smith, A. Matthew; Alsing, Paul M.; Tison, Christopher C.; Preble, Stefan F.; Lott, Gordon E.; Osman, Joseph M.; Szep, Attila; Kim, Richard S.
2014-10-01
The research detailed in this paper describes a Periodic Cluster State Generator (PCSG) consisting of a monolithic integrated waveguide device that employs four wave mixing, an array of probabilistic photon guns, single mode sequential entanglers and an array of controllable entangling gates between modes to create arbitrary cluster states. Utilizing the PCSG one is able to produce a cluster state with nearest neighbor entanglement in the form of a linear or square lattice. Cluster state resources of this type have been proven to be able to perform universal quantum computation.
Quantum-enhanced spectroscopy with entangled multiphoton states
NASA Astrophysics Data System (ADS)
Dinani, Hossein T.; Gupta, Manish K.; Dowling, Jonathan P.; Berry, Dominic W.
2016-06-01
Traditionally, spectroscopy is performed by examining the position of absorption lines. However, at frequencies near the transition frequency, additional information can be obtained from the phase shift. In this work we consider the information about the transition frequency obtained from both the absorption and the phase shift, as quantified by the Fisher information in an interferometric measurement. We examine the use of multiple single-photon states, NOON states, and numerically optimized states that are entangled and have multiple photons. We find the optimized states that improve over the standard quantum limit set by independent single photons for some atom number densities.
Entanglement classification with matrix product states
NASA Astrophysics Data System (ADS)
Sanz, M.; Egusquiza, I. L.; di Candia, R.; Saberi, H.; Lamata, L.; Solano, E.
2016-07-01
We propose an entanglement classification for symmetric quantum states based on their diagonal matrix-product-state (MPS) representation. The proposed classification, which preserves the stochastic local operation assisted with classical communication (SLOCC) criterion, relates entanglement families to the interaction length of Hamiltonians. In this manner, we establish a connection between entanglement classification and condensed matter models from a quantum information perspective. Moreover, we introduce a scalable nesting property for the proposed entanglement classification, in which the families for N parties carry over to the N + 1 case. Finally, using techniques from algebraic geometry, we prove that the minimal nontrivial interaction length n for any symmetric state is bounded by .
Optical microscope using an interferometric source of two-color, two-beam entangled photons
Dress, William B.; Kisner, Roger A.; Richards, Roger K.
2004-07-13
Systems and methods are described for an optical microscope using an interferometric source of multi-color, multi-beam entangled photons. A method includes: downconverting a beam of coherent energy to provide a beam of multi-color entangled photons; converging two spatially resolved portions of the beam of multi-color entangled photons into a converged multi-color entangled photon beam; transforming at least a portion of the converged multi-color entangled photon beam by interaction with a sample to generate an entangled photon specimen beam; and combining the entangled photon specimen beam with an entangled photon reference beam within a single beamsplitter. An apparatus includes: a multi-refringent device providing a beam of multi-color entangled photons; a condenser device optically coupled to the multi-refringent device, the condenser device converging two spatially resolved portions of the beam of multi-color entangled photons into a converged multi-color entangled photon beam; a beam probe director and specimen assembly optically coupled to the condenser device; and a beam splitter optically coupled to the beam probe director and specimen assembly, the beam splitter combining an entangled photon specimen beam from the beam probe director and specimen assembly with an entangled photon reference beam.
Exploring Entangled Two-Photon Absorption in Molecules
NASA Astrophysics Data System (ADS)
Caraher, John
2014-05-01
Goodson and colleagues have reported anomalously large cross-sections (of order σ =10-17 cm2) for the two-photon absorption of entangled photons in a number of molecules. This poster reports on attempts to replicate and expand upon their results for one of these, zinc tetraphenylporphyrin (Zn TPP) in chloroform solution. It will also discuss the interpretation of the Goodson group's experimental data, particularly their results regarding entanglement area and entanglement time (the spatial and temporal widths of the fourth-order coherence functions, respectively). Results of direct measurement of entanglement time (via a Hong-Ou-Mandel interferometer) for a laser and optical system essentially identical to the one used in Goodson's work will be presented and compared with their reported values. Supported by the DePauw University Faculty Development Committee.
Maximal atom-photon entanglement in a double- quantum system
NASA Astrophysics Data System (ADS)
Kordi, Zeinab; Ghanbari, Saeed; Mahmoudi, Mohammad
2015-06-01
The atom-photon entanglement of a dressed atom and its spontaneous emission in a double- closed-loop atomic system is studied under multi-photon resonance condition. It is shown that even in the absence of quantum interference due to the spontaneous emission, the von Neumann entropy is phase-sensitive and it can be controlled by either intensity or relative phase of the applied fields. It is demonstrated that for the special case of Rabi frequency of the applied fields, the system is maximally entangled. Moreover, an open-loop configuration is considered, and it is shown that the degree of entanglement can be controlled by intensity of the applied fields. Furthermore, in electromagnetically induced transparency condition, the system is disentangled. Such a system can be used for quantum information processing via entanglement using optical switching.
Up-conversion dynamics for temporally entangled two-photon pulses
Nakatani, Masatoshi; Shimizu, Ryosuke; Koshino, Kazuki
2011-01-15
We analyze the up conversion of a two-photon pulse having temporal entanglement on the basis of a full quantum formalism that treats both photons and optical media quantum mechanically. We derive a formula of the up-converted photon wave function, which is applicable to arbitrary input two-photon states for a three-level system, as the simplest second-order nonlinear optical system. As the input, we employ three kinds of temporally entangled two-photon pulses: correlated, uncorrelated, and anticorrelated. We observe the up-conversion efficiency and the temporal profile of the up-converted photon. Our results reveal the crossover behavior of the up conversion from anticorrelation to correlation and show how the temporal correlation in the input is reflected in the up-conversion process.
Teleportation with insurance of an entangled atomic state via cavity decay
Chimczak, Grzegorz; Tanas, Ryszard; Miranowicz, Adam
2005-03-01
We propose a scheme to teleport an entangled state of two {lambda}-type three-level atoms via photons. The teleportation protocol involves the local redundant encoding protecting the initial entangled state and allowing for repeating the detection until quantum information transfer is successful. We also show how to manipulate a state of many {lambda}-type atoms trapped in a cavity.
Measuring Entanglement in a Photonic Embedding Quantum Simulator.
Loredo, J C; Almeida, M P; Di Candia, R; Pedernales, J S; Casanova, J; Solano, E; White, A G
2016-02-19
Measuring entanglement is a demanding task that usually requires full tomography of a quantum system, involving a number of observables that grows exponentially with the number of parties. Recently, it was suggested that adding a single ancillary qubit would allow for the efficient measurement of concurrence, and indeed any entanglement monotone associated with antilinear operations. Here, we report on the experimental implementation of such a device-an embedding quantum simulator-in photonics, encoding the entangling dynamics of a bipartite system into a tripartite one. We show that bipartite concurrence can be efficiently extracted from the measurement of merely two observables, instead of 15, without full tomographic information. PMID:26943521
Entangled States, Holography and Quantum Surfaces
Chapline, G F
2003-08-13
Starting with an elementary discussion of quantum holography, we show that entangled quantum states of qubits provide a ''local'' representation of the global geometry and topology of quantum Riemann surfaces. This representation may play an important role in both mathematics and physics. Indeed, the simplest way to represent the fundamental objects in a ''theory of everything'' may be as muti-qubit entangled states.
Polarization Engineering in Photonic Crystal Waveguides for Spin-Photon Entanglers.
Young, A B; Thijssen, A C T; Beggs, D M; Androvitsaneas, P; Kuipers, L; Rarity, J G; Hughes, S; Oulton, R
2015-10-01
By performing a full analysis of the projected local density of states (LDOS) in a photonic crystal waveguide, we show that phase plays a crucial role in the symmetry of the light-matter interaction. By considering a quantum dot (QD) spin coupled to a photonic crystal waveguide (PCW) mode, we demonstrate that the light-matter interaction can be asymmetric, leading to unidirectional emission and a deterministic entangled photon source. Further we show that understanding the phase associated with both the LDOS and the QD spin is essential for a range of devices that can be realized with a QD in a PCW. We also show how suppression of quantum interference prevents dipole induced reflection in the waveguide, and highlight a fundamental breakdown of the semiclassical dipole approximation for describing light-matter interactions in these spin dependent systems. PMID:26550722
Diagnosing Topological Edge States via Entanglement Monogamy
NASA Astrophysics Data System (ADS)
Meichanetzidis, K.; Eisert, J.; Cirio, M.; Lahtinen, V.; Pachos, J. K.
2016-04-01
Topological phases of matter possess intricate correlation patterns typically probed by entanglement entropies or entanglement spectra. In this Letter, we propose an alternative approach to assessing topologically induced edge states in free and interacting fermionic systems. We do so by focussing on the fermionic covariance matrix. This matrix is often tractable either analytically or numerically, and it precisely captures the relevant correlations of the system. By invoking the concept of monogamy of entanglement, we show that highly entangled states supported across a system bipartition are largely disentangled from the rest of the system, thus, usually appearing as gapless edge states. We then define an entanglement qualifier that identifies the presence of topological edge states based purely on correlations present in the ground states. We demonstrate the versatility of this qualifier by applying it to various free and interacting fermionic topological systems.
Diagnosing Topological Edge States via Entanglement Monogamy.
Meichanetzidis, K; Eisert, J; Cirio, M; Lahtinen, V; Pachos, J K
2016-04-01
Topological phases of matter possess intricate correlation patterns typically probed by entanglement entropies or entanglement spectra. In this Letter, we propose an alternative approach to assessing topologically induced edge states in free and interacting fermionic systems. We do so by focussing on the fermionic covariance matrix. This matrix is often tractable either analytically or numerically, and it precisely captures the relevant correlations of the system. By invoking the concept of monogamy of entanglement, we show that highly entangled states supported across a system bipartition are largely disentangled from the rest of the system, thus, usually appearing as gapless edge states. We then define an entanglement qualifier that identifies the presence of topological edge states based purely on correlations present in the ground states. We demonstrate the versatility of this qualifier by applying it to various free and interacting fermionic topological systems. PMID:27081962
NASA Astrophysics Data System (ADS)
Joo, Jaewoo; Ginossar, Eran
2016-06-01
We propose a deterministic scheme for teleporting an unknown qubit state through continuous-variable entangled states in superconducting circuits. The qubit is a superconducting two-level system and the bipartite quantum channel is a microwave photonic entangled coherent state between two cavities. A Bell-type measurement performed on the hybrid state of solid and photonic states transfers a discrete-variable unknown electronic state to a continuous-variable photonic cat state in a cavity mode. In order to facilitate the implementation of such complex protocols we propose a design for reducing the self-Kerr nonlinearity in the cavity. The teleporation scheme enables quantum information processing operations with circuit-QED based on entangled coherent states. These include state verification and single-qubit operations with entangled coherent states. These are shown to be experimentally feasible with the state of the art superconducting circuits.
Joo, Jaewoo; Ginossar, Eran
2016-01-01
We propose a deterministic scheme for teleporting an unknown qubit state through continuous-variable entangled states in superconducting circuits. The qubit is a superconducting two-level system and the bipartite quantum channel is a microwave photonic entangled coherent state between two cavities. A Bell-type measurement performed on the hybrid state of solid and photonic states transfers a discrete-variable unknown electronic state to a continuous-variable photonic cat state in a cavity mode. In order to facilitate the implementation of such complex protocols we propose a design for reducing the self-Kerr nonlinearity in the cavity. The teleporation scheme enables quantum information processing operations with circuit-QED based on entangled coherent states. These include state verification and single-qubit operations with entangled coherent states. These are shown to be experimentally feasible with the state of the art superconducting circuits. PMID:27245775
Joo, Jaewoo; Ginossar, Eran
2016-01-01
We propose a deterministic scheme for teleporting an unknown qubit state through continuous-variable entangled states in superconducting circuits. The qubit is a superconducting two-level system and the bipartite quantum channel is a microwave photonic entangled coherent state between two cavities. A Bell-type measurement performed on the hybrid state of solid and photonic states transfers a discrete-variable unknown electronic state to a continuous-variable photonic cat state in a cavity mode. In order to facilitate the implementation of such complex protocols we propose a design for reducing the self-Kerr nonlinearity in the cavity. The teleporation scheme enables quantum information processing operations with circuit-QED based on entangled coherent states. These include state verification and single-qubit operations with entangled coherent states. These are shown to be experimentally feasible with the state of the art superconducting circuits. PMID:27245775
Ming, Yang; Wu, Zi-jian; Xu, Fei Lu, Yan-qing; Cui, Guo-xin; Tan, Ai-hong
2014-04-28
The nonmaximally entangled state is a special kind of entangled state, which has important applications in quantum information processing. It has been generated in quantum circuits based on bulk optical elements. However, corresponding schemes in integrated quantum circuits have been rarely considered. In this Letter, we propose an effective solution for this problem. An electro-optically tunable nonmaximally mode-entangled photon state is generated in an on-chip domain-engineered lithium niobate (LN) waveguide. Spontaneous parametric down-conversion and electro-optic interaction are effectively combined through suitable domain design to transform the entangled state into our desired formation. Moreover, this is a flexible approach to entanglement architectures. Other kinds of reconfigurable entanglements are also achievable through this method. LN provides a very promising platform for future quantum circuit integration.
Entanglement concentration of three-partite states
Groisman, Berry; Linden, Noah; Popescu, Sandu
2005-12-15
We investigate the concentration of multiparty entanglement by focusing on a simple family of three-partite pure states, superpositions of Greenberger-Horne-Zeilinger states and singlets. Despite the simplicity of the states, we show that they cannot be reversibly concentrated by the standard entanglement concentration procedure, to which they seem ideally suited. Our results cast doubt on the idea that for each N there might be a finite set of N-party states into which any pure state can be reversibly transformed. We further relate our results to the concept of locking of entanglement of formation.
Entanglement of quantum circular states of light
NASA Astrophysics Data System (ADS)
Horoshko, D. B.; De Bièvre, S.; Kolobov, M. I.; Patera, G.
2016-06-01
We present a general approach to calculating the entanglement of formation for superpositions of two-mode coherent states, placed equidistantly on a circle in phase space. We show that in the particular case of rotationally invariant circular states the Schmidt decomposition of two modes, and therefore the value of their entanglement, are given by analytical expressions. We analyze the dependence of the entanglement on the radius of the circle and number of components in the superposition. We also show that the set of rotationally invariant circular states creates an orthonormal basis in the state space of the harmonic oscillator, and this basis is advantageous for representation of other circular states of light.
Entanglement of trapped-ion clock states
Haljan, P. C.; Lee, P. J.; Brickman, K-A.; Acton, M.; Deslauriers, L.; Monroe, C.
2005-12-15
A Moelmer-Soerensen entangling gate is realized for pairs of trapped {sup 111}Cd{sup +} ions using magnetic-field insensitive 'clock' states and an implementation offering reduced sensitivity to optical phase drifts. The gate is used to generate the complete set of four entangled states, which are reconstructed and evaluated with quantum-state tomography. An average target-state fidelity of 0.79 is achieved, limited by available laser power and technical noise. The tomographic reconstruction of entangled states demonstrates universal quantum control of two ion qubits, which through multiplexing can provide a route to scalable architectures for trapped-ion quantum computing.
Bell-state diagonal-entanglement witnesses
Jafarizadeh, M. A.; Rezaee, M.; Seyed Yagoobi, S. K. A.
2005-12-15
It has been shown that finding generic Bell-state diagonal-entanglement witnesses for d{sub 1}xd{sub 2}x{center_dot}{center_dot}{center_dot}xd{sub n} systems reduces to linear programming if the feasible region is a polygon by itself, and it can be solved approximately via linear programming if the feasible region is encircled by a polygon. Since solving linear programming for the generic case is difficult, multiqubit, 2xN and 3x3 systems for the special case of generic Bell-state diagonal-entanglement witnesses for some particular choice of parameters have been considered. We obtain the optimal nondecomposable entanglement witness for a 3x3 system for some particular choice of parameters. By proving the optimality of the well-known reduction map and combining it with the optimal and nondecomposable 3x3 Bell-state diagonal-entanglement witnesses (named critical entanglement witnesses) the family of optimal and nondecomposable 3x3 Bell-state diagonal-entanglement witnesses has also been obtained. Using the approximately critical entanglement witnesses, some 3x3 bound entangled states are so detected. So the well-known Choi map as a particular case of the positive map in connection with this witness via Jamiolkowski isomorphism has been considered.
Bi- and uni-photon entanglement in two-way cascaded fiber-coupled atom-cavity systems
NASA Astrophysics Data System (ADS)
Mirza, Imran M.
2015-08-01
We theoretically investigate the two-photon entanglement in fiber-coupled, two-way cascaded atom-cavity systems. In particular, we demonstrate that, it is possible to generate two-photon entanglement in both weak coupling (atom-cavity coupling rate | g | smaller than the cavity leakage rate κ) and strong coupling regimes (κ < | g |) in this system, when both atoms start off in an excited state. By employing the quantum trajectory method, we characterize the two-photon entanglement in terms of von-Neumann entropy and show that the amount of entanglement exceed considerably (almost double) when κ > | g |. We also quantified the amount of entanglement when instead of two excitations there is a single excitation in the system in the beginning.
CW-pumped telecom band polarization entangled photon pair generation in a Sagnac interferometer.
Li, Yan; Zhou, Zhi-Yuan; Ding, Dong-Sheng; Shi, Bao-Sen
2015-11-01
Polarization entangled photon pair source is widely used in many quantum information processing applications such as teleportation, quantum communications, quantum computation and high precision quantum metrology. We report on the generation of a continuous-wave pumped 1550 nm polarization entangled photon pair source at telecom wavelength using a type-II periodically poled KTiOPO(4) (PPKTP) crystal in a Sagnac interferometer. Hong-Ou-Mandel (HOM) interference measurement yields signal and idler photon bandwidth of 2.4 nm. High quality of entanglement is verified by various kinds of measurements, for example two-photon interference fringes, Bell inequality and quantum states tomography. The source can be tuned over a broad range against temperature or pump power without loss of visibilities. This source will be used in our future experiments such as generation of orbital angular momentum entangled source at telecom wavelength for quantum frequency up-conversion, entanglement based quantum key distributions and many other quantum optics experiments at telecom wavelengths. PMID:26561148
Simple scheme for expanding photonic cluster states for quantum information
Kalasuwan, P.; Laing, A.; Coggins, J.; Callaway, M.; O'Brien, J. L.; Mendoza, G.; Nagata, T.; Takeuchi, S.; Stefanov, A.
2010-06-15
We show how an entangled cluster state encoded in the polarization of single photons can be straightforwardly expanded by deterministically entangling additional qubits encoded in the path degree of freedom of the constituent photons. This can be achieved using a polarization-path controlled-phase gate. We experimentally demonstrate a practical and stable realization of this approach by using a Sagnac interferometer to entangle a path qubit and polarization qubit on a single photon. We demonstrate precise control over phase of the path qubit to change the measurement basis and experimentally demonstrate properties of measurement-based quantum computing using a two-photon, three-qubit cluster state.
Heralded entanglement between solid-state qubits separated by three metres.
Bernien, H; Hensen, B; Pfaff, W; Koolstra, G; Blok, M S; Robledo, L; Taminiau, T H; Markham, M; Twitchen, D J; Childress, L; Hanson, R
2013-05-01
Quantum entanglement between spatially separated objects is one of the most intriguing phenomena in physics. The outcomes of independent measurements on entangled objects show correlations that cannot be explained by classical physics. As well as being of fundamental interest, entanglement is a unique resource for quantum information processing and communication. Entangled quantum bits (qubits) can be used to share private information or implement quantum logical gates. Such capabilities are particularly useful when the entangled qubits are spatially separated, providing the opportunity to create highly connected quantum networks or extend quantum cryptography to long distances. Here we report entanglement of two electron spin qubits in diamond with a spatial separation of three metres. We establish this entanglement using a robust protocol based on creation of spin-photon entanglement at each location and a subsequent joint measurement of the photons. Detection of the photons heralds the projection of the spin qubits onto an entangled state. We verify the resulting non-local quantum correlations by performing single-shot readout on the qubits in different bases. The long-distance entanglement reported here can be combined with recently achieved initialization, readout and entanglement operations on local long-lived nuclear spin registers, paving the way for deterministic long-distance teleportation, quantum repeaters and extended quantum networks. PMID:23615617
Long distance measurement-device-independent quantum key distribution with entangled photon sources
Xu, Feihu; Qi, Bing; Liao, Zhongfa; Lo, Hoi-Kwong
2013-08-05
We present a feasible method that can make quantum key distribution (QKD), both ultra-long-distance and immune, to all attacks in the detection system. This method is called measurement-device-independent QKD (MDI-QKD) with entangled photon sources in the middle. By proposing a model and simulating a QKD experiment, we find that MDI-QKD with one entangled photon source can tolerate 77 dB loss (367 km standard fiber) in the asymptotic limit and 60 dB loss (286 km standard fiber) in the finite-key case with state-of-the-art detectors. Our general model can also be applied to other non-QKD experiments involving entanglement and Bell state measurements.
Symmetric states: Their nonlocality and entanglement
Wang, Zizhu; Markham, Damian
2014-12-04
The nonlocality of permutation symmetric states of qubits is shown via an extension of the Hardy paradox and the extension of the associated inequality. This is achieved by using the Majorana representation, which is also a powerful tool in the study of entanglement properties of symmetric states. Through the Majorana representation, different nonlocal properties can be linked to different entanglement properties of a state, which is useful in determining the usefulness of different states in different quantum information processing tasks.
Collective two-particle resonances induced by photon entanglement
Richter, Marten; Mukamel, Shaul
2011-06-15
An assembly of noninteracting atoms may become correlated upon interaction with entangled photons, and certain elements of their joint density matrix can then show collective resonances. We explore experimental signatures of these resonances in the nonlinear response of a pair of two-level atoms. We find that these resonances are canceled out in stimulated signals such as pump-probe and two-photon absorption due to the destructive interference of two-photon-absorption and emission pathways in the joint two-particle space. However, they may be observed in photon statistics (Hanbury-Brown-Twiss) measurements through the attenuation of two-time intensity correlations.
Construction of bound entangled states based on permutation operators
NASA Astrophysics Data System (ADS)
Zhao, Hui; Guo, Sha; Jing, Naihuan; Fei, Shaoming
2016-04-01
We present a construction of new bound entangled states from given bound entangled states for arbitrary dimensional bipartite systems. One way to construct bound entangled states is to show that these states are positive partial transpose (PPT) and violate the range criterion at the same time. By applying certain operators to given bound entangled states or to one of the subsystems of the given bound entangled states, we obtain a set of new states which are both PPT and violate the range criterion. We show that the derived bound entangled states are not local unitary equivalent to the original bound entangled states by detail examples.
All entangled quantum states are nonlocal.
Buscemi, Francesco
2012-05-18
Departing from the usual paradigm of local operations and classical communication adopted in entanglement theory, we study here the interconversion of quantum states by means of local operations and shared randomness. A set of necessary and sufficient conditions for the existence of such a transformation between two given quantum states is given in terms of the payoff they yield in a suitable class of nonlocal games. It is shown that, as a consequence of our result, such a class of nonlocal games is able to witness quantum entanglement, however weak, and reveal nonlocality in any entangled quantum state. An example illustrating this fact is provided. PMID:23003127
Macroscopic entanglement of many-magnon states
Morimae, Tomoyuki; Shimizu, Akira; Sugita, Ayumu
2005-03-01
We study macroscopic entanglement of various pure states of a one-dimensional N-spin system with N>>1. Here, a quantum state is said to be macroscopically entangled if it is a superposition of macroscopically distinct states. To judge whether such superposition is hidden in a general state, we use an essentially unique index p: A pure state is macroscopically entangled if p=2, whereas it may be entangled but not macroscopically if p<2. This index is directly related to fundamental stabilities of many-body states. We calculate the index p for various states in which magnons are excited with various densities and wave numbers. We find macroscopically entangled states (p=2) as well as states with p=1. The former states are unstable in the sense that they are unstable against some local measurements. On the other hand, the latter states are stable in the senses that they are stable against any local measurements and that their decoherence rates never exceed O(N) in any weak classical noises. For comparison, we also calculate the von Neumann entropy S{sub N/2}(N) of a subsystem composed of N/2 spins as a measure of bipartite entanglement. We find that S{sub N/2}(N) of some states with p=1 is of the same order of magnitude as the maximum value N/2. On the other hand, S{sub N/2}(N) of the macroscopically entangled states with p=2 is as small as O(log N)<
Observation of strongly entangled photon pairs from a nanowire quantum dot
Versteegh, Marijn A. M.; Reimer, Michael E.; Jöns, Klaus D.; Dalacu, Dan; Poole, Philip J.; Gulinatti, Angelo; Giudice, Andrea; Zwiller, Val
2014-01-01
A bright photon source that combines high-fidelity entanglement, on-demand generation, high extraction efficiency, directional and coherent emission, as well as position control at the nanoscale is required for implementing ambitious schemes in quantum information processing, such as that of a quantum repeater. Still, all of these properties have not yet been achieved in a single device. Semiconductor quantum dots embedded in nanowire waveguides potentially satisfy all of these requirements; however, although theoretically predicted, entanglement has not yet been demonstrated for a nanowire quantum dot. Here, we demonstrate a bright and coherent source of strongly entangled photon pairs from a position-controlled nanowire quantum dot with a fidelity as high as 0.859±0.006 and concurrence of 0.80±0.02. The two-photon quantum state is modified via the nanowire shape. Our new nanoscale entangled photon source can be integrated at desired positions in a quantum photonic circuit, single-electron devices and light-emitting diodes. PMID:25358656
Qubit-Photon Entanglement and Hong-Ou-Mandel Interference with Propagating Microwaves
NASA Astrophysics Data System (ADS)
Eichler, Christopher; Lang, Christian; Fink, Johannes; Govenius, Joonas; Steffen, Lars; Filipp, Stefan; Wallraff, Andreas; Woolley, Matthew; Blais, Alexandre
2013-03-01
Itinerant microwave photons offer an attractive carrier of quantum information in superconducting circuits. However, until recently it remained challenging to measure photon statistics and coherence properties of microwave fields beyond the Gaussian level - mainly due to the absence of efficient detectors in this frequency range. Here, we present the on-demand generation and efficient characterization of microwave radiation and its entanglement with stationary qubits. Based on novel tomography techniques and low noise parametric amplification we are able to resolve all relevant quantum correlations between the propagating field and the superconducting qubit to demonstrate entanglement with high fidelity. We have also created entangled microwave fields traveling in two spatially separated modes. Making use of the two-photon interference at a microwave beamsplitter we are able to prepare propagating NOON-type states, which we fully characterize by measuring the joint photon statistics of the two modes. The possibility to synthesize, guide and detect entanglement correlations between itinerant microwave photons and stationary qubits put microwave based quantum network experiments within reach.
Lee, Su-Yong; Kim, Ho-Joon; Ji, Se-Wan; Nha, Hyunchul
2011-07-15
We investigate how the entanglement properties of a two-mode state can be improved by performing a coherent superposition operation ta+ra{sup {dagger}} of photon subtraction and addition, proposed by Lee and Nha [Phys. Rev. A 82, 053812 (2010)], on each mode. We show that the degree of entanglement, the Einstein-Podolsky-Rosen-type correlation, and the performance of quantum teleportation can be all enhanced for the output state when the coherent operation is applied to a two-mode squeezed state. The effects of the coherent operation are more prominent than those of the mere photon subtraction a and the addition a{sup {dagger}} particularly in the small-squeezing regime, whereas the optimal operation becomes the photon subtraction (case of r=0) in the large-squeezing regime.
Resolution of ghost imaging with entangled photons for different types of momentum correlation
NASA Astrophysics Data System (ADS)
Zhong, MaLin; Xu, Ping; Lu, LiangLiang; Zhu, ShiNing
2016-07-01
We present an analytical analysis of the spatial resolution of quantum ghost imaging implemented by entangled photons from a general, spontaneously parametric, down-conversion process. We find that the resolution is affected by both the pump beam waist and the nonlinear crystal length. Hence, we determined a method to improve the resolution for a certain imaging setup. It should be noted that the resolution is not uniquely related to the degree of entanglement of the photon pair since the resolution can be optimized for a certain degree of entanglement. For certain types of Einstein-Podolsky-Rosen (EPR) states——namely the momentum-correlated or momentum-positively correlated states——the resolution exhibits a simpler relationship with the pump beam waist and crystal length. Further, a vivid numerical simulation of ghost imaging is presented for different types of EPR states, which supports our analysis. This work discusses applicable references to the applications of quantum ghost imaging.
NASA Astrophysics Data System (ADS)
Guo, Ying; Zhao, Zhisheng; Wang, Yijun; Wang, Ping; Huang, Dazu; Lee, Moon Ho
2014-09-01
We investigate an novel implementation of a Toffoli gate using multiple independent auxiliary photons prepared beforehand in single-qubit states. This gate can be performed nondestructively with entanglement swapping via the Greenberger-Horne-Zeilinger state analysis. We evaluate the performance of the proposed Toffoli gate with the fidelity based on different computation bases. The multi-qubit-entanglement gate is no longer theoretical since it can be implemented in principle with single-qubit photons.
Atom-photon entanglement beyond the multi-photon resonance condition
NASA Astrophysics Data System (ADS)
Kordi, Zeinab; Ghanbari, Saeed; Mahmoudi, Mohammad
2016-01-01
Atom-photon entanglement between the dressed atom and its spontaneous emission is studied in a near-degenerate three-level V-type atomic system in multi-photon resonance condition and beyond it. Taking into account the quantum interference due to the spontaneous emission, the density matrix equations of motion are numerically calculated in two-photon resonance condition and beyond it. The dynamical behavior of these two subsystems is investigated by using the von Neumann entropy. We apply the Floquet decomposition to the equations of motion to solve this time-dependent problem and identify the contribution of the different scattering processes to the atom-photon entanglement. In addition, the impact of the various nonlinear effects on the atom-photon entanglement is introduced in two-photon resonance condition. It is shown that the degree of entanglement (DEM) can be controlled via the intensity and the detuning of the coupling field as well as the quantum interference induced by spontaneous emission. We find that vacuum-induced interference has a major role in phase sensitivity of the DEM; however, beyond the two-photon resonance condition the DEM does not depend on the relative phase of the applied fields. Our results can be used for quantum information processing via entanglement.
Beamlike photon-pair generation for two-photon interference and polarization entanglement
Lo, Hsin-Pin; Yabushita, Atsushi; Luo, Chih-Wei; Chen, Pochung; Kobayashi, Takayoshi
2011-02-15
Beamlike photon pairs were generated by spontaneous parametric down-conversion using a type-II {beta}-BaB{sub 2}O{sub 4} crystal. A pump laser generated photon pairs when it transmitted through the crystal and was reflected back into the crystal by a mirror to generate more photon pairs. The photon pairs generated when the pump laser first transmitted through the crystal (first photon pairs) were also reflected back into the crystal to overlap with the light path of the photon pairs generated in the second transmission of the pump laser through the crystal (second photon pairs). We observed interference between the first and second photon pairs modulated with a half period of the wavelength of the photon pairs, which demonstrates two-photon interference using the beamlike photon pairs. The fringe period confirms that the observed interference is not classical interference but quantum two-photon interference. Through rotating the angles of quarter-wave plates in the light paths of the photon pairs, we generated beamlike photon pairs with entangled polarization. The phase between the first and second photon pairs could be tuned by changing the position of mirrors reflecting the pump pulses and photon pairs. The fringes of coincidence counts showed that the beamlike photon pairs have polarization entanglement.
Genuine multiparticle entanglement of permutationally invariant states
NASA Astrophysics Data System (ADS)
Novo, Leonardo; Moroder, Tobias; Gühne, Otfried
2013-07-01
We consider the problem of characterizing genuine multiparticle entanglement for permutationally invariant states using the approach of positive partial transpose mixtures. We show that the evaluation of this necessary biseparability criterion scales polynomially with the number of particles. In practice, it can be evaluated easily up to ten qubits and improves existing criteria significantly. Finally, we show that our approach solves the problem of characterizing genuine multiparticle entanglement for permutationally invariant three-qubit states.
NASA Astrophysics Data System (ADS)
Shi, Ronghua; Liu, Shaorong; Wang, Shuo; Guo, Ying
2015-02-01
We present two deterministic entanglement purifications protocols for χ-type entangled states, resorting to multiple degrees of freedom. One protocol is implemented with the spatial entanglement to distill the maximally entangled states from the mixed states, resorting to some linear optical elements. Another one is implemented with the frequency entanglement for the purification. All the parties can jointly distill the maximally entangled states from the mixed states affected by the environmental noise during transmission. Both of the protocols can work in a deterministic way with the success probability 100 %, in principle. The derived features may make the protocols useful in the practical long-distance quantum communication.
Entanglement and the shareability of quantum states
NASA Astrophysics Data System (ADS)
Doherty, Andrew C.
2014-10-01
This brief review discusses the problem of determining whether a given quantum state is separable or entangled. I describe an established approach to this problem that is based on the monogamy of entanglement, which is the observation that a pair of quantum systems that are strongly entangled must be uncorrelated with the rest of the world. Unentangled states on the other hand involve correlations that can be shared with many other parties. Checking whether a given quantum state is shareable involves constructing certain symmetric quantum state extensions and I discuss how to do this using a class of optimizations known as semidefinite programs. An attractive feature of this approach is that it generates explicit entanglement witnesses that can be measured to demonstrate the entanglement experimentally. In recent years analysis of this approach has greatly increased our understanding of the complexity of determining whether a given quantum state is entangled and this review aims to give a unified discussion of these developments. Specifically, I describe how to use finite quantum de Finetti theorems to prove that highly shareable states are nearly separable and use these results to understand the computational complexity of the problem. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘50 years of Bell’s theorem’.
Entanglement classification with matrix product states
Sanz, M.; Egusquiza, I. L.; Di Candia, R.; Saberi, H.; Lamata, L.; Solano, E.
2016-01-01
We propose an entanglement classification for symmetric quantum states based on their diagonal matrix-product-state (MPS) representation. The proposed classification, which preserves the stochastic local operation assisted with classical communication (SLOCC) criterion, relates entanglement families to the interaction length of Hamiltonians. In this manner, we establish a connection between entanglement classification and condensed matter models from a quantum information perspective. Moreover, we introduce a scalable nesting property for the proposed entanglement classification, in which the families for N parties carry over to the N + 1 case. Finally, using techniques from algebraic geometry, we prove that the minimal nontrivial interaction length n for any symmetric state is bounded by . PMID:27457273
Entanglement classification with matrix product states.
Sanz, M; Egusquiza, I L; Di Candia, R; Saberi, H; Lamata, L; Solano, E
2016-01-01
We propose an entanglement classification for symmetric quantum states based on their diagonal matrix-product-state (MPS) representation. The proposed classification, which preserves the stochastic local operation assisted with classical communication (SLOCC) criterion, relates entanglement families to the interaction length of Hamiltonians. In this manner, we establish a connection between entanglement classification and condensed matter models from a quantum information perspective. Moreover, we introduce a scalable nesting property for the proposed entanglement classification, in which the families for N parties carry over to the N + 1 case. Finally, using techniques from algebraic geometry, we prove that the minimal nontrivial interaction length n for any symmetric state is bounded by . PMID:27457273
Entanglement of remote transmon qubits by concurrent photon detection - Part 2
NASA Astrophysics Data System (ADS)
Narla, A.; Shankar, S.; Hatridge, M.; Pfaff, W.; Leghtas, Z.; Sliwa, K. M.; Zalys-Geller, E.; Frunzio, L.; Devoret, M. H.
One proposed realization for a quantum computer is the modular architecture, which consists of error-corrected quantum memories that are connected via a quantum router. A fundamental requirement for this modular quantum computer is the ability to entangle arbitrary, distant qubits on demand. This can be realized in circuit QED using a protocol inspired by recent experiments based on trapped ions and nitrogen-vacancy centers. First, each qubit is entangled with a single cavity photon (Fock state n=1) using sideband pulses. On their way out of the cavity, the now flying photons interfere on a beam-splitter and are concurrently detected by a novel microwave photo-multiplier that employs a third qubit-cavity system. In this protocol, the presence of losses in the photon flight path only affect the success probability of creating an entangled state but not its fidelity. In this talk, we present experimental results for this protocol and discuss the factors influencing the success probability and the fidelity of the generated entangled states. Work supported by ARO, AFOSR and YINQE.
Telecloning of qudits via partially entangled states
NASA Astrophysics Data System (ADS)
Araneda, Gabriel; Cisternas, Nataly; Delgado, Aldo
2016-08-01
We study the process of quantum telecloning of d-dimensional pure quantum states using partially entangled pure states as quantum channel. This process efficiently mixes optimal universal symmetric cloning with quantum teleportation. It is shown that it is possible to implement universal symmetric telecloning in a probabilistic way using unambiguous state discrimination and quantum state separation schemes. It is also shown that other strategies, such as minimum error discrimination, lead to a decrease in the fidelity of the copies and that certain partially entangled pure states with maximal Schmidt rank lead to an average telecloning fidelity which is always above the optimal fidelity of measuring and preparation of quantum states. We also discuss the case of partially entangled pure states with non-maximal Schmidt rank. The results presented here are valid for arbitrary numbers of copies of a single-input qudit state of any dimension.
Telecloning of qudits via partially entangled states
NASA Astrophysics Data System (ADS)
Araneda, Gabriel; Cisternas, Nataly; Delgado, Aldo
2016-05-01
We study the process of quantum telecloning of d-dimensional pure quantum states using partially entangled pure states as quantum channel. This process efficiently mixes optimal universal symmetric cloning with quantum teleportation. It is shown that it is possible to implement universal symmetric telecloning in a probabilistic way using unambiguous state discrimination and quantum state separation schemes. It is also shown that other strategies, such as minimum error discrimination, lead to a decrease in the fidelity of the copies and that certain partially entangled pure states with maximal Schmidt rank lead to an average telecloning fidelity which is always above the optimal fidelity of measuring and preparation of quantum states. We also discuss the case of partially entangled pure states with non-maximal Schmidt rank. The results presented here are valid for arbitrary numbers of copies of a single-input qudit state of any dimension.
Correlation properties of entangled multiphoton states and Bernstein's paradox
Chirkin, A. S. Belyaeva, O. V. Belinsky, A. V.
2013-01-15
A normally ordered characteristic function (NOCF) of Bose operators is calculated for a number of discrete-variable entangled states (Greenberger-Horne-Zeilinger (GHZ) and Werner (W) qubit states and a cluster state). It is shown that such NOCFs contain visual information on two types of correlations: pseudoclassical and quantum correlations. The latter manifest themselves in the interference terms of the NOCFs and lead to quantum paradoxes, whereas the pseudoclassical correlations of photons and their cumulants satisfy the relations for classical random variables. Three- and four-qubit states are analyzed in detail. An implementation of an analog of Bernstein's paradox on discrete quantum variables is discussed. A measure of quantumness of an entangled state is introduced that is not related to the entropy approach. It is established that the maximum of the degree of quantumness substantiates the numerical values of the coefficients in multiqubit vector states derived from intuitive considerations.
Entanglement witnesses and geometry of entanglement of two-qutrit states
Bertlmann, Reinhold A. Krammer, Philipp
2009-07-15
We construct entanglement witnesses with regard to the geometric structure of the Hilbert-Schmidt space and investigate the geometry of entanglement. In particular, for a two-parameter family of two-qutrit states that are part of the magic simplex, we calculate the Hilbert-Schmidt measure of entanglement. We present a method to detect bound entanglement which is illustrated for a three-parameter family of states. In this way, we discover new regions of bound entangled states. Furthermore, we outline how to use our method to distinguish entangled from separable states.
Lougovski, P.; Uskov, D. B.
2015-08-04
Entanglement can effectively increase communication channel capacity as evidenced by dense coding that predicts a capacity gain of 1 bit when compared to entanglement-free protocols. However, dense coding relies on Bell states and when implemented using photons the capacity gain is bounded by 0.585 bits due to one's inability to discriminate between the four optically encoded Bell states. In this research we study the following question: Are there alternative entanglement-assisted protocols that rely only on linear optics, coincidence photon counting, and separable single-photon input states and at the same time provide a greater capacity gain than 0.585 bits? In thismore » study, we show that besides the Bell states there is a class of bipartite four-mode two-photon entangled states that facilitate an increase in channel capacity. We also discuss how the proposed scheme can be generalized to the case of two-photon N-mode entangled states for N=6,8.« less
Lougovski, P.; Uskov, D. B.
2015-08-04
Entanglement can effectively increase communication channel capacity as evidenced by dense coding that predicts a capacity gain of 1 bit when compared to entanglement-free protocols. However, dense coding relies on Bell states and when implemented using photons the capacity gain is bounded by 0.585 bits due to one's inability to discriminate between the four optically encoded Bell states. In this research we study the following question: Are there alternative entanglement-assisted protocols that rely only on linear optics, coincidence photon counting, and separable single-photon input states and at the same time provide a greater capacity gain than 0.585 bits? In this study, we show that besides the Bell states there is a class of bipartite four-mode two-photon entangled states that facilitate an increase in channel capacity. We also discuss how the proposed scheme can be generalized to the case of two-photon N-mode entangled states for N=6,8.
Maximal entanglement versus entropy for mixed quantum states
Wei, T.-C.; Goldbart, Paul M.; Kwiat, Paul G.; Nemoto, Kae; Munro, William J.; Verstraete, Frank
2003-02-01
Maximally entangled mixed states are those states that, for a given mixedness, achieve the greatest possible entanglement. For two-qubit systems and for various combinations of entanglement and mixedness measures, the form of the corresponding maximally entangled mixed states is determined primarily analytically. As measures of entanglement, we consider entanglement of formation, relative entropy of entanglement, and negativity; as measures of mixedness, we consider linear and von Neumann entropies. We show that the forms of the maximally entangled mixed states can vary with the combination of (entanglement and mixedness) measures chosen. Moreover, for certain combinations, the forms of the maximally entangled mixed states can change discontinuously at a specific value of the entropy. Along the way, we determine the states that, for a given value of entropy, achieve maximal violation of Bell's inequality.
Nonbilocal measurement via an entangled state
Shmaya, Eran
2005-08-15
Two observers, who share a pair of particles in an entangled mixed state, can use it to perform some nonbilocal measurements over another bipartite system. In particular, one can construct a specific game played by the observers against a coordinator, in which they can score better than a pair of observers who only share a classical communication channel. The existence of such a game is an operational implication of an entanglement witness.
Multi-user distribution of polarization entangled photon pairs
NASA Astrophysics Data System (ADS)
Trapateau, J.; Ghalbouni, J.; Orieux, A.; Diamanti, E.; Zaquine, I.
2015-10-01
We experimentally demonstrate multi-user distribution of polarization entanglement using commercial telecom wavelength division demultiplexers. The entangled photon pairs are generated from a broadband source based on spontaneous parametric down conversion in a periodically poled lithium niobate crystal using a double path setup employing a Michelson interferometer and active phase stabilisation. We test and compare demultiplexers based on various technologies and analyze the effect of their characteristics, such as losses and polarization dependence, on the quality of the distributed entanglement for three channel pairs of each demultiplexer. In all cases, we obtain a Bell inequality violation, whose value depends on the demultiplexer features. This demonstrates that entanglement can be distributed to at least three user pairs of a network from a single source. Additionally, we verify for the best demultiplexer that the violation is maintained when the pairs are distributed over a total channel attenuation corresponding to 20 km of optical fiber. These techniques are therefore suitable for resource-efficient practical implementations of entanglement-based quantum key distribution and other quantum communication network applications.
Multi-user distribution of polarization entangled photon pairs
Trapateau, J.; Orieux, A.; Diamanti, E.; Zaquine, I.; Ghalbouni, J.
2015-10-14
We experimentally demonstrate multi-user distribution of polarization entanglement using commercial telecom wavelength division demultiplexers. The entangled photon pairs are generated from a broadband source based on spontaneous parametric down conversion in a periodically poled lithium niobate crystal using a double path setup employing a Michelson interferometer and active phase stabilisation. We test and compare demultiplexers based on various technologies and analyze the effect of their characteristics, such as losses and polarization dependence, on the quality of the distributed entanglement for three channel pairs of each demultiplexer. In all cases, we obtain a Bell inequality violation, whose value depends on the demultiplexer features. This demonstrates that entanglement can be distributed to at least three user pairs of a network from a single source. Additionally, we verify for the best demultiplexer that the violation is maintained when the pairs are distributed over a total channel attenuation corresponding to 20 km of optical fiber. These techniques are therefore suitable for resource-efficient practical implementations of entanglement-based quantum key distribution and other quantum communication network applications.
Photon exchange and entanglement formation during transmission through a rectangular quantum barrier
Sulyok, Georg; Durstberger-Rennhofer, Katharina; Summhammer, Johann
2015-01-01
When a quantum particle traverses a rectangular potential created by a quantum field both photon exchange and entanglement between particle and field take place. We present the full analytic solution of the Schrödinger equation of the composite particle–field system allowing investigation of these phenomena in detail and comparison to the results of a classical field treatment. Besides entanglement formation, remarkable differences also appear with respect to the symmetry between energy emission and absorption, resonance effects and if the field initially occupies the vacuum state. PMID:26345629
Entanglement of remote transmon qubits by concurrent photon detection - Part 1
NASA Astrophysics Data System (ADS)
Shankar, S.; Narla, A.; Hatridge, M.; Pfaff, W.; Leghtas, Z.; Sliwa, K. M.; Zalys-Geller, E.; Frunzio, L.; Devoret, M. H.
One proposed realization for a quantum computer is the modular architecture, which consists of error-corrected quantum memories that are connected via a quantum router. A fundamental requirement for this modular quantum computer is the ability to entangle arbitrary, distant qubits on demand. This can be realized in circuit QED using a protocol inspired by recent experiments based on trapped ions and nitrogen-vacancy centers. First, each qubit is entangled with a single cavity photon (Fock state n=1) using sideband pulses. On their way out of the cavity, the now flying photons interfere on a beam-splitter and are concurrently detected by a novel microwave photo-multiplier that employs a third qubit-cavity system. In this protocol, the presence of losses in the photon flight path only affect the success probability of creating an entangled state but not its fidelity. In this talk, we present the experimental realization of this protocol for entangling two transmon qubits, focusing on the implementation and optimization of the microwave photo-multiplier. Work supported by ARO, AFOSR and YINQE.
Spatial entanglement of nonvacuum Gaussian states
NASA Astrophysics Data System (ADS)
Kiałka, Filip; Ahmadi, Mehdi; Dragan, Andrzej
2016-06-01
The vacuum state of a relativistic quantum field contains entanglement between regions separated by spacelike intervals. Such spatial entanglement can be revealed using an operational method introduced in [M. Rodriguez-Vazquez, M. del Rey, H. Westman, and J. Leon, Ann. Phys. (N.Y.) 351, 112 (2014), E. G. Brown, M. del Rey, H. Westman, J. Leon, and A. Dragan, Phys. Rev. D 91, 016005 (2015)]. In this approach, a cavity is instantaneously divided into halves by an introduction of an extra perfect mirror. Causal separation of the two regions of the cavity reveals nonlocal spatial correlations present in the field, which can be quantified by measuring particles generated in the process. We use this method to study spatial entanglement properties of nonvacuum Gaussian field states. In particular, we show how to enhance the amount of harvested spatial entanglement by an appropriate choice of the initial state of the field in the cavity. We find a counterintuitive influence of the initial entanglement between cavity modes on the spatial entanglement which is revealed by dividing the cavity in half.
Detection of nonlocal atomic entanglement assisted by single photons
NASA Astrophysics Data System (ADS)
Zhou, Lan; Sheng, Yu-Bo
2014-08-01
We present an efficient way for measuring the entanglement of atoms. The concurrence of atomic entanglement can be obtained according to the probability of picking up the singlet states of the atoms. In this protocol, we require the phenomenon of optical Faraday rotation, but the entangled atoms do not need to be in contact with each other and the atomic entanglement can be distributed nonlocally. Moreover, our way of measuring the concurrence for atoms can also be suitable for other solid systems, such as quantum dots inside microcavities and the nitrogen-vacancy (N-V) defect centers in diamonds, which can also induce the optical Faraday rotation. All these advantages provide important applications in future distributed quantum computations.
Entanglement and Coherence in Quantum State Merging.
Streltsov, A; Chitambar, E; Rana, S; Bera, M N; Winter, A; Lewenstein, M
2016-06-17
Understanding the resource consumption in distributed scenarios is one of the main goals of quantum information theory. A prominent example for such a scenario is the task of quantum state merging, where two parties aim to merge their tripartite quantum state parts. In standard quantum state merging, entanglement is considered to be an expensive resource, while local quantum operations can be performed at no additional cost. However, recent developments show that some local operations could be more expensive than others: it is reasonable to distinguish between local incoherent operations and local operations which can create coherence. This idea leads us to the task of incoherent quantum state merging, where one of the parties has free access to local incoherent operations only. In this case the resources of the process are quantified by pairs of entanglement and coherence. Here, we develop tools for studying this process and apply them to several relevant scenarios. While quantum state merging can lead to a gain of entanglement, our results imply that no merging procedure can gain entanglement and coherence at the same time. We also provide a general lower bound on the entanglement-coherence sum and show that the bound is tight for all pure states. Our results also lead to an incoherent version of Schumacher compression: in this case the compression rate is equal to the von Neumann entropy of the diagonal elements of the corresponding quantum state. PMID:27367369
Entanglement and Coherence in Quantum State Merging
NASA Astrophysics Data System (ADS)
Streltsov, A.; Chitambar, E.; Rana, S.; Bera, M. N.; Winter, A.; Lewenstein, M.
2016-06-01
Understanding the resource consumption in distributed scenarios is one of the main goals of quantum information theory. A prominent example for such a scenario is the task of quantum state merging, where two parties aim to merge their tripartite quantum state parts. In standard quantum state merging, entanglement is considered to be an expensive resource, while local quantum operations can be performed at no additional cost. However, recent developments show that some local operations could be more expensive than others: it is reasonable to distinguish between local incoherent operations and local operations which can create coherence. This idea leads us to the task of incoherent quantum state merging, where one of the parties has free access to local incoherent operations only. In this case the resources of the process are quantified by pairs of entanglement and coherence. Here, we develop tools for studying this process and apply them to several relevant scenarios. While quantum state merging can lead to a gain of entanglement, our results imply that no merging procedure can gain entanglement and coherence at the same time. We also provide a general lower bound on the entanglement-coherence sum and show that the bound is tight for all pure states. Our results also lead to an incoherent version of Schumacher compression: in this case the compression rate is equal to the von Neumann entropy of the diagonal elements of the corresponding quantum state.
Liu, Siping; Yu, Rong; Li, Jiahua; Wu, Ying
2013-12-28
We explore the entanglement generation and the corresponding dynamics between two separate nitrogen-vacancy (NV) centers in diamond nanocrystal coupled to a photonic molecule consisting of a pair of coupled photonic crystal (PC) cavities. By calculating the entanglement concurrence with readily available experimental parameters, it is found that the entanglement degree strongly depends on the cavity-cavity hopping strength and the NV-center-cavity detuning. High concurrence peak and long-lived entanglement plateau can be achieved by properly adjusting practical system parameters. Meanwhile, we also discuss the influence of the coupling strength between the NV centers and the cavity modes on the behavior of the concurrence. Such a PC-NV system can be employed for quantum entanglement generation and represents a building block for an integrated nanophotonic network in a solid-state cavity quantum electrodynamics platform. In addition, the present theory can also be applied to other similar systems, such as two single quantum emitters positioned close to a microtoroidal resonator with the whispering-gallery-mode fields propagating inside the resonator.
Schaibley, J R; Burgers, A P; McCracken, G A; Duan, L-M; Berman, P R; Steel, D G; Bracker, A S; Gammon, D; Sham, L J
2013-04-19
The electron spin state of a singly charged semiconductor quantum dot has been shown to form a suitable single qubit for quantum computing architectures with fast gate times. A key challenge in realizing a useful quantum dot quantum computing architecture lies in demonstrating the ability to scale the system to many qubits. In this Letter, we report an all optical experimental demonstration of quantum entanglement between a single electron spin confined to a single charged semiconductor quantum dot and the polarization state of a photon spontaneously emitted from the quantum dot's excited state. We obtain a lower bound on the fidelity of entanglement of 0.59±0.04, which is 84% of the maximum achievable given the timing resolution of available single photon detectors. In future applications, such as measurement-based spin-spin entanglement which does not require sub-nanosecond timing resolution, we estimate that this system would enable near ideal performance. The inferred (usable) entanglement generation rate is 3×10(3) s(-1). This spin-photon entanglement is the first step to a scalable quantum dot quantum computing architecture relying on photon (flying) qubits to mediate entanglement between distant nodes of a quantum dot network. PMID:23679636
Multipartite entangled states in particle mixing
Blasone, M.; Dell'Anno, F.; De Siena, S.; Di Mauro, M.; Illuminati, F.
2008-05-01
In the physics of flavor mixing, the flavor states are given by superpositions of mass eigenstates. By using the occupation number to define a multiqubit space, the flavor states can be interpreted as multipartite mode-entangled states. By exploiting a suitable global measure of entanglement, based on the entropies related to all possible bipartitions of the system, we analyze the correlation properties of such states in the instances of three- and four-flavor mixing. Depending on the mixing parameters, and, in particular, on the values taken by the free phases, responsible for the CP-violation, entanglement concentrates in certain bipartitions. We quantify in detail the amount and the distribution of entanglement in the physically relevant cases of flavor mixing in quark and neutrino systems. By using the wave packet description for localized particles, we use the global measure of entanglement, suitably adapted for the instance of multipartite mixed states, to analyze the decoherence, induced by the free evolution dynamics, on the quantum correlations of stationary neutrino beams. We define a decoherence length as the distance associated with the vanishing of the coherent interference effects among massive neutrino states. We investigate the role of the CP-violating phase in the decoherence process.
Nonlocal entanglement of coherent states, complementarity, and quantum erasure
Gerry, Christopher C.; Grobe, R.
2007-03-15
We describe a nonlocal method for generating entangled coherent states of a two-mode field wherein the field modes never meet. The proposed method is an extension of an earlier proposal [C. C. Gerry, Phys. Rev. A 59, 4095 (1999)] for the generation of superpositions of coherent states. A single photon injected into a Mach-Zehnder interferometer with cross-Kerr media in both arms coupling with two external fields in coherent states produces entangled coherent states upon detection at one of the output ports. We point out that our proposal can be alternatively viewed as a 'which path' experiment, and in the case of only one external field, we describe the implementation of a quantum eraser.
A bright PPKTP waveguide source of polarization entangled photons
Fanto, Michael; Tison, Christoper C.; Holwand, Gregory A; Preble, Dr. Stefan F; Alsing, Paul; Smith IV, Amos M
2015-01-01
The need for bright efficient sources of entangled photons has been a subject of tremendous research over the last decade. Researchers have been working to increase the brightness and purity to help overcome the spontaneous nature of the sources. Periodic poling has been implemented to allow for the use of crystals that would not normally satisfy the phase matching conditions. Utilizing periodic poling and single mode waveguide confinement of the pump field has yielded extremely large effective nonlinearities in sources easily producing millions of photon pairs. Here we will demonstrate these large nonlinearity effects in a periodically poled potassium titanyl phosphate (PPKTP) waveguide as well as characterizing the source purity.
Entanglement purification protocol for a mixture of a pure entangled state and a pure product state
Czechlewski, Mikolaj; Wojcik, Antoni; Grudka, Andrzej; Ishizaka, Satoshi
2009-07-15
We present an entanglement purification protocol for a mixture of a pure entangled state and a pure product state, which are orthogonal to each other. The protocol is a combination of bisection method and one-way hashing protocol. We give recursive formula for the rate of the protocol for different states, i.e., the number of maximally entangled two-qubit pairs obtained with the protocol per a single copy of the initial state. We also calculate numerically the rate for some states.
Ultrafast time-division demultiplexing of polarization-entangled photons.
Donohue, John M; Lavoie, Jonathan; Resch, Kevin J
2014-10-17
Maximizing the information transmission rate through quantum channels is essential for practical implementation of quantum communication. Time-division multiplexing is an approach for which the ultimate rate requires the ability to manipulate and detect single photons on ultrafast time scales while preserving their quantum correlations. Here we demonstrate the demultiplexing of a train of pulsed single photons using time-to-frequency conversion while preserving their polarization entanglement with a partner photon. Our technique converts a pulse train with 2.69 ps spacing to a frequency comb with 307 GHz spacing which may be resolved using diffraction techniques. Our work enables ultrafast multiplexing of quantum information with commercially available single-photon detectors. PMID:25361257
Deterministic Generation of Arbitrary Photonic States Assisted by Dissipation
NASA Astrophysics Data System (ADS)
González-Tudela, A.; Paulisch, V.; Chang, D. E.; Kimble, H. J.; Cirac, J. I.
2015-10-01
A scheme to utilize atomlike emitters coupled to nanophotonic waveguides is proposed for the generation of many-body entangled states and for the reversible mapping of these states of matter to photonic states of an optical pulse in the waveguide. Our protocol makes use of decoherence-free subspaces (DFSs) for the atomic emitters with coherent evolution within the DFSs enforced by strong dissipative coupling to the waveguide. By switching from subradiant to superradiant states, entangled atomic states are mapped to photonic states with high fidelity. An implementation using ultracold atoms coupled to a photonic crystal waveguide is discussed.
Total teleportation of a single-photon state
Humble, Travis S; Bennink, Ryan S; Grice, Warren P
2008-01-01
Recent demonstrations of teleportation have transferred quantum information encoded into either polarization or field-quadrature degrees of freedom (DOFs), but an outstanding question is how to simultaneously teleport quantum information encoded into multiple DOFs. We describe how the transverse-spatial, spectral and polarization states of a single photon can be simultaneously teleported using a pair of multimode, polarization-entangled photons derived from spontaneous parametric down-conversion. Furthermore, when the initial photon pair is maximally entangled in the spatial, spectral, and polarization DOFs then the photon s full quantum state can be reliably teleported using a Bell-state measurement based on sum-frequency generation.
Total teleportation of a single-photon state
NASA Astrophysics Data System (ADS)
Humble, Travis S.; Bennink, Ryan S.; Grice, Warren P.
2008-08-01
Recent demonstrations of teleportation have transferred quantum information encoded into either polarization or fieldquadrature degrees of freedom (DOFs), but an outstanding question is how to simultaneously teleport quantum information encoded into multiple DOFs. We describe how the transverse-spatial, spectral and polarization states of a single photon can be simultaneously teleported using a pair of multimode, polarization-entangled photons derived from spontaneous parametric down-conversion. Furthermore, when the initial photon pair is maximally entangled in the spatial, spectral, and polarization DOFs then the photon's full quantum state can be reliably teleported using a Bell-state measurement based on sum-frequency generation.
NASA Astrophysics Data System (ADS)
Richardson, Chris; Sabottke, Carl; Yurtsever, Ulvi; Lamas, Antia; Dowling, Jonathan; Anisimov, Petr
2012-02-01
We develop an improvement to the weak laser pulse BB84 scheme for quantum key distribution, which utilizes entanglement to improve the security of the scheme and enhance its resilience to the photon number splitting attack. This protocol relies on the non-commutation of photon phase and number to detect an eavesdropper performing quantum non-demolition measurement on number. The potential advantages and disadvantages of this scheme are compared to the coherent decoy state solution. Most entanglement based quantum key distribution schemes rely on violations of Bell's inequalities to ensure security. However, this is not the strategy that our entanglement enhanced (EE) BB84 employs here. Instead, we detect Eve by introducing an entangled quantum state into the system that is sensitive to Eve's QND measurements. This allows for a recovery of an approximately linear dependence on transmittivity for the key rate. EE BB84 shares this advantage with coherent decoy state protocols as well as schemes that utilize strong phase reference pulses to eliminate Eve's ability to send Bob vacuum signals.
Tripartite information of highly entangled states
NASA Astrophysics Data System (ADS)
Rota, Massimiliano
2016-04-01
Holographic systems require monogamous mutual information for validity of semiclassical geometry. This is encoded by the sign of the tripartite information ( I3). We investigate the behaviour of I3 for all partitionings of systems in states which are highly entangled in a multipartite or bipartite sense. In the case of multipartite entanglement we propose an algorithmic construction that we conjecture can be used to build local maxima of I3 for any partitioning. In case of bipartite entanglement we classify the possible values of I3 for perfect states and investigate, in some examples, the effect on its sign definiteness due to deformations of the states. Finally we comment on the proposal of using I3 as a parameter of scrambling, arguing that in general its average over qubits permutations could be a more sensible measure.
Delayed birth of distillable entanglement in the evolution of bound entangled states
Derkacz, Lukasz; Jakobczyk, Lech
2010-08-15
The dynamical creation of entanglement between three-level atoms coupled to the common vacuum is investigated. For the class of bound entangled initial states, we show that the dynamics of closely separated atoms generates stationary distillable entanglement of asymptotic states. We also find that the effect of delayed sudden birth of distillable entanglement occurs in the case of atoms separated by a distance comparable with the radiation wavelength.
Comment on 'Teleportation of entangled states without Bell-state measurement'
Zela, F. de
2006-08-15
We consider a protocol recently proposed by Cardoso et al. for teleporting entangled photon states from a bimodal cavity to another one. It is shown that the proposed protocol can afford full fidelity instead of the 97% fidelity that the authors ascribed to their scheme.
Towards quantum-dot arrays of entangled photon emitters
NASA Astrophysics Data System (ADS)
Juska, Gediminas; Dimastrodonato, Valeria; Mereni, Lorenzo O.; Gocalinska, Agnieszka; Pelucchi, Emanuele
2013-07-01
To make photonic quantum information a reality, a number of extraordinary challenges need to be overcome. One challenge is to achieve large arrays of reproducible `entangled' photon generators, while maintaining compatibility for integration with optical devices and detectors. Semiconductor quantum dots are potentially ideal for this as they allow photons to be generated on demand without relying on probabilistic processes. Nevertheless, most quantum-dot systems are limited by their intrinsic lack of symmetry, which allows only a small number (typically 1 out of 100, or worse) of good dots to be achieved per chip. The recent retraction of Mohan et al. seemed to question the very possibility of simultaneously achieving site control and high symmetry. Here, we show that with a new family of (111)-grown pyramidal site-controlled InGaAs1-δNδ quantum dots it is possible to overcome previous hurdles and obtain areas with up to 15% of polarization-entangled photon emitters, with fidelities as high as 0.721 +/- 0.043.
Entanglement and symmetry in permutation-symmetric states
Markham, Damian J. H.
2011-04-15
We investigate the relationship between multipartite entanglement and symmetry, focusing on permutation symmetric states. We give a highly intuitive geometric interpretation to entanglement via the Majorana representation, where these states correspond to points on a unit sphere. We use this to show how various entanglement properties are determined by the symmetry properties of the states. The geometric measure of entanglement is thus phrased entirely as a geometric optimization and a condition for the equivalence of entanglement measures written in terms of point symmetries. Finally, we see that different symmetries of the states correspond to different types of entanglement with respect to interconvertibility under stochastic local operations and classical communication.
Kang, Dongpeng; Anirban, Ankita; Helmy, Amr S
2016-06-27
Generating entangled photons from a monolithic chip is a major milestone towards real-life applications of optical quantum information processing including quantum key distribution and quantum computing. Ultrabroadband entangled photons are of particular interest to various applications such as quantum metrology and multi-party entanglement distribution. In this work, we demonstrate the direct generation of broadband wavelength-multiplexed polarization entangled photons from a semiconductor chip for the first time. Without the use of any off-chip compensation or interferometry, entangled photons with a signal-idler separation as large as 95 nm in the telecom band were observed. The highest concurrence of 0.98±0.01 achieved in this work is also the highest, to the best of our knowledge, comparing to all previously demonstrated semiconductor waveguide sources. This work paves the way for fully integrated, ultrabroadband sources of polarization entangled photons. PMID:27410667
Atomic and Photonic Entanglement Generation in n Coupled Atom-Cavity Systems
NASA Astrophysics Data System (ADS)
Sufiani, R.; Darkhosh, A.
2015-07-01
Based on two-photon Jaynes-Cummings Hamiltonian for the n coupled optical cavities each of them containing a single three level atom, the n-qubit and n-photonic state transfer between the corresponding atoms and cavities is investigated. In fact, we consider that the cavities are located at the nodes (vertices) of the complete network (graph) K n at which all of the nodes are connected, so that the cavities are interact with each other (via two photon exchange) completely. Then, quantum state transfer, photon transition between cavities and entanglement generations between n atoms are discussed. More clearly, by employing the consistency of number of photons and atomic excitations (the symmetry of Hamiltonian), the hamiltonian of the system is reduced from 3 n dimensional space into 2 n dimensional one. Moreover, by introducing suitable basis for the atom-cavity state space based on Fourier transform, the reduced Hamiltonian is block-diagonalized, with 2 dimensional blocks. Then, the initial state of the system is evolved under the corresponding Hamiltonian and the suitable times T at which the initially unentangled atoms, become maximally entangled, are determined in terms of the hopping strength ξ between cavities.
Quantifying asymmetry of quantum states using entanglement
NASA Astrophysics Data System (ADS)
Toloui, Borzu
2013-03-01
For open systems, symmetric dynamics do not always lead to conservation laws. We show that, for a dynamic symmetry associated with a compact Lie group, one can derive new selection rules from entanglement theory. These selection rules apply to both closed and open systems as well as reversible and irreversible time evolutions. Our approach is based on an embedding of the system's Hilbert space into a tensor product of two Hilbert spaces allowing for the symmetric dynamics to be simulated with local operations. The entanglement of the embedded states determines which transformations are forbidden because of the symmetry. In fact, every bipartite entanglement monotone can be used to quantify the asymmetry of the initial states. Moreover, where the dynamics is reversible, each of these monotones becomes a new conserved quantity. This research has been supported by the Institute for Quantum Information Science (IQIS) at the University of Calgary, Alberta Innovates, NSERC, General Dynamics Canada, and MITACS.
A monolithically integrated polarization entangled photon pair source on a silicon chip
Matsuda, Nobuyuki; Le Jeannic, Hanna; Fukuda, Hiroshi; Tsuchizawa, Tai; Munro, William John; Shimizu, Kaoru; Yamada, Koji; Tokura, Yasuhiro; Takesue, Hiroki
2012-01-01
Integrated photonic circuits are one of the most promising platforms for large-scale photonic quantum information systems due to their small physical size and stable interferometers with near-perfect lateral-mode overlaps. Since many quantum information protocols are based on qubits defined by the polarization of photons, we must develop integrated building blocks to generate, manipulate, and measure the polarization-encoded quantum state on a chip. The generation unit is particularly important. Here we show the first integrated polarization-entangled photon pair source on a chip. We have implemented the source as a simple and stable silicon-on-insulator photonic circuit that generates an entangled state with 91 ± 2% fidelity. The source is equipped with versatile interfaces for silica-on-silicon or other types of waveguide platforms that accommodate the polarization manipulation and projection devices as well as pump light sources. Therefore, we are ready for the full-scale implementation of photonic quantum information systems on a chip. PMID:23150781
Entangled, guided photon generation in (1+1)-dimensional photonic crystals
Sciscione, L.; Centini, M.; Sibilia, C.; Bertolotti, M.; Scalora, M.
2006-07-15
A scheme based on photonic crystal technology is proposed as an ultrabright source of entangled photons on a miniaturized scale. The geometry consists of a multilayer microcavity, excited by a resonant pump frequency, such that the emitted photons are guided transversally to the direction of the incident pump. The entanglement occurs in direction, frequency, and polarization, and the bandwidth of the emitted photons is of the order of 1 nm. We propose a feasible design based on Al{sub 0.3}Ga{sub 0.7}As/Al{sub 2}O{sub 3} structures and predict an emission rate 10{sup 5} pairs per second with 100 mW pump power. These results are promising for realization of chip and future quantum computer applications.
Rice, Perry R.
2005-07-01
I consider several interesting aspects of a new light source, a two-level atom, or N two-level atoms inside an optical parametric oscillator. I find that in the weak driving limit, detection of a transmitted or fluorescent photon generates a highly entangled state of the atom and the cavity. This entanglement can be used with beam splitters to create more complex quantum states and implement teleportation protocols. Also, one can store a single photon in the atoms, along the lines of recent slow and stopped light proposals and experiments.
NASA Astrophysics Data System (ADS)
Snyder, Douglas
2014-03-01
It is shown theoretically that the reduced density matrix is not applicable to the case where the states of one of two entangled particles relevant to the entanglement of the particles, and which provide ww info to the other particle, are eliminated before any particle detections are made. Instead, the entanglement is eliminated and the particle whose states are not eliminated enters into a pure state. A proposed experiment where this case (option 1) is tested is presented. The experiment has a second option (option 2) in which the states of both of the entangled particles that are relevant to the entanglement are preserved. In the experiment, the entangled particles become spatially separated. Elimination of the states of one of the entangled particles relevant to the entanglement results in the elimination of the entanglement and the placement of the other particle into a pure state. We have a delayed choice with regard to the particle whose states can be eliminated that affects the overall distribution (either reflecting interference or ww info) of the other particle that it is initially entangled with and that becomes physically distant from it. If the overall distribution of the signal photons in option 1 exhibits fringes and the overall distribution of the signal photons in option 2 is characteristic of ww info, then the reduced density matrix is not applicable to the case where the states of the signal photon relevant to the entanglement are eliminated before any detections are made.
Entanglement bound for multipartite pure states based on local measurements
Jiang Lizhen; Chen Xiaoyu; Ye Tianyu
2011-10-15
An entanglement bound based on local measurements is introduced for multipartite pure states. It is the upper bound of the geometric measure and the relative entropy of entanglement. It is the lower bound of the minimal-measurement entropy. For pure bipartite states, the bound is equal to the entanglement entropy. The bound is applied to pure tripartite qubit states and the exact tripartite relative entropy of entanglement is obtained for a wide class of states.
Entanglement purification of unknown quantum states
Brun, Todd A.; Caves, Carlton M.; Schack, Ru''diger
2001-04-01
A concern has been expressed that ''the Jaynes principle can produce fake entanglement'' [R. Horodecki , Phys. Rev. A 59, 1799 (1999)]. In this paper we discuss the general problem of distilling maximally entangled states from N copies of a bipartite quantum system about which only partial information is known, for instance, in the form of a given expectation value. We point out that there is indeed a problem with applying the Jaynes principle of maximum entropy to more than one copy of a system, but the nature of this problem is classical and was discussed extensively by Jaynes. Under the additional assumption that the state {rho}{sup (N)} of the N copies of the quantum system is exchangeable, one can write down a simple general expression for {rho}{sup (N)}. By measuring one or more of the subsystems, one can gain information and update the state estimate for the remaining subsystems with the quantum version of the Bayes rule. Using this rule, we show how to modify two standard entanglement purification protocols, one-way hashing and recurrence, so that they can be applied to exchangeable states. We thus give an explicit algorithm for distilling entanglement from an unknown or partially known quantum state.
NASA Astrophysics Data System (ADS)
Assadi, Leila; Jafarpour, Mojtaba
2016-07-01
We use concurrence to study bipartite entanglement, Meyer-Wallach measure and its generalizations to study multi-partite entanglement and MABK and SASA inequalities to study the non-local properties of the 4-qubit entangled graph states, quantitatively. Then, we present 3 classifications, each one in accordance with one of the aforementioned properties. We also observe that the classification according to multipartite entanglement does exactly coincide with that according to nonlocal properties, but does not match with that according to bipartite entanglement. This observation signifies the fact that non-locality and multipartite entanglement enjoy the same basic underlying principles, while bipartite entanglement may not reveal the non-locality issue in its entirety.
Highly entangled photons from hybrid piezoelectric-semiconductor quantum dot devices.
Trotta, Rinaldo; Wildmann, Johannes S; Zallo, Eugenio; Schmidt, Oliver G; Rastelli, Armando
2014-06-11
Entanglement resources are key ingredients of future quantum technologies. If they could be efficiently integrated into a semiconductor platform, a new generation of devices could be envisioned, whose quantum-mechanical functionalities are controlled via the mature semiconductor technology. Epitaxial quantum dots (QDs) embedded in diodes would embody such ideal quantum devices, but a fine-structure splitting (FSS) between the bright exciton states lowers dramatically the degree of entanglement of the sources and hampers severely their real exploitation in the foreseen applications. In this work, we overcome this hurdle using strain-tunable optoelectronic devices, where any QD can be tuned for the emission of photon pairs featuring the highest degree of entanglement ever reported for QDs, with concurrence as high as 0.75 ± 0.02. Furthermore, we study the evolution of Bell's parameters as a function of FSS and demonstrate for the first time that filtering-free violation of Bell's inequalities requires the FSS to be smaller than 1 μeV. This upper limit for the FSS also sets the tuning range of exciton energies (∼1 meV) over which our device operates as an energy-tunable source of highly entangled photons. A moderate temporal filtering further increases the concurrence and the tunability of exciton energies up to 0.82 and 2 meV, respectively, though at the expense of 60% reduction of count rate. PMID:24845369
Li, Ming; Zou, Chang-Ling; Ren, Xi-Feng; Xiong, Xiao; Cai, Yong-Jing; Guo, Guo-Ping; Tong, Li-Min; Guo, Guang-Can
2015-04-01
Photonic quantum technologies have been extensively studied in quantum information science, owing to the high-speed transmission and outstanding low-noise properties of photons. However, applications based on photonic entanglement are restricted due to the diffraction limit. In this work, we demonstrate for the first time the maintaining of quantum polarization entanglement in a nanoscale hybrid plasmonic waveguide composed of a fiber taper and a silver nanowire. The transmitted state throughout the waveguide has a fidelity of 0.932 with the maximally polarization entangled state Φ(+). Furthermore, the Clauser, Horne, Shimony, and Holt (CHSH) inequality test performed, resulting in value of 2.495 ± 0.147 > 2, demonstrates the violation of the hidden variable model. Because the plasmonic waveguide confines the effective mode area to subwavelength scale, it can bridge nanophotonics and quantum optics and may be used as near-field quantum probe in a quantum near-field micro/nanoscope, which can realize high spatial resolution, ultrasensitive, fiber-integrated, and plasmon-enhanced detection. PMID:25775140
Sheng Yubo; Deng Fuguo
2010-03-15
Entanglement purification is a very important element for long-distance quantum communication. Different from all the existing entanglement purification protocols (EPPs) in which two parties can only obtain some quantum systems in a mixed entangled state with a higher fidelity probabilistically by consuming quantum resources exponentially, here we present a deterministic EPP with hyperentanglement. Using this protocol, the two parties can, in principle, obtain deterministically maximally entangled pure states in polarization without destroying any less-entangled photon pair, which will improve the efficiency of long-distance quantum communication exponentially. Meanwhile, it will be shown that this EPP can be used to complete nonlocal Bell-state analysis perfectly. We also discuss this EPP in a practical transmission.
Generating coherent states of entangled spins
Yu Hongyi; Luo Yu; Yao Wang
2011-09-15
A coherent state of many spins contains quantum entanglement, which increases with a decrease in the collective spin value. We present a scheme to engineer this class of pure state based on incoherent spin pumping with a few collective raising or lowering operators. In a pumping scenario aimed for maximum entanglement, the steady state of N-pumped spin qubits realizes the ideal resource for the 1{yields}(N/2) quantum telecloning. We show how the scheme can be implemented in a realistic system of atomic spin qubits in an optical lattice. Error analysis shows that high-fidelity state engineering is possible for N{approx}O(100) spins in the presence of decoherence. The scheme can also prepare a resource state for the secret sharing protocol and for the construction of the large-scale Affleck-Kennedy-Lieb-Tasaki state.
NASA Astrophysics Data System (ADS)
Dai, Hong-Yi; Zhang, Ming; Li, Cheng-Zu
2008-04-01
We present a scheme for probabilistically teleporting an unknown three-level bipartite entangled state by using a partial entangled three-level bipartite state as quantum channel. This scheme can be directly generalized to probabilistically teleport an unknown three-level k-particle entangled state by a partial three-level bipartite entangled state. All kinds of unitary transformations are given in detail. We calculate the successful total probability and the total classical communication cost required for this scheme.
Superposition and entanglement of mesoscopic squeezed vacuum states in cavity QED
Chen Changyong; Feng Mang; Gao Kelin
2006-03-15
We propose a scheme to generate superposition and entanglement between the mesoscopic squeezed vacuum states by considering the two-photon interaction of N two-level atoms in a cavity with high quality factor, assisted by a strong driving field. By virtue of specific choices of the cavity detuning, a number of multiparty entangled states can be prepared, including the entanglement between the atomic and the squeezed vacuum cavity states and between the squeezed vacuum states and the coherent states of the cavities. We also present how to prepare entangled states and 'Schroedinger cats' states regarding the squeezed vacuum states of the cavity modes. The possible extension and application of our scheme are discussed. Our scheme is close to the reach with current cavity QED techniques.
Yang Jian; Zhang Han; Peng Chengzhi; Chen Zengbing; Bao Xiaohui; Chen Shuai; Pan Jianwei
2009-10-15
In this paper, we report a realization of synchronization-free quantum teleportation and narrowband three-photon entanglement through interfering narrowband photon sources. Since both the single-photon and the entangled photon pair utilized are completely autonomous, it removes the requirement of high-demanding synchronization techniques in long-distance quantum communication with pulsed spontaneous parametric down-conversion sources. The frequency linewidth of the three-photon entanglement realized is on the order of several MHz, which matches the requirement of atomic ensemble based quantum memories. Such a narrowband multiphoton source will have applications in some advanced quantum communication protocols and linear optical quantum computation.
NASA Astrophysics Data System (ADS)
Qin, Su-Juan; Wen, Qiao-Yan; Lin, Song; Guo, Fen-Zhuo; Zhu, Fu-Chen
2009-10-01
The security of a deterministic secure quantum communication using four-particle genuine entangled state and entanglement swapping [X.M. Xiu, H.K. Dong, L. Dong, Y.J. Cao, F. Chi, Opt. Commun. 282 (2009) 2457] is analyzed. It is shown that an eavesdropper can entangle an ancilla without introducing any error in the security test utilizing a speciality of the four-particle genuine entangled state. Moreover, the eavesdropper can distill a quarter of the secret information from her entangled ancilla. Finally, a simple improvement to resist this attack is proposed.
Negative entanglement measure for bipartite separable mixed states
NASA Astrophysics Data System (ADS)
Zhang, Cheng-Jie; Han, Yong-Jian; Zhang, Yong-Sheng; Wu, Yu-Chun; Zhou, Xiang-Fa; Guo, Guang-Can
2010-12-01
We define a negative entanglement measure for separable states which shows how much entanglement one should compensate the unentangled state, at the least, to change it into an entangled state. For two-qubit systems and some special classes of states in higher-dimensional systems, the explicit formula and the lower bounds for the negative entanglement measure (NEM) have been presented, and it always vanishes for bipartite separable pure states. The negative entanglement measure can be used as a useful quantity to describe the entanglement dynamics and the quantum phase transition. In the transverse Ising model, the first derivatives of negative entanglement measure diverge on approaching the critical value of the quantum phase transition, although these two-site reduced density matrices have no entanglement at all. In the one-dimensional (1D) Bose-Hubbard model, the NEM as a function of t/U changes from zero to negative on approaching the critical point of quantum phase transition.
Negative entanglement measure for bipartite separable mixed states
Zhang Chengjie; Han Yongjian; Zhang Yongsheng; Wu Yuchun; Zhou Xiangfa; Guo Guangcan
2010-12-15
We define a negative entanglement measure for separable states which shows how much entanglement one should compensate the unentangled state, at the least, to change it into an entangled state. For two-qubit systems and some special classes of states in higher-dimensional systems, the explicit formula and the lower bounds for the negative entanglement measure (NEM) have been presented, and it always vanishes for bipartite separable pure states. The negative entanglement measure can be used as a useful quantity to describe the entanglement dynamics and the quantum phase transition. In the transverse Ising model, the first derivatives of negative entanglement measure diverge on approaching the critical value of the quantum phase transition, although these two-site reduced density matrices have no entanglement at all. In the one-dimensional (1D) Bose-Hubbard model, the NEM as a function of t/U changes from zero to negative on approaching the critical point of quantum phase transition.
Entangled exciton states in quantum dot molecules
NASA Astrophysics Data System (ADS)
Bayer, Manfred
2002-03-01
Currently there is strong interest in quantum information processing(See, for example, The Physics of Quantum Information, eds. D. Bouwmeester, A. Ekert and A. Zeilinger (Springer, Berlin, 2000).) in a solid state environment. Many approaches mimic atomic physics concepts in which semiconductor quantum dots are implemented as artificial atoms. An essential building block of a quantum processor is a gate which entangles the states of two quantum bits. Recently a pair of vertically aligned quantum dots has been suggested as optically driven quantum gate(P. Hawrylak, S. Fafard, and Z. R. Wasilewski, Cond. Matter News 7, 16 (1999).)(M. Bayer, P. Hawrylak, K. Hinzer, S. Fafard, M. Korkusinski, Z.R. Wasilewski, O. Stern, and A. Forchel, Science 291, 451 (2001).): The quantum bits are individual carriers either on dot zero or dot one. The different dot indices play the same role as a "spin", therefore we call them "isospin". Quantum mechanical tunneling between the dots rotates the isospin and leads to superposition of these states. The quantum gate is built when two different particles, an electron and a hole, are created optically. The two particles form entangled isospin states. Here we present spectrocsopic studies of single self-assembled InAs/GaAs quantum dot molecules that support the feasibility of this proposal. The evolution of the excitonic recombination spectrum with varying separation between the dots allows us to demonstrate coherent tunneling of carriers across the separating barrier and the formation of entangled exciton states: Due to the coupling between the dots the exciton states show a splitting that increases with decreasing barrier width. For barrier widths below 5 nm it exceeds the thermal energy at room temperature. For a given barrier width, we find only small variations of the tunneling induced splitting demonstrating a good homogeneity within a molecule ensemble. The entanglement may be controlled by application of electromagnetic field. For
NASA Astrophysics Data System (ADS)
Shimizu, Kaoru; Imoto, Nobuyuki
2000-11-01
We propose a single-photon interferometer which provides cryptographic quantum communication equivalent to that obtained using a pair of polarization entangled photon twins as a carrier [Phys. Rev. A 60, 157 (1999)]. Instead of manipulating and measuring the internal states of entangled photon twins, cryptographic quantum communication is possible by manipulating a single photon in an extended interferometer. The use of the single-photon interferometer offers significant experimental advantages compared to our previous approach.
NASA Astrophysics Data System (ADS)
Wang, Li-Die; Wang, Li-Tao; Yang, Mou; Xu, Jing-Zhou; Wang, Z. D.; Bai, Yan-Kui
2016-06-01
The maximally entangled state can be in a mixed state as well as the well-known pure state. Taking the negativity as a measure of entanglement, we study the entanglement dynamics of bipartite, mixed maximally entangled states (MMESs) in multipartite cavity-reservoir systems. It is found that the MMES can exhibit the phenomenon of entanglement sudden death, which is quite different from the asymptotic decay of the pure-Bell-state case. We also find that maximal entanglement cannot guarantee maximal nonlocality, and the MMES does not correspond to the state with maximal measurement-induced nonlocality (MIN). In fact, the value and dynamic behavior of the MIN for the MMESs are dependent on the mixed-state probability. In addition, we investigate the distributions of negativity and the MIN in a multipartite system, where the two types of correlations have different monogamous properties.
Interferometric source of multi-color, multi-beam entangled photons with mirror and mixer
Dress, William B.; Kisner, Roger A.; Richards, Roger K.
2004-06-01
53 Systems and methods are described for an interferometric source of multi-color, multi-beam entangled photons. An apparatus includes: a multi-refringent device optically coupled to a source of coherent energy, the multi-refringent device providing a beam of multi-color entangled photons; a condenser device optically coupled to the multi-refringent device, the condenser device i) including a mirror and a mixer and ii) converging two spatially resolved portions of the beam of multi-color entangled photons into a converged multi-color entangled photon beam; a tunable phase adjuster optically coupled to the condenser device, the tunable phase adjuster changing a phase of at least a portion of the converged multi-color entangled photon beam to generate a first interferometeric multi-color entangled photon beam; and a beam splitter optically coupled to the condenser device, the beam splitter combining the first interferometeric multi-color entangled photon beam with a second interferometric multi-color entangled photon beam.
Generation of hybrid four-qubit entangled decoherence-free states assisted by the cavity-QED system
NASA Astrophysics Data System (ADS)
Zhou, You-Sheng; Li, Xian; Deng, Yun; Li, Hui-Ran; Luo, Ming-Xing
2016-05-01
We propose three effective protocols to generate four-qubit entangled decoherence-free states assisted by the cavity-QED system. These schemes are based on optical selection rules realized with a single electron charged self-assembled GaAs/InAs quantum dot in a micropillar resonator. Compared with previous photonic protocols, the first scheme is to replace the entangled-state resources with much simpler single-photon resources and has a deterministic success probability. Moreover, the cavity-QED system may be used to generate four-spin entangled decoherence-free states and hybrid four-qubit of spin-photon entangled decoherence-free states. These states may be applied up to different requirements because of different superiorities of photons and spins. All schemes may be implemented with current physical technologies.
Unitarily localizable entanglement of Gaussian states
Serafini, Alessio; Adesso, Gerardo; Illuminati, Fabrizio
2005-03-01
We consider generic (mxn)-mode bipartitions of continuous-variable systems, and study the associated bisymmetric multimode Gaussian states. They are defined as (m+n)-mode Gaussian states invariant under local mode permutations on the m-mode and n-mode subsystems. We prove that such states are equivalent, under local unitary transformations, to the tensor product of a two-mode state and of m+n-2 uncorrelated single-mode states. The entanglement between the m-mode and the n-mode blocks can then be completely concentrated on a single pair of modes by means of local unitary operations alone. This result allows us to prove that the PPT (positivity of the partial transpose) condition is necessary and sufficient for the separability of (m+n)-mode bisymmetric Gaussian states. We determine exactly their negativity and identify a subset of bisymmetric states whose multimode entanglement of formation can be computed analytically. We consider explicit examples of pure and mixed bisymmetric states and study their entanglement scaling with the number of modes.
Simultaneous Teleportation of the Spectral and Polarization States of a Photon
Humble, Travis S; Bennink, Ryan S; Grice, Warren P
2008-01-01
We describe how spectrally multimode, polarization-entangled photons simultaneously teleport quantum information encoded into the spectral and polarization degrees of freedom of a single photon using sum frequency generation to implement a Bell-state measurement.
NASA Astrophysics Data System (ADS)
Zhang, Wei; Ding, Dong-Sheng; Shi, Shuai; Li, Yan; Zhou, Zhi-Yuan; Shi, Bao-Sen; Guo, Guang-Can
2016-02-01
Quantum memory is an essential building block for quantum communication and scalable linear quantum computation. Storing two-color entangled photons with one photon being at the telecommunication (telecom) wavelength while the other photon is compatible with quantum memory has great advantages toward the realization of the fiber-based long-distance quantum communication with the aid of quantum repeaters. Here, we report an experimental realization of storing a photon entangled with a telecom photon in polarization as an atomic spin wave in a cold atomic ensemble, thus establishing the entanglement between the telecom-band photon and the atomic-ensemble memory in a polarization degree of freedom. The reconstructed density matrix and the violation of the Clauser-Horne-Shimony-Holt inequality clearly show the preservation of quantum entanglement during storage. Our result is very promising for establishing a long-distance quantum network based on cold atomic ensembles.
Multiple teleportation via partially entangled GHZ state
NASA Astrophysics Data System (ADS)
Xiong, Pei-Ying; Yu, Xu-Tao; Zhan, Hai-Tao; Zhang, Zai-Chen
2016-08-01
Quantum teleportation is important for quantum communication. We propose a protocol that uses a partially entangled Greenberger-Horne-Zeilinger (GHZ) state for single hop teleportation. Quantum teleportation will succeed if the sender makes a Bell state measurement, and the receiver performs the Hadamard gate operation, applies appropriate Pauli operators, introduces an auxiliary particle, and applies the corresponding unitary matrix to recover the transmitted state.We also present a protocol to realize multiple teleportation of partially entangled GHZ state without an auxiliary particle. We show that the success probability of the teleportation is always 0 when the number of teleportations is odd. In order to improve the success probability of a multihop, we introduce the method used in our single hop teleportation, thus proposing a multiple teleportation protocol using auxiliary particles and a unitary matrix. The final success probability is shown to be improved significantly for the method without auxiliary particles for both an odd or even number of teleportations.
Orbital angular momentum entanglement via fork-poling nonlinear photonic crystals.
Lu, L L; Xu, P; Zhong, M L; Bai, Y F; Zhu, S N
2015-01-26
We report a compact scheme for the generation and manipulation of photon pairs entangled in the orbital angular momentum (OAM) from the fork-poling quadratic nonlinear crystal. The χ^{(2)}-modulation in this crystal is designed for fulfilling a tilted quasi-phase-matching geometry to ensure the efficient generation of entangled photons as well as for transferring of topological charge of the crystal to the photon pairs. Numerical results show that the OAM of photon pair is anti-correlated and the degree of OAM entanglement can be enhanced by modulating the topological charge of crystal, which indicates a feasible extension to high-dimensional OAM entanglement. These studies suggest that the fork-poling nonlinear photonic crystal a unique platform for compact generation and manipulation of high-dimensional and high-order OAM entanglement, which may have potential applications in quantum communication, quantum cryptography and quantum remote sensing. PMID:25835879
Negative Correlations and Entanglement in Higher-Spin Dicke States
NASA Astrophysics Data System (ADS)
Wang, Xiaoqian; Zhong, Wei; Wang, Xiaoguang
2016-06-01
We consider entanglement criteria based on the spin squeezing inequalities for arbitrary spin systems. Here we use the negative correlations to detect the entanglement in the system with exchange symmetry. For arbitrary spin systems, we can find that the state is entangled, when the minimal pairwise correlation is negative. Then we give a parameter which is defined by the collective angular momentum operator, to detect the entanglement for the Dicke state with N spin -1 particles, and the results are as the same as negative correlation. We also consider the directions of negative correlation, the state is entangled in two orthogonal directions for the superposition of Dicke state without parity.
Wavelength-tunable sources of entangled photons interfaced with atomic vapours
Trotta, Rinaldo; Martín-Sánchez, Javier; Wildmann, Johannes S.; Piredda, Giovanni; Reindl, Marcus; Schimpf, Christian; Zallo, Eugenio; Stroj, Sandra; Edlinger, Johannes; Rastelli, Armando
2016-01-01
The prospect of using the quantum nature of light for secure communication keeps spurring the search and investigation of suitable sources of entangled photons. A single semiconductor quantum dot is one of the most attractive, as it can generate indistinguishable entangled photons deterministically and is compatible with current photonic-integration technologies. However, the lack of control over the energy of the entangled photons is hampering the exploitation of dissimilar quantum dots in protocols requiring the teleportation of quantum entanglement over remote locations. Here we introduce quantum dot-based sources of polarization-entangled photons whose energy can be tuned via three-directional strain engineering without degrading the degree of entanglement of the photon pairs. As a test-bench for quantum communication, we interface quantum dots with clouds of atomic vapours, and we demonstrate slow-entangled photons from a single quantum emitter. These results pave the way towards the implementation of hybrid quantum networks where entanglement is distributed among distant parties using optoelectronic devices. PMID:26815609
Wavelength-tunable sources of entangled photons interfaced with atomic vapours
NASA Astrophysics Data System (ADS)
Trotta, Rinaldo; Martín-Sánchez, Javier; Wildmann, Johannes S.; Piredda, Giovanni; Reindl, Marcus; Schimpf, Christian; Zallo, Eugenio; Stroj, Sandra; Edlinger, Johannes; Rastelli, Armando
2016-01-01
The prospect of using the quantum nature of light for secure communication keeps spurring the search and investigation of suitable sources of entangled photons. A single semiconductor quantum dot is one of the most attractive, as it can generate indistinguishable entangled photons deterministically and is compatible with current photonic-integration technologies. However, the lack of control over the energy of the entangled photons is hampering the exploitation of dissimilar quantum dots in protocols requiring the teleportation of quantum entanglement over remote locations. Here we introduce quantum dot-based sources of polarization-entangled photons whose energy can be tuned via three-directional strain engineering without degrading the degree of entanglement of the photon pairs. As a test-bench for quantum communication, we interface quantum dots with clouds of atomic vapours, and we demonstrate slow-entangled photons from a single quantum emitter. These results pave the way towards the implementation of hybrid quantum networks where entanglement is distributed among distant parties using optoelectronic devices.
Wavelength-tunable sources of entangled photons interfaced with atomic vapours.
Trotta, Rinaldo; Martín-Sánchez, Javier; Wildmann, Johannes S; Piredda, Giovanni; Reindl, Marcus; Schimpf, Christian; Zallo, Eugenio; Stroj, Sandra; Edlinger, Johannes; Rastelli, Armando
2016-01-01
The prospect of using the quantum nature of light for secure communication keeps spurring the search and investigation of suitable sources of entangled photons. A single semiconductor quantum dot is one of the most attractive, as it can generate indistinguishable entangled photons deterministically and is compatible with current photonic-integration technologies. However, the lack of control over the energy of the entangled photons is hampering the exploitation of dissimilar quantum dots in protocols requiring the teleportation of quantum entanglement over remote locations. Here we introduce quantum dot-based sources of polarization-entangled photons whose energy can be tuned via three-directional strain engineering without degrading the degree of entanglement of the photon pairs. As a test-bench for quantum communication, we interface quantum dots with clouds of atomic vapours, and we demonstrate slow-entangled photons from a single quantum emitter. These results pave the way towards the implementation of hybrid quantum networks where entanglement is distributed among distant parties using optoelectronic devices. PMID:26815609
Faithful teleportation with partially entangled states
Gour, Gilad
2004-10-01
We write explicitly a general protocol for faithful teleportation of a d-state particle (qudit) via a partially entangled pair of (pure) n-state particles. The classical communication cost (CCC) of the protocol is log{sub 2}(nd) bits, and it is implemented by a projective measurement performed by Alice, and a unitary operator performed by Bob (after receiving from Alice the measurement result). We prove the optimality of our protocol by a comparison with the concentrate and teleport strategy. We also show that if d>n/2, or if there is no residual entanglement left after the faithful teleportation, the CCC of any protocol is at least log{sub 2}(nd) bits. Furthermore, we find a lower bound on the CCC in the process transforming one bipartite state to another by means of local operation and classical communication.
Entanglement dynamics via coherent-state propagators
Ribeiro, A. D.; Angelo, R. M.
2010-11-15
The dynamical generation of entanglement in closed bipartite systems is investigated in the semiclassical regime. We consider a model of two particles, initially prepared in a product of coherent states, evolving in time according to a generic Hamiltonian, and derive a formula for the linear entropy of the reduced density matrix using the semiclassical propagator in the coherent-state representation. The formula is explicitly written in terms of quantities that define the stability of classical trajectories of the underlying classical system. The formalism is then applied to the problem of two nonlinearly coupled harmonic oscillators, and the result is shown to be in remarkable agreement with the exact quantum measure of entanglement in the short-time regime. An important by-product of our approach is a unified semiclassical formula, which contemplates both the coherent-state propagator and its complex conjugate.
Entanglement of phase-random states
NASA Astrophysics Data System (ADS)
Nakata, Yoshifumi; Turner, Peter; Murao, Mio
2014-12-01
In order to study generic properties of time-evolving states by time-independent Hamiltonian dynamics, we introduce phase-random states, an ensemble of pure states with fixed amplitudes and uniformly distributed phases in a fixed basis. We compute the average amount of entanglement of phase-random states analytically, and show that the average can be extremely large when the amplitudes are equal and the basis is separable. We also study implications on Hamiltonian dynamics, in particular the realization of the canonical state in a subsystem.
Femtosecond Laser--Pumped Source of Entangled Photons for Quantum Cryptography Applications
Pan, D.; Donaldson, W.; Sobolewski, R.
2007-07-31
We present an experimental setup for generation of entangled-photon pairs via spontaneous parametric down-conversion, based on the femtosecond-pulsed laser. Our entangled-photon source utilizes a 76-MHz-repetition-rate, 100-fs-pulse-width, mode-locked, ultrafast femtosecond laser, which can produce, on average, more photon pairs than a cw laser of an equal pump power. The resulting entangled pairs are counted by a pair of high-quantum-efficiency, single-photon, silicon avalanche photodiodes. Our apparatus is intended as an efficient source/receiver system for the quantum communications and quantum cryptography applications.
NASA Astrophysics Data System (ADS)
Jen, H. H.
2016-02-01
We consider a scheme of multiplexed cold atomic ensembles that generate a frequency-entangled biphoton state with controllable entropy of entanglement. The biphoton state consists of a telecommunication photon (signal) immediately followed by an infrared one (idler) via four-wave mixing with two classical pump fields. Multiplexing the atomic ensembles with frequency and phase-shifted signal and idler emissions, we can manipulate and can control the spectral property of the biphoton state. Mapping out the entropy of entanglement in the scheme provides the optimal configuration for entanglement resources. This paves the way for efficient long-distance quantum communication and for potentially useful multimode structures in quantum information processing.
NASA Astrophysics Data System (ADS)
Takeuchi, Shigeki
Quantum information science has been attracting significant attention recently. It harnesses the intrinsic nature of quantum mechanics such as quantum superposition, the uncertainty principle, and quantum entanglement to realize novel functions. Recently, quantum metrology has been emerging as an application of quantum information science. Among the many physical quanta, photons are an indispensable tool for metrology, as light-based measurements are applicable to fields ranging from astronomy to life science. In quantum metrology, quantum entanglement between photons is the phenomenon utilized.In this chapter, we will try to give a brief overview of this emerging field mainly focusing on two topics: Optical phase measurements beyond the standard quantum limit (SQL) and quantum optical coherence tomography (QOCT). The sensitivity of an optical phase measurement for a given photon number N is usually limited by $\sqrt{N}sqrt\{N\}\; ,\; which\; is\; called\; the\; SQL\; or\; shot\; noise\; limit.\; However,\; the\; SQL\; can\; be\; overcome\; when\; non-classical\; light\; is\; used.\; We\; explain\; the\; basic\; concepts\; and\; the\; recent\; experimental\; results\; that\; exceed\; the\; SQL,\; and\; an\; application\; of\; this\; technology\; for\; microscopy.\; QOCT\; harnesses\; the\; quantum$entanglement of photons in frequency to cancel out the dispersion effect, which degrades the resolution of conventional OCT. The mechanism of the dispersion cancellation and the latest experimental results will be given.
NASA Astrophysics Data System (ADS)
Zhao, Jie; Zheng, Chun-Hong; Shi, Peng; Ren, Chun-Nian; Gu, Yong-Jian
2014-07-01
We present schemes for deterministically generating multi-qubit electron-spin entangled cluster states by the giant circular birefringence, induced by the interface between the spin of a photon and the spin of an electron confined in a quantum dot embedded in a double-sided microcavity. Based on this interface, we construct the controlled phase flip (CPF) gate deterministically which is performed on electron-spin qubits and is the essential component of the cluster-state generation. As one of the universal gates, the CPF gate constructed can also be utilized in achieving scalable quantum computing. Besides, we propose the entanglement concentration protocol to reconstruct a partially entangled cluster state into a maximally entangled one, resorting to the projection measurement on an ancillary photon. By iterating the concentration scheme several times, the maximum success probability can be achieved. The fidelities and experimental feasibilities are analyzed with respect to currently available techniques, indicating that our schemes can work well in both the strong and weak (Purcell) coupling regimes.
Characterizing entanglement of an artificial atom and a cavity cat state with Bell's inequality
NASA Astrophysics Data System (ADS)
Vlastakis, Brian; Petrenko, Andrei; Ofek, Nissim; Sun, Luyan; Leghtas, Zaki; Sliwa, Katrina; Liu, Yehan; Hatridge, Michael; Blumoff, Jacob; Frunzio, Luigi; Mirrahimi, Mazyar; Jiang, Liang; Devoret, M. H.; Schoelkopf, R. J.
2015-11-01
The Schrodinger's cat thought experiment highlights the counterintuitive concept of entanglement in macroscopically distinguishable systems. The hallmark of entanglement is the detection of strong correlations between systems, most starkly demonstrated by the violation of a Bell inequality. No violation of a Bell inequality has been observed for a system entangled with a superposition of coherent states, known as a cat state. Here we use the Clauser-Horne-Shimony-Holt formulation of a Bell test to characterize entanglement between an artificial atom and a cat state, or a Bell-cat. Using superconducting circuits with high-fidelity measurements and real-time feedback, we detect correlations that surpass the classical maximum of the Bell inequality. We investigate the influence of decoherence with states up to 16 photons in size and characterize the system by introducing joint Wigner tomography. Such techniques demonstrate that information stored in superpositions of coherent states can be extracted efficiently, a crucial requirement for quantum computing with resonators.
Quantum storage of entangled telecom-wavelength photons in an erbium-doped optical fibre
NASA Astrophysics Data System (ADS)
Saglamyurek, Erhan; Jin, Jeongwan; Verma, Varun B.; Shaw, Matthew D.; Marsili, Francesco; Nam, Sae Woo; Oblak, Daniel; Tittel, Wolfgang
2015-02-01
The realization of a future quantum Internet requires the processing and storage of quantum information at local nodes and interconnecting distant nodes using free-space and fibre-optic links. Quantum memories for light are key elements of such quantum networks. However, to date, neither an atomic quantum memory for non-classical states of light operating at a wavelength compatible with standard telecom fibre infrastructure, nor a fibre-based implementation of a quantum memory, has been reported. Here, we demonstrate the storage and faithful recall of the state of a 1,532 nm wavelength photon entangled with a 795 nm photon, in an ensemble of cryogenically cooled erbium ions doped into a 20-m-long silica fibre, using a photon-echo quantum memory protocol. Despite its currently limited efficiency and storage time, our broadband light-matter interface brings fibre-based quantum networks one step closer to reality.
Usefulness of classical communication for local cloning of entangled states
Demkowicz-Dobrzanski, Rafal; Sen, Aditi; Sen, Ujjwal; Bruss, Dagmar
2006-03-15
We solve the problem of the optimal cloning of pure entangled two-qubit states with a fixed degree of entanglement using local operations and classical communication. We show that, amazingly, classical communication between the parties can improve the fidelity of local cloning if and only if the initial entanglement is higher than a certain critical value. It is completely useless for weakly entangled states. We also show that bound entangled states with positive partial transpose are not useful as a resource to improve the best local cloning fidelity.
Tight bound on coherent-state-based entanglement generation over lossy channels
Azuma, Koji; Sota, Naoya; Koashi, Masato; Imoto, Nobuyuki
2010-02-15
The first stage of the hybrid quantum repeaters is entanglement generation based on transmission of pulses in coherent states over a lossy channel. Protocols to make entanglement with only one type of error are favorable for rendering subsequent entanglement distillation efficient. Here we provide the tight upper bound on performances of these protocols that is determined only by the channel loss. In addition, we show that this bound is achievable by utilizing a proposed protocol [K. Azuma, N. Sota, R. Namiki, S. K. Oezdemir, T. Yamamoto, M. Koashi, and N. Imoto, Phys. Rev. A 80, 060303(R) (2009)] composed of a simple combination of linear optical elements and photon-number-resolving detectors.
Local cloning of genuinely entangled states of three qubits
Choudhary, Sujit K.; Kar, Guruprasad; Rahaman, Ramij; Roy, Anirban; Kunkri, Samir
2007-12-15
We discuss the (im)possibility of the exact cloning of orthogonal but genuinely entangled three qubit states aided with entangled ancilla under local operation and classical communication. Whereas any two orthogonal Greenberger-Horne-Zeilinger (GHZ) states taken from the canonical GHZ basis can be cloned with the help of a known GHZ state, surprisingly we find that no two W states can be cloned by using any known three qubit (possibly entangled) state as a blank copy.
NASA Astrophysics Data System (ADS)
Pan, Jun; Zhou, Lan; Gu, Shi-Pu; Wang, Xing-Fu; Sheng, Yu-Bo; Wang, Qin
2016-04-01
Concatenated Greenberger-Horne-Zeilinger (C-GHZ) state, which encodes physical qubits in a logic qubit, has great application in the future quantum communication. We present an efficient entanglement concentration protocol (ECP) for recovering less-entangled C-GHZ state into the maximally entangled C-GHZ state with the help of cross-Kerr nonlinearities and photon detectors. With the help of the cross-Kerr nonlinearity, the obtained maximally entangled C-GHZ state can be remained for other applications. Moreover, the ECP can be used repeatedly, which can increase the success probability largely. Based on the advantages above, our ECP may be useful in the future long-distance quantum communication.
Entanglement of remote transmon qubits by concurrent measurement using Fock states
NASA Astrophysics Data System (ADS)
Narla, A.; Hatridge, M.; Shankar, S.; Leghtas, Z.; Sliwa, K. M.; Vlastakis, B.; Zalys-Geller, E.; Mirrahimi, M.; Devoret, M. H.
2015-03-01
A requirement of any modular quantum computer is the ability to maintain individual qubits in isolated environments while also being able to entangle arbitrary distant qubits on demand. For superconducting qubits, such a protocol can be realized by first entangling the qubits with flying microwave coherent states which are then concurrently detected by a parametric amplifier. This protocol has a 50% success probability but is vulnerable to losses between the qubits and the amplifier which reduce the entanglement fidelity. An alternative is to use itinerant Fock states, since losses now tend to reduce the success probability of creating an entangled state but not its fidelity. Such single-photon protocols have been implemented in trapped-ion and NV-center experiments. We present such a protocol tailored for entangling two transmon qubits in the circuit QED architecture. Each qubit is entangled with a Fock state of its cavity using sideband pulses. The Fock states leak out of the cavity, interfere on a beam-splitter which erases their which-path information, and are subsequently detected using a novel photo-detector realized by another qubit-cavity system. Simulations suggest that we can realize a high-fidelity entangled state with a success probability as large as 1%.
Teleportation of continuous variable multimode Greeberger Horne Zeilinger entangled states
NASA Astrophysics Data System (ADS)
He, Guangqiang; Zhang, Jingtao; Zeng, Guihua
2008-11-01
Quantum teleportation protocols of continuous variable (CV) Greeberger-Horne-Zeilinger (GHZ) and Einstein-Podolsky-Rosen (EPR) entangled states are proposed, and are generalized to teleportation of arbitrary multimode GHZ entangled states described by Van Loock and Braunstein (2000 Phys. Rev. Lett. 84 3482). Each mode of a multimode entangled state is teleported using a CV EPR entangled pair and classical communication. The analytical expression of fidelity for the multimode Gaussian states which evaluates the teleportation quality is presented. The analytical results show that the fidelity is a function of both the squeezing parameter r, which characterizes the multimode entangled state to be teleported, and the channel parameter p, which characterizes the EPR pairs shared by Alice and Bob. The fidelity increases with increasing p, but decreases with increasing r, i.e., it is more difficult to teleport the more perfect multimode entangled states. The entanglement degree of the teleported multimode entangled states increases with increasing both r and p. In addition, the fact is proved that our teleportation protocol of EPR entangled states using parallel EPR pairs as quantum channels is the best case of the protocol using four-mode entangled states (Adhikari et al 2008 Phys. Rev. A 77 012337).
Quantum Conditional Cloning of Continuous Variable Entangled States
NASA Astrophysics Data System (ADS)
Liu, K.; Gao, J. R.
2014-12-01
We extend the technique of conditional preparation to a quantum cloning machine, and present a protocol of 1 -> 2 conditional cloning of squeezed state and entanglement states. It is shown that the entanglement degree of the cloned entangled states can be well preserved even when the fidelity between the input and output states is beyond the limit of 4/9. This scheme is practicable since only the linear elements of beam splitters, homodyne detections, optical modulations and electrical trigger system, are involved.
Controlled Teleportation of the Two-Ion Entangled State
NASA Astrophysics Data System (ADS)
Zhang, Fujun; Wang, Dongxin; Liu, Kun; Liu, Chuanming
2016-01-01
A simple scheme for controlled teleportation of an arbitrary two-ion entangled state using a bell and GHZ entangled state as quantum channel is proposed in trapped ion systems. An arbitrary two-ion entangled state can be teleported perfectly with the help of the cooperation. In our scheme the ions are simultaneously excited by a laser. Our scheme is insensitive to both the initial vibrational state and heating. The probability of the success in our scheme is 1.0.
Spontaneous emission of a photon: Wave-packet structures and atom-photon entanglement
Fedorov, M.V.; Efremov, M.A.; Kazakov, A.E.; Chan, K.W.; Eberly, J.H.; Law, C.K.
2005-09-15
Spontaneous emission of a photon by an atom is described theoretically in three dimensions with the initial wave function of a finite-mass atom taken in the form of a finite-size wave packet. Recoil and wave-packet spreading are taken into account. The total atom-photon wave function is found in the momentum and coordinate representations as the solution of an initial-value problem. The atom-photon entanglement arising in such a process is shown to be closely related to the structure of atom and photon wave packets which can be measured in the coincidence and single-particle schemes of measurements. Two predicted effects, arising under the conditions of high entanglement, are anomalous narrowing of the coincidence wave packets and, under different conditions, anomalous broadening of the single-particle wave packets. Fundamental symmetry relations between the photon and atom single-particle and coincidence wave-packet widths are established. The relationship with the famous scenario of Einstein-Podolsky-Rosen is discussed.
Theory of Multipartite Entanglement for X-states
NASA Astrophysics Data System (ADS)
Hashemi Rafsanjani, Seyed Mohammad
More than a century after the seminal work of Schmidt and with all the enthusiasm that have surrounded entanglement ever since the controversial EPR paper, it remains an open challenge to determine whether a given state possesses entanglement or not. The problem is even more dicult if one considers the entanglement among more than two parties, i.e. multipartite entanglement. In the following we first introduce the concept of multipartite entanglement and discuss what it means to quantify the entanglement of a given state. We then introduce a class of multiqubit states, called X- states, and find an algebraic formula for the multipartite entanglement of such states. We show that using this formula one can find a lower bound for the entanglement of any multiqubit state. We then explore the connection between the entanglement and purity in multiqubit states. In the fourth chapter, we introduce a geometrical measure of entanglement and quantify it for the set of GHZ-diagonal states. These are states that can be written as a convex sum of completely bit-flipped states. Using these results we can develop an upper and a lower bound for the entanglement of any density matrix. In the final chapter we survey some of the insights that can be developed using the results of the preceding chapters. We first explore the decay of entanglement in a decoherence scenario where each qubit is experiences decay through an amplitude damping channel, and finally we make a proposal to preserve and control multipartite entanglement through the phenomenon of collapse and revival.
Secured Optical Communications Using Quantum Entangled Two-Photon Transparency Modulation
NASA Technical Reports Server (NTRS)
Kojima, Jun (Inventor); Nguyen, Quang-Viet (Inventor); Lekki, John (Inventor)
2015-01-01
A system and method is disclosed wherein optical signals are coded in a transmitter by tuning or modulating the interbeam delay time (which modulates the fourth-order coherence) between pairs of entangled photons. The photon pairs are either absorbed or not absorbed (transparent) by an atomic or molecular fluorescer in a receiver, depending on the inter-beam delay that is introduced in the entangled photon pairs. Upon the absorption, corresponding fluorescent optical emissions follow at a certain wavelength, which are then detected by a photon detector. The advantage of the disclosed system is that it eliminates a need of a coincidence counter to realize the entanglement-based secure optical communications because the absorber acts as a coincidence counter for entangled photon pairs.
Quantum key distribution using entangled-photon trains with no basis selection
Inoue, Kyo; Takesue, Hiroki
2006-03-15
Conventional quantum key distribution (QKD) protocols include a basis selection process for providing a secure secret key. In contrast, this paper proposes an entanglement-based QKD with no basis selection procedure. Entangled-photon pulse trains with an average photon number less than one per pulse are sent to two legitimate parties, from which a secret key is created utilizing the entanglement nature. Eavesdropping on a transmission line is prevented by a condition of less than one photon per pulse, and sending classically correlated coherent pulses instead of quantum correlated ones is revealed by monitoring coincident count rate000.
NASA Astrophysics Data System (ADS)
Jen, Hsiang-Hua
2016-05-01
We consider a scheme of multiplexed cold atomic ensembles that generate a frequency-entangled biphoton state with controllable entropy of entanglement. The biphoton state consists of a telecommunication photon (signal) immediately followed by an infrared one (idler) via four-wave mixing with two classical pump fields. Multiplexing the atomic ensembles with frequency and phase-shifted signal and idler emissions, we can manipulate and control the spectral property of the biphoton state. Mapping out the entropy of entanglement in the scheme provides the optimal configuration for entanglement resources. This paves the way for efficient long-distance quantum communication and for potentially useful multimode structures in quantum information processing. Ministry of Science and Technology, Taiwan, under Grant No. MOST-101-2112-M-001-021-MY3 and the support of NCTS.
Entanglement entropy of multipartite pure states
Bravyi, Sergei
2003-01-01
Consider a system consisting of n d-dimensional quantum particles and an arbitrary pure state vertical bar {psi}> of the whole system. Suppose we simultaneously perform complete von Neumann measurements on each particle. The Shannon entropy of the outcomes' joint probability distribution is a functional of the state vertical bar {psi}> and of n measurements chosen for each particle. Denote S[{psi}] the minimum of this entropy over all choices of the measurements. We show that S[{psi}] coincides with the entropy of entanglement for bipartite states. We compute S[{psi}] for some special multipartite states: the hexacode state vertical bar H> (n=6, d=2) and the determinant states vertical bar Det{sub n}> (d=n). The computation yields S[H]=4 log 2 and S[Det{sub n}]=log(n{exclamation_point}). Counterparts of the determinant state defined for d
Demonstration of a Stable Atom-Photon Entanglement Source for Quantum Repeaters
Chen Shuai; Chen Yuao; Zhao Bo; Yuan Zhensheng; Pan Jianwei; Schmiedmayer, Joerg
2007-11-02
We demonstrate a novel way to efficiently create a robust entanglement between an atomic and a photonic qubit. A single laser beam is used to excite one atomic ensemble and two different modes of Raman fields are collected to generate the atom-photon entanglement. With the help of built-in quantum memory, the entanglement still exists after 20.5 {mu}s storage time which is further proved by the violation of Clauser-Horne-Shimony-Holt type Bell's inequality. The entanglement procedure can serve as a building block for a novel robust quantum repeater architecture [Zhao et al., Phys. Rev. Lett. 98, 240502 (2007)] and can be extended to generate high-dimensional atom-photon entanglements.
Experimental demonstration of high two-photon time-energy entanglement
Ali Khan, Irfan; Howell, John C.
2006-03-15
We report on the experimental demonstration of high energy-time entanglement in two-photon states created in the process of spontaneous parametric down-conversion. We show that the classical variance product, which we violate by three orders of magnitude, actually represents a lower bound estimate of the number of information eigenmodes K. Explicit measurements estimate K to be greater than 100, with theoretical estimates predicting a value of as high as 1x10{sup 6}. These results provide incentive for the practical feasibility of large bandwidth quantum information processing, particularly in cryptography over large distances.
Nonclassical properties and quantum resources of hierarchical photonic superposition states
Volkoff, T. J.
2015-11-15
We motivate and introduce a class of “hierarchical” quantum superposition states of N coupled quantum oscillators. Unlike other well-known multimode photonic Schrödinger-cat states such as entangled coherent states, the hierarchical superposition states are characterized as two-branch superpositions of tensor products of single-mode Schrödinger-cat states. In addition to analyzing the photon statistics and quasiprobability distributions of prominent examples of these nonclassical states, we consider their usefulness for highprecision quantum metrology of nonlinear optical Hamiltonians and quantify their mode entanglement. We propose two methods for generating hierarchical superpositions in N = 2 coupled microwave cavities, exploiting currently existing quantum optical technology for generating entanglement between spatially separated electromagnetic field modes.
NASA Astrophysics Data System (ADS)
Poddubny, Alexander N.; Sukhorukov, Andrey A.
2015-09-01
The practical development of quantum plasmonic circuits incorporating non-classical interference [1] and sources of entangled states calls for a versatile quantum theoretical framework which can fully describe the generation and detection of entangled photons and plasmons. However, majority of the presently used theoretical approaches are typically limited to the toy models assuming loss-less and nondispersive elements or including just a few resonant modes. Here, we present a rigorous Green function approach describing entangled photon-plasmon state generation through spontaneous wave mixing in realistic metal-dielectric nanostructures. Our approach is based on the local Huttner-Barnett quantization scheme [2], which enables problem formulation in terms of a Hermitian Hamiltonian where the losses and dispersion are fully encoded in the electromagnetic Green functions. Hence, the problem can be addressed by the standard quantum mechanical perturbation theory, overcoming mathematical difficulties associated with other quantization schemes. We derive explicit expressions with clear physical meaning for the spatially dependent two-photon detection probability, single-photon detection probability and single-photon density matrix. In the limiting case of low-loss nondispersive waveguides our approach reproduces the previous results [3,4]. Importantly, our technique is far more general and can quantitatively describe generation and detection of spatially-entangled photons in arbitrary metal-dielectric structures taking into account actual losses and dispersion. This is essential to perform the design and optimization of plasmonic structures for generation and control of quantum entangled states. [1] J.S. Fakonas, H. Lee, Y.A. Kelaita and H.A. Atwater, Nature Photonics 8, 317(2014) [2] W. Vogel and D.-G. Welsch, Quantum Optics, Wiley (2006). [3] D.A. Antonosyan, A.S. Solntsev and A.A. Sukhorukov, Phys. Rev. A 90 043845 (2014) [4] L.-G. Helt, J.E. Sipe and M.J. Steel, ar
Entanglement concentration for concatenated Greenberger-Horne-Zeilinger state
NASA Astrophysics Data System (ADS)
Qu, Chang-Cheng; Zhou, Lan; Sheng, Yu-Bo
2015-11-01
The concatenated Greenberger-Horne-Zeilinger state is a new type of logic-qubit entanglement, which attracts a lot of attentions recently. In this paper, we discuss the entanglement concentration for such logic-qubit entanglement. We present two groups of entanglement concentration protocols (ECPs) for logic-qubit entanglement. In the first group, the parties do not know the initial coefficients of the partially logic-qubit entanglement. In the second group, the parties know the initial coefficients of the partially logic-qubit entanglement. In our ECPs, the unsuccessful cases can be reused to increase the total success probability in the next step. These ECPs may be useful in future long-distant quantum communication.
NASA Astrophysics Data System (ADS)
Huang, Li-Yuan; Fang, Mao-Fa
2008-07-01
The thermal entanglement and teleportation of a thermally mixed entangled state of a two-qubit Heisenberg XXX chain under the Dzyaloshinski-Moriya (DM) anisotropic antisymmetric interaction through a noisy quantum channel given by a Werner state is investigated. The dependences of the thermal entanglement of the teleported state on the DM coupling constant, the temperature and the entanglement of the noisy quantum channel are studied in detail for both the ferromagnetic and the antiferromagnetic cases. The result shows that a minimum entanglement of the noisy quantum channel must be provided in order to realize the entanglement teleportation. The values of fidelity of the teleported state are also studied for these two cases. It is found that under certain conditions, we can transfer an initial state with a better fidelity than that for any classical communication protocol.
The Local Orthogonality Between Quantum States and Entanglement Decomposition
NASA Astrophysics Data System (ADS)
Kim, Sunho; Wu, Junde; Zhang, Lin; Cho, Minhyung
2016-06-01
In the paper, we show that when a quantum state can be decomposed as a convex combination of locally orthogonal mixed states, its entanglement can be decomposed into the entanglement of these mixed states without losing them. The obtained result generalizes a corresponding one proved by Horodecki (Acta Phys. Slov. 48, 141 1998). But, for the entanglement cost it requires certain conditions for holding the decomposition, and the distillable entanglement only has a week result as inequality. Finally, we presented an example to show that the conditions of our conclusions are existence.
Purification and switching protocols for dissipatively stabilized entangled qubit states
NASA Astrophysics Data System (ADS)
Hein, Sven M.; Aron, Camille; Türeci, Hakan E.
2016-06-01
Pure dephasing processes limit the fidelities achievable in driven-dissipative schemes for stabilization of entangled states of qubits. We propose a scheme which, combined with already existing entangling methods, purifies the desired entangled state by driving out of equilibrium auxiliary dissipative cavity modes coupled to the qubits. We lay out the specifics of our scheme and compute its efficiency in the particular context of two superconducting qubits in a cavity-QED architecture, where the strongly coupled auxiliary modes provided by collective cavity excitations can drive and sustain the qubits in maximally entangled Bell states with fidelities reaching 90% for experimentally accessible parameters.
Channel capacities versus entanglement measures in multiparty quantum states
Sen, Aditi; Sen, Ujjwal
2010-01-15
For quantum states of two subsystems, highly entangled states have a higher capacity of transmitting classical as well as quantum information, and vice versa. We show that this is no more the case in general: Quantum capacities of multiaccess channels, motivated by communication in quantum networks, do not have any relation with genuine multiparty entanglement measures. Importantly, the statement is demonstrated for arbitrary multipartite entanglement measures. Along with revealing the structural richness of multiaccess channels, this gives us a tool to classify multiparty quantum states from the perspective of its usefulness in quantum networks, which cannot be visualized by any genuine multiparty entanglement measure.
Halevy, A; Megidish, E; Dovrat, L; Eisenberg, H S; Becker, P; Bohatý, L
2011-10-10
We describe the full characterization of the biaxial nonlinear crystal BiB₃O₆ (BiBO) as a polarization entangled photon source using non-collinear type-II parametric down-conversion. We consider the relevant parameters for crystal design, such as cutting angles, polarization of the photons, effective nonlinearity, spatial and temporal walk-offs, crystal thickness and the effect of the pump laser bandwidth. Experimental results showing entanglement generation with high rates and a comparison to the well investigated β-BaB₂O₄ (BBO) crystal are presented as well. Changing the down-conversion crystal of a polarization entangled photon source from BBO to BiBO enhances the generation rate as if the pump power was increased by 2.5 times. Such an improvement is currently required for the generation of multiphoton entangled states. PMID:21997051
Genuinely multipartite entangled states and orthogonal arrays
NASA Astrophysics Data System (ADS)
Goyeneche, Dardo; Życzkowski, Karol
2014-08-01
A pure quantum state of N subsystems with d levels each is called k-multipartite maximally entangled state, which we call a k-uniform state, if all its reductions to k qudits are maximally mixed. These states form a natural generalization of N-qudit Greenberger-Horne-Zeilinger states which belong to the class 1-uniform states. We establish a link between the combinatorial notion of orthogonal arrays and k-uniform states and prove the existence of several classes of such states for N-qudit systems. In particular, known Hadamard matrices allow us to explicitly construct 2-uniform states for an arbitrary number of N >5 qubits. We show that finding a different class of 2-uniform states would imply the Hadamard conjecture, so the full classification of 2-uniform states seems to be currently out of reach. Furthermore, we establish links between the existence of k-uniform states and classical and quantum error correction codes and provide a graph representation for such states.
Strong violations of Bell-type inequalities for path-entangled number states
Wildfeuer, Christoph F.; Dowling, Jonathan P.; Lund, Austin P.
2007-11-15
We show that nonlocal correlation experiments on the two spatially separated modes of a maximally path-entangled number state may be performed. They lead to a violation of a Clauser-Horne Bell inequality for any finite photon number N. We also present an analytical expression for the two-mode Wigner function of a maximally path-entangled number state and investigate a Clauser-Horne-Shimony-Holt Bell inequality for such a state. We test other Bell-type inequalities. Some are violated by a constant amount for any N.
Quantum-state purity of heralded single photons produced from frequency-anticorrelated biphotons
NASA Astrophysics Data System (ADS)
Du, Shengwang
2015-10-01
We analyze the quantum-state purity of heralded single photons produced from frequency-anticorrelated biphotons. We find that the quantum-state purity in the time-frequency domain depends strongly on the response time uncertainty of the trigger-photon detector that heralds the generation of its paired photon. If the trigger response time is much shorter than the two-photon coherence time, the time-frequency quantum-state purity of heralded single photons approaches unity and the heralded single photon is in a nearly pure state. If the trigger response time is much longer than the two-photon coherence time, the heralded photon is then projected onto a mixed state. Making use of the time-frequency entanglement, heralded single photons with a well-defined temporal wave function or a frequency superposition state can be produced and engineered. This time-frequency entanglement allows for shaping heralded single photons through nonlocal spectral modulation.
NASA Astrophysics Data System (ADS)
Wang, He; Zhang, Yu Qing; Liu, Xue Feng; Hu, Yu Pu
2016-06-01
We propose a novel quantum dialogue protocol by using the generalized Bell states and entanglement swapping. In the protocol, a sequence of ordered two-qutrit entangled states acts as quantum information channel for exchanging secret messages directly and simultaneously. Besides, a secret key string is shared between the communicants to overcome information leakage. Different from those previous information leakage-resistant quantum dialogue protocols, the particles, composed of one of each pair of entangled states, are transmitted only one time in the proposed protocol. Security analysis shows that our protocol can overcome information leakage and resist several well-known attacks. Moreover, the efficiency of our scheme is acceptable.
NASA Astrophysics Data System (ADS)
Wang, He; Zhang, Yu Qing; Liu, Xue Feng; Hu, Yu Pu
2016-03-01
We propose a novel quantum dialogue protocol by using the generalized Bell states and entanglement swapping. In the protocol, a sequence of ordered two-qutrit entangled states acts as quantum information channel for exchanging secret messages directly and simultaneously. Besides, a secret key string is shared between the communicants to overcome information leakage. Different from those previous information leakage-resistant quantum dialogue protocols, the particles, composed of one of each pair of entangled states, are transmitted only one time in the proposed protocol. Security analysis shows that our protocol can overcome information leakage and resist several well-known attacks. Moreover, the efficiency of our scheme is acceptable.
Coherent Control to Prepare an InAs Quantum Dot for Spin-Photon Entanglement
NASA Astrophysics Data System (ADS)
Webster, L. A.; Truex, K.; Duan, L.-M.; Steel, D. G.; Bracker, A. S.; Gammon, D.; Sham, L. J.
2014-03-01
We optically generated an electronic state in a single InAs /GaAs self-assembled quantum dot that is a precursor to the deterministic entanglement of the spin of the electron with an emitted photon in the proposal of W. Yao, R.-B. Liu, and L. J. Sham [Phys. Rev. Lett. 95, 030504 (2005).]. A superposition state is prepared by optical pumping to a pure state followed by an initial pulse. By modulating the subsequent pulse arrival times and precisely controlling them using interferometric measurement of path length differences, we are able to implement a coherent control technique to selectively drive exactly one of the two components of the superposition to the ground state. This optical transition contingent on spin was driven with the same broadband pulses that created the superposition through the use of a two pulse coherent control sequence. A final pulse affords measurement of the coherence of this "preentangled" state.
Coherent control to prepare an InAs quantum dot for spin-photon entanglement.
Webster, L A; Truex, K; Duan, L-M; Steel, D G; Bracker, A S; Gammon, D; Sham, L J
2014-03-28
We optically generated an electronic state in a single InAs/GaAs self-assembled quantum dot that is a precursor to the deterministic entanglement of the spin of the electron with an emitted photon in the proposal of W. Yao, R.-B. Liu, and L. J. Sham [Phys. Rev. Lett. 95, 030504 (2005). A superposition state is prepared by optical pumping to a pure state followed by an initial pulse. By modulating the subsequent pulse arrival times and precisely controlling them using interferometric measurement of path length differences, we are able to implement a coherent control technique to selectively drive exactly one of the two components of the superposition to the ground state. This optical transition contingent on spin was driven with the same broadband pulses that created the superposition through the use of a two pulse coherent control sequence. A final pulse affords measurement of the coherence of this "preentangled" state. PMID:24724666
Effect of spatial filtering on the Schmidt decomposition of entangled photons
Exter, M. P. van; Aiello, A.; Oemrawsingh, S. S. R.; Nienhuis, G.; Woerdman, J. P.
2006-07-15
A simple analytic decomposition of the spatially entangled two-photon field allows us to generalize the earlier results of Law and Eberly [Phys. Rev. Lett. 92, 127903 (2004)] to more realistic experimental geometries of spontaneous parametric down-conversion. We quantify analytically how spatial filtering reduces the Schmidt number or dimensionality of the two-photon entanglement from a 'generated' value to a generally much lower 'usable or detected' value, for both collinear and noncollinear phase matching. We also discuss the intimate relation between the (two-photon) Schmidt number and the classical (one-photon) concept of etendue or geometric extent.
Bright source of spectrally pure polarization-entangled photon with nearly single-mode emission
Evans, Philip G; Schaake, Jason; Bennink, Ryan S; Grice, Warren P; Humble, Travis S
2010-12-01
We present results of a bright entangled photon source operating at 1552 nm via type-II collinear degenerate spontaneous parametric down-conversion in periodically poled KTP crystal. We report a conservative inferred pair generation rate of 44,000/s/mW into collection modes. Minimization of spectral and spatial entanglement was achieved by group velocity matching the pump, signal and idler modes and through properly focusing the pump beam. By utilizing a pair of calcite beam displacers, we are able to overlap photons from adjacent collinear sources to obtain polarization-entanglement visibility of 94.7 +/- 1.1% with accidentals subtracted.
Full Multipartite Entanglement of Frequency-Comb Gaussian States
NASA Astrophysics Data System (ADS)
Gerke, S.; Sperling, J.; Vogel, W.; Cai, Y.; Roslund, J.; Treps, N.; Fabre, C.
2015-02-01
An analysis is conducted of the multipartite entanglement for Gaussian states generated by the parametric down-conversion of a femtosecond frequency comb. Using a recently introduced method for constructing optimal entanglement criteria, a family of tests is formulated for mode decompositions that extends beyond the traditional bipartition analyses. A numerical optimization over this family is performed to achieve maximal significance of entanglement verification. For experimentally prepared 4-, 6-, and 10-mode states, full entanglement is certified for all of the 14, 202, and 115 974 possible nontrivial partitions, respectively.
Entanglement criteria for noise resistance of two-qudit states
NASA Astrophysics Data System (ADS)
Dutta, Arijit; Ryu, Junghee; Laskowski, Wiesław; Żukowski, Marek
2016-06-01
Noise affects production and transmission of entanglement. We use a handy approach for a noise resistance of entanglement of two-qudit systems. A geometric concept using correlation tensors of separable and entangled states is implemented to formulate entanglement criterion. We apply the criterion to the various types of noise (white, colored, local depolarizing and amplitude damping) admixtures with the initial (pure) state. We also study the noise resistance with respect to the violation of specific family of Bell inequalities (CGLMP). A broad set of numerical and analytical results is presented.
Fusion of entangled coherent W and GHZ states in cavity QED
NASA Astrophysics Data System (ADS)
Zang, Xue-Ping; Yang, Ming; Song, Wei; Cao, Zhuo-Liang
2016-07-01
Efficient preparation of W and GHZ states encoded in various degrees of freedom of quantum particles is vital in quantum information science. So far, most of the studies have focused on polarization encoded photonic W and GHZ states. In this paper, we focus on W- and GHZ-class entangled coherent states, and propose schemes to fuse small W- and GHZ-entangled coherent states into larger ones. Based on successive detuned interactions between optical modes and an ancilla atom, an (N + M - 2)-mode entangled coherent W state can be probabilistically prepared from an N-mode and an M-mode entangled coherent W states. This fusion scheme applies to entangled coherent GHZ states too, and it can succeed in a deterministic way. The ancilla atom only interacts with a single optical mode, which avoids the problem of synchronizing many atoms in the previous cavity QED based fusion schemes. The detuning property of the interaction makes the current fusion scheme more feasible that the ones based on resonant atom-light interactions. In addition, the two levels of the ancilla atom for encoding quantum information are two degenerate ground states, and the excited state is adiabatically eliminated during the fusion process, so the atomic decay from excited states does not affect the quality of the fusion process.
Optimal amount of entanglement to distinguish quantum states instantaneously
NASA Astrophysics Data System (ADS)
Groisman, Berry; Strelchuk, Sergii
2015-11-01
We introduce an aspect of nonlocality which arises when the task of quantum states distinguishability is considered under local operations and shared entanglement in the absence of classical communication. We find the optimal amount of entanglement required to accomplish the task perfectly for sets of orthogonal states and argue that it quantifies information nonlocality.
Strong monogamy of quantum entanglement for multiqubit W -class states
NASA Astrophysics Data System (ADS)
Kim, Jeong San
2014-12-01
We provide strong evidence for the strong monogamy inequality of multiqubit entanglement recently proposed [B. Regula et al., Phys. Rev. Lett. 113, 110501 (2014), 10.1103/PhysRevLett.113.110501]. We consider a large class of multiqubit generalized W -class states and analytically show that the strong monogamy inequality of multiqubit entanglement is saturated by this class of states.
Parameter Estimation with Entangled Photons Produced by Parametric Down-Conversion
NASA Technical Reports Server (NTRS)
Cable, Hugo; Durkin, Gabriel A.
2010-01-01
We explore the advantages offered by twin light beams produced in parametric down-conversion for precision measurement. The symmetry of these bipartite quantum states, even under losses, suggests that monitoring correlations between the divergent beams permits a high-precision inference of any symmetry-breaking effect, e.g., fiber birefringence. We show that the quantity of entanglement is not the key feature for such an instrument. In a lossless setting, scaling of precision at the ultimate "Heisenberg" limit is possible with photon counting alone. Even as photon losses approach 100% the precision is shot-noise limited, and we identify the crossover point between quantum and classical precision as a function of detected flux. The predicted hypersensitivity is demonstrated with a Bayesian simulation.
Entanglement spectrum and entangled modes of highly excited states in random XX spin chains
NASA Astrophysics Data System (ADS)
Pouranvari, Mohammad; Yang, Kun
We examine the newly developed real space renormalization group method of finding excited eigenstate (RSRG-X) of the XX spin-1/2 chain, from entanglement perspectives. Eigenmodes of the entanglement Hamiltonian, especially the maximally entangled mode (that contributes the most to the entanglement entropy) and corresponding entanglement energies are studied and compared with predictions of RSRG-X. Our numerical results demonstrate the accuracy of the RSRG-X method in the strong disorder limit, and quantify its error when applied to weak disorder regime. Overall, our results validate the RSRG-X method qualitatively, but as in the case of real space renormalization group method for the ground state (RSRG) there are quantitative errors for weaker randomness, and also such error grows with increasing temperature/excitation energy density.
Classification of multipartite entangled states by multidimensional determinants
Miyake, Akimasa
2003-01-01
We find that multidimensional determinants 'hyperdeterminants', related to entanglement measures (the so-called concurrence, or 3-tangle for two or three qubits, respectively), are derived from a duality between entangled states and separable states. By means of the hyperdeterminant and its singularities, the single copy of multipartite pure entangled states is classified into an onion structure of every closed subset, similar to that by the local rank in the bipartite case. This reveals how inequivalent multipartite entangled classes are partially ordered under local actions. In particular, the generic entangled class of the maximal dimension, distinguished as the nonzero hyperdeterminant, does not include the maximally entangled states in Bell's inequalities in general (e.g., in the n{>=}4 qubits), contrary to the widely known bipartite or three-qubit cases. It suggests that not only are they never locally interconvertible with the majority of multipartite entangled states, but they would have no grounds for the canonical n-partite entangled states. Our classification is also useful for the mixed states.
Tsirelson's bound and supersymmetric entangled states
Borsten, L.; Brádler, K.; Duff, M. J.
2014-01-01
A superqubit, belonging to a (2|1)-dimensional super-Hilbert space, constitutes the minimal supersymmetric extension of the conventional qubit. In order to see whether superqubits are more non-local than ordinary qubits, we construct a class of two-superqubit entangled states as a non-local resource in the CHSH game. Since super Hilbert space amplitudes are Grassmann numbers, the result depends on how we extract real probabilities and we examine three choices of map: (1) DeWitt (2) Trigonometric and (3) Modified Rogers. In cases (1) and (2), the winning probability reaches the Tsirelson bound pwin=cos2π/8≃0.8536 of standard quantum mechanics. Case (3) crosses Tsirelson's bound with pwin≃0.9265. Although all states used in the game involve probabilities lying between 0 and 1, case (3) permits other changes of basis inducing negative transition probabilities. PMID:25294964
Tsirelson's bound and supersymmetric entangled states.
Borsten, L; Brádler, K; Duff, M J
2014-10-01
A superqubit, belonging to a (2|1)-dimensional super-Hilbert space, constitutes the minimal supersymmetric extension of the conventional qubit. In order to see whether superqubits are more non-local than ordinary qubits, we construct a class of two-superqubit entangled states as a non-local resource in the CHSH game. Since super Hilbert space amplitudes are Grassmann numbers, the result depends on how we extract real probabilities and we examine three choices of map: (1) DeWitt (2) Trigonometric and (3) Modified Rogers. In cases (1) and (2), the winning probability reaches the Tsirelson bound [Formula: see text] of standard quantum mechanics. Case (3) crosses Tsirelson's bound with p win≃0.9265. Although all states used in the game involve probabilities lying between 0 and 1, case (3) permits other changes of basis inducing negative transition probabilities. PMID:25294964
Time-resolved double-slit interference pattern measurement with entangled photons
Kolenderski, Piotr; Scarcella, Carmelo; Johnsen, Kelsey D.; Hamel, Deny R.; Holloway, Catherine; Shalm, Lynden K.; Tisa, Simone; Tosi, Alberto; Resch, Kevin J.; Jennewein, Thomas
2014-01-01
The double-slit experiment strikingly demonstrates the wave-particle duality of quantum objects. In this famous experiment, particles pass one-by-one through a pair of slits and are detected on a distant screen. A distinct wave-like pattern emerges after many discrete particle impacts as if each particle is passing through both slits and interfering with itself. Here we present a temporally- and spatially-resolved measurement of the double-slit interference pattern using single photons. We send single photons through a birefringent double-slit apparatus and use a linear array of single-photon detectors to observe the developing interference pattern. The analysis of the buildup allows us to compare quantum mechanics and the corpuscular model, which aims to explain the mystery of single-particle interference. Finally, we send one photon from an entangled pair through our double-slit setup and show the dependence of the resulting interference pattern on the twin photon's measured state. Our results provide new insight into the dynamics of the buildup process in the double-slit experiment, and can be used as a valuable resource in quantum information applications. PMID:24770360
Time-resolved double-slit interference pattern measurement with entangled photons.
Kolenderski, Piotr; Scarcella, Carmelo; Johnsen, Kelsey D; Hamel, Deny R; Holloway, Catherine; Shalm, Lynden K; Tisa, Simone; Tosi, Alberto; Resch, Kevin J; Jennewein, Thomas
2014-01-01
The double-slit experiment strikingly demonstrates the wave-particle duality of quantum objects. In this famous experiment, particles pass one-by-one through a pair of slits and are detected on a distant screen. A distinct wave-like pattern emerges after many discrete particle impacts as if each particle is passing through both slits and interfering with itself. Here we present a temporally- and spatially-resolved measurement of the double-slit interference pattern using single photons. We send single photons through a birefringent double-slit apparatus and use a linear array of single-photon detectors to observe the developing interference pattern. The analysis of the buildup allows us to compare quantum mechanics and the corpuscular model, which aims to explain the mystery of single-particle interference. Finally, we send one photon from an entangled pair through our double-slit setup and show the dependence of the resulting interference pattern on the twin photon's measured state. Our results provide new insight into the dynamics of the buildup process in the double-slit experiment, and can be used as a valuable resource in quantum information applications. PMID:24770360
Integrable optical-fiber source of polarization-entangled photon pairs in the telecom band
Li Xiaoying; Liang Chuang; Fook Lee, Kim; Chen, Jun; Voss, Paul L.; Kumar, Prem
2006-05-15
We demonstrate an optical-fiber-based source of polarization-entangled photon pairs with improved quality and efficiency, which has been integrated with off-the-shelf telecom components and is, therefore, well suited for quantum communication applications in the 1550-nm telecom band. Polarization entanglement is produced by simultaneously pumping a loop of standard dispersion-shifted fiber with two orthogonally polarized pump pulses, one propagating in the clockwise and the other in the counterclockwise direction. We characterize this source by investigating two-photon interference between the generated signal-idler photon pairs under various conditions. The experimental parameters are carefully optimized to maximize the generated photon-pair correlation and to minimize contamination of the entangled photon pairs from extraneously scattered background photons that are produced by the pump pulses for two reasons: (i) spontaneous Raman scattering causes uncorrelated photons to be emitted in the signal and idler bands and (ii) broadening of the pump-pulse spectrum due to self-phase modulation causes pump photons to leak into the signal and idler bands. We obtain two-photon interference with visibility >90% without subtracting counts caused by the background photons (only dark counts of the detectors are subtracted), when the mean photon number in the signal (idler) channel is about 0.02/pulse, while no interference is observed in direct detection of either the signal or idler photons.
NASA Astrophysics Data System (ADS)
Deng, Li; Chen, Ai-Xi; Zhang, Jian-Song
2011-11-01
We provide a scheme with which the transfer of the entangled state and the entanglement swapping can be realized in a system of neutral atoms via the Rydberg blockade. Our idea can be extended to teleport an unknown atomic state. According to the latest theoretical research of the Rydberg excitation and experimental reports of the Rydberg blockade effect in quantum information processing, we discuss the experimental feasibility of our scheme.
Entanglement dynamics in three-qubit X states
Weinstein, Yaakov S.
2010-09-15
I explore the entanglement dynamics of a three-qubit system in an initial X state undergoing decoherence including the possible exhibition of entanglement sudden death. To quantify entanglement I utilize negativity measures and make use of appropriate entanglement witnesses. The negativity results are then extended to X states with an arbitraty number of qubits. I also demonstrate nonstandard behavior of the tripartite negativity entanglement metric: its sudden appearance after some amount of decoherence, followed quickly by its disappearance. Finally, I solve for a lower bound on the three-qubit X-state concurrence, demonstrate when this bound goes to 0, and outline simplifcations for the calculation of higher-order X-state concurrences.
Nonclassical properties and teleportation in the two-mode photon-added displaced squeezed states
NASA Astrophysics Data System (ADS)
Hoai, Nguyen Thi Xuan; Duc, Truong Minh
2016-01-01
In this paper, we study the nonclassical properties and find out the effect of photon addition on these properties as well as the process of teleportation in the two-mode photon-added displaced squeezed (TMPADS) states. We derive the analytic expressions of the Wigner function, the photon number distribution and the intermode photon antibunching for these states. We show that photon addition operation not only makes the Wigner function become negative but also leads to increase the degree of antibunching. The peak of the photon number distribution becomes flatter and shifts to the greater number of photons by adding photons to both modes simultaneously. Furthermore, it is proved that the degree of intermodal entanglement becomes bigger and bigger through increasing the number of photons added to both modes. As expected, when using these states as an entanglement resource to teleport a state, the average fidelity of teleportation process is also improved by increasing the number of added photons.
A note on initial state entanglement in inflationary cosmology
NASA Astrophysics Data System (ADS)
Kanno, Sugumi
2015-09-01
We give a new interpretation of the effect of initial state entanglement on the spectrum of vacuum fluctuations. We consider an initially entangled state between two free massive scalar fields in de Sitter space. We construct the initial state by making use of a Bogoliubov transformation between the Bunch-Davies vacuum and a four-mode squeezed state, and then derive the exact power spectrum for one of the scalar fields. We demonstrate that an oscillatory spectrum hardly appears for the initially entangled state unless an ad hoc absolute value of the Bogoliubov coefficients is chosen.
Deterministic controlled remote state preparation using partially entangled quantum channel
NASA Astrophysics Data System (ADS)
Chen, Na; Quan, Dong Xiao; Yang, Hong; Pei, Chang Xing
2016-04-01
In this paper, we propose a novel scheme for deterministic controlled remote state preparation (CRSP) of arbitrary two-qubit states. Suitably chosen partially entangled state is used as the quantum channel. With proper projective measurements carried out by the sender and controller, the receiver can reconstruct the target state by means of appropriate unitary operation. Unit success probability can be achieved for arbitrary two-qubit states. Different from some previous CRSP schemes utilizing partially entangled channels, auxiliary qubit is not required in our scheme. We also show that the success probability is independent of the parameters of the partially entangled quantum channel.
Cluster-type entangled coherent states: Generation and application
NASA Astrophysics Data System (ADS)
An, Nguyen Ba; Kim, Jaewan
2009-10-01
We consider a type of (M+N) -mode entangled coherent states and propose a simple deterministic scheme to generate these states that can fly freely in space. We then exploit such free-flying states to teleport certain kinds of superpositions of multimode coherent states. We also address the issue of manipulating size and type of entangled coherent states by means of linear optics elements only.
Cluster-type entangled coherent states: Generation and application
An, Nguyen Ba; Kim, Jaewan
2009-10-15
We consider a type of (M+N)-mode entangled coherent states and propose a simple deterministic scheme to generate these states that can fly freely in space. We then exploit such free-flying states to teleport certain kinds of superpositions of multimode coherent states. We also address the issue of manipulating size and type of entangled coherent states by means of linear optics elements only.
Semiquantum secret sharing using entangled states
Li Qin; Chan, W. H.; Long Dongyang
2010-08-15
Secret sharing is a procedure for sharing a secret among a number of participants such that only the qualified subsets of participants have the ability to reconstruct the secret. Even in the presence of eavesdropping, secret sharing can be achieved when all the members are quantum. So what happens if not all the members are quantum? In this paper, we propose two semiquantum secret sharing protocols by using maximally entangled Greenberger-Horne-Zeilinger-type states in which quantum Alice shares a secret with two classical parties, Bob and Charlie, in a way that both parties are sufficient to obtain the secret, but one of them cannot. The presented protocols are also shown to be secure against eavesdropping.
Entanglement Concentration of Partially Entangled Multi-electron Spin W States with CNOT Gates
NASA Astrophysics Data System (ADS)
Gu, Bin; Huang, Yugai; Fang, Xia; Wang, Haibin
2014-04-01
We propose a novel entanglement concentration protocol (ECP) for nonlocal N-electron systems in a partially entangled W state, resorting to an ancillary single electron and controlled-not gates. Compared with other ECPs for W states, our ECP has some illustrious advantages. First, each N-electron entangled system can be used to complete the entanglement concentration with only an ancillary electron. It does not require that there are two copies of N-electron entangled systems in each round of entanglement concentration. Second, only one of the users, say Charlie, needs to perform the protocol, while all parties should perform the same operations as Charlie in other ECPs for W-class states. Third, only Charlie asks other parities to retain or discard their electrons, and they do not need to check their measurement results, which greatly simplifies the complication of classical communication. Fourth, our ECP has a higher success probability than other ECPs for W-class states as its success probability equals to the limit value of an ECP for a W state in theory. These advantages maybe make our ECP more useful in practical applications.
NASA Astrophysics Data System (ADS)
Youn, Sun-Hyun
2016-08-01
Conditions to generate high-purity entangled vacuum-evacuated coherent states (| 0 > | α>0 - | - α>0 | 0 >) were studied for two cascade-placed beam splitters, with one squeezed state input and two coherent state inputs whenever a single photon is detected. Controlling the amplitudes and the phases of the beams allows for various amplitudes of the vacuum-evacuated coherent states (| α>0 = | α > -e - | α|2 | 0 >) up to α = 2.160 to be manipulated with high-purity.
Ultrafast double-quantum-coherence spectroscopy of excitons with entangled photons
Richter, Marten; Mukamel, Shaul
2010-07-15
We calculate the four-wave-mixing signal of excitons generated at k{sub 4}=k{sub 1}+k{sub 2}-k{sub 3} by two pulsed entangled photon pairs (k{sub 1}, k{sub 2}) and (k{sub 3}, k{sub 4}), where all four modes are chronologically ordered. Entangled photons offer an unusual combination of bandwidths and temporal resolution not possible by classical beams. Contributions from different resonances can be selected by varying the parameters of the photon wave function. The signal scales linearly rather than quadratically with the laser field intensity, which allows performance of the measurements at low powers.
Conditions for entangled photon emission from (111)B site-controlled pyramidal quantum dots
Juska, G. Murray, E.; Dimastrodonato, V.; Chung, T. H.; Moroni, S. T.; Gocalinska, A.; Pelucchi, E.
2015-04-07
A study of highly symmetric site-controlled pyramidal In{sub 0.25}Ga{sub 0.75}As quantum dots (QDs) is presented. It is discussed that polarization-entangled photons can be also obtained from pyramidal QDs of different designs from the one already reported in Juska et al. [Nat. Photonics 7, 527 (2013)]. Moreover, some of the limitations for a higher density of entangled photon emitters are addressed. Among these issues are (1) a remaining small fine-structure splitting and (2) an effective QD charging under non-resonant excitation conditions, which strongly reduce the number of useful biexciton-exciton recombination events. A possible solution of the charging problem is investigated exploiting a dual-wavelength excitation technique, which allows a gradual QD charge tuning from strongly negative to positive and, eventually, efficient detection of entangled photons from QDs, which would be otherwise ineffective under a single-wavelength (non-resonant) excitation.
Groverian entanglement measure of pure quantum states with arbitrary partitions
Shimoni, Yishai; Biham, Ofer
2007-02-15
The Groverian entanglement measure of pure quantum states of n qubits is generalized to the case in which the qubits are divided into any p{<=}n parties. The entanglement between these parties is evaluated numerically using an efficient parametrization. To demonstrate this measure we apply it to symmetric states such as the Greenberg-Horne-Zeiliner state and the W state. Interestingly, this measure is equivalent to an entanglement measure introduced earlier [H. Barnum and N. Linden, J. Phys. A 34, 6787 (2001)], using different considerations.
Quantum steganography with large payload based on entanglement swapping of χ-type entangled states
NASA Astrophysics Data System (ADS)
Qu, Zhi-Guo; Chen, Xiu-Bo; Luo, Ming-Xing; Niu, Xin-Xin; Yang, Yi-Xian
2011-04-01
In this paper, we firstly propose a new simple method to calculate entanglement swapping of χ-type entangled states, and then present a novel quantum steganography protocol with large payload. The new protocol adopts entanglement swapping to build up the hidden channel within quantum secure direct communication with χ-type entangled states for securely transmitting secret messages. Comparing with the previous quantum steganographies, the capacity of the hidden channel is much higher, which is increased to eight bits. Meanwhile, due to the quantum uncertainty theorem and the no-cloning theorem its imperceptibility is proved to be great in the analysis, and its security is also analyzed in detail, which is proved that intercept-resend attack, measurement-resend attack, ancilla attack, man-in-the-middle attack or even Dos(Denial of Service) attack couldn't threaten it. As a result, the protocol can be applied in various fields of quantum communication.
Preparation of the entanglement states with distant atoms trapped in separate cavities
NASA Astrophysics Data System (ADS)
Ou, Yong-Cheng; Yuan, Chun-Hua; Zhang, Zhi-Ming
2006-01-01
We present an experimental scheme of preparing the Greenberger-Horne-Zeilinger (GHZ) state and the W state with distant atoms trapped in spatially separate cavities by detecting cavity decay through single-photon detectors, based on the original ideas of photon-interference-induced entanglement between bipartite (Feng X L, Zhang Z M, Li X D, Li S D, Gong S Q and Xu Z Z 2003 Phys. Rev. Lett. 90 217902). The scheme can be generalized to prepare the general n-qubit GHZ state and W state.
NASA Astrophysics Data System (ADS)
Simon, David S.; Fitzpatrick, Casey A.; Sergienko, Alexander V.
2016-04-01
The concept of directionally unbiased optical multiports is introduced, in which photons may reflect back out the input direction. A linear-optical implementation is described, and the simplest three-port version studied. Symmetry arguments demonstrate potential for unusual quantum information processing applications. The devices impose group structures on two-photon entangled Bell states and act as universal Bell-state processors to implement probabilistic quantum gates acting on state symmetries. These multiports allow optical scattering experiments to be carried out on arbitrary undirected graphs via linear optics and raise the possibility of linear-optical information processing using group structures formed by optical qudit states.
Zhang, Jiaxiang; Wildmann, Johannes S.; Ding, Fei; Trotta, Rinaldo; Huo, Yongheng; Zallo, Eugenio; Huber, Daniel; Rastelli, Armando; Schmidt, Oliver G.
2015-01-01
Triggered sources of entangled photon pairs are key components in most quantum communication protocols. For practical quantum applications, electrical triggering would allow the realization of compact and deterministic sources of entangled photons. Entangled-light-emitting-diodes based on semiconductor quantum dots are among the most promising sources that can potentially address this task. However, entangled-light-emitting-diodes are plagued by a source of randomness, which results in a very low probability of finding quantum dots with sufficiently small fine structure splitting for entangled-photon generation (∼10−2). Here we introduce strain-tunable entangled-light-emitting-diodes that exploit piezoelectric-induced strains to tune quantum dots for entangled-photon generation. We demonstrate that up to 30% of the quantum dots in strain-tunable entangled-light-emitting-diodes emit polarization-entangled photons. An entanglement fidelity as high as 0.83 is achieved with fast temporal post selection. Driven at high speed, that is 400 MHz, strain-tunable entangled-light-emitting-diodes emerge as promising devices for high data-rate quantum applications. PMID:26621073
NASA Astrophysics Data System (ADS)
Zhang, Jiaxiang; Wildmann, Johannes S.; Ding, Fei; Trotta, Rinaldo; Huo, Yongheng; Zallo, Eugenio; Huber, Daniel; Rastelli, Armando; Schmidt, Oliver G.
2015-12-01
Triggered sources of entangled photon pairs are key components in most quantum communication protocols. For practical quantum applications, electrical triggering would allow the realization of compact and deterministic sources of entangled photons. Entangled-light-emitting-diodes based on semiconductor quantum dots are among the most promising sources that can potentially address this task. However, entangled-light-emitting-diodes are plagued by a source of randomness, which results in a very low probability of finding quantum dots with sufficiently small fine structure splitting for entangled-photon generation (~10-2). Here we introduce strain-tunable entangled-light-emitting-diodes that exploit piezoelectric-induced strains to tune quantum dots for entangled-photon generation. We demonstrate that up to 30% of the quantum dots in strain-tunable entangled-light-emitting-diodes emit polarization-entangled photons. An entanglement fidelity as high as 0.83 is achieved with fast temporal post selection. Driven at high speed, that is 400 MHz, strain-tunable entangled-light-emitting-diodes emerge as promising devices for high data-rate quantum applications.
Zhang, Jiaxiang; Wildmann, Johannes S; Ding, Fei; Trotta, Rinaldo; Huo, Yongheng; Zallo, Eugenio; Huber, Daniel; Rastelli, Armando; Schmidt, Oliver G
2015-01-01
Triggered sources of entangled photon pairs are key components in most quantum communication protocols. For practical quantum applications, electrical triggering would allow the realization of compact and deterministic sources of entangled photons. Entangled-light-emitting-diodes based on semiconductor quantum dots are among the most promising sources that can potentially address this task. However, entangled-light-emitting-diodes are plagued by a source of randomness, which results in a very low probability of finding quantum dots with sufficiently small fine structure splitting for entangled-photon generation (∼10(-2)). Here we introduce strain-tunable entangled-light-emitting-diodes that exploit piezoelectric-induced strains to tune quantum dots for entangled-photon generation. We demonstrate that up to 30% of the quantum dots in strain-tunable entangled-light-emitting-diodes emit polarization-entangled photons. An entanglement fidelity as high as 0.83 is achieved with fast temporal post selection. Driven at high speed, that is 400 MHz, strain-tunable entangled-light-emitting-diodes emerge as promising devices for high data-rate quantum applications. PMID:26621073
Quantum frequency up-conversion of continuous variable entangled states
Liu, Wenyuan; Wang, Ning; Li, Zongyang; Li, Yongmin
2015-12-07
We demonstrate experimentally quantum frequency up-conversion of a continuous variable entangled optical field via sum-frequency-generation process. The two-color entangled state initially entangled at 806 and 1518 nm with an amplitude quadrature difference squeezing of 3.2 dB and phase quadrature sum squeezing of 3.1 dB is converted to a new entangled state at 530 and 1518 nm with the amplitude quadrature difference squeezing of 1.7 dB and phase quadrature sum squeezing of 1.8 dB. Our implementation enables the observation of entanglement between two light fields spanning approximately 1.5 octaves in optical frequency. The presented scheme is robust to the excess amplitude and phase noises of the pump field, making it a practical building block for quantum information processing and communication networks.
Entanglement as a resource to distinguish orthogonal product states
Zhang, Zhi-Chao; Gao, Fei; Cao, Tian-Qing; Qin, Su-Juan; Wen, Qiao-Yan
2016-01-01
It is known that there are many sets of orthogonal product states which cannot be distinguished perfectly by local operations and classical communication (LOCC). However, these discussions have left the following open question: What entanglement resources are necessary and/or sufficient for this task to be possible with LOCC? In m ⊗ n, certain classes of unextendible product bases (UPB) which can be distinguished perfectly using entanglement as a resource, had been presented in 2008. In this paper, we present protocols which use entanglement more efficiently than teleportation to distinguish some classes of orthogonal product states in m ⊗ n, which are not UPB. For the open question, our results offer rather general insight into why entanglement is useful for such tasks, and present a better understanding of the relationship between entanglement and nonlocality. PMID:27458034
Heralded entangled coherent states between spatially separated massive resonators
NASA Astrophysics Data System (ADS)
Asadian, Ali; Abdi, Mehdi
2016-05-01
We put forward an experimentally feasible scheme for heralded entanglement generation between two distant macroscopic mechanical resonators. The protocol exploits a hybrid quantum device, a qubit interacting with a mechanical resonator as well as a cavity mode, for each party. The cavity modes interfere on a beam splitter followed by suitable heralding detections, which postselect a hybrid entangled state with success probability 1/2. Subsequently, by local measurements on the qubits, a mechanically entangled coherent state can be achieved. The mechanical entanglement can be further verified via monitoring the entanglement of the qubit pair. The setup is envisioned as a test bed for sensing gravitational effects on the quantum dynamics of gravitationally coupled massive objects. As a concrete example, we illustrate the implementation of our protocol using the current circuit QED architectures.
Topological entanglement entropy, ground state degeneracy and holography
NASA Astrophysics Data System (ADS)
Parnachev, Andrei; Poovuttikul, Napat
2015-10-01
Topological entanglement entropy, a measure of the long-ranged entanglement, is related to the degeneracy of the ground state on a higher genus surface. The exact relation depends on the details of the topological theory. We consider a class of holographic models where such relation might be similar to the one exhibited by Chern-Simons theory in a certain large N limit. Both the non-vanishing topological entanglement entropy and the ground state degeneracy in these holographic models are consequences of the topological Gauss-Bonnet term in the dual gravitational description. A soft wall holographic model of confinement is used to generate finite correlation length but keep the disk topology of the entangling surface in the bulk, necessary for nonvanishing topological entanglement entropy.
Quantum frequency up-conversion of continuous variable entangled states
NASA Astrophysics Data System (ADS)
Liu, Wenyuan; Wang, Ning; Li, Zongyang; Li, Yongmin
2015-12-01
We demonstrate experimentally quantum frequency up-conversion of a continuous variable entangled optical field via sum-frequency-generation process. The two-color entangled state initially entangled at 806 and 1518 nm with an amplitude quadrature difference squeezing of 3.2 dB and phase quadrature sum squeezing of 3.1 dB is converted to a new entangled state at 530 and 1518 nm with the amplitude quadrature difference squeezing of 1.7 dB and phase quadrature sum squeezing of 1.8 dB. Our implementation enables the observation of entanglement between two light fields spanning approximately 1.5 octaves in optical frequency. The presented scheme is robust to the excess amplitude and phase noises of the pump field, making it a practical building block for quantum information processing and communication networks.
Hang Chao; Huang Guoxiang
2010-11-15
We present a scheme for obtaining entangled photons and quantum phase gates in a room-temperature four-state tripod-type atomic system with two-mode active Raman gain (ARG). We analyze the linear and nonlinear optical responses of this ARG system and show that the scheme is fundamentally different from those based on electromagnetically induced transparency and hence can avoid significant probe-field absorption as well as a temperature-related Doppler effect. We demonstrate that highly entangled photon pairs can be produced and rapidly responding polarization qubit phase gates can be constructed based on the unique features of the enhanced cross-phase-modulation and superluminal probe-field propagation of the system.
NASA Astrophysics Data System (ADS)
Lee, Sang Min; Kim, Heonoh; Cha, Myoungsik; Moon, Han Seb
2016-02-01
We demonstrate a polarization-entangled photon-pair source obtained via a type-II non-collinear quasi-phase-matched spontaneous parametric down-conversion process with a 10-mm periodically poled KTiOPO$_4$ crystal, which is as stable and wavelength-tunable as the well-known Sagnac configuration scheme. A brightness of 4.2 kHz/mW is detected and a concurrence of 0.975 is estimated using quantum state tomography. Without loss of entanglement and brightness, the photon-pair wavelengths are tunable through control of the crystal temperature. This improvement is achieved using the non-collinear configuration and a stable interferometric distinguishability compensator.
Lee, Sang Min; Kim, Heonoh; Cha, Myoungsik; Moon, Han Seb
2016-02-01
We demonstrate a polarization-entangled photon-pair source obtained via a type-II non-collinear quasi-phase-matched spontaneous parametric down-conversion process with a 10-mm periodically poled KTiOPO4 crystal, which is as stable and wavelength-tunable as the well-known Sagnac configuration scheme. A brightness of 4.2 kHz/mW is detected and a concurrence of 0.975 is estimated using quantum state tomography. Without loss of entanglement and brightness, the photon-pair wavelengths are tunable through control of the crystal temperature. This improvement is achieved using the non-collinear configuration and a stable interferometric distinguishability compensator. PMID:26906861
Autonomous quantum thermal machine for generating steady-state entanglement
NASA Astrophysics Data System (ADS)
Bohr Brask, Jonatan; Haack, Géraldine; Brunner, Nicolas; Huber, Marcus
2015-11-01
We discuss a simple quantum thermal machine for the generation of steady-state entanglement between two interacting qubits. The machine is autonomous in the sense that it uses only incoherent interactions with thermal baths, but no source of coherence or external control. By weakly coupling the qubits to thermal baths at different temperatures, inducing a heat current through the system, steady-state entanglement is generated far from thermal equilibrium. Finally, we discuss two possible implementations, using superconducting flux qubits or a semiconductor double quantum dot. Experimental prospects for steady-state entanglement are promising in both systems.
Multi-state Quantum Teleportation via One Entanglement State
NASA Astrophysics Data System (ADS)
Guo, Ying; Zeng, Gui-Hua; Moon Ho, Lee
2008-08-01
A multi-sender-controlled quantum teleportation scheme is proposed to teleport several secret quantum states from different senders to a distance receiver based on only one Einstein Podolsky Rosen (EPR) pair with controlled-NOT (CNOT) gates. In the present scheme, several secret single-qubit quantum states are encoded into a multi-qubit entangled quantum state. Two communication modes, i.e., the detecting mode and the message mode, are employed so that the eavesdropping can be detected easily and the teleported message may be recovered efficiently. It has an advantage over teleporting several different quantum states for one scheme run with more efficiency than the previous quantum teleportation schemes.
Long-range quantum entanglement in noisy cluster states
Raussendorf, Robert; Bravyi, Sergey; Harrington, Jim
2005-06-15
We describe a phase transition for long-range entanglement in a three-dimensional cluster state affected by noise. The partially decohered state is modeled by the thermal state of a short-range translation-invariant Hamiltonian. We find that the temperature at which the entanglement length changes from infinite to finite is nonzero. We give an upper and lower bound to this transition temperature.
Generation and purification of maximally entangled atomic states in optical cavities
Lougovski, P.; Walther, H.; Solano, E.
2005-01-01
We present a probabilistic scheme for generating and purifying maximally entangled states of two atoms inside an optical cavity via no-photon detection at the cavity output, where ideal detectors are not required. The intermediate mixed states can be continuously purified so as to violate Bell inequalities in a parametrized manner. The scheme relies on an additional strong-driving field that realizes, atypically, simultaneous Jaynes-Cummings and anti-Jaynes-Cummings interactions.
Generating multi-photon W-like states for perfect quantum teleportation and superdense coding
NASA Astrophysics Data System (ADS)
Li, Ke; Kong, Fan-Zhen; Yang, Ming; Ozaydin, Fatih; Yang, Qing; Cao, Zhuo-Liang
2016-08-01
An interesting aspect of multipartite entanglement is that for perfect teleportation and superdense coding, not the maximally entangled W states but a special class of non-maximally entangled W-like states are required. Therefore, efficient preparation of such W-like states is of great importance in quantum communications, which has not been studied as much as the preparation of W states. In this paper, we propose a simple optical scheme for efficient preparation of large-scale polarization-based entangled W-like states by fusing two W-like states or expanding a W-like state with an ancilla photon. Our scheme can also generate large-scale W states by fusing or expanding W or even W-like states. The cost analysis shows that in generating large-scale W states, the fusion mechanism achieves a higher efficiency with non-maximally entangled W-like states than maximally entangled W states. Our scheme can also start fusion or expansion with Bell states, and it is composed of a polarization-dependent beam splitter, two polarizing beam splitters and photon detectors. Requiring no ancilla photon or controlled gate to operate, our scheme can be realized with the current photonics technology and we believe it enable advances in quantum teleportation and superdense coding in multipartite settings.
Generating multi-photon W-like states for perfect quantum teleportation and superdense coding
NASA Astrophysics Data System (ADS)
Li, Ke; Kong, Fan-Zhen; Yang, Ming; Ozaydin, Fatih; Yang, Qing; Cao, Zhuo-Liang
2016-05-01
An interesting aspect of multipartite entanglement is that for perfect teleportation and superdense coding, not the maximally entangled W states but a special class of non-maximally entangled W-like states are required. Therefore, efficient preparation of such W-like states is of great importance in quantum communications, which has not been studied as much as the preparation of W states. In this paper, we propose a simple optical scheme for efficient preparation of large-scale polarization-based entangled W-like states by fusing two W-like states or expanding a W-like state with an ancilla photon. Our scheme can also generate large-scale W states by fusing or expanding W or even W-like states. The cost analysis shows that in generating large-scale W states, the fusion mechanism achieves a higher efficiency with non-maximally entangled W-like states than maximally entangled W states. Our scheme can also start fusion or expansion with Bell states, and it is composed of a polarization-dependent beam splitter, two polarizing beam splitters and photon detectors. Requiring no ancilla photon or controlled gate to operate, our scheme can be realized with the current photonics technology and we believe it enable advances in quantum teleportation and superdense coding in multipartite settings.
Manipulation of Entangled States for Quantum Information Processing
NASA Astrophysics Data System (ADS)
Bose, S.; Huelga, S. F.; Jonathan, D.; Knight, P. L.; Murao, M.; Plenio, M. B.; Vedral, V.
Entanglement manipulation, and especially Entanglement Swapping is at the heart of current work on quantum information processing, purification and quantum teleportation. We will discuss how it may be generalized to multiparticle systems and how this enables multi-user quantum cryptographic protocols to be developed. Our scheme allows us to establish multiparticle entanglement between particles which belong to distant users in a communication network through a prior distribution of Bell state singlets followed by local measurements. We compare our method for generating entanglement with existing schemes using simple quantum networks, and highlight the advantages and applications in cryptographic conferencing and in reading messages from more than one source through a single quantum measurement. We also discuss how entanglement leads to the idea of `telecloning', in which a teleportation-like protocol can be found which reproduces the output of an optimal quantum cloning machine.
Protecting remote atomic entanglement against spontaneous emission by separated photonic pulses
NASA Astrophysics Data System (ADS)
Zong, Xiao-Lan; Du, Chao-Qun; Yang, Ming; Zhang, Gang; Yang, Qing; Cao, Zhuo-Liang
2015-07-01
We study the entanglement dynamics between two spatially separated atoms trapped in two separate optical cavities. Based on cavity-assisted interactions between the atoms and separated photonic pulses, we propose a scheme for the implemention of a controlled-phase-flip gate (CPF gate) between each of the atoms and the photonic pulse to protect the remote atomic quantum entanglement against the decaying caused by spontaneous emission. What we need to do is to shoot the horizontally polarized photons onto the cavity mirror successively, plus a train of Hadamard operations on the atoms, and no measurement is needed here. It is shown that the quantum entanglement of the two remote atoms can be protected effectively in this way. We also extend our scheme to the case of weak coupling and low Q cavity cases. The simplicity of the current scheme may warrant its experimental realization.
Nonexistence of entangled continuous-variable Werner states with positive partial transpose
NASA Astrophysics Data System (ADS)
McNulty, Daniel; Tatham, Richard; Mišta, Ladislav
2014-03-01
We address an open question about the existence of entangled continuous-variable (CV) Werner states with positive partial transpose (PPT). We prove that no such state exists by showing that all PPT CV Werner states are separable. The separability follows by observing that these CV Werner states can be approximated by truncating the states into a finite-dimensional convex mixture of product states. In addition, the constituents of the product states comprise a generalized non-Gaussian measurement which gives, rather surprisingly, a strictly tighter upper bound on quantum discord than photon counting. These results uncover the presence of only negative partial transpose entanglement and illustrate the complexity of more general nonclassical correlations in this paradigmatic class of genuine non-Gaussian quantum states.
Operational entanglement families of symmetric mixed N -qubit states
NASA Astrophysics Data System (ADS)
Bastin, T.; Mathonet, P.; Solano, E.
2015-02-01
We introduce an operational entanglement classification of symmetric mixed states for an arbitrary number of qubits based on stochastic local operations assisted with classical communication (SLOCC operations). We define families of SLOCC entanglement classes successively embedded into each other, we prove that they are of nonzero measure, and we construct witness operators to distinguish them. Moreover, we discuss how arbitrary symmetric mixed states can be realized in the laboratory via a one-to-one correspondence between well-defined sets of controllable parameters and the corresponding entanglement families.
Steady-state entanglement activation in optomechanical cavities
NASA Astrophysics Data System (ADS)
Farace, Alessandro; Ciccarello, Francesco; Fazio, Rosario; Giovannetti, Vittorio
2014-02-01
Quantum discord, and related indicators, are raising a relentless interest as a novel paradigm of nonclassical correlations beyond entanglement. Here, we discover a discord-activated mechanism yielding steady-state entanglement production in a realistic continuous-variable setup. This comprises two coupled optomechanical cavities, where the optical modes (OMs) communicate through a fiber. We first use a simplified model to highlight the creation of steady-state discord between the OMs. We show next that such discord improves the level of stationary optomechanical entanglement attainable in the system, making it more robust against temperature and thermal noise.
Systematic generation of entanglement measures for pure states
NASA Astrophysics Data System (ADS)
Sugita, Ayumu
2008-05-01
We propose a method to generate entanglement measures systematically by using the irreducible decomposition of some copies of a state under the local unitary (LU) transformations. It is applicable to general multipartite systems. We show that there are entanglement monotones corresponding to singlet representations of the LU group. They can be evaluated efficiently in an algebraic way, and experimentally measurable by local projective measurements of the copies of the state. Nonsinglet representations are also shown to be useful to classify entanglement. Our method reproduces many well-known measures in a unified way.
NASA Astrophysics Data System (ADS)
Dong, Li; Wang, Jun-Xi; Li, Qing-Yang; Shen, Hong-Zhi; Dong, Hai-Kuan; Xiu, Xiao-Ming; Ren, Yuan-Peng; Gao, Ya-Jun
2015-12-01
We propose a quantum secure direct communication protocol via a collective noise channel, exploiting polarization-entangled Bell states and the nondemolition parity analysis based on weak cross-Kerr nonlinearities. The participant Bob, who will receive the secret information, sends one of two photons in a polarization-entangled Bell state exploiting the transmission circuit against the collective noise to the participant Alice, who will send the secret information, by the means of photon block transmission. If the first security check employing the nondemolition parity analysis is passed, the task of securely distributing the quantum channel is fulfilled. Encoding secret information on the photons sent from Bob by performing single-photon unitary transformation operations, Alice resends these photons to Bob through the transmission circuit against the collective noise. Exploiting the nondemolition parity analysis to distinguish Bell states, Bob can obtain the secret information from Alice after the second security check is passed, and the resulting Bell states can be applied to other tasks of quantum information processing. Under the condition of the secure quantum channel being confirmed, the photons that are utilized in the role of the security check can be applied to the function of secure direct communication, thus enhancing the efficiency of transmitting secret information and saving a lot of resources.
Entangled photon generation using four-wave mixing in azimuthally symmetric microresonators.
Camacho, Ryan M
2012-09-24
A novel quantum mechanical formulation of the bi-photon wavefunction and spectra resulting from four-wave mixing is developed for azimuthally symmetric systems. Numerical calculations are performed verifying the use of the angular group velocity and angular group velocity dispersion in such systems, as opposed their commonly used linear counterparts. The dispersion profile and bi-photon spectra of two illustrative examples are given, emphasizing the physical origin of the effects leading to the conditions for angular momentum and energy conservation. A scheme is proposed in which widely spaced narrowband entangled photons may be produced through a four-wave mixing process in a chip-scale ring resonator. The entangled photon pairs are found to conserve energy and momentum in the four-wave mixing interaction, even though both photon modes lie in spectral regions of steep angular group velocity dispersion. PMID:23037348
Protecting quantum entanglement and nonlocality for tripartite states under decoherence
NASA Astrophysics Data System (ADS)
Zhang, Rui; Yin, Yu Hao; Ma, Wen Chao; Ye, Liu
2016-06-01
Quantum entanglement and nonlocality will suffer inevitable harm from decoherence environment. Based on GHZ state, we study the harm of the generalized amplitude damping (GAD) operation and the protection by the single local filtering (SLF) operation in this paper. We verify that the SLF functions to depress the loss of entanglement and nonlocality from GAD. This conclusion will guide us to select the best method to protect the GHZ state from GAD decoherence.
Steady atomic entanglement in cavity QED without state initialization
Zhang Shengli; Zou Xubo; Yang Song; Li Chuanfeng; Guo Guangcan; Jin Chenhui
2009-12-15
We present a scheme for realizing a steady entanglement state between two trapped atoms, without requiring the initialization of atom-cavity system nor fine time-controlling of evolution dynamics. We show that high-fidelity entanglement of atomic state can be obtained in a period of time equal to a few times the inverse of atomic's spontaneous decay rate. The robustness against cavity decay kappa and cavity thermal field n{sub T} has also been examined.
Significant-Loophole-Free Test of Bell's Theorem with Entangled Photons.
Giustina, Marissa; Versteegh, Marijn A M; Wengerowsky, Sören; Handsteiner, Johannes; Hochrainer, Armin; Phelan, Kevin; Steinlechner, Fabian; Kofler, Johannes; Larsson, Jan-Åke; Abellán, Carlos; Amaya, Waldimar; Pruneri, Valerio; Mitchell, Morgan W; Beyer, Jörn; Gerrits, Thomas; Lita, Adriana E; Shalm, Lynden K; Nam, Sae Woo; Scheidl, Thomas; Ursin, Rupert; Wittmann, Bernhard; Zeilinger, Anton
2015-12-18
Local realism is the worldview in which physical properties of objects exist independently of measurement and where physical influences cannot travel faster than the speed of light. Bell's theorem states that this worldview is incompatible with the predictions of quantum mechanics, as is expressed in Bell's inequalities. Previous experiments convincingly supported the quantum predictions. Yet, every experiment requires assumptions that provide loopholes for a local realist explanation. Here, we report a Bell test that closes the most significant of these loopholes simultaneously. Using a well-optimized source of entangled photons, rapid setting generation, and highly efficient superconducting detectors, we observe a violation of a Bell inequality with high statistical significance. The purely statistical probability of our results to occur under local realism does not exceed 3.74×10^{-31}, corresponding to an 11.5 standard deviation effect. PMID:26722905
Quantum-dot spin-photon entanglement via frequency downconversion to telecom wavelength.
De Greve, Kristiaan; Yu, Leo; McMahon, Peter L; Pelc, Jason S; Natarajan, Chandra M; Kim, Na Young; Abe, Eisuke; Maier, Sebastian; Schneider, Christian; Kamp, Martin; Höfling, Sven; Hadfield, Robert H; Forchel, Alfred; Fejer, M M; Yamamoto, Yoshihisa
2012-11-15
Long-distance quantum teleportation and quantum repeater technologies require entanglement between a single matter quantum bit (qubit) and a telecommunications (telecom)-wavelength photonic qubit. Electron spins in III-V semiconductor quantum dots are among the matter qubits that allow for the fastest spin manipulation and photon emission, but entanglement between a single quantum-dot spin qubit and a flying (propagating) photonic qubit has yet to be demonstrated. Moreover, many quantum dots emit single photons at visible to near-infrared wavelengths, where silica fibre losses are so high that long-distance quantum communication protocols become difficult to implement. Here we demonstrate entanglement between an InAs quantum-dot electron spin qubit and a photonic qubit, by frequency downconversion of a spontaneously emitted photon from a singly charged quantum dot to a wavelength of 1,560 nanometres. The use of sub-10-picosecond pulses at a wavelength of 2.2 micrometres in the frequency downconversion process provides the necessary quantum erasure to eliminate which-path information in the photon energy. Together with previously demonstrated indistinguishable single-photon emission at high repetition rates, the present technique advances the III-V semiconductor quantum-dot spin system as a promising platform for long-distance quantum communication. PMID:23151585
Experimental preparation of two-photon Knill-Laflamme-Milburn states
Lemr, Karel; Cernoch, Antonin; Soubusta, Jan; Fiurasek, Jaromir
2010-01-15
We report an experimental preparation of the so-called Knill-Laflamme-Milburn states (KLM states) that have been known to have interesting properties related to quantum information processing. Our experiment has demonstrated successful preparation of entangled two-photon four-mode KLM states using spontaneous parametric down-conversion as a source of entangled photon pairs, linear optical components, and avalanche photodiodes for single-photon detection. We have verified the successful generation of KLM states by complete quantum state tomography.
Quantum entanglement distribution with 810 nm photons through active telecommunication fibers.
Holloway, Catherine; Meyer-Scott, Evan; Erven, Chris; Jennewein, Thomas
2011-10-10
We demonstrate the distribution of polarization-entangled photons for the purpose of quantum key distribution (QKD) along active telecom fibers. Entangled photon pairs of 810 nm wavelength generated by a Sagnac interferometer source were coupled into standard telecom single mode fibers. The fibers were either dark or carrying a standardized 1550 nm ethernet signals (1000BASE-ZX) with a nominal speed of 1 GBps from regular media converter devices, without any requirements on the optical power or spectrum transmitted. Our system demonstrates a QKD network covering 6 km in distance with a central service provider for classical and quantum data. PMID:21997067
Wang, Mei-Yu; Yan, Feng-Li; Gao, Ting
2016-01-01
We present two deterministic quantum entanglement distribution protocols for a four-photon Dicke polarization entangled state resorting to the frequency and spatial degrees of freedom, which are immune to an arbitrary collective-noise channel. Both of the protocols adopt the X homodyne measurement based on the cross-Kerr nonlinearity to complete the task of the single-photon detection with nearly unit probability in principle. After the four receivers share the photons, they add some local unitary operations to obtain a standard four-photon Dicke polarization entangled state. PMID:27412489
Wang, Mei-Yu; Yan, Feng-Li; Gao, Ting
2016-01-01
We present two deterministic quantum entanglement distribution protocols for a four-photon Dicke polarization entangled state resorting to the frequency and spatial degrees of freedom, which are immune to an arbitrary collective-noise channel. Both of the protocols adopt the X homodyne measurement based on the cross-Kerr nonlinearity to complete the task of the single-photon detection with nearly unit probability in principle. After the four receivers share the photons, they add some local unitary operations to obtain a standard four-photon Dicke polarization entangled state. PMID:27412489
NASA Astrophysics Data System (ADS)
Wang, Mei-Yu; Yan, Feng-Li; Gao, Ting
2016-07-01
We present two deterministic quantum entanglement distribution protocols for a four-photon Dicke polarization entangled state resorting to the frequency and spatial degrees of freedom, which are immune to an arbitrary collective-noise channel. Both of the protocols adopt the X homodyne measurement based on the cross-Kerr nonlinearity to complete the task of the single-photon detection with nearly unit probability in principle. After the four receivers share the photons, they add some local unitary operations to obtain a standard four-photon Dicke polarization entangled state.
NASA Astrophysics Data System (ADS)
Hu, Juju; Xu, Lin
2015-07-01
We demonstrate the controllable generation of entangled coherent states in circuit quantum electrodynamics (circuit QED). In our scheme, the easy integration of solid-state quantum circuit is exploited. In particular, through manipulating the external capacitor or external classical microwave impulse, the coupling between superconducting qubits and cavity can be manipulated, the entanglement effect between qubit and field modes can be enhanced and the decoherence effect can be effectively suppressed. We further discuss the correspondence between quantum entanglement and some non-classical effects such as the squeezing of entangled coherent state field, the anti-buching effect. The results show that the time evolution of the quantum entanglement between field modes is always accompanied by the synchronous changes of certain non-classical effect. When the quantum entanglement reaches maximum, the anti-bunching (or compression effect) almost reaches maximum synchronously. Once entanglement sudden death occurs, the non-classical effects disappear.
Strong violations of locality by testing Bell’s inequality with improved entangled-photon systems
NASA Astrophysics Data System (ADS)
Wang, Yao; Fan, Dai-He; Guo, Wei-Jie; Wei, Lian-Fu
2015-08-01
Bell’s theorem states that quantum mechanics cannot be accounted for by any local theory. One of the examples is the existence of quantum non-locality is essentially violated by the local Bell’s inequality. Therefore, the violation of Bell’s inequality (BI) has been regarded as one of the robust evidences of quantum mechanics. Until now, BI has been tested by many experiments, but the maximal violation (i.e., Cirel’son limit) has never been achieved. By improving the design of entangled sources and optimizing the measurement settings, in this work we report the stronger violations of the Clauser-Horne-Shimony-Holt (CHSH)-type Bell’s inequality. The biggest value of Bell’s function in our experiment reaches to a significant one: S = 2.772± 0.063, approaching to the so-called Cirel’son limit in which the Bell function value is . Further improvement is possible by optimizing the entangled-photon sources. Project supported by the National Natural Science Foundation of China (Grant Nos. 61308008, 91321104, U1330201, and 11174373) and the Fundamental Research Funds for the Central Universities (Grant No. 2682014CX081).
Duality in entanglement of macroscopic states of light
NASA Astrophysics Data System (ADS)
Lee, Su-Yong; Lee, Chang-Woo; Kurzyński, Paweł; Kaszlikowski, Dagomir; Kim, Jaewan
2016-08-01
We investigate duality in entanglement of a bipartite multiphoton system generated from a coherent state of light. The system can exhibit polarization entanglement if the two parts are distinguished by their parity, or parity entanglement if the parts are distinguished by polarization. It was shown in Phys. Rev. Lett. 110, 140404 (2013), 10.1103/PhysRevLett.110.140404 that this phenomenon can be exploited as a method to test indistinguishability of two particles and it was conjectured that one can also test indistinguishability of macroscopic systems. We propose a setup to test this conjecture. Contrary to the previous studies using two-particle interference effect as in the Hong-Ou- Mandel setup, our setup neither assumes that the tested state is composed of single particles nor requires that the total number of particles be fixed. Consequently, the notion of entanglement duality is shown to be compatible with a broader class of physical systems. Moreover, by observing duality in entanglement in the above system one can confirm that macroscopic systems exhibit quantum behavior. As a practical side, entanglement duality is a useful concept that enables adaptive conversion of entanglement of one degree of freedom (DOF) to that of another DOF according to varying quantum protocols.
NASA Astrophysics Data System (ADS)
Vallés, Adam; D'Ambrosio, Vincenzo; Hendrych, Martin; Mičuda, Michal; Marrucci, Lorenzo; Sciarrino, Fabio; Torres, Juan P.
2014-11-01
We demonstrate a scheme to generate noncoherent and coherent correlations, i.e., a tunable degree of entanglement, between degrees of freedom of a single photon. Its nature is analogous to the tuning of the purity (first-order coherence) of a single photon forming part of a two-photon state by tailoring the correlations between the paired photons. Therefore, well-known tools such as the Clauser-Horne-Shimony-Holt (CHSH) Bell-like inequality can also be used to characterize entanglement between degrees of freedom. More specifically, CHSH inequality tests are performed, making use of the polarization and the spatial shape of a single photon. The four modes required are two polarization modes and two spatial modes with different orbital angular momentum.
Entanglement witnesses for graph states: General theory and examples
Jungnitsch, Bastian; Moroder, Tobias; Guehne, Otfried
2011-09-15
We present a general theory for the construction of witnesses that detect genuine multipartite entanglement in graph states. First, we present explicit witnesses for all graph states of up to six qubits which are better than all criteria so far. Therefore, lower fidelities are required in experiments that aim at the preparation of graph states. Building on these results, we develop analytical methods to construct two different types of entanglement witnesses for general graph states. For many classes of states, these operators exhibit white noise tolerances that converge to 1 when increasing the number of particles. We illustrate our approach for states such as the linear and the 2D cluster state. Finally, we study an entanglement monotone motivated by our approach for graph states.
Splitting Unknown Qubit State Using Five-Qubit Entangled State
NASA Astrophysics Data System (ADS)
Li, Dong-fen; Wang, Rui-jin; Zhang, Feng-li; Qin, Zhi-guang; Baagyere, Edward
2016-04-01
In this paper, we demonstrate how a five-qubit entangled state can be used to realize the deterministic Quantum State Sharing (QSTS) of a single and two-qubit state among three parties by performing von-Neumann measurement and bell-state measurements. In our scheme, any of the two agents has the ability to reconstruct the original state if he/she collaborates with the other agent,otherwise an individual agent does not have enough information to reconstruct the original state. The paper also outlines the various measurements and mathematical framework of the scheme. The security analysis of our scheme against two attacks scenarios prove that the scheme is secure against an eavesdropper attack and a malicious attacks.
Entangled states close to the maximally mixed state
Hildebrand, Roland
2007-06-15
This paper deals with the radius of the largest ball of separable mixed states around the maximally mixed state for multiqubit systems. This radius determines how close entangled states can be to the maximally mixed state. In Aubrun and Szarek (e-print arXiv:quant-ph/0503221) an upper bound on the radius was given, while in Gurvits and Barnum (e-print arXiv:quant-ph/0409095) a lower bound was provided. In this paper we improve both the upper and the lower bound, bringing the ratio of these bounds down to a constant c={radical}(34/27){approx_equal}1.122, as opposed to a term of order {radical}(m log m) for the best bounds known previously, where m is the number of qubits in the system. We construct concrete examples of separable states on the boundary to entanglement which realize the upper bounds. As a by-product, we compute the radii of the largest balls that fit into the projective tensor product of three and four unit balls in R{sup 3} and in the projective tensor product of an arbitrary number of unit balls in R{sup n} for n=2, 4, and 8.
Multi-mode entangled states represented as Grassmannian polynomials
NASA Astrophysics Data System (ADS)
Maleki, Y.
2016-06-01
We introduce generalized Grassmannian representatives of multi-mode state vectors. By implementing the fundamental properties of Grassmann coherent states, we map the Hilbert space of the finite-dimensional multi-mode states to the space of some Grassmannian polynomial functions. These Grassmannian polynomials form a well-defined space in the framework of Grassmann variables; namely Grassmannian representative space. Therefore, a quantum state can be uniquely defined and determined by an element of Grassmannian representative space. Furthermore, the Grassmannian representatives of some maximally entangled states are considered, and it is shown that there is a tight connection between the entanglement of the states and their Grassmannian representatives.
Experiments on a compact and robust polarization-entangled photon source
NASA Astrophysics Data System (ADS)
Zhang, Shi-Wei; Zhang, Tong-Yi; Yao, Yin-Ping; Wan, Ren-Gang; Zou, Sheng-Wu
2012-02-01
We construct a compact polarization-entangled photon source using type-II degenerate spontaneous parametric down-conversion (SPDC) in beta-barium borate (BBO) crystal pumped by a 405 nm violet laser diode. In order to compensate the spatial displacement and the temporal delay due to the birefringence and dispersion effect of signal and idler photons, we make the down-converted photon pairs pass through a half wave plate and an additional BBO crystal with the half thickness of the original one. This improves the visibility of two-photon interference by eliminating the distinguishability of the paired photons. We measure the polarization correlations by two adjustable polarization analyzers in two conjugate bases, H/V and +45°/-45°, respectively. The polarization analyzer consists of a polarization beam splitter cube preceded by a rotatable half wave plate. When rotating one of the half wave plates and keeping the other one at fixed angle, we obtain the expected sin2 dependence of the coincidence counts. The highly visible sinusoidal coincidence indicates the violation of the Bell inequality and demonstrates the high quality of the polarization-entangled photon source. This compact polarization-entangled photon source is easily configurable and robust to demonstrate optical quantum information processing.
Experimental demonstration on the deterministic quantum key distribution based on entangled photons.
Chen, Hua; Zhou, Zhi-Yuan; Zangana, Alaa Jabbar Jumaah; Yin, Zhen-Qiang; Wu, Juan; Han, Yun-Guang; Wang, Shuang; Li, Hong-Wei; He, De-Yong; Tawfeeq, Shelan Khasro; Shi, Bao-Sen; Guo, Guang-Can; Chen, Wei; Han, Zheng-Fu
2016-01-01
As an important resource, entanglement light source has been used in developing quantum information technologies, such as quantum key distribution(QKD). There are few experiments implementing entanglement-based deterministic QKD protocols since the security of existing protocols may be compromised in lossy channels. In this work, we report on a loss-tolerant deterministic QKD experiment which follows a modified "Ping-Pong"(PP) protocol. The experiment results demonstrate for the first time that a secure deterministic QKD session can be fulfilled in a channel with an optical loss of 9 dB, based on a telecom-band entangled photon source. This exhibits a conceivable prospect of ultilizing entanglement light source in real-life fiber-based quantum communications. PMID:26860582
Experimental demonstration on the deterministic quantum key distribution based on entangled photons
NASA Astrophysics Data System (ADS)
Chen, Hua; Zhou, Zhi-Yuan; Zangana, Alaa Jabbar Jumaah; Yin, Zhen-Qiang; Wu, Juan; Han, Yun-Guang; Wang, Shuang; Li, Hong-Wei; He, De-Yong; Tawfeeq, Shelan Khasro; Shi, Bao-Sen; Guo, Guang-Can; Chen, Wei; Han, Zheng-Fu
2016-02-01
As an important resource, entanglement light source has been used in developing quantum information technologies, such as quantum key distribution(QKD). There are few experiments implementing entanglement-based deterministic QKD protocols since the security of existing protocols may be compromised in lossy channels. In this work, we report on a loss-tolerant deterministic QKD experiment which follows a modified “Ping-Pong”(PP) protocol. The experiment results demonstrate for the first time that a secure deterministic QKD session can be fulfilled in a channel with an optical loss of 9 dB, based on a telecom-band entangled photon source. This exhibits a conceivable prospect of ultilizing entanglement light source in real-life fiber-based quantum communications.
Experimental demonstration on the deterministic quantum key distribution based on entangled photons
Chen, Hua; Zhou, Zhi-Yuan; Zangana, Alaa Jabbar Jumaah; Yin, Zhen-Qiang; Wu, Juan; Han, Yun-Guang; Wang, Shuang; Li, Hong-Wei; He, De-Yong; Tawfeeq, Shelan Khasro; Shi, Bao-Sen; Guo, Guang-Can; Chen, Wei; Han, Zheng-Fu
2016-01-01
As an important resource, entanglement light source has been used in developing quantum information technologies, such as quantum key distribution(QKD). There are few experiments implementing entanglement-based deterministic QKD protocols since the security of existing protocols may be compromised in lossy channels. In this work, we report on a loss-tolerant deterministic QKD experiment which follows a modified “Ping-Pong”(PP) protocol. The experiment results demonstrate for the first time that a secure deterministic QKD session can be fulfilled in a channel with an optical loss of 9 dB, based on a telecom-band entangled photon source. This exhibits a conceivable prospect of ultilizing entanglement light source in real-life fiber-based quantum communications. PMID:26860582
Excitonic entanglement of protected states in quantum dot molecules
NASA Astrophysics Data System (ADS)
Borges, H. S.; Sanz, L.; Alcalde, A. M.
2016-09-01
The entanglement of an optically generated electron-hole pair in artificial quantum dot molecules is calculated considering the effects of decoherence by interaction with environment. Since the system evolves into mixed states and due to the complexity of energy level structure, we use the negativity as entanglement quantifier, which is well defined in D ⊗D‧ composite vector spaces. By a numerical analysis of the non-unitary dynamics of the exciton states, we establish the feasibility of producing protected entangled superposition by an appropriate tuning of bias electric field, F. A stationary state with a high value of negativity (high degree of entanglement) is obtained by fine tuning of F close to a resonant condition between indirect excitons. We also found that when the optical excitation is approximately equal to the electron tunneling coupling, Ω /Te ∼ 1, the entanglement reaches a maximum value. In front of the experimental feasibility of the specific condition mentioned before, our proposal becomes an useful strategy to find robust entangled states in condensed matter systems.
Hybrid entanglement concentration assisted with single coherent state
NASA Astrophysics Data System (ADS)
Rui, Guo; Lan, Zhou; Shi-Pu, Gu; Xing-Fu, Wang; Yu-Bo, Sheng
2016-03-01
Hybrid entangled state (HES) is a new type of entanglement, which combines the advantages of an entangled polarization state and an entangled coherent state. HES is widely discussed in the applications of quantum communication and computation. In this paper, we propose three entanglement concentration protocols (ECPs) for Bell-type HES, W-type HES, and cluster-type HES, respectively. After performing these ECPs, we can obtain the maximally entangled HES with some success probability. All the ECPs exploit the single coherent state to complete the concentration. These protocols are based on the linear optics, which are feasible in future experiments. Project supported by the National Natural Science Foundation of China (Grant Nos. 11474168 and 61401222), the Natural Science Foundation of Jiangsu Province, China (Grant No. BK20151502), the Qing Lan Project in Jiangsu Province, China, the Natural Science Foundation of Jiangsu Higher Education Institutions, China (Grant No. 15KJA120002), and the Priority Academic Development Program of Jiangsu Higher Education Institutions, China.
Modified E91 protocol demonstration with hybrid entanglement photon source.
Fujiwara, Mikio; Yoshino, Ken-ichiro; Nambu, Yoshihiro; Yamashita, Taro; Miki, Shigehito; Terai, Hirotaka; Wang, Zhen; Toyoshima, Morio; Tomita, Akihisa; Sasaki, Masahide
2014-06-01
We report on an experimental demonstration of the modified Ekert 91 protocol of quantum key distribution using a hybrid entanglement source with two different degrees of freedoms, a 1550 nm time-bin qubit and 810 nm polarization qubit. The violation of the Clauser-Horne-Shimony-Holt inequality could be demonstrated for the entanglement between the polarization qubit in free space and the time-bin qubit through 20 km fiber transmission. The secure key rate in our system is estimated 70-150 bps. PMID:24921555
Production of bright entangled photons from moving optical boundaries
Guerreiro, Ariel; Ferreira, Aires; Mendonca, J. T.
2011-05-15
We discuss a mechanism of generating two separable beams of light with a high degree of entanglement in momentum using a fast and sharp optical boundary. Three regimes of light generation are identified depending on the number of resonant interactions between the optical perturbation and the electromagnetic field. The intensity of the process is discussed in terms of the relevant physical parameters: variation of refractive index and apparent velocity of the optical boundary. Our results suggest a different class of generation entangled light that is robust against thermal degradation by exciting zero point fluctuations using parametric resonant optical modulations.
Ground-state entanglement in the XXZ model
Gu Shijian; Lin Haiqing; Tian Guangshan
2005-05-15
In this paper, we investigate spin entanglement in the XXZ model defined on a d-dimensional bipartite lattice. The concurrence, a measure of the entanglement between two spins, is analyzed. We prove rigorously that the ground-state concurrence reaches maximum at the isotropic point. For dimensionality d{>=}2, the concurrence develops a cusp at the isotropic point and we attribute it to the existence of magnetic long-range order.
Entanglement of photons with complex spatial structure in Hermite-Laguerre-Gaussian modes
NASA Astrophysics Data System (ADS)
Tang, Jie; Ming, Yang; Chen, Zhao-xian; Hu, Wei; Xu, Fei; Lu, Yan-qing
2016-07-01
Photons with complicated spatial mode structures can be applied for different quantum information tasks. Here, we show the entanglement of photons with complex singularity patterns called Hermite-Laguerre-Gaussian (HLG) modes. Measuring one photon of the entangled pairs by HLG mode basis to define its singularity pattern, we can steer the singularity structure of its partner, while the initial singularity structure of the photons is undefined. We also calculate the HLG specific quantum-correlation function. It can be used to extend the quantum key distribution protocols and to tune experiments dealing with high-order transverse modes. In addition we discuss orbital angular momentum properties of the HLG modes and summarize some features of the singularity pattern of the HLG modes with varying angle parameter.
Phase Sensitivity and Entanglement of Mach-Zehnder Interferometer
NASA Astrophysics Data System (ADS)
Hu, Xiu-Xia
2016-06-01
We investigate the dependence of phase sensitivity and entanglement of two streams of photons that they incident upon Mach-Zehnder interferometer on the initial input states and the phase difference. Phase sensitivity and entanglement are periodic function of the phase difference. The initial input state with the more photons or smaller population difference induces the better phase sensitivity and entanglement.
Concurrence-based entanglement measures for isotropic states
Rungta, Pranaw; Caves, Carlton M.
2003-01-01
We discuss properties of entanglement measures called I-concurrence and tangle. For a bipartite pure state, I-concurrence and tangle are simply related to the purity of the marginal density operators. The I-concurrence (tangle) of a bipartite mixed state is the minimum average I-concurrence (tangle) of ensemble decompositions of pure states of the joint density operator. Terhal and Vollbrecht [Phys. Rev. Lett. 85, 2625 (2000)] have given an explicit formula for the entanglement of formation of isotropic states in arbitrary dimensions. We use their formalism to derive comparable expressions for the I-concurrence and tangle of isotropic states.
Multiboson Correlation Interferometry with Arbitrary Single-Photon Pure States.
Tamma, Vincenzo; Laibacher, Simon
2015-06-19
We provide a compact full description of multiboson correlation measurements of arbitrary order N in passive linear interferometers with arbitrary input single-photon pure states. This allows us to physically analyze the novel problem of multiboson correlation sampling at the output of random linear interferometers. Our results also describe general multiboson correlation landscapes for an arbitrary number of input single photons and arbitrary interferometers. In particular, we use two different schemes to demonstrate, respectively, arbitrary-order quantum beat interference and 100% visibility entanglement correlations even for input photons distinguishable in their frequencies. PMID:26196976
Characterizing entanglement of an artificial atom and a cavity cat state with Bell's inequality.
Vlastakis, Brian; Petrenko, Andrei; Ofek, Nissim; Sun, Luyan; Leghtas, Zaki; Sliwa, Katrina; Liu, Yehan; Hatridge, Michael; Blumoff, Jacob; Frunzio, Luigi; Mirrahimi, Mazyar; Jiang, Liang; Devoret, M H; Schoelkopf, R J
2015-01-01
The Schrodinger's cat thought experiment highlights the counterintuitive concept of entanglement in macroscopically distinguishable systems. The hallmark of entanglement is the detection of strong correlations between systems, most starkly demonstrated by the violation of a Bell inequality. No violation of a Bell inequality has been observed for a system entangled with a superposition of coherent states, known as a cat state. Here we use the Clauser-Horne-Shimony-Holt formulation of a Bell test to characterize entanglement between an artificial atom and a cat state, or a Bell-cat. Using superconducting circuits with high-fidelity measurements and real-time feedback, we detect correlations that surpass the classical maximum of the Bell inequality. We investigate the influence of decoherence with states up to 16 photons in size and characterize the system by introducing joint Wigner tomography. Such techniques demonstrate that information stored in superpositions of coherent states can be extracted efficiently, a crucial requirement for quantum computing with resonators. PMID:26611724
NASA Astrophysics Data System (ADS)
Jiang, Zhang; Lang, Mattihas; Caves, Carlton; CenterQuantum Information and Control Collaboration
2014-03-01
In quantum optics a pure state is considered classical, relative to the statistics of photodetection, if and only if it is a coherent state. A different and newer notion of nonclassicality is based on modal entanglement. One example that relates these two notions is the Hong-Ou-Mandel effect, where modal entanglement is generated by a beamsplitter from the nonclassical photon-number state | 1 > ⊗ | 1 > . This suggests the beamsplitter or, more generally, linear-optical networks as a mediator of the two notions of nonclassicality. We show the following: Given a nonclassical pure product state input to an N-port linear-optical network, the output is almost always mode entangled; the only exception is a product of squeezed states, all with the same squeezing strength, input to a network that does not mix the squeezed and anti-squeezed quadratures. Our work thus gives a necessary and sufficient condition for a linear network to generate modal entanglement from pure product inputs, a result that is of immediate relevance to the boson sampling problem.
NASA Astrophysics Data System (ADS)
Jiang, Zhang; Lang, Matthias D.; Caves, Carlton M.
2013-10-01
In quantum optics a pure state is considered classical, relative to the statistics of photodetection, if and only if it is a coherent state. A different and newer notion of nonclassicality is based on modal entanglement. One example that relates these two notions is the Hong-Ou-Mandel effect, where modal entanglement is generated by a beamsplitter from the nonclassical photon-number state |1>⊗|1>. This suggests that beamsplitters or, more generally, linear-optical networks are mediators of the two notions of nonclassicality. In this Brief Report, we show the following: Given a nonclassical pure-product-state input to an N-port linear-optical network, the output is almost always mode entangled; the only exception is a product of squeezed states, all with the same squeezing strength, input to a network that does not mix the squeezed and antisqueezed quadratures. Our work thus gives a necessary and sufficient condition for a linear network to generate modal entanglement from pure-product inputs, a result that is of immediate relevance to the boson-sampling problem.
Characterizing entanglement of an artificial atom and a cavity cat state with Bell's inequality
Vlastakis, Brian; Petrenko, Andrei; Ofek, Nissim; Sun, Luyan; Leghtas, Zaki; Sliwa, Katrina; Liu, Yehan; Hatridge, Michael; Blumoff, Jacob; Frunzio, Luigi; Mirrahimi, Mazyar; Jiang, Liang; Devoret, M. H.; Schoelkopf, R. J.
2015-01-01
The Schrodinger's cat thought experiment highlights the counterintuitive concept of entanglement in macroscopically distinguishable systems. The hallmark of entanglement is the detection of strong correlations between systems, most starkly demonstrated by the violation of a Bell inequality. No violation of a Bell inequality has been observed for a system entangled with a superposition of coherent states, known as a cat state. Here we use the Clauser–Horne–Shimony–Holt formulation of a Bell test to characterize entanglement between an artificial atom and a cat state, or a Bell-cat. Using superconducting circuits with high-fidelity measurements and real-time feedback, we detect correlations that surpass the classical maximum of the Bell inequality. We investigate the influence of decoherence with states up to 16 photons in size and characterize the system by introducing joint Wigner tomography. Such techniques demonstrate that information stored in superpositions of coherent states can be extracted efficiently, a crucial requirement for quantum computing with resonators. PMID:26611724
Entangled Coherent States Generation in two Superconducting LC Circuits
Chen Meiyu; Zhang Weimin
2008-11-07
We proposed a novel pure electronic (solid state) device consisting of two superconducting LC circuits coupled to a superconducting flux qubit. The entangled coherent states of the two LC modes is generated through the measurement of the flux qubit states. The interaction of the flux qubit and two LC circuits is controlled by the external microwave control lines. The geometrical structure of the LC circuits is adjustable and makes a strong coupling between them achievable. This entangled coherent state generator can be realized by using the conventional microelectronic fabrication techniques which increases the feasibility of the experiment.
Quantum teleportation of composite systems via mixed entangled states
Bandyopadhyay, Somshubhro; Sanders, Barry C.
2006-09-15
We analyze quantum teleportation for composite systems, specifically for concatenated teleporation (decomposing a large composite state into smaller states of dimension commensurate with the channel) and partial teleportation (teleporting one component of a larger quantum state). We obtain an exact expression for teleportation fidelity that depends solely on the dimension and singlet fraction for the entanglement channel and entanglement (measures by I concurrence) for the state; in fact quantum teleportation for composite systems provides an operational interpretation for I concurrence. In addition we obtain tight bounds on teleportation fidelity and prove that the average fidelity approaches the lower bound of teleportation fidelity in the high-dimension limit.
Entanglement equivalence of N-qubit symmetric states
Mathonet, P.; Krins, S.; Bastin, T.; Godefroid, M.; Solano, E.
2010-05-15
We study the interconversion of multipartite symmetric N-qubit states under stochastic local operations and classical communication (SLOCC). We demonstrate that if two symmetric states can be connected with a nonsymmetric invertible local operation (ILO), then they belong necessarily to the separable, W, or Greenberger-Horne-Zeilinger (GHZ) entanglement class, establishing a practical method of discriminating subsets of entanglement classes. Furthermore, we prove that there always exists a symmetric ILO connecting any pair of symmetric N-qubit states equivalent under SLOCC, simplifying the requirements for experimental implementations of local interconversion of those states.
Entanglement and Majorana edge states in the Kitaev model
NASA Astrophysics Data System (ADS)
Mandal, Saptarshi; Maiti, Moitri; Varma, Vipin Kerala
2016-07-01
We investigate the von Neumann entanglement entropy and Schmidt gap in the vortex-free ground state of the Kitaev model on the honeycomb lattice for square/rectangular and cylindrical subsystems. We find that, for both the subsystems, the free-fermionic contribution to the entanglement entropy SE exhibits signatures of the phase transitions between the gapless and gapped phases. However, within the gapless phase, we find that SE does not show an expected monotonic behavior as a function of the coupling Jz between the suitably defined one-dimensional chains for either geometry; moreover, the system generically reaches a point of minimum entanglement within the gapless phase before the entanglement saturates or increases again until the gapped phase is reached. This may be attributed to the onset of gapless modes in the bulk spectrum and the competition between the correlation functions along various bonds. In the gapped phase, on the other hand, SE always monotonically varies with Jz independent of the subregion size or shape. Finally, further confirming the Li-Haldane conjecture, we find that the Schmidt gap Δ defined from the entanglement spectrum also signals the topological transitions but only if there are corresponding zero-energy Majorana edge states that simultaneously appear or disappear across the transitions. We analytically corroborate some of our results on entanglement entropy, the Schmidt gap, and the bulk-edge correspondence using perturbation theory.
Complete Distributed Hyper-Entangled-Bell-State Analysis and Quantum Super Dense Coding
NASA Astrophysics Data System (ADS)
Zheng, Chunhong; Gu, Yongjian; Li, Wendong; Wang, Zhaoming; Zhang, Jiying
2016-02-01
We propose a protocol to implement the distributed hyper-entangled-Bell-state analysis (HBSA) for photonic qubits with weak cross-Kerr nonlinearities, QND photon-number-resolving detection, and some linear optical elements. The distinct feature of our scheme is that the BSA for two different degrees of freedom can be implemented deterministically and nondestructively. Based on the present HBSA, we achieve quantum super dense coding with double information capacity, which makes our scheme more significant for long-distance quantum communication.
Controlled Teleportation of a Qudit State by Partially Entangled GHZ States
NASA Astrophysics Data System (ADS)
Wang, Jin-wei; Shu, Lan; Mo, Zhi-wen; Zhang, Zhi-hua
2014-08-01
In this paper, we propose a controlled teleportation scheme which communicates an arbitrary ququart state via two sets of partially entangled GHZ state. The necessary measurements and operations are given detailedly. Furthmore the scheme is generalized to teleport a qudit state via s sets of partially entangled GHZ state.
Entanglement universality of two-qubit X-states
Mendonça, Paulo E.M.F.; Marchiolli, Marcelo A.; Galetti, Diógenes
2014-12-15
We demonstrate that for every two-qubit state there is a X-counterpart, i.e., a corresponding two-qubit X-state of same spectrum and entanglement, as measured by concurrence, negativity or relative entropy of entanglement. By parametrizing the set of two-qubit X-states and a family of unitary transformations that preserve the sparse structure of a two-qubit X-state density matrix, we obtain the parametric form of a unitary transformation that converts arbitrary two-qubit states into their X-counterparts. Moreover, we provide a semi-analytic prescription on how to set the parameters of this unitary transformation in order to preserve concurrence or negativity. We also explicitly construct a set of X-state density matrices, parametrized by their purity and concurrence, whose elements are in one-to-one correspondence with the points of the concurrence versus purity (CP) diagram for generic two-qubit states. - Highlights: • Parametrization of separable, entangled and rank-specific two-qubit X-states. • Construction of a set of two-qubit X-states exhausting a two-qubit CP-diagram. • Parametrization of a disentangling unitary transformation for any two-qubit X-state. • Unitary transformation of any two-qubit state into a X-state of same entanglement.
Quantum entangled supercorrelated states in the Jaynes-Cummings model
NASA Astrophysics Data System (ADS)
Rajagopal, A. K.; Jensen, K. L.; Cummings, F. W.
1999-08-01
The regions of independent quantum states, maximally classically correlated states, and purely quantum entangled (supercorrelated) states described in a recent formulation of quantum information theory by Cerf and Adami are explored here numerically in the parameter space of the well-known exactly soluble Jaynes-Cummings model for equilibrium and nonequilibrium time-dependent ensembles.
Ran, Du; Hu, Chang-Sheng; Yang, Zhen-Biao
2016-01-01
We study the entanglement transfer from a two-mode continuous variable system (initially in the two-mode SU(2) cat states) to a couple of discrete two-state systems (initially in an arbitrary mixed state), by use of the resonant Jaynes-Cummings (JC) interaction. We first quantitatively connect the entanglement transfer to non-Gaussianity of the two-mode SU(2) cat states and find a positive correlation between them. We then investigate the behaviors of the entanglement transfer and find that it is dependent on the initial state of the discrete systems. We also find that the largest possible value of the transferred entanglement exhibits a variety of behaviors for different photon number as well as for the phase angle of the two-mode SU(2) cat states. We finally consider the influences of the noise on the transferred entanglement. PMID:27553881
Ran, Du; Hu, Chang-Sheng; Yang, Zhen-Biao
2016-01-01
We study the entanglement transfer from a two-mode continuous variable system (initially in the two-mode SU(2) cat states) to a couple of discrete two-state systems (initially in an arbitrary mixed state), by use of the resonant Jaynes-Cummings (JC) interaction. We first quantitatively connect the entanglement transfer to non-Gaussianity of the two-mode SU(2) cat states and find a positive correlation between them. We then investigate the behaviors of the entanglement transfer and find that it is dependent on the initial state of the discrete systems. We also find that the largest possible value of the transferred entanglement exhibits a variety of behaviors for different photon number as well as for the phase angle of the two-mode SU(2) cat states. We finally consider the influences of the noise on the transferred entanglement. PMID:27553881
Identifying non-Abelian topological order through minimal entangled states.
Zhu, W; Gong, S S; Haldane, F D M; Sheng, D N
2014-03-01
The topological order is encoded in the pattern of long-range quantum entanglements, which cannot be measured by any local observable. Here we perform an exact diagonalization study to establish the non-Abelian topological order for topological band models through entanglement entropy measurement. We focus on the quasiparticle statistics of the non-Abelian Moore-Read and Read-Rezayi states on the lattice models with bosonic particles. We identify multiple independent minimal entangled states (MESs) in the ground state manifold on a torus. The extracted modular S matrix from MESs faithfully demonstrates the Ising anyon or Fibonacci quasiparticle statistics, including the quasiparticle quantum dimensions and the fusion rules for such systems. These findings unambiguously demonstrate the topological nature of the quantum states for these flatband models without using the knowledge of model wave functions. PMID:24655269
Geometric descriptions of entangled states by auxiliary varieties
Holweck, Frederic; Luque, Jean-Gabriel; Thibon, Jean-Yves
2012-10-15
The aim of the paper is to propose geometric descriptions of multipartite entangled states using algebraic geometry. In the context of this paper, geometric means each stratum of the Hilbert space, corresponding to an entangled state, is an open subset of an algebraic variety built by classical geometric constructions (tangent lines, secant lines) from the set of separable states. In this setting, we describe well-known classifications of multipartite entanglement such as 2 Multiplication-Sign 2 Multiplication-Sign (n+ 1), for n Greater-Than-Or-Slanted-Equal-To 1, quantum systems and a new description with the 2 Multiplication-Sign 3 Multiplication-Sign 3 quantum system. Our results complete the approach of Miyake and make stronger connections with recent work of algebraic geometers. Moreover, for the quantum systems detailed in this paper, we propose an algorithm, based on the classical theory of invariants, to decide to which subvariety of the Hilbert space a given state belongs.
Experimental generation of a high-fidelity four-photon linear cluster state
NASA Astrophysics Data System (ADS)
Zhang, Chao; Huang, Yun-Feng; Liu, Bi-Heng; Li, Chuan-Feng; Guo, Guang-Can
2016-06-01
Cluster state plays a crucial role in one-way quantum computation. Here, we propose and experimentally demonstrate a scheme to prepare an ultrahigh-fidelity four-photon linear cluster state via a spontaneous parametric down-conversion process. The state fidelity is measured to be 0.9517 ±0.0027 . Our scheme can be directly extended to more photons to generate an N -qubit linear cluster state. Furthermore, our scheme is optimal for generating photonic linear cluster states in the sense of achieving the maximal success probability and having the simplest strategy. The key idea is that the photon pairs are prepared in some special nonmaximally entangled states instead of the normal Bell states. To generate a 2 N -qubit linear cluster state from N pairs of entangled photons, only (N -1 ) Hong-Ou-Mandel interferences are needed and a success probability of (1/4) N -1 is achieved.
Gong, Yan-Xiao; Zhang, ShengLi; Xu, P; Zhu, S N
2016-03-21
We propose to generate a single-mode-squeezing two-mode squeezed vacuum state via a single χ^{(2)} nonlinear photonic crystal. The state is favorable for existing Gaussian entanglement distillation schemes, since local squeezing operations can enhance the final entanglement and the success probability. The crystal is designed for enabling three concurrent quasi-phase-matching parametric-down conversions, and hence relieves the auxiliary on-line bi-side local squeezing operations. The compact source opens up a way for continuous-variable quantum technologies and could find more potential applications in future large-scale quantum networks. PMID:27136831
Teleportation of atomic and photonic states in low-Q cavity QED
NASA Astrophysics Data System (ADS)
Peng, Zhao-Hui; Zou, Jian; Liu, Xiao-Juan; Kuang, Le-Man
2012-11-01
We propose two alternative teleportation protocols in low-Q cavity QED. Through the input-output process of photons, we can generate atom-photon entangled states as the quantum channel. Then we propose to teleport single-atom (two-atom entangled) state using coherent photonic states, and to teleport single photonic state with the assistance of three-level atom. The distinct feature of our protocols is that we can teleport both atomic and photonic states via the input-output process of photons in the low-Q cavity. Furthermore, as our protocols work in low-Q cavities and only involve virtual excitation of atoms, they are insensitive to both cavity decay and atomic spontaneous emission, and may be feasible with current technology.
Low-energy-state dynamics of entanglement for spin systems
Jafari, R.
2010-11-15
We develop the ideas of the quantum renormalization group and quantum information by exploring the low-energy-state dynamics of entanglement resources of a system close to its quantum critical point. We demonstrate that low-energy-state dynamical quantities of one-dimensional magnetic systems can show a quantum phase transition point and show scaling behavior in the vicinity of the transition point. To present our idea, we study the evolution of two spin entanglements in the one-dimensional Ising model in the transverse field. The system is initialized as the so-called thermal ground state of the pure Ising model. We investigate the evolution of the generation of entanglement with increasing magnetic field. We obtain that the derivative of the time at which the entanglement reaches its maximum with respect to the transverse field diverges at the critical point and its scaling behaviors versus the size of the system are the same as the static ground-state entanglement of the system.
Bipartite quantum channels using multipartite cluster-type entangled coherent states
Munhoz, P. P.; Semiao, F. L.; Roversi, J. A.; Vidiella-Barranco, A.
2010-04-15
We propose a particular encoding for bipartite entangled states derived from multipartite cluster-type entangled coherent states (CTECSs). We investigate the effects of amplitude damping on the entanglement content of this bipartite state, as well as its usefulness as a quantum channel for teleportation. We find interesting relationships among the amplitude of the coherent states constituting the CTECSs, the number of subsystems forming the logical qubits (redundancy), and the extent to which amplitude damping affects the entanglement of the channel. For instance, in the sense of sudden death of entanglement, given a fixed value of the initial coherent state amplitude, the entanglement life span is shortened if redundancy is increased.
Jeong, Hyunseok; Ralph, Timothy C.
2007-10-15
We study characteristics of superpositions and entanglement of thermal states at high temperatures and discuss their applications to quantum-information processing. We introduce thermal-state qubits and thermal-Bell states, which are a generalization of pure-state qubits and Bell states to thermal mixtures. A scheme is then presented to discriminate between the four thermal-Bell states without photon number resolving detection but with Kerr nonlinear interactions and two single-photon detectors. This enables one to perform quantum teleportation and gate operations for quantum computation with thermal-state qubits.
Quantum entanglement of localized excited states at finite temperature
NASA Astrophysics Data System (ADS)
Caputa, Pawel; Simón, Joan; Štikonas, Andrius; Takayanagi, Tadashi
2015-01-01
In this work we study the time evolutions of (Renyi) entanglement entropy of locally excited states in two dimensional conformal field theories (CFTs) at finite temperature. We consider excited states created by acting with local operators on thermal states and give both field theoretic and holographic calculations. In free field CFTs, we find that the growth of Renyi entanglement entropy at finite temperature is reduced compared to the zero temperature result by a small quantity proportional to the width of the localized excitations. On the other hand, in finite temperature CFTs with classical gravity duals, we find that the entanglement entropy approaches a characteristic value at late time. This behaviour does not occur at zero temperature. We also study the mutual information between the two CFTs in the thermofield double (TFD) formulation and give physical interpretations of our results.
Bell states and entanglement dynamics on two coupled quantum molecules
Oliveira, P.A.; Sanz, L.
2015-05-15
This work provides a complete description of entanglement properties between electrons inside coupled quantum molecules, nanoestructures which consist of two quantum dots. Each electron can tunnel between the two quantum dots inside the molecule, being also coupled by Coulomb interaction. First, it is shown that Bell states act as a natural basis for the description of this physical system, defining the characteristics of the energy spectrum and the eigenstates. Then, the entanglement properties of the eigenstates are discussed, shedding light on the roles of each physical parameters on experimental setup. Finally, a detailed analysis of the dynamics shows the path to generate states with a high degree of entanglement, as well as physical conditions associated with coherent oscillations between separable and Bell states.
Quantum state and quantum entanglement protection using quantum measurements
NASA Astrophysics Data System (ADS)
Wang, Shuchao; Li, Ying; Wang, Xiangbin; Kwek, Leong Chuan; Yu, Zongwen; Zou, Wenjie
2015-03-01
The time evolution of some quantum states can be slowed down or even stopped under frequent measurements. This is the usual quantum Zeno effect. Here we report an operator quantum Zeno effect, in which the evolution of some physical observables is slowed down through measurements even though thequantum state changes randomly with time. Based on the operator quantum Zeno effect, we show how we can protect quantum information from decoherence with two-qubit measurements, realizable with noisy two-qubit interactions. Besides, we report the quantum entanglement protection using weak measurement and measurement reversal scheme. Exposed in the nonzero temperature environment, a quantum system can both lose and gain excitations by interacting with the environment. In this work, we show how to optimally protect quantum states and quantum entanglement in such a situation based on measurement reversal from weak measurement. In particular, we present explicit formulas of protection. We find that this scheme can circumvent the entanglement sudden death in certain conditions.
Detecting highly entangled states with a joint qubit readout
Chow, J. M.; DiCarlo, L.; Nunnenkamp, A.; Bishop, Lev S.; Frunzio, L.; Devoret, M. H.; Girvin, S. M.; Schoelkopf, R. J.; Gambetta, J. M.
2010-06-15
A single-channel joint readout is used to analyze highly entangled two-qubit states in a circuit quantum electrodynamics architecture. The measurement model for the readout is fully characterized, demonstrating a large sensitivity to two-qubit correlations. We quantify the high degree of entanglement by measuring a violation of the Clauser-Horne-Shimony-Holt inequality with a value of 2.61{+-}0.04, without optimizing the preparation of the two-qubit state. In its present form, this joint readout can resolve improvements to the fidelity of two-qubit operations and be extended to three or four qubits.
Entangling power of permutation-invariant quantum states
Popkov, Vladislav; Salerno, Mario; Schuetz, Gunter
2005-09-15
We investigate the von Neumann entanglement entropy as function of the size of a subsystem for permutation invariant ground states in models with finite number of states per site, e.g., in quantum spin models. We demonstrate that the entanglement entropy of n sites in a system of length L generically grows as {sigma} log{sub 2}[2{pi}en(L-n)/L]+C, where {sigma} is the on-site spin and C is a function depending only on magnetization.
Minimum Copies of Schrödinger’s Cat State in the Multi-Photon System
Lu, Yiping; Zhao, Qing
2016-01-01
Multi-photon entanglement has been successfully studied by many theoretical and experimental groups. However, as the number of entangled photons increases, some problems are encountered, such as the exponential increase of time necessary to prepare the same number of copies of entangled states in experiment. In this paper, a new scheme is proposed based on the Lagrange multiplier and Feedback, which cuts down the required number of copies of Schrödinger’s Cat state in multi-photon experiment, which is realized with some noise in actual measurements, and still keeps the standard deviation in the error of fidelity unchanged. It reduces about five percent of the measuring time of eight-photon Schrödinger’s Cat state compared with the scheme used in the usual planning of actual measurements, and moreover it guarantees the same low error in fidelity. In addition, we also applied the same approach to the simulation of ten-photon entanglement, and we found that it reduces in priciple about twenty two percent of the required copies of Schrödinger’s Cat state compared with the conventionally used scheme of the uniform distribution; yet the distribution of optimized copies of the ten-photon Schrödinger’s Cat state gives better fidelity estimation than the uniform distribution for the same number of copies of the ten-photon Schrödinger’s Cat state. PMID:27576585
Minimum Copies of Schrödinger's Cat State in the Multi-Photon System.
Lu, Yiping; Zhao, Qing
2016-01-01
Multi-photon entanglement has been successfully studied by many theoretical and experimental groups. However, as the number of entangled photons increases, some problems are encountered, such as the exponential increase of time necessary to prepare the same number of copies of entangled states in experiment. In this paper, a new scheme is proposed based on the Lagrange multiplier and Feedback, which cuts down the required number of copies of Schrödinger's Cat state in multi-photon experiment, which is realized with some noise in actual measurements, and still keeps the standard deviation in the error of fidelity unchanged. It reduces about five percent of the measuring time of eight-photon Schrödinger's Cat state compared with the scheme used in the usual planning of actual measurements, and moreover it guarantees the same low error in fidelity. In addition, we also applied the same approach to the simulation of ten-photon entanglement, and we found that it reduces in priciple about twenty two percent of the required copies of Schrödinger's Cat state compared with the conventionally used scheme of the uniform distribution; yet the distribution of optimized copies of the ten-photon Schrödinger's Cat state gives better fidelity estimation than the uniform distribution for the same number of copies of the ten-photon Schrödinger's Cat state. PMID:27576585
Entropy and Entanglement Bounds for Reduced Density Matrices of Fermionic States
NASA Astrophysics Data System (ADS)
Carlen, Eric A.; Lieb, Elliott H.; Reuvers, Robin
2016-06-01
Unlike bosons, fermions always have a non-trivial entanglement. Intuitively, Slater determinantal states should be the least entangled states. To make this intuition precise we investigate entropy and entanglement of fermionic states and prove some extremal and near extremal properties of reduced density matrices of Slater determinantal states.
Entanglements in polymer networks: two-state invariant
NASA Astrophysics Data System (ADS)
Müller-Nedebock, Kristian
2001-03-01
At the time of crosslinking of polymer chains, entanglements of these chains become permanent features of the resulting network. In a statistical physics formulation these constraints on the polymers can be dealt with by inclusion of invariants for the entangled states of chains. Analytical results are presented based upon an extension of a variational formalism for mechanical properties of entangled gels with a two-state invariant by Edwards and Müller-Nedebock (J. Phys. A: Math. Gen.32 3301 (1999)). Apart from showing Mooney-Rivlin-like behaviour of the reduced stress the theory is applied to olympic gels and discussed in the context of the limitations due to the approximations in this approach.
Bulk Entanglement Spectrum Reveals Quantum Criticality within a Topological State
NASA Astrophysics Data System (ADS)
Hsieh, Timothy; Fu, Liang
2014-03-01
A quantum phase transition is usually achieved by tuning physical parameters in a Hamiltonian at zero temperature. Here, we demonstrate that the ground state of a topological phase itself encodes critical properties of its transition to a trivial phase. To extract this information, we introduce a partition of the system into two subsystems both of which extend throughout the bulk in all directions. The resulting bulk entanglement spectrum has a low-lying part that resembles the excitation spectrum of a bulk Hamiltonian, which allows us to access a topological phase transition from a single wavefunction by tuning either the geometry of the partition or the entanglement temperature. As an example, this remarkable correspondence between topological phase transition and entanglement criticality is rigorously established for integer quantum Hall states. TH is supported by NSF Graduate Research Fellowship No. 0645960. LF is partly supported by the DOE Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under award DE-SC0010526.
Centini, M.; Sciscione, L.; Sibilia, C.; Bertolotti, M.; Perina, J. Jr.; Scalora, M.; Bloemer, M.J.
2005-09-15
A description of spontaneous parametric down-conversion in finite-length one-dimensional nonlinear photonic crystals is developed using semiclassical and quantum approaches. It is shown that if a suitable averaging is added to the semiclassical model, its results are in very good agreement with the quantum approach. We propose two structures made with GaN/AlN that generate both degenerate and nondegenerate entangled photon pairs. Both structures are designed so as to achieve a high efficiency of the nonlinear process.
Teleportation via thermally entangled states of a two-qubit Heisenberg XX chain
Yeo Ye
2002-12-01
Recently, entanglement teleportation has been investigated by Lee and Kim [Phys. Rev. Lett. 84, 4236 (2000)]. In this paper we study entanglement teleportation via two separate thermally entangled states of a two-qubit Heisenberg XX chain. We established the condition under which the parameters of the model have to satisfy in order to teleport entanglement. The necessary minimum amount of thermal entanglement for some fixed strength of exchange coupling is a function of the magnetic field and the temperature.
NASA Astrophysics Data System (ADS)
Snyder, Douglas
For a pair of entangled signal-idler photons, one may ``lose'' the idler photon (that provides which-way information to the entangled signal photon) in many other photons with similar characteristics to the idler photon before the signal photon is detected, thereby losing the which-way information supplied to the signal photon and eliminating the entanglement. The experiment allows for a delayed choice on the idler photons (whether or not to lose the idler photon before the signal photon is detected) to determine the distribution of distant signal photons (either overall which-way or overall interference) without making correlations between signal and idler photon detections. When the idler photon is lost, it is lost in an optical microcavity filled with photons in the same mode as the idler photon. The experiment could provide the basis for a useful quantum communications device. It might be possible to use a micropost coated with a material such as Vantablack in place of the optical microcavity.
Topological states in photonic systems
NASA Astrophysics Data System (ADS)
Lu, Ling; Joannopoulos, John D.; Soljačić, Marin
2016-07-01
Optics played a key role in the discovery of geometric phase. It now joins the journey of exploring topological physics, bringing bosonic topological states that equip us with the ability to make perfect photonic devices using imperfect interfaces.
Remote State Preparation of a Two-Atom Entangled State in Cavity QED
NASA Astrophysics Data System (ADS)
Xiao, Xiao-Qi; Xiao, Junfang; Ren, Yuan; Li, Yuan; Ji, Chunlei; Huang, Xin-Gang
2016-06-01
A physical scheme for remotely preparing a diatomic entangled state based on the cavity QED technique is presented in this paper. The quantum channel is composed of a two-atom entangled state and a three-atom entangled W state. The non-resonant interaction between two atoms and cavity is utilized at sender's side to distribute the information among the quantum channel, and the original state can be transmitted to either one of the two receivers. It shows that an extra cavity and an atom are needed at the final receiver's side as an auxiliary system if the non-maximally entangled states are worked as the quantum channel. The total success probabilities for the two receivers are not equal to each other except that the states of the quantum channel are maximally entangled.
Steady-state entanglement of spatially separated qubits via quantum bath engineering
NASA Astrophysics Data System (ADS)
Aron, Camille; Kulkarni, Manas; Tureci, Hakan
2015-03-01
We propose a scheme for driving a dimer of spatially separated qubits into a maximally entangled non-equilibrium steady state. A photon-mediated retarded interaction between the qubits is realized by coupling them to two tunnel-coupled leaky cavities where each cavity is driven by a coherent microwave tone. The proposed cooling mechanism relies on striking the right balance between the unitary and driven-dissipative dynamics of the qubit subsystem. We map the dimer to an effective transverse-field XY model coupled to a non-equilibrium bath that can be suitably engineered through the choice of drive frequencies and amplitudes. We show that both singlet and triplet states can be obtained with remarkable fidelities. The proposed protocol can be implemented with a superconducting circuit architecture that was recently experimentally realized and paves the way to achieving large-scale entangled systems that are arbitrarily long lived.
Steady-state entanglement of spatially separated qubits via quantum bath engineering
NASA Astrophysics Data System (ADS)
Aron, Camille; Kulkarni, Manas; Türeci, Hakan E.
2014-12-01
We propose a scheme for driving a dimer of spatially separated qubits into a maximally entangled nonequilibrium steady state. A photon-mediated retarded interaction between the qubits is realized by coupling them to two tunnel-coupled leaky cavities where each cavity is driven by a coherent microwave tone. The proposed cooling mechanism relies on striking the right balance between the unitary and driven-dissipative dynamics of the qubit subsystem. We map the dimer to an effective transverse-field isotropic X Y model coupled to a nonequilibrium bath that can be suitably engineered through the choice of drive frequencies and amplitudes. We show that both singlet and triplet states can be obtained with remarkable fidelities. The proposed protocol can be implemented with a superconducting circuit architecture that was recently experimentally realized and paves the way to achieving large-scale entangled systems that are arbitrarily long lived.
Generation of multiphoton entangled quantum states by means of integrated frequency combs.
Reimer, Christian; Kues, Michael; Roztocki, Piotr; Wetzel, Benjamin; Grazioso, Fabio; Little, Brent E; Chu, Sai T; Johnston, Tudor; Bromberg, Yaron; Caspani, Lucia; Moss, David J; Morandotti, Roberto
2016-03-11
Complex optical photon states with entanglement shared among several modes are critical to improving our fundamental understanding of quantum mechanics and have applications for quantum information processing, imaging, and microscopy. We demonstrate that optical integrated Kerr frequency combs can be used to generate several bi- and multiphoton entangled qubits, with direct applications for quantum communication and computation. Our method is compatible with contemporary fiber and quantum memory infrastructures and with chip-scale semiconductor technology, enabling compact, low-cost, and scalable implementations. The exploitation of integrated Kerr frequency combs, with their ability to generate multiple, customizable, and complex quantum states, can provide a scalable, practical, and compact platform for quantum technologies. PMID:26965623
Entanglement of remote atomic qubits.
Matsukevich, D N; Chanelière, T; Jenkins, S D; Lan, S-Y; Kennedy, T A B; Kuzmich, A
2006-01-27
We report observations of entanglement of two remote atomic qubits, achieved by generating an entangled state of an atomic qubit and a single photon at site , transmitting the photon to site in an adjacent laboratory through an optical fiber, and converting the photon into an atomic qubit. Entanglement of the two remote atomic qubits is inferred by performing, locally, quantum state transfer of each of the atomic qubits onto a photonic qubit and subsequent measurement of polarization correlations in violation of the Bell inequality [EQUATION: SEE TEXT]. We experimentally determine [EQUATION: SEE TEXT]. Entanglement of two remote atomic qubits, each qubit consisting of two independent spin wave excitations, and reversible, coherent transfer of entanglement between matter and light represent important advances in quantum information science. PMID:16486672
Experimental observation of sub-Rayleigh quantum imaging with a two-photon entangled source
Xu, De-Qin; Song, Xin-Bing; Li, Hong-Guo; Zhang, De-Jian; Wang, Hai-Bo; Xiong, Jun Wang, Kaige
2015-04-27
It has been theoretically predicted that N-photon quantum imaging can realize either an N-fold resolution improvement (Heisenberg-like scaling) or a √(N)-fold resolution improvement (standard quantum limit) beyond the Rayleigh diffraction bound, over classical imaging. Here, we report the experimental study on spatial sub-Rayleigh quantum imaging using a two-photon entangled source. Two experimental schemes are proposed and performed. In a Fraunhofer diffraction scheme with a lens, two-photon Airy disk pattern is observed with subwavelength diffraction property. In a lens imaging apparatus, however, two-photon sub-Rayleigh imaging for an object is realized with super-resolution property. The experimental results agree with the theoretical prediction in the two-photon quantum imaging regime.
Quantification of Entanglement Entropies for Doubly Excited States in Helium
NASA Astrophysics Data System (ADS)
Lin, Chien-Hao; Ho, Yew Kam
2015-05-01
In this work, we study the quantum entanglement for doubly excited resonance states in helium by using highly correlated Hylleraas type functions to represent such states of the two-electron system. The doubly-excited resonance states are determined by calculation of density of resonance states under the framework of the stabilization method. The spatial (electron-electron orbital) entanglement measures for the low-lying doubly excited 2 s 2, 2 s3 s, and 2 p 2 1 S e states are carried out. Once a resonance state wave function is obtained, the linear entropy and von Neumann entropy for such a state are quantified using the Schmidt-Slater decomposition method. To check the consistence, linear entropy is also determined by solving analytically the needed four-electron (12-dimensional) integrals.
NASA Astrophysics Data System (ADS)
Cardoso B., W.; Almeida G. de, N.
2008-07-01
We propose a scheme to partially teleport an unknown entangled atomic state. A high-Q cavity, supporting one mode of a weak coherent state, is needed to accomplish this process. By partial teleportation we mean that teleportation will occur by changing one of the partners of the entangled state to be teleported. The entangled state to be teleported is composed by one pair of particles, we called this surprising characteristic of maintaining the entanglement, even when one of the particle of the entangled pair being teleported is changed, of divorce of entangled states.
Generating and probing entangled states for optical atomic clocks
NASA Astrophysics Data System (ADS)
Braverman, Boris; Kawasaki, Akio; Vuletic, Vladan
2016-05-01
The precision of quantum measurements is inherently limited by projection noise caused by the measurement process itself. Spin squeezing and more complex forms of entanglement have been proposed as ways of surpassing this limitation. In our system, a high-finesse asymmetric micromirror-based optical cavity can mediate the atom-atom interaction necessary for generating entanglement in an 171 Yb optical lattice clock. I will discuss approaches for creating, characterizing, and optimally utilizing these nonclassical states for precision measurement, as well as recent progress toward their realization. This research is supported by DARPA QuASAR, NSF, and NSERC.
Maximally Entangled States of a Two-Qubit System
NASA Astrophysics Data System (ADS)
Singh, Manu P.; Rajput, B. S.
2013-12-01
Entanglement has been explored as one of the key resources required for quantum computation, the functional dependence of the entanglement measures on spin correlation functions has been established, correspondence between evolution of maximally entangled states (MES) of two-qubit system and representation of SU(2) group has been worked out and the evolution of MES under a rotating magnetic field has been investigated. Necessary and sufficient conditions for the general two-qubit state to be maximally entangled state (MES) have been obtained and a new set of MES constituting a very powerful and reliable eigen basis (different from magic bases) of two-qubit systems has been constructed. In terms of the MES constituting this basis, Bell’s States have been generated and all the qubits of two-qubit system have been obtained. It has shown that a MES corresponds to a point in the SO(3) sphere and an evolution of MES corresponds to a trajectory connecting two points on this sphere. Analysing the evolution of MES under a rotating magnetic field, it has been demonstrated that a rotating magnetic field is equivalent to a three dimensional rotation in real space leading to the evolution of a MES.
Comment I on ''Dense coding in entangled states''
Wojcik, Antoni; Grudka, Andrzej
2003-07-01
In this Comment we question the recent analysis of two dense coding protocols presented by Lee, Ahn, and Hwang [Phys. Rev. A 66, 024304 (2002)]. We argue that in the case of two-party communication protocol, there is no reason for using a maximally entangled state of more than two qubits.
Entanglement and quantum state transfer between two atoms trapped in two indirectly coupled cavities
NASA Astrophysics Data System (ADS)
Zheng, Bin; Shen, Li-Tuo; Chen, Ming-Feng
2016-05-01
We propose a one-step scheme for implementing entanglement generation and the quantum state transfer between two atomic qubits trapped in two different cavities that are not directly coupled to each other. The process is realized through engineering an effective asymmetric X-Y interaction for the two atoms involved in the gate operation and an auxiliary atom trapped in an intermediate cavity, induced by virtually manipulating the atomic excited states and photons. We study the validity of the scheme as well as the influences of the dissipation by numerical simulation and demonstrate that it is robust against decoherence.
NASA Astrophysics Data System (ADS)
Beggs, Daryl; Lang, Ben; Young, Andrew; Oulton, Ruth
A polarisation singularity occurs at a position in a vector field where one of the parameters of the local polarisation ellipse (handedness, eccentricity or orientation) becomes singular. With the vector nature of electromagnetic fields, optics is an obvious place for the study of polarisation singularities, and they can be found in systems ranging from tightly focused beams to speckle fields. Here we demonstrate that photonic crystal waveguides support on-chip polarisation singularities. As Bloch waves, the eigenmodes of photonic crystal waveguides possess a strong longitudinal, as well as transverse, component of their electric field. The spatial dependence of both these components and the phase between them ensures a rich and complex polarisation landscape in the waveguide. Recently, the use of polarisation singularities found in photonic crystal waveguides is generating much interest for integrated quantum information applications, as they can couple the spin-states of electrons confined to quantum dots to the optical modes of the waveguide. For example, at a circular-point (C-point), the sign of the local helicity is governed by the propagation direction of the optical mode, which allows for spin-photon coupling to one direction only. However, any real system will inevitably contain imperfections, and it is not obvious that the polarisation singularities will persist in the disordered waveguides. Here, we use calculations of the eigenmodes of disordered waveguides to demonstrate that the polarisation singularities persist far beyond realistically expected levels of disorder.
Bandyopadhyay, Somshubhro
2010-02-15
It is shown that while entanglement ensures difficulty in discriminating a set of mutually orthogonal states perfectly by local operations and classical communication (LOCC), entanglement content does not. In particular, for a class of entangled multiqubit states, the maximum number of perfectly LOCC distinguishable orthogonal states is shown to be independent of the average entanglement of the states, and the spatial configuration with respect to which LOCC operations may be carried out. It is also pointed out that for this class, the makeup of an ensemble, that is whether it consists only of entangled states or not, determines the maximum number of perfectly distinguishable states.
A note on entanglement entropy, coherent states and gravity
NASA Astrophysics Data System (ADS)
Varadarajan, Madhavan
2016-03-01
The entanglement entropy of a free quantum field in a coherent state is independent of its stress energy content. We use this result to highlight the fact that while the Einstein equations for first order variations about a locally maximally symmetric vacuum state of geometry and quantum fields seem to follow from Jacobson's principle of maximal vacuum entanglement entropy, their possible derivation from this principle for the physically relevant case of finite but small variations remains an open issue. We also apply this result to the context of Bianchi's identification, independent of unknown Planck scale physics, of the first order variation of Bekenstein-Hawking area with that of vacuum entanglement entropy. We argue that under certain technical assumptions this identification seems not to be extendible to the context of finite but small variations to coherent states. Our particular method of estimation of entanglement entropy variation reveals the existence of certain contributions over and above those of References Jacobson (arXiv:1505.04753, 2015), Bianchi (arXiv:1211.0522 [gr-qc], 2012). We discuss the sense in which these contributions may be subleading to those in References Jacobson (arXiv:1505.04753, 2015), Bianchi (arXiv:1211.0522 [gr-qc], 2012).
Ghost imaging with entangled photons and orbital angular momentum
NASA Astrophysics Data System (ADS)
Padgett, Miles
We utilise the position and orbital angular momentum (OAM) correlations between the signal and idler photons generated in the down-conversion process to obtain ghost images of a phase object. By using an OAM phase filter, which is non-local with respect to the object, the ghost images exhibit isotropic edge-enhancement. The strong spatial correlations between the signal and idler photons generated by spontaneous parametric downconversion have been widely utilised in many different imaging systems. The use of a scanning single element detector to recover the spatial information in the signal and idler beams fundamentally limits the detection efficiency of the imaging system to a maximum of 1/N where N is the number of pixels in the image. Our approach overcomes this limitation by replacing the scanning detector by an intensified CCD camera, therefore detecting all photons irrespective of their position within the image. Using a camera in this way, coupled with the OAM edge-enhancement and image reconstruction techniques allows us to obtain images of phase objects with an average of fewer than one photon per image pixel.
Various quantum nonlocality tests with a commercial two-photon entanglement source
Pomarico, Enrico; Bancal, Jean-Daniel; Sanguinetti, Bruno; Rochdi, Anas; Gisin, Nicolas
2011-05-15
Nonlocality is a fascinating and counterintuitive aspect of nature, revealed by the violation of a Bell inequality. The standard and easiest configuration in which Bell inequalities can be measured has been proposed by Clauser-Horne-Shimony-Holt (CHSH). However, alternative nonlocality tests can also be carried out. In particular, Bell inequalities requiring multiple measurement settings can provide deeper fundamental insights about quantum nonlocality, as well as offering advantages in the presence of noise and detection inefficiency. In this paper we show how these nonlocality tests can be performed using a commercially available source of entangled photon pairs. We report the violation of a series of these nonlocality tests (I{sub 3322}, I{sub 4422}, and chained inequalities). With the violation of the chained inequality with 4 settings per side we put an upper limit at 0.49 on the local content of the states prepared by the source (instead of 0.63 attainable with CHSH). We also quantify the amount of true randomness that has been created during our experiment (assuming fair sampling of the detected events).
Speedup of quantum evolution of multiqubit entanglement states
NASA Astrophysics Data System (ADS)
Zhang, Ying-Jie; Han, Wei; Xia, Yun-Jie; Tian, Jian-Xiang; Fan, Heng
2016-06-01
As is well known, quantum speed limit time (QSLT) can be used to characterize the maximal speed of evolution of quantum systems. We mainly investigate the QSLT of generalized N-qubit GHZ-type states and W-type states in the amplitude-damping channels. It is shown that, in the case N qubits coupled with independent noise channels, the QSLT of the entangled GHZ-type state is closely related to the number of qubits in the small-scale system. And the larger entanglement of GHZ-type states can lead to the shorter QSLT of the evolution process. However, the QSLT of the W-type states are independent of the number of qubits and the initial entanglement. Furthermore, by considering only M qubits among the N-qubit system respectively interacting with their own noise channels, QSLTs for these two types states are shorter than in the case N qubits coupled with independent noise channels. We therefore reach the interesting result that the potential speedup of quantum evolution of a given N-qubit GHZ-type state or W-type state can be realized in the case the number of the applied noise channels satisfying M < N.
Speedup of quantum evolution of multiqubit entanglement states.
Zhang, Ying-Jie; Han, Wei; Xia, Yun-Jie; Tian, Jian-Xiang; Fan, Heng
2016-01-01
As is well known, quantum speed limit time (QSLT) can be used to characterize the maximal speed of evolution of quantum systems. We mainly investigate the QSLT of generalized N-qubit GHZ-type states and W-type states in the amplitude-damping channels. It is shown that, in the case N qubits coupled with independent noise channels, the QSLT of the entangled GHZ-type state is closely related to the number of qubits in the small-scale system. And the larger entanglement of GHZ-type states can lead to the shorter QSLT of the evolution process. However, the QSLT of the W-type states are independent of the number of qubits and the initial entanglement. Furthermore, by considering only M qubits among the N-qubit system respectively interacting with their own noise channels, QSLTs for these two types states are shorter than in the case N qubits coupled with independent noise channels. We therefore reach the interesting result that the potential speedup of quantum evolution of a given N-qubit GHZ-type state or W-type state can be realized in the case the number of the applied noise channels satisfying M < N. PMID:27283757