The evolutional optical behaviours (turn-on dynamics) of a four-level N-configuration atomic system are considered based on the transient solution to the equations of motion of atomic probability amplitudes. It is shown that the quantum interference between the signal and control fields can lead to the controllable absorption and transparency properties of the atomic vapour. One of the most remarkable properties of the present scheme is that the absorption (or transmittance) of the probe light in the atomic vapour depends on the intensity ratio of the signal field to the control field, and thus the tunable optical features (transparency or opaqueness to the probe light) can be realized by tuning the quantum interferences between the signal and control fields. The present mechanism can be applicable to designs of some new photonic and quantum optical devices such as logic and functional devices as well as optical switches. Two typical photonic logic gates (NOT and NOR gates) designed based on the tunable four-level optical responses are presented as illustrative examples.
A layered Korringa-Kohn-Rostoker method is exploited to study the subwavelength imaging through a slab of rods-in-air photonic crystal. Both the intensity and phase spectra of transmission are investigated. The high transmission of evanescent waves arises due to the excitation of some slab-guided bound modes and the high coupling between the incident evanescent field and some bulk-guided Bloch modes. Through a study of the phase spectrum of transmission, it is shown that the self-collimation effect occurs at smaller incident angles whereas the negative refraction effect occurs at relatively larger incident angles. The existence of imaging aberrations is also explained with the phase spectrum. The focusing properties of the photonic crystal slab are mainly due to the negative-refraction effect for large incident angles, rather than the self-collimation effect.
A new mechanism for realizing negative permeability with a three-level ladder-type atomic (or molecular) system at microwave frequency is suggested. The explicit expressions for the magnetic permeability of both steady and transient cases are presented. Compared with the previous schemes to realize negative permeability within the framework of classical electromagnetic theory, the most remarkable feature in the present mechanism is that it can realize the isotropic material with negative permeability. Such a permeability can be controllably manipulated by external coupling fields and could lead to potential applications in quantum optical devices.
A new scenario for realizing a gain left-handed atomic vapor medium based on both dressed-state mixed-parity transitions (for simultaneous electric-and magnetic-dipole resonance) and incoherently-pumped population transfer (for high gain amplification) in a four-level atomic system is suggested. Dressed-state assisted simultaneous electric-and magnetic-dipole allowed transitions in such a four-level atomic system (of, e.g., neutral alkali-metal atoms such as lithium and potassium atoms) are utilized for achieving negative refractive index with impedance perfectly matched to vacuum. The attractive features of the present scenario include: i) three-dimensionally isotropic negative indices; ii) incoherent-gain wave amplification; iii) perfect impedance matching to vacuum. All these important properties of the double-negative medium would have potential applications in designing some optical and photonic devices, including particularly subwavelength focusing system and negative-index superlens for perfect imaging.
Multilevel quantum coherence and its quantum-vacuum counterpart, where a three-level dark state is involved, are suggested in order to achieve new photonic and quantum optical applications. It is shown that such a three-level dark state in a four-level tripod-configuration atomic system consists of three lower levels, where constructive and destructive quantum interference between two control transitions (driven by two control fields) arises. We point out that the controllable optical response due to the double-control tunable quantum interference can be utilized to design some fascinating new photonic devices such as logic gates, photonic transistors and switches at quantum level. A single-photon two-input XOR logic gate (in which the incident gate photons are the individual light quanta of the two control fields) based on such an effect of optical switching control with an EIT (electromagnetically induced transparency) microcavity is suggested as an illustrative example of the application of the dark-state manipulation via the double-control quantum interference. The present work would open up possibility of new applications in both fundamental physics (e.g., field quantization and relevant quantum optical effects in artificial systems that can mimic atomic energy levels) and applied physics (e.g., photonic devices such as integrated optical circuits at quantum level).
A new scheme for realizing a nonadiabatic conditional geometric phase shift via a noncoplanar (coiled) fibre system is presented. It is shown that the effective Hamiltonian that describes the interaction of polarized photons with a fibre medium is just the Wang-Matsumoto type of Hamiltonian. This, therefore, means that the coiled fibre system may be an ideal implementation for realizing the nonadiabatic geometric phase gates involved in the topological quantum computation. A remarkable feature of the present method is that it can automatically meet the conditions and requirements proposed in the Wang-Matsumoto nuclear magnetic resonance (NMR) scheme: specifically, (i) in the coiled fibre system, the dynamical phase of photon wavefunction caused by the interaction Hamiltonian automatically vanishes; (ii) the Wang-Matsumoto requirement for the parameters in the Wang-Matsumoto NMR Hamiltonian can be exactly satisfied automatically in such a fibre system; and (iii) the conditional initial state can be easily achieved by manipulating the initial wave vector of polarized photons.
In a conventional formalism of acoustics, acoustic pressure p and velocity field u are used for characterizing acoustic waves propagating inside elastic/acoustic materials. We shall treat some fundamental problems relevant to acoustic wave propagation alternatively by using canonical acoustics (a more concise and compact formalism of acoustic dynamics), in which an acoustic scalar potential and an acoustic vector potential (Phi, V), instead of the conventional acoustic field quantities such as acoustic pressure and velocity field (p, u) for characterizing acoustic waves, have been defined as the fundamental variables. The canonical formalism of the acoustic energy-momentum tensor is derived in terms of the acoustic potentials. Both the acoustic Hamiltonian density and the acoustic Lagrangian density have been defined, and based on this formulation, the acoustic wave quantization in a fluid is also developed. Such a formalism of acoustic potentials is employed to the problem of negative-mass-density assisted surface acoustic wave that is a highly localized surface bound state (an eigenstate of the acoustic wave equations). Since such a surface acoustic wave can be strongly confined to an interface between an acoustic metamaterial (e.g., fluid-solid composite structures with a negative dynamical mass density) and an ordinary material (with a positive mass density), it will give rise to an effect of acoustic field enhancement on the acoustic interface, and would have potential applications in acoustic device design for acoustic wave control.
An experimentally feasible scheme of a four-level atomic system driven by two microwaves and one optical field is suggested in order to realize destructive and constructive quantum interference between the two microwave-driven transition pathways and hence to coherently manipulate the applied optical field. The destructive quantum interference can be switched to the constructive interference and vice versa if one tunes the intensity ratio of the two microwaves. Such an effect of tunable optical response based on microwave quantum interference may have some potential applications to the technique for designing new photonic and quantum optical devices, e. g., photonic logic gates, optical switches, and photonic transistors.
A three-level system with pumped electric-dipole allowed transition for incoherent-gain negative permittivity is suggested in order to realize dispersion-sensitive surface plasmon wave. The present surface wave modes occurring at an interface between an incoherent-gain negative-permittivity "plasmonic" medium (e.g., a semiconductor-quantum-dot material) and an ordinary dielectric can be amplified due to population transfer in the three-level system of the negative-permittivity medium. The issues of complex phase constant and the attenuation coefficients in the adjacent media are considered for addressing the problem of loss compensation of surface plasmon wave. The effect of incoherent-gain amplification exhibited by the dispersion-sensitive surface plasmon wave can be utilized for designing new quantum optical and photonic devices, e.g., photonic transistors and logic gates.
A scenario for realizing simultaneously negative permittivity and permeability of a two-photon quantum-coherent atomic vapor is suggested in order to achieve a left-handed atomic medium with a negative refractive index. One of the remarkable features of the present scheme is that it can lead to a controllable manipulation of the negative refractive index of the atomic vapor. Since the electric- and magnetic-dipole allowed transitions of atoms can be excited by visible and infrared lightwaves, the refractive index of the atomic vapor can exhibit its negative refractive index at optical and near-optical frequency bands. This may be a new scheme to fabricate a negatively refracting material based on the quantum optical approach. Such a three-dimensionally isotropic negative refractive index at visible and infrared wavelengths induced by the two-photon-resonant quantum coherence would find a potential application in fabrication of superlenses for perfect imaging and subwavelength focusing.
Since previous negative-index atomic media based on quantum optical approaches are highly lossy, a proposal for realizing a three-dimensionally isotropic left-handed atomic vapor medium is suggested based on a mechanism of incoherent gain assisted atomic transitions. Two three-level atomic systems are utilized for producing simultaneously negative permittivity and negative permeability, respectively, in the same frequency band. We suggest that fine and hyperfine level transitions of atoms (e.g., a hyperfine level transition in a hydrogen atomic system and a fine level transition in an alkali-metal atomic system) would be applicable to realization of such a negatively refracting atomic vapor. The attractive features of the present scenario include: i) three-dimensionally isotropic negative indices; ii) incoherent gain wave amplification in the negative-index atomic vapor; iii) tunable negative indices depending upon external fields. Such a left-handed quantum optical medium can serve as a supporting substrate for lossy negative-index materials for loss compensation. It can also be used in designing new quantum optical and photonic devices (e.g., a subwavelength focusing system and a negative-index superlens for perfect imaging) because of its attractive properties of three-dimensional isotropy and high-gain wave amplification.
An experimentally feasible configuration of a prism coupler with an electromagnetically-induced-transparency (EIT) medium layer, e.g., a semiconductor-quantum-dot (SQD) medium, deposited upon its prism base is suggested for generating tunable surface-plasmon-polariton resonance. Such surface-plasmon-polariton resonance and optical excitation of a surface plasmon wave can be manipulated by switchable quantum interference among SQD multilevel transitions driven by two external control fields. When an incident probe field is coupled into a surface plasmon wave excitation mode, the surface-plasmon-polariton (SPP) resonance at the interface between the SQD medium layer and the substrate will arise, and the quantum-coherently controllable reflection spectrum of the probe field on the prism base can be achieved. In this process, destructive and constructive quantum interference (determined by the intensity ratio of the two external control fields) in the SQD multilevel system plays a key role for achieving the tunable reflection spectrum. The EIT-based surface-plasmon-polariton resonance presented here will have three characteristics (some of them would be attractive): (i) switchable quantum interference exhibited by surface plasmon wave excitation, (ii) quantum-coherently controllable surface plasmon polaritons by external optical fields, (iii) surface wave sensitive to dispersion of the SQD quantum coherent medium. Such an effect of controllable optical response based on the quantum-interference switchable surface-plasmon-polariton resonance in the EIT-prism coupler may find some potential applications in design of new photonic and quantum optical devices.
A three-dimensionally isotropic negative permeability of a neutral alkali-metal atomic medium, in which a fine-structure magnetic dipole-allowed transition in terahertz band is pumped for population transfer (and hence incoherent gain for negative permeability can be realized), is suggested based on quantum optical approach. The effects relevant to photonic resonance and quantum coherence are involved in the present quantum optical scheme of pumped magnetic-dipole allowed transition. The incoherent-gain assisted atomic medium (with fine-structure transition involved) may have some attractive features, e. g., three-dimensionally isotropic and homogeneous negative permeability for high-gain wave amplification at terahertz frequencies. Such a gain-assisted negative-permeability medium can be a candidate of magnetically resonant materials for artificial composite metamaterials, e.g., it may serve as a substrate of lossy negative-index materials for loss compensation or as a supporting medium for high-gain amplification of a TE-mode surface plasmon-like wave.
A new scenario to realize negative refraction with a photonic-resonant vapor material that can exhibit both electric and magnetic responses via multilevel quantum coherence is suggested. Compared with the previous method of artificial composite metamaterial, where the mechanism was considered by means of classical electromagnetic theory and the materials produced have anisotropic millimetre-scale composite structures, the present scheme suggested within the framework of quantum optics can be used to design and fabricate isotropic negatively-refracting materials with atomic-scale microscopic structure units. Such an advantage may lead to a potentially important application in the techniques of superlens and perfect imaging.
A new mechanism for realizing negative refractive index with a four-level atomic system is suggested. The explicit expressions for the electric permittivity and magnetic permeability at probe frequency are presented. It is shown that there is a frequency band in which the four-level photonic-resonant atomic vapour may exhibit simultaneously negative permittivity and permeability, and that such an atomic vapour may become a left-handed material ( negatively refracting medium). Compared with the previous schemes to realize negative refraction within the framework of classical electromagnetic theory, the most remarkable features of the present scenario are as follows: ( i) isotropic material with microscopic structure units at atomic-scale level, ( ii) negative refraction in visible and infrared frequency bands, ( iii) controllable manipulation by external fields and ( iv) based on quantum coherence in a multilevel atomic system.
A new scheme to realize simultaneously negative permittivity and permeability in a coherent atomic vapor medium (photonic-resonant material) via a coherent driving mechanism is suggested. It is verified that the atomic system coherently driven by a strong optical field will give rise to a negative refractive index in certain probe frequency ranges. One of the most remarkable features of the present scheme is such that a slab fabricated by the left-handed vapor medium is an ideal candidate for designing perfect lenses since the photonic-resonant atomic vapor cannot only exhibit an isotropic negative refractive index, but also provide a good impedance match at the air-medium interfaces.
A tripod-configuration four-level atomic system can exhibit nontrivial quantum destructive and constructive interference that could manipulate the optical response of an atomic vapour. It is shown that the tunable double-control electromagnetically induced transparency (EIT) would be controlled via the quantum interference between two control fields interacting with the present atomic system. If a metallic waveguide is filled with such a double-control four-level atomic vapour, the quantum vacuum mode structure in the present EIT waveguide would have a novel influence on the atomic spontaneous emission decay (and hence on the EIT optical behavior). As the waveguide dimension change (i.e., the change in length scale of cross section of waveguide) can vary the vacuum mode structure, which can lead to spontaneous emission enhancement or inhibition, the optical response (including absorption and transparency induced by the tunable double-control quantum destructive and constructive interference) of the atomic vapour in the waveguide is quite sensitive to small change in the waveguide dimension caused by external environmental factors (such as electric signal voltage, environmental temperature change and acoustic pressure). The sensitive optical response based on the mechanisms of both double-control quantum interference and quantum-vacuum manipulation presented here may have some potential applications to the technique for designing new photonic and quantum optical devices.
A new quantum optical mechanism to realize simultaneously negative electric permittivity and magnetic permeability is suggested. In order to obtain a negative permeability, we choose a proper atomic configuration that can dramatically enhance the contribution of the magnetic- dipole allowed transition via the atomic phase coherence. It is shown that the atomic system chosen with proper optical parameters can give rise to striking electromagnetic responses (leading to a negative refractive index) and that the atomic vapour becomes a left-handed medium in an optical frequency band. Differing from the previous schemes of artificial composite metamaterials (based on classical electromagnetic theory) to achieve the left-handed materials, which consist of anisotropic millimetre- scale composite structure units, the left- handed atomic vapour presented here is isotropic and homogeneous at the atomic-scale level. Such an advantage may be valuable in realizing the superlens (and hence perfect image) with left- handed atomic vapour.
A strongly confined acoustic surface wave is an acoustic eigenstate localized on an interface between an ordinary acoustic medium and an acoustic metamaterial with negative effective dynamical mass density. Here we show that there is a new unconventional acoustic surface wave sustained by a parity-time (PT)-symmetric acoustic interface system, in which the negative effective dynamical mass density is not required (but the effective mass densities of the two adjacent acoustic media should fulfill the parity-time symmetry). Such an acoustic parity-time symmetry in the effective mass density can be used to manipulate acoustic wave propagation, e. g., it can exhibit both weak and strong confinement of the unusual PT -symmetric acoustic surface wave, and can offer mechanisms for designing acoustic metamaterial devices that would have specific functions in controlling and guiding acoustic wave, including acoustic field enhancement and extraordinary acoustic transmission.
An experimentally feasible and promising scheme for realizing simultaneously negative permittivity and permeability in a single-photon off-resonant atomic vapor is suggested by taking full advantage of the mechanism of two-photon resonance that is assisted by atomic phase coherence. The present quantum-coherent atomic vapor can exhibit three-dimensionally isotropic negative refractive index (NRI) at visible and near-infrared wavelengths, and would find potential applications in design of NRI-based quantum optical and photonic devices.
An incoherent-gain prism coupler that can lead to enhanced total reflection is suggested by taking full advantage of pumped electric-dipole allowed transition that leads to gain-assisted negative permittivity. The tunable reflection spectrum of the prism coupler is quite sensitive to frequency detuning (e.g., 10(7) times that in conventional metal-substrate prism couplers) since the incoherent-gain optical response presented here results from atomic dipole-allowed transition. The present gain-assisted prism coupler, which can exhibit an unusual effect of dispersion-sensitive tunable reflection enhancement, has potential applications in design of new quantum optical and photonic devices, e.g., frequency-sensitive optical switches and photonic transistors.
it is demonstrated that many novel vacuum effects will be caused if an anisotropic electromagnetic environment, which can break the universal symmetry of vacuum, is achieved. It is thus possible for the momentum to be transferred from the vacuum zero-point field to the anisotropic electromagnetic media. In addition to the effect considered by Feigel more recently [A. Feigel, Phys. Rev. Lett. 92 (2004) 020404], there may exist another vacuum-fluctuation contribution to the momentum of a medium. Such an effect has a relativistic origin (resulting from the relativistic transformation of the optical constants), which, however, was not taken into account by Feigel.
The breaking of universal symmetry of electromagnetic field distribution in an anisotropic magnetoelectric material will give rise to nonzero vacuum momentum. This may lead to the transfer of momentum between the anisotropic quantum vacuum and the magnetoelectric material. Very recently, Feigel considered the quantum vacuum contribution to the momentum transfer effect [Phys. Rev. Lett. 92 (2004) 020404]. An alternative approach is proposed based on the eigenvector equation of electromagnetic field to calculate the total mechanical contribution of all anisotropic quantum-vacuum modes to the material momentum. It is suggested that the said macroscopic mechanical effect of quantum vacuum on the anisotropic material can be detected by current technology (e. g. fiber optical sensor), which can measure nanoscale velocity. Physical mechanism of such quantum vacuum effects and potential applications are discussed.
A scheme of double-negative left-handed atomic vapor medium based on dressed-state assisted simultaneous electric and magnetic resonances is suggested. In this mechanism, simultaneous electric-and magnetic-dipole allowed transitions of atoms are driven by an optical wave by taking full advantage of both mixed-parity dressed-state assisted resonance and incoherent population pumping in a quantum-coherent atomic medium (e.g., alkali-metal atomic vapor). Since the simultaneously negative permittivity and permeability can be achieved in a same frequency band, such an atomic vapor will exhibit an incoherent-gain double-negative refractive index that is three-dimensionally isotropic and homogeneous. The imaginary part of the negative refractive index of the present atomic vapor would be drastically suppressed or would become negative because of loss compensation through incoherent population transfer. The quantum-coherent left-handed atomic vapor presented here will have four characteristics: i) three-dimensionally isotropic and homogeneous negative refractive index, ii) double-negative atomic medium at visible (and infrared) wavelengths, iii) tunable negative refractive index based on dressed-state quantum coherence, and iv) high gain due to incoherent pumping action.
We study the quantum-vacuum geometric phases resulting from the vacuum fluctuation of photon fields in a Tomita-Chiao-Wu noncoplanar curved fibre system, and suggest a scheme to test for the potential existence of such a vacuum effect. Since the signs of the quantum-vacuum geometric phases of left- and right-handed (LRH) circularly polarized light are opposite, the sum of the geometric phases at the vacuum level is necessarily zero in the fibre experiments performed previously by other authors. By using the present approach where a fibre made of gyroelectric media is employed, the quantum-vacuum geometric phases of LRH light cannot be exactly cancelled, and it may therefore be possible to test this experimentally.
A chiral medium can create an anisotropic electromagnetic environment, which leads to anisotropic quantum-vacuum fields (and observable quantum-vacuum effects). As the noncompensation effect of a pair of counterpropagating (and counterpolarized) vacuum modes will arise in the chiral medium, the physical effects resulting from the quantum-vacuum fluctuation of left- and right-handed polarized modes will no longer be exactly canceled. This may lead to an observable quantum vacuum contribution to the Berry phases of circularly polarized modes in a time-dependent quantum system (e.g., a coiled light propagating in a noncoplanarly curved fiber). A scheme to separate the quantum-vacuum Berry phase of one polarized mode from another by using a chiral-medium fiber is suggested, and the time evolution of the vacuum zero-point energy in a coiled fiber is considered.
The oscillator algebra of Pegg-Barnett (P-B) oscillator with a finite-dimensional number-state space is considered. It is found that such a finite-dimensional oscillator possesses an su(n) Lie algebraic structure. A so-called supersymmetric P-B oscillator is suggested, and some related topics (such as the algebraic structure and the occupation number operator of the supersymmetric P-B oscillator) are briefly discussed. In addition, as one of the applications of the P-B quantization, a potential formula for the masses of charged leptons, which agrees reasonably well with the experimental values, is constructed based on the concept of supersymmetric P-B oscillator.
An anisotropic electromagnetic environment that can be created inside a Faraday chiral material may cause breaking of the universal symmetry of vacuum mode structure and hence lead to a nonzero electromagnetic momentum density of the quantum vacuum. A novel quantum vacuum effect (i.e., transfer of linear momentum from an anisotropic quantum-vacuum fluctuation field to a Faraday chiral material) is predicted. This is a macroscopic quantum vacuum mechanical effect that may provide us with new insight into the electromagnetic structures of quantum vacuum fluctuation fields inside anisotropic artificial materials.
The possibility to realize a negative refractive index in gyrotropically magnetoelectric materials is studied. Since the Tellegen (nonreciprocity) parameter may probably dramatically reduce the refractive indices, the negative refractive indices of a gyrotropic chiral material with positive permittivity and permeability can be achieved. By using the concept of equivalent isotropic medium, the respective negative equivalent permittivity and permeability corresponding to the eigenmodes inside the anisotropic material can be derived. This is a scheme to realize the negative refractive index (and hence the backward wave propagation) in artificial composite materials. Besides this scheme, we consider an alternative way to realize negative refraction by means of a magnetoelectrically anisotropic material.
The nonanalytic property of metric resulting from the presence of gravitomagnetic monopoles is considered. The curvature tensors, dual curvature tensors, dual Einstein tensor (and hence the gravitational field equation of gravitomagnetic matter) expressed in terms of nonanalytic metric are analyzed. It is shown that the spinor gravitomagnetic monopole may be one of the potential origins of the cosmological constant. An alternative approach to the cosmological constant problem is thus proposed based on the concept of gravitomagnetic monopole.
In this Letter the expression for the refractive index of de Broglie wave in the presence of a potential field is obtained and based on this, the physical meanings of negative index of refraction is revealed. We demonstrate that the electromagnetic wave propagation in a left-handed medium with negative refractive index behaves just like that of antiphotons, which is required of the complex vector field theory. It is believed that the complex vector field theory is helpful in considering the wave propagation and photonic band gap structures in the left-handed medium photonic crystals with a periodicity in negative and positive indices of refraction.
The author of this thesis concentrates his attention on quantum optical properties of some artificial electromagnetic media, such as quantum coherent atomic vapors (various multilevel electromagnetically induced transparency vapors) and negative refractive index materials, and suggests some possible ways to manipulate wave propagations inside the artificial electromagnetic materials based on quantum coherence and quantum vacuum effects. In Chapters 1 and 2, the author reviews the previous papers on quantum coherence as well as the relevant work such as electromagnetically induced transparency (EIT), atomic population trapping and their various applications. The basic concepts of quantum coherence (atomic phase coherence, quantum interferences within atomic energy levels) and quantum vacuum are introduced, and the theoretical formulations for treating wave propagations in quantum coherent media are presented. In Chapter 3, the author considers three topics on the manipulation of light propagations via quantum coherence and quantum interferences: i) the evolutional optical behaviors (turn-on dynamics) of a four-level N-configuration atomic system is studied and the tunable optical behavior that depends on the intensity ratio of the signal field to the control field is considered. Some typical photonic logic gates (e.g. NOT and NOR gates) are designed based on the tunable four-level optical responses of the N-configuration atomic system; ii) the destructive and constructive quantum interferences between two control transitions (driven by the control fields) in a tripod-type four-level system is suggested. The double-control quantum interferences can be utilized to realize some photonic devices such as the logic-gate devices, e.g., NOT, OR, NOR and EXNOR gates; iii) some new quantum coherent schemes (using EIT and dressed-state mixed-parity transitions) for realizing negative refractive indices are proposed. The most remarkable characteristic (and advantage) of the present scenarios is such that the isotropic left-handed media (with microscopic structure units at the atomic level) in the optical frequency band can be achieved. Quantum vacuum (the ground state of quantized fields) can exhibit many interesting effects. In Chapter 4, we investigate two quantum-vacuum effects in artificial materials: i) the anisotropic distribution of quantum-vacuum momentum density in a moving electromagnetic medium; ii) the angular momentum transfer between quantum vacuum and anisotropic medium. Such quantum-vacuum macroscopic mechanical effects could be detected by current technology, e.g., the so-called fiber optical sensor that can measure motion with nanoscale sensitivity. We expect that these vacuum effects could be utilized to develop sensitive sensor techniques or to design new quantum optical and photonic devices.In Chapter 5, the author suggests some interesting effects due to the combination of quantum coherence and quantum vacuum, i.e., the quantum coherent effects, in which the quantum-vacuum fluctuation field is involved. Two topics are addressed: i) spontaneous emission inhibition due to quantum interference in a three-level system; ii) quantum light-induced guiding potentials for coherent manipulation of atomic matter waves (containing multilevel atoms). These quantum guiding potentials could be utilized to cool and trap atoms, and may be used for the development of new techniques of atom fibers and atom chips, where the coherent manipulation of atomic matter waves is needed.In Chapter 6, we conclude this thesis with some remarks, briefly discuss new work that deserves further consideration in the future, and present a guide to the previously published papers by us.
Phase coherence in atoms and semiconductor quantum dots driven by light fields are extremely sensitive to probe field frequency, and the corresponding optical responses can be controllably manipulated by the applied external control light fields (i.e., controlling one light with the other lights via atomic phase coherence or quantum interference in multilevel transitions). Some theoretical scenarios of '‘quantumcoherent plasmonics’' have been developed on the basis of such frequencysensitive and fieldcontrolled optical effects. For example, an experimentally feasible configuration of prism coupler with an EIT (electromagnetically induced transparency) medium layer deposited upon its prism base is suggested for generating tunable surfaceplasmonlike resonance via switchable quantum interference among multilevel transitions driven by control fields. Since the surfaceplasmonlike resonance at the interface between the EIT layer and the bounding medium arises, and an incident probe field is then coupled into surfaceplasmonlike excitation modes, the quantumcoherently controllable reflection spectrum of the probe field on the prism base can be achieved because of destructive and constructive quantum interference (determined by the intensity ratio of the external control fields) occurring in the multilevel system, e.g., atom and quantum dot (artificial atom) that can exhibit quantum coherent effects. In this chapter, we will address the following topics of '‘quantumcoherent plasmonics’': 1) Tunable attenuated total reflection (ATR) in an EITprism coupler via quantum interference of a fourlevel atomic system; ii) Dispersionsensitive surface plasmon wave assisted by incoherent gain; iii) A threedimensionally isotropic bulk quantumcoherent negativepermeability medium with pumped magneticdipole hyperfine transition; iv) Dressedstate assisted mixedparity transition between two atomic levels; v) A doublenegative medium assisted by twophoton quantum coherence. In addition, we also suggest some alternative quantum optical schemes for realizing negative optical indices aiming at supporting surface plasmon modes, e.g., '‘threelevel simultaneous electric and magnetic resonance’' and '‘simultaneously negative permittivity and permeability via mixedparity transition’'. Such quantumcoherent lefthanded media would have three fascinating characteristics: i) negative refractive index at visible/infrared frequencies, ii) threedimensionally isotropic negative refractive index (this would lead to a potential application in fabrication of superlenses for perfect imaging and subwavelength focusing), and iii) tunable negative refractive index that depends on the Rabi frequency of the incident propagating light. Therefore, the present intriguing effects (and properties) based on quantum coherent control can be employed to designs of new photonic and quantum optical devices that make use of the quantum coherence to manipulate electromagnetic waves.
The connection between the quantum-vacuum geometric phases (which originates from the vacuum zero-point electromagnetic fluctuation) and the non-normal order for operator product is considered in the present paper. In order to investigate this physically interesting geometric phases at quantum-vacuum level, we suggest an experimentally feasible scheme to test it by means of a noncoplanarly curved fiber made of gyrotropic media. A remarkable feature of the present experimental realization is that one can easily extract the nonvanishing and nontrivial quantum-vacuum geometric phases of left- and/or right-handed circularly polarized light from the vanishing and trivial total quantum-vacuum geometric phases. Since the normal-order procedure may remove globally the vacuum energy of time-dependent quantum systems, the potential physical vacuum effects (e.g., quantum-vacuum geometric phases) may also be removed by this procedure. Thus the detection of the geometric phases at quantum-vacuum level may answer whether the normal-order technique is valid or not in the time-dependent quantum field theory.
An EIT (electromagnetically induced transparency)-based prism coupler is suggested for realizing tunable reflection spectrum via quantum coherence of phases in a multilevel system, where destructive and constructive quantum interference will occur among multilevel transition pathways that are driven by two external control fields. In this prism coupler, a semiconductor-quantum-dot (SQD) medium layer, which can exhibit EIT and relevant quantum coherent effects, bounds the prism base, and the two external control fields are used to manipulate the probe field and the excited surface plasmon wave (on the SQD layer surface). Then the surface plasmon wave modes, which are generated by the probe field incident into this multilevel SQD medium layer, can be coherently tunable through the switchable quantum interference (destructive and constructive quantum interference) among the energy levels in the SQD systems. Such switchable quantum interference can be realized if we tune the intensities (i.e., adjust a proper intensity ratio) of the two control fields that drive the SQD multilevel EIT system. New switchable photonic devices, which could find applications in photonic microcircuits as well as some areas in integrated optical circuits, could be designed based on this quantum-interference switchable surface plasmon resonance.
The su(n) Lie algebraic structure of the Pegg-Barnett oscillator that possesses a finite-dimensional number-state space is demonstrated. The supersymmetric generalization of the Pegg-Barnett oscillator is suggested. It is shown that such a supersymmetric Pegg-Barnett oscillator may have some potential applications, e.g., the mass spectrum of the charged leptons.
The evolutional optical behaviours (turn-on dynamics) of a four-level double-control tripod-configuration (electromagnetically induced transparency) system are considered based on the transient solution to the equation of motion of the probability amplitudes of the atomic levels. As the most remarkable property (quantum interference between the two control transitions) will arise in the present tripod-configuration system, the transient evolution of the permittivity in cases of both destructive and constructive quantum interferences is presented. It can be shown that the four-level double-control vapour can become a destructive-interference medium, (exhibiting a two-level resonant absorption) and a constructive-interference medium, (exhibiting transparency to the probe field), respectively, under certain conditions ( related to the ratio of the two control field intensities). The present double-control scenario can be applicable to designs of some new photonic and quantum optical devices such as logic and functional devices (logic gate circuits) and the key component of the technology of quantum coherent information storage.
A new approach is suggested to realize negative magnetic permeability that follows directly from quantum mechanics. It is shown that a Delta-type three-level atomic system with proper atomic parameters can give rise to striking magnetic responses, which could exhibit negative permeability in an optical frequency band. Both steady and transient behaviors of the magnetic permeability in the atomic vapor are studied. The present negative-permeability vapor could be mixed with a quantum coherent vapor whose electric permittivity is negative. Such a mixed vapor may give an isotropic left-handed vapor medium at the atomic-scale level.
Exact solutions to the time-dependent Schrodinger equation that governs the spiral motions of spinning particles are obtained, and the geometric phases that can be written as path integral of the vector potential of gravitomagnetic monopole (dual mass) are studied. Two illustrative examples of the confined spinning particles (e. g. a photon moving in a helical fiber and an electron confined by a planar radial electric field) are considered. It is shown that the confined spinning particles undergoing spiral motions seem to move inside a gravitomagnetic field produced by an equivalent gravitomagnetic monopole, i.e. the wavefunctions in the spiral motions of confined spinning particles acquire geometric phases, which are equivalent to the phase shift of a zero-spin particle that moves in the vector potential of a gravitomagnetic monopole. This means that the spiral motions of the confined spinning particles in proper potential fields can be used to simulate the gravitomagnetic vector potentials of dual mass. Though there is at present no evidence for the existence of gravitomagnetic monopole, the work presented here may stimulate interest in some areas such as the gravitationally induced quantum effects (relativistic quantum gravitational effects).
Energy spectrum of a multiphoton-transition Jaynes-Cummings model with supersymmetry breaking and some relevant topics such as multiphoton dark state (photon-atom dark-state polariton) and multiphoton coherent population trapping are considered in this paper. We show that for a moving atom, because of Doppler effect and the relativistic electromagnetic induction for the incident optical field, there appears supersymmetric gauge potentials induced by the multiphoton transition and then this can lead to some interesting physical effects such as supersymmetric "spin" Hall effect and supersymmetric Aharonov-Bohm effect of atoms. Both supersymmetric vectorial gauge potential and scalar gauge potential can drive the population transition in the supersymmetric "isospin" doublet states in this Jaynes-Cummings model. As an illustrative example, we address the quantum collapse and revival in atomic population inversion driven by squeezed vacuum states and displaced squeezed vacuum states in such a multiphoton-transition Jaynes-Cummings model. It can be found that different from a coherent state that drives the Jaynes-Cummings model, where quantum collapse-revival effect in atomic level population inversion can be exhibited, a squeezed vacuum state, which excites the Jaynes-Cummings model, cannot give rise to the quantum collapse and revival because there is no Fock-state probability peak in the distribution function in the squeezed vacuum state. If, however, the Jaynes-Cummings model with multiphoton transition is driven by a displaced squeezed vacuum state, it can exhibit the effect of collapse and revival in the energy-level population inversion. In addition, we shall consider the interaction among atom paths (spatial wavefunctions), atomic internal levels and the photon field. Such a coupling leads to an atomic path-level-photon entangled state, and the traditional atomic-level quantum Rabi oscillation and quantum collapse-revival effect that occurred in time domain would be exhibited in the atom spatial wavefunctions (or in atomic paths).
The possibility of the backward waves and negative refractive indices of the gyrotropic chiralmaterials is studied, and the impedances of the eigenmodes arederived. Since the gyrotropic parameters in the permittivity and permeabilitytensors favour the realization of the negative refractive index in the gyrotropicchiral material, the negatively refracting medium can be achieved even far offthe resonances of the permittivity and permeability. A potential effect of the field quantization in a compact subwavelength cavity resonator containing thegyrotropic chiral material is suggested.
A three-level EIT (electromagnetically induced transparency) vapor is used to manipulate the transparency and absorption properties of the probe light in a waveguide. The most remarkable feature of the present scheme is such that the optical responses resulting from both electromagnetically induced transparency and large spontaneous emission enhancement are very sensitive to the frequency detunings of the probe light as well as to the small changes of the waveguide dimension. The potential applications of the dimension- and dispersion-sensitive EIT responses are discussed, and the sensitivity limits of some waveguide-based sensors, including electric absorption modulator, optical switch, wavelength sensor, and sensitive magnetometer, are analyzed.
The local field contribution to some three- and four-level coherent atomic vapors is considered, and a significant modification to optical properties due to dipole-dipole interaction between neighboring atoms is discussed. It is found that the local field effect can reduce loss of a four-level N-type vapor medium at the resonant frequency in both the steady and transient cases. In order to achieve a left-handed medium with a negative refractive index, a scenario to realize simultaneously negative permittivity and permeability inside a mixed coherent atomic vapor by using quantum coherence effect is suggested. One of the remarkable features of the present scheme is such that it can lead to a controllable manipulation of negative refractive index of an atomic vapor by using external coupling and signal fields. This may be a new scheme to fabricate the negatively refracting materials based on quantum optical approach.
Some nontrivial effects (negative refraction and quantum vacuum effects) in gyroelectric chiral medium and magnetoelectric material are studied. It is shown that the refractive indices corresponding to some of the eigen modes in the gyroelectric chiral medium and magnetoelectric material may have negative real parts since both the gyroelectric and magnetoelectric parameters can dramatically reduce the refractive indices in certain frequency bands. As an anisotropic electromagnetic environment could be created due to the breaking of universal symmetry of vacuum mode distribution (and hence the noncompensation effect of a pair of counter-propagating vacuum modes arises) inside the magnetoelectric material, the quantum vacuum in such an anisotropic electromagnetic environment may have a nonzero angular momentum. A novel quantum vacuum effect (angular momentum transfer between the quantum vacuum and the anisotropic magnetoelectric material) that may accompany the effect of magnetoelectric negative refraction is suggested. Such a nontrivial effect can be utilized to design sensitive, accurate measurement techniques, e.g., nanoscale-sensitivity sensor.
General formulae for the transient evolution of the susceptibility (absorption) induced by the quantum interference effect in a four-level N-type EIT medium is presented. The influence of the signal light on the transient susceptibility for the probe beam is studied for two typical cases when the strength of the coupling beam is much greater or less than that of the signal field. An interesting level reciprocity relationship between these two cases is found.
Quantum-dot-molecular phase coherence (and the relevant quantum-interference-switchable optical response) can be utilized to control electromagnetic wave propagation via a gate voltage, since quantum-dot molecules can exhibit an effect of quantum coherence (phase coherence) when quantum-dot-molecular discrete multilevel transitions are driven by an electromagnetic wave. Interdot tunneling of carriers (electrons and holes) controlled by the gate voltage can lead to destructive quantum interference in a quantum-dot molecule that is coupled to an incident electromagnetic wave, and gives rise to a quantum coherence effect (e.g., electromagnetically induced transparency, EIT) in a quantum-dot-molecule dielectric film. The tunable on- and off-resonance tunneling effect of an incident electromagnetic wave (probe field) through such a quantum-coherent quantum-dot-molecule dielectric film is investigated. It is found that a high gate voltage can lead to the EIT phenomenon of the quantum-dot-molecular systems. Under the condition of on-resonance light tunneling through the present quantum-dot-molecule dielectric film, the probe field should propagate without loss if the probe frequency detuning is zero. Such an effect caused by both EIT and resonant tunneling, which is sensitive to the gate voltage, can be utilized for designing devices such as photonic switching, transistors, and logic gates.
A new scheme is suggested to manipulate the probe transitions (and hence the optical properties of atomic vapors) via double-control destructive and constructive quantum interferences. The influence of phase coherence between the two control transitions on the probe transition is also studied. The most remarkable feature of the present scheme is that the optical properties (absorption, transparency and dispersion) of an atomic system can be manipulated using this double-control multi-pathway interferences (multiple routes to excitation). It is also shown that a four-level system will exhibit a two-level resonant absorption because the two control levels (driven by the two control fields) form a dark state (and hence a destructive quantum interference occurs between the two control transitions). However, the present four-level system will exhibit electromagnetically induced transparency to the probe field when the three lower levels (including the probe level and the two control levels) form a three-level dark state. The present scenario has potential applications in new devices (e.g. logic gates and sensitive optical switches) and new techniques (e.g. quantum coherent information storage).
The nonadiabatic conditional geometric phase gate is required in the topological quantum computation in order to overcome the conflict between the requirement of adiabatic condition(to avoid the severe distortion from the nonadiabaticity to the results) and the removal of decoherence effects. It was demonstrated that the effective Hamiltonian that describes the propagation of photon fields inside the coiled fiber is just the Wang-Matsumoto type of Hamiltonian. Thus, the coiled fiber system will automatically generate the nonadiabatic conditional geometric phase shift. In addition, it was shown that the dynamical phase (resulting from the effective Hamiltonian) acquired by the polarized photons vanishes, and the conditional initial state can be easily prepared only by controlling the initial wave vector of photons. In a word, the coiled fiber system can automatically satisfy the requirements and conditions, which were proposed by Wang and Matsumoto in order to create the nonadiabatic conditional geometric phase shift in their NMR scheme.