Showing papers on "Coherent states published in 2005"
TL;DR: It is demonstrated coherent control of a quantum two-level system based on two-electron spin states in a double quantum dot, allowing state preparation, coherent manipulation, and projective readout based on rapid electrical control of the exchange interaction.
Abstract: We demonstrated coherent control of a quantum two-level system based on two-electron spin states in a double quantum dot, allowing state preparation, coherent manipulation, and projective readout. These techniques are based on rapid electrical control of the exchange interaction. Separating and later recombining a singlet spin state provided a measurement of the spin dephasing time, T2*, of E10 nanoseconds, limited by hyperfine interactions with the gallium arsenide host nuclei. Rabi oscillations of two-electron spin states were demonstrated, and spin-echo pulse sequences were used to suppress hyperfine-induced dephasing. Using these quantum control techniques, a coherence time for two-electron spin states exceeding 1 microsecond was observed.
2,789 citations
Book•
01 Jan 2005TL;DR: In this article, the authors provide an elementary introduction to the subject of quantum optics, the study of the quantum mechanical nature of light and its interaction with matter, and present a presentation almost entirely concerned with the quantized electromagnetic field.
Abstract: This book provides an elementary introduction to the subject of quantum optics, the study of the quantum mechanical nature of light and its interaction with matter. The presentation is almost entirely concerned with the quantized electromagnetic field. Topics covered include single-mode field quantization in a cavity, quantization of multimode fields, quantum phase, coherent states, quasi-probability distribution in phase space, atom-field interactions, the Jaynes-Cummings model, quantum coherence theory, beam splitters and interferometers, dissipative interactions, nonclassical field states with squeezing etc., 'Schrodinger cat' states, tests of local realism with entangled photons from down-conversion, experimental realizations of cavity quantum electrodynamics, trapped ions, decoherence, and some applications to quantum information processing, particularly quantum cryptography. The book contains many homework problems and an extensive bibliography. This text is designed for upper-level undergraduates taking courses in quantum optics who have already taken a course in quantum mechanics, and for first and second year graduate students.
1,404 citations
TL;DR: It is shown that spontaneous emission can coherently interfere with the continuum modes and gives interesting transport properties and analytical solutions are given.
Abstract: A two-level system coupled to a one-dimensional continuum is investigated By using a real-space model Hamiltonian, we show that spontaneous emission can coherently interfere with the continuum modes and gives interesting transport properties The technique is applied to various related problems with different configurations, and analytical solutions are given
458 citations
TL;DR: The behavior of H2+ in an intense oscillating field computed using the TDHF method with a STO-3G basis set reproduces the analytic solution for the two-state coherent excitation model.
Abstract: For molecules in high intensity oscillating electric fields, the time-dependent Hartree–Fock (TDHF) method is used to simulate the behavior of the electronic density prior to ionization. Since a perturbative approach is no longer valid at these intensities, the full TDHF equations are used to propagate the electronic density. A unitary transform approach is combined with the modified midpoint method to provide a stable and efficient algorithm to integrate these equations. The behavior of H2+ in an intense oscillating field computed using the TDHF method with a STO-3G basis set reproduces the analytic solution for the two-state coherent excitation model. For H2 with a 6-311++G(d,p) basis set, the TDHF results are nearly indistinguishable from calculations using the full time-dependent Schrodinger equation. In an oscillating field of 3.17 × 1013 W cm−2 and 456 nm, the molecular orbital energies, electron populations, and atomic charges of H2 follow the field adiabatically. As the field intensity is increased, the response becomes more complicated as a result of contributions from excited states. Simulations of N2 show even greater complexity, yet the average charge still follows the field adiabatically.
192 citations
TL;DR: In this paper, a single photon-added coherent state is obtained by the action of the photon creation operator on a coherent state and can thus be regarded as the result of the most elementary excitation process of a classical light field.
Abstract: When a single quantum of electromagnetic field excitation is added to the same spatiotemporal mode of a coherent state, a new field state is generated that exhibits intermediate properties between those of the two parents. Such a single-photon-added coherent state is obtained by the action of the photon creation operator on a coherent state and can thus be regarded as the result of the most elementary excitation process of a classical light field. Here we present and describe in depth the experimental realization of such states and their complete analysis by means of a novel ultrafast, time-domain, quantum homodyne tomography technique clearly revealing their nonclassical character.
182 citations
TL;DR: An efficient decoy-state protocol for practical quantum key distribution using coherent states that uses four intensities of different coherent light to achieve a good final key rate.
Abstract: We propose an efficient decoy-state protocol for practical quantum key distribution using coherent states. The protocol uses four intensities of different coherent light. A good final key rate is achieved by our protocol with typical parameters of existing practical setups, even with a very low channel transmittance.
165 citations
TL;DR: In this paper, a general method and geometrical picture is developed and shown to agree with effective action results, commonly derived through path integration, for perturbations around a harmonic oscillator ground state.
Abstract: In many situations, one can approximate the behavior of a quantum system, i.e. a wave function subject to a partial differential equation, by effective classical equations which are ordinary differential equations. A general method and geometrical picture is developed and shown to agree with effective action results, commonly derived through path integration, for perturbations around a harmonic oscillator ground state. The same methods are used to describe dynamical coherent states, which in turn provide means to compute quantum corrections to the symplectic structure of an effective system.
148 citations
TL;DR: It is shown how to quantize the spin chain by mapping its states to a bosonic lattice of finite length with sources and sinks of particles at the boundaries, which gives the correct description of semiclassical open strings ending on giant gravitons.
Abstract: We study an XXX open spin chain with variable number of sites, where the variability is introduced only at the boundaries. This model arises naturally in the study of giant gravitons in the anti-de Sitter-space/conformal field-theory correspondence. We show how to quantize the spin chain by mapping its states to a bosonic lattice of finite length with sources and sinks of particles at the boundaries. Using coherent states, we show how the Hamiltonian for the bosonic lattice gives the correct description of semiclassical open strings ending on giant gravitons.
134 citations
TL;DR: The coherence of core electrons in N2 is observed through a direct measurement of the interference exhibited in their emission, and the gradual transition to a symmetry-broken system of localized electrons is explored by comparing different isotope-substituted species.
Abstract: Because of inversion symmetry and particle exchange, all constituents of homonuclear diatomic molecules are in a quantum mechanically non-local coherent state; this includes the nuclei and deep-lying core electrons. Hence, the molecular photoemission can be regarded as a natural double-slit experiment: coherent electron emission originates from two identical sites, and should give rise to characteristic interference patterns. However, the quantum coherence is obscured if the two possible symmetry states of the electronic wavefunction ('gerade' and 'ungerade') are degenerate; the sum of the two exactly resembles the distinguishable, incoherent emission from two localized core sites. Here we observe the coherence of core electrons in N_2 through a direct measurement of the interference exhibited in their emission. We also explore the gradual transition to a symmetry-broken system of localized electrons by comparing different isotope-substituted species—a phenomenon analogous to the acquisition of partial 'which-way' information in macroscopic double-slit experiments.
133 citations
TL;DR: In this article, the authors investigated the nonclassicality of a photon-subtracted Gaussian field, which was produced in a recent experiment, using negativity of the Wigner function and the nonexistence of well-behaved positive P function.
Abstract: We investigate the nonclassicality of a photon-subtracted Gaussian field, which was produced in a recent experiment, using negativity of the Wigner function and the nonexistence of well-behaved positive P function. We obtain the condition to see negativity of the Wigner function for the case including the mixed Gaussian incoming field, the threshold photodetection and the inefficient homodyne measurement. We show how similar the photon-subtracted state is to a superposition of coherent states.
127 citations
TL;DR: It is shown that the single-clone fidelity of the optimal 1-to-infinity cloner is 1/2 and it is achieved by a Gaussian scheme and cannot be surpassed even with supplemental bound entangled states.
Abstract: We consider the optimal cloning of quantum coherent states with single-clone and joint fidelity as figures of merit. While the latter is maximized by a Gaussian cloner, the former is not: the optimal single-clone fidelity for a symmetric 1-to-2 cloner is 0.6826, compared to 2/3 in a Gaussian setting. This cloner can be realized with an optical parametric amplifier and certain non-Gaussian bimodal states. Finally, we show that the single-clone fidelity of the optimal 1-to-infinity cloner is 1/2. It is achieved by a Gaussian scheme and cannot be surpassed even with supplemental bound entangled states.
TL;DR: In this article, the decoherence of quantum states of continuous variable systems under the action of a quantum optical master equation resulting from the interaction with general Gaussian uncorrelated environments is quantified by relating it to the decay rates of various complementary measures of the quantum nature of a state, such as the purity, some non-classicality indicators in phase space, and, for two-mode states, entanglement measures and total correlations between the modes.
Abstract: We present a detailed report on the decoherence of quantum states of continuous variable systems under the action of a quantum optical master equation resulting from the interaction with general Gaussian uncorrelated environments. The rate of decoherence is quantified by relating it to the decay rates of various, complementary measures of the quantum nature of a state, such as the purity, some non-classicality indicators in phase space, and, for two-mode states, entanglement measures and total correlations between the modes. Different sets of physically relevant initial configurations are considered, including one- and two-mode Gaussian states, number states, and coherent superpositions. Our analysis shows that, generally, the use of initially squeezed configurations does not help to preserve the coherence of Gaussian states, whereas it can be effective in protecting coherent superpositions of both number states and Gaussian wavepackets.
TL;DR: In this article, the authors review the higher-order supersymmetric quantum mechanics (H-SUSY QM), which involves differential intertwining operators of order greater than one.
Abstract: We review the higher-order supersymmetric quantum mechanics (H-SUSY QM), which involves differential intertwining operators of order greater than one. The iterations of first-order SUSY transformations are used to derive in a simple way the higher-order case. The second order technique is addressed directly, and through this approach unexpected possibilities for designing spectra are uncovered. The formalism is applied to the harmonic oscillator: the corresponding H-SUSY partner Hamiltonians are ruled by polynomial Heisenberg algebras which allow a straight construction of the coherent states.
TL;DR: When a one-photon state is mixed with a (separate) weak coherent state at a beamsplitter, the probability for seeing one photon in each beam-plitter output approaches zero due to destructive interference as discussed by the authors.
Abstract: When a one-photon state is mixed with a (separate) weak coherent state at a beamsplitter the probability for seeing one photon in each beamsplitter output approaches zero due to destructive interference. We demonstrate this non-classical interference effect using pulse-gated single photons and weak mode-locked laser pulses.
TL;DR: In this article, the nonclassicality of a quantum state of the harmonic oscillator was investigated in terms of the normally ordered moments of quadratures of the oscillator, and inequalities were obtained that are equivalent to failure of the Glauber-Sudarshan $P$ function to be a probability density.
Abstract: Criteria for the nonclassicality of a quantum state of the harmonic oscillator are formulated in terms of normally ordered moments of quadratures. Inequalities are obtained that are equivalent to the failure of the Glauber-Sudarshan $P$ function to be a probability density. A possibility to measure the required moments is proposed.
TL;DR: In this paper, the pair-coherent states for a two-mode radiation field are known to belong to a family of states with non-Gaussian wave functions and the nature of quantum entanglement between the two modes and some features of non-classicality are studied.
Abstract: The pair-coherent states for a two-mode radiation field are known to belong to a family of states with non-Gaussian wavefunction. The nature of quantum entanglement between the two modes and some features of non-classicality are studied for such states. The existing criterion for inseparability are examined in the context of pair-coherent states.
TL;DR: In this paper, the superposition of two macroscopically distinguishable coherent states of a single-mode cavity field can be generated by a controllable interaction between a cavity field and a superconducting charge qubit.
Abstract: We propose how to generate macroscopic quantum superposition states using a microwave cavity containing a superconducting charge qubit Based on the measurement of charge states, we show that the superpositions of two macroscopically distinguishable coherent states of a single-mode cavity field can be generated by a controllable interaction between a cavity field and a charge qubit After such superpositions of the cavity field are created, the interaction can be switched off by the classical magnetic field, and there is no information transfer between the cavity field and the charge qubit We also discuss the generation of the superpositions of two squeezed coherent states
TL;DR: In this article, a scheme for optimal Gaussian cloning of optical coherent states is proposed and experimentally demonstrated, which is based entirely on simple linear optical elements and homodyne detection.
Abstract: A scheme for optimal Gaussian cloning of optical coherent states is proposed and experimentally demonstrated. Its optical realization is based entirely on simple linear optical elements and homodyne detection. The optimality of the presented scheme is limited only by detection inefficiencies. Experimentally, we achieved a cloning fidelity of about 65%, which almost touches the optimal value of $2/3$.
TL;DR: In this paper, the effects of gravitational induced uncertainty on quantum optics issues were considered and it was shown that it is impossible to have complete coherency and vanishing broadening in usual quantum optics, and that there is an additional wave packet broadening due to quantum gravitational effects.
TL;DR: In this article, the notion of semiclassical states is sharpened by clarifying two issues that appear to have been overlooked in the literature, and the group averaging procedure is applied to kinematical coherent states to obtain physical semiclassic states.
Abstract: The notion of semiclassical states is first sharpened by clarifying two issues that appear to have been overlooked in the literature. Systems with linear and quadratic constraints are then considered and the group averaging procedure is applied to kinematical coherent states to obtain physical semiclassical states. In the specific examples considered, the technique turns out to be surprisingly efficient, suggesting that it may well be possible to use kinematical structures to analyze the semiclassical behavior of physical states of an interesting class of constrained systems.
TL;DR: In this article, an all-optical scheme to generate superpositions of macroscopically distinguishable coherent states in traveling optical fields is presented. But the scheme is not suitable for quantum computing.
Abstract: We develop an all-optical scheme to generate superpositions of macroscopically distinguishable coherent states in traveling optical fields. It nondeterministically distills coherent-state superpositions (CSS's) with large amplitudes out of CSS's with small amplitudes using inefficient photon detection. The small CSS's required to produce CSS's with larger amplitudes are extremely well approximated by squeezed single photons. We discuss some remarkable features of this scheme: it effectively purifies mixed initial states emitted from inefficient single-photon sources and boosts negativity of Wigner functions of quantum states.
TL;DR: In this article, a scheme to engineer quantum superpositions of coherent states of propagating optical pulses was proposed, where multidimensional and multipartite cat states can be generated by reflecting coherent optical pulses successively from a single-atom cavity.
Abstract: We propose a scheme to engineer quantum superpositions of coherent states (``Schr\"odinger-cat states'') of propagating optical pulses. Multidimensional and multipartite cat states can be generated simply by reflecting coherent optical pulses successively from a single-atom cavity. The influences of various sources of noise, including atomic spontaneous emission and pulse-shape distortion, are characterized through detailed numerical simulation, which demonstrates the practicality of this scheme within the reach of current experimental technology.
TL;DR: Using the analytic representation of the so-called Gazeau-klauder coherent states (CSs), a new class of generalized CSs, namely the family of dual states associated with the states, can be constructed through viewing these states as temporally stable nonlinear CSs as discussed by the authors.
Abstract: Using the analytic representation of the so-called Gazeau–Klauder coherent states (CSs), we shall demonstrate that how a new class of generalized CSs, namely the family of dual states associated with theses states, can be constructed through viewing these states as temporally stable nonlinear CSs Also we find that the ladder operators, as well as the displacement type operator corresponding to these two pairs of generalized CSs, may be easily obtained using our formalism, without employing the supersymmetric quantum mechanics (SUSYQM) techniques Then, we have applied this method to some physical systems with known spectrum, such as Poschl–Teller, infinite well, Morse potential and hydrogenlike spectrum as some quantum mechanical systems Finally, we propose the generalized form of the Gazeau–Klauder CS and the corresponding dual family
TL;DR: In this article, a generalization of the leading-order matching of coherent state actions for semiclassical states on the super Yang-Mills and the superstring sides of the AdS/CFT duality to sectors with fermions was considered.
TL;DR: In this paper, the Cahill-Glauber approach for quantum mechanics on phase space is extended to the finite-dimensional case through the use of discrete coherent states, and properties and features of the continuous formalism are appropriately generalized.
Abstract: The Cahill–Glauber approach for quantum mechanics on phase space is extended to the finite-dimensional case through the use of discrete coherent states All properties and features of the continuous formalism are appropriately generalized The continuum results are promptly recovered as a limiting case The Jacobi theta functions are shown to have a prominent role in the context
TL;DR: In this article, the authors define what it means for a state in a convex cone of states on a space of observables to be generalized-entangled relative to a subspace of the observables, in a general ordered linear spaces framework for operational theories.
Abstract: We define what it means for a state in a convex cone of states on a space of observables to be generalized-entangled relative to a subspace of the observables, in a general ordered linear spaces framework for operational theories. This extends the notion of ordinary entanglement in quantum information theory to a much more general framework. Some important special cases are described, in which the distinguished observables are subspaces of the observables of a quantum system, leading to results like the identification of generalized unentangled states with Lie-group-theoretic coherent states when the special observables form an irreducibly represented Lie algebra. Some open problems, including that of generalizing the semigroup of local operations with classical communication to the convex cones case, are discussed.
TL;DR: In this article, it is shown that the inflationary primordial spectra retains quantum properties such as a squeezed spread in some direction of phase space, nonvanishing off-diagonal matrix elements, non-P$ representability and nonseparability.
Abstract: It is generally expected that decoherence processes will erase the quantum properties of the inflationary primordial spectra. However, given the weakness of gravitational interactions, one might end up with a distribution which is only partially decohered. Below a certain critical change, we show that the inflationary distribution retains quantum properties. We identify four of these: a squeezed spread in some direction of phase space, nonvanishing off-diagonal matrix elements, and two properties used in quantum optics called non-$P$ representability and nonseparability. The last two are necessary conditions to violate Bell's inequalities. The critical value above which all these properties are lost is associated with the ``grain`` of coherent states. The corresponding value of the entropy is equal to half the maximal (thermal) value. Moreover it coincides with the entropy of the effective distribution obtained by neglecting the decaying modes. By considering backreaction effects, we also provide an upper bound for this entropy at the onset of the radiation dominated era.
TL;DR: In this article, the authors proposed a theoretical scheme to generate various families of nonlinear (f-deformed) coherent states of the radiation field in a micromaser.
Abstract: In this paper we propose a theoretical scheme to show the possibility of
generating various families of nonlinear (f-deformed) coherent states of the
radiation field in a micromaser. We show that these states can be provided
in a lossless micromaser cavity under the weak Jaynes-Cummings interaction
with intensity–dependent coupling of large number of individually injected
two-level atoms in a coherent superposition of the upper and lower states.
In particular, we show that the so-called nonlinear squeezed vacuum and
nonlinear squeezed first excited states, as well as the even and odd
nonlinear coherent states can be generated in a two-photon micromaser.
TL;DR: In this article, a cavity quantum electrodynamics (CQED) experiment is proposed to test the violation of a Bell-type inequality using non-local mesoscopic states (NLMS), which involve coherent field superpositions stored in two spatially-separated high-Q cavities.
Abstract: We propose a cavity quantum electrodynamics (CQED) experiment to test the violation of a Bell-type inequality using non-local mesoscopic states (NLMS). These states involve coherent field superpositions stored in two spatially-separated high-Q cavities. The inequality is expressed in terms of the measured Wigner function of the entangled two-field-mode system at four points in phase space, as proposed in [Banaszek and Wodkiewicz, Phys. Rev. Lett. 82, 2009 (1999)]. We examine the production of these entangled NLMS and the measurement of their Wigner function. The experiment involves circular Rydberg atoms and superconducting millimeter-wave cavities. We present a detailed numerical study of the optimal inequality violation and of the effect of decoherence. We discuss the range of experimental parameters making it possible to observe a locality violation and show that they correspond to realistic, albeit demanding, conditions.
TL;DR: In this paper, the Gazeau-Klauder vector coherent states (GKCS) were constructed for the case of a two-dimensional electron placed in a constant magnetic field, orthogonal to the plane which contains the electron.
Abstract: In the spirit of some earlier work on the construction of vector coherent states (VCS) over matrix domains, we compute here such states associated to some physical Hamiltonians. In particular, we construct vector coherent states of the Gazeau–Klauder type. As a related problem, we also suggest a way to handle degeneracies in the Hamiltonian for building coherent states. Specific physical Hamiltonians studied include a single photon mode interacting with a pair of fermions, a Hamiltonian involving a single boson and a single fermion, a charged particle in a three-dimensional harmonic force field and the case of a two-dimensional electron placed in a constant magnetic field, orthogonal to the plane which contains the electron. In this last example, which is related to the fractional quantum Hall effect, an interesting modular structure emerges for two underlying von Neumann algebras, related to opposite directions of the magnetic field. This leads to the existence of coherent states built out of Kubo-Martin-Schwinger (KMS) states for the system.