Surface acoustic wave(SAW)is a powerful technique for investigating quantum phases appearing in twodimensional electron systems.The electrons respond to the piezoelectric field of SAW through screening,attenuating its...Surface acoustic wave(SAW)is a powerful technique for investigating quantum phases appearing in twodimensional electron systems.The electrons respond to the piezoelectric field of SAW through screening,attenuating its amplitude,and shifting its velocity,which is described by the relaxation model.In this work,we systematically study this interaction using orders of magnitude lower SAW amplitude than those in previous studies.At high magnetic fields,when electrons form highly correlated states such as the quantum Hall effect,we observe an anomalously large attenuation of SAW,while the acoustic speed remains considerably high,inconsistent with the conventional relaxation model.This anomaly exists only when the SAW power is sufficiently low.展开更多
This review summarizes the requirement of low temperature conditions in existing experimental approaches to quantum computation and quantum simulation.
We present a quantum adiabatic algorithm for a set of quantum 2-satisfiability(Q2SAT)problem,which is a generalization of 2-satisfiability(2SAT)problem.For a Q2SAT problem,we construct the Hamiltonian which is similar...We present a quantum adiabatic algorithm for a set of quantum 2-satisfiability(Q2SAT)problem,which is a generalization of 2-satisfiability(2SAT)problem.For a Q2SAT problem,we construct the Hamiltonian which is similar to that of a Heisenberg chain.All the solutions of the given Q2SAT problem span the subspace of the degenerate ground states.The Hamiltonian is adiabatically evolved so that the system stays in the degenerate subspace.Our numerical results suggest that the time complexity of our algorithm is O(n^(3.9))for yielding non-trivial solutions for problems with the number of clauses m=dn(n-1)/2(d■0.1).We discuss the advantages of our algorithm over the known quantum and classical algorithms.展开更多
We present a quantum algorithm for approximating maximum independent sets of a graph based on quantum non-Abelian adiabatic mixing in the sub-Hilbert space of degenerate ground states,which generates quantum annealing...We present a quantum algorithm for approximating maximum independent sets of a graph based on quantum non-Abelian adiabatic mixing in the sub-Hilbert space of degenerate ground states,which generates quantum annealing in a secondary Hamiltonian.For both sparse and dense random graphs G,numerical simulation suggests that our algorithm on average finds an independent set of size close to the maximum size α(G) in low polynomial time.The best classical algorithms,by contrast,produce independent sets of size about half of α(G)in polynomial time.展开更多
A Weyl node is characterized by its chirality and tilt.We develop a theory of how nth-order nonlinear optical conductivity behaves under transformations of anisotropic tensor and tilt, which clarifies how chirality-de...A Weyl node is characterized by its chirality and tilt.We develop a theory of how nth-order nonlinear optical conductivity behaves under transformations of anisotropic tensor and tilt, which clarifies how chirality-dependent and-independent parts of optical conductivity transform under the reversal of tilt and chirality.Built on this theory, we propose ferromagnetic Mn Bi2Te4as a magnetoelectrically regulated, terahertz optical device, by magnetoelectrically switching the chiralitydependent and-independent DC photocurrents.These results are useful for creating nonlinear optical devices based on the topological Weyl semimetals.展开更多
Inspired by the recent quantum oscillation measurement on the kagome lattice antiferromagnet in finite magnetic fields,we raise the question about the physical contents of the emergent fermions and the gauge fields if...Inspired by the recent quantum oscillation measurement on the kagome lattice antiferromagnet in finite magnetic fields,we raise the question about the physical contents of the emergent fermions and the gauge fields if the U(1)spin liquid is relevant for the finite-field kagome lattice antiferromagnet.Clearly,the magnetic field is non-perturbative in this regime,and the finite-field state has no direct relation with the U(1)Dirac spin liquid proposal at zero field.We here consider the fermionized dual vortex liquid state as one possible candidate theory to understand the magnetized kagome spin liquid.Within the dual vortex theory,the S^(z) magnetization is the emergent U(1)gauge flux,and the fermionized dual vortex is the emergent fermion.The magnetic field polarizes the spin component that modulates the U(1)gauge flux for the fermionized vortices and generates the quantum oscillation.Within the mean-field theory,we discuss the gauge field correlation,the vortex–antivortex continuum and the vortex thermal Hall effect.展开更多
To gain further understanding of the luminescence properties of multiquantum wells and the factors affecting them on a microscopic level,cathodoluminescence combined with scanning transmission electron microscopy and ...To gain further understanding of the luminescence properties of multiquantum wells and the factors affecting them on a microscopic level,cathodoluminescence combined with scanning transmission electron microscopy and spectroscopy was used to measure the luminescence of In_(0.15)Ga_(0.85)N five-period multiquantum wells.The lattice-composition-energy relationship was established with the help of energy-dispersive x-ray spectroscopy,and the bandgaps of In_(0.15)Ga_(0.85)N and GaN in multiple quantum wells were extracted by electron energy loss spectroscopy to understand the features of cathodoluminescence spectra.The luminescence differences between different periods of multiquantum wells and the effects of defects such as composition fluctuation and dislocations on the luminescence of multiple quantum wells were revealed.Our study establishing the direct relationship between the atomic structure of In_(x)Ga_(1-x)N multiquantum wells and photoelectric properties provides useful information for nitride applications.展开更多
The discovery of phase changings in two-dimensional(2D)materials driven by external stimuli not only helps to understand the various intriguing phases in 2D materials but also provides directions for constructing new ...The discovery of phase changings in two-dimensional(2D)materials driven by external stimuli not only helps to understand the various intriguing phases in 2D materials but also provides directions for constructing new functional devices.Here,by combining angle-resolved photoemission spectroscopy(ARPES)and in-situ alkali-metal deposition,we studied how alkali-metal adatoms affect the electronic structure of T_(d)-WTe_(2)on two different cleaved surfaces.We found that depending on the polarization direction of the cleaved surface,the alkali-metal deposition triggered two successive phase transitions on one surface of WTe_(2),while on the other surface,no phase transition was found.We attributed the observed phase transitions to a Td↑-1T′-Td↓structural transition driven by an alkali-metal induced sliding of WTe2layers.By comparing the band structure obtained in different structural phases of WTe_(2),we found that the evolution of band structure across different phases is characterized by an energy scale that could be related to the degree of orbital hybridization between two adjacent WTe_(2)layers.Our results demonstrate a method that manipulates the surface structure of bulk 2D materials.It also builds a direct correlation between the electronic structure and the degree of interlayer misalignment in this intriguing 2D material.展开更多
The Kitaev honeycomb model has received significant attention due to its exactly solvable quantum spin liquid ground states and fractionalized excitations.Layered cobalt oxides have been considered as a promising plat...The Kitaev honeycomb model has received significant attention due to its exactly solvable quantum spin liquid ground states and fractionalized excitations.Layered cobalt oxides have been considered as a promising platform for realizing this model.However,in contrast to the conventional wisdom regarding the single-q zigzag magnetic order inferred from previous studies of the candidate materials Na_(2)IrO_(3) and α-RuCl_(3),recent experiments on two representative honeycomb cobalt oxides,hexagonal Na_(2)Co_(2)TeO_(6) and monoclinic Na_(3)Co_(2)SbO_(6),have uncovered evidence for more complex multi-q zigzag order variants.This review surveys the experimental strategies used to distinguish between single-and multi-q orders,along with the crystallographic symmetries of cobalt oxides,in comparison with previously studied systems.The general formation mechanism of multi-q order is also briefly discussed.The goal is to provide a solid ground for examining the relevance of multi-q order in honeycomb cobalt oxides and discuss its implications for the microscopic model of these intriguing quantum magnets.展开更多
Moiré superlattices provide a new platform to engineer various many-body problems. In this work, we consider arrays of quantum dots(QD) realized on semiconductor moiré superlattices with a deep moiré po...Moiré superlattices provide a new platform to engineer various many-body problems. In this work, we consider arrays of quantum dots(QD) realized on semiconductor moiré superlattices with a deep moiré potential. We diagonalize single QD with multiple electrons, and find degenerate ground states serving as local degrees of freedom(qudits) in the superlattice. With a deep moiré potential, the hopping and exchange interaction between nearby QDs become irrelevant,and the direct Coulomb interaction of the density–density type dominates. Therefore, nearby QDs must arrange the spatial densities to optimize the Coulomb energy. When the local Hilbert space has a two-fold orbital degeneracy, we find that a square superlattice realizes an anisotropic XY model, while a triangular superlattice realizes a generalized XY model with geometric frustration.展开更多
In unconventional high-temperature(high-T_(c))superconductors,the pair density wave state,an exotic superconducting order showing spatially periodic order parameter modulations with the period of several unit cells an...In unconventional high-temperature(high-T_(c))superconductors,the pair density wave state,an exotic superconducting order showing spatially periodic order parameter modulations with the period of several unit cells and translational symmetry breaking,has attracted broad attention.However,the superconducting pair density modulation(PDM)within a single unit cell has never been carefully investigated before.Here,using scanning tunneling microscopy/spectroscopy,we report the observation of PDM in monolayer high-T_(c) iron chalcogenide films epitaxially grown on SrTiO_(3)(001).The superconductivity modulations are characterized by the superconducting gap size and the coherence peak sharpness.Further analysis shows that the local maxima and minima in the superconducting gap modulation are centered at the crystallographic locations of the chalcogen atoms,revealing the breaking of the glide-mirror symmetry of the chalcogen atoms in monolayer high-T_(c) iron chalcogenide films grown on SrTiO_(3)(001).Our findings provide precise microscopic information on superconductivity within the lattice unit cell and may promote the understanding of unconventional high-T_(c) superconductivity.展开更多
We report the experimental investigation of the superconductor-metal quantum phase transition of the Eu O/KTa O3 interface.Around the transition,a divergence of the dynamical critical exponent is observed,which suppor...We report the experimental investigation of the superconductor-metal quantum phase transition of the Eu O/KTa O3 interface.Around the transition,a divergence of the dynamical critical exponent is observed,which supports the quantum Griffiths singularity in the Eu O/KTa O3 interface.The quantum Griffiths singularity could be attributed to large rare superconducting regions and quenched disorders at the interface.Our results could pave the way for studying the exotic superconducting properties at the Eu O/KTa O3 interface.展开更多
Superlattice potentials are theoretically predicted to modify the single-particle electronic structures. The resulting Coulomb-interaction-dominated low-energy physics would generate highly novel many-body phenomena. ...Superlattice potentials are theoretically predicted to modify the single-particle electronic structures. The resulting Coulomb-interaction-dominated low-energy physics would generate highly novel many-body phenomena. Here,by in situ tunneling spectroscopy, we show the signatures of superstructure-modulated correlated electron states in epitaxial bilayer graphene(BLG) on 6H-Si C(0001). As the carrier density is locally quasi-‘tuned’ by the superlattice potentials of a 6 × 6 interface reconstruction phase, the spectral-weight transfer occurs between the two broad peaks flanking the charge-neutral point. Such a detected non-rigid band shift beyond the single-particle band description implies the existence of correlation effects, probably attributed to the modified interlayer coupling in epitaxial BLG by the 6×6 reconstruction as in magic-angle BLG by the moiré potentials. Quantitative analysis suggests that the intrinsic interface reconstruction shows a high carrier tunability of ~1/2 filling range, equivalent to the back gating by a voltage of ~70 V in a typical gated BLG/SiO_(2)/Si device. The finding in interfacemodulated epitaxial BLG with reconstruction phase extends the BLG platform with electron correlations beyond the magic-angle situation, and may stimulate further investigations on correlated states in graphene systems and other van der Waals materials.展开更多
The hydrogen bond （HB） is an important type of intermolecular interaction, which is generally weak, ubiquitous, and essential to life on earth. The small mass of hydrogen means that many properties of HBs are quantu...The hydrogen bond （HB） is an important type of intermolecular interaction, which is generally weak, ubiquitous, and essential to life on earth. The small mass of hydrogen means that many properties of HBs are quantum mechanical in nature. In recent years, because of the development of computer simulation methods and computational power, the influence of nuclear quantum effects （NQEs） on the structural and energetic properties of some hydrogen bonded systems has been intensively studied. Here, we present a review of these studies by focussing on the explanation of the principles underlying the simulation methods, i.e., the ab initio path-integral molecular dynamics. Its extension in combination with the thermodynamic integration method for the calculation of free energies will also be introduced. We use two examples to show how this influence of NQEs in realistic systems is simulated in practice.展开更多
Quantum computers are in hot-spot with the potential to handle more complex problems than classical computers can.Realizing the quantum computation requires the universal quantum gate set {T,H,CNOT} so as to perform a...Quantum computers are in hot-spot with the potential to handle more complex problems than classical computers can.Realizing the quantum computation requires the universal quantum gate set {T,H,CNOT} so as to perform any unitary transformation with arbitrary accuracy.Here we first briefly review the Majorana fermions and then propose the realization of arbitrary two-qubit quantum gates based on chiral Majorana fermions.Elementary cells consist of a quantum anomalous Hall insulator surrounded by a topological superconductor with electric gates and quantum-dot structures,which enable the braiding operation and the partial exchange operation.After defining a qubit by four chiral Majorana fermions,the singlequbit T and H quantum gates are realized via one partial exchange operation and three braiding operations,respectively.The entangled CNOT quantum gate is performed by braiding six chiral Majorana fermions.Besides,we design a powerful device with which arbitrary two-qubit quantum gates can be realized and take the quantum Fourier transform as an example to show that several quantum operations can be performed with this space-limited device.Thus,our proposal could inspire further utilization of mobile chiral Majorana edge states for faster quantum computation.展开更多
We image optical near-field patterns at subwavelength circular hole arrays in Au film by using scanning near-field optical microscopy in near-infrared wavelengths. Periodical oscillation features are found in the near...We image optical near-field patterns at subwavelength circular hole arrays in Au film by using scanning near-field optical microscopy in near-infrared wavelengths. Periodical oscillation features are found in the near-field images at the air/Au interface and exhibit two typical kinds of standing wave oscillation forms at the wavelengths corresponding to the transmission minimum and maximum in the transmission spectrum, and the latter one originates from the excitation and interference of a surface plasmon wave at the metallic hole arrays. Our work indicates that monitoring optical near-field patterns can help to reveal many interesting properties of surface plasmon waves at metallic nanostructures and understand their underlying physical mechanisms.展开更多
This study explores the use of neural network-based analytic continuation to extract spectra from Monte Carlo data.We apply this technique to both synthetic and Monte Carlo-generated data.The training sets for neural ...This study explores the use of neural network-based analytic continuation to extract spectra from Monte Carlo data.We apply this technique to both synthetic and Monte Carlo-generated data.The training sets for neural networks are carefully synthesized without“data leakage”.We find that the training set should match the input correlation functions in terms of statistical error properties,such as noise level,noise dependence on imaginary time,and imaginary time-displaced correlations.We have developed a systematic method to synthesize such training datasets.Our improved algorithm outperforms the widely used maximum entropy method in highly noisy situations.As an example,our method successfully extracted the dynamic structure factor of the spin-1/2 Heisenberg chain from quantum Monte Carlo simulations.展开更多
We study ultra-high-mobility two-dimensional(2D)electron/hole systems with high precision capacitance measurement.It is found that the capacitance charge appears only at the fringe of the gate at high magnetic field w...We study ultra-high-mobility two-dimensional(2D)electron/hole systems with high precision capacitance measurement.It is found that the capacitance charge appears only at the fringe of the gate at high magnetic field when the 2D conductivity decreases significantly.At integer quantum Hall effects,the capacitance vanishes and forms a plateau at high temperatures T≥300 m K,which surprisingly disappears at T≤100 m K.This anomalous behavior is likely a manifestation that dilute particles/vacancies in the top-most Landau level form Wigner crystals,which have finite compressibility and can host polarization current.展开更多
We theoretically study the Josephson effect in a quantum anomalous Hall insulator(QAHI)nanoribbon with a domain wall structure and covered by the superconductor.The anomalous Josephson current,the nonzero supercurrent...We theoretically study the Josephson effect in a quantum anomalous Hall insulator(QAHI)nanoribbon with a domain wall structure and covered by the superconductor.The anomalous Josephson current,the nonzero supercurrent at the zero superconducting phase difference,appears with the nonzero magnetization and the suitable azimuth angle of the domain wall.Dependent on the configuration of the domain wall,the anomalous current peaks in the Bloch type but disappears in the Néel type because the y-component of magnetization is necessary to break symmetry to arouse the anomalous current.The phase shift of the anomalous current is tunable by the magnetization,the azimuth angle,or the thickness of the domain wall.By introducing a bare QAHI region in the middle of the junction which is not covered by the superconductor,the anomalous Josephson effect is enhanced such that the phase shift can exceedπ.Thus,a continuous change between 0 andπjunctions is realized via regulating the configuration of the domain wall or the magnetization strength.As long as an s-wave superconductor is placed on the top of the QAHI with a domain wall structure,this proposal can be experimentally fabricated and useful for the phase battery or superconducting quantum bit.展开更多
A theoretical model of computation is proposed based on Lorentz quantum mechanics.Besides the standard qubits,this model has an additional bit,which we call hyperbolic bit(or hybit in short).A set of basic logical gat...A theoretical model of computation is proposed based on Lorentz quantum mechanics.Besides the standard qubits,this model has an additional bit,which we call hyperbolic bit(or hybit in short).A set of basic logical gates are constructed and their universality is proved.As an application,a search algorithm is designed for this computer model and is found to be exponentially faster than Grover's search algorithm.展开更多
基金supported by the National Key Research and Development Program of China(Grant Nos.2021YFA1401900 and 2019YFA0308403)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB33030000)+1 种基金the National Natural Science Foundation of China(Grant Nos.92065104,12074010,and 12141001)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302602)for sample fabrication and measurement。
文摘Surface acoustic wave(SAW)is a powerful technique for investigating quantum phases appearing in twodimensional electron systems.The electrons respond to the piezoelectric field of SAW through screening,attenuating its amplitude,and shifting its velocity,which is described by the relaxation model.In this work,we systematically study this interaction using orders of magnitude lower SAW amplitude than those in previous studies.At high magnetic fields,when electrons form highly correlated states such as the quantum Hall effect,we observe an anomalously large attenuation of SAW,while the acoustic speed remains considerably high,inconsistent with the conventional relaxation model.This anomaly exists only when the SAW power is sufficiently low.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFA0303301)the National Natural Science Foundation of China(Grant Nos.11674009 and 11921005)+1 种基金the Beijing Natural Science Foundation,China(Grant No.JQ18002)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB28000000)。
文摘This review summarizes the requirement of low temperature conditions in existing experimental approaches to quantum computation and quantum simulation.
基金Project supported by the National Key R&D Program of China(Grant Nos.2017YFA0303302 and 2018YFA0305602)the National Natural Science Foundation of China(Grant No.11921005)Shanghai Municipal Science and Technology Major Project,China(Grant No.2019SHZDZX01)。
文摘We present a quantum adiabatic algorithm for a set of quantum 2-satisfiability(Q2SAT)problem,which is a generalization of 2-satisfiability(2SAT)problem.For a Q2SAT problem,we construct the Hamiltonian which is similar to that of a Heisenberg chain.All the solutions of the given Q2SAT problem span the subspace of the degenerate ground states.The Hamiltonian is adiabatically evolved so that the system stays in the degenerate subspace.Our numerical results suggest that the time complexity of our algorithm is O(n^(3.9))for yielding non-trivial solutions for problems with the number of clauses m=dn(n-1)/2(d■0.1).We discuss the advantages of our algorithm over the known quantum and classical algorithms.
基金supported in part by the U.S.Department of Energy(Grant No.DE-SC0012567)the European Research Council(Grant No.742104)+3 种基金the Swedish Research Council(Grant No.335–2014-7424)supported by the National Key R&D Program of China(Grant Nos.2017YFA0303302 and 2018YFA0305602)the National Natural Science Foundation of China(Grant No.11921005)Shanghai Municipal Science and Technology Major Project(Grant No.2019SHZDZX01)。
文摘We present a quantum algorithm for approximating maximum independent sets of a graph based on quantum non-Abelian adiabatic mixing in the sub-Hilbert space of degenerate ground states,which generates quantum annealing in a secondary Hamiltonian.For both sparse and dense random graphs G,numerical simulation suggests that our algorithm on average finds an independent set of size close to the maximum size α(G) in low polynomial time.The best classical algorithms,by contrast,produce independent sets of size about half of α(G)in polynomial time.
基金Project supported by the National Key R&D Program of China (Grant Nos.2018YFA, 0305601, and 2021YFA1400100)the National Natural Science Foundation of China (Grant Nos.12274003, 11725415, and 11934001)the Innovation Program for Quantum Science and Technology (Grant No.2021ZD0302600)。
文摘A Weyl node is characterized by its chirality and tilt.We develop a theory of how nth-order nonlinear optical conductivity behaves under transformations of anisotropic tensor and tilt, which clarifies how chirality-dependent and-independent parts of optical conductivity transform under the reversal of tilt and chirality.Built on this theory, we propose ferromagnetic Mn Bi2Te4as a magnetoelectrically regulated, terahertz optical device, by magnetoelectrically switching the chiralitydependent and-independent DC photocurrents.These results are useful for creating nonlinear optical devices based on the topological Weyl semimetals.
基金supported by the National Key Research and Development Program of China(Grant No.2021YFA1400300)the National Science Foundation of China(Grant No.92065203)the Fundamental Research Funds for the Centrals Universities,Peking University。
文摘Inspired by the recent quantum oscillation measurement on the kagome lattice antiferromagnet in finite magnetic fields,we raise the question about the physical contents of the emergent fermions and the gauge fields if the U(1)spin liquid is relevant for the finite-field kagome lattice antiferromagnet.Clearly,the magnetic field is non-perturbative in this regime,and the finite-field state has no direct relation with the U(1)Dirac spin liquid proposal at zero field.We here consider the fermionized dual vortex liquid state as one possible candidate theory to understand the magnetized kagome spin liquid.Within the dual vortex theory,the S^(z) magnetization is the emergent U(1)gauge flux,and the fermionized dual vortex is the emergent fermion.The magnetic field polarizes the spin component that modulates the U(1)gauge flux for the fermionized vortices and generates the quantum oscillation.Within the mean-field theory,we discuss the gauge field correlation,the vortex–antivortex continuum and the vortex thermal Hall effect.
基金Project supported by the National Key R&D Program of China (Grant No. 2019YFA0708202)the National Natural Science Foundation of China (Grant Nos. 11974023, 52021006, 61974139, 12074369, and 12104017)+1 种基金the “2011 Program” from the Peking–Tsinghua–IOP Collaborative Innovation Center of Quantum Matterthe Youth Supporting Program of Institute of Semiconductors
文摘To gain further understanding of the luminescence properties of multiquantum wells and the factors affecting them on a microscopic level,cathodoluminescence combined with scanning transmission electron microscopy and spectroscopy was used to measure the luminescence of In_(0.15)Ga_(0.85)N five-period multiquantum wells.The lattice-composition-energy relationship was established with the help of energy-dispersive x-ray spectroscopy,and the bandgaps of In_(0.15)Ga_(0.85)N and GaN in multiple quantum wells were extracted by electron energy loss spectroscopy to understand the features of cathodoluminescence spectra.The luminescence differences between different periods of multiquantum wells and the effects of defects such as composition fluctuation and dislocations on the luminescence of multiple quantum wells were revealed.Our study establishing the direct relationship between the atomic structure of In_(x)Ga_(1-x)N multiquantum wells and photoelectric properties provides useful information for nitride applications.
基金Project supported by the National Key Research and Development Program of China(Grant No.2022YFA1403502)the National Natural Science Foundation of China(Grant No.11888101)。
文摘The discovery of phase changings in two-dimensional(2D)materials driven by external stimuli not only helps to understand the various intriguing phases in 2D materials but also provides directions for constructing new functional devices.Here,by combining angle-resolved photoemission spectroscopy(ARPES)and in-situ alkali-metal deposition,we studied how alkali-metal adatoms affect the electronic structure of T_(d)-WTe_(2)on two different cleaved surfaces.We found that depending on the polarization direction of the cleaved surface,the alkali-metal deposition triggered two successive phase transitions on one surface of WTe_(2),while on the other surface,no phase transition was found.We attributed the observed phase transitions to a Td↑-1T′-Td↓structural transition driven by an alkali-metal induced sliding of WTe2layers.By comparing the band structure obtained in different structural phases of WTe_(2),we found that the evolution of band structure across different phases is characterized by an energy scale that could be related to the degree of orbital hybridization between two adjacent WTe_(2)layers.Our results demonstrate a method that manipulates the surface structure of bulk 2D materials.It also builds a direct correlation between the electronic structure and the degree of interlayer misalignment in this intriguing 2D material.
基金supported by the National Basic Research Program of China(Grant No.2021YFA1401901)the National Natural Science Foundation of China(Grant No.12474138)。
文摘The Kitaev honeycomb model has received significant attention due to its exactly solvable quantum spin liquid ground states and fractionalized excitations.Layered cobalt oxides have been considered as a promising platform for realizing this model.However,in contrast to the conventional wisdom regarding the single-q zigzag magnetic order inferred from previous studies of the candidate materials Na_(2)IrO_(3) and α-RuCl_(3),recent experiments on two representative honeycomb cobalt oxides,hexagonal Na_(2)Co_(2)TeO_(6) and monoclinic Na_(3)Co_(2)SbO_(6),have uncovered evidence for more complex multi-q zigzag order variants.This review surveys the experimental strategies used to distinguish between single-and multi-q orders,along with the crystallographic symmetries of cobalt oxides,in comparison with previously studied systems.The general formation mechanism of multi-q order is also briefly discussed.The goal is to provide a solid ground for examining the relevance of multi-q order in honeycomb cobalt oxides and discuss its implications for the microscopic model of these intriguing quantum magnets.
基金Project supported by the National Natural Science Foundation of China (Grant No. 12274005)the National Key Research and Development Program of China (Grant No. 2021YFA1401903)Innovation Program for Quantum Science and Technology (Grant No. 2021ZD0302403)。
文摘Moiré superlattices provide a new platform to engineer various many-body problems. In this work, we consider arrays of quantum dots(QD) realized on semiconductor moiré superlattices with a deep moiré potential. We diagonalize single QD with multiple electrons, and find degenerate ground states serving as local degrees of freedom(qudits) in the superlattice. With a deep moiré potential, the hopping and exchange interaction between nearby QDs become irrelevant,and the direct Coulomb interaction of the density–density type dominates. Therefore, nearby QDs must arrange the spatial densities to optimize the Coulomb energy. When the local Hilbert space has a two-fold orbital degeneracy, we find that a square superlattice realizes an anisotropic XY model, while a triangular superlattice realizes a generalized XY model with geometric frustration.
基金supported by the National Natural Science Foundation of China(Grant Nos.12488201 and 12404215)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302403)+1 种基金Guangdong Provincial Quantum Science Strategic Initiative(Grant Nos.GDZX2401001 and GDZX2401009)supported by the U.S.Department of Energy,Basic Energy Sciences(Grant No.DE-FG02-99ER45747)。
文摘In unconventional high-temperature(high-T_(c))superconductors,the pair density wave state,an exotic superconducting order showing spatially periodic order parameter modulations with the period of several unit cells and translational symmetry breaking,has attracted broad attention.However,the superconducting pair density modulation(PDM)within a single unit cell has never been carefully investigated before.Here,using scanning tunneling microscopy/spectroscopy,we report the observation of PDM in monolayer high-T_(c) iron chalcogenide films epitaxially grown on SrTiO_(3)(001).The superconductivity modulations are characterized by the superconducting gap size and the coherence peak sharpness.Further analysis shows that the local maxima and minima in the superconducting gap modulation are centered at the crystallographic locations of the chalcogen atoms,revealing the breaking of the glide-mirror symmetry of the chalcogen atoms in monolayer high-T_(c) iron chalcogenide films grown on SrTiO_(3)(001).Our findings provide precise microscopic information on superconductivity within the lattice unit cell and may promote the understanding of unconventional high-T_(c) superconductivity.
基金Supported by the National Key R&D Program of China(Grant Nos.2019YFA0308401 and 2017YFA0303301)the National Natural Science Foundation of China(Grant Nos.11974025,11674009,and 11934016)+1 种基金the Beijing Natural Science Foundation(Grant No.1192009)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB28000000)。
文摘We report the experimental investigation of the superconductor-metal quantum phase transition of the Eu O/KTa O3 interface.Around the transition,a divergence of the dynamical critical exponent is observed,which supports the quantum Griffiths singularity in the Eu O/KTa O3 interface.The quantum Griffiths singularity could be attributed to large rare superconducting regions and quenched disorders at the interface.Our results could pave the way for studying the exotic superconducting properties at the Eu O/KTa O3 interface.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11888101 and 11774008)the National Key R&D Program of China (Grant Nos. 2018YFA0305604 and 2017YFA0303302)+1 种基金the Beijing Natural Science Foundation (Grant No. Z180010)the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB28000000)。
文摘Superlattice potentials are theoretically predicted to modify the single-particle electronic structures. The resulting Coulomb-interaction-dominated low-energy physics would generate highly novel many-body phenomena. Here,by in situ tunneling spectroscopy, we show the signatures of superstructure-modulated correlated electron states in epitaxial bilayer graphene(BLG) on 6H-Si C(0001). As the carrier density is locally quasi-‘tuned’ by the superlattice potentials of a 6 × 6 interface reconstruction phase, the spectral-weight transfer occurs between the two broad peaks flanking the charge-neutral point. Such a detected non-rigid band shift beyond the single-particle band description implies the existence of correlation effects, probably attributed to the modified interlayer coupling in epitaxial BLG by the 6×6 reconstruction as in magic-angle BLG by the moiré potentials. Quantitative analysis suggests that the intrinsic interface reconstruction shows a high carrier tunability of ~1/2 filling range, equivalent to the back gating by a voltage of ~70 V in a typical gated BLG/SiO_(2)/Si device. The finding in interfacemodulated epitaxial BLG with reconstruction phase extends the BLG platform with electron correlations beyond the magic-angle situation, and may stimulate further investigations on correlated states in graphene systems and other van der Waals materials.
基金supported by the National Natural Science Foundation of China(Grant Nos.11275008,91021007,and 10974012)the China Postdoctoral Science Foundation(Grant No.2014M550005)
文摘The hydrogen bond （HB） is an important type of intermolecular interaction, which is generally weak, ubiquitous, and essential to life on earth. The small mass of hydrogen means that many properties of HBs are quantum mechanical in nature. In recent years, because of the development of computer simulation methods and computational power, the influence of nuclear quantum effects （NQEs） on the structural and energetic properties of some hydrogen bonded systems has been intensively studied. Here, we present a review of these studies by focussing on the explanation of the principles underlying the simulation methods, i.e., the ab initio path-integral molecular dynamics. Its extension in combination with the thermodynamic integration method for the calculation of free energies will also be introduced. We use two examples to show how this influence of NQEs in realistic systems is simulated in practice.
基金Project supported by the National Key R&D Program of China(Grant No.2017YFA0303301)the National Natural Science Foundation of China(Grant No.11921005)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB28000000)Beijing Municipal Science&Technology Commission,China(Grant No.Z191100007219013)。
文摘Quantum computers are in hot-spot with the potential to handle more complex problems than classical computers can.Realizing the quantum computation requires the universal quantum gate set {T,H,CNOT} so as to perform any unitary transformation with arbitrary accuracy.Here we first briefly review the Majorana fermions and then propose the realization of arbitrary two-qubit quantum gates based on chiral Majorana fermions.Elementary cells consist of a quantum anomalous Hall insulator surrounded by a topological superconductor with electric gates and quantum-dot structures,which enable the braiding operation and the partial exchange operation.After defining a qubit by four chiral Majorana fermions,the singlequbit T and H quantum gates are realized via one partial exchange operation and three braiding operations,respectively.The entangled CNOT quantum gate is performed by braiding six chiral Majorana fermions.Besides,we design a powerful device with which arbitrary two-qubit quantum gates can be realized and take the quantum Fourier transform as an example to show that several quantum operations can be performed with this space-limited device.Thus,our proposal could inspire further utilization of mobile chiral Majorana edge states for faster quantum computation.
基金Project supported by the National Basic Research Program of China(Grant Nos.2011CB922002 and 2013CB632704)the Knowledge Innovation Program of the Chinese Academy of Sciences
文摘We image optical near-field patterns at subwavelength circular hole arrays in Au film by using scanning near-field optical microscopy in near-infrared wavelengths. Periodical oscillation features are found in the near-field images at the air/Au interface and exhibit two typical kinds of standing wave oscillation forms at the wavelengths corresponding to the transmission minimum and maximum in the transmission spectrum, and the latter one originates from the excitation and interference of a surface plasmon wave at the metallic hole arrays. Our work indicates that monitoring optical near-field patterns can help to reveal many interesting properties of surface plasmon waves at metallic nanostructures and understand their underlying physical mechanisms.
基金support from the National Natural Science Foundation of China (Grant Nos. 12274004 and 11888101)
文摘This study explores the use of neural network-based analytic continuation to extract spectra from Monte Carlo data.We apply this technique to both synthetic and Monte Carlo-generated data.The training sets for neural networks are carefully synthesized without“data leakage”.We find that the training set should match the input correlation functions in terms of statistical error properties,such as noise level,noise dependence on imaginary time,and imaginary time-displaced correlations.We have developed a systematic method to synthesize such training datasets.Our improved algorithm outperforms the widely used maximum entropy method in highly noisy situations.As an example,our method successfully extracted the dynamic structure factor of the spin-1/2 Heisenberg chain from quantum Monte Carlo simulations.
基金supported by the National Natural Science Foundation of China(Grant Nos.92065104 and 12074010)in part by the Gordon and Betty Moore Foundation’s EPi QS Initiative(Grant No.GBMF9615)to L.N.Pfeifferby the National Science Foundation MRSEC(Grant No.DMR 2011750)to Princeton University。
文摘We study ultra-high-mobility two-dimensional(2D)electron/hole systems with high precision capacitance measurement.It is found that the capacitance charge appears only at the fringe of the gate at high magnetic field when the 2D conductivity decreases significantly.At integer quantum Hall effects,the capacitance vanishes and forms a plateau at high temperatures T≥300 m K,which surprisingly disappears at T≤100 m K.This anomalous behavior is likely a manifestation that dilute particles/vacancies in the top-most Landau level form Wigner crystals,which have finite compressibility and can host polarization current.
基金Project supported by the National Key R&D Program of China(Grant No.2017YFA0303301)the National Natural Science Foundation of China(Grant Nos.11921005 and 11574007)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB28000000)Beijing Municipal Science&Technology Commission,China(Grant No.Z191100007219013).
文摘We theoretically study the Josephson effect in a quantum anomalous Hall insulator(QAHI)nanoribbon with a domain wall structure and covered by the superconductor.The anomalous Josephson current,the nonzero supercurrent at the zero superconducting phase difference,appears with the nonzero magnetization and the suitable azimuth angle of the domain wall.Dependent on the configuration of the domain wall,the anomalous current peaks in the Bloch type but disappears in the Néel type because the y-component of magnetization is necessary to break symmetry to arouse the anomalous current.The phase shift of the anomalous current is tunable by the magnetization,the azimuth angle,or the thickness of the domain wall.By introducing a bare QAHI region in the middle of the junction which is not covered by the superconductor,the anomalous Josephson effect is enhanced such that the phase shift can exceedπ.Thus,a continuous change between 0 andπjunctions is realized via regulating the configuration of the domain wall or the magnetization strength.As long as an s-wave superconductor is placed on the top of the QAHI with a domain wall structure,this proposal can be experimentally fabricated and useful for the phase battery or superconducting quantum bit.
基金supported by the National Key R&D Program of China(Grant Nos.2017YFA0303302 and 2018YFA0305602)the National Natural Science Foundation of China(Grant No.11921005)Shanghai Municipal Science and Technology Major Project(Grant No.2019SHZDZX01)。
文摘A theoretical model of computation is proposed based on Lorentz quantum mechanics.Besides the standard qubits,this model has an additional bit,which we call hyperbolic bit(or hybit in short).A set of basic logical gates are constructed and their universality is proved.As an application,a search algorithm is designed for this computer model and is found to be exponentially faster than Grover's search algorithm.
