Dynamic control of coherent pulses via Fano-type interference in asymmetric double quantum wells
We study the temporal and spatial dynamics of two light pulses, a probe and a switch, propagating through an asymmetric double quantum well where tunneling-induced quantum interference may be observed. When such an interference takes place, in the absence of the switch, the quantum well is transparent to the probe which propagates over sufficiently long distances at very small group velocities. In the presence of a relatively strong switch, however, the probe pulse is absorbed due to the quenching of tunneling-induced quantum interference. The probe may be made to vanish even when switch and probe are somewhat delayed with respect to one another. Conversely, our asymmetric double quantum well may be rendered either opaque or transparent to the switch pulse. Such a probe-switch 'reciprocity' can be used to devise a versatile all-optical quantum interference-based solid-state switch for optical communication devices
Kang, Chengxian; Wang, Zhiping; Yu, Benli
2016-03-01
We investigate the absorptive-dispersive properties of a weak probe field in a four-level asymmetrical double semiconductor quantum well. It is found that the enhanced refraction index without absorption can be easily controlled via adjusting properly the corresponding parameters of the system. Our scheme may provide some new possibilities for technological applications in dispersion compensation and solid-state quantum communication for quantum information processing.
Buchholz, S. S.; Fischer, S. F.; Kunze, U.; Schuh, D.; Abstreiter, G.
2008-03-01
Vertically stacked quantum point contacts (QPCs) are prepared by atomic force microscope (AFM) lithography from an asymmetric GaAs/AlGaAs double quantum well (DQW) heterostructure. Top- and back-gate voltages are used to tune the tunnel-coupled QPCs, and back-gate bias cooling is employed to investigate coupled and decoupled one-dimensional (1D) modes. Parity dependent mode coupling is invoked by the particular asymmetry in the vertical DQW confinement.
Asymmetric double quantum well structure as a tunable detector in the far-infrared range
Shin, U; Park, M J; Lee, S J
1999-01-01
The eigenvalues and the wave functions of GaAs/Al sub x Ga sub 1 sub - sub x As asymmetric double quantum well structure have been calculated by using of complex energy method. Based on theoretical calculations, tuning ranges from 9 to 14 mu m are predicted for the proposed asymmetric coupled-quantum-well structure. In addition we calculated the energy eigenvalues and the wave functions of an electron in GaAs/Al sub x Ga sub 1 sub - sub x As single quantum well structure (including delta-perturbation). the variation in E sub 1 , the ground state energy eigenvalue of the electron, depends on the strength and position of the perturbation within the well.
Optical absorption in asymmetric double quantum wells driven by two intense terahertz fields
Optical absorption is investigated for asymmetric double quantum wells driven by a resonant terahertz field and a varied terahertz field, both polarized along the growth direction. Rich nonlinear dynamics of the replica peak and the Autler-Townes splitting of various dressed states are systematically studied in undoped asymmetric double quantum wells by taking account of multiple factors, such as the frequency of the varied terahertz field and the strength of the resonant terahertz field. Each electron subband splits into two dressed states when the resonant terahertz field is applied in the absence of the varied terahertz field, the optical absorption spectrum shows the first-order Autler-Townes splitting of the electron subbands. When a varied terahertz field is added into the resonant system, the replica peak and the second-order Autler-Townes splitting of the dressed states near the band edge respectively emerge when the varied terahertz field is non-resonant and resonant with these dressed states. When the strength of the resonant terahertz field is increased, the first-order Autler-Townes double peaks and the replica peak in the optical absorption spectrum shift with the shifts of the dressed states. The presented results have potential applications in electro-optical devices
Optical absorption in asymmetric double quantum wells driven by two intense terahertz fields
Wu Hong-Wei; Mi Xian-Wu
2013-01-01
Optical absorption is investigated for asymmetric double quantum wells driven by a resonant terahertz field and a varied terahertz field,both polarized along the growth direction.Rich nonlinear dynamics of the replica peak and the Autler-Townes splitting of various dressed states are systematically studied in undoped asymmetric double quantum wells by taking account of multiple factors,such as the frequency of the varied terahertz field and the strength of the resonant terahertz field.Each electron subband splits into two dressed states when the resonant terahertz field is applied in the absence of the varied terahertz field,the optical absorption spectrum shows the first-order Autler-Townes splitting of the electron subbands.When a varied terahertz field is added into the resonant system,the replica peak and the second-order Autler-Townes splitting of the dressed states near the band edge respectively emerge when the varied terahertz field is non-resonant and resonant with these dressed states.Wben the strength of the resonant terahertz field is increased,the first-order Autler-Townes double peaks and the replica peak in the optical absorption spectrum shift with the shifts of the dressed states.The presented results have potential applications in electro-optical devices.
Gain of intersubband Raman lasing in modulation-doped asymmetric coupled double quantum wells
Maung, S. M.; Katayama, S.
2004-03-01
A microscopic theory is developed for the laser gain due to stimulated intersubband electronic Raman effect pumped by CO 2 laser in modulation-doped asymmetric coupled double quantum wells. We focus on the charge density excitation mechanism for electronic Raman scattering, taking into account the coupling between intersubband plasmons and LO phonons. Numerical simulations for the temporal variation of stimulated Stokes photon density, subband populations and output Raman laser power are carried out by using the self-consistent conventional rate equations with stimulated Raman gain coefficient.
Chen, Yuan; Deng, Li [Department of Applied Physics, East China Jiaotong University, Nanchang, 330013 (China); Chen, Aixi, E-mail: aixichen@ecjtu.jx.cn [Department of Applied Physics, East China Jiaotong University, Nanchang, 330013 (China); Institute for Quantum Computing, University of Waterloo, Ontario N2L 3G1 (Canada)
2015-02-15
We investigate the nonlinear optical phenomena of the optical bistability and multistability via spontaneously generated coherence in an asymmetric double quantum well structure coupled by a weak probe field and a controlling field. It is shown that the threshold and hysteresis cycle of the optical bistability can be conveniently controlled only by adjusting the intensity of the SGC or the controlling field. Moreover, switching between optical bistability and multistability can be achieved. These studies may have practical significance for the preparation of optical bistable switching device.
Theory of Intersubband Raman Laser in Modulation-doped Asymmetric Coupled Double Quantum Wells
Maung, S. M.; Katayama, S.
2004-09-01
A microscopic theory is developed for the laser gain due to stimulated intersubband electronic Raman scattering pumped by CO2 laser in modulation-doped GaAs/AlGaAs asymmetric coupled double quantum wells (ACDQWs). Based on the charge-density-excitation (CDE) mechanism, the formula for electronic Raman scattering cross-section is given, taking into account the coupling between intersubband plasmon and optical phonons including GaAs confined LO phonons and interface phonons. Stimulated Raman gain factor is then derived from the cross-section. The optimization of Raman gain, the gain saturation and threshold condition are also discussed. Numerical analysis for temporal variation of stimulated Stokes photon density, subband populations and output Raman laser power is carried out by using the self-consistent conventional rate equations. The theory can predict the presence or lack of coupled modes in lasing in agreement with the recent experimental results.
Phase control of light propagation via Fano interference in asymmetric double quantum wells
Yang, Wen-Xing, E-mail: wenxingyang2@126.com [Department of Physics, Southeast University, Nanjing 210096 (China); Institute of Photonics Technologies, National Tsing-Hua University, Hsinchu 300, Taiwan (China); Lu, Jia-Wei; Zhou, Zhi-Kang; Yang, Long [Department of Physics, Southeast University, Nanjing 210096 (China); Lee, Ray-Kuang [Institute of Photonics Technologies, National Tsing-Hua University, Hsinchu 300, Taiwan (China)
2014-05-28
We investigate the light propagation and dynamical control of a weak pulsed probe field in asymmetric double quantum wells via Fano interference, which is caused by tunneling from the excited subbands to the same continuum. Our results show that the system can produce anomalous and normal dispersion regions with negligible absorption by choosing appropriate coupling strength of the tunneling and the Fano interference. Interesting enough, the dispersion can be switched between normal and anomalous by adjusting the relative phase between the pulsed probe and coherent control fields owing to the existence of the perfectly Fano interference. Thus, the relative phase can be regarded as a switch to manipulate light propagation with subluminal or superluminal. The temporal and spatial dynamics of the pulsed probe field with hyperbolic secant envelope are analyzed.
Phase control of light propagation via Fano interference in asymmetric double quantum wells
We investigate the light propagation and dynamical control of a weak pulsed probe field in asymmetric double quantum wells via Fano interference, which is caused by tunneling from the excited subbands to the same continuum. Our results show that the system can produce anomalous and normal dispersion regions with negligible absorption by choosing appropriate coupling strength of the tunneling and the Fano interference. Interesting enough, the dispersion can be switched between normal and anomalous by adjusting the relative phase between the pulsed probe and coherent control fields owing to the existence of the perfectly Fano interference. Thus, the relative phase can be regarded as a switch to manipulate light propagation with subluminal or superluminal. The temporal and spatial dynamics of the pulsed probe field with hyperbolic secant envelope are analyzed.
Maung, S. M.; Katayama, S.
2005-06-01
A theory of Raman laser gain due to coupled intersubband (ISB) plasmon-optical phonon modes in asymmetric coupled double quantum wells (ACDQWs) is presented. Based on the charge-density-excitations (CDE) mechanism, we take into account the electron-electron and electron-phonon (confined LO phonon and interface (IF) phonons) interactions in the scattering cross-section. For Al0.35Ga0.65As/GaAs ACDQWs the calculated coupled mode energies which are responsible for the lasing Stokes emission are well consistent with recent experiments.
Dispersive properties of tunnelling-induced transparency in an asymmetric double quantum well
苏雪梅; 卓仲畅; 王立军; 高锦岳
2002-01-01
We have investigated the dispersive properties of tunnelling-induced transparency in asymmetric double quantumwell structures where two excited states are coupled by resonant tunnelling through a thin barrier in a three-levelsystem of electronic subbands. The intersubband transitions exhibit high dispersion at zero absorption, which leads tothe slow light velocity in this medium as compared with that in vacuum (c＝3× 108). The group velocity in a specificGaAs/AlGaAs sample is calculated to be vg＝c/4.30. This structure can be used to compensate for the dispersion andenergy loss in fibre optical communications.
Asymmetric effects on the optical properties of double-quantum well systems
Silotia, Poonam; Batra, Kriti; Prasad, Vinod
2014-02-01
Linear, nonlinear, and total absorption coefficient and refractive index changes of double-quantum well (DQW) systems are studied theoretically in the presence of external static electric field applied along the growth direction. The analytical expression for the linear and nonlinear optical properties is obtained using density matrix method. Emphasis is laid on the effect of asymmetry in the shapes of DQW system on optical properties. Some interesting results are obtained and explained.
Nayak, R. K.; Das, S.; Panda, A. K.; Sahu, T., E-mail: tsahu-bu@rediffmail.com [Department of Electronics and Communication Engineering, National Institute of Science and Technology, Palur Hills, Berhampur-761 008, Odisha (India)
2015-11-15
We show that sharp nonmonotic variation of low temperature electron mobility μ can be achieved in GaAs/Al{sub x}Ga{sub 1-x}As barrier delta-doped double quantum well structure due to quantum mechanical transfer of subband electron wave functions within the wells. We vary the potential profile of the coupled structure as a function of the doping concentration in order to bring the subbands into resonance such that the subband energy levels anticross and the eigen states of the coupled structure equally share both the wells thereby giving rise to a dip in mobility. When the wells are of equal widths, the dip in mobility occurs under symmetric doping of the side barriers. In case of unequal well widths, the resonance can be obtained by suitable asymmetric variation of the doping concentrations. The dip in mobility becomes sharp and also the wavy nature of mobility takes a rectangular shape by increasing the barrier width. We show that the dip in mobility at resonance is governed by the interface roughness scattering through step like changes in the subband mobilities. It is also gratifying to show that the drop in mobility at the onset of occupation of second subband is substantially supressed through the quantum mechanical transfer of subband wave functions between the wells. Our results can be utilized for performance enhancement of coupled quantum well devices.
We show that sharp nonmonotic variation of low temperature electron mobility μ can be achieved in GaAs/AlxGa1-xAs barrier delta-doped double quantum well structure due to quantum mechanical transfer of subband electron wave functions within the wells. We vary the potential profile of the coupled structure as a function of the doping concentration in order to bring the subbands into resonance such that the subband energy levels anticross and the eigen states of the coupled structure equally share both the wells thereby giving rise to a dip in mobility. When the wells are of equal widths, the dip in mobility occurs under symmetric doping of the side barriers. In case of unequal well widths, the resonance can be obtained by suitable asymmetric variation of the doping concentrations. The dip in mobility becomes sharp and also the wavy nature of mobility takes a rectangular shape by increasing the barrier width. We show that the dip in mobility at resonance is governed by the interface roughness scattering through step like changes in the subband mobilities. It is also gratifying to show that the drop in mobility at the onset of occupation of second subband is substantially supressed through the quantum mechanical transfer of subband wave functions between the wells. Our results can be utilized for performance enhancement of coupled quantum well devices
Bejan, Doina; Niculescu, Ecaterina Cornelia
2016-06-01
We investigated the combined effects of a non-resonant intense laser field and a static electric field on the electronic structure and the nonlinear optical properties (absorption, optical rectification) of a GaAs asymmetric double quantum dot under a strong probe field excitation. The calculations were performed within the compact density-matrix formalism under steady state conditions using the effective mass approximation. Our results show that: (i) the electronic structure and optical properties are sensitive to the dressed potential; (ii) under applied electric fields, an increase of the laser intensity induces a redshift of the optical absorption and rectification spectra; (iii) the augment of the electric field strength leads to a blueshift of the spectra; (iv) for high electric fields the optical spectra show a shoulder-like feature, related with the occurrence of an anti-crossing between the two first excited levels.
Asymmetric quantum cloning machines
A family of asymmetric cloning machines for quantum bits and N-dimensional quantum states is introduced. These machines produce two approximate copies of a single quantum state that emerge from two distinct channels. In particular, an asymmetric Pauli cloning machine is defined that makes two imperfect copies of a quantum bit, while the overall input-to-output operation for each copy is a Pauli channel. A no-cloning inequality is derived, characterizing the impossibility of copying imposed by quantum mechanics. If p and p' are the probabilities of the depolarizing channels associated with the two outputs, the domain in (√p,√p')-space located inside a particular ellipse representing close-to-perfect cloning is forbidden. This ellipse tends to a circle when copying an N-dimensional state with N→∞, which has a simple semi-classical interpretation. The symmetric Pauli cloning machines are then used to provide an upper bound on the quantum capacity of the Pauli channel of probabilities px, py and pz. The capacity is proven to be vanishing if (√px, √py, √pz) lies outside an ellipsoid whose pole coincides with the depolarizing channel that underlies the universal cloning machine. Finally, the tradeoff between the quality of the two copies is shown to result from a complementarity akin to Heisenberg uncertainty principle. (author)
810-nm InGaA1As/A1GaAs double quantum well semiconductor lasers with asymmetric waveguide structures
Lin Li; Guojun Liu; Zhanguo Li; Mei Li; Xiaohua Wang; Hui Li; Chunming Wan
2008-01-01
@@ The 810-nm InGaA1As/A1GaAs double quantum well (QW) semiconductor lasers with asymmetric waveguide structures, grown by molecular beam epitaxy, show high quantum efficiency and high-power conversion efficiency at continuous-wave (CW) power output. The threshold current density and slope efficiency of the device are 180 A/cm2 and 1.3 W/A, respectively. The internal loss and the internal quantum efficiency are 1.7 cm-1 and 93%, respectively. The 70% maximum power conversion efficiency is achieved with narrow far-field patterns.
Hamedi, H.R., E-mail: Hamid.r.Hamedi@gmail.com
2014-10-01
This letter explores the one dimensional (1D) and two-dimensional (2D) position dependent probe absorption spectrum in a four-subband semiconductor quantum-well (QW) system in presence of Fano-type interference. Compared with obtained results for the maximal detecting probability of electron in Hamedi (2014. Physica B 440, 83) which was 50%, in this paper, we show that the detecting probability and precision of electron localization in one period can be significantly improved and reaches to 100% at the origin of coordinates, through proper tuning the strength of Fano-type interference. Also, the influence of other controlling parameters on the localization behavior of the QW system is discussed. The obtained results may provide some new possibilities for technological applications in laser cooling or nanolithography via high-precision and high-resolution electron localization.
This letter explores the one dimensional (1D) and two-dimensional (2D) position dependent probe absorption spectrum in a four-subband semiconductor quantum-well (QW) system in presence of Fano-type interference. Compared with obtained results for the maximal detecting probability of electron in Hamedi (2014. Physica B 440, 83) which was 50%, in this paper, we show that the detecting probability and precision of electron localization in one period can be significantly improved and reaches to 100% at the origin of coordinates, through proper tuning the strength of Fano-type interference. Also, the influence of other controlling parameters on the localization behavior of the QW system is discussed. The obtained results may provide some new possibilities for technological applications in laser cooling or nanolithography via high-precision and high-resolution electron localization
Cen Long-Bin; Shen Bo; qin Zhi-Xin; Zhang Guo-Yi
2009-01-01
The influence of applied electric fields on the absorption coefficient and subband distances in asymmetrical AlN/GaN coupled double quantum wells (CDQWs) has been investigated by solving Schrodinger and Poisson equations self-consistently. It is found that the absorption coefficient of the intersubband transition (ISBT) between the ground state and the third excited state (1odd -2even) can be equal to zero when the electric fields are applied in asymmetrical A1N/GaN CDQWs,which is related to applied electric fields induced symmetry recovery of these states. Meanwhile,the energy distances between 1odd -2even and 1even - 2even subbands have different relationships from each other with the increase of applied electric fields due to the different polarization-induced potential drops between the lett and the right wells. The results indicate that an electrical-optical modulator operated within the opto-communication wavelength range can be realized in spite of the strong polarization-induced electric fields in asymmetrical AIN/GaN CDQWs.
Time Asymmetric Quantum Mechanics
Arno R. Bohm
2011-09-01
Full Text Available The meaning of time asymmetry in quantum physics is discussed. On the basis of a mathematical theorem, the Stone-von Neumann theorem, the solutions of the dynamical equations, the Schrödinger equation (1 for states or the Heisenberg equation (6a for observables are given by a unitary group. Dirac kets require the concept of a RHS (rigged Hilbert space of Schwartz functions; for this kind of RHS a mathematical theorem also leads to time symmetric group evolution. Scattering theory suggests to distinguish mathematically between states (defined by a preparation apparatus and observables (defined by a registration apparatus (detector. If one requires that scattering resonances of width Γ and exponentially decaying states of lifetime τ=h/Γ should be the same physical entities (for which there is sufficient evidence one is led to a pair of RHS's of Hardy functions and connected with it, to a semigroup time evolution t_0≤t<∞, with the puzzling result that there is a quantum mechanical beginning of time, just like the big bang time for the universe, when it was a quantum system. The decay of quasi-stable particles is used to illustrate this quantum mechanical time asymmetry. From the analysis of these processes, we show that the properties of rigged Hilbert spaces of Hardy functions are suitable for a formulation of time asymmetry in quantum mechanics.
Excitons in asymmetric quantum wells
Grigoryev, P. S.; Kurdyubov, A. S.; Kuznetsova, M. S.; Ignatiev, I. V.; Efimov, Yu. P.; Eliseev, S. A.; Petrov, V. V.; Lovtcius, V. A.; Shapochkin, P. Yu.
2016-09-01
Resonance dielectric response of excitons is studied for the high-quality InGaAs/GaAs heterostructures with wide asymmetric quantum wells (QWs). To highlight effects of the QW asymmetry, we have grown and studied several heterostructures with nominally square QWs as well as with triangle-like QWs. Several quantum confined exciton states are experimentally observed as narrow exciton resonances. A standard approach for the phenomenological analysis of the profiles is generalized by introducing different phase shifts for the light waves reflected from the QWs at different exciton resonances. Good agreement of the phenomenological fit to the experimentally observed exciton spectra for high-quality structures allowed us to reliably obtain parameters of the exciton resonances: the exciton transition energies, the radiative broadenings, and the phase shifts. A direct numerical solution of the Schrödinger equation for the heavy-hole excitons in asymmetric QWs is used for microscopic modeling of the exciton resonances. Remarkable agreement with the experiment is achieved when the effect of indium segregation is taken into account. The segregation results in a modification of the potential profile, in particular, in an asymmetry of the nominally square QWs.
Yesilgul, U.; Al, E. B.; Martínez-Orozco, J. C.; Restrepo, R. L.; Mora-Ramos, M. E.; Duque, C. A.; Ungan, F.; Kasapoglu, E.
2016-08-01
In the present study, the effects of electric and magnetic fields on the linear and third-order nonlinear optical absorption coefficients and relative change of the refractive index in asymmetric GaAs/GaAlAs double quantum wells under intense laser fields are theoretically investigated. The electric field is oriented along the growth direction of the heterostructure while the magnetic field is taken in-plane. The intense laser field is linear polarization along the growth direction. Our calculations are made using the effective-mass approximation and the compact density-matrix approach. Intense laser effects on the system are investigated with the use of the Floquet method with the consequent change in the confinement potential of heterostructures. Our results show that the increase of the electric and magnetic fields blue-shifts the peak positions of the total absorption coefficient and of the total refractive index while the increase of the intense laser field firstly blue-shifts the peak positions and later results in their red-shifting.
Symmetric and asymmetric quantum channels in quantum communication systems
Symmetric and asymmetric quantum channels which act on bipartite bosonic states are considered. The linear dissipative channel and the quantum teleportation channel are applied. The influences of the symmetric and asymmetric quantum channels on bipartite Gaussian states are investigated by means of the inseparability condition. Furthermore, quantum teleportation and quantum dense coding of continuous variables performed by means of two-mode squeezed-vacuum states under the influence of the noisy quantum channels are discussed
New asymmetric quantum codes over Fq
Ma, Yuena; Feng, Xiaoyi; Xu, Gen
2016-07-01
Two families of new asymmetric quantum codes are constructed in this paper. The first family is the asymmetric quantum codes with length n=qm-1 over Fq, where qge 5 is a prime power. The second one is the asymmetric quantum codes with length n=3m-1. These asymmetric quantum codes are derived from the CSS construction and pairs of nested BCH codes. Moreover, let the defining set T1=T2^{-q}, then the real Z-distance of our asymmetric quantum codes are much larger than δ _max+1, where δ _max is the maximal designed distance of dual-containing narrow-sense BCH code, and the parameters presented here have better than the ones available in the literature.
In this work, the conduction band electron states and the associated intersubband-related linear and nonlinear optical absorption coefficient and relative refractive index change are calculated for an asymmetric double n-type δ-doped quantum well in a GaAs-matrix. The effects of an external applied static electric field are included. Values of the two-dimensional impurities density (N2d) of each single δ-doped quantum well are taken to vary within the range of 1.0×1012 to 7.0×1012 cm−2, consistent with the experimental data growth regime. The optical responses are reported as a function of the δ-doped impurities density and the applied electric field. It is shown that single electron states and the related optical quantities are significantly affected by the structural asymmetry of the double δ-doped quantum well system. In addition, a brief comparison with the free-carrier-related optical response is presented. -- Highlights: • Nonlinear optics in asymmetric double n-type δ-doped quantum well in a GaAs-matrix. • The system is considered under external applied electric field in growth direction. • The 2D impurity density is consistent with the experimental data growth regime. • The optical quantities are significantly affected by the structural asymmetry of the system
Rodríguez-Magdaleno, K.A.; Martínez-Orozco, J.C.; Rodríguez-Vargas, I. [Unidad Académica de Física, Universidad Autónoma de Zacatecas, Calz. Solidaridad Esq. Paseo a La Bufa S/N. C.P. 98060 Zacatecas (Mexico); Mora-Ramos, M.E. [Facultad de Ciencias, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, CP 62209 Cuernavaca, Morelos (Mexico); Física Teórica y Aplicada, Escuela de Ingeniería de Antioquia, AA 7516 Medellín (Colombia); Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia); Duque, C.A., E-mail: cduque@fisica.udea.edu.co [Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia)
2014-03-15
In this work, the conduction band electron states and the associated intersubband-related linear and nonlinear optical absorption coefficient and relative refractive index change are calculated for an asymmetric double n-type δ-doped quantum well in a GaAs-matrix. The effects of an external applied static electric field are included. Values of the two-dimensional impurities density (N{sub 2d}) of each single δ-doped quantum well are taken to vary within the range of 1.0×10{sup 12} to 7.0×10{sup 12} cm{sup −2}, consistent with the experimental data growth regime. The optical responses are reported as a function of the δ-doped impurities density and the applied electric field. It is shown that single electron states and the related optical quantities are significantly affected by the structural asymmetry of the double δ-doped quantum well system. In addition, a brief comparison with the free-carrier-related optical response is presented. -- Highlights: • Nonlinear optics in asymmetric double n-type δ-doped quantum well in a GaAs-matrix. • The system is considered under external applied electric field in growth direction. • The 2D impurity density is consistent with the experimental data growth regime. • The optical quantities are significantly affected by the structural asymmetry of the system.
In this work we are reporting the energy level spectrum for a quantum system consisting of an n-type double δ-doped quantum well with a Schottky barrier potential in a Gallium Arsenide matrix. The calculated states are taken as the basis for the evaluation of the linear and third-order nonlinear contributions to the optical absorption coefficient and to the relative refractive index change, making particular use of the asymmetry of the potential profile. These optical properties are then reported as a function of the Schottky barrier height (SBH) and the separation distance between the δ-doped quantum wells. Also, the effects of the application of hydrostatic pressure are studied. The results show that the amplitudes of the resonant peaks are of the same order of magnitude of those obtained in the case of single δ-doped field effect transistors; but tailoring the asymmetry of the confining potential profile allows the control the resonant peak positions
Rojas-Briseño, J.G.; Martínez-Orozco, J.C.; Rodríguez-Vargas, I. [Unidad Académica de Física, Universidad Autónoma de Zacatecas, Calzada Solidaridad esquina con Paseo la Bufa S/N, C.P. 98060, Zacatecas, Zac. (Mexico); Mora-Ramos, M.E. [Facultad de Ciencias, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, CP 62209, Cuernavaca, Morelos (Mexico); Instituto de Física, Universidad de Antioquia, AA 1226, Medellín (Colombia); Duque, C.A., E-mail: cduque@fisica.udea.edu.co [Instituto de Física, Universidad de Antioquia, AA 1226, Medellín (Colombia)
2013-09-01
In this work we are reporting the energy level spectrum for a quantum system consisting of an n-type double δ-doped quantum well with a Schottky barrier potential in a Gallium Arsenide matrix. The calculated states are taken as the basis for the evaluation of the linear and third-order nonlinear contributions to the optical absorption coefficient and to the relative refractive index change, making particular use of the asymmetry of the potential profile. These optical properties are then reported as a function of the Schottky barrier height (SBH) and the separation distance between the δ-doped quantum wells. Also, the effects of the application of hydrostatic pressure are studied. The results show that the amplitudes of the resonant peaks are of the same order of magnitude of those obtained in the case of single δ-doped field effect transistors; but tailoring the asymmetry of the confining potential profile allows the control the resonant peak positions.
The intersubband electron-related nonlinear optical absorption and nonlinear optical rectification in GaAs-Ga1-xAlxAs asymmetric double quantum wells are studied, under the influence of combined or independent applied electric and magnetic fields as well as hydrostatic pressure. The outcome of the density matrix formalism and the effective mass, and parabolic-band approximations have been considered as main theoretical tools for the description. It is obtained that under particular geometrical conditions, with or without electric and/or magnetic field strength, the optical rectification is null and, simultaneously, in such circumstances the optical absorption has a relative maximum. It is also detected that the influence of the hydrostatic pressure leads to increasing or decreasing behaviors of the nonlinear optical absorption in dependence of the particular regime of pressure values considered, with significant distinction of the cases of opposite electric field orientations. - Highlights: → Maxima of the NOA correspond to zero in the NOR. → Electric fields can couple the double quantum wells. → Hydrostatic pressure can couple the double quantum wells. → NOA can increase/decrease with hydrostatic pressure. → Overlap between wave functions depends on the magnetic field.
Karabulut, I. [Department of Physics, Selcuk University, Konya 42075 (Turkey); Mora-Ramos, M.E. [Facultad de Ciencias, Universidad Autonoma del Estado de Morelos, Ave. Universidad 1001, CP 62209, Cuernavaca, Morelos (Mexico); Duque, C.A., E-mail: cduque_echeverri@yahoo.e [Instituto de Fisica, Universidad de Antioquia, AA 1226, Medellin (Colombia)
2011-07-15
The intersubband electron-related nonlinear optical absorption and nonlinear optical rectification in GaAs-Ga{sub 1-x}Al{sub x}As asymmetric double quantum wells are studied, under the influence of combined or independent applied electric and magnetic fields as well as hydrostatic pressure. The outcome of the density matrix formalism and the effective mass, and parabolic-band approximations have been considered as main theoretical tools for the description. It is obtained that under particular geometrical conditions, with or without electric and/or magnetic field strength, the optical rectification is null and, simultaneously, in such circumstances the optical absorption has a relative maximum. It is also detected that the influence of the hydrostatic pressure leads to increasing or decreasing behaviors of the nonlinear optical absorption in dependence of the particular regime of pressure values considered, with significant distinction of the cases of opposite electric field orientations. - Highlights: {yields} Maxima of the NOA correspond to zero in the NOR. {yields} Electric fields can couple the double quantum wells. {yields} Hydrostatic pressure can couple the double quantum wells. {yields} NOA can increase/decrease with hydrostatic pressure. {yields} Overlap between wave functions depends on the magnetic field.
2016-01-01
Conspectus Pairs of coupled quantum dots with controlled coupling between the two potential wells serve as an extremely rich system, exhibiting a plethora of optical phenomena that do not exist in each of the isolated constituent dots. Over the past decade, coupled quantum systems have been under extensive study in the context of epitaxially grown quantum dots (QDs), but only a handful of examples have been reported with colloidal QDs. This is mostly due to the difficulties in controllably growing nanoparticles that encapsulate within them two dots separated by an energetic barrier via colloidal synthesis methods. Recent advances in colloidal synthesis methods have enabled the first clear demonstrations of colloidal double quantum dots and allowed for the first exploratory studies into their optical properties. Nevertheless, colloidal double QDs can offer an extended level of structural manipulation that allows not only for a broader range of materials to be used as compared with epitaxially grown counterparts but also for more complex control over the coupling mechanisms and coupling strength between two spatially separated quantum dots. The photophysics of these nanostructures is governed by the balance between two coupling mechanisms. The first is via dipole–dipole interactions between the two constituent components, leading to energy transfer between them. The second is associated with overlap of excited carrier wave functions, leading to charge transfer and multicarrier interactions between the two components. The magnitude of the coupling between the two subcomponents is determined by the detailed potential landscape within the nanocrystals (NCs). One of the hallmarks of double QDs is the observation of dual-color emission from a single nanoparticle, which allows for detailed spectroscopy of their properties down to the single particle level. Furthermore, rational design of the two coupled subsystems enables one to tune the emission statistics from single
Colloidal Double Quantum Dots.
Teitelboim, Ayelet; Meir, Noga; Kazes, Miri; Oron, Dan
2016-05-17
Pairs of coupled quantum dots with controlled coupling between the two potential wells serve as an extremely rich system, exhibiting a plethora of optical phenomena that do not exist in each of the isolated constituent dots. Over the past decade, coupled quantum systems have been under extensive study in the context of epitaxially grown quantum dots (QDs), but only a handful of examples have been reported with colloidal QDs. This is mostly due to the difficulties in controllably growing nanoparticles that encapsulate within them two dots separated by an energetic barrier via colloidal synthesis methods. Recent advances in colloidal synthesis methods have enabled the first clear demonstrations of colloidal double quantum dots and allowed for the first exploratory studies into their optical properties. Nevertheless, colloidal double QDs can offer an extended level of structural manipulation that allows not only for a broader range of materials to be used as compared with epitaxially grown counterparts but also for more complex control over the coupling mechanisms and coupling strength between two spatially separated quantum dots. The photophysics of these nanostructures is governed by the balance between two coupling mechanisms. The first is via dipole-dipole interactions between the two constituent components, leading to energy transfer between them. The second is associated with overlap of excited carrier wave functions, leading to charge transfer and multicarrier interactions between the two components. The magnitude of the coupling between the two subcomponents is determined by the detailed potential landscape within the nanocrystals (NCs). One of the hallmarks of double QDs is the observation of dual-color emission from a single nanoparticle, which allows for detailed spectroscopy of their properties down to the single particle level. Furthermore, rational design of the two coupled subsystems enables one to tune the emission statistics from single photon
Quantum optics of lossy asymmetric beam splitters.
Uppu, Ravitej; Wolterink, Tom A W; Tentrup, Tristan B H; Pinkse, Pepijn W H
2016-07-25
We theoretically investigate quantum interference of two single photons at a lossy asymmetric beam splitter, the most general passive 2×2 optical circuit. The losses in the circuit result in a non-unitary scattering matrix with a non-trivial set of constraints on the elements of the scattering matrix. Our analysis using the noise operator formalism shows that the loss allows tunability of quantum interference to an extent not possible with a lossless beam splitter. Our theoretical studies support the experimental demonstrations of programmable quantum interference in highly multimodal systems such as opaque scattering media and multimode fibers. PMID:27464096
Quantum optics of lossy asymmetric beam splitters
Uppu, Ravitej; Tentrup, Tristan B H; Pinkse, Pepijn W H
2016-01-01
We theoretically investigate quantum interference of two single photons at a lossy asymmetric beam splitter, the most general passive 2$\\times$2 optical circuit. The losses in the circuit result in a non-unitary scattering matrix with a non-trivial set of constraints on the elements of the scattering matrix. Our analysis using the noise operator formalism shows that the loss allows tunability of quantum interference to an extent not possible with a lossless beam splitter. Our theoretical studies support the experimental demonstrations of programmable quantum interference in highly multimodal systems such as opaque scattering media and multimode fibers.
Generation of infrared entangled light in asymmetric semiconductor quantum wells
Lü, Xin-You; Wu, Jing; Zheng, Li-Li; Huang, Pei
2010-12-01
We proposed a scheme to achieve two-mode CV entanglement with the frequencies of entangled modes in the infrared range in an asymmetric semiconductor double-quantum-wells (DQW), where the required quantum coherence is obtained by inducing the corresponding intersubband transitions (ISBTs) with a classical field. By numerically simulating the dynamics of system, we show that the entanglement period can be prolonged via enhancing the intensity of classical field, and the generation of entanglement doesn't depend intensively on the initial condition of system in our scheme. Moreover, we also show that a bipartite entanglement amplifier can be realized in our scheme. The present research provides an efficient approach to achieve infrared entangled light in the semiconductor nanostructure, which may have significant impact on the progress of solid-state quantum information theory.
Lateral current density fronts in asymmetric double-barrier resonant-tunneling structures
Rodin, Pavel; Schoell, Eckehard
2003-01-01
We present a theoretical analysis and numerical simulations of lateral current density fronts in bistable resonant-tunneling diodes with Z-shaped current-voltage characteristics. The bistability is due to the charge accumulation in the quantum well of the double-barrier structure. We focus on asymmetric structures in the regime of sequential incoherent tunneling and study the dependence of the bistability range, the front velocity and the front width on the structure parameters. We propose a ...
Semiconductor double quantum dot micromaser.
Liu, Y-Y; Stehlik, J; Eichler, C; Gullans, M J; Taylor, J M; Petta, J R
2015-01-16
The coherent generation of light, from masers to lasers, relies upon the specific structure of the individual emitters that lead to gain. Devices operating as lasers in the few-emitter limit provide opportunities for understanding quantum coherent phenomena, from terahertz sources to quantum communication. Here we demonstrate a maser that is driven by single-electron tunneling events. Semiconductor double quantum dots (DQDs) serve as a gain medium and are placed inside a high-quality factor microwave cavity. We verify maser action by comparing the statistics of the emitted microwave field above and below the maser threshold. PMID:25593187
Bound states in a hyperbolic asymmetric double-well
Hartmann, R. R., E-mail: richard.hartmann@dlsu.edu.ph [Physics Department, De La Salle University, 2401 Taft Avenue, Manila (Philippines)
2014-01-15
We report a new class of hyperbolic asymmetric double-well whose bound state wavefunctions can be expressed in terms of confluent Heun functions. An analytic procedure is used to obtain the energy eigenvalues and the criterion for the potential to support bound states is discussed.
Three-party quantum teleportation with asymmetric states
In this paper, we consider the three-party quantum teleportation using non-symmetric states. Considering all possible teleportation scenarios in the three-party quantum teleportation, we show that the asymmetric teleportation would carry more information than symmetrical ones. We also discuss the relation between teleportation protocols and quantum states classficition
Spin-polarized current in double quantum dots
Li Ai-Xian; Duan Su-Qing
2012-01-01
We analyze the transport through asymmetric double quantum dots with an inhomogeneous Zeeman splitting in the presence of crossed dc and ac magnetic fields.A strong spin-polarized current can be obtained by changing the dc magnetic field.It is mainly due to the resonant tunnelling.But for the ferromagnetic right electrode,the electron spin resonance also plays an important role in transport.We show that the double quantum dots with three-level mixing under crossed dc and ac magnetic fields can act not only as a bipolar spin filter but also as a spin inverter under suitable conditions.
The Quantum Double in Integrable Quantum Field Theory
Bernard, D.; Leclair, A.
1992-01-01
Various aspects of recent works on affine quantum group symmetry of integrable 2d quantum field theory are reviewed and further clarified. A geometrical meaning is given to the quantum double, and other properties of quantum groups. Multiplicative presentations of the Yangian double are analyzed.
Tripartite fully asymmetric universal quantum cloning
Full text: We investigate the universal asymmetric cloning of states in a Hilbert space of arbitrary dimension d. We derive the class of optimal and fully asymmetric universal 1 → 3 cloners, which produce three copies, each having a different fidelity. A simple parametric expression for the maximum achievable cloning fidelity triplets will be provided. As a side-product, we also prove the optimality of the 1 → 2 asymmetric cloning machines that have been proposed in the literature. (author)
Asymmetric double-well potential for single-atom interferometry
We consider the evolution of a single-atom wave function in a time-dependent double-well interferometer in the presence of a spatially asymmetric potential. We examine a case where a single trapping potential is split into an asymmetric double well and then recombined again. The interferometer involves a measurement of the first excited state population as a sensitive measure of the asymmetric potential. Based on a two-mode approximation a Bloch vector model provides a simple and satisfactory description of the dynamical evolution. We discuss the roles of adiabaticity and asymmetry in the double-well interferometer. The Bloch model allows us to account for the effects of asymmetry on the excited state population throughout the interferometric process and to choose the appropriate splitting, holding, and recombination periods in order to maximize the output signal. We also compare the outcomes of the Bloch vector model with the results of numerical simulations of the multistate time-dependent Schroedinger equation
Controlling the flow of information in quantum cloners: asymmetric cloning
We show that the distribution of information at the output of the quantum cloner can be efficiently controlled via preparation of the quantum cloner. We present a universal cloning network with the help of which asymmetric cloning can be performed. (author)
We report a quantum eraser experiment which actually uses a Young double slit to create interference. The experiment can be considered an optical analogy of an experiment proposed by Scully, Englert, and Walther [Nature (London) 351, 111 (1991)]. One photon of an entangled pair is incident on a Young double slit of appropriate dimensions to create an interference pattern in a distant detection region. Quarter-wave plates, oriented so that their fast axes are orthogonal, are placed in front of each slit to serve as which-path markers. The quarter-wave plates mark the polarization of the interfering photon and thus destroy the interference pattern. To recover interference, we measure the polarization of the other entangled photon. In addition, we perform the experiment under 'delayed erasure' circumstances
Bredtmann, Timm; Manz, Jörn; Zhao, Jian-Ming
2016-05-19
The quantum theory of concerted electronic and nuclear fluxes (CENFs) during coherent periodic tunnelling from reactants (R) to products (P) and back to R in molecules with asymmetric double-well potentials is developed. The results are deduced from the solution of the time-dependent Schrödinger equation as a coherent superposition of two eigenstates; here, these are the two states of the lowest tunnelling doublet. This allows the periodic time evolutions of the resulting electronic and nuclear probability densities (EPDs and NPDs) as well as the CENFs to be expressed in terms of simple sinusodial functions. These analytical results reveal various phenomena during coherent tunnelling in asymmetric double-well potentials, e.g., all EPDs and NPDs as well as all CENFs are synchronous. Distortion of the symmetric reference to a system with an asymmetric double-well potential breaks the spatial symmetry of the EPDs and NPDs, but, surprisingly, the symmetry of the CENFs is conserved. Exemplary application to the Cope rearrangement of semibullvalene shows that tunnelling of the ideal symmetric system can be suppressed by asymmetries induced by rather small external electric fields. The amplitude for the half tunnelling, half nontunnelling border is as low as 0.218 × 10(-8) V/cm. At the same time, the delocalized eigenstates of the symmetric reference, which can be regarded as Schrödinger's cat-type states representing R and P with equal probabilities, get localized at one or the other minima of the asymmetric double-well potential, representing either R or P. PMID:26799383
Control of indirect exciton population in an asymmetric quantum dot molecule
We analyze the problem of coherent population transfer to the indirect exciton state in an asymmetric double semiconductor quantum dot molecule that interacts with an external electromagnetic field. Using the controlled rotation method, we obtain analytical solutions of the time-dependent Schrödinger equation and determine closed-form conditions for the parameters of the applied field and the quantum system that lead to complete population transfer to the indirect exciton state, in the absence of decay effects. Then, by numerical solution of the relevant density matrix equations we study the influence of decay mechanisms to the efficiency of population transfer.
Quantum asymmetric cryptography with symmetric keys
无
2009-01-01
Based on quantum encryption,we present a new idea for quantum public-key cryptography (QPKC) and construct a whole theoretical framework of a QPKC system. We show that the quantum-mechanical nature renders it feasible and reasonable to use symmetric keys in such a scheme,which is quite different from that in conventional public-key cryptography. The security of our scheme is analyzed and some features are discussed. Furthermore,the state-estimation attack to a prior QPKC scheme is demonstrated.
Quantum Stackelberg Duopoly of Continuous Distributed Asymmetric Information
WANG Xia; YANG Xiao-Hua; MIAO Lin; ZHOU Xiang; HU Cheng-Zheng
2007-01-01
The minimal quantization structure is employed to investigate the quantum version of the Stackelberg duopoly with continuous distributed asymmetric information, I.e. The first mover has incomplete information that obeys a continuous distribution while the second mover has complete information. It is found that the effects of the positive quantum entanglement on the outcomes exhibit many interesting features due to the information asymmetry. Moreover, although the first-mover advantage is counteracted by the information asymmetry, the positive quantum entanglement still enhances the first-mover advantage and improves the first-mover tolerance of the information asymmetry beyond the classical limit.
Distribution of quantum Fisher information in asymmetric cloning machines
Xiao, Xing; Yao, Yao; Zhou, Lei-Ming; Wang, Xiaoguang
2014-12-01
An unknown quantum state cannot be copied and broadcast freely due to the no-cloning theorem. Approximate cloning schemes have been proposed to achieve the optimal cloning characterized by the maximal fidelity between the original and its copies. Here, from the perspective of quantum Fisher information (QFI), we investigate the distribution of QFI in asymmetric cloning machines which produce two nonidentical copies. As one might expect, improving the QFI of one copy results in decreasing the QFI of the other copy. It is perhaps also unsurprising that asymmetric phase-covariant cloning outperforms universal cloning in distributing QFI since a priori information of the input state has been utilized. However, interesting results appear when we compare the distributabilities of fidelity (which quantifies the full information of quantum states), and QFI (which only captures the information of relevant parameters) in asymmetric cloning machines. Unlike the results of fidelity, where the distributability of symmetric cloning is always optimal for any d-dimensional cloning, we find that any asymmetric cloning outperforms symmetric cloning on the distribution of QFI for d cloning strategies could be worse than symmetric ones when d > 18.
An asymmetric relativistic model for classical double radio sources
Arshakian, T G
2000-01-01
There is substantial observational evidence against the symmetric relativistic model of FRII radio sources. An asymmetric relativistic model is proposed which takes account of both relativistic effects and intrinsic/environmental asymmetries to explain the structural asymmetries of their radio lobes. A key parameter of the model is the jet-side of the double sources, which is estimated for 80% of the FRII sources in the 3CRR complete sample. Statistical analyses of the properties of these sources show that the asymmetric model is in agreement with a wide range of observational data, and that the relativistic and intrinsic asymmetry effects are of comparable importance. Intrinsic/environmental asymmetry effects are more important at high radio luminosities and small physical scales. The mean translational speed of the lobes is found to be 0.11c, consistent with the speeds found from spectral ageing arguments. According to a Gaussian model, the standard deviation of lobe speeds is 0.04c. The results are in agre...
Pentamode metamaterials with asymmetric double-cone elements
Pentamode metamaterials are a very interesting set of artificial solids. They are difficult to compress but flow easily, hence imitating somehow the behaviours of liquids. In this paper, three-dimensional (3D) pentamode metamaterials based on the asymmetric double-cone element (ADCE) are proposed. The ADCE is composed by two connected truncated cones with different thin diameters. The phonon band structures of the ADCEs pentamode metamaterials are numerically analysed by using the finite element method (FEM). Besides the single phonon mode, the complete 3D band gaps are also found in the phonon band structures. Here, the influence of the degree of asymmetry of ADCE to the figure of merit (FOM), which is the ratio of bulk modulus and shear modulus, is discussed. The FOM can be increased by 21–30% (at FOM ≥ 103) when the degree of asymmetry m ranges from 0.4 to 0.6. (paper)
Independently tunable double Fano resonances in asymmetric MIM waveguide structure.
Qi, Jiwei; Chen, Zongqiang; Chen, Jing; Li, Yudong; Qiang, Wu; Xu, Jingjun; Sun, Qian
2014-06-16
In this paper, an asymmetric plasmonic structure composed of a MIM (metal-insulator-metal) waveguide and a rectangular cavity is reported, which can support double Fano resonances originating from two different mechanisms. One of Fano resonance originates from the interference between a horizontal and a vertical resonance in the rectangular cavity. And the other is induced by the asymmetry of the plasmonic structure. Just because the double Fano resonances originate from two different mechanisms, each Fano resonance can be well tuned independently by changing the parameters of the rectangular cavity. And during the tuning process, the FOMs (figure of merit) of both the Fano resonances can keep unchanged almost with large values, both larger than 650. Such, the transmission spectra of the plasmonic structure can be well modulated to form transmission window with the position and the full width at half maximum (FWHM) can be tuned freely, which is useful for the applications in sensors, nonlinear and slow-light devices. PMID:24977564
Binding energies of indirect excitons in double quantum well systems
Rossokhaty, Alex; Schmult, Stefan; Dietsche, Werner; von Klitzing, Klaus; Kukushkin, Igor
2011-03-01
A prerequisite towards Bose-Einstein condensation is a cold and dense system of bosons. Indirect excitons in double GaAs/AlGaAs quantum wells (DQWs) are believed to be suitable candidates. Indirect excitons are formed in asymmetric DQW structures by mass filtering, a method which does not require external electric fields. The exciton density and the electron-hole balance can be tuned optically. Binding energies are measured by a resonant microwave absorption technique. Our results show that screening of the indirect excitons becomes already relevant at densities as low as ~ 5 × 109 cm-2 and results in their destruction.
Double-partition Quantum Cluster Algebras
Jakobsen, Hans Plesner; Zhang, Hechun
2012-01-01
A family of quantum cluster algebras is introduced and studied. In general, these algebras are new, but sub-classes have been studied previously by other authors. The algebras are indexed by double parti- tions or double flag varieties. Equivalently, they are indexed by broken lines L. By grouping...... together neighboring mutations into quantum line mutations we can mutate from the cluster algebra of one broken line to another. Compatible pairs can be written down. The algebras are equal to their upper cluster algebras. The variables of the quantum seeds are given by elements of the dual canonical basis....
Entanglement via tunable Fano-type interference in asymmetric semiconductor quantum wells
Entanglement is realized in asymmetric coupled double quantum wells (DQWs) trapped in a doubly resonant cavity by means of Fano-type interference through a tunneling barrier, which is different from the previous studies on entanglement induced by strong external driven fields in atomic media. We investigate the generation and evolution of entanglement and show that the strength of Fano interference can influence effectively the degree of the entanglement between two cavity modes and the enhanced entanglement can be generated in this DQW system. The present investigation may provide research opportunities in quantum entangled experiments in the DQW solid-state nanostructures and may result in a substantial impact on the technology for entanglement engineering in quantum information processing.
Entanglement via tunable Fano-type interference in asymmetric semiconductor quantum wells
Hao Xiangying, E-mail: xyhao.321@163.co [Wuhan National Laboratory for Optoelectronics and School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China); Li Jiahua, E-mail: ai_li@126.co [Wuhan National Laboratory for Optoelectronics and School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China); Lv Xinyou; Si Liugang; Yang Xiaoxue [Wuhan National Laboratory for Optoelectronics and School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China)
2009-10-12
Entanglement is realized in asymmetric coupled double quantum wells (DQWs) trapped in a doubly resonant cavity by means of Fano-type interference through a tunneling barrier, which is different from the previous studies on entanglement induced by strong external driven fields in atomic media. We investigate the generation and evolution of entanglement and show that the strength of Fano interference can influence effectively the degree of the entanglement between two cavity modes and the enhanced entanglement can be generated in this DQW system. The present investigation may provide research opportunities in quantum entangled experiments in the DQW solid-state nanostructures and may result in a substantial impact on the technology for entanglement engineering in quantum information processing.
Entanglement via tunable Fano-type interference in asymmetric semiconductor quantum wells
Hao, Xiangying; Li, Jiahua; Lv, Xin-You; Si, Liu-Gang; Yang, Xiaoxue
2009-10-01
Entanglement is realized in asymmetric coupled double quantum wells (DQWs) trapped in a doubly resonant cavity by means of Fano-type interference through a tunneling barrier, which is different from the previous studies on entanglement induced by strong external driven fields in atomic media. We investigate the generation and evolution of entanglement and show that the strength of Fano interference can influence effectively the degree of the entanglement between two cavity modes and the enhanced entanglement can be generated in this DQW system. The present investigation may provide research opportunities in quantum entangled experiments in the DQW solid-state nanostructures and may result in a substantial impact on the technology for entanglement engineering in quantum information processing.
LIU Yu-Shen; CHEN Hao
2004-01-01
@@ We investigate the dynamics of two interacting electrons in an asymmetric double coupled quantum dot under an ac electric field. The numerical results demonstrate that dynamical localization and Rabi oscillation still exist in such a system under the stronger electron correlation. The two electrons can be regarded as a quasiparticle,which move together between two dots similarly to a boson. The dynamics of two electrons in such a quantum system are mainly confined in a Q subspace, which is constructed by two double-occupied states.
Electromagnetically induced grating in asymmetric quantum wells via Fano interference.
Zhou, Fengxue; Qi, Yihong; Sun, Hui; Chen, Dijun; Yang, Jie; Niu, Yueping; Gong, Shangqing
2013-05-20
We propose a scheme for obtaining an electromagnetically induced grating in an asymmetric semiconductor quantum well (QW) structure via Fano interference. In our structure, owing to Fano interference, the diffraction intensity of the grating, especially the first-order diffraction, can be significantly enhanced. The diffraction efficiency of the grating can be controlled efficiently by tuning the control field intensity, the interaction length, the coupling strength of tunneling, etc. This investigation may be used to develop novel photonic devices in semiconductor QW systems. PMID:23736445
Double-pass quantum volume hologram
We propose a scheme for parallel, spatially multimode quantum memory for light. The scheme is based on the propagation in different directions of a quantum signal wave and strong classical reference wave, like in a classical volume hologram and the previously proposed quantum volume hologram [D. V. Vasilyev et al., Phys. Rev. A 81, 020302(R) (2010)]. The medium for the hologram consists of a spatially extended ensemble of cold spin-polarized atoms. In the absence of the collective spin rotation during the interaction, two passes of light for both storage and retrieval are required, and therefore the present scheme can be called a double-pass quantum volume hologram. The scheme is less sensitive to diffraction and therefore is capable of achieving a higher density of storage of spatial modes as compared to the previously proposed thin quantum hologram [D. V. Vasilyev et al., Phys. Rev. A 77, 020302(R) (2008)], which also requires two passes of light for both storage and retrieval. However, the present scheme allows one to achieve a good memory performance with a lower optical depth of the atomic sample as compared to the quantum volume hologram. A quantum hologram capable of storing entangled images can become an important ingredient in quantum information processing and quantum imaging.
Double Acceptor Interaction in Semimagnetic Quantum Dot
A. Merwyn Jasper D. Reuben
2011-01-01
Full Text Available The effect of geometry of the semimagnetic Quantum Dot on the Interaction energy of a double acceptor is computed in the effective mass approximation using the variational principle. A peak is observed at the lower dot sizes as a magnetic field is increased which is attributed to the reduction in confinement.
Luminescence upconversion in colloidal double quantum dots.
Deutsch, Zvicka; Neeman, Lior; Oron, Dan
2013-09-01
Luminescence upconversion nanocrystals capable of converting two low-energy photons into a single photon at a higher energy are sought-after for a variety of applications, including bioimaging and photovoltaic light harvesting. Currently available systems, based on rare-earth-doped dielectrics, are limited in both tunability and absorption cross-section. Here we present colloidal double quantum dots as an alternative nanocrystalline upconversion system, combining the stability of an inorganic crystalline structure with the spectral tunability afforded by quantum confinement. By tailoring its composition and morphology, we form a semiconducting nanostructure in which excited electrons are delocalized over the entire structure, but a double potential well is formed for holes. Upconversion occurs by excitation of an electron in the lower energy transition, followed by intraband absorption of the hole, allowing it to cross the barrier to a higher energy state. An overall conversion efficiency of 0.1% per double excitation event is achieved. PMID:23912060
无
2002-01-01
We propose a method of controlling the dc-SQUID(superconductiong quantum interference device)system by changing the gate voltages,which controls the amplitude of the fictitious magnetic fields Bz,and the externally applied current that produces the piercing magnetic flux Φx for the dc-SQUID system,we have also introduced a physical model for the dc-SQUID system.Using this physical model,one can obtain the non-adiabatic geometric phase gate for the single qubit and the non-adiabatic conditional geometric phase gate (controlled NOT gate) for the two qubits.It is shown that when the gate voltage and the externally applied current of the dc-SQUID system satisfies an appropriate constraint condition,the charge state evolution can be controlled exactly on a dynamic phase free path.The non-adiabatic evolution of the charge states is given as well.
Detection of entanglement in asymmetric quantum networks and multipartite quantum steering.
Cavalcanti, D; Skrzypczyk, P; Aguilar, G H; Nery, R V; Ribeiro, P H Souto; Walborn, S P
2015-01-01
The future of quantum communication relies on quantum networks composed by observers sharing multipartite quantum states. The certification of multipartite entanglement will be crucial to the usefulness of these networks. In many real situations it is natural to assume that some observers are more trusted than others in the sense that they have more knowledge of their measurement apparatuses. Here we propose a general method to certify all kinds of multipartite entanglement in this asymmetric scenario and experimentally demonstrate it in an optical experiment. Our results, which can be seen as a definition of genuine multipartite quantum steering, give a method to detect entanglement in a scenario in between the standard entanglement and fully device-independent scenarios, and provide a basis for semi-device-independent cryptographic applications in quantum networks. PMID:26235944
Detection of entanglement in asymmetric quantum networks and multipartite quantum steering
Cavalcanti, D.; Skrzypczyk, P.; Aguilar, G. H.; Nery, R. V.; Ribeiro, P. H. Souto; Walborn, S. P.
2015-08-01
The future of quantum communication relies on quantum networks composed by observers sharing multipartite quantum states. The certification of multipartite entanglement will be crucial to the usefulness of these networks. In many real situations it is natural to assume that some observers are more trusted than others in the sense that they have more knowledge of their measurement apparatuses. Here we propose a general method to certify all kinds of multipartite entanglement in this asymmetric scenario and experimentally demonstrate it in an optical experiment. Our results, which can be seen as a definition of genuine multipartite quantum steering, give a method to detect entanglement in a scenario in between the standard entanglement and fully device-independent scenarios, and provide a basis for semi-device-independent cryptographic applications in quantum networks.
Walborn, S. P.; Cunha, M. O. Terra; Padua, S.; Monken, C. H.
2001-01-01
We report a quantum eraser experiment which actually uses a Young double-slit to create interference. The experiment can be considered an optical analogy of an experiment proposed by Scully, Englert and Walther. One photon of an entangled pair is incident on a Young double-slit of appropriate dimensions to create an interference pattern in a distant detection region. Quarter-wave plates, oriented so that their fast axes are orthogonal, are placed in front of each slit to serve as which-path m...
Tunneling rate in double quantum dots
Filikhin, Igor; Matinyan, Sergei; Vlahovic, Branislav
2014-03-01
We study spectral properties of electron tunneling in double quantum dots (DQDs) (and double quantum wells (DQWs)) and their relation to the geometry. In particular we compare the tunneling in DQW with chaotic and regular geometry, taking into account recent evidence about regularization of the tunneling rate when the QW geometry is chaotic. Our calculations do not support this assumption. We confirm high influence of the QW geometry boundaries on the rate fluctuation along the spectrum. The factors of the effective mass anisotropy and violation of the symmetry of DQD and DQW are also considered. Generally, we found that the small violation of the symmetry drastically affects tunneling. This work is supported by the NSF (HRD-0833184) and NASA (NNX09AV07A).
Energy transfer processes in ZnSe/(Zn,Mn)Se double quantum wells
Jankowski, Stephanie; Horst, Swantje; Chernikov, Alexej; Chatterjee, Sangam; Heimbrodt, Wolfram
2009-10-01
The complex interplay of energy transfer and tunneling processes in a series of asymmetric ZnSe/(Zn,Mn)Se double quantum-well (DQW) structures is investigated. Steady-state and time-resolved photoluminescence at low temperatures and external magnetic fields up to 7 T in this system show remarkable differences to earlier studies on CdTe/(Cd,Mn)Te DQWs. The pure quantum-mechanical tunneling process is only a minor contribution to the magnetic field dependence of the emission even in case of small barriers and strong QW coupling. The experimental results are supported by quantum-well calculations.
Young's Double Slit Experiment in Quantum Field Theory
Kenmoku, Masakatsu; Kume, Kenji
2011-01-01
Young's double slit experiment is formulated in the framework of canonical quantum field theory in view of the modern quantum optics. We adopt quantum scalar fields instead of quantum electromagnetic fields ignoring the vector freedom in gauge theory. The double slit state is introduced in Fock space corresponding to experimental setup. As observables, expectation values of energy density and positive frequency part of current with respect to the double slit state are calculated which give th...
Zhao Yi Fan
2016-01-01
Full Text Available paper presents a new use of double queues asymmetric gated service polling system in the intelligent traffic light control system.Usually there are more vehicles in main road than minor road,so there are more green light time be needed in the main road.From the computer simulation and theory analysis,we can find that the application of double queues asymmetric gated service polling theory in intelligent traffic system can balance intersections load and set suitable passing time for vehicles to assure the roads open.
Simultaneous measurements of plasma flow and ion temperature using the asymmetric double probe
The asymmetric double probe method is extended to measure not only the ion temperature but also plasma flow in the tokamak edge plasma under a strong magnetic field. The plasma flow or the Mach number is determined by the ratio of ion saturation currents of the double probe pins, where the axes of the cylindrical pins are oriented perpendicular to the magnetic field and face up-or downstream. An experiment was performed in the JFT-2M tokamak. (author)
Dual emission in asymmetric ``giant'' PbS/CdS/CdS core/shell/shell quantum dots
Zhao, Haiguang; Sirigu, Gianluca; Parisini, Andrea; Camellini, Andrea; Nicotra, Giuseppe; Rosei, Federico; Morandi, Vittorio; Zavelani-Rossi, Margherita; Vomiero, Alberto
2016-02-01
Semiconducting nanocrystals optically active in the infrared region of the electromagnetic spectrum enable exciting avenues in fundamental research and novel applications compatible with the infrared transparency windows of biosystems such as chemical and biological optical sensing, including nanoscale thermometry. In this context, quantum dots (QDs) with double color emission may represent ultra-accurate and self-calibrating nanosystems. We present the synthesis of giant core/shell/shell asymmetric QDs having a PbS/CdS zinc blende (Zb)/CdS wurtzite (Wz) structure with double color emission close to the near-infrared (NIR) region. We show that the double emission depends on the excitation condition and analyze the electron-hole distribution responsible for the independent and simultaneous radiative exciton recombination in the PbS core and in the CdS Wz shell, respectively. These results highlight the importance of the driving force leading to preferential crystal growth in asymmetric QDs, and provide a pathway for the rational control of the synthesis of double color emitting giant QDs, leading to the effective exploitation of visible/NIR transparency windows.Semiconducting nanocrystals optically active in the infrared region of the electromagnetic spectrum enable exciting avenues in fundamental research and novel applications compatible with the infrared transparency windows of biosystems such as chemical and biological optical sensing, including nanoscale thermometry. In this context, quantum dots (QDs) with double color emission may represent ultra-accurate and self-calibrating nanosystems. We present the synthesis of giant core/shell/shell asymmetric QDs having a PbS/CdS zinc blende (Zb)/CdS wurtzite (Wz) structure with double color emission close to the near-infrared (NIR) region. We show that the double emission depends on the excitation condition and analyze the electron-hole distribution responsible for the independent and simultaneous radiative exciton
Time-symmetrized description of nonunitary time asymmetric quantum evolution
We discuss how systems which evolve manifestly asymmetrically in time can be described within the framework of the time-symmetrized quantum mechanics. An obvious case of asymmetry arises when a pure state evolves into a mixed state via effectively non-unitary evolution. A two-state method for finding the intermediate probability in postselected systems under such evolution is developed and the time-symmetry aspects of the method are explicitly considered. A specific feature is the existence of the so-called second scenario in which the state originating from the postselection measurement evolves under different evolution superoperator than the state from the preselection measurement. The evolution of the second scenario is explicitly defined. We illustrate the method with two characteristic examples: the spontaneous deexcitation of atoms and the systems approaching thermal equilibrium. We consider the systems with two energy levels and calculate the time-symmetrized probability of finding the system in excited state, under general preselection and postselection conditions. The consequences of the asymmetry of the time evolution on this probability are discussed. It is demonstrated that the arrow of time can be reconstructed in some special cases of postselected systems, while, for a general system, this is not the case. (paper)
From Skew-Cyclic Codes to Asymmetric Quantum Codes
Ezerman, Martianus Frederic; Sole, Patrick; Yemen, Olfa
2010-01-01
We introduce an additive but not $\\F_{4}$-linear map $S$ from $\\F_{4}^{n}$ to $\\F_{4}^{2n}$ and exhibit some of its interesting structural properties. If $C$ is a linear $[n,k,d]_4$-code, then $S(C)$ is an additive $(2n,2^{2k},2d)_4$-code. If $C$ is an additive cyclic code then $S(C)$ is an additive quasi-cyclic code of index $2$. Moreover, if $C$ is a module $\\theta$-cyclic code, a recently introduced type of code which will be explained below, then $S(C)$ is equivalent to an additive cyclic code if $n$ is odd and to an additive quasi-cyclic code of index $2$ if $n$ is even. Given any $(n,M,d)_4$-code $C$, the code $S(C)$ is self-orthogonal under the trace Hermitian inner product. Since the mapping $S$ preserves nestedness, it can be used as a tool in constructing additive asymmetric quantum codes.
Real two-stage Kondo effect in parallel double quantum dot
We study the two-stage Kondo effect in asymmetric parallel double quantum dots. In the triplet, the magnetic moment screenings on two dots occur at the same Kondo temperature. In the critical regime of the triplet–singlet quantum phase transition, a two-stage Kondo screening accompanied with two kinds of Kondo resonance with two energy scales is observed. This is contrast to previous works, in which the Kondo peak in the second screening has not been observed. For large asymmetry of the Kondo coupling, the Kondo resonance in the second step is very weak, which indicates that the screening occurs mainly between two dots and is not a real Kondo screening. Therefore, the side-coupled double quantum dots, which have been extensively studied in the literature, are not an ideal candidate to show a real two-stage Kondo screening. - Highlights: • A real two-stage Kondo screening is not observable in side-coupled 2 quantum dots. • A two-stage Kondo screening is observed in asymmetric parallel 2 quantum dots. • The Kosterlitz–Thouless-type quantum phase transition is studied
Tunneling and energy splitting in an asymmetric double-well potential
An asymmetric double-well potential is considered, assuming that the minima of the wells are quadratic with a frequency ω and the difference of the minima is close to a multiple of hω. A WKB wave function is constructed on both sides of the local maximum between the wells, by matching the WKB function to the exact wave functions near the classical turning points. The continuities of the wave function and its first derivative at the local maximum then give the energy-level splitting formula, which not only reproduces the instanton result for a symmetric potential, but also elucidates the appearance of resonances of tunneling in the asymmetric potential
3D Lorentzian Quantum Gravity from the asymmetric ABAB matrix model
Ambjørn, J.; Jurkiewicz, J.; Loll, R.; Vernizzi, G
2003-01-01
The asymmetric ABAB-matrix model describes the transfer matrix of three-dimensional Lorentzian quantum gravity. We study perturbatively the scaling of the ABAB-matrix model in the neighbourhood of its symmetric solution and deduce the associated renormalization of three-dimensional Lorentzian quantum gravity.
Topological Excitations in Double-Layer Quantum Hall systems
Moon, Kyungsun
1996-01-01
Double-layer quantum Hall systems with spontaneous broken symmetry can exhibit a novel manybody quantum Hall effect due to the strong interlayer coherence. When the layer separation becomes close to the critical value, quantum fluctuations can destroy the interlayer coherence and the quantum Hall effect will disappear. We calculate the renormalized isospin stiffness $\\rho_s$ due to quantum fluctuations within the Hartree-Fock-RPA formalism. The activation energy of the topological excitations...
Dual emission in asymmetric "giant" PbS/CdS/CdS core/shell/shell quantum dots.
Zhao, Haiguang; Sirigu, Gianluca; Parisini, Andrea; Camellini, Andrea; Nicotra, Giuseppe; Rosei, Federico; Morandi, Vittorio; Zavelani-Rossi, Margherita; Vomiero, Alberto
2016-02-21
Semiconducting nanocrystals optically active in the infrared region of the electromagnetic spectrum enable exciting avenues in fundamental research and novel applications compatible with the infrared transparency windows of biosystems such as chemical and biological optical sensing, including nanoscale thermometry. In this context, quantum dots (QDs) with double color emission may represent ultra-accurate and self-calibrating nanosystems. We present the synthesis of giant core/shell/shell asymmetric QDs having a PbS/CdS zinc blende (Zb)/CdS wurtzite (Wz) structure with double color emission close to the near-infrared (NIR) region. We show that the double emission depends on the excitation condition and analyze the electron-hole distribution responsible for the independent and simultaneous radiative exciton recombination in the PbS core and in the CdS Wz shell, respectively. These results highlight the importance of the driving force leading to preferential crystal growth in asymmetric QDs, and provide a pathway for the rational control of the synthesis of double color emitting giant QDs, leading to the effective exploitation of visible/NIR transparency windows. PMID:26837955
The zero-temperature current-phase (I-φ) relation (CPR) of a mesoscopic, ballistic, and asymmetrically stacked, double superconductor-normal-metal-superconduc tor (SNS) junction is studied. Here φ is the phase difference between the two superconducting end-electrodes. The lack of configuration symmetry in such asymmetric SNSNS junctions forbids a simple choice of values for the phase φ2 of the middle superconductor. We propose to determine the values of φ2 by equating the currents in the two normal regions. Two features in the CPR are found. First, the CPR of the asymmetric junction has a cutoff feature, whose origin is best demonstrated in the long middle superconductor (large L2) cases, when the critical current of the double SNS junction is bounded by the SNS junction that has the longer normal region. This cutoff feature is more pronounced for longer L2 and for higher degree of junction asymmetry. Second, in regions other than the cutoff region, the CPR of the asymmetric junction deviates only within a few percent from the CPR of the symmetric junction which has the same total length LTotal in the normal regions and the same L2. This is in contrast with the greater sensitivity the CPR has to the changes in LTotal or L2. (orig.)
Electron Transport through Magnetic Superlattices with Asymmetric Double-Barrier Units in Graphene
We investigate the transport properties through magnetic superlattices with asymmetric double-barrier units in monolayer graphene. In N-periodic asymmetric double-barrier units, there is (N − 1)-fold resonant peak splitting for transmission, but the splitting is (2N − 1)-fold in N-periodic symmetric units. The transmission depends not only on the value of incident wavevectors but also on the value and the direction of transverse wavevectors. This renders the structure's efficient wavevector filters. In addition, the conductance of standard electrons with a parabolic energy spectrum is suppressed more strongly than that of Dirac electrons, whereas the resonances are more pronounced for Dirac electrons than for standard ones. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Quantum theory of light double-slit diffraction
Wu, Xiang-Yao; Li, Hong; Zhang, Bo-Jun; Ma, Ji; Liu, Xiao-Jing; Ba, Nuo; Dong, He; Zhang, Si-Qi; Wang, Jing; Wu, Yi-Heng; Yin, Xin-Guo
2013-01-01
In this paper, we study the light double-slit diffraction experiment with quantum theory approach. Firstly, we calculate the light wave function in slits by quantum theory of photon. Secondly, we calculate the diffraction wave function with Kirchhoff's law. Thirdly, we give the diffraction intensity of light double-slit diffraction, which is proportional to the square of diffraction wave function. Finally, we compare calculation result of quantum theory and classical electromagnetic theory wi...
The Double Rotation as Invariant of Motion in Quantum Mechanics
Zeps, Dainis
2010-01-01
Quantum mechanics may loose its weirdness if systematically geometric algebra methods would be used more and more. Crucial aspect is to find laws of quantum mechanics be present in macroworld in form of description of motions rather than objects. To help to reach this goal we suggest to use double rotation as one of base invariants in quantum mechanics.
Young's Double Slit Experiment in Quantum Field Theory
Kenmoku, Masakatsu
2011-01-01
Young's double slit experiment is formulated in the framework of canonical quantum field theory in view of the modern quantum optics. We adopt quantum scalar fields instead of quantum electromagnetic fields ignoring the vector freedom in gauge theory. The double slit state is introduced in Fock space corresponding to experimental setup. As observables, expectation values of energy density and positive frequency part of current with respect to the double slit state are calculated which give the interference term. Classical wave states are realized by coherent double slit states in Fock space which connect quantum particle states with classical wave states systematically. In case of incoherent sources, the interference term vanishes by averaging random phase angles as expected.
Gasser, U.; Gustavsson, S.; Küng, B.; Ensslin, K.; Ihn, T.; Driscoll, D C; Gossard, A. C.
2008-01-01
We investigate experimentally the influence of current flow through two independent quantum point contacts to a nearby double quantum dot realized in a GaAs-AlGaAs heterostructure. The observed current through the double quantum dot can be explained in terms of coupling to a bosonic bath. The temperature of the bath depends on the power generated by the current flow through the quantum point contact. We identify the dominant absorption and emission mechanisms in a double quantum dot as an int...
Yu, Da-Ming; Wang, Ling-Ling; Lin, Qi; Zhai, Xiang; Li, Hong-Ju; Xia, Sheng-Xuan
2016-05-01
Double electromagnetically induced transparency (EIT)-like resonances are numerically achieved by detuning and bright-dark coupling in an asymmetric plasmonic waveguide resonator system. The transmission properties of the system are simulated by the finite-difference time-domain (FDTD) method. Just because double EIT-like resonances originate from different mechanisms, a single EIT-like resonance can be well tuned independently, namely, one induced transparency window can be tuned in the horizontal direction while the other one is nearly invariable. The present design idea will be applicable in highly integrated optical circuits. Moreover, the formation of double EIT-like resonances may play a guiding role when designing plasmonic devices.
Deformed quantum double realization of the toric code and beyond
Padmanabhan, Pramod; Ibieta-Jimenez, Juan Pablo; Bernabe Ferreira, Miguel Jorge; Teotonio-Sobrinho, Paulo
2016-09-01
Quantum double models, such as the toric code, can be constructed from transfer matrices of lattice gauge theories with discrete gauge groups and parametrized by the center of the gauge group algebra and its dual. For general choices of these parameters the transfer matrix contains operators acting on links which can also be thought of as perturbations to the quantum double model driving it out of its topological phase and destroying the exact solvability of the quantum double model. We modify these transfer matrices with perturbations and extract exactly solvable models which remain in a quantum phase, thus nullifying the effect of the perturbation. The algebra of the modified vertex and plaquette operators now obey a deformed version of the quantum double algebra. The Abelian cases are shown to be in the quantum double phase whereas the non-Abelian phases are shown to be in a modified phase of the corresponding quantum double phase. These are illustrated with the groups Zn and S3. The quantum phases are determined by studying the excitations of these systems namely their fusion rules and the statistics. We then go further to construct a transfer matrix which contains the other Z2 phase namely the double semion phase. More generally for other discrete groups these transfer matrices contain the twisted quantum double models. These transfer matrices can be thought of as being obtained by introducing extra parameters into the transfer matrix of lattice gauge theories. These parameters are central elements belonging to the tensor products of the algebra and its dual and are associated to vertices and volumes of the three dimensional lattice. As in the case of the lattice gauge theories we construct the operators creating the excitations in this case and study their braiding and fusion properties.
Magnetophonon resonance in double quantum wells
Ploch, D.; Sheregii, E. M.; Marchewka, M.; Wozny, M.; Tomaka, G.
2009-05-01
The experimental results obtained for the magnetotransport in pulsed magnetic fields in the InGaAs/InAlAs double quantum well (DQW) structures of two different shapes of wells and different values of the electron density are reported. The magnetophonon resonance (MPR) was observed for both types of structures within the temperature range 77-125 K. Four kinds of LO phonons are taken into account to interpret the MPR oscillations in the DQW and a method of the Landau level calculation in the DQW is elaborated for this aim. The peculiarity of the MPR in the DQW is the large number of the Landau levels caused by SAS splitting of the electron states (splitting on the symmetric and anti-symmetric states) and the large number of the phonon assistance electron transitions between Landau levels. The significant role of the carrier statistics is shown too. The behavior of the electron states in the DQWs at comparably high temperatures has been studied using the MPR. It is shown that the Huang and Manasreh [Manasreh [Phys. Rev. B 54, 2044 (1996)] model involving screening of exchange interaction is confirmed.
Bozkaya, Uǧur
2016-04-01
An efficient implementation of the asymmetric triples correction for the coupled-cluster singles and doubles [ΛCCSD(T)] method [S. A. Kucharski and R. J. Bartlett, J. Chem. Phys. 108, 5243 (1998); T. D. Crawford and J. F. Stanton, Int. J. Quantum Chem. 70, 601 (1998)] with the density-fitting [DF-ΛCCSD(T)] approach is presented. The computational time for the DF-ΛCCSD(T) method is compared with that of ΛCCSD(T). Our results demonstrate that the DF-ΛCCSD(T) method provide substantially lower computational costs than ΛCCSD(T). Further application results show that the ΛCCSD(T) and DF-ΛCCSD(T) methods are very beneficial for the study of single bond breaking problems as well as noncovalent interactions and transition states. We conclude that ΛCCSD(T) and DF-ΛCCSD(T) are very promising for the study of challenging chemical systems, where the coupled-cluster singles and doubles with perturbative triples method fails.
Optical toroidal dipolar response by an asymmetric double-bar metamaterial
Dong, Zheng-Gao; Rho, Junsuk; Li, Jia-Qi; Lu, Changgui; Yin, Xiaobo; Zhang, X; 10.1063/1.4757613
2012-01-01
We demonstrate that the toroidal dipolar response can be realized in the optical regime by designing a feasible nanostructured metamaterial, comprising asymmetric double-bar magnetic resonators assembled into a toroid-like configuration. It is confirmed numerically that an optical toroidal dipolar moment dominates over other moments. This response is characterized by a strong confinement of an E-field component at the toroid center, oriented perpendicular to the H-vortex plane. The resonance-enhanced optical toroidal response can provide an experimental avenue for various interesting optical phenomena associated with the elusive toroidal moment.
A Portable Double-Slit Quantum Eraser with Individual Photons
Dimitrova, T. L.; Weis, A.
2011-01-01
The double-slit experiment has played an important role in physics, from supporting the wave theory of light, via the discussions of the wave-particle duality of light (and matter) to the foundations of modern quantum optics. Today it keeps playing an active role in the context of quantum optics experiments involving single photons. In this paper,…
Condensate Splitting in an Asymmetric Double Well for Atom Chip Based Sensors
We report on the adiabatic splitting of a Bose-Einstein condensate of 87Rb atoms by an asymmetric double-well potential located above the edge of a perpendicularly magnetized TbGdFeCo film atom chip. By controlling the barrier height and double-well asymmetry, the sensitivity of the axial splitting process is investigated through observation of the fractional atom distribution between the left and right wells. This process constitutes a novel sensor for which we infer a single shot sensitivity to gravity fields of δg/g≅2x10-4. From a simple analytic model, we propose improvements to chip-based gravity detectors using this demonstrated methodology
A portable double-slit quantum eraser with individual photons
Dimitrova, Todorka Lulcheva; Weis, Antoine
2012-01-01
The double-slit experiment has played an important role in physics, from supporting the wave theory of light, via the discussions of the wave–particle duality of light (and matter) to the foundations of modern quantum optics. Today it keeps playing an active role in the context of quantum optics experiments involving single photons. In this paper, we present a truly portable double-slit apparatus which demonstrates both the wave–particle duality of light and the phenomenon of quantum erasing....
Asymmetric quantum-well structures for AlGaN/GaN/AlGaN resonant tunneling diodes
Yang, Lin'an; Li, Yue; Wang, Ying; Xu, Shengrui; Hao, Yue
2016-04-01
Asymmetric quantum-well (QW) structures including the asymmetric potential-barrier and the asymmetric potential-well are proposed for AlGaN/GaN/AlGaN resonant tunneling diodes (RTDs). Theoretical investigation gives that an appropriate decrease in Al composition and thickness for emitter barrier as well as an appropriate increase of both for collector barrier can evidently improve the negative-differential-resistance characteristic of RTD. Numerical simulation shows that RTD with a 1.5-nm-thick GaN well sandwiched by a 1.3-nm-thick Al0.15Ga0.85N emitter barrier and a 1.7-nm-thick Al0.25Ga0.75N collector barrier can yield the I-V characteristic having the peak current (Ip) and the peak-to-valley current ratio (PVCR) of 0.39 A and 3.6, respectively, about double that of RTD with a 1.5-nm-thick Al0.2Ga0.8N for both barriers. It is also found that an introduction of InGaN sub-QW into the diode can change the tunneling mode and achieve higher transmission coefficient of electron. The simulation demonstrates that RTD with a 2.8-nm-thick In0.03Ga0.97N sub-well in front of a 2.0-nm-thick GaN main-well can exhibit the I-V characteristic having Ip and PVCR of 0.07 A and 11.6, about 7 times and double the value of RTD without sub-QW, respectively. The purpose of improving the structure of GaN-based QW is to solve apparent contradiction between the device structure and the device manufacturability of new generation RTDs for sub-millimeter and terahertz applications.
Enhanced confinement energy in strained asymmetric T-shaped quantum wires
Jensen, Jacob Riis; Hvam, Jørn Märcher; Langbein, W.
2001-01-01
A new type of T-shaped quantum wire, based on a sri strained asymmetric structure, has been grown and characterised. A narrow GaAs well is overgrown on an multi quantum well structure consisting of wide InAlGaAs c ells with Al0.3Ga0.7As barriers. Since the lattice constants of the InAlGaAs wells ......-10 meV is found for In molefractions of 10% and 15%, in the multi quantum wells. For an In mole fraction of 20% no quantum wire states are observed, probably due to dislocation formation in the overgrown layers.......A new type of T-shaped quantum wire, based on a sri strained asymmetric structure, has been grown and characterised. A narrow GaAs well is overgrown on an multi quantum well structure consisting of wide InAlGaAs c ells with Al0.3Ga0.7As barriers. Since the lattice constants of the InAlGaAs wells...
Asymmetric and double-cathode-pad wire chambers for the LHCb muon system
Kachtchouk, A; Riegler, W; Schmidt, B; Schneider, T; Souvorov, V
2005-01-01
We present results from two types of Multi-Wire Proportional Chambers (MWPCs) with wire pitch of 1.5 mm and cathode–cathode distance of 5 mm intended for triggering purposes in the LHCb experiment. Both prototypes use cathode readout because this allows arbitrary segmentation in order to achieve the required granularity. One MWPC prototype uses a symmetric wire–cathode distance (2.5/2.5 mm) with double cathode readout, which doubles the signal compared to reading only one cathode. The second prototype uses an asymmetric wire–cathode distance (1.25/3.75 mm) with single cathode readout which also doubles the signal and in addition reduces the width of the induced charge distribution and therefore reduces the crosstalk for small cathode pads. We also performed a dedicated optimization of readout traces and guard traces in order to reduce the pad–pad crosstalk. Both prototypes show a few hundred volts of operating plateau defined as the region with 99% efficiency in a 20 ns time window. Close to the plate...
The Application of Asymmetric Entangled States in Quantum Game
Li, Y; Qin, G; Du, Jiangfeng; Li, Ye; Qin, Gan
2005-01-01
In the present letter, we propose a more general entangling operator to the quantization of Cournot economic model, in which players can access to a continuous set of strategies. By analyzing the relation between the von Neumann entropy of the entangled state and the total profit of two players precisely, we find that the total profit at the Nash equilibrium always achieves its maximal value as long as the entropy tends to infinity. Moreover, since the asymmetry is introduced in the entangled state, the quantum model shows some kind of "encouraging" and "suppressing" effect in profit functions of different players.
Full time nonexponential decay in double-barrier quantum structures
Garcia-Calderon, Gaston; Villavicencio, Jorge
2006-01-01
We examine an analytical expression for the survival probability for the time evolution of quantum decay to discuss a regime where quantum decay is nonexponential at all times. We find that the interference between the exponential and nonexponential terms of the survival amplitude modifies the usual exponential decay regime in systems where the ratio of the resonance energy to the decay width, is less than 0.3. We suggest that such regime could be observed in semiconductor double-barrier reso...
Useinov, Arthur
2012-06-01
In this paper, we study the value of the tunnel magnetoresistance (TMR) as a function of the applied voltage in double barrier magnetic tunnel junctions (DMTJs) with the left and right ferromagnetic (FM) layers being pinned and numerically estimate the possible difference of the TMR curves for negative and positive voltages in the homojunctions (equal barriers and electrodes). DMTJs are modeled as two single barrier junctions connected in series with consecutive tunneling (CST). We investigated the asymmetric voltage behavior of the TMR for the CST in the range of a general theoretical model. Significant asymmetries of the experimental curves, which arise due to different annealing regimes, are mostly explained by different heights of the tunnel barriers and asymmetries of spin polarizations in magnetic layers. © (2012) Trans Tech Publications.
Useinov, Arthur
2011-10-22
In this paper we study the asymmetric voltage behavior (AVB) of the tunnel magnetoresistance (TMR) for single and double barrier magnetic tunnel junctions (MTJs) in range of a quasi-classical free electron model. Numerical calculations of the TMR-V curves, output voltages and I-V characteristics for negative and positive values of applied voltages were carried out using MTJs with CoFeB/MgO interfaces as an example. Asymmetry of the experimental TMR-V curves is explained by different values of the minority and majority Fermi wave vectors for the left and right sides of the tunnel barrier, which arises due to different annealing regimes. Electron tunneling in DMTJs was simulated in two ways: (i) Coherent tunneling, where the DMTJ is modeled as one tunnel system and (ii) consecutive tunneling, where the DMTJ is modeled by two single barrier junctions connected in series. © 2012 Elsevier B.V. All rights reserved.
Li, Ruchun; Hu, Zhaoxia; Shao, Xiaofeng; Cheng, Pengpeng; Li, Shoushou; Yu, Wendan; Lin, Worong; Yuan, Dingsheng
2016-01-01
We report a new environmentally-friendly synthetic strategy for large-scale preparation of 16 nm-ultrathin NiCo based layered double hydroxides (LDH). The Ni50Co50-LDH electrode exhibited excellent specific capacitance of 1537 F g-1 at 0.5 A g-1 and 1181 F g-1 even at current density as high as 10 A g-1, which 50% cobalt doped enhances the electrical conductivity and porous and ultrathin structure is helpful with electrolyte diffusion to improve the material utilization. An asymmetric ultracapacitor was assembled with the N-doped graphitic ordered mesoporous carbon as negative electrode and the NiCo LDH as positive electrode. The device achieves a high energy density of 33.7 Wh kg-1 (at power density of 551 W kg-1) with a 1.5 V operating voltage.
Two kinds of double Fano resonances induced by an asymmetric MIM waveguide structure
Zhang, Bing-Hua; Wang, Ling-Ling; Li, Hong-Ju; Zhai, Xiang; Xia, Sheng-Xuan
2016-06-01
Asymmetric plasmonic waveguides with a shoulder-coupled rectangle cavity are proposed and investigated numerically by using the finite-difference time-domain (FDTD) method. The symmetry breaking of the structure results in a new discrete mode supported by the cavity. The extreme interference between two discrete states and an intrinsic wide continuous state gives rise to novel double Fano resonances with symmetric and anti-symmetric configurations. Coupled-mode theory (CMT) further confirms that two Fano profiles originate from the different coupling conditions of the cavity modes with the waveguides. Moreover, the sensing characters are performed. The Fano responses with the higher sensitivity and figure of merit (FOM) up to 57 are realized. Undoubtedly, the studied structure will play an important role in the nano-integrated plasmonic devices for optical switching and sensing.
Tunable multi-band chiral metamaterials based on double-layered asymmetric split ring resonators
Jia, Xiuli; Wang, Xiaoou; Meng, Qingxin; Zhou, Zhongxiang
2016-07-01
We have numerically demonstrated chiral metamaterials based on double-layered asymmetric Au film with hollow out design of split ring resonators on either side of the polyimide. Multiple electric dipoles and magnetic dipoles resulted from parallel and antiparallel currents between the eight split ring resonators. Multi-band circular dichroism is found in the visible frequency regime by studying the transmission properties. Huge optical activity and the induced multi-band negative refractive index are obtained at resonance by calculating the optical activity and ellipticity of the transmitted E-fields. Chirality parameter and effective refractive index are retrieved to illustrate the tunable optical properties of the metamaterials. The underlying mechanisms for the observed circular dichroism are analyzed. These metamaterials would offer flexible electromagnetic applications in the infrared and visible regime.
Bosonization study of quantum phase transitions in the one-dimensional asymmetric Hubbard model
Wang, Z. G.; Chen, Y G; Gu, S. J.
2007-01-01
The quantum phase transitions in the one-dimensional asymmetric Hubbard model are investigated with the bosonization approach. The conditions for the phase transition from density wave to phase separation, the correlation functions and their exponents are obtained analytically. Our results show that the difference between the hopping integrals for up- and down-spin electrons is crucial for the happening of the phase separation. When the difference is large enough, the phase separation will ap...
Temporal mode sorting using dual-stage quantum frequency conversion by asymmetric Bragg scattering.
Christensen, Jesper B; Reddy, Dileep V; McKinstrie, C J; Rottwitt, K; Raymer, M G
2015-09-01
The temporal shape of single photons provides a high-dimensional basis of temporal modes, and can therefore support quantum computing schemes that go beyond the qubit. However, the lack of linear optical components to act as quantum gates has made it challenging to efficiently address specific temporal-mode components from an arbitrary superposition. Recent progress towards realizing such a "quantum pulse gate," has been proposed using nonlinear optical signal processing to add coherently the effect of multiple stages of quantum frequency conversion. This scheme, called temporal-mode interferometry [D. V. Reddy, Phys. Rev. A 91, 012323 (2015)], has been shown in the case of three-wave mixing to promise near-unity mode-sorting efficiency. Here we demonstrate that it is also possible to achieve high mode-sorting efficiency using four-wave mixing, if one pump pulse is long and the other short - a configuration we call asymmetrically-pumped Bragg scattering. PMID:26368430
Quantum interference in an asymmetric Mach-Zehnder interferometer
Trenti, A.; Borghi, M.; Mancinelli, M.; Price, H. M.; Fontana, G.; Pavesi, L.
2016-08-01
A re-visitation of the well known free space Mach-Zehnder interferometer is reported here. The coexistence between one-photon and two-photons interference from collinear color entangled photon pairs is investigated. Thisarises from an arbitrarily small unbalance in the arm transmittance. The tuning of such asymmetry is reflected in dramatic changes in the coincidence detection, revealing beatings between one particle and two particle interference patterns. In particular, the role of the losses and of the intrinsic phase imperfectness of the lossy beamsplitter are explored in a single-port excited Mach-Zehnder interferometer. This configuration is especially useful for quantum optics on a chip, where the guiding geometry forces photons to travel in the same spatial mode.
Bose Condensation of Interwell Excitons in Double Quantum Wells
Larionov, A. V.; Timofeev, V. B.; Ni, P. A.; Dubonos, S. V.; Hvam, Jørn Märcher; Soerensen, K.
2002-01-01
The luminescence of interwell excitons in double quantum wells GaAs/AlGaAs (n–i–n heterostructures) with large-scale fluctuations of random potential in the heteroboundary planes was studied. The properties of excitons whose photoexcited electron and hole are spatially separated in the neighboring...
Cotunneling effects in GaAs vertical double quantum dot
Badrutdinov, A. O.; Huang, S. M.; Kono, K; Ono, K.; Tayurskii, D. A.
2010-01-01
We observed lifting of Coulomb blockade in GaAs vertical double quantum dot with low potential barriers, induced by cotunneling mechanisms at dilution fridge temperature of 10 mK. Several distinct features were observed, compared to single dot case, and appropriate explanation for them was given
Multiple Nuclear Polarization States in a Double Quantum Dot
Danon, J.; Vink, I.T.; Koppens, F.H.L.; Nowack, K.C.; Vandersypen, L.M.K.; Nazarov, Y.V.
2009-01-01
We observe multiple stable states of nuclear polarization and nuclear self-tuning over a large range of fields in a double quantum dot under conditions of electron spin resonance. The observations can be understood within an elaborated theoretical rate equation model for the polarization in each of
Wei, Hai-Rui; Deng, Fu-Guo
2013-01-01
We present some deterministic schemes to construct universal quantum gates, that is, controlled- NOT, three-qubit Toffoli, and Fredkin gates, between flying photon qubits and stationary electron-spin qubits assisted by quantum dots inside double-sided optical microcavities. The control qubit of our gates is encoded on the polarization of the moving single photon and the target qubits are encoded on the confined electron spins in quantum dots inside optical microcavities. Our schemes for these...
Perturbative quantum gravity in double field theory
Boels, Rutger H.; Horst, Christoph
2016-04-01
We study perturbative general relativity with a two-form and a dilaton using the double field theory formulation which features explicit index factorisation at the Lagrangian level. Explicit checks to known tree level results are performed. In a natural covariant gauge a ghost-like scalar which contributes even at tree level is shown to decouple consistently as required by perturbative unitarity. In addition, a lightcone gauge is explored which bypasses the problem altogether. Using this gauge to study BCFW on-shell recursion, we can show that most of the D-dimensional tree level S-matrix of the theory, including all pure graviton scattering amplitudes, is reproduced by the double field theory. More generally, we argue that the integrand may be reconstructed from its single cuts and provide limited evidence for off-shell cancellations in the Feynman graphs. As a straightforward application of the developed technology double field theory-like expressions for four field string corrections are derived.
Development of a theory of the variable quantum yield of the photoproducts from asymmetric bilirubin
Full text: Bilirubin (BR) is the molecule responsible for neonatal jaundice, curable by phototherapy, and hence has been extensively studied. It is an asymmetric bichromophoric molecule; the excited states of the chromophores undergo the Davidoff (exciton, electric dipole) interaction. One of the peculiarities of BR is that the quantum yield of its photoproducts varies with wavelength. An account of the development of a theory for this will be given: part was given at a previous Wagga conference. It may well be that the Davidoff interaction parameter varies with wavelength, even though a constant interaction parameter gives rise to a variable quantum yield. Differences in the linewidths of the Davidoff lines also affect the quantum yield behaviour
Restrepo, R.L., E-mail: pfrire@eia.edu.co [Department of Physics, Cumhuriyet University, 58140 Sivas (Turkey); Escuela de Ingeniería de Antioquia-EIA, Envigado (Colombia); Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia-UdeA, Calle 70 No. 52-21, Medellín (Colombia); Ungan, F.; Kasapoglu, E. [Department of Physics, Cumhuriyet University, 58140 Sivas (Turkey); Mora-Ramos, M.E. [Facultad de Ciencias, Universidad Autonóma del Estado de Morelos, Ave. Universidad 1001, CP 62209, Cuernavaca, Morelos (Mexico); Morales, A.L.; Duque, C.A. [Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia-UdeA, Calle 70 No. 52-21, Medellín (Colombia)
2015-01-15
This paper presents the results of the theoretical study of the effects of non-resonant intense laser field and electric and magnetic fields on the optical properties (the linear and third-order nonlinear refractive index and absorption coefficients) in an asymmetric quantum well. The electric field and intense laser field are applied along the growth direction of the asymmetric quantum well and the magnetic field is oriented perpendicularly. To calculate the energy and the wave functions of the electron in the asymmetric quantum well, the effective mass approximation and the method of envelope wave function are used. The asymmetric quantum well is constructed by using different aluminium concentrations in both right and left barriers. The confinement in the quantum well is changed drastically by either the effect of electric and magnetic fields or by the application of intense laser field. The optical properties are calculated using the compact density matrix approach. The results show that the effect of the intense laser field competes with the effects of the electric and magnetic fields. Consequently, peak position shifts to lower photon energies due to the effect of the intense laser field and it shifts to higher photon energies by the effects of electric and magnetic fields. In general, it is found that the concentration of aluminum, electric and magnetic fields and intense laser field are external agents that modify the optical responses in the asymmetric quantum well.
This paper presents the results of the theoretical study of the effects of non-resonant intense laser field and electric and magnetic fields on the optical properties (the linear and third-order nonlinear refractive index and absorption coefficients) in an asymmetric quantum well. The electric field and intense laser field are applied along the growth direction of the asymmetric quantum well and the magnetic field is oriented perpendicularly. To calculate the energy and the wave functions of the electron in the asymmetric quantum well, the effective mass approximation and the method of envelope wave function are used. The asymmetric quantum well is constructed by using different aluminium concentrations in both right and left barriers. The confinement in the quantum well is changed drastically by either the effect of electric and magnetic fields or by the application of intense laser field. The optical properties are calculated using the compact density matrix approach. The results show that the effect of the intense laser field competes with the effects of the electric and magnetic fields. Consequently, peak position shifts to lower photon energies due to the effect of the intense laser field and it shifts to higher photon energies by the effects of electric and magnetic fields. In general, it is found that the concentration of aluminum, electric and magnetic fields and intense laser field are external agents that modify the optical responses in the asymmetric quantum well
Braunstein, Samuel L.; Buzek, Vladimir; Hillery, Mark
2000-01-01
We show that for any Hilbert-space dimension, the optimal universal quantum cloner can be constructed from essentially the same quantum circuit, i.e., we find a universal design for universal cloners. In the case of infinite dimensions (which includes continuous variable quantum systems) the universal cloner reduces to an essentially classical device. More generally, we construct a universal quantum circuit for distributing qudits in any dimension which acts covariantly under generalized disp...
A fast "hybrid" silicon double quantum dot qubit
Shi, Zhan; Prance, J R; Gamble, John King; Koh, Teck Seng; Shim, Yun-Pil; Hu, Xuedong; Savage, D E; Lagally, M G; Eriksson, M A; Friesen, Mark; Coppersmith, S N
2011-01-01
We propose a quantum dot qubit architecture that has an attractive combination of speed and fabrication simplicity. It consists of a double quantum dot with one electron in one dot and two electrons in the other. The qubit itself is a set of two states with total spin quantum numbers $S^2=3/4$ ($S=\\half$) and $S_z = -\\half$, with the two different states being singlet and triplet in the doubly occupied dot. The architecture is relatively simple to fabricate, a universal set of fast operations can be implemented electrically, and the system has potentially long decoherence times. These are all extremely attractive properties for use in quantum information processing devices.
Single electron tunneling in double and triple quantum wells
Filikhin, I.; Karoui, A.; Vlahovic, B.
2016-03-01
Electron localization and tunneling in laterally distributed double quantum well (DQW) and triple quantum well (TQW) are studied. Triangular configuration for the TQWs as well as various quantum well (QW) shapes and asymmetry are considered. The effect of adding a third well to a DQW is investigated as a weakly coupled system. InAs/GaAs DQWs and TQWs were modeled using single subband effective mass approach with effective potential simulating the strain effect. Electron localization dynamics in DQW and TQW over the whole spectrum is studied by varying the inter-dot distances. The electron tunneling appeared highly sensitive to small violations of the DQW mirror symmetry. We show that the presence of a third dot increases the tunneling in the DQW. The dependence of the tunneling in quantum dot (QD) arrays on inter-dot distances is also discussed.
Second-harmonic generation in asymmetric quantum dots in the presence of a static magnetic field
Li Xue-Chao; Wang An-Min; Wang Zhao-Liang; Yang Yang
2012-01-01
The second-harmonic generation (SHG) coefficient in an asymmetric quantum dot (QD) with a static magnetic field is theoretically investigated.Within the framework of the effective-mass approximation,we obtain the confined wave functions and energies of electrons in the QD.We also obtain the SHG coefficient by the compact-density-matrix approach and the iterative method.The numerical results for the typical GaAs/AlGaAs QD show that the SHG coefficient depends strongly on the magnitude of magnetic field,parameters of the asymmetric potential and the radius of the QD.The resonant peak shifts with the magnetic field or the radius of the QD changing.
QCAD simulation and optimization of semiconductor double quantum dots
Nielsen, Erik [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Gao, Xujiao [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Kalashnikova, Irina [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Muller, Richard Partain [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Salinger, Andrew Gerhard [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Young, Ralph Watson [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2013-12-01
We present the Quantum Computer Aided Design (QCAD) simulator that targets modeling quantum devices, particularly silicon double quantum dots (DQDs) developed for quantum qubits. The simulator has three di erentiating features: (i) its core contains nonlinear Poisson, e ective mass Schrodinger, and Con guration Interaction solvers that have massively parallel capability for high simulation throughput, and can be run individually or combined self-consistently for 1D/2D/3D quantum devices; (ii) the core solvers show superior convergence even at near-zero-Kelvin temperatures, which is critical for modeling quantum computing devices; (iii) it couples with an optimization engine Dakota that enables optimization of gate voltages in DQDs for multiple desired targets. The Poisson solver includes Maxwell- Boltzmann and Fermi-Dirac statistics, supports Dirichlet, Neumann, interface charge, and Robin boundary conditions, and includes the e ect of dopant incomplete ionization. The solver has shown robust nonlinear convergence even in the milli-Kelvin temperature range, and has been extensively used to quickly obtain the semiclassical electrostatic potential in DQD devices. The self-consistent Schrodinger-Poisson solver has achieved robust and monotonic convergence behavior for 1D/2D/3D quantum devices at very low temperatures by using a predictor-correct iteration scheme. The QCAD simulator enables the calculation of dot-to-gate capacitances, and comparison with experiment and between solvers. It is observed that computed capacitances are in the right ballpark when compared to experiment, and quantum con nement increases capacitance when the number of electrons is xed in a quantum dot. In addition, the coupling of QCAD with Dakota allows to rapidly identify which device layouts are more likely leading to few-electron quantum dots. Very efficient QCAD simulations on a large number of fabricated and proposed Si DQDs have made it possible to provide fast feedback for design
Maximally extended sl(2|2) as a quantum double
Beisert, Niklas; Hecht, Reimar
2016-01-01
We derive the universal R-matrix of the quantum-deformed enveloping algebra of centrally extended sl(2|2) using Drinfeld's quantum double construction. We are led to enlarging the algebra by additional generators corresponding to an sl(2) automorphism. For this maximally extended algebra we construct a consistent Hopf algebra structure where the extensions exhibit several uncommon features. We determine the corresponding universal R-matrix containing some non-standard functions. Curiously, this Hopf algebra has one extra deformation parameter for which the R-matrix does not factorize into products of exponentials.
Hall Drag in Correlated Double Layer Quantum Hall Systems
Yang, Kun
1998-01-01
We show that in the limit of zero temperature, double layer quantum Hall systems exhibit a novel phenomena called Hall drag, namely a current driven in one layer induces a voltage drop in the other layer, in the direction perpendicular to the driving current. The two-by-two Hall resistivity tensor is quantized and proportional to the ${\\bf K}$ matrix that describes the topological order of the quantum Hall state, even when the ${\\bf K}$ matrix contains a zero eigenvalue, in which case the Hal...
Catalytic asymmetric synthesis of spirocyclic azlactones by a double Michael-addition approach.
Weber, Manuel; Frey, Wolfgang; Peters, René
2013-06-17
Spirocyclic azlactones are shown to be useful precursors of cyclic quaternary amino acids, such as the constrained cyclohexane analogues of phenylalanine. These compounds are of interest as building blocks for the synthesis of artificial peptide analogues with controlled folds in the peptide backbone. They were prepared in the present study by a step- and atom-economic catalytic asymmetric tandem approach, requiring two steps starting from N-benzoyl glycine and divinylketones. The key of this protocol is the enantioselective formation of the azlactone spirocycles, which involves a PdII-catalyzed double 1,4-addition of an in situ generated azlactone intermediate to the dienone (a formal [5+1] cycloaddition). As the catalyst, a planar chiral ferrocene bispalladacycle was used. Mechanistic studies suggest a monometallic reaction pathway. Although the diastereoselectivity was found to be moderate, the enantioselectivity is usually high for the formation of the azlactone spirocycles, which contain up to three contiguous stereocenters. Spectroscopic studies have shown that the spirocycles often prefer a twist over a chair conformation of the cyclohexanone moiety. PMID:23613333
We show that oscillation of low temperature electron mobility μ can be obtained by applying an electric field F along the growth direction of the asymmetrically barrier delta doped AlxGa1-xAs parabolic double quantum well structure. The drastic changes in the subband Fermi energies and distributions of subband wave functions as a function of F yield nonmonotonic intra- and intersubband scattering rate matrix elements mediated by intersubband effects. The oscillatory enhancement of μ, which is attributed to the subband mobilities governed by the ionized impurity scattering, magnifies with increase in well width and decrease in height of the parabolic structure potential. The results can be utilized for nanoscale low temperature device applications
Akbas, H.; Sucu, S.; Minez, S.; Dane, C.; Akankan, O.; Erdogan, I.
2016-06-01
We have studied and computed variationally the impurity energy, impurity energy turning points, and ground state normalized binding energy as functions of the impurity position for shallow impurity in asymmetric quantum wells under hydrostatic pressure. We found that the normalized binding energy significantly depends on the asymmetry of the well, besides depending on the impurity position and hydrostatic pressure. Also, the dependence of the positive normalized binding energy on the pressure can be used to find out the degree of the asymmetry of the well or the impurity position in the well.
Zhang, Zhi-Hai; Zou, LiLi; Liu, Chenglin; Yuan, Jian-Hui
2015-09-01
In the present work, the optical absorption coefficients (OACs) and the changes in the refractive index (RI) in asymmetrical Gaussian potential quantum wells (QWs) with the applied electric field are studied in detail. We find both energy and wavefunction for low-lying state are wrong in the previous work (Guo and Du, 2013; Wu et al., 2014; Zhai, 2014). Simultaneously, we obtain new and reliable results via the differential method. Finally, the applied electric field, well width, and well depth have great influence on the optical absorption coefficients and refractive index changes in this system.
Anomalous capacitance of quantum well double-barrier diodes
Boric, Olga; Tolmunen, Timo J.; Kollberg, Erik; Frerking, Margaret A.
1992-01-01
The S-parameters of several different quantum well double barrier diodes have been measured. A technique has been developed for measuring whisker contacted diodes with an HP 8510B automatic network analyzer. Special coaxial mounts using K-connectors were designed to enable measurements up to 20 GHz. The voltage-dependent conductance and capacitance were derived from the measured reflection coefficient of each device. The C/V characteristics were observed to exhibit an anomalous increase at voltages corresponding to the negative differential resistance region (NDR). These are the first reported S-parameter measurements in the negative differential resistance region of quantum well double barrier diodes. A theory is presented that explains, in part, the observed results.
Dephasing and hyperfine interaction in carbon nanotubes double quantum dots
Reynoso, Andres Alejandro; Flensberg, Karsten
2012-01-01
We study theoretically the return probability experiment, which is used to measure the dephasing time T-2*, in a double quantum dot (DQD) in semiconducting carbon nanotubes with spin-orbit coupling and disorder-induced valley mixing. Dephasing is due to hyperfine interaction with the spins of the C...... with these for DQDs in clean nanotubes, whereas the disorder effect is always relevant when the magnetic field is perpendicular to the nanotube axis....
Thermoelectric effect in a parallel double quantum dot structure
Gong, Wei-Jiang; Wei, Guo-Zhu
2011-01-01
We discuss the thermoelectric properties assisted by the Fano effect of a parallel double quantum dot (QD) structure. By adjusting the couplings between the QDs and leads, we facilitate the nonresonant and resonant channels for the Fano interference. It is found that at low temperature, Fano lineshapes appear in the electronic and thermal conductance spectra, which can also be reversed by an applied local magnetic flux with its phase factor $\\phi=\\pi$. And, the Fano effect contributes decisiv...
Second harmonic generation in an asymmetric rectangular quantum well under hydrostatic pressure
The effects of structure parameters and hydrostatic pressure on the electronic states and the second harmonic generation (SHG) susceptibility of asymmetric rectangular quantum well (ARQW) are studied. The asymmetry of the potential can be controlled by changing the structural parameters and this adjustable asymmetry is important for optimizing the SHG susceptibility. We have calculated analytically the electronic states in ARQW within the framework of the envelope function approach. Numerical results for Al xl Ga1-xl As/GaAs/Al xr Ga1-xr As quantum well are presented. The results obtained show that the hydrostatic pressure and the structure parameters of ARQW significantly influence the SHG susceptibility. This behavior in the SHG susceptibility gives a new degree of freedom in regions of interest for device applications
Spin polarization and conductance of the laterally asymmetric quantum point contact
Wolf, G.V.; Chuburin, Yu.P., E-mail: chuburin@ftiudm.ru
2014-06-13
We calculate conductance and polarization for the laterally asymmetric quantum point contact. We consider both Rashba coupling and spin–orbit interaction induced by asymmetric lateral confinement, without external magnetic field. We show that a conductance plateau may appear at 0.5G{sub 0}(G{sub 0}=2e{sup 2}/h), without Rashba coupling and lateral spin–orbit interaction. For a spin-polarized injected current, the lateral spin–orbit interaction gives additional control of the conductance by varying the side gates potential. For unpolarized electrons, the spin polarization arises along all coordinate axes. There is a possibility of switching of spin polarization by the gates potential. - Highlights: • Spin-dependent conductance for the laterally asymmetric quasi-1D system is studied. • The 0.5 conductance feature may appear without spin–orbit interaction. • The lateral spin–orbit interaction gives the control of the spin polarization. • For unpolarized electrons the lateral spin–orbit coupling is a switch of polarization.
Dynamical cooling of nuclear spins in double quantum dots
Electrons trapped in quantum dots can exhibit quantum-coherent spin dynamics over long timescales. These timescales are limited by the coupling of electron spins to the disordered nuclear spin background, which is a major source of noise and dephasing in such systems. We propose a scheme for controlling and suppressing fluctuations of nuclear spin polarization in double quantum dots, which uses nuclear spin pumping in the spin-blockade regime. We show that nuclear spin polarization fluctuations can be suppressed when electronic levels in the two dots are properly positioned near resonance. The proposed mechanism is analogous to that of optical Doppler cooling. The Overhauser shift due to fluctuations of nuclear polarization brings electron levels in and out of resonance, creating internal feedback to suppress fluctuations. Estimates indicate that a better than 10-fold reduction of fluctuations is possible.
The connection between noise and quantum correlations in a double quantum dot
Bodoky, F.; Belzig, W.; Bruder, C.
2007-01-01
We investigate the current and noise characteristics of a double quantum dot system. The strong correlations induced by the Coulomb interaction create entangled two-electron states and lead to signatures in the transport properties. We show that the interaction parameter phi, which measures the admixture of the double-occupancy contribution to the singlet state and thus the degree of entanglement, can be directly accessed through the Fano factor of super-Poissonian shot noise.
Noise Estimation and Adaptive Encoding for Asymmetric Quantum Error Correcting Codes
Florjanczyk, Jan; Brun, Todd; Center for Quantum Information Science; Technology Team
We present a technique that improves the performance of asymmetric quantum error correcting codes in the presence of biased qubit noise channels. Our study is motivated by considering what useful information can be learned from the statistics of syndrome measurements in stabilizer quantum error correcting codes (QECC). We consider the case of a qubit dephasing channel where the dephasing axis is unknown and time-varying. We are able to estimate the dephasing angle from the statistics of the standard syndrome measurements used in stabilizer QECC's. We use this estimate to rotate the computational basis of the code in such a way that the most likely type of error is covered by the highest distance of the asymmetric code. In particular, we use the [ [ 15 , 1 , 3 ] ] shortened Reed-Muller code which can correct one phase-flip error but up to three bit-flip errors. In our simulations, we tune the computational basis to match the estimated dephasing axis which in turn leads to a decrease in the probability of a phase-flip error. With a sufficiently accurate estimate of the dephasing axis, our memory's effective error is dominated by the much lower probability of four bit-flips. Aro MURI Grant No. W911NF-11-1-0268.
Wang, Hainan; Thiele, Alexander; Pilon, Laurent [UCLA
2013-11-15
This paper presents a generalized modified Poisson–Nernst–Planck (MPNP) model derived from first principles based on excess chemical potential and Langmuir activity coefficient to simulate electric double-layer dynamics in asymmetric electrolytes. The model accounts simultaneously for (1) asymmetric electrolytes with (2) multiple ion species, (3) finite ion sizes, and (4) Stern and diffuse layers along with Ohmic potential drop in the electrode. It was used to simulate cyclic voltammetry (CV) measurements for binary asymmetric electrolytes. The results demonstrated that the current density increased significantly with decreasing ion diameter and/or increasing valency |z_{i}| of either ion species. By contrast, the ion diffusion coefficients affected the CV curves and capacitance only at large scan rates. Dimensional analysis was also performed, and 11 dimensionless numbers were identified to govern the CV measurements of the electric double layer in binary asymmetric electrolytes between two identical planar electrodes of finite thickness. A self-similar behavior was identified for the electric double-layer integral capacitance estimated from CV measurement simulations. Two regimes were identified by comparing the half cycle period τ_{CV} and the “RC time scale” τ_{RC} corresponding to the characteristic time of ions’ electrodiffusion. For τ_{RC} ← τ_{CV}, quasi-equilibrium conditions prevailed and the capacitance was diffusion-independent while for τ_{RC} → τ_{CV}, the capacitance was diffusion-limited. The effect of the electrode was captured by the dimensionless electrode electrical conductivity representing the ratio of characteristic times associated with charge transport in the electrolyte and that in the electrode. The model developed here will be useful for simulating and designing various practical electrochemical, colloidal, and biological systems for a wide range of applications.
Spin-dependent thermoelectric transport through double quantum dots
Wang Qiang; Xie Hai-Qing; Jiao Hu-Jun; Li Zhi-Jian; Nie Yi-Hang
2012-01-01
We study the thermoelectric transport through a double-quantum-dot system with spin-dependent interdot coupling and ferromagnetic electrodes by means of the non-equilibrium Green's function in the linear response regime.It is found that the thermoelectric coefficients are strongly dependent on the splitting of the interdot coupling,the relative magnetic configurations,and the spin polarization of leads.In particular,the thermoelectric efficiency can reach a considerable value in the parallel configuration when the effective interdot coupling and the tunnel coupling between the quantum dots and the leads for the spin-down electrons are small.Moreover,the thermoelectric efficiency increases with the intradot Coulomb interaction increasing and can reach very high values at appropriate temperatures.In the presence of the magnetic field,the spin accumulation in the leads strongly suppresses the thermoelectric efficiency,and a pure spin thermopower can be obtained.
Bose Condensation of Interwell Excitons in Double Quantum Wells
Larionov, A. V.; Timofeev, V. B.; Ni, P. A.; Dubonos, S. V.; Hvam, Jørn Märcher; Soerensen, K.
2002-01-01
The luminescence of interwell excitons in double quantum wells GaAs/AlGaAs (n–i–n heterostructures) with large-scale fluctuations of random potential in the heteroboundary planes was studied. The properties of excitons whose photoexcited electron and hole are spatially separated in the neighboring...... quantum wells were studied as functions of density and temperature within the domains on the scale less than one micron. For this purpose, the surfaces of the samples were coated with a metallic mask containing specially prepared holes (windows) of a micron size an less for the photoexcitation and...... observation of luminescence. For weak pumping (less than 50 µW), the interwell excitons are strongly localized because of small-scale fluctuations of a random potential, and the corresponding photoluminescence line is inhomogeneously broadened (up to 2.5 meV). As the resonant excitation power increases, the...
Polarization converters on double hetero structures containing strained quantum wells
Khalique, U.; van der Tol, J. J. G. M.; Nötzel, R.; Smit, M. K.
2009-02-01
The importance of polarization manipulation is increased as optical fiber systems evolve to higher data rates. Photonic integrated circuits should be insensitive to the state of polarization of the light emanating from fibers if they are to be used as detectors, add-drop mutiplexers or cross connects. Either all the integrated components have to be polarization independent or only one polarization direction should be used. For either method, a compact polarization converter is useful. A model is developed for the mode propagation in the waveguide of the slanted side polarization converter based on double hetero structures. The model is extended to include polarization dependent absorption and mismatch. Polarization converters on different double heterostructures (with and without quantum wells) have been designed and are realized by contact optical lithography. The performance of the realized converters is well described with the model.
Ac response of a coupled double quantum dot
Xu Jie; W.Z. Shangguan; Zhan Shi-Chang
2005-01-01
The effect of phase-breaking process on the ac response of a coupled double quantum dot is studied in this paper based on the nonequilibrium Green function formalism. A general expression is derived for the ac current in the presence of electron-phonon interaction. The ac conductance is numerically computed and the results are compared with those in [Anatram M P and Datts S 1995 Phys. Rev. B 51 7632]. Our results reveal that the inter-dot electron tunnelling interplays with that between dots and electron reservoirs, and contributes prominently to the ac current when inter-dot tunnelling coupling is much larger than the tunnelling coupling between dots and electron reservoirs. In addition, the phase-breaking process is found to have a significant effect on the ac transport through the coupled double dot.
Quantum theory of electronic double-slit diffraction
Wu, Xiang-Yao; Zhang, Bai-Jun; Liu, Xiao-Jing; Wang, Li; Liu, Bing; Fan, Xi-Hui; Guo, Yi-Qing
2006-01-01
The phenomena of electron, neutron, atomic and molecular diffraction have been studied by many experiments, and these experiments are explained by some theoretical works. In this paper, we study electronic double-slit diffraction with quantum mechanical approach. We can obtain the results: (1) When the slit width $a$ is in the range of $3\\lambda\\sim 50\\lambda$ we can obtain the obvious diffraction patterns. (2) when the ratio of $\\frac{d+a}{a}=n (n=1, 2, 3,\\cdot\\cdot\\cdot)$, order $2n, 3n, 4n...
Controlling Below-Threshold Nonsequential Double Ionization via Quantum Interference
Maxwell, A S
2015-01-01
We show through simulation that quantum interference in non-sequential double ionization can be used to control the recollision with subsequent ionization (RESI) mechanism. This includes the shape, localization and symmetry of RESI electron-momentum distributions, which may be shifted from a correlated to an anti-correlated distribution or vice versa, far below the direct ionization threshold intensity. As a testing ground, we reproduce recent experimental results by employing specific coherent superpositions of excitation channels. We examine two types of interference, from electron indistinguishability and intra-cycle events, and from different excitation channels.
Localized double-quantum-filtered 1H NMR spectroscopy
Thomas, M. A.; Hetherington, H. P.; Meyerhoff, D. J.; Twieg, D. B.
The image-guided in vivo spectroscopic (ISIS) pulse sequence has been combined with a double-quantum-filter scheme in order to obtain localized and water-suppressed 1H NMR spectra of J-coupled metabolites. The coherence-transfer efficiency associated with the DQ filter for AX and A 3X spin systems is described. Phantom results of carnosine, alanine, and ethanol in aqueous solution are presented. For comparison, the 1H NMR spectrum of alanine in aqueous solution with the binomial (1331, 2662) spin-echo sequence is also shown.
Double-layer-gate architecture for few-hole GaAs quantum dots
Wang, D. Q.; Hamilton, A. R.; Farrer, I.; Ritchie, D. A.; Klochan, O.
2016-08-01
We report the fabrication of single and double hole quantum dots using a double-layer-gate design on an undoped accumulation mode {{Al}}x{{Ga}}1-x{As}/GaAs heterostructure. Electrical transport measurements of a single quantum dot show varying addition energies and clear excited states. In addition, the two-level-gate architecture can also be configured into a double quantum dot with tunable inter-dot coupling.
Double-layer-gate architecture for few-hole GaAs quantum dots.
Wang, D Q; Hamilton, A R; Farrer, I; Ritchie, D A; Klochan, O
2016-08-19
We report the fabrication of single and double hole quantum dots using a double-layer-gate design on an undoped accumulation mode [Formula: see text]/GaAs heterostructure. Electrical transport measurements of a single quantum dot show varying addition energies and clear excited states. In addition, the two-level-gate architecture can also be configured into a double quantum dot with tunable inter-dot coupling. PMID:27389108
Entanglement evolution in the open quantum systems consisting of asymmetric oscillators
Afshar, Davood; Mehrabankar, Somayeh; Abbasnezhad, Farkhondeh
2016-03-01
Using the theory of open quantum systems, we study the entanglement evolution in two and three-mode systems consisting of uncoupled harmonic oscillators which interact with a thermal bath as the environment. The evolution of the system is obtained with the use of the master equation in the Lindblad form with the Markovian approximation. The coherent states of a spinless charged particle in an anisotropic harmonic potential and a uniform magnetic field are considered as the initial states of two and three-mode systems. Then by the use of the positive partial transpose criterion for three-mode system and the logarithmic negativity for two-mode system, the entanglement evolution is obtained as a function of the temperature, dissipation coefficient, magnetic field and asymmetric parameter. In both two and three-mode systems, by increasing the dissipation coefficient and temperature, the entanglement sudden death occurs sooner. Also, for certain values of the magnetic field and asymmetric parameter which depend on the other parameters, the entanglement survives the most.
Generalized asymmetric phase-covariant quantum cloning within a nonextensive approach
Boudjema, R.; Hamici, A.-H.; Hachemane, M.; Smida, A.
2016-01-01
In this paper, we present a generalized transformation of the optimal asymmetric 1longrightarrow 2 phase-covariant quantum cloning. This generalization is based on the deformed forms of the exponential that emerge from nonextensive statistical mechanics. In particular, two distinct definitions of the q-exponential are discussed. The case where the cloning is symmetric is also studied. In order to highlight the influence of nonextensive treatment on the perfection of clones and entanglement, the effect of the q-index has been clearly illustrated in figures depicting the fidelities in terms of the entanglement parameter θ for different values of q. Our study shows that due to the intrinsic properties of the system, the entanglement is not preserved. Thus, entanglement can be controlled by the nonextensive parameter. As an illustration, the incoherent attack on the BB84 protocol has also been considered in the economical case.
Afzal, Muhammad Imran; Lee, Yong Tak
2016-01-01
Von Neumann and Wigner theorized bounding of asymmetric eigenstates and anti-crossing of symmetric eigenstates. Experiments have shown that owing to anti-crossing and similar radiation rates, graphene-like resonance of inhomogeneously strained photonic eigenstates can generate pseudomagnetic field, bandgaps and Landau levels, while dissimilar rates induce non-Hermicity. Here, we showed experimentally higher-order supersymmetry and quantum phase transitions by resonance between similar one dimensional lattices. The lattices consisted of inhomgeneously strain-like phases of triangular solitons. The resonance created two dimensional inhomogeneously deformed photonic graphene. All parent eigenstates are annihilated. Where eigenstates of mildly strained solitons are annihilated with similar (power law) rates through one tail only and generated Hermitianally bounded eigenstates. The strongly strained solitons, positive defects are annihilated exponentially through both tails with dissimilar rates. Which bounded eig...
Energy dynamics in ZnSe/ZnMnSe double-quantum-well structures
Jankowski, Stephanie; Heimbrodt, Wolfram; Horst, Swantje; Chernikov, Alexej; Chatterjee, Sangam [Department of Physics and Material Sciences Center, Phillipps-University Marburg (Germany)
2009-07-01
Asymmetric ZnSe/ZnMnSe double-quantum-well (DQW) structures with different barrier width have been grown between dilute magnetic ZnMnSe cladding layers on a (100)GaAs substrate with a ZnSe buffer. The DQWs have been studied by cw and time resolved spectroscopy in external magnetic fields up to 7 Tesla. The ZnSe quantum wells are under tensile strain in these DQW structures yielding the light-hole exciton states to be the energetically lowest lying states. This is the main difference to earlier papers, where tunnelling of carriers and excitons have been studied in DQW structures with heavy hole excitons being the lowest lying states. In the magnetic field we were able to change the barrier height, to split the states of the wells due to the Giant-Zeeman-effect of the ZnMnSe barriers and to manipulate the radiationless energy transfer processes between the 3d-internal transitions and the excitonic states. As a result of the sophisticated interaction of these mechanisms a unique excitation energy dynamics was found and is discussed in detail.
Using nonequilibrium Green's function techniques, we investigate Andreev reflection and Aharonov-Bohm oscillations through a parallel-coupled double quantum dot connected with a ferromagnetic lead and a superconductor lead. The possibility of controlling Andreev reflection and Aharonov-Bohm oscillations of the system is explored by tuning the interdot coupling, the gate voltage, the magnetic flux, and the intradot spin-flip scattering. When the spin-flip scattering increases, Fano resonant peaks resulting from the asymmetrical levels of the two quantum dots begin to split, and Aharonov-Bohm oscillations are suppressed. Due to the interdot coupling, one strongly and one weakly coupled state of the system can be formed. The magnetic flux can exchange the function of the two states, which leads to a swap effect.
Zeros in single-channel transmission through double quantum dots.
Rotter, I; Sadreev, A F
2005-04-01
By using a simple model we consider single-channel transmission through a double quantum dot that consists of two single dots coupled by a wire of finite length L . Each of the two single dots is characterized by a few energy levels only, and the wire is assumed to have only one level whose energy depends on the length L . The transmission is described by using S matrix theory and the effective non-Hermitian Hamilton operator H(eff) of the system. The decay widths of the eigenstates of H(eff) depend strongly on energy. The model explains the origin of the transmission zeros of the double dot that is considered by us. Mostly, they are caused by (destructive) interferences between neighboring levels and are of first order. When, however, both single dots are identical and their transmission zeros are of first order, those of the double dot are of second order. First-order transmission zeros cause phase jumps of the transmission amplitude by pi, while there are no phase jumps related to second-order transmission zeros. In this latter case, a phase jump occurs due to the fact that the width of one of the states vanishes when crossing the energy of the transmission zero. The parameter dependence of the widths of the resonance states is determined by the spectral properties of the two single dots. PMID:15903767
Tollerud, Jonathan O
2016-01-01
We identify carrier scattering at densities below which it has previously been observed in semiconductor quantum wells. These effects are evident in the peakshapes of 2D double-quantum spectra, which change as a function of excitation density. At high excitation densities ($\\geq 10^{9}$ carriers/,cm$^{-2}$) we observe untilted peaks similar to those reported in previous experiments. At low excitation densities (<$10^{8}$ carriers cm$^{-2}$) we observe narrower, tilted peaks. Using a simple simulation, we show that tilted peak-shapes are expected in double-quantum spectra when inhomogeneous broadening is much larger than homogeneous broadening, and that fast pure-decoherence of the double-quantum coherence can obscure this peak tilt. These results show that carrier interactions are important at lower densities than previously expected, and that the `natural' double-quantum peakshapes are hidden by carrier interactions at the excitation densities typically used. Furthermore, these results demonstrate that an...
The Double-Well Potential in Quantum Mechanics: A Simple, Numerically Exact Formulation
Jelic, V.; Marsiglio, F.
2012-01-01
The double-well potential is arguably one of the most important potentials in quantum mechanics, because the solution contains the notion of a state as a linear superposition of "classical" states, a concept which has become very important in quantum information theory. It is therefore desirable to have solutions to simple double-well potentials…
Double Rashba Quantum Dots Ring as a Spin Filter
Chi Feng
2008-01-01
Full Text Available AbstractWe theoretically propose a double quantum dots (QDs ring to filter the electron spin that works due to the Rashba spin–orbit interaction (RSOI existing inside the QDs, the spin-dependent inter-dot tunneling coupling and the magnetic flux penetrating through the ring. By varying the RSOI-induced phase factor, the magnetic flux and the strength of the spin-dependent inter-dot tunneling coupling, which arises from a constant magnetic field applied on the tunneling junction between the QDs, a 100% spin-polarized conductance can be obtained. We show that both the spin orientations and the magnitude of it can be controlled by adjusting the above-mentioned parameters. The spin filtering effect is robust even in the presence of strong intra-dot Coulomb interactions and arbitrary dot-lead coupling configurations.
Quantum chaos and the double-slit experiment
We report on the numerical simulation of the double-slit experiment, where the initial wave packet is bounded inside a billiard domain with perfectly reflecting walls. If the shape of the billiard is such that the classical ray dynamics is regular, we obtain interference fringes whose visibility can be controlled by changing the parameters of the initial state. However, if we modify the shape of the billiard thus rendering classical (ray) dynamics fully chaotic, the interference fringes disappear and the intensity on the screen becomes the (classical) sum of intensities for the two corresponding one-slit experiments. Thus we show a clear and fundamental example in which transition to chaotic motion in a deterministic classical system, in absence of any external noise, leads to a profound modification in the quantum behavior
Spin transport properties in double quantum rings connected in series*
Du Jian; Wang Suxin; Pan Jianghong
2011-01-01
A new model of metal/semiconductor/metal double-quantum-ring connected in series is proposed and the transport properties in this model are theoretically studied. The results imply that the transmission coefficient shows periodic variations with increasing semiconductor ring size. The effects of the magnetic field and Rashba spin-orbit interaction on the transmission coefficient for two kinds of spin state electrons are different. The number of the transmission coefficient peaks is related to the length ratio between the upper ann and the half circumference of the ring. In addition, the transmission coefficient shows oscillation behavior with enhanced external magnetic field, and the corresponding average value is related to the two leads' relative position.
Transport, Charge Sensing, and Quantum Control in Si/SiGe Double Quantum Dots
Wang, Ke; Koppinen, Panu; Dovzhenko, Yuliya; Petta, Jason
2011-03-01
Si/SiGe quantum dots hold great promise as ultra-coherent qubits. In comparison with the GaAs system, Si has a weaker hyperfine interaction due to the zero nuclear spin of 28 Si and smaller spin-orbit coupling due to its lighter atomic weight. However, the fabrication of highly controllable Si/SiGe quantum dots is complicated by valley degeneracy, the larger effective electron mass, and the difficulty of obtaining high quality samples. Here we develop a robust fabrication process for depletion mode Si/SiGe quantum dots, demonstrating high quality ohmic contacts and low-leakage Pd top gates. We report DC transport measurements as well as charge sensing in single and double quantum dots. The quantum dot gate electrode pattern allows a relatively high level of control over the confinement potential, tunneling rates, and electron occupation. Funded by the Sloan and Packard Foundations, NSF, and DARPA QuEST. We thank Jag Shah for logistical support.
Two-band electron transport in a double quantum well
Fletcher, R.; Tsaousidou, M.; Smith, T.; Coleridge, P. T.; Wasilewski, Z. R.; Feng, Y.
2005-04-01
The carrier densities and mobilities have been measured for the first two populated subbands in a GaAs double quantum well (DQW) as a function of the top gate voltage Vg . The densities and quantum mobilities ( μiq , i=1,2 ) were obtained from the de Haas-Shubnikov oscillations. The transport mobilities (μit) were determined from the semiclassical low-field magnetoresistance with intersubband scattering taken into account. At 0.32K the experimental data on both μit and μiq , as a function of Vg , lie on two curves which cross at the resonance point as expected from theoretical considerations. At 1.09K and 4.2K the μit curves no longer cross at resonance, but show a gap. The reason for this is not known. The mobilities have been calculated in the low-temperature limit within the Boltzmann framework by assuming that they are limited by scattering due to ionized impurities located at the outside interfaces. The assumption of short-range scattering is justified by the relatively small value of the ratio μit/μiq that is measured in the present system. The theoretical values obtained for μit and μiq are in reasonable agreement with the experiment for all values of Vg examined. We have also calculated the resistivity and intersubband scattering rates of the DQW as a function of Vg and again find good agreement with measured values.
Adaptive double chain quantum genetic algorithm for constrained optimization problems
Kong Haipeng; Li Ni; Shen Yuzhong
2015-01-01
Optimization problems are often highly constrained and evolutionary algorithms (EAs) are effective methods to tackle this kind of problems. To further improve search efficiency and con-vergence rate of EAs, this paper presents an adaptive double chain quantum genetic algorithm (ADCQGA) for solving constrained optimization problems. ADCQGA makes use of double-individuals to represent solutions that are classified as feasible and infeasible solutions. Fitness (or evaluation) functions are defined for both types of solutions. Based on the fitness function, three types of step evolution (SE) are defined and utilized for judging evolutionary individuals. An adaptive rotation is proposed and used to facilitate updating individuals in different solutions. To further improve the search capability and convergence rate, ADCQGA utilizes an adaptive evolution process (AEP), adaptive mutation and replacement techniques. ADCQGA was first tested on a widely used benchmark function to illustrate the relationship between initial parameter values and the convergence rate/search capability. Then the proposed ADCQGA is successfully applied to solve other twelve benchmark functions and five well-known constrained engineering design problems. Multi-aircraft cooperative target allocation problem is a typical constrained optimization problem and requires efficient methods to tackle. Finally, ADCQGA is successfully applied to solving the target allocation problem.
Černoch, Antonín; Soubusta, Jan; Čelechovská, L.; Dušek, M.; Fiurášek, J.
2009-01-01
Roč. 80, č. 6 (2009), 062306/1-062306/6. ISSN 1050-2947 R&D Projects: GA MŠk(CZ) 1M06002 Institutional research plan: CEZ:AV0Z10100522 Keywords : kvantová informace * asymetrické klonování * částečná symetrizace quantum information * asymmetric cloning * partial symmetrization Subject RIV: BH - Optics, Masers, Lasers Impact factor: 2.866, year: 2009
Intersubband absorption with difference-frequency generation in GaAs asymmetric quantum wells
An asymmetric quantum well (AQW) is designed to emit terahertz (THz) waves by using difference frequency generation (DFG) with the structure of GaAs/Al0.2Ga0.8As/Al0.5Ga0.5As. The characteristics of absorption coefficients are analysed under the parabolic and non-parabolic energy-band conditions in detail. We find that the absorption coefficients vary with the two pump optical intensities, and they reach the maxima when the pump wavelengths are given as λp1 = 9.70 μm and λp2 = 10.64 μm, respectively. Compared with non-parabolic conditions, the total absorption coefficient under parabolic conditions shows a blue shift, which is due to the increase in the energy difference between the ground and excited states. By adjusting the two pump optical intensities, the wave vector phase-matching condition inside the AQW is satisfied. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)
Tunnelling process in ZnSe/ZnMnSe double-quantum-well structures
Jankowski, Stephanie; Niebling, Tobias; Heimbrodt, Wolfram [Phillipps-University Marburg (Germany). Department of Physics and Matrial Science Center
2008-07-01
Asymmetric ZnSe/ZnMnSe double-quantum-well (DQW) structures with different barrier width have been grown between ZnMnSe cladding layers on a (100)GaAs substrate with a ZnSe buffer. The ZnSe wells are under tensile strain in these DQW structures yielding the light-hole exciton states to be the energetically lowest lying states. This is different to earlier papers, where tunnelling of carriers and excitons have been studied in DQW structures made of diluted magnetic semiconductors with heavy hole excitons to be the lowest lying states. In an external magnetic field we were able to manipulate the barrier height due to Giant Zeeman effect of the ZnMnSe barriers. Hence we can study the tunnelling processes in these structures in dependence of the height and width of the barrier by photoluminescence, photomodulated reflectivity as well as time resolved measurements. Surprisingly, very different results to heavy hole tunnelling have been found. The obtained results and differences will be discussed in detail.
S Ghosh; S P Bhattacharyya
2012-01-01
The quantum dynamics of intramolecular H-atom transfer in malonaldehyde is investigated with a model two-dimensional Hamiltonian constructed with the help of available ab initio theoretical data on the relevant portion of the potential energy surface. At zero temperature, the H-atom transfer takes place by tunnelling leading to cis-cis isomerization while the cis-trans channel remains closed. Local excitation of the cis-trans mode by an external field is predicted to quench cis-cis tunnelling isomerization while excitation of the cis-cis mode is found to enhance the isomerization by tunnelling.
Hysteresis in the Quantum Hall Regimes in Electron Double-Quantum Structures
Pan, W.; Reno, J. L.; Simmons, J. A.
2005-04-01
We present in this paper the experimental results of transport hysteresis in an extremely imbalanced electron double-quantum-well (DQW) structure. The ratio of the top layer density (ntop) to bottom layer density (nbot) is continuously tuned by applying voltage to a front gate. Under a condition when the top layer is nearly depleted (ntop ~ 3×1010 cm-2) while the bottom layer remains at nbot = 1.9 × 1011 cm-2, the hysteresis is absent in the B sweeps as long as the total Landau level filling ν < 1 and the 2D electron systems are in the fractional quantum Hall effect regime. Surprisingly, a large hysteresis is observed during the gate sweeps at the same values of B and ntop. We attribute this unexpected hysteresis to the formation of an insulating state, probably a weakly pinned Wigner solid state, in the top layer.
Bandyopadhyay, Supriyo
1999-01-01
Intriguing dichotomies in quantum measurement theory involving the role of the obersever, objective reality, collapse of wavefunctions and actualization of a measurement outcome are cast into a patholigical gedanken experiment involving a single electron in a double quantum dot system coupled via a weak link.
Vignesh, G.; Nithiananthi, P., E-mail: nithyauniq@gmail.com [Nanostructure Lab, Department of Physics, Gandhigram Rural University, Gandhigram, Tamilnadu (India)
2015-06-24
Diamagnetic susceptibility of a randomly distributed donor in a GaAs/Al{sub 0.3}Ga{sub 0.7}As Double Quantum Well has been calculated in its ground state as a function of barrier and well width. It is shown that the modification in the barrier and well dimension significantly influences the dimensional character of the donor through modulating the subband distribution and in turn the localization of the donor. The effect of barrier and well thickness on the interparticle distance has also been observed. Interestingly it opens up the possibility of tuning the susceptibility and monitoring the tunnel coupling among the wells.
Diamagnetic susceptibility of a randomly distributed donor in a GaAs/Al0.3Ga0.7As Double Quantum Well has been calculated in its ground state as a function of barrier and well width. It is shown that the modification in the barrier and well dimension significantly influences the dimensional character of the donor through modulating the subband distribution and in turn the localization of the donor. The effect of barrier and well thickness on the interparticle distance has also been observed. Interestingly it opens up the possibility of tuning the susceptibility and monitoring the tunnel coupling among the wells
Quantum spin and charge pumping through double quantum dots with ferromagnetic leads
The pumping of electrons through double quantum dots (DQDs) attached to ferromagnetic leads have been theoretically investigated by using the nonequilibrium Green's function method. It is found that an oscillating electric field applied to the quantum dot may give rise to the pumped charge and spin currents. In the case that both leads are ferromagnet, a pure spin current can be generated in the antiparallel magnetization configuration, where no net charge current exists. The possibility of manipulating the pumped spin current is explored by tuning the dot level and the ac field. By making use of various tunings, the magnitude and direction of the pumped spin current can be well controlled. For the case that only one lead is ferromagnetic, both of the charge and spin currents can be pumped and flow in opposite directions on the average. The control of the magnitude and direction of the pumped charge and spin currents is also discussed by means of the magnetic flux threading through the DQD ring. -- Highlights: → We theoretically investigate the pumping of electrons through double quantum dots attached to ferromagnetic leads. → An oscillating electric field applied to the quantum dot may give rise to the pumped charge and spin currents. → When both leads are ferromagnet, a pure spin current can be generated in the antiparallel magnetization configuration. → By making use of various tunings, the magnitude and direction of the pumped spin current can be well controlled. → When only one lead is ferromagnetic, both of the charge and spin currents can be pumped and flow in opposite directions.
Shokrieh, M. M.; Zeinedini, A.
2014-06-01
In this research, a novel data reduction method for calculation of the strain energy release rate ( SERR) of asymmetric double cantilever beams ( ADCB) is presented. For this purpose the elastic beam theory ( EBT) is modified and the new method is called as the modified elastic beam theory ( MEBT). Also, the ADCB specimens are modeled using ABAQUS/Standard software. Then, the initiation of delamination of ADCB specimens is modeled using the virtual crack closure technique ( VCCT). Furthermore, magnitudes of the SERR for different samples are also calculated by an available data reduction method, called modified beam theory ( MBT). Using the hand lay-up method, different laminated composite samples are manufactured by E-glass/epoxy unidirectional plies. In order to measure the SERR, all samples are tested using an experimental setup. The results determined by the new data reduction method ( MEBT) show good agreements with the results of the VCCT and the MBT.
Spin-polarized currents in double and triple quantum dots driven by ac magnetic fields
Busl, Maria; Platero, Gloria
2010-01-01
We analyze transport through both a double quantum dot and a triple quantum dot with inhomogeneous Zeeman splittings in the presence of crossed dc and ac magnetic fields. We find that strongly spin-polarized current can be achieved by tuning the relative energies of the Zeeman-split levels of the dots, by means of electric gate voltages: depending on the energy level detuning, the double quantum dot works either as spin-up or spin-down filter. We show that a triple quantum dot in series under...
Orlita, M.; Byszewski, M.; Döhler, G. H.; Grill, M.; Hlídek, P.; Malzer, S.; Zvára, M.
2006-08-01
We report on photoluminescence (PL) measurements of a GaAs/AlGaAs double quantum well (DQW) in high magnetic fields. Measurements were carried out on a selectively contacted symmetric p- δn-DQW- δn-p structure, which allows a variation of the electron density in DQW by a p-n bias and simultaneously a tilting of DQW, when a p-p bias is applied. Attention was paid to phenomena in in-plane magnetic fields, theoretically studied by Huang and Lyo (HL), [Phys. Rev. B 59, (1999) 7600]. In this paper, we compare our results for both symmetric and asymmetric DQWs with the theoretical model made by HL. Whereas the spectra from a symmetric DQW fully confirmed the theoretical predictions, the results gained from DQW with an electric-field-induced asymmetry did not allow a proper study of anticipated effects. The reasons for that are discussed.
Kinetic analysis of the thermal isomerisation pathways in an asymmetric double azobenzene switch
Robertus, Jort; Reker, Siebren F.; Pijper, Thomas C.; Deuzeman, Albert; Browne, Wesley R.; Feringa, Ben L.
2012-01-01
Here we report a photochemical and kinetic study of the thermal relaxation reaction of a double azobenzene system, in which two azobenzene photochromic units are connected via a phenyl ring. Upon UV irradiation, three thermally unstable isomers are formed. Kinetic studies using arrayed H-1-NMR spect
Shifted one-parameter supersymmetric family of quartic asymmetric double-well potentials
Extending our previous work (Rosu, 2014), we define supersymmetric partner potentials through a particular Riccati solution of the form F(x)=(x−c)2−1, where c is a real shift parameter, and work out the quartic double-well family of one-parameter isospectral potentials obtained by using the corresponding general Riccati solution. For these parametric double well potentials, we study how the localization properties of the two wells depend on the parameter of the potentials for various values of the shifting parameter. We also consider the supersymmetric parametric family of the first double-well potential in the Razavy chain of double well potentials corresponding to F(x)=1/2 sinh2x−2((1+√(2))sinh2x)/((1+√(2))cosh2x+1) , both unshifted and shifted, to test and compare the localization properties. - Highlights: • Quartic one-parameter DWs with an additional shift parameter are introduced. • Anomalous localization feature of their zero modes is confirmed at different shifts. • Razavy one-parameter DWs are also introduced and shown not to have this feature
Moquin, Alexandre; Neibert, Kevin D; Maysinger, Dusica; Winnik, Françoise M
2015-01-01
The molecular composition of the biological environment of nanoparticles influences their physical properties and changes their pristine physicochemical identity. In order to understand, or predict, the interactions of cells with specific nanoparticles, it is critical to know their size, shape, and agglomeration state not only in their nascent state but also in biological media. Here, we use asymmetrical flow field-flow fractionation (AF4) with on-line multiangle light scattering (MALS), dynamic light scattering (DLS) and UV-Visible absorption detections to determine the relative concentration of isolated nanoparticles and agglomerates in the case of three types of semi-conductor quantum dots (QDs) dispersed in Dulbecco's Modified Eagle Media (DMEM) containing 10% of fetal bovine serum (DMEM-FBS). AF4 analysis also yielded the size and size distribution of the agglomerates as a function of the time of QDs incubation in DMEM-FBS. The preferred modes of internalization of the QDs are assessed for three cell-types, N9 microglia, human hepatocellular carcinoma cells (HepG2) and human embryonic kidney cells (Hek293), by confocal fluorescence imaging of live cells, quantitative determination of the intracellular QD concentration, and flow cytometry. There is an excellent correlation between the agglomeration status of the three types of QDs in DMEM-FBS determined by AF4 analysis and their preferred mode of uptake by the three cell lines, which suggests that AF4 yields an accurate description of the nanoparticles as they encounter cells and advocates its use as a means to characterize particles under evaluation. PMID:25542679
Hysteresis in the quantum Hall regimes in electron double quantum well structures
Pan, W.; Reno, J. L.; Simmons, J. A.
2005-04-01
We present here experimental results on magnetotransport coefficients in electron double quantum well (DQW) structures. Consistent with previous studies, transport hysteresis is is observed in the electron DQWs. Furthermore, in our gated DQW samples, by varying the top layer Landau level filling (νtop) while maintaining a relatively constant filling factor in the bottom layer (νbot) , we are able to explain the sign of Rxx(up)-Rxx(down) , where Rxx(up) is the magnetoresistance when the gate voltage Vg is swept up and Rxx(down) when Vg is swept down. Interestingly, at small magnetic fields hysteresis is generally stronger when the top quantum well is in the even integer quantum Hall effect (IQHE) regime (e.g., νtop=2 ) than in the odd IQHE regime (e.g, νtop=1 ). While at higher B fields, the hysteresis at νtop=1 becomes the strongest. The switching occurs around the B field at νbot=3 .
Highlights: • We found a coupling between quantum states of two asymmetric circular loops in series. • Distance between the loops was such large that the coupling should not be expected. • In order to detect the coupling we measured two types of quantum voltage oscillations. • Rectified direct and dc voltages versus normal magnetic field were recorded. • The rectified voltage appeared in the loops biased by an ac (without a dc component). -- Abstract: We measured both quantum oscillations of a rectified time-averaged direct voltage Vrec(B) and a dc voltage Vdc(B) as a function of normal magnetic field B, in a thin-film aluminum structure of two asymmetric circular loops in series at temperatures below the superconducting critical temperature Tc. The Vrec(B) and Vdc(B) voltages were observed in the structure biased only with an alternating current (without a dc component) and only with a direct current (without an ac component), respectively. The aim of the measurements was to find whether interaction (nonlinear coupling) exists between quantum magnetic-resistive states of two loops at a large distance from each other. The distance between the loop centers was by an order of magnitude longer than the Ginzburg–Landau coherence length ξ(T). At such distance, one would not expect to detect any interaction between the quantum states of the loops. But we did find such an interaction. Moreover, we found that Vdc(B) functions (like Vrec(B) ones) can be used to describe the quantum states of the loops
Repulsion of Single-well Fundamental Edge Magnetoplasmons in Double Quantum Wells
Balev, O. G.; Vasilopoulos, P.
1998-01-01
A {\\it microscopic} treatment of fundamental edge magnetoplasmons (EMPs) along the edge of a double quantum well (DQW) is presented for strong magnetic fields, low temperatures, and total filling factor \
KAMBIZ ABEDI
2011-08-01
Full Text Available This paper presents the effects of geometrical structure on microwave and optical properties of traveling wave electroabsorption modulators (TWEAMs based on asymmetric intra-step-barrier coupled double strained quantum wells (AICD-SQW active layer. The AICD-SQW active layer structure has advantages such as very low insertion loss, zero chirp, large Stark shift and high extinction ratio in comparison with the intra-step quantum well (IQW structure. Firstly, the influences of the intrinsic (active layer thickness and width on effective optical index and confinement factor are analyzed. Furthermore, the effect of the intrinsic layer thickness on their transmission line microwave properties such as microwave index, microwave loss, andcharacteristic impedance are evaluated. The thickness and width of active layer are changed from 0 μm to 1.4 μm and 1 μm to 3 μm, respectively. Finally, the frequency response of TWEAM based on AICD-SQW active layer is calculated using circuit model.
Multiple-path Quantum Interference Effects in a Double-Aharonov-Bohm Interferometer
Yang XF
2010-01-01
Full Text Available Abstract We investigate quantum interference effects in a double-Aharonov-Bohm (AB interferometer consisting of five quantum dots sandwiched between two metallic electrodes in the case of symmetric dot-electrode couplings by the use of the Green’s function equation of motion method. The analytical expression for the linear conductance at zero temperature is derived to interpret numerical results. A three-peak structure in the linear conductance spectrum may evolve into a double-peak structure, and two Fano dips (zero conductance points may appear in the quantum system when the energy levels of quantum dots in arms are not aligned with one another. The AB oscillation for the magnetic flux threading the double-AB interferometer is also investigated in this paper. Our results show the period of AB oscillation can be converted from 2π to π by controlling the difference of the magnetic fluxes threading the two quantum rings.
Spin-coupled double-quantum-dot behavior inside a single-molecule transistor
Bernand-Mantel, A.; Seldenthuis, J. S.; Beukman, A.; van der Zant, H. S. J.; Meded, V.; Chandrasekhar, R; Fink, K.; Ruben, M; Evers, F.
2010-01-01
We report on the observation of Kondo and split Kondo peaks in single-molecule transistors containing a single spin transition molecule with a Fe2+ ion. Coulomb blockade characteristics reveal a double quantum dot behavior in a parallel configuration, making our system a molecular equivalent to a semiconducting double-quantum-dot system. As the gate voltage is increased the charging of the second dot by an additional electron induces a splitting of the Kondo peak. We discuss possible origins ...
Jagadale, Ajay D.; Guan, Guoqing; Li, Xiumin; Du, Xiao; Ma, Xuli; Hao, Xiaogang; Abudula, Abuliti
2016-02-01
CoMn LDH electrode is successfully prepared via facile and cost-effective electrodeposition method. The effect of Co2+/Mn2+ molar ratio on supercapacitive performance is systematically investigated. It is found that the presence of Mn(OH)6 unit in CoMn LDH offers an excellent reversibility as well as highly electrochemical activity for supercapacitor application. The CoMn LDH film with a Co2+/Mn2+ molar ratio of 9:1 loaded on Ni foam electrode exhibits the maximum specific capacitance of 1062.6 F/g at the current density of 0.7 A/g with an excellent cyclic stability of 96.3% over 5000 CD cycles. It indicates that CoMn LDH nanoflakes loaded on Ni foam can minimize the lattice mismatch which leads to an excellent cyclic stability. The asymmetric supercapacitor assembled with CoMn LDH/Ni foam and AC electrodes shows an excellent cyclic life of 84.2% and an energy density of 4.4 Wh/kg with a power density of 2500 W/kg.
Spin-orbit effects in carbon-nanotube double quantum dots
Weiss, S; Rashba, E I; Kuemmeth, Ferdinand;
2010-01-01
We study the energy spectrum of symmetric double quantum dots in narrow-gap carbon nanotubes with one and two electrostatically confined electrons in the presence of spin-orbit and Coulomb interactions. Compared to GaAs quantum dots, the spectrum exhibits a much richer structure because of the spin...
A Ge/Si heterostructure nanowire-based double quantum dot with integrated charge sensor
Hu, Yongjie; Churchill, Hugh; Reilly, David;
2007-01-01
between the dots and to the leads. We also demonstrate a novel approach to charge sensing in a one-dimensional nanostructure by capacitively coupling the double dot to a single dot on an adjacent nanowire. The double quantum dot and integrated charge sensor serve as an essential building block required to...
Practical quantum repeaters with linear optics and double-photon guns
Kok, Pieter; Williams, Colin P.; Dowling, Jonathan P.
2002-01-01
We show how to create practical, efficient, quantum repeaters, employing double-photon guns, for long-distance optical quantum communication. The guns create polarization-entangled photon pairs on demand. One such source might be a semiconducter quantum dot, which has the distinct advantage over parametric down-conversion that the probability of creating a photon pair is close to one, while the probability of creating multiple pairs vanishes. The swapping and purifying components are implemen...
Schuetz, M. J. A.; Kessler, E. M.; Vandersypen, L. M. K.; Cirac, J. I.; Giedke, G.
2014-01-01
We theoretically study the nuclear spin dynamics driven by electron transport and hyperfine interaction in an electrically-defined double quantum dot (DQD) in the Pauli-blockade regime. We derive a master-equation-based framework and show that the coupled electron-nuclear system displays an instability towards the buildup of large nuclear spin polarization gradients in the two quantum dots. In the presence of such inhomogeneous magnetic fields, a quantum interference effect in the collective ...
Time resolved quantum dynamics of double ionization in strong laser fields
Prauzner-Bechcicki, Jakub S.; Sacha, Krzysztof; Eckhardt, Bruno; Zakrzewski, Jakub
2006-01-01
Quantum calculations of a 1+1-dimensional model for double ionization in strong laser fields are used to trace the time evolution from the ground state through ionization and rescattering to the two electron escape. The subspace of symmetric escape, a prime characteristic of nonsequential double ionization, remains accessible by a judicious choice of 1-d coordinates for the electrons. The time resolved ionization fluxes show the onset of single and double ionization, the sequence of events du...
Therm splitting in a quantum mechanical double center problem for the Dirac equation
An asymptotic (by large internuclear distance) theory of a quantum mechanical double center problem for the Dirac equation is presented. An asymptotic behaviour of the double center wave function of the Dirac electron for the system: an arbitrary ion plus atom is constructed. By using this function the leading term of the therm splitting asymptotic in the relativistic double center problem is found. 37 refs
Alshal, Mohamed A.; Allam, Nageh K.
2016-07-01
A design for a highly efficient modified grating crystalline silicon (c-Si) thin film solar cell is demonstrated and analyzed using the two-dimensional (2-D) finite element method. The suggested grating has a double-sided pyramidal structure. The incorporation of the modified grating in a c-Si thin film solar cell offers a promising route to harvest light into the few micrometers active layer. Furthermore, a layer of silicon nitride is used as an antireflection coating (ARC). Additionally, the light trapping through the suggested design is significantly enhanced by the asymmetry of the top and bottom pyramids. The effects of the thickness of the active layer and facet angle of the pyramid on the spectral absorption, ultimate efficiency (η), and short-circuit current density (J sc) are investigated. The numerical results showed 87.9% efficiency improvement over the conventional thin film c-Si solar cell counterpart without gratings.
Quantum double actions on operator algebras and orbifold quantum field theories
Starting from a local quantum field theory with an unbroken compact symmetry group G in 1+1 dimensional spacetime we construct disorder fields implementing gauge transformations on the fields (order variables) localized in a wedge region. Enlarging the local algebras by these disorder fields we obtain a nonlocal field theory, the fixpoint algebras of which under the appropriately extended action of the group G are shown to satisfy Haag duality in every simple sector. The specifically 1+1 dimensional phenomenon of violation of Haag duality of fixpoint nets is thereby clarified. In the case of a finite group G the extended theory is acted upon in a completely canonical way by the quantum double D(G) and satisfies R-matrix commutation relations as well as a Verlinde algebra. Furthermore, our methods are suitable for a concise and transparent approach to bosonization. The main technical ingredient is a strengthened version of the split property which should hold in all reasonable massive theories. In the appendices (part of) the results are extended to arbitary locally compact groups and our methods are adapted to chiral theories on the circle. (orig.)
Tunability of capacitive coupling in the Si double-quantum-dot system is discussed by changing the number of electrons in quantum dots (QDs), in which the QDs are fabricated using pattern-dependent oxidation (PADOX) of a Si nanowire and multi-fine-gate structure. A single QD formed by PADOX is divided into multiple QDs by additional oxidation through the gap between the fine gates. When the number of electrons occupying the QDs is large, the coupling capacitance increases gradually and almost monotonically with the number of electrons. This phenomenon is attributed to the gradual growth in the effective QD size due to the increase in the number of electrons in the QDs. On the other hand, when the number of electrons changes in the few-electron regime, the coupling capacitance irregularly changes. This irregularity can be observed even up to 40 electrons. This behavior is attributable the rough structure of Si nano-dots made by PADOX. This roughness is thought to induce complicated change in the electron wave function when an electron is added to or subtracted from a QD
Quantum Hall effect in an InAs /AlSb double quantum well
Yakunin, M. V.; Podgornykh, S. M.; Sadofyev, Yu. G.
2009-01-01
Double quantum wells (DQWs) were first implemented in the InAs /AlSb heterosystem, which is characterized by a large Landé g factor ∣g∣=15 of the InAs layers forming the well, much larger than the bulk g factor ∣g∣=0.4 of the GaAs in conventional GaAs /AlGaAs DQWs. The quality of the samples is good enough to permit observation of a clear picture of the quantum Hall effect (QHE). Despite the small tunneling gap, which is due to the large barrier height (1.4eV), features with odd filling factors ν =3,5,7,… are present in the QHE, due to collectivized interlayer states of the DQW. When the field is rotated relative to the normal to the layers, the ν =3 state is suppressed, confirming the collectivized nature of that state and denying that it could owe its existence to a strong asymmetry of the DQW. Previously the destruction of the collectivized QHE states by a parallel field had been observed only for the ν =1 state. The observation of a similar effect for ν =3 in an InAs /AlSb DQW may be due to the large bulk g factor of InAs.
Quantum fluctuations of the antiferro-antiferromagnetic double-layer
Jiang Wei; Zhu Cheng-Bo; Yu Gui-Hong; Lo Veng-Cheong
2009-01-01
This paper stuides the magnetization and quantum fluctuations of an antiferro-antiferromagnetic (AF-AF) doublelayer at zero temperature.It is found that the exchanges and anisotropy constants affect the quantum fluctuations of spins. If the anisotropy exists,there will be no acoustic energy branch in the system. The anisotropy constant,antiferromagnetic intralayer and interlayer coupling have important roles in a balance of the quantum competition.
Velásquez, Rober
2003-04-01
In this work we report on field-induced features appearing in the tunneling current traces of a biased asymmetric triple barrier resonant tunneling device in the presence of an in-plane magnetic field. A theoretical model that satisfactorily explains the origin of these features is discussed. The reported data evidences the localized nature of the quantum states in thin layer asymmetric double-quantum-well structures.
Low frequency noise in asymmetric double barrier magnetic tunnel junctions with a top thin MgO layer
Guo, Hui-Qiang; Tang, Wei-Yue; Liu, Liang; Wei, Jian; Li, Da-Lai; Feng, Jia-Feng; Han, Xiu-Feng
2015-07-01
Low frequency noise has been investigated at room temperature for asymmetric double barrier magnetic tunnel junctions (DBMTJs), where the coupling between the top and middle CoFeB layers is antiferromagnetic with a 0.8-nm thin top MgO barrier of the CoFeB/MgO/CoFe/CoFeB/MgO/CoFeB DBMTJ. At enough large bias, 1/f noise dominates the voltage noise power spectra in the low frequency region, and is conventionally characterized by the Hooge parameter αmag. With increasing external field, the top and bottom ferromagnetic layers are aligned by the field, and then the middle free layer rotates from antiparallel state (antiferromagnetic coupling between top and middle ferromagnetic layers) to parallel state. In this rotation process αmag and magnetoresistance-sensitivity-product show a linear dependence, consistent with the fluctuation dissipation relation. With the magnetic field applied at different angles (θ) to the easy axis of the free layer, the linear dependence persists while the intercept of the linear fit satisfies a cos(θ) dependence, similar to that for the magnetoresistance, suggesting intrinsic relation between magnetic losses and magnetoresistance. Project supported by the National Basic Research Program of China (Grant Nos. 2011CBA00106, 2012CB927400, 2010CB934401, and 2014AA032904), the National High Technology Research and Development Program of China (Grant No. 2014AA032904), and the National Natural Science Foundation of China (Grant Nos. 11434014 and 11104252).
Transport hysteresis in AlGaAs/GaAs double quantum well systems with InAs quantum dots
We report on the charge storage effect of InAs quantum dots (QDs) embedded in the upper well of the AlGaAs/GaAs double quantum well structure. Zero field longitudinal resistivity and Hall resistance at weak magnetic fields exhibited a hysteresis effect during the sweeping of the gate voltage due to the accumulation of charges in the quantum dots. On reverse sweeping the gate voltage, the accumulated charges are prevented from being rapidly depleted due to the screening effect of the upper two-dimensional electron gas, which could significantly enhance the operation and reliability of QD-based non-volatile memory devices
Double coupling: modeling subjectivity and asymmetric organization in social-ecological systems
David Manuel-Navarrete
2015-09-01
Full Text Available Social-ecological organization is a multidimensional phenomenon that combines material and symbolic processes. However, the coupling between social and ecological subsystem is often conceptualized as purely material, thus reducing the symbolic dimension to its behavioral and actionable expressions. In this paper I conceptualize social-ecological systems as doubly coupled. On the one hand, material expressions of socio-cultural processes affect and are affected by ecological dynamics. On the other hand, coupled social-ecological material dynamics are concurrently coupled with subjective dynamics via coding, decoding, personal experience, and human agency. This second coupling operates across two organizationally heterogeneous dimensions: material and symbolic. Although resilience thinking builds on the recognition of organizational asymmetry between living and nonliving systems, it has overlooked the equivalent asymmetry between ecological and socio-cultural subsystems. Three guiding concepts are proposed to formalize double coupling. The first one, social-ecological asymmetry, expands on past seminal work on ecological self-organization to incorporate reflexivity and subjectivity in social-ecological modeling. Organizational asymmetry is based in the distinction between social rules, which are symbolically produced and changed through human agents' reflexivity and purpose, and biophysical rules, which are determined by functional relations between ecological components. The second guiding concept, conscious power, brings to the fore human agents' distinctive capacity to produce our own subjective identity and the consequences of this capacity for social-ecological organization. The third concept, congruence between subjective and objective dynamics, redefines sustainability as contingent on congruent relations between material and symbolic processes. Social-ecological theories and analyses based on these three guiding concepts would support the
Study of electro-optic effect in asymmetrically ramped AlInGaAs multiple quantum well structures
Sadiq, Muhammad Usman; Peters, Frank H.; Corbett, Brian [Tyndall National Institute, Lee Maltings, Cork (Ireland); Department of Physics, University College Cork, Cork (Ireland); O' Callaghan, James; Roycroft, Brendan; Thomas, Kevin; Pelucchi, Emanuele [Tyndall National Institute, Lee Maltings, Cork (Ireland)
2016-04-15
We investigate the electro-optic properties of two oppositely ramped asymmetric quantum well structures in the AlInGaAs material system. The grading of the bandgap in the quantum wells has been achieved by changing the ratio of Al to Ga in the quaternary alloy during the epitaxial growth. The surface normal photo-response and the Fabry-Perot fringe shift in straight waveguides are compared for both structures as a function of applied voltage at 1550 nm for TE-polarized light. The measurements show a change in the refractive index due to a red shift of the excitonic resonances due to the quantum-confined Stark effect. The 10 quantum well structure with a ramp up of the bandgap in the growth direction leads to the figure of merit of the voltage for a π phase shift, V{sub π} by length, L, V{sub π} x L, of 6 as compared to 7 V . mm in the structure with a ramp in opposite direction. Further investigations show that the reduction in V{sub π} is due to increased absorption at high reverse bias which induces a non-linear phase change. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Study of electro-optic effect in asymmetrically ramped AlInGaAs multiple quantum well structures
We investigate the electro-optic properties of two oppositely ramped asymmetric quantum well structures in the AlInGaAs material system. The grading of the bandgap in the quantum wells has been achieved by changing the ratio of Al to Ga in the quaternary alloy during the epitaxial growth. The surface normal photo-response and the Fabry-Perot fringe shift in straight waveguides are compared for both structures as a function of applied voltage at 1550 nm for TE-polarized light. The measurements show a change in the refractive index due to a red shift of the excitonic resonances due to the quantum-confined Stark effect. The 10 quantum well structure with a ramp up of the bandgap in the growth direction leads to the figure of merit of the voltage for a π phase shift, Vπ by length, L, Vπ x L, of 6 as compared to 7 V . mm in the structure with a ramp in opposite direction. Further investigations show that the reduction in Vπ is due to increased absorption at high reverse bias which induces a non-linear phase change. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Determination of energy scales in few-electron double quantum dots
Taubert, Daniela; Schuh, D.; Wegscheider, W.; Ludwig, Stefan
2011-01-01
The capacitive couplings between gate-defined quantum dots and their gates vary considerably as a function of applied gate voltages. The conversion between gate voltages and the relevant energy scales is usually performed in a regime of rather symmetric dot-lead tunnel couplings strong enough to allow direct transport measurements. Unfortunately, this standard procedure fails for weak and possibly asymmetric tunnel couplings, often the case in realistic devices. We have developed methods to d...
Time resolved quantum dynamics of double ionization in strong laser fields
Prauzner-Bechcicki, J S; Sacha, K; Zakrzewski, J; Eckhardt, Bruno; Prauzner-Bechcicki, Jakub S.; Sacha, Krzysztof; Zakrzewski, Jakub
2006-01-01
Quantum calculations of a 1+1-dimensional model for double ionization in strong laser fields are used to trace the time evolution from the ground state through ionization and rescattering to the two electron escape. The subspace of symmetric escape, a prime characteristic of nonsequential double ionization, remains accessible by a judicious choice of 1-d coordinates for the electrons. The time resolved ionization fluxes show the onset of single and double ionization, the sequence of events during the pulse, and the influences of pulse duration, and reveal the relative importance of sequential and non-sequential double ionization, even when ionization takes place during the same field cycle.
Domínguez, Fernando; Platero, Gloria
2009-01-01
We apply an elementary measurement scheme to calculate the electronic triplet-singlet transition mediated by hyperfine interaction in a double quantum dot. We show how the local character of the hyperfine interaction and the nuclear back-action process (flip-flop) are crucial to cancel destructive interferences of the triplet-singlet transition probability. It is precisely this cancellation which differentiates the hyperfine interaction from an anisotropic magnetic field which mixes the tripl...
Dual-wavelength of 1.3um and 1.55um AlGaSb/GaSb asymmetric quantum-well laser
Sim, Steven K. H.; Mutamba, Kabula; Herbert Li, E.
1999-01-01
A dual-wavelength laser diode of 1.3um and 1.55um operating wavelength is under analysis. The structure of this laser diode involves an asymmetric dual quantum-well of AlGaSb/GaSb . The longer-wavelength quantum-well is doped with a 50A Si at the barrier near the well. This will enable a localized intermixing during an anneal under a SiNx cap, while the shorter-wavelength quantum-well is not affected. The area where GaSb is exposed has no intermixing in both the quantum-wells. It is possible ...
Fano effect and Andreev bound states in T-shape double quantum dots
Calle, A.M.; Pacheco, M. [Departamento de Física, Universidad Técnica Federico Santa María, Casilla 110-V, Valparaíso (Chile); Orellana, P.A., E-mail: orellana@ucn.cl [Departamento de Física, Universidad Católica del Norte, Casilla 1280, Antofagasta (Chile)
2013-09-02
In this Letter, we investigate the transport through a T-shaped double quantum dot coupled to two normal metal leads left and right and a superconducting lead. Analytical expressions of Andreev transmission and local density of states of the system at zero temperature have been obtained. We study the role of the superconducting lead in the quantum interferometric features of the double quantum dot. We report for first time the Fano effect produced by Andreev bound states in a side quantum dot. Our results show that as a consequence of quantum interference and proximity effect, the transmission from normal to normal lead exhibits Fano resonances due to Andreev bound states. We find that this interference effect allows us to study the Andreev bound states in the changes in the conductance between two normal leads. - Highlights: • Transport properties of a double quantum dot coupled in T-shape configuration to conducting and superconducting leads are studied. • We report Fano antiresonances in the normal transmission due to the Andreev reflections in the superconducting lead. • We report for first time the Fano effect produced by Andreev bound states in a side quantum dot. • Fano effect allows us to study the Andreev bound states in the changes in the conductance between two normal leads. • Andreev bound states survives even for strong dot-superconductor coupling.
Fano effect and Andreev bound states in T-shape double quantum dots
In this Letter, we investigate the transport through a T-shaped double quantum dot coupled to two normal metal leads left and right and a superconducting lead. Analytical expressions of Andreev transmission and local density of states of the system at zero temperature have been obtained. We study the role of the superconducting lead in the quantum interferometric features of the double quantum dot. We report for first time the Fano effect produced by Andreev bound states in a side quantum dot. Our results show that as a consequence of quantum interference and proximity effect, the transmission from normal to normal lead exhibits Fano resonances due to Andreev bound states. We find that this interference effect allows us to study the Andreev bound states in the changes in the conductance between two normal leads. - Highlights: • Transport properties of a double quantum dot coupled in T-shape configuration to conducting and superconducting leads are studied. • We report Fano antiresonances in the normal transmission due to the Andreev reflections in the superconducting lead. • We report for first time the Fano effect produced by Andreev bound states in a side quantum dot. • Fano effect allows us to study the Andreev bound states in the changes in the conductance between two normal leads. • Andreev bound states survives even for strong dot-superconductor coupling
Janjua, Bilal
2013-01-01
A novel design based on an asymmetrically graded-well, Al(a→b)Ga(1-a→1-b) N / Al(c)Ga(1-c) N,where b>c>a, to enhance the optical matrix element of radiative transitions in an AlGaN based UV-LED, is theoretically studied.
Dissipatively driven entanglement of two nuclear spin ensembles in a double quantum dot
Schuetz, Martin J.A.; Kessler, Eric M.; Cirac, Juan Ignacio; Giedke, Geza [Max-Planck-Institut fuer Quantenoptik, Hans-Kopfermann-Str. 1, D-85748 Garching (Germany)
2013-07-01
Typically, quantum information schemes have been discussed in the context of isolated many-body systems subject to unitary dynamics. Here, dissipation has been identified as a mechanism that corrupts the useful quantum properties of the system under study. Recently, however, with the advent of novel ideas such as dissipative engineering, a paradigm shift could be observed in quantum physics. More and more approaches actively utilize dissipation as a driving force behind the emergence of coherent quantum phenomena. In this spirit, we propose a transport scheme for an electrically defined double quantum dot in which the two nuclear ensembles in the host environment are actively pumped into an entangled target state. Based on a self-consistent Holstein-Primakoff approximation, we derive an effective quantum master equation for the nuclear spins which features an unique entangled steady state; accordingly, long lasting entanglement is created deterministically. Prospects for the experimental realization of this proposal are briefly discussed.
Dissipatively driven entanglement of two nuclear spin ensembles in a double quantum dot
Typically, quantum information schemes have been discussed in the context of isolated many-body systems subject to unitary dynamics. Here, dissipation has been identified as a mechanism that corrupts the useful quantum properties of the system under study. Recently, however, with the advent of novel ideas such as dissipative engineering, a paradigm shift could be observed in quantum physics. More and more approaches actively utilize dissipation as a driving force behind the emergence of coherent quantum phenomena. In this spirit, we propose a transport scheme for an electrically defined double quantum dot in which the two nuclear ensembles in the host environment are actively pumped into an entangled target state. Based on a self-consistent Holstein-Primakoff approximation, we derive an effective quantum master equation for the nuclear spins which features an unique entangled steady state; accordingly, long lasting entanglement is created deterministically. Prospects for the experimental realization of this proposal are briefly discussed.
Koerting, Verena
2007-01-01
In this thesis we study two exchange-coupled quantum dots with an emphasis on non-equilibrium physics. Assuming a single electron on each quantum dot, the double quantum dot system is characterized by an interplay between the Kondo spin coupling of the dots with the leads and the spin-exchange coupling between the dots. We find that a finite voltage on one quantum dot drives the other quantum dot out of equilibrium.
Double-slit experiment with single wave-driven particles and its relation to quantum mechanics
Andersen, Anders Peter; Madsen, Jacob; Reichelt, Christian Günther;
2015-01-01
In a thought-provoking paper, Couder and Fort [Phys. Rev. Lett.97, 154101 (2006)] describe a version of the famous double-slit experiment performed with droplets bouncing on a vertically vibrated fluid surface. In the experiment, an interference pattern in the single-particle statistics is found...... reproduce quantum mechanics in general, and we show that the single-particle statistics for our model in a double-slit experiment with an additional splitter plate differs qualitatively from that of quantum mechanics....
Thermopower in parallel double quantum dots with Rashba spin-orbit interaction
Xue Hui-Jie; Lü Tian-Quan; Zhang Hong-Chen; Yin Hai-Tao; Cui Lian; He Ze-Long
2011-01-01
Based on the Green's function technique and the equation of motion approach, this paper theoretically studies the thermoelectric effect in parallel coupled double quantum dots (DQDs), in which Rashba spin-orbit interaction is taken into account. Rashba spin-orbit interaction contributions, even in a magnetic field, are exhibited obviously in the double quantum dots system for the thermoelectric effect. The periodic oscillation of thermopower can be controlled by tunning the Rashba spin-orbit interaction induced phase. The interesting spin-dependent thermoelectric effects will arise which has important influence on thermoelectric properties of the studied system.
Relaxation of electron energy in the polar semiconductor double quantum dots
Král, Karel; Khás, Zdeněk; Zdeněk, Petr; Čerňanský, Marian; Lin, C. Y.
2002-01-01
Roč. 314, - (2002), s. 490-493. ISSN 0921-4526 R&D Projects: GA AV ČR IAA1010113; GA MŠk OC P5.20 Institutional research plan: CEZ:AV0Z1010914 Keywords : quantum dots * relaxation * double quantum dots * electron-photon interaction Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.609, year: 2002
Tunable Molecular Resonances of Double Quantum Dots Embedded in an Aharonov-Bohm Interferometer
Kang, Kicheon; Cho, Sam Young
2002-01-01
We investigate resonant tunneling through molecular states of coupled double quantum dots embedded in an Aharonov-Bohm (AB) interferometer. The conductance through the system consists of two resonances associated with the bonding and the antibonding quantum states. We predict that the two resonances are composed of a Breit-Wigner resonance and a Fano resonance, those widths and Fano factor depending on the AB phase very sensitively. Further, we point out that the bonding properties, such as t...
Full characterization of a carbon nanotube based parallel double quantum dot
Abulizi, Gulibusitan; Baumgartner, Andreas; Schönenberger, Christian
2016-01-01
We have measured the differential conductance of a parallel carbon nanotube (CNT) double quantum dot (DQD) with strong inter-dot capacitance and inter-dot tunnel coupling. Nominally, the device consists of a single CNT with two contacts. However, we identify two sets of Coulomb blockade (CB) diamonds that do not block transport individually, which suggests that two quantum dots (QDs) are contacted in parallel. We find strong and periodic anti-crossings in the gate and bias dependence, which a...
Kuwahara, Y; Nakamura, Y; Yamanaka, Y
2013-01-01
The $2 \\times 2$-matrix structure of Green's functions is a common feature for the real-time formalisms of quantum field theory under thermal situations, such as the closed time path formalism and Thermo Field Dynamics (TFD). It has been believed to originate from quantum nature. Recently, Galley has proposed the Hamilton's principle with initial data for nonconservative classical systems, doubling each degree of freedom [Phys. Rev. Lett. 110, 174301 (2013)]. We show that the Galley's Hamilto...
Top-gate defined double quantum dots in InAs nanowires
Pfund, A.; Shorubalko, I.; Leturcq, R.; Ensslin, K.
2006-01-01
We present low temperature transport measurements on double quantum dots in InAs nanowires grown by metal-organic vapor phase epitaxy. Two dots in series are created by lithographically defined top-gates with a procedure involving no extra insulating layer. We demonstrate the full tunability from strong to weak coupling between the dots. The quantum mechanical nature of the coupling leads to the formation of a molecular state extending over both dots. The excitation spectra of the individual ...
Equations of motion in Double Field Theory: from classical particles to quantum cosmology
Kan, Nahomi; Shiraishi, Kiyoshi
2012-01-01
The equation of motion for a point particle in the background field of double field theory is considered. We find that the motion is described by a geodesic flow in the doubled geometry. Inspired by analysis on the particle motion, we propose a modified model of quantum string cosmology, which includes two scale factors. The report is based on Phys. Rev. D84 (2011) 124049 [arXiv:1108.5795].
We propose a generalization of quantum teleportation: the so-called many-to-many quantum communication of the information of a d-level system from N spatially separated senders to M>N receivers situated at different locations. We extend the concept of asymmetric telecloning from qubits to d-dimensional systems. We investigate the broadcasting of entanglement by using local 1→2 optimal universal asymmetric Pauli machines and show that the maximal fidelities of the two final entangled states are obtained when symmetric machines are applied. Cloning of entanglement is studied using a nonlocal optimal universal asymmetric cloning machine and we show that the symmetric machine optimally copies the entanglement. The 'many-to-many' teleportation scheme is applied in order to distribute entanglement shared between two observers to two pairs of spatially separated observers
Simulated quantum annealing of double-well and multiwell potentials.
Inack, E M; Pilati, S
2015-11-01
We analyze the performance of quantum annealing as a heuristic optimization method to find the absolute minimum of various continuous models, including landscapes with only two wells and also models with many competing minima and with disorder. The simulations performed using a projective quantum Monte Carlo (QMC) algorithm are compared with those based on the finite-temperature path-integral QMC technique and with classical annealing. We show that the projective QMC algorithm is more efficient than the finite-temperature QMC technique, and that both are inferior to classical annealing if this is performed with appropriate long-range moves. However, as the difficulty of the optimization problem increases, classical annealing loses efficiency, while the projective QMC algorithm keeps stable performance and is finally the most effective optimization tool. We discuss the implications of our results for the outstanding problem of testing the efficiency of adiabatic quantum computers using stochastic simulations performed on classical computers. PMID:26651813
Taro; Arakawa; Ryuji; Iino; Tetsuya; Ishie; Terumasa; Kawabata; Kunio; Tada
2003-01-01
An InGaAs/InAlAs five-layer asymmetric coupled quantum well (FACQW) is expected to show very large electrorefractive index change . n in a wideband transparency region. Band structures of the FACQW are analyzed with Luttinger-Kohn Hamiltonian. The electrorefractive characteristics of the FACQW are discussed.
Yuan, R.-Y., E-mail: yuanry@cnu.edu.cn [Center for Theoretical Physics, Department of Physics, Capital Normal University, Beijing 100048 (China); Zhao, X.; Ji, A.-C. [Center for Theoretical Physics, Department of Physics, Capital Normal University, Beijing 100048 (China); Guo, Y., E-mail: guoy66@tsinghua.edu.cn [Department of Physics and State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University, Beijing 100084 (China); Collaborative Innovation Center of Quantum Matter, Beijing 100084 (China); Yan, H. [Laboratory of Thin Film Materials, Beijing University of Technology, Beijing 100022 (China)
2015-09-04
Both the charging and orbital quantization energies of InAs quantum dot (QD) typically correspond to the terahertz (THz) region. In this letter, under the asymmetric THz irradiations on two leads, electron transport through a two-level InAs QD is theoretically discussed. We demonstrate that when both the frequencies and amplitudes of THz irradiations on two leads are different with the higher asymmetry, the photon–electron pump effect vanishes, even a negative platform appears on the left of the Coulomb peak and a positive platform occurs on the right of the Coulomb interaction related energy level, respectively. This behavior is favorable for the design of THz optoelectronic device. - Highlights: • Asymmetric terahertz waves are irradiated on two leads in two-level InAs QD system. • Only with different frequencies, a negative current resonance is obtained. • A negative platform appears on the left of the Coulomb peak with higher asymmetry. • For the low terahertz field strength, a positive platform occurs. • We report the behaviors are favorable for the design of THz optoelectronic device.
Fast response of the optical nonlinearity in a GaAs/AlGaAs asymmetric triple quantum well structure
Ahn, S H; Sawaki, N
1999-01-01
The time response of the optical nonlinear behavior in a GaAs/AlGaAs asymmetric triple quantum well structure is estimated by using a picosecond pump-probe method at 77 K. From the results of the transmission of the probe pulse as a function of the delay time at the excitation wavelengths, a rise time of 5 approx 10 ps and a fall time of 8 approx 16 ps are obtained. The nonlinear behavior is attributed to the triple resonance of the electronic states due to the build-up of the internal field induced by the separation of photo-excited electrons and holes. It is found that the rise time is determined by the tunneling transfer time of the electrons in the narrowest well to an adjacent well separated by a thin potential barrier.
A duality map for the quantum symplectic double
Allegretti, Dylan G L
2016-01-01
This paper is a continuation of the author's work with Kim (arXiv:1509.01567), which provided a natural $q$-deformation of Fock and Goncharov's canonical basis for the coordinate ring of a cluster variety associated to a punctured surface. Here we consider a cluster variety called the symplectic double, defined for an oriented disk with finitely many marked points on its boundary. We construct a natural map from the tropical integral points of the symplectic double into its quantized algebra of rational functions. Using this construction, we extend the results of arXiv:1509.01567 to the case of a disk with marked points.
On the relation between the modular double of Uq(sl(2,R)) and the quantum Teichmueller theory
We exhibit direct relations between the modular double of Uq(sl(2,R)) and the quantum Teichmueller theory. Explicit representations for the fusion- and braiding operations of the quantum Teichmueller theory are immediate consequences. Our results include a simplified derivation of the Clebsch-Gordan decomposition for the principal series of representation of the modular double of Uq(sl(2,R)).
Transient gain-absorption of the probe field in triple quantum dots coupled by double tunneling
Tian, Si-Cong; Zhang, Xiao-Jun; Wan, Ren-Gang; Zhao, Shuai; Wu, Hao; Shu, Shi-Li; Wang, Li-Jie; Tong, Cun-Zhu
2016-06-01
The transient gain-absorption property of the probe field in a linear triple quantum dots coupled by double tunneling is investigated. It is found that the additional tunneling can dramatically affect the transient behaviors under the transparency condition. The dependence of transient behaviors on other parameters, such as probe detuning, the pure dephasing decay rate of the quantum dots and the initial conditions of the population, are also discussed. The results can be explained by the properties of the dressed states generated by the additional tunneling. The scheme may have important application in quantum information network and communication.
Kuwahara, Y.; Nakamura, Y.; Yamanaka, Y.
2013-12-01
The 2×2-matrix structure of Green's functions is a common feature for the real-time formalisms of quantum field theory under thermal situations, such as the closed time path formalism and Thermo Field Dynamics (TFD). It has been believed to originate from quantum nature. Recently, Galley has proposed the Hamilton's principle with initial data for nonconservative classical systems, doubling each degree of freedom [1]. We show that the Galley's Hamilton formalism can be extended to quantum field and that the resulting theory is naturally identical with nonequilibrium TFD.
Kuwahara, Y., E-mail: a.kuwahara1224@asagi.waseda.jp; Nakamura, Y., E-mail: nakamura@aoni.waseda.jp; Yamanaka, Y., E-mail: yamanaka@waseda.jp
2013-12-09
The 2×2-matrix structure of Green's functions is a common feature for the real-time formalisms of quantum field theory under thermal situations, such as the closed time path formalism and Thermo Field Dynamics (TFD). It has been believed to originate from quantum nature. Recently, Galley has proposed the Hamilton's principle with initial data for nonconservative classical systems, doubling each degree of freedom. We show that the Galley's Hamilton formalism can be extended to quantum field and that the resulting theory is naturally identical with nonequilibrium TFD.
Majorana fermions in the interacting T-shaped double quantum dot
Napitu, B. D.
2015-11-01
Non-equilibrium transport properties of the interacting T-shaped double quantum dot coupled with the topological superconductor are analyzed within the Keldysh Green's function formalism. The low energy characteristics are found to be influenced by the interplay of quantum interference, electronic correlation, and the Majorana induced interaction such that the system can be driven onto either Kondo, Fano or Majorana dominated regime. It is demonstrated that the presence of the Majorana fermions at the edges of superconducting wire can be realized in the differential conductance and the zero-frequency shot noise when the system's low energy is strongly influenced by the quantum interference effect.
Quantum dynamics of a particle interacting with a double barrier
Following a previously developed method, the problem of a particle scattered by a double barrier is studied. Instead of the simple transmission or reflection, the more difficult case of the arrival in the region between the barriers is considered and solved explicitly by using matrix methods
The geometry of the Double Gyroid wire network: Quantum and Classical
Kaufmann, Ralph M; Wehefritz-Kaufmann, Birgit
2010-01-01
Quantum wire networks have recently become of great interest. Here we deal with a novel nano material structure of a Double Gyroid wire network. We use methods of commutative and non-commutative geometry to describe this wire network. Its non--commutative geometry is closely related to non-commutative 3-tori as we discuss in detail.
Tunnelling through a GaAs/(AlGa) as coupled double-quantum-well heterostructure
A splitting of the main resonant peaks is observed in the current-voltage characteristics of a double-quantum-well resonant tunnelling device, due to coupling between well states. Under a high magnetic field applied in the current direction, the peaks collapse into a single peak and from the magnetotunnelling data we are able to estimate the energy splitting between the coupled states
A New Type of Photoelectric Response in a Double Barrier Structure with a Wide Quantum Well
ZHOU Xia; ZHENG Hou-Zhi
2005-01-01
@@ We have calculated the photoelectric response in a specially designed double barrier structure. It has been verified that a transfer of the internal photovoltaic effect in the quantum well to the tunnelling transport through above-barrier quasibound states of the emitter barrier may give rise to a remarkable photocurrent.
Double-resonance spectroscopy of InAs/GaAs self-assembled quantum dots
Murdin, B. N.; Hollingworth, A. R.; Barker, J. A.; Clarke, D. G.; Findlay, P. C.; Pidgeon, C. R.; Wells, J. P. R.; Bradley, I. V.; Malik, S.; Murray, R.
2000-01-01
We present far-/near-infrared double resonance measurements of self-assembled InAs/GaAs quantum dots. The far-infrared resonance is unambiguously associated with a bound-bound intraband transition in the neutral dots. The results show that the interband photoluminescence (PL) lines originate from co
A tunable single-mode double-ring quantum-cascade laser
The design, fabrication and characterization of a monolithic double-ring quantum- cascade laser (DRQCL) are described. At a wavelength of 4.6 µm, we demonstrate tunable, single-mode operation of a DRQCL and use it as a source for spectroscopy of CO gas. (paper)
Zhang, Kuanshou; Xie, Changde; Peng, Kunchi
1996-01-01
The dependence of the quantum fluctuation of the output fundamental and second-harmonic waves upon cavity configuration has been numerically calculated for the intracavity frequency-doubled laser. The results might provide a direct reference for the design of squeezing system through the second-harmonic-generation.
Young's double-slit experiment with single photons and quantum eraser
Rueckner, Wolfgang; Peidle, Joseph
2013-12-01
An apparatus for a double-slit interference experiment in the single-photon regime is described. The apparatus includes a which-path marker that destroys the interference as well as a quantum eraser that restores it. We present data taken with several light sources, coherent and incoherent and discuss the efficacy of these as sources of single photons.
Nonequilibrium electron spin polarization in a double quantum dot. Lande mechanism
Serebrennikov, Yuri A.
2005-01-01
In moderately strong magnetic fields, the difference in Lande g-factors in each of the dots of a coupled double quantum dot device may induce oscillations between singlet and triplet states of the entangled electron pair and lead to a nonequilibrium electron spin polarization. We will show that this polarization may partially survive the rapid inhomogeneous decoherence due to random nuclear magnetic fields.
Correlation Effects on the Coupled Plasmon Modes of a Double Quantum Well
Hill, N. P. R.; Nicholls, J. T.; Linfield, E. H.; Pepper, M.; Ritchie, D. A.; Jones, G. A. C.; Hu, Ben Yu-Kuang; Flensberg, Karsten
1997-01-01
At temperatures comparable to the Fermi temperature, we have measured a plasmon enhanced Coulomb drag in a GaAs/AlGaAs double quantum well electron system. This measurement provides a probe of the many-body corrections to the coupled plasmon modes, and we present a detailed comparison between exp...
Closed form solution for a double quantum well using Gr\\"obner basis
Acus, A
2011-01-01
Analytical expressions for spectrum, eigenfunctions and dipole matrix elements of a square double quantum well (DQW) are presented for a general case when the potential in different regions of the DQW has different heights and effective masses are different. This was achieved by Gr\\"obner basis algorithm which allows to disentangle the resulting coupled polynomials without explicitly solving the transcendental eigenvalue equation.
Asymmetric transmission: a generic property of two-dimensional periodic patterns
Asymmetric transmission of circularly polarized waves is a well-established property of lossy, anisotropic, two-dimensionally chiral patterns. Here we show that asymmetric transmission can be observed for oblique incidence onto any lossy periodically structured plane. Our results greatly expand the range of natural and artificial materials in which directionally asymmetric transmission can be expected, making it a cornerstone electromagnetic effect rather than a curiosity of planar chiral metamaterials. Prime candidates for asymmetric transmission at oblique incidence are rectangular arrays of plasmonic spheres or semiconductor quantum dots, lossy double-periodic gratings and planar metamaterial structures
Optical analogue of 2D heteronuclear double-quantum NMR
Tollerud, Jonathan
2016-01-01
Heteronuclear multi-quantum spectroscopy is a powerful part of the NMR toolbox, commonly used to identify specific sequences of atoms in complex pulse sequences designed to determine the structure of complex molecules, including proteins. Optical coherent multidimensional spectroscopy (CMDS) is analogous to multidimensional NMR and many of the techniques of NMR have been adapted for application in the optical regime. This has been highly successful, with CMDS being used to understand energy transfer in photosynthesis and many body effects in semiconductor nanostructures amongst many other scientific breakthroughs. Experimental challenges have, however, prevented the translation of heteronuclear multi-quantum NMR to the optical regime, where capabilities to isolate signals in otherwise congested spectra, reduce acquisition times and enable more incisive probes of multi-particle correlations and complex electronic systems would have great benefit. Here we utilise a diffraction based pulseshaper to impose the tw...
Double-slit and electromagnetic models to complete quantum mechanics
De Luca, Jayme
2010-01-01
We analyze a realistic microscopic model for electronic scattering based on the neutral-delay-equations for point charges of the Wheeler-Feynman electrodynamics. We propose a microscopic model according to the electrodynamics of point-charges, complex enough to describe the essential physics. Our microscopic model reaches a simple qualitative agreement with the experimental results as regards interference in double-slit scattering and in electronic scattering by crystals. We discuss our model in the light of existing experimental results, including a qualitative disagreement found for the double-slit experiment. We discuss an approximation for the complex neutral-delay dynamics of our model using piecewise-defined (discontinuous) velocities for all charges and piecewise-constant-velocities for the scattered charge. Our approximation predicts the De Broglie wavelength as an inverse function of the incoming velocity and in the correct order of magnitude. We explain the scattering by crystals in the light of the...
Double-slit and electromagnetic models to complete quantum mechanics
De Luca, Jayme
2010-01-01
We analyze a realistic microscopic model for electronic scattering with the neutral differential delay equations of motion of point charges of the Wheeler-Feynman electrodynamics. We propose a microscopic model according to the electrodynamics of point charges, complex enough to describe the essential physics. Our microscopic model reaches a simple qualitative agreement with the experimental results as regards interference in double-slit scattering and in electronic scattering by crystals. We...
Quantum chaos and the double-slit experiment
Casati, Giulio; Prosen, Tomaz
2004-01-01
We report on the numerical simulation of the double-slit experiment, where the initial wave-packet is bounded inside a billiard domain with perfectly reflecting walls. If the shape of the billiard is such that the classical ray dynamics is regular, we obtain interference fringes whose visibility can be controlled by changing the parameters of the initial state. However, if we modify the shape of the billiard thus rendering classical (ray) dynamics fully chaotic, the interference fringes disap...
Zhao, Dongxing; Wu, Jiarui [State Key Laboratory for Mesoscopic Physics, Department of Physics, Peking University, Beijing 100871 (China); Gu, Ying, E-mail: ygu@pku.edu.cn; Gong, Qihuang [State Key Laboratory for Mesoscopic Physics, Department of Physics, Peking University, Beijing 100871 (China); Collaborative Innovation Center of Quantum Matter, Beijing (China)
2014-09-15
We propose tailoring of the double Fano profiles via plasmon-assisted quantum interference in a hybrid exciton-plasmon system. Tailoring is performed by the interference between two exciton channels interacting with a common localized surface plasmon. Using an applied field of low intensity, the absorption spectrum of the hybrid system reveals a double Fano lineshape with four peaks. For relatively large field intensity, a broad flat window in the absorption spectrum appears which results from the destructive interference between excitons. Because of strong constructive interference, this window vanishes as intensity is further increased. We have designed a nanometer bandpass optical filter for visible light based on tailoring of the optical spectrum. This study provides a platform for quantum interference that may have potential applications in ultracompact tunable quantum devices.
Four-Electron Systems in a Coupled Double-Layer Quantum Dots
XIE Wen-Fang
2003-01-01
Making use of the method of few-body physics, the energy spectrum of a four-electron system consisting in a vertically coupled double-layer quantum dot as a function of the strength ofa magnetic field is investigated. Discontinuous ground-state transitions induced by an external magnetic field are shown. We find that, in the strong coupling case, the ground-state transitions depend not only on the external magnetic field B but also on the distance d between double-layer quantum dots. However, in the case of weak coupling, the ground-state transitions occur in the new sequence of the values of the magic angular momentum. Hence, the interlayer separation d and electron-electron interaction strongly affect the ground state of the coupled quantum dots.
Magnetic Anticrossing of 1D Subbands in Coupled Ballistic Double Quantum Wires
We study the low-temperature in-plane magnetoconductance of vertically coupled double quantum wires. Using a novel flip-chip technique, the wires are defined by two pairs of mutually aligned split gates on opposite sides of a s 1 micron thick AlGaAs/GaAs double quantum well heterostructure. We observe quantized conductance steps due to each quantum well and demonstrate independent control of each ID wire. A broad dip in the magnetoconductance at -6 T is observed when a magnetic field is applied perpendicular to both the current and growth directions. This conductance dip is observed only when 1D subbands are populated in both the top and bottom constrictions. This data is consistent with a counting model whereby the number of subbands crossing the Fermi level changes with field due to the formation of an anticrossing in each pair of 1D subbands
Quantum mechanical compact modeling of symmetric double-gate MOSFETs using variational approach
A physics-based analytical model for symmetrically biased double-gate (DG) MOSFETs considering quantum mechanical effects is proposed. Schrödinger's and Poisson's equations are solved simultaneously using a variational approach. Solving the Poisson and Schrödinger equations simultaneously reveals quantum mechanical effects (QME) that influence the performance of DG MOSFETs. The inversion charge and electrical potential distributions perpendicular to the channel are expressed in closed forms. We systematically evaluated and analyzed the potentials and inversion charges, taking QME into consideration, in Si based double gate devices. The effect of silicon thickness variation in inversion-layer charge and potentials are quantitatively defined. The analytical solutions provide good physical insight into the quantization caused by quantum confinement under various gate biases. (semiconductor devices)
We propose tailoring of the double Fano profiles via plasmon-assisted quantum interference in a hybrid exciton-plasmon system. Tailoring is performed by the interference between two exciton channels interacting with a common localized surface plasmon. Using an applied field of low intensity, the absorption spectrum of the hybrid system reveals a double Fano lineshape with four peaks. For relatively large field intensity, a broad flat window in the absorption spectrum appears which results from the destructive interference between excitons. Because of strong constructive interference, this window vanishes as intensity is further increased. We have designed a nanometer bandpass optical filter for visible light based on tailoring of the optical spectrum. This study provides a platform for quantum interference that may have potential applications in ultracompact tunable quantum devices.