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Engineering bilinear mode coupling in circuit QED: Theory and experiment
摘要： Photonic states of high-Q superconducting microwave cavities controlled by superconducting transmon ancillas provide a platform for encoding and manipulating quantum information. A key challenge in scaling up the platform towards practical quantum computation is the requirement to communicate on demand the quantum information stored in the cavities. It has been recently demonstrated that a tunable bilinear interaction between two cavity modes can be realized by coupling the modes to a bichromatically driven superconducting transmon ancilla, which allows swapping and interfering the multiphoton states stored in the cavity modes [Gao et al., Phys. Rev. X 8, 021073 (2018)]. Here we explore both theoretically and experimentally the regime of relatively strong drives on the ancilla needed to achieve fast SWAP gates but which can also lead to undesired nonperturbative effects that lower the SWAP fidelity. We develop a theoretical formalism based on linear response theory that allows one to calculate the rate of ancilla-induced interaction, decay, and frequency shift of the cavity modes in terms of a susceptibility matrix. We go beyond the usual perturbative treatment of the drives by using Floquet theory, and find that the interference of the two drives can strongly alter the system dynamics even in the regime where the standard rotating wave approximation applies. The drive-induced ac Stark shift on the ancilla depends nontrivially on the drive and ancilla parameters which in turn modify the strength of the engineered interaction. We identify two major sources of infidelity due to ancilla decoherence. (i) Ancilla dissipation and dephasing lead to incoherent hopping among Floquet states which occurs even when the ancilla is at zero temperature; this hopping results in a sudden change of the SWAP rate, thereby decohering the SWAP operation. (ii) The cavity modes inherit finite decay from the relatively lossy ancilla through the inverse Purcell effect; the effect becomes particularly strong when the ac Stark shift pushes certain ancilla transition frequencies to the vicinity of the cavity mode frequencies. The theoretical predictions agree quantitatively with the experimental results, paving the way for using the developed theory for optimizing future experiments and architecture designs.
关键词： decoherence,transmon ancilla,superconducting cavities,ac Stark shift,quantum information,circuit QED,inverse Purcell effect,bilinear mode coupling,SWAP gates,Floquet theory
更新于2025-09-23 15:23:52
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Purcell Effect and Nonlinear Behavior of the Emission in a Periodic Structure Composed of InAs Monolayers Embedded in a GaAs Matrix
摘要： Enhancement of spontaneous emission in a resonant Bragg quantum well (QW) structure with 60 periods of triple InAs monolayers embedded in a GaAs matrix is studied experimentally and theoretically. From measurements of the time-resolved photoluminescence, besides the QW exciton at 1.47 eV, a specific super-radiant (SR) emission demonstrating nonlinear properties is found. The SR mode shows a near-quadratic dependence of intensity on excitation power, while its energy position follows the Bragg condition. It is revealed that the SR mode shows a peculiar non-monotonic dependence of intensity on direction, with a maximum observed at approximately 40°. The enhancement in the SR emission at a specific direction is correlated well with suggested theoretical consideration of the modal Purcell factor for periodic quantum well structures.
关键词： Purcell effect,Bragg conditions,monolayer-thick InAs quantum wells,super-radiance
更新于2025-09-23 15:22:29
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Optical diffraction radiation from a dielectric and a metal nanowire excited by a modulated electron beam
摘要： The optical diffraction radiation that accompanies the motion of a modulated beam of electrons near a dielectric and silver nanowire scatterers is investigated in the two-dimensional formulation. Our goal is to compute the field in the near and far zones and analyze how it depends on electron beam parameters. We demonstrate the excitation of internal resonances of such a scatterer that can be useful in the design of nanoscale non-invasive beam position monitors.
关键词： Plasmon resonance,Diffraction radiation,Nanowire scatterers,Total scattering cross-section,Absorption cross-section,Smith–Purcell effect,Surface wave
更新于2025-09-23 15:22:29
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Rapid Optical Spin Initialization of a Quantum Dot in the Voigt Geometry Coupled to a Two-Dimensional Semiconductor
摘要： We study the interaction of a quantum dot in the Voigt con?guration with a laser pulse and particularly analyze the potential for rapid spin initialization by putting the quantum dot near a molybdenum disul?de (MoS2) monolayer. The MoS2 monolayer in?uences the spontaneous decay rates of the quantum dot, leading to anisotropically enhanced decay rates, for the quantum dot’s electric dipole moments parallel and perpendicular to the layer. By solving the relevant density matrix equations, we ?nd that high spin initialization ?delity is obtained at short times. The ?delity is signi?cantly higher than when the quantum dot is in free-space vacuum. We examine two different cases of the interaction of the quantum dot with the applied optical ?eld. First, we use a continuous wave laser ?eld and determine for various quantum dot—MoS2 layer distances the ?eld strength that leads to acceptable ?delity levels. The effect of the quality of the MoS2 material on the ?delity of spin initialization is also examined. We also study the interaction of the quantum dot with a laser pulse and apply numerical optimal control to obtain the time-dependent ?eld strength, which leads to maximum ?nal ?delity for short time intervals. The latter approach gives bene?cial results in comparison to the continuous wave ?eld excitation.
关键词： spin initialization,quantum dot,Voigt geometry,optical pumping,Purcell effect,optimal control,spin dynamics
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE Research and Applications of Photonics in Defense Conference (RAPID) - Miramar Beach, FL, USA (2019.8.19-2019.8.21)] 2019 IEEE Research and Applications of Photonics in Defense Conference (RAPID) - Enhanced MWIR Led Performance with a Plasmonic Grating
摘要： To improve the efficiency of GaSb-based mid-wave infrared LEDs, we investigated the enhanced spontaneous emission by a dipole in a thin slab numerically. A Purcell factor around 5 was achieved by combining a thin waveguide and plasmonic grating.
关键词： surface plasmonic grating,Purcell effect,LED
更新于2025-09-16 10:30:52
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Greatly amplified spontaneous emission of colloidal quantum dots mediated by a dielectric-plasmonic hybrid nanoantenna
摘要： Optical nanoantennas can efficiently harvest electromagnetic energy from nanoscale space and boost the local radiation to the far field. The dielectric-metal nanogap is a novel design that can help to overcome the core issue of optical loss in all-metal nanostructures while enabling photon density of states larger than that in all-dielectric counterparts. This article reports that a crystalline spherical silicon nanoparticle on metal film (SiNPoM) nanoantenna can largely enhance the spontaneous emission intensity of quantum dots by an area-normalized factor of 69 and the decay rate by 42-fold compared with quantum dots on glass. A high total quantum efficiency of over 80%, including ~20% for far-field radiation and ~60% for surface plasmon polaritons, is obtained in simulation. Thanks to not only the low optical loss in dielectric nanoparticles but also the appropriate gap thickness which weakens the non-radiative decay due to the quenching from metal. Mie resonant modes additionally provide the flexible control of far-field emission patterns. Such a simple optical nanoantenna can be combined with various nanoscale optical emitters and easily extended to form large area metasurfaces functioning as active regions in light-emitting devices in applications such as advanced display, wireless optical communication, and quantum technology.
关键词： silicon nanoparticle,spontaneous emission,Purcell effect,plasmonics,nanoantenna
更新于2025-09-16 10:30:52
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The interplay of electron-photon and cavity-environment coupling on the electron transport through a quantum dot system
摘要： We theoretically investigate the characteristics of the electron transport through a two-dimensional a quantum dot system in the xy-plane coupled to a photon cavity and a photon reservoir, the environment. The electron-photon coupling, gγ, and the cavity-reservoir coupling, κ, are tuned to study the system in the weak, gγ ≤ κ, and the strong coupling regime, gγ > κ. An enhancement of current is both seen with increasing gγ and κ in the weak coupling regime for both x- and y-polarization of the photon field. This is a direct consequence of the Purcell effect. The current enhancement is due to the contribution of the photon replica states to the electron transport in which intraband transitions play an important role. The properties of the electron transport are drastically changed in the strong coupling regime with an x-polarized photon field in which the current is suppressed with increasing gγ, but it is still increasing with κ. This behavior of the current is related to the population of purely electronic states and depopulation of photon replica states.
关键词： Quantum master equation,Quantum Dot,Cavity-Quantum electrodynamics,Quantum transport,Purcell effect
更新于2025-09-16 10:30:52
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Direct enhancement of luminescence of CdxZn1?xSeyS1?y/ZnS nanocrystals with gradient chemical composition by plasmonic nanoantennas
摘要： Flat photonic materials such as thin films or metasurfaces form the basis of new optics and laser technology. However, their characteristics, for example, absorption and luminescence, are drastically limited in contrast to bulk materials. This problem can be overcome using plasmonic nanostructures. While the quantum dots absorption is enhanced by the plasmonic nanostructure near fields in almost all circumstances, more sophisticated approaches are needed to obtain the fluorescent enhancement because of the concurrent quenching by the metallic surface. Here we report on the results of an illustrative experiment demonstrating the luminescence enhancement of a new type of semiconductor nanocrystals CdxZn1?xSeyS1?y/ZnS (alloyed quantum dots) at their direct contact with a monolayer of silver nanoparticles. This type of nanocrystals consists of a CdSe core, a ZnS shell, and a transition layer in between where the composition smoothly changes, thus representing an alloy with variable x and y. We found that at the resonant plasmon–exciton coupling of such nanostructures, the fluorescence enhancement is accompanied by the reduction of the luminescence decay time – the main signature of the Purcell effect. Unlike previously studied compositions, these new hybrid structures do not require additional components to avoid fluorescence quenching which is promising for practical applications in flat optical devices.
关键词： Quantum dot,Fluorescence,Enhancement,Purcell effect,Plasmon
更新于2025-09-11 14:15:04
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[IEEE 2019 IEEE Photonics Conference (IPC) - San Antonio, TX, USA (2019.9.29-2019.10.3)] 2019 IEEE Photonics Conference (IPC) - Indistinguishable On-Chip Single-Photon Sources
摘要： Progress on integrating InGaAs quantum-dot single-photon sources within GaAs semiconductor photonic chips is reviewed. With resonant excitation, a radiative lifetime as short as 23 ps has been observed for a dot in a photonic-crystal nano-cavity, leading to single-photon emission with both high purity and indistinguishability.
关键词： Purcell effect,photonic nano-structure,single-photon source,integrated quantum photonics,quantum dot
更新于2025-09-11 14:15:04