Generally, natural scientific problems are so complicated that one has to establish some effective perturbation or nonperturbation theories with respect to some associated ideal models. We construct a new theory that ...Generally, natural scientific problems are so complicated that one has to establish some effective perturbation or nonperturbation theories with respect to some associated ideal models. We construct a new theory that combines perturbation and nonperturbation. An artificial nonlinear homotopy parameter plays the role of a perturbation parameter, while other artificial nonlinear parameters, which are independent of the original problems, introduced in the nonlinear homotopy models are nonperturbatively determined by means of the principle of minimal sensitivity. The method is demonstrated through several quantum anharmonic oscillators and a non-hermitian parity-time symmetric Hamiltonian system. In fact, the framework of the theory is rather general and can be applied to a broad range of natural phenomena. Possible applications to condensed matter physics, matter wave systems, and nonfinear optics are briefly discussed.展开更多
How to manipulate （operate or measure） single photons efficiently and simply is the basic problem in optical quantum information processing. We first present an efficient scheme to transform a biphoton polarization ...How to manipulate （operate or measure） single photons efficiently and simply is the basic problem in optical quantum information processing. We first present an efficient scheme to transform a biphoton polarization state to a corresponding single-photon state encoded by its polarization and spatial modes. This single-photon state carries both the information of the controlled and target photons. It will make the realization of bipartite positive- operator-valued measurements efficiently and simply. Moreover, the inverse transformation from the single-photon state back to the corresponding biphoton polarization state is also proposed. Using both the transformations, the realization of the arbitrary two-qubit unitary operation is simple with an M-Z interferometer. All the schemes are feasible with the current experimental technology.展开更多
Based on the classical time division multi-channel communication theory, we present a scheme of quantum time- division multi-channel communication （QTDMC）. Moreover, the model of quantum time division switch （QTDS...Based on the classical time division multi-channel communication theory, we present a scheme of quantum time- division multi-channel communication （QTDMC）. Moreover, the model of quantum time division switch （QTDS） and correlative protocol of QTDMC are proposed. The quantum bit error rate （QBER） is analyzed and the QBER simulation test is performed. The scheme shows that the QTDS can carry out multi-user communication through quantum channel, the QBER can also reach the reliability requirement of communication, and the protocol of QTDMC has high practicability and transplantable. The scheme of QTDS may play an important role in the establishment of quantum communication in a large scale in the future.展开更多
In the case of bipartite two-qubit systems, we derive an analytical expression of bound Bell operator for any given pure state. Our result not only manifests some properties of Bell inequality, for example, which may ...In the case of bipartite two-qubit systems, we derive an analytical expression of bound Bell operator for any given pure state. Our result not only manifests some properties of Bell inequality, for example, which may be violated by any pure entangled state and only be maximally violated for a maximally entangled state, but also gives the explicit values of maximal violation for any pure state. Finally we point out that any mixed states which can produce maximal violation of Bell inequality must have a maximal concurrence value.展开更多
We illustrate the dichotomy of classical/quantum correlations by virtue of monogamy. More precisely, we show that correlations in a bipartite state are classical if and only it each party ot the state can be perfectly...We illustrate the dichotomy of classical/quantum correlations by virtue of monogamy. More precisely, we show that correlations in a bipartite state are classical if and only it each party ot the state can be perfectly correlated with other ancillary systems. In particular, this means that if there are quantum correlations between two parties, then the classical （as well as quantum） correlating capabilities of the two parties with other systems have to be strictly reduced.展开更多
We review the historical fact of multipartite Bell inequalities with an arbitrary number of settings. An explicit local realistic model for the values of a correlation function, given in a two-setting Bell experiment ...We review the historical fact of multipartite Bell inequalities with an arbitrary number of settings. An explicit local realistic model for the values of a correlation function, given in a two-setting Bell experiment （two-setting model）, works only for the specific set of settings in the given experiment, but cannot construct a local realistic model for the values of a correlation function, given in a continuous-infinite settings Bell experiment （infinite-setting model）, even though there exist two-setting models for all directions in space. Hence, the two-setting model does not have the property that the infinite-setting model has. Here, we show that an explicit two-setting model cannot construct a local realistic model for the values of a correlation function, given in an M-setting Bell experiment （M-setting model）, even though there exist two-setting models for the M measurement directions chosen in the given M-setting experiment. Hence, the two-setting model does not have the property that the M-setting model has.展开更多
Using the method presented recently [Phys.Rev.A 77（2008）014306; Phys.Lett.A 369（2007）377], the transformation operator （TO） is explicitly given for teleporting an arbitrary three-qubit state with a six-qubit cha...Using the method presented recently [Phys.Rev.A 77（2008）014306; Phys.Lett.A 369（2007）377], the transformation operator （TO） is explicitly given for teleporting an arbitrary three-qubit state with a six-qubit channel and Bell-state measurements. A criterion on whether such quantum teleportation can be perfectly realized is educed in terms of TO. Moreover, six instantiations on TO and criterion are concisely shown.展开更多
We investigate how an initial thermo vacuum state, in the context of thermo field dynamics, evolves in a single-mode amplitude dissipative channel, and find that in this process the thermo squeezing effect decreases w...We investigate how an initial thermo vacuum state, in the context of thermo field dynamics, evolves in a single-mode amplitude dissipative channel, and find that in this process the thermo squeezing effect decreases while the fictitious-mode vacuum becomes chaotic.展开更多
A new implementation of high-dimensional quantum key distribution （QKD） protocol is discussed. Using three mutual unbiased bases, we present a d？level six-state QKD protocol that exploits the orbital angular moment...A new implementation of high-dimensional quantum key distribution （QKD） protocol is discussed. Using three mutual unbiased bases, we present a d？level six-state QKD protocol that exploits the orbital angular momentum with the spatial mode of the light beam. The protocol shows that the feature of a high capacity since keys are encoded using photon modes in d-level Hilbert space. The devices for state preparation and measurement are also discussed. This protocol has high security and the alignment of shared reference frames is not needed between sender and receiver.展开更多
The generation of various entangled states is an essential task in quantum information processing. Recently, a scheme （PRA 79, 022304） has been suggested for generating Greenberger-Horne-Zeilinger state and cluster ...The generation of various entangled states is an essential task in quantum information processing. Recently, a scheme （PRA 79, 022304） has been suggested for generating Greenberger-Horne-Zeilinger state and cluster state with atomic ensembles based on the Rydberg blockade. Using similar resources as the earlier scheme, here we propose an experimentally feasible scheme of preparing arbitrary four-qubit W class of maximally and non- maximally entangled states with atomic ensembles in a single step. Moreover, we carefully analyze the realistic noises and predict that four-qubit W states can be produced with high fidelity （F - 0.994） via our scheme.展开更多
We study the spin-weighted spheroidal wave functions in the case of s = m = 0. Their eigenvalue problem is investigated by the perturbation method in supersymmetric quantum mechanics. In the first three terms of param...We study the spin-weighted spheroidal wave functions in the case of s = m = 0. Their eigenvalue problem is investigated by the perturbation method in supersymmetric quantum mechanics. In the first three terms of parameter a = a^2 w^2, the ground eigenvalue and eigenfunction are obtained. The obtained ground eigenfunction is elegantly in dosed forms. These results are new and very useful for the application of the spheroidal wave functions.展开更多
In a recent paper [Yan F L et al. Chin.Phys.Lett. 25（2008）1187], a quantum secret sharing the protocol between multiparty and multiparty with single photons and unitary transformations was presented. We analyze the ...In a recent paper [Yan F L et al. Chin.Phys.Lett. 25（2008）1187], a quantum secret sharing the protocol between multiparty and multiparty with single photons and unitary transformations was presented. We analyze the security of the protocol and find that a dishonest participant can eavesdrop the key by using a special attack. Finally, we give a description of this strategy and put forward an improved version of this protocol which can stand against this kind of attack.展开更多
In terms of the intermediate coordinate-momentum representation （Chin. Phys. Lett. 18 （2001） 850） and using the technique of integration within an ordered product of operators, we put the tomography theory into op...In terms of the intermediate coordinate-momentum representation （Chin. Phys. Lett. 18 （2001） 850） and using the technique of integration within an ordered product of operators, we put the tomography theory into operator version. We reveal the new relation between the tomogram and the characteristic function of the density operator. The new expansion of the density operator in terms of the intermediate coordinate-momentum representation is also obtained.展开更多
We propose an optical scheme to generate cluster states of atomic qubits, with each trapped in separate optical cavity, via atom-cavity-laser interaction. The quantum information of each qubit is encoded on the degene...We propose an optical scheme to generate cluster states of atomic qubits, with each trapped in separate optical cavity, via atom-cavity-laser interaction. The quantum information of each qubit is encoded on the degenerate ground states of the atom, hence the entanglement between them is relatively stable against spontaneous emission. A single-photon source and two classical fields are employed in the present scheme. By controlling the sequence and time of atom-cavity-laser interaction, we show that the atomic cluster states can be produced deterministically.展开更多
A protocol is proposed to implement a three-qubit phase gate for photonic qubits in a three-mode cavity. The idea can be extended to directly implement a N-qubit phase gate. We also show that the interaction time rema...A protocol is proposed to implement a three-qubit phase gate for photonic qubits in a three-mode cavity. The idea can be extended to directly implement a N-qubit phase gate. We also show that the interaction time remains unchanged with the increasing number of qubits. In addition, the influence of cavity decay and atomic spontaneous emission on the gate fidelity and photon loss probability is also discussed by numerical calculation.展开更多
We present a simple method to realize a swap gate at one step with two molecular ensembles in a stripline cavity. In this scheme, we can benefit from the enhancement of the coherent coupling and acquire a long coheren...We present a simple method to realize a swap gate at one step with two molecular ensembles in a stripline cavity. In this scheme, we can benefit from the enhancement of the coherent coupling and acquire a long coherent time with encoding qubits in different spin states of the rotational ground state in the molecular ensembles. As a by-product, a scheme to create an entangled state with one excitation stored in two ensembles is proposed.展开更多
The existing theory of decoy-state quantum cryptography assumes that the dark count rate is a constant, but in practice there exists fluctuation. We develop a new scheme of the decoy state, achieve a more practical ke...The existing theory of decoy-state quantum cryptography assumes that the dark count rate is a constant, but in practice there exists fluctuation. We develop a new scheme of the decoy state, achieve a more practical key generation rate in the presence of fluctuation of the dark count rate, and compare the result with the result of the decoy-state without fluctuation. It is found that the key generation rate and maximal secure distance will be decreased under the influence of the fluctuation of the dark count rate.展开更多
We propose a new scheme to achieve the tripartite entanglement based on the standard criteria [Phys. Rev. A 67（2003） 052315] in a inverse-tripod atomic system. In our scheme, the atomic coherence is introduced by tw...We propose a new scheme to achieve the tripartite entanglement based on the standard criteria [Phys. Rev. A 67（2003） 052315] in a inverse-tripod atomic system. In our scheme, the atomic coherence is introduced by two microwave fields which drive the upper three levels of atom. By numerically simulating the dynamics of system, we investigate the generation and evolution of entanglement in the presence of atom and cavity decay. As a result, the present research provides an efficient approach to achieve fully tripartite entanglement with different frequencies and initial states for each entangled mode, which may have impact on the progress of multicolored multi-notes quantum information networks.展开更多
We propose a scheme for realizing the 1 → 2 universal quantum cloning machine （UQCM） with superconducting quantum interference device （SQUID） qubits in circuit quantum electrodynamics （circuit QED）. In this sch...We propose a scheme for realizing the 1 → 2 universal quantum cloning machine （UQCM） with superconducting quantum interference device （SQUID） qubits in circuit quantum electrodynamics （circuit QED）. In this scheme, in order to implement UQCM, we only need phase shift gate operation on SQUID qubits and the Raman transitions. The cavity number we need is only one. Thus our scheme is simple and has advantages in the experimental realization. Furthermore, both the cavity and the SQUID qubits are virtually excited, so the decoherence can be neglected.展开更多
We present a wavelength-tunable narrow-band fiber-coupled source to generate correlated photon pairs at 539 nm and 1550nm. Using a lO-mm PPLN crystal, we obtain more than 50ram tunable range near 1550nm. This source, ...We present a wavelength-tunable narrow-band fiber-coupled source to generate correlated photon pairs at 539 nm and 1550nm. Using a lO-mm PPLN crystal, we obtain more than 50ram tunable range near 1550nm. This source, given its spectral property and tunable property, is well suited for tasks in fiber-optic quantum communication and cryptography networks.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 10735030 and 90503006, the National Basic Research Program of China under Grant No 2007CB814800, and the PCSIRT （IRT0734）. The authors thank two referees for their helpful advice. We also thank Dr. C. L. Chen and M. Jia for their helpful discussions.
文摘Generally, natural scientific problems are so complicated that one has to establish some effective perturbation or nonperturbation theories with respect to some associated ideal models. We construct a new theory that combines perturbation and nonperturbation. An artificial nonlinear homotopy parameter plays the role of a perturbation parameter, while other artificial nonlinear parameters, which are independent of the original problems, introduced in the nonlinear homotopy models are nonperturbatively determined by means of the principle of minimal sensitivity. The method is demonstrated through several quantum anharmonic oscillators and a non-hermitian parity-time symmetric Hamiltonian system. In fact, the framework of the theory is rather general and can be applied to a broad range of natural phenomena. Possible applications to condensed matter physics, matter wave systems, and nonfinear optics are briefly discussed.
基金Supported by the National Natural Science Foundation of China under Grant No 11005040the Natural Science Foundation of Fujian Province under Grant No 2010J05008.
文摘How to manipulate （operate or measure） single photons efficiently and simply is the basic problem in optical quantum information processing. We first present an efficient scheme to transform a biphoton polarization state to a corresponding single-photon state encoded by its polarization and spatial modes. This single-photon state carries both the information of the controlled and target photons. It will make the realization of bipartite positive- operator-valued measurements efficiently and simply. Moreover, the inverse transformation from the single-photon state back to the corresponding biphoton polarization state is also proposed. Using both the transformations, the realization of the arbitrary two-qubit unitary operation is simple with an M-Z interferometer. All the schemes are feasible with the current experimental technology.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61072057 and 60672119, the 111 Project （B08038）, the State Key Lab of Integrated Services Networks （ISN 1001004）, the Fundamental Research Funds for the Central Universities （No K50510010004）, the Natural Science Basic Research Project in Shaanxi Province （2010JM8021）, Young Teacher Research Funds of Xilan Institute of Post and Telecommunication （ZL2010-05）, and Scientific Research Project of the Education Department of Shaanxi （2010JK834）.
文摘Based on the classical time division multi-channel communication theory, we present a scheme of quantum time- division multi-channel communication （QTDMC）. Moreover, the model of quantum time division switch （QTDS） and correlative protocol of QTDMC are proposed. The quantum bit error rate （QBER） is analyzed and the QBER simulation test is performed. The scheme shows that the QTDS can carry out multi-user communication through quantum channel, the QBER can also reach the reliability requirement of communication, and the protocol of QTDMC has high practicability and transplantable. The scheme of QTDS may play an important role in the establishment of quantum communication in a large scale in the future.
基金Supported by the National Natural Science Foundation of China Grant Nos 10947142 and 11005031.
文摘In the case of bipartite two-qubit systems, we derive an analytical expression of bound Bell operator for any given pure state. Our result not only manifests some properties of Bell inequality, for example, which may be violated by any pure entangled state and only be maximally violated for a maximally entangled state, but also gives the explicit values of maximal violation for any pure state. Finally we point out that any mixed states which can produce maximal violation of Bell inequality must have a maximal concurrence value.
基金Supported by the National Natural Science Foundation of China under Grant No 10771208, the Science Fund for Creative Research Groups under Grant No 10721101, and the Key Lab of Random Complex Structures and Data Science of Chinese Academy of Sciences under Grant No 2008DP173182.
文摘We illustrate the dichotomy of classical/quantum correlations by virtue of monogamy. More precisely, we show that correlations in a bipartite state are classical if and only it each party ot the state can be perfectly correlated with other ancillary systems. In particular, this means that if there are quantum correlations between two parties, then the classical （as well as quantum） correlating capabilities of the two parties with other systems have to be strictly reduced.
文摘We review the historical fact of multipartite Bell inequalities with an arbitrary number of settings. An explicit local realistic model for the values of a correlation function, given in a two-setting Bell experiment （two-setting model）, works only for the specific set of settings in the given experiment, but cannot construct a local realistic model for the values of a correlation function, given in a continuous-infinite settings Bell experiment （infinite-setting model）, even though there exist two-setting models for all directions in space. Hence, the two-setting model does not have the property that the infinite-setting model has. Here, we show that an explicit two-setting model cannot construct a local realistic model for the values of a correlation function, given in an M-setting Bell experiment （M-setting model）, even though there exist two-setting models for the M measurement directions chosen in the given M-setting experiment. Hence, the two-setting model does not have the property that the M-setting model has.
基金Supported by the New Century Excellent Talent Project （NCET） of the Ministry of Education of China under Grant No NCET-06-0554, the National Natural Science Foundation of China under Grant Nos 10975001, 60677001, 10747146 and 10874122, the Science-Technology Fund of Anhui Province for Outstanding Youth under Grant No 06042087, the Key Fund of the Ministry of Education of China under Grant No 206063, the General Fund of the Educational Committee of Anhui Province under Grant No 2006KJ260B, the Natural Science Foundation of Guangdong Province under Grant Nos 06300345 and 7007806, and the Talent Foundation of High Education of Anhui Province for Outstanding Youth under Grant No 2009SQRZ018.
文摘Using the method presented recently [Phys.Rev.A 77（2008）014306; Phys.Lett.A 369（2007）377], the transformation operator （TO） is explicitly given for teleporting an arbitrary three-qubit state with a six-qubit channel and Bell-state measurements. A criterion on whether such quantum teleportation can be perfectly realized is educed in terms of TO. Moreover, six instantiations on TO and criterion are concisely shown.
文摘We investigate how an initial thermo vacuum state, in the context of thermo field dynamics, evolves in a single-mode amplitude dissipative channel, and find that in this process the thermo squeezing effect decreases while the fictitious-mode vacuum becomes chaotic.
基金Supported by the National Basic Research Program of China under Grant Nos 2006CB921106 and 2010CB923202, the Fundamental Research Funds for the Central Universities No BUPT2009RC0710, the Specialized Research Fund for the Doctoral Program of Higher Education of China under Grant No 20090005120008, and the National Natural Science Foundation of China under Grant No 10947151.
文摘A new implementation of high-dimensional quantum key distribution （QKD） protocol is discussed. Using three mutual unbiased bases, we present a d？level six-state QKD protocol that exploits the orbital angular momentum with the spatial mode of the light beam. The protocol shows that the feature of a high capacity since keys are encoded using photon modes in d-level Hilbert space. The devices for state preparation and measurement are also discussed. This protocol has high security and the alignment of shared reference frames is not needed between sender and receiver.
基金Supported by the National Natural Science Foundation of China under Grant No 10774192, the Fund of Innovation of Graduate School of National University of Defense Technology under Grant No 080201.
文摘The generation of various entangled states is an essential task in quantum information processing. Recently, a scheme （PRA 79, 022304） has been suggested for generating Greenberger-Horne-Zeilinger state and cluster state with atomic ensembles based on the Rydberg blockade. Using similar resources as the earlier scheme, here we propose an experimentally feasible scheme of preparing arbitrary four-qubit W class of maximally and non- maximally entangled states with atomic ensembles in a single step. Moreover, we carefully analyze the realistic noises and predict that four-qubit W states can be produced with high fidelity （F - 0.994） via our scheme.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10875018 and 10773002.
文摘We study the spin-weighted spheroidal wave functions in the case of s = m = 0. Their eigenvalue problem is investigated by the perturbation method in supersymmetric quantum mechanics. In the first three terms of parameter a = a^2 w^2, the ground eigenvalue and eigenfunction are obtained. The obtained ground eigenfunction is elegantly in dosed forms. These results are new and very useful for the application of the spheroidal wave functions.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60873191, 60903152 and 60821001, the SRFDP under Grant No 200800131016, Beijing Nova Program under Grant No 2008B51, Key Project of the Ministry of Education of China under Grant No 109014, China Postdoctoral Science Foundation under Grant No 20090450018, Fujian Provincial Natural Science Foundation under Grant No 2008J0013, and the Foundation of Fujian Education Bureau under Grant No 3A08044.
文摘In a recent paper [Yan F L et al. Chin.Phys.Lett. 25（2008）1187], a quantum secret sharing the protocol between multiparty and multiparty with single photons and unitary transformations was presented. We analyze the security of the protocol and find that a dishonest participant can eavesdrop the key by using a special attack. Finally, we give a description of this strategy and put forward an improved version of this protocol which can stand against this kind of attack.
基金Supported by the National Natural Science Foundation of China under Grant No 10874174, and the President Foundation of Chinese Academy of Sciences.
文摘In terms of the intermediate coordinate-momentum representation （Chin. Phys. Lett. 18 （2001） 850） and using the technique of integration within an ordered product of operators, we put the tomography theory into operator version. We reveal the new relation between the tomogram and the characteristic function of the density operator. The new expansion of the density operator in terms of the intermediate coordinate-momentum representation is also obtained.
基金Supported by the National Basic Research Program under Grant No 2007CB925204, the National Natural Science Foundation of China under Grant Nos 10947135 and 10775048, the Opening Project of Key Laboratory of Low Dimensional Quantum Structures and Quantum Control （Hunan Normal University）, the Ministry of Education under Grant No QSQC0903, the Scientific Research Fund of Hunan Provincial Education Department under Grant No 09C062, the Construct Prograzn of the Key Discipline in Hunan Province and the Construct Program of the Key Discipline in Changsha University of Science and Technology.
文摘We propose an optical scheme to generate cluster states of atomic qubits, with each trapped in separate optical cavity, via atom-cavity-laser interaction. The quantum information of each qubit is encoded on the degenerate ground states of the atom, hence the entanglement between them is relatively stable against spontaneous emission. A single-photon source and two classical fields are employed in the present scheme. By controlling the sequence and time of atom-cavity-laser interaction, we show that the atomic cluster states can be produced deterministically.
文摘A protocol is proposed to implement a three-qubit phase gate for photonic qubits in a three-mode cavity. The idea can be extended to directly implement a N-qubit phase gate. We also show that the interaction time remains unchanged with the increasing number of qubits. In addition, the influence of cavity decay and atomic spontaneous emission on the gate fidelity and photon loss probability is also discussed by numerical calculation.
文摘We present a simple method to realize a swap gate at one step with two molecular ensembles in a stripline cavity. In this scheme, we can benefit from the enhancement of the coherent coupling and acquire a long coherent time with encoding qubits in different spin states of the rotational ground state in the molecular ensembles. As a by-product, a scheme to create an entangled state with one excitation stored in two ensembles is proposed.
基金Supported by the National Natural Science Foundation of China under Grant No 10504042.
文摘The existing theory of decoy-state quantum cryptography assumes that the dark count rate is a constant, but in practice there exists fluctuation. We develop a new scheme of the decoy state, achieve a more practical key generation rate in the presence of fluctuation of the dark count rate, and compare the result with the result of the decoy-state without fluctuation. It is found that the key generation rate and maximal secure distance will be decreased under the influence of the fluctuation of the dark count rate.
基金Supported in part by the National Natural Science Foundation of China under Grant Nos 10634060, 10704017, 10874050 and 10975054, the National Basic Research Program of China under Contract No 2005CB724508, and the Foundation from the Ministry of Education of China under Grant Nos 200804870051） The authors would like to thank Professor Wu Ying for helpful discussion and encouragement.
文摘We propose a new scheme to achieve the tripartite entanglement based on the standard criteria [Phys. Rev. A 67（2003） 052315] in a inverse-tripod atomic system. In our scheme, the atomic coherence is introduced by two microwave fields which drive the upper three levels of atom. By numerically simulating the dynamics of system, we investigate the generation and evolution of entanglement in the presence of atom and cavity decay. As a result, the present research provides an efficient approach to achieve fully tripartite entanglement with different frequencies and initial states for each entangled mode, which may have impact on the progress of multicolored multi-notes quantum information networks.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60978009 and 60578055, and by the National Basic Research Program of China under Grant Nos 2009CB929604 and 2007CB925204.
文摘We propose a scheme for realizing the 1 → 2 universal quantum cloning machine （UQCM） with superconducting quantum interference device （SQUID） qubits in circuit quantum electrodynamics （circuit QED）. In this scheme, in order to implement UQCM, we only need phase shift gate operation on SQUID qubits and the Raman transitions. The cavity number we need is only one. Thus our scheme is simple and has advantages in the experimental realization. Furthermore, both the cavity and the SQUID qubits are virtually excited, so the decoherence can be neglected.
基金Supported by the National Basic Research Program under Grant No 2006CB921907, the National Natural Science Foundation of China under Grant Nos 10774139 and 60621064, Knowledge Innovation Project of Chinese Academy of Sciences, the Program for New Century Excellent Talents in University, International Cooperation Program of Chinese Academy of Sciences, and Ministry of Science and Technology of China, the Foundation for Author of National Excellent Doctoral Dissertation of China under Grant 200729, and China Postdoctoral Science Foundation under Grant No 20070420736.
文摘We present a wavelength-tunable narrow-band fiber-coupled source to generate correlated photon pairs at 539 nm and 1550nm. Using a lO-mm PPLN crystal, we obtain more than 50ram tunable range near 1550nm. This source, given its spectral property and tunable property, is well suited for tasks in fiber-optic quantum communication and cryptography networks.
