Pub Date : 2005-08-02DOI: 10.1088/1464-4266/7/9/005
Nian-quan Jiang
For an n-partite entangled system, based on the newly constructed n-partite EPR entangled state for continuous variables, we find the entangled state representation of the n-mode Wigner operator, using it we have conveniently discussed the Wigner function of some entangled states.
{"title":"The n-partite entangled Wigner operator and its applications in Wigner function","authors":"Nian-quan Jiang","doi":"10.1088/1464-4266/7/9/005","DOIUrl":"https://doi.org/10.1088/1464-4266/7/9/005","url":null,"abstract":"For an n-partite entangled system, based on the newly constructed n-partite EPR entangled state for continuous variables, we find the entangled state representation of the n-mode Wigner operator, using it we have conveniently discussed the Wigner function of some entangled states.","PeriodicalId":87441,"journal":{"name":"Journal of optics. B, Quantum and semiclassical optics : journal of the European Optical Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2005-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1088/1464-4266/7/9/005","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"60920535","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-08-01DOI: 10.1088/1464-4266/7/8/L01
C. Gerry
I study a model of photon absorption by a collection of two-level atoms interacting resonantly with two degenerate modes of the quantized electromagnetic field. The two fields provide two channels by which the atoms may be excited and the interference between these channels gives rise to nontrivial steady states, the trivial state just being the two-mode vacuum. The model studied is soluble.
{"title":"Interference effects in a model of two-channel photon absorption by a collection of two-level atoms","authors":"C. Gerry","doi":"10.1088/1464-4266/7/8/L01","DOIUrl":"https://doi.org/10.1088/1464-4266/7/8/L01","url":null,"abstract":"I study a model of photon absorption by a collection of two-level atoms interacting resonantly with two degenerate modes of the quantized electromagnetic field. The two fields provide two channels by which the atoms may be excited and the interference between these channels gives rise to nontrivial steady states, the trivial state just being the two-mode vacuum. The model studied is soluble.","PeriodicalId":87441,"journal":{"name":"Journal of optics. B, Quantum and semiclassical optics : journal of the European Optical Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2005-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1088/1464-4266/7/8/L01","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"60920074","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-08-01DOI: 10.1088/1464-4266/7/8/001
V. Peřinová, A. Luks
The derivation of the relative electric permittivity tensor from a fully classical model is known, and a calculation of this quantity from a semiclassical model in the first order of perturbation theory is familiar as well. In applications to commonly occurring uniaxial crystalline media without optical activity, the whole discrete lattice is represented by a single atomic oscillator. We calculate the relative electric permittivity tensor provided that the discrete lattice can be represented by a continuum of quantum harmonic oscillators.
{"title":"Quantization of the electromagnetic field in uniaxial crystalline dielectric media: long-wave limit","authors":"V. Peřinová, A. Luks","doi":"10.1088/1464-4266/7/8/001","DOIUrl":"https://doi.org/10.1088/1464-4266/7/8/001","url":null,"abstract":"The derivation of the relative electric permittivity tensor from a fully classical model is known, and a calculation of this quantity from a semiclassical model in the first order of perturbation theory is familiar as well. In applications to commonly occurring uniaxial crystalline media without optical activity, the whole discrete lattice is represented by a single atomic oscillator. We calculate the relative electric permittivity tensor provided that the discrete lattice can be represented by a continuum of quantum harmonic oscillators.","PeriodicalId":87441,"journal":{"name":"Journal of optics. B, Quantum and semiclassical optics : journal of the European Optical Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2005-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1088/1464-4266/7/8/001","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"60919295","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-07-20DOI: 10.1088/1464-4266/7/10/007
T. Ralph, A. Lund, H. Wiseman
Photon counting induces an effective non-linear optical phase shift in certain states derived by linear optics from single photons. Although this non-linearity is non-deterministic, it is sufficient in principle to allow scalable linear optics quantum computation (LOQC). The most obvious way to encode a qubit optically is as a superposition of the vacuum and a single photon in one mode-so-called 'single-rail' logic. Until now this approach was thought to be prohibitively expensive (in resources) compared to 'dual-rail' logic where a qubit is stored by a photon across two modes. Here we attack this problem with real-time feedback control, which can realize a quantum-limited phase measurement on a single mode, as has been recently demonstrated experimentally. We show that with this added measurement resource, the resource requirements for single-rail LOQC are not substantially different from those of dual-rail LOQC. In particular, with adaptive phase measurements an arbitrary qubit state a alpha/0 > + beta/1 > can be prepared deterministically.
{"title":"Adaptive phase measurements in linear optical quantum computation","authors":"T. Ralph, A. Lund, H. Wiseman","doi":"10.1088/1464-4266/7/10/007","DOIUrl":"https://doi.org/10.1088/1464-4266/7/10/007","url":null,"abstract":"Photon counting induces an effective non-linear optical phase shift in certain states derived by linear optics from single photons. Although this non-linearity is non-deterministic, it is sufficient in principle to allow scalable linear optics quantum computation (LOQC). The most obvious way to encode a qubit optically is as a superposition of the vacuum and a single photon in one mode-so-called 'single-rail' logic. Until now this approach was thought to be prohibitively expensive (in resources) compared to 'dual-rail' logic where a qubit is stored by a photon across two modes. Here we attack this problem with real-time feedback control, which can realize a quantum-limited phase measurement on a single mode, as has been recently demonstrated experimentally. We show that with this added measurement resource, the resource requirements for single-rail LOQC are not substantially different from those of dual-rail LOQC. In particular, with adaptive phase measurements an arbitrary qubit state a alpha/0 > + beta/1 > can be prepared deterministically.","PeriodicalId":87441,"journal":{"name":"Journal of optics. B, Quantum and semiclassical optics : journal of the European Optical Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2005-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1088/1464-4266/7/10/007","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"60911664","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-07-20DOI: 10.1088/1464-4266/7/10/024
M. Dykman, L. F. Santos, M. Shapiro
Many-particle confinement (localization) is studied for a 1D system of spinless fermions with nearest-neighbour hopping and interaction, or equivalently, for an anisotropic Heisenberg spin-1/2 chain. This system is frequently used to model quantum computers with perpetually coupled qubits. We construct a bounded sequence of site energies that leads to strong single-particle confinement of all states on individual sites. We show that this sequence also leads to a confinement of all many-particle states in an infinite system for a time that scales as a high power of the reciprocal hopping integral. The confinement is achieved for strong interaction between the particles while keeping the overall bandwidth of site energies comparatively small. The results show the viability of quantum computing with time-independent qubit coupling.
{"title":"Many-particle confinement by constructed disorder and quantum computing","authors":"M. Dykman, L. F. Santos, M. Shapiro","doi":"10.1088/1464-4266/7/10/024","DOIUrl":"https://doi.org/10.1088/1464-4266/7/10/024","url":null,"abstract":"Many-particle confinement (localization) is studied for a 1D system of spinless fermions with nearest-neighbour hopping and interaction, or equivalently, for an anisotropic Heisenberg spin-1/2 chain. This system is frequently used to model quantum computers with perpetually coupled qubits. We construct a bounded sequence of site energies that leads to strong single-particle confinement of all states on individual sites. We show that this sequence also leads to a confinement of all many-particle states in an infinite system for a time that scales as a high power of the reciprocal hopping integral. The confinement is achieved for strong interaction between the particles while keeping the overall bandwidth of site energies comparatively small. The results show the viability of quantum computing with time-independent qubit coupling.","PeriodicalId":87441,"journal":{"name":"Journal of optics. B, Quantum and semiclassical optics : journal of the European Optical Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2005-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1088/1464-4266/7/10/024","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"60912247","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-07-14DOI: 10.1088/1464-4266/7/12/015
A. Solomon
Starting with a thermal squeezed state defined as a conventional thermal state based on an appropriate Hamiltonian, we show how an important physical property, the signal-to-noise ratio, is degraded, and propose a simple model of thermalization (Kraus thermalization).
{"title":"Thermalization of squeezed states","authors":"A. Solomon","doi":"10.1088/1464-4266/7/12/015","DOIUrl":"https://doi.org/10.1088/1464-4266/7/12/015","url":null,"abstract":"Starting with a thermal squeezed state defined as a conventional thermal state based on an appropriate Hamiltonian, we show how an important physical property, the signal-to-noise ratio, is degraded, and propose a simple model of thermalization (Kraus thermalization).","PeriodicalId":87441,"journal":{"name":"Journal of optics. B, Quantum and semiclassical optics : journal of the European Optical Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2005-07-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1088/1464-4266/7/12/015","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"60914686","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-07-11DOI: 10.1088/1464-4266/7/8/002
L. Ye, L. Ye, G. Guo
We propose a scheme for transferring an entanglement of zero- and one-photon states from one cavity to another. The scheme, which has 100% success probability, is mainly based on a two-mode cavity dispersively interacting with a three-level atom in the Λ configuration and does not involve Bell-state measurement. This scheme can also be used to teleport an unknown atomic state.
{"title":"Transferring a cavity field entangled state in cavity QED","authors":"L. Ye, L. Ye, G. Guo","doi":"10.1088/1464-4266/7/8/002","DOIUrl":"https://doi.org/10.1088/1464-4266/7/8/002","url":null,"abstract":"We propose a scheme for transferring an entanglement of zero- and one-photon states from one cavity to another. The scheme, which has 100% success probability, is mainly based on a two-mode cavity dispersively interacting with a three-level atom in the Λ configuration and does not involve Bell-state measurement. This scheme can also be used to teleport an unknown atomic state.","PeriodicalId":87441,"journal":{"name":"Journal of optics. B, Quantum and semiclassical optics : journal of the European Optical Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2005-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1088/1464-4266/7/8/002","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"60919362","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-07-11DOI: 10.1088/1464-4266/7/8/003
C. Bendjaballah
Various random point processes occurring in the detection of photons in different states are considered. Statistics of the times between these points and their correlation are analysed.
考虑了探测不同状态光子时出现的各种随机点过程。分析了这些点之间的时间统计和它们之间的相关性。
{"title":"Correlation of time intervals for random point processes","authors":"C. Bendjaballah","doi":"10.1088/1464-4266/7/8/003","DOIUrl":"https://doi.org/10.1088/1464-4266/7/8/003","url":null,"abstract":"Various random point processes occurring in the detection of photons in different states are considered. Statistics of the times between these points and their correlation are analysed.","PeriodicalId":87441,"journal":{"name":"Journal of optics. B, Quantum and semiclassical optics : journal of the European Optical Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2005-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1088/1464-4266/7/8/003","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"60919511","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-07-07DOI: 10.1088/1464-4266/7/10/004
T. Lynn, K. Birnbaum, H. Kimble
Recent realizations of single-atom trapping and tracking in cavity QED open the door for feedback schemes which actively stabilize the motion of a single atom in real time. We present feedback algorithms for cooling the radial component of motion for a single atom trapped by strong coupling to single-photon fields in an optical cavity. Performance of various algorithms is studied through simulations of single-atom trajectories, with full dynamical and measurement noise included. Closed loop feedback algorithms compare favourably to open loop 'switching' analogues, demonstrating the importance of applying actual position information in real time. The high optical information rate in current experiments enables real-time tracking that approaches the standard quantum limit for broadband position measurements, suggesting that realistic active feedback schemes may reach a regime where measurement backaction appreciably alters the motional dynamics.
{"title":"Strategies for real-time position control of a single atom in cavity QED","authors":"T. Lynn, K. Birnbaum, H. Kimble","doi":"10.1088/1464-4266/7/10/004","DOIUrl":"https://doi.org/10.1088/1464-4266/7/10/004","url":null,"abstract":"Recent realizations of single-atom trapping and tracking in cavity QED open the door for feedback schemes which actively stabilize the motion of a single atom in real time. We present feedback algorithms for cooling the radial component of motion for a single atom trapped by strong coupling to single-photon fields in an optical cavity. Performance of various algorithms is studied through simulations of single-atom trajectories, with full dynamical and measurement noise included. Closed loop feedback algorithms compare favourably to open loop 'switching' analogues, demonstrating the importance of applying actual position information in real time. The high optical information rate in current experiments enables real-time tracking that approaches the standard quantum limit for broadband position measurements, suggesting that realistic active feedback schemes may reach a regime where measurement backaction appreciably alters the motional dynamics.","PeriodicalId":87441,"journal":{"name":"Journal of optics. B, Quantum and semiclassical optics : journal of the European Optical Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2005-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1088/1464-4266/7/10/004","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"60910786","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-07-07DOI: 10.1088/1464-4266/7/12/021
J. Laurat, G. Keller, J. Oliveira-Huguenin, C. Fabre, T. Coudreau, A. Serafini, G. Adesso, F. Illuminati
A powerful theoretical structure has emerged in recent years on the characterization and quantification of entanglement in continuous-variable systems. After reviewing this framework, we will illustrate it with an original set-up based on a type-II OPO (optical parametric oscillator) with adjustable mode coupling. Experimental results allow a direct verification of many theoretical predictions and provide a sharp insight into the general properties of two-mode Gaussian states and entanglement resource manipulation.
{"title":"Entanglement of two-mode Gaussian states: characterization and experimental production and manipulation","authors":"J. Laurat, G. Keller, J. Oliveira-Huguenin, C. Fabre, T. Coudreau, A. Serafini, G. Adesso, F. Illuminati","doi":"10.1088/1464-4266/7/12/021","DOIUrl":"https://doi.org/10.1088/1464-4266/7/12/021","url":null,"abstract":"A powerful theoretical structure has emerged in recent years on the characterization and quantification of entanglement in continuous-variable systems. After reviewing this framework, we will illustrate it with an original set-up based on a type-II OPO (optical parametric oscillator) with adjustable mode coupling. Experimental results allow a direct verification of many theoretical predictions and provide a sharp insight into the general properties of two-mode Gaussian states and entanglement resource manipulation.","PeriodicalId":87441,"journal":{"name":"Journal of optics. B, Quantum and semiclassical optics : journal of the European Optical Society","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2005-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1088/1464-4266/7/12/021","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"60914533","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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