By means of the transfer matrix approach, the linear conductance spectrum for electronic transport through a T-shaped quantum waveguide is calculated. The resonant peaks and the antiresonant dips in the conductance sp...By means of the transfer matrix approach, the linear conductance spectrum for electronic transport through a T-shaped quantum waveguide is calculated. The resonant peaks and the antiresonant dips in the conductance spectrum are mainly focused. The previous prediction about their positions by other theoretical approaches is checked. In addition, a function of spin filtering is suggested based on the interplay of the resonance and antiresonance in this T-shaped quantum waveguide.展开更多
Collective quantum states, such as subradiant and superradiant states, are useful for controlling optical responses in many-body quantum systems. In this work, we study novel collective quantum phenomena in waveguide-...Collective quantum states, such as subradiant and superradiant states, are useful for controlling optical responses in many-body quantum systems. In this work, we study novel collective quantum phenomena in waveguide-coupled Bragg atom arrays with inhomogeneous frequencies.For atoms without free-space dissipation, collectively induced transparency is produced by destructive quantum interference between subradiant and superradiant states. In a large Bragg atom array, multi-frequency photon transparency can be obtained by considering atoms with different frequencies. Interestingly, we find collectively induced absorption(CIA) by studying the influence of free-space dissipation on photon transport. Tunable atomic frequencies nontrivially modify decay rates of subradiant states. When the decay rate of a subradiant state equals to the free-space dissipation, photon absorption can reach a limit at a certain frequency. In other words, photon absorption is enhanced with low free-space dissipation, distinct from previous photon detection schemes. We also show multi-frequency CIA by properly adjusting atomic frequencies. Our work presents a way to manipulate collective quantum states and exotic optical properties in waveguide quantum electrodynamics(QED) systems.展开更多
Based on Rayleigh-Sommerfeld scalar diffraction formula, analyzed is the diffraction field distribution of the restricted output end surface of multiple quantum wells planar waveguide by slit. Obtained is its analytic...Based on Rayleigh-Sommerfeld scalar diffraction formula, analyzed is the diffraction field distribution of the restricted output end surface of multiple quantum wells planar waveguide by slit. Obtained is its analytical expression of field distribution, which permits accurate and effective study on the characteristic of diffraction field from the restricted output end surface of the waveguide by slit. Then, the variation curve of the beam propagation factor M2 versus the slit width is computed by the second moment method. It is useful for understanding the restricted diffraction properties of the multiple quantum wells planar waveguide. When the slit half width is bigger than the core layer's half width, the beam propagation factor M2 value tends to a constant 1.108. Therefore, the corresponding field amplitude distribution is approximated by Gaussian function, and the far field divergence half angle(θ0,G=0.091 8) is calculated by matching efficiency method.展开更多
We theoretically investigate spin transport in the elliptical ring and the circular ring with Rashba spin-orbit interaction. It is shown that when Rashba spin-orbit interaction is relatively weak, a single circular ri...We theoretically investigate spin transport in the elliptical ring and the circular ring with Rashba spin-orbit interaction. It is shown that when Rashba spin-orbit interaction is relatively weak, a single circular ring can not realize spin flip, however an elliptical ring may work as a spin-inverter at this time, and the influence of the defect of the geometry is not obvious. Howerver if a giant Rashba spin-orbit interaction strength has been obtained, a circular ring can work as a spin-inverter with a high stability.展开更多
Quantum spin transport in a mesoscopic Aharonov-Bohm ring with two leads subject to a magnetic field with circular configuration is investigated by means of one-dimensional quantum waveguide theory. Within the framewo...Quantum spin transport in a mesoscopic Aharonov-Bohm ring with two leads subject to a magnetic field with circular configuration is investigated by means of one-dimensional quantum waveguide theory. Within the framework of Landauer-Bfittiker formalism, the polarization direction of transmitted electrons can be controlled either by the AB magnetic flux or by the tangent magnetic field. In particular, the spin flips can be induced by hopping the AB magnetic flux or the tangent field.展开更多
We investigate theoretically single photon transport in one-dimensional waveguide coupled to a pair of cavities,which are denoted by the first cavity and the auxiliary cavity.Two cases with no atom and one atom embedd...We investigate theoretically single photon transport in one-dimensional waveguide coupled to a pair of cavities,which are denoted by the first cavity and the auxiliary cavity.Two cases with no atom and one atom embedded in the first cavity are discussed.The Fano dips in the transmission spectrum and locations of transparency window are calculated.When no atom is embedded in the first cavity,there exists a transparency window under the condition that the first cavity and the auxiliary cavity are not resonant.The locations of the transparency window and Fano line type depend strongly on the eigen frequency of the auxiliary cavity and the coupling strength between the auxiliary cavity and the waveguide.When one atom is embedded in the first cavity,we show that the transparency window exists even though the first cavity,the atom and the auxiliary cavity are resonant.The Fano line type is strongly dependent on the eigen frequency of the auxiliary cavity and the coupling strength.Our results have potential applications in design of quantum devices at the level of single photon,such as single photon switch and single photon routers.展开更多
Unlike conventional topological edge states confined at a domain wall between two topologically distinct media,the recently proposed large-area topological waveguide states in three-layer heterostructures,which consis...Unlike conventional topological edge states confined at a domain wall between two topologically distinct media,the recently proposed large-area topological waveguide states in three-layer heterostructures,which consist of a domain featuring Dirac points sandwiched between two domains of different topologies,have introduced the mode width degree of freedom for more flexible manipulation of electromagnetic waves.Until now,the experimental realizations of photonic large-area topological waveguide states have been exclusively based on quantum Hall and quantum valley-Hall systems.We propose a new way to create large-area topological waveguide states based on the photonic quantum spin-Hall system and observe their unique feature of pseudo-spin-momentum-locking unidirectional propagation for the first time in experiments.Moreover,due to the new effect provided by the mode width degree of freedom,the propagation of these large-area quantum spin-Hall waveguide states exhibits unusually strong robustness against defects,e.g.,large voids with size reaching several unit cells,which has not been reported previously.Finally,practical applications,such as topological channel intersection and topological energy concentrator,are further demonstrated based on these novel states.Our work not only completes the last member of such states in the photonic quantum Hall,quantum valley-Hall,and quantum spin-Hall family,but also provides further opportunities for high-capacity energy transport with tunable mode width and exceptional robustness in integrated photonic devices and on-chip communications.展开更多
We study persistent currents in the double Aharonov-Bohm ring connected to two electron reservoirs by quantum waveguide theory. It is found that the persistent currents in the double Aharonov-Bohm ring depend .on the ...We study persistent currents in the double Aharonov-Bohm ring connected to two electron reservoirs by quantum waveguide theory. It is found that the persistent currents in the double Aharonov-Bohm ring depend .on the direction of the current flow from one reservoir to another. When the direction of the current flow reverses, tl2e persistent current in each ring of the double Aharonov-Bohm ring changes. If the two rings are of the same size, the persistent currents in the left and the right rings exchange at the reversal of the current flow direction.展开更多
The 810-nm InGaAlAs/AlGaAs double quantum well （QW） semiconductor lasers with asymmetric waveguide structures, grown by molecular beam epitaxy, show high quantum efficiency and high-power conver- sion efficiency at ...The 810-nm InGaAlAs/AlGaAs double quantum well （QW） semiconductor lasers with asymmetric waveguide structures, grown by molecular beam epitaxy, show high quantum efficiency and high-power conver- sion efficiency at continuous-wave （CW） power output. The threshold current density and slope efficiency of the device are 180 A/cm^2 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.展开更多
文摘By means of the transfer matrix approach, the linear conductance spectrum for electronic transport through a T-shaped quantum waveguide is calculated. The resonant peaks and the antiresonant dips in the conductance spectrum are mainly focused. The previous prediction about their positions by other theoretical approaches is checked. In addition, a function of spin filtering is suggested based on the interplay of the resonance and antiresonance in this T-shaped quantum waveguide.
基金supported by the National Natural Science Foundation of China (Grant No. 12105025)。
文摘Collective quantum states, such as subradiant and superradiant states, are useful for controlling optical responses in many-body quantum systems. In this work, we study novel collective quantum phenomena in waveguide-coupled Bragg atom arrays with inhomogeneous frequencies.For atoms without free-space dissipation, collectively induced transparency is produced by destructive quantum interference between subradiant and superradiant states. In a large Bragg atom array, multi-frequency photon transparency can be obtained by considering atoms with different frequencies. Interestingly, we find collectively induced absorption(CIA) by studying the influence of free-space dissipation on photon transport. Tunable atomic frequencies nontrivially modify decay rates of subradiant states. When the decay rate of a subradiant state equals to the free-space dissipation, photon absorption can reach a limit at a certain frequency. In other words, photon absorption is enhanced with low free-space dissipation, distinct from previous photon detection schemes. We also show multi-frequency CIA by properly adjusting atomic frequencies. Our work presents a way to manipulate collective quantum states and exotic optical properties in waveguide quantum electrodynamics(QED) systems.
基金Program of the Science and technology Depart ment of Fujian Province(2007F5040)Natural Science Foundation of Fujian Province(A0540001)
文摘Based on Rayleigh-Sommerfeld scalar diffraction formula, analyzed is the diffraction field distribution of the restricted output end surface of multiple quantum wells planar waveguide by slit. Obtained is its analytical expression of field distribution, which permits accurate and effective study on the characteristic of diffraction field from the restricted output end surface of the waveguide by slit. Then, the variation curve of the beam propagation factor M2 versus the slit width is computed by the second moment method. It is useful for understanding the restricted diffraction properties of the multiple quantum wells planar waveguide. When the slit half width is bigger than the core layer's half width, the beam propagation factor M2 value tends to a constant 1.108. Therefore, the corresponding field amplitude distribution is approximated by Gaussian function, and the far field divergence half angle(θ0,G=0.091 8) is calculated by matching efficiency method.
基金Project supported by the National Natural Science Foundation of China(Grant No.11504016)
文摘We theoretically investigate spin transport in the elliptical ring and the circular ring with Rashba spin-orbit interaction. It is shown that when Rashba spin-orbit interaction is relatively weak, a single circular ring can not realize spin flip, however an elliptical ring may work as a spin-inverter at this time, and the influence of the defect of the geometry is not obvious. Howerver if a giant Rashba spin-orbit interaction strength has been obtained, a circular ring can work as a spin-inverter with a high stability.
基金Project supported by the Youth Science Foundation of Shanxi Province, China （Grant No 20031003）.
文摘Quantum spin transport in a mesoscopic Aharonov-Bohm ring with two leads subject to a magnetic field with circular configuration is investigated by means of one-dimensional quantum waveguide theory. Within the framework of Landauer-Bfittiker formalism, the polarization direction of transmitted electrons can be controlled either by the AB magnetic flux or by the tangent magnetic field. In particular, the spin flips can be induced by hopping the AB magnetic flux or the tangent field.
基金supported by the National Natural Science Foundation of China(Grant Nos.11774262 and 11975023)。
文摘We investigate theoretically single photon transport in one-dimensional waveguide coupled to a pair of cavities,which are denoted by the first cavity and the auxiliary cavity.Two cases with no atom and one atom embedded in the first cavity are discussed.The Fano dips in the transmission spectrum and locations of transparency window are calculated.When no atom is embedded in the first cavity,there exists a transparency window under the condition that the first cavity and the auxiliary cavity are not resonant.The locations of the transparency window and Fano line type depend strongly on the eigen frequency of the auxiliary cavity and the coupling strength between the auxiliary cavity and the waveguide.When one atom is embedded in the first cavity,we show that the transparency window exists even though the first cavity,the atom and the auxiliary cavity are resonant.The Fano line type is strongly dependent on the eigen frequency of the auxiliary cavity and the coupling strength.Our results have potential applications in design of quantum devices at the level of single photon,such as single photon switch and single photon routers.
基金supported by the National Natural Science Foundation of China (Grant Nos.U2230114 and 12004425)the Natural Science Foundation of Jiangsu Province (Grant No.BK20200630)the National Key Research and Development Program of China (Grant No.2022YFA1203500).
文摘Unlike conventional topological edge states confined at a domain wall between two topologically distinct media,the recently proposed large-area topological waveguide states in three-layer heterostructures,which consist of a domain featuring Dirac points sandwiched between two domains of different topologies,have introduced the mode width degree of freedom for more flexible manipulation of electromagnetic waves.Until now,the experimental realizations of photonic large-area topological waveguide states have been exclusively based on quantum Hall and quantum valley-Hall systems.We propose a new way to create large-area topological waveguide states based on the photonic quantum spin-Hall system and observe their unique feature of pseudo-spin-momentum-locking unidirectional propagation for the first time in experiments.Moreover,due to the new effect provided by the mode width degree of freedom,the propagation of these large-area quantum spin-Hall waveguide states exhibits unusually strong robustness against defects,e.g.,large voids with size reaching several unit cells,which has not been reported previously.Finally,practical applications,such as topological channel intersection and topological energy concentrator,are further demonstrated based on these novel states.Our work not only completes the last member of such states in the photonic quantum Hall,quantum valley-Hall,and quantum spin-Hall family,but also provides further opportunities for high-capacity energy transport with tunable mode width and exceptional robustness in integrated photonic devices and on-chip communications.
基金The project supported by National Natural Science Foundation of China under Grant No. 10347004
文摘We study persistent currents in the double Aharonov-Bohm ring connected to two electron reservoirs by quantum waveguide theory. It is found that the persistent currents in the double Aharonov-Bohm ring depend .on the direction of the current flow from one reservoir to another. When the direction of the current flow reverses, tl2e persistent current in each ring of the double Aharonov-Bohm ring changes. If the two rings are of the same size, the persistent currents in the left and the right rings exchange at the reversal of the current flow direction.
文摘The 810-nm InGaAlAs/AlGaAs double quantum well （QW） semiconductor lasers with asymmetric waveguide structures, grown by molecular beam epitaxy, show high quantum efficiency and high-power conver- sion efficiency at continuous-wave （CW） power output. The threshold current density and slope efficiency of the device are 180 A/cm^2 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.
