Engineering lattice models with tailored inter-site tunnelings and onsite energies could synthesize essentially arbitrary Riemannian surfaces with highly tunable local curvatures.Here,we point out that discrete synthe...Engineering lattice models with tailored inter-site tunnelings and onsite energies could synthesize essentially arbitrary Riemannian surfaces with highly tunable local curvatures.Here,we point out that discrete synthetic Poincaréhalf-planes and Poincarédisks,which are created by lattices in flat planes,support infinitely degenerate eigenstates for any nonzero eigenenergies.Such Efimov-like states exhibit a discrete scaling symmetry and imply an unprecedented apparatus for studying quantum anomaly using hyperbolic surfaces.Furthermore,all eigenstates are exponentially localized in the hyperbolic coordinates,signifying the first example of quantum funneling effects in Hermitian systems.As such,any initial wave packet travels towards the edge of the Poincaréhalf-plane or its equivalent on the Poincarédisk,delivering an efficient scheme to harvest light and atoms in two dimensions.Our findings unfold the intriguing properties of hyperbolic spaces and suggest that Efimov states may be regarded as a projection from a curved space with an extra dimension.展开更多
We show that reactive molecules with a unit probability of reaction naturally provide a simulator of some intriguing black hole physics.The unit reaction at the short distance acts as an event horizon and delivers a o...We show that reactive molecules with a unit probability of reaction naturally provide a simulator of some intriguing black hole physics.The unit reaction at the short distance acts as an event horizon and delivers a one-way traffic for matter waves passing through the potential barrier when two molecules interact by high partialwave scatterings or dipole-dipole interactions.In particular,the scattering rate as a function of the incident energy exhibits a thermal-like distribution near the maximum of the interaction energy in the same manner as a scalar field scatters with the potential barrier outside the event horizon of a black hole.Such a thermal-like scattering can be extracted from the temperature-dependent two-body loss rate measured in experiments on KRb and other molecules.展开更多
We study the nonlinear process of second harmonic generation in photonic time-crystals,materials with refractive index that varies abruptly and periodically in time,and obtain the phase matching condition for this pro...We study the nonlinear process of second harmonic generation in photonic time-crystals,materials with refractive index that varies abruptly and periodically in time,and obtain the phase matching condition for this process.We find conditions for which the second harmonic generation is highly enhanced even in the absence of phase matching,governed by the exponential growth of the modes residing in the momentum gap of the photonic time crystal.Additionally,under these conditions,a cascade of higher-order harmonics is generated at growing exponential rates.The process is robust,with no requirement for phase-matching,the presence of a resonance or a threshold,drawing energy from the modulation.展开更多
Ten years ago,three teams experimentally demonstrated the first spasers,or plasmonic nanolasers,after the spaser concept was first proposed theoretically in 2003.An overview of the significant progress achieved over t...Ten years ago,three teams experimentally demonstrated the first spasers,or plasmonic nanolasers,after the spaser concept was first proposed theoretically in 2003.An overview of the significant progress achieved over the last 10 years is presented here,together with the original context of and motivations for this research.After a general introduction,we first summarize the fundamental properties of spasers and discuss the major motivations that led to the first demonstrations of spasers and nanolasers.This is followed by an overview of crucial technological progress,including lasing threshold reduction,dynamic modulation,room-temperature operation,electrical injection,the control and improvement of spasers,the array operation of spasers,and selected applications of single-particle spasers.Research prospects are presented in relation to several directions of development,including further miniaturization,the relationship with Bose-Einstein condensation,novel spaser-based interconnects,and other features of spasers and plasmonic lasers that have yet to be realized or challenges that are still to be overcome.展开更多
The recently proposed concept of graphene photodetectors offers remarkable properties such as unprecedented compactness,ultrabroadband detection,and an ultrafast response speed.However,owing to the low optical absorpt...The recently proposed concept of graphene photodetectors offers remarkable properties such as unprecedented compactness,ultrabroadband detection,and an ultrafast response speed.However,owing to the low optical absorption of pristine monolayer graphene,the intrinsically low responsivity of graphene photodetectors significantly hinders the development of practical devices.To address this issue,numerous efforts have thus far been made to enhance the light–graphene interaction using plasmonic structures.These approaches,however,can be significantly advanced by leveraging the other critical aspect of graphene photoresponsivity enhancement-electrical junction control.It has been reported that the dominant photocarrier generation mechanism in graphene is the photothermoelectric(PTE)effect.Thus,the two energy conversion mechanisms involved in the graphene photodetection process are light-to-heat and heat-to-electricity conversions.In this work,we propose a meticulously designed device architecture to simultaneously enhance the two conversion efficiencies.Specifically,a gap plasmon structure is used to absorb a major portion of the incident light to induce localized heating,and a pair of split gates is used to produce a p-n junction in graphene to augment the PTE current generation.The gap plasmon structure and the split gates are designed to share common key components so that the proposed device architecture concurrently realizes both optical and electrical enhancements.We experimentally demonstrate the dominance of the PTE effect in graphene photocurrent generation and observe a 25-fold increase in the generated photocurrent compared to the un-enhanced cases.While further photocurrent enhancement can be achieved by applying a DC bias,the proposed device concept shows vast potential for practical applications.展开更多
Almost half of the sunlight striking a silicon solar cell is lost to reflection—a fundamental inefficiency that limits real-world energy conversion.1,2The root of the problem lies in the stark refractive index contra...Almost half of the sunlight striking a silicon solar cell is lost to reflection—a fundamental inefficiency that limits real-world energy conversion.1,2The root of the problem lies in the stark refractive index contrast between air and crystalline silicon,which causes a significant mismatch in optical impedance at the interface,leading to strong Fresnel reflections across much of the solar spectrum.展开更多
基金supported by the National Natural Science Foundation of China(11804268)the National Key R&D Program of China(2018YFA0307601)。
文摘Engineering lattice models with tailored inter-site tunnelings and onsite energies could synthesize essentially arbitrary Riemannian surfaces with highly tunable local curvatures.Here,we point out that discrete synthetic Poincaréhalf-planes and Poincarédisks,which are created by lattices in flat planes,support infinitely degenerate eigenstates for any nonzero eigenenergies.Such Efimov-like states exhibit a discrete scaling symmetry and imply an unprecedented apparatus for studying quantum anomaly using hyperbolic surfaces.Furthermore,all eigenstates are exponentially localized in the hyperbolic coordinates,signifying the first example of quantum funneling effects in Hermitian systems.As such,any initial wave packet travels towards the edge of the Poincaréhalf-plane or its equivalent on the Poincarédisk,delivering an efficient scheme to harvest light and atoms in two dimensions.Our findings unfold the intriguing properties of hyperbolic spaces and suggest that Efimov states may be regarded as a projection from a curved space with an extra dimension.
基金the National Natural Science Foundation of China(Grant No.12174300)the National Key R&D Program of China(Grant No.2018YFA0307601)supported by the National Science Foundation(Grant No.PHY-2110614)。
文摘We show that reactive molecules with a unit probability of reaction naturally provide a simulator of some intriguing black hole physics.The unit reaction at the short distance acts as an event horizon and delivers a one-way traffic for matter waves passing through the potential barrier when two molecules interact by high partialwave scatterings or dipole-dipole interactions.In particular,the scattering rate as a function of the incident energy exhibits a thermal-like distribution near the maximum of the interaction energy in the same manner as a scalar field scatters with the potential barrier outside the event horizon of a black hole.Such a thermal-like scattering can be extracted from the temperature-dependent two-body loss rate measured in experiments on KRb and other molecules.
基金supported by the Israel Science Foundation through the MAPATS programby the US Air Force Office for Scientific Research,AFOSR.
文摘We study the nonlinear process of second harmonic generation in photonic time-crystals,materials with refractive index that varies abruptly and periodically in time,and obtain the phase matching condition for this process.We find conditions for which the second harmonic generation is highly enhanced even in the absence of phase matching,governed by the exponential growth of the modes residing in the momentum gap of the photonic time crystal.Additionally,under these conditions,a cascade of higher-order harmonics is generated at growing exponential rates.The process is robust,with no requirement for phase-matching,the presence of a resonance or a threshold,drawing energy from the modulation.
基金financial support from the DARPA/DSO Extreme Optics and Imaging(EXTREME)Program(Award HR00111720032)financial support from AFOSR Grant FA9550-18-1-0002+8 种基金supported by the National Natural Science Foundation of China(Grant Nos.91950115,11774014,and 61521004)the Beijing Natural Science Foundation(Grant No.Z180011)the National Key R&D Program of China(Grant No.2018YFA0704401)supported by the“UK Engineering and Physical Sciences Research Council”support from the Beijing Innovation Centre for Future Chips at Tsinghua Universityprovided by Grant No.DE-SC0007043 from the Materials Sciences and Engineering Division of the Office of the Basic Energy Sciences,Office of Science,U.S.Department of Energyperformed using support from Grant No.DE-FG02-01ER15213 from the Chemical Sciences,Biosciences and Geosciences Division,Office of Basic Energy Sciences,Office of Science,US Department of EnergyAdditional support for MIS came from NSF EFRI NewLAW Grant EFMA-1741691MURI Grant No.N00014-17-1-2588 from the Office of Naval Research(ONR).
文摘Ten years ago,three teams experimentally demonstrated the first spasers,or plasmonic nanolasers,after the spaser concept was first proposed theoretically in 2003.An overview of the significant progress achieved over the last 10 years is presented here,together with the original context of and motivations for this research.After a general introduction,we first summarize the fundamental properties of spasers and discuss the major motivations that led to the first demonstrations of spasers and nanolasers.This is followed by an overview of crucial technological progress,including lasing threshold reduction,dynamic modulation,room-temperature operation,electrical injection,the control and improvement of spasers,the array operation of spasers,and selected applications of single-particle spasers.Research prospects are presented in relation to several directions of development,including further miniaturization,the relationship with Bose-Einstein condensation,novel spaser-based interconnects,and other features of spasers and plasmonic lasers that have yet to be realized or challenges that are still to be overcome.
基金financial support from the Air Force Office of Scientific Research MURI Grants(FA9550-14-1-0389 and AFOSR grant on transdimensional photonics)NSF Materials Research Science and Engineering Center(MRSEC)program(DMR 1120923)+3 种基金NSF Civil,Mechanical,and Manufacturing Innovation(CMMI)program(1538360)NSF Emerging Frontiers&Multidisciplinary Activities(EFMA#1641101)Purdue Discovery Park Big Idea Challenge programthe financial support from the DARPA/DSO Extreme Optics and Imaging(EXTREME)program(HR00111720032).
文摘The recently proposed concept of graphene photodetectors offers remarkable properties such as unprecedented compactness,ultrabroadband detection,and an ultrafast response speed.However,owing to the low optical absorption of pristine monolayer graphene,the intrinsically low responsivity of graphene photodetectors significantly hinders the development of practical devices.To address this issue,numerous efforts have thus far been made to enhance the light–graphene interaction using plasmonic structures.These approaches,however,can be significantly advanced by leveraging the other critical aspect of graphene photoresponsivity enhancement-electrical junction control.It has been reported that the dominant photocarrier generation mechanism in graphene is the photothermoelectric(PTE)effect.Thus,the two energy conversion mechanisms involved in the graphene photodetection process are light-to-heat and heat-to-electricity conversions.In this work,we propose a meticulously designed device architecture to simultaneously enhance the two conversion efficiencies.Specifically,a gap plasmon structure is used to absorb a major portion of the incident light to induce localized heating,and a pair of split gates is used to produce a p-n junction in graphene to augment the PTE current generation.The gap plasmon structure and the split gates are designed to share common key components so that the proposed device architecture concurrently realizes both optical and electrical enhancements.We experimentally demonstrate the dominance of the PTE effect in graphene photocurrent generation and observe a 25-fold increase in the generated photocurrent compared to the un-enhanced cases.While further photocurrent enhancement can be achieved by applying a DC bias,the proposed device concept shows vast potential for practical applications.
文摘Almost half of the sunlight striking a silicon solar cell is lost to reflection—a fundamental inefficiency that limits real-world energy conversion.1,2The root of the problem lies in the stark refractive index contrast between air and crystalline silicon,which causes a significant mismatch in optical impedance at the interface,leading to strong Fresnel reflections across much of the solar spectrum.
