Dirac’s rule in which only special phase space variables should be promoted to operators in canonical quantization is applied to loop quantum gravity. For this theory, Dirac’s rule is violated, and as a result loop ...Dirac’s rule in which only special phase space variables should be promoted to operators in canonical quantization is applied to loop quantum gravity. For this theory, Dirac’s rule is violated, and as a result loop quantum gravity fails the test to be a valid quantization. Indications are included on how to create and deal with valid versions of quantum gravity.展开更多
The quantum characters of particles also apply to the human society in 21st century.Many countries including China have gradually entered into the club of quantum society,it means the policies on education,economy,cul...The quantum characters of particles also apply to the human society in 21st century.Many countries including China have gradually entered into the club of quantum society,it means the policies on education,economy,culture and politics should be adjus ted accordingly.This article a ttempts to explore some practical thoughts on those critical issues.展开更多
Topological Weyl semimetal WTe2 with large-scale Him form has a promising prospect for new-generation spintronic devices.However,it remains a hard task to suppress the defect states in large-scale WTe2 films due to th...Topological Weyl semimetal WTe2 with large-scale Him form has a promising prospect for new-generation spintronic devices.However,it remains a hard task to suppress the defect states in large-scale WTe2 films due to the chemical nature.Here we significantly improve the crystalline quality and remove the Te vacancies in WTe2 films by post annealing.We observe the distinct Shubnikov-de Haas quantum oscillations in WTe2 films.The nontrivial Berry phase can be revealed by Landau fan diagram analysis.The Hall mobility of WTe2 films can reach 1245cm^2V^-1s^-1 and 1423cm^2V^-1s^-1 for holes and electrons with the carrier density of 5× 10^19 cm^-3 and 2 × 10^19 cm^-3,respectively.Our work provides a feasible route to obtain high-quality Weyl semimetal films for the future topological quantum device applications.展开更多
We investigate the evolution of entanglement spectra under a global quantum quench from a short-range correlated state to the quantum critical point.Motivated by the conformal mapping,we find that the dynamical entang...We investigate the evolution of entanglement spectra under a global quantum quench from a short-range correlated state to the quantum critical point.Motivated by the conformal mapping,we find that the dynamical entanglement spectra demonstrate distinct finite-size scaling behaviors from the static case.As a prototypical example,we compute real-time dynamics of the eritanglement spectra of a one-dimensional transverse-field Ising chain.Numerical simulation confirms that the entanglement spectra scale with the subsystem size I as for the dynamical equilibrium state,much faster thanαIn^-1 l for the critical ground state.In particular,as a byproduct,the entanglement spectra at the long time limit faithfully gives universal tower structure of underlying Ising criticality,which shows the emergence of operator-state correspondence in the quantum dynamics.展开更多
Brillouin zone.The closed graphene system has proven to be the ideal model to investigate relativistic quantum chaos phenomena.The electromagnetic material photonic graphene(PG)and electronic graphene not only have th...Brillouin zone.The closed graphene system has proven to be the ideal model to investigate relativistic quantum chaos phenomena.The electromagnetic material photonic graphene(PG)and electronic graphene not only have the same structural symmetry,but also have the similar band structure.Thus,we consider a stadium shaped resonant cavity filled with PG to demonstrate the relativistic quantum chaos phenomenon by numerical simulation.It is interesting that the relativistic quantum scars not only are identified in the PG cavities,but also appear and disappear repeatedly.The wave vector difference between repetitive scars on the same orbit is analyzed and confirmed to follow the quantization rule.The exploration will not only demonstrate a visual simulation of relativistic quantum scars but also propose a physical system for observing valley-dependent relativistic quantum scars,which is helpful for further understanding of quantum chaos.展开更多
Highly sensitive methods are important for monitoring the concentration of metal ions in industrial wastewater.Here,we developed a new probe for the determination of metal ions by fluorescence quenching.The probe cons...Highly sensitive methods are important for monitoring the concentration of metal ions in industrial wastewater.Here,we developed a new probe for the determination of metal ions by fluorescence quenching.The probe consists of hydroxylated graphene quantum dots(H-GQDs),prepared from GQDs by electrochemical method followed by surface hydroxylation.It is a non-reactive indicator with high sensitivity and detection limits of 0.01μM for Cu2+,0.005μM for Al3+,0.04μM for Fe3+,and 0.02μM for Cr3+.In addition,the low biotoxicity and excellent solubility of H-GQDs make them promising for application in wastewater metal ion detection.展开更多
Advanced machine learning(ML)approaches such as transfer learning have seldom been applied to approximate quantum many-body systems.Here we demonstrate that a simple recurrent unit(SRU)based efficient and transferable...Advanced machine learning(ML)approaches such as transfer learning have seldom been applied to approximate quantum many-body systems.Here we demonstrate that a simple recurrent unit(SRU)based efficient and transferable sequence learning framework is capable of learning and accurately predicting the time evolution of the one-dimensional(ID)Ising model with simultaneous transverse and parallel magnetic fields,as quantitatively corroborated by relative entropy measurements between the predicted and exact state distributions.At a cost of constant computational complexity,a larger many-body state evolution is predicted in an autoregressive way from just one initial state,without any guidance or knowledge of any Hamiltonian.Our work paves the way for future applications of advanced ML methods in quantum many-body dynamics with knowledge only from a smaller system.展开更多
Electrically-pumped semiconductor lasers based on monolithic chip configuration possess plenty of advantages such as small volume,light weight,long lifetime and stable performance.Nevertheless this type of lasers rely...Electrically-pumped semiconductor lasers based on monolithic chip configuration possess plenty of advantages such as small volume,light weight,long lifetime and stable performance.Nevertheless this type of lasers rely on the interband transition,which sets the bounds for emission wavelength typically below 4μm,and state of the art performance has been attained below 3μm.Attempts to employ small bandgap meterials like antimonide or lead salts ended with poor performance mainly due to imperfect crystal quality and severe Auger recombination.In view of the broad application prospects of infrared spectral range above 3μm,more attention was casted again on the low-dimensional quantum structure materials,such as quantum wells and quantum dots,which have been applied in the near infrared successfully decades ago.展开更多
Semiconductor quantum dots are leading candidates for the on-demand generation of single photons and entangled photon pairs.High photon quality and indistinguishability of photons from different sources are critical f...Semiconductor quantum dots are leading candidates for the on-demand generation of single photons and entangled photon pairs.High photon quality and indistinguishability of photons from different sources are critical for quantum information applications.The inability to grow perfectly identical quantum dots with ideal optical properties necessitates the application of post-growth tuning techniques via e.g.temperature,electric,magnetic or strain fields.In this review,we summarize the state-of-the-art and highlight the advantages of strain tunable non-classical photon sources based on epitaxial quantum dots.Using piezoelectric crystals like PMN-PT,the wavelength of single photons and entangled photon pairs emitted by InGaAs/GaAs quantum dots can be tuned reversibly.Combining with quantum light-emitting diodes simultaneously allows for electrical triggering and the tuning of wavelength or exciton fine structure.Emission from light hole exciton can be tuned,and quantum dot containing nanostructure such as nanowires have been piezo-integrated.To ensure the indistinguishability of photons from distant emitters,the wavelength drift caused by piezo creep can be compensated by frequency feedback,which is verified by two-photon interference with photons from two stabilized sources.Therefore,strain tuning proves to be a flexible and reliable tool for the development of scalable quantum dots-based non-classical photon sources.展开更多
Quantum cascade(QC)superluminescent light emitters(SLEs)have emerged as desirable broadband mid-infrared(MIR)light sources for growing number of applications in areas like medical imaging,gas sensing and national defe...Quantum cascade(QC)superluminescent light emitters(SLEs)have emerged as desirable broadband mid-infrared(MIR)light sources for growing number of applications in areas like medical imaging,gas sensing and national defense.However,it is challenging to obtain a practical high-power device due to the very low efficiency of spontaneous emission in the intersubband transitions in QC structures.Herein a design of~5μm SLEs is demonstrated with a two-phonon resonancebased QC active structure coupled with a compact combinatorial waveguide structure which comprises a short straight part adjacent to a tilted stripe and to a J-shaped waveguide.The as-fabricated SLEs achieve a high output power of 1.8 mW,exhibiting the potential to be integrated into array devices without taking up too much chip space.These results may facilitate the realization of SLE arrays to attain larger output power and pave the pathway towards the practical applications of broadband MIR light sources.展开更多
In recent years,rapid developments of quantum computer are witnessed in both the hardware and the algorithm domains,making it necessary to have an updated review of some major techniques and applications in quantum al...In recent years,rapid developments of quantum computer are witnessed in both the hardware and the algorithm domains,making it necessary to have an updated review of some major techniques and applications in quantum algorithm design. In this survey as well as tutorial article,the authors first present an overview of the development of quantum algorithms,then investigate five important techniques:Quantum phase estimation,linear combination of unitaries,quantum linear solver,Grover search,and quantum walk,together with their applications in quantum state preparation,quantum machine learning,and quantum search.In the end,the authors collect some open problems influencing the development of future quantum algorithms.展开更多
This research aims to review the developments in the field of quantum private query(QPQ), a type of practical quantum cryptographic protocol. The primary protocol, as proposed by Jacobi et al., and the improvements in...This research aims to review the developments in the field of quantum private query(QPQ), a type of practical quantum cryptographic protocol. The primary protocol, as proposed by Jacobi et al., and the improvements in the protocol are introduced.Then, the advancements made in sability, theoretical security, and practical security are summarized. Additionally, we describe two new results concerning QPQ security. We emphasize that a procedure to detect outside adversaries is necessary for QPQ, as well as for other quantum secure computation protocols, and then briefly propose such a strategy. Furthermore, we show that the shift-and-addition or low-shift-and-addition technique can be used to obtain a secure real-world implementation of QPQ, where a weak coherent source is used instead of an ideal single-photon source.展开更多
Quantum state transfer between two distant parties is at the heart of quantum computation and quantum communication.Among the various protocols,the counterdiabatic driving(CD)method,by suppressing the unwanted transit...Quantum state transfer between two distant parties is at the heart of quantum computation and quantum communication.Among the various protocols,the counterdiabatic driving(CD)method,by suppressing the unwanted transitions with an auxiliary Hamiltonian Hcd(t),offers a fast and robust strategy to transfer quantum states.However,Hcd(t)term often takes a complicated form in higherdimensional systems and is difficult to realize in experiment.Recently,the Floquet-engineered method was proposed to emulate the dynamics induced by Hcd(t)without the need for complex interactions in multi-qubit systems,which can accelerate the adiabatic process through the fast-oscillating control in the original Hamiltonian H0(t).Here,we apply this method in the Heisenberg spin chains,with only control of the two marginal couplings,to achieve the fast,high-fidelity,and robust quantum state transfer.Then we report an experimental implementation of our scheme using a nuclear magnetic resonance simulator.The experimental results demonstrate the feasibility of this method in complex many-body system and thus provide a new alternative to realize the high-fidelity quantum state manipulation in practice.展开更多
Based on a hybrid system consisting of a quantum dot coupled with a double-sided micropillar cavity, we investigate the implementation of an error-detected photonic quantum routing controlled by the other photon. The ...Based on a hybrid system consisting of a quantum dot coupled with a double-sided micropillar cavity, we investigate the implementation of an error-detected photonic quantum routing controlled by the other photon. The computational errors from unexpected experimental imperfections are heralded by single photon detections, resulting in a unit fidelity for the present scheme, so that this scheme is intrinsically robust. We discuss the performance of the scheme with currently achievable experimental parameters. Our results show that the present scheme is efficient. Furthermore, our scheme could provide a promising building block for quantum networks and distributed quantum information processing in the future.展开更多
We studied quantum correlation and quantum entanglement of a quantum system in which a coherent state light field interacts with two qubits that are initially prepared in a separable and mixed state.The influence of m...We studied quantum correlation and quantum entanglement of a quantum system in which a coherent state light field interacts with two qubits that are initially prepared in a separable and mixed state.The influence of mean photon number of the coherent field and distribution probability of the atom on the geometrical quantum discord and the negativity are discussed.Our results show that the mean photon number of light field and distribution function of the atom can regulate and control the quantum correlation and quantum entanglement.展开更多
Gaussian Boson sampling(GBS) provides a highly efficient approach to make use of squeezed states from parametric down-conversion to solve a classically hard-to-solve sampling problem. The GBS protocol not only signifi...Gaussian Boson sampling(GBS) provides a highly efficient approach to make use of squeezed states from parametric down-conversion to solve a classically hard-to-solve sampling problem. The GBS protocol not only significantly enhances the photon generation probability, compared to standard Boson sampling with single photon Fock states, but also links to potential applications such as dense subgraph problems and molecular vibronic spectra. Here, we report the first experimental demonstration of GBS using squeezed-state sources with simultaneously high photon indistinguishability and collection efficiency.We implement and validate 3-, 4- and 5-photon GBS with high sampling rates of 832, 163 and 23 kHz,respectively, which is more than 4.4, 12.0, and 29.5 times faster than the previous experiments.Further, we observe a quantum speed-up on a NP-hard optimization problem when comparing with simulated thermal sampler and uniform sampler.展开更多
Green-Horne-Zeilinger states are a typical type of multipartite entangled states, which plays a central role in quantum information processing. For the generation of multipartite entangled states, the singlestep metho...Green-Horne-Zeilinger states are a typical type of multipartite entangled states, which plays a central role in quantum information processing. For the generation of multipartite entangled states, the singlestep method is more preferable as the needed time will not increase with the increasing of the qubit number. However, this scenario has a strict requirement that all two-qubit interaction strengths should be the same, or the generated state will be of low quality. Here, we propose a scheme for generating multipartite entangled states of superconducting qubits, from a coupled circuit cavities scenario, where we rigorously achieve the requirement via adding an extra z-direction ac classical field for each qubit, leading the individual qubit-cavity coupling strength to be tun able in a wide range, and t hus can be tuned to the same value. Meanwhile, in order to obtain our wanted multi-qubits interaction, xdirection ac classical field for each qubit is also introduced. By selecting the appropriate parameters, we numerically shown that high-fidelity multi-qubit GHZ states can be generated. In add计ion, we also show that the coupled cavities scenario is better than a single cavity case. Therefore, our proposal represents a promising alternative for multipartite entangled states generation.展开更多
An unknown unitary gate, which is secretly chosen from several known ones, can always be distinguished perfectly. In this paper, we implement such a task on IBM’s quantum processor. More precisely,we experimentally d...An unknown unitary gate, which is secretly chosen from several known ones, can always be distinguished perfectly. In this paper, we implement such a task on IBM’s quantum processor. More precisely,we experimentally demonstrate the discrimination of two qubit unitary gates, the identity gate and the 2/3π-phase shift gate, using two discrimination schemes — the parallel scheme and the sequential scheme. We program these two schemes on the ibmqx4, a 5-qubit superconducting quantum processor via IBM cloud,with the help of the QSI modules. We report that both discrimination schemes achieve success probabilities at least 85%.展开更多
Bell-state analysis(BSA) has great application in the quantum communication. To our best knowledge, the current works are devoted to the physical realization of symmetrical 2×2-dimensional or 2^N× 2^N-dimens...Bell-state analysis(BSA) has great application in the quantum communication. To our best knowledge, the current works are devoted to the physical realization of symmetrical 2×2-dimensional or 2^N× 2^N-dimensional 2-qudit BSA, and there is no work focused on the physical realization of the asymmetrical high-dimensional(for example 3×4-dimensional 2-qudit) Bell-states complete analysis. In this paper, by using the nonlinear interaction between the atoms and photons, we propose a scheme to completely distinguish the asymmetrical 3×4-dimensional 2-qudit Bell states of a hybrid system. We use the quantum information splitting, which is exploited to resolve the degree-mismatch issue in the quantum state sharing schemes, as an example to show the application of the asymmetrical BSA. Finally, we discuss its possible realization with current experimental techniques. Our asymmetrical high-dimensional BSA protocol may pave a new way for high-capacity long-distance quantum communication.展开更多
The quantum characters of particles are depicted as w ave-particle duality, state uncertainty, entanglement, etc. Hereby the similarities also apply to the modern human society. Has many countries gradually entered in...The quantum characters of particles are depicted as w ave-particle duality, state uncertainty, entanglement, etc. Hereby the similarities also apply to the modern human society. Has many countries gradually entered into the club of quantum society? This article attempts to explore some practical thoughts on those critical issues.展开更多
文摘Dirac’s rule in which only special phase space variables should be promoted to operators in canonical quantization is applied to loop quantum gravity. For this theory, Dirac’s rule is violated, and as a result loop quantum gravity fails the test to be a valid quantization. Indications are included on how to create and deal with valid versions of quantum gravity.
文摘The quantum characters of particles also apply to the human society in 21st century.Many countries including China have gradually entered into the club of quantum society,it means the policies on education,economy,culture and politics should be adjus ted accordingly.This article a ttempts to explore some practical thoughts on those critical issues.
基金the National Key R&D Program of China(Grant Nos.2017YFA0206304 and 2016YFA0300803)the National Natural Science Foundation of China(Grant Nos 61822403,11874203,11774160,61427812 and U1732159)+2 种基金the Fundamental Research Funds for the Central Universities(Grant Nos 021014380080 and 021014380113)the Natural Science Foundation of Jiangsu Province of China(Grant No BK20192006)Collaborative Innovation Center of Solid-State Lighting and Energy-Saving Elec tronics.
文摘Topological Weyl semimetal WTe2 with large-scale Him form has a promising prospect for new-generation spintronic devices.However,it remains a hard task to suppress the defect states in large-scale WTe2 films due to the chemical nature.Here we significantly improve the crystalline quality and remove the Te vacancies in WTe2 films by post annealing.We observe the distinct Shubnikov-de Haas quantum oscillations in WTe2 films.The nontrivial Berry phase can be revealed by Landau fan diagram analysis.The Hall mobility of WTe2 films can reach 1245cm^2V^-1s^-1 and 1423cm^2V^-1s^-1 for holes and electrons with the carrier density of 5× 10^19 cm^-3 and 2 × 10^19 cm^-3,respectively.Our work provides a feasible route to obtain high-quality Weyl semimetal films for the future topological quantum device applications.
基金the start-up funding from Westlake Universitythe National Natural Science Foundation of China under Grant No 11974288.
文摘We investigate the evolution of entanglement spectra under a global quantum quench from a short-range correlated state to the quantum critical point.Motivated by the conformal mapping,we find that the dynamical entanglement spectra demonstrate distinct finite-size scaling behaviors from the static case.As a prototypical example,we compute real-time dynamics of the eritanglement spectra of a one-dimensional transverse-field Ising chain.Numerical simulation confirms that the entanglement spectra scale with the subsystem size I as for the dynamical equilibrium state,much faster thanαIn^-1 l for the critical ground state.In particular,as a byproduct,the entanglement spectra at the long time limit faithfully gives universal tower structure of underlying Ising criticality,which shows the emergence of operator-state correspondence in the quantum dynamics.
基金the National Natural Science Foundation of China under Grant No.11847067the Natural Science Foundation of Shanxi Province under Grant No.201801D221178+1 种基金the Science and Technology Innovation Project of Shanxi Higher Education under Grant No.2019L0648Taiyuan University of Science and Technology Scientific Research Initial Funding under Grant No.20152044.
文摘Brillouin zone.The closed graphene system has proven to be the ideal model to investigate relativistic quantum chaos phenomena.The electromagnetic material photonic graphene(PG)and electronic graphene not only have the same structural symmetry,but also have the similar band structure.Thus,we consider a stadium shaped resonant cavity filled with PG to demonstrate the relativistic quantum chaos phenomenon by numerical simulation.It is interesting that the relativistic quantum scars not only are identified in the PG cavities,but also appear and disappear repeatedly.The wave vector difference between repetitive scars on the same orbit is analyzed and confirmed to follow the quantization rule.The exploration will not only demonstrate a visual simulation of relativistic quantum scars but also propose a physical system for observing valley-dependent relativistic quantum scars,which is helpful for further understanding of quantum chaos.
基金This work was financially supported by the National Natural Science Foundation of China(No.21674011)Beijing Municipal Natural Science Foundation(No.2172040).
文摘Highly sensitive methods are important for monitoring the concentration of metal ions in industrial wastewater.Here,we developed a new probe for the determination of metal ions by fluorescence quenching.The probe consists of hydroxylated graphene quantum dots(H-GQDs),prepared from GQDs by electrochemical method followed by surface hydroxylation.It is a non-reactive indicator with high sensitivity and detection limits of 0.01μM for Cu2+,0.005μM for Al3+,0.04μM for Fe3+,and 0.02μM for Cr3+.In addition,the low biotoxicity and excellent solubility of H-GQDs make them promising for application in wastewater metal ion detection.
基金the National Natural Science Foundation of China under Grant Nos 11874431 and 11804181the National Key R&D Program of China under Grant No 2018YFA0306800+1 种基金the Guangdong Science and Technology Innovation Youth Talent Program under Grant Nos 2016TQ03X688 and 2018YFA0306504the Research Fund Program of the State Key Laboratory of Low-Dimensional Quantum Physics under Grant No ZZ201803.
文摘Advanced machine learning(ML)approaches such as transfer learning have seldom been applied to approximate quantum many-body systems.Here we demonstrate that a simple recurrent unit(SRU)based efficient and transferable sequence learning framework is capable of learning and accurately predicting the time evolution of the one-dimensional(ID)Ising model with simultaneous transverse and parallel magnetic fields,as quantitatively corroborated by relative entropy measurements between the predicted and exact state distributions.At a cost of constant computational complexity,a larger many-body state evolution is predicted in an autoregressive way from just one initial state,without any guidance or knowledge of any Hamiltonian.Our work paves the way for future applications of advanced ML methods in quantum many-body dynamics with knowledge only from a smaller system.
文摘Electrically-pumped semiconductor lasers based on monolithic chip configuration possess plenty of advantages such as small volume,light weight,long lifetime and stable performance.Nevertheless this type of lasers rely on the interband transition,which sets the bounds for emission wavelength typically below 4μm,and state of the art performance has been attained below 3μm.Attempts to employ small bandgap meterials like antimonide or lead salts ended with poor performance mainly due to imperfect crystal quality and severe Auger recombination.In view of the broad application prospects of infrared spectral range above 3μm,more attention was casted again on the low-dimensional quantum structure materials,such as quantum wells and quantum dots,which have been applied in the near infrared successfully decades ago.
基金The work was financially supported by the ERC Starting Grant No.715770(QD-NOMS)the National Natural Science Foundation of China(No.61728501).
文摘Semiconductor quantum dots are leading candidates for the on-demand generation of single photons and entangled photon pairs.High photon quality and indistinguishability of photons from different sources are critical for quantum information applications.The inability to grow perfectly identical quantum dots with ideal optical properties necessitates the application of post-growth tuning techniques via e.g.temperature,electric,magnetic or strain fields.In this review,we summarize the state-of-the-art and highlight the advantages of strain tunable non-classical photon sources based on epitaxial quantum dots.Using piezoelectric crystals like PMN-PT,the wavelength of single photons and entangled photon pairs emitted by InGaAs/GaAs quantum dots can be tuned reversibly.Combining with quantum light-emitting diodes simultaneously allows for electrical triggering and the tuning of wavelength or exciton fine structure.Emission from light hole exciton can be tuned,and quantum dot containing nanostructure such as nanowires have been piezo-integrated.To ensure the indistinguishability of photons from distant emitters,the wavelength drift caused by piezo creep can be compensated by frequency feedback,which is verified by two-photon interference with photons from two stabilized sources.Therefore,strain tuning proves to be a flexible and reliable tool for the development of scalable quantum dots-based non-classical photon sources.
基金This work was supported by the Key Research and Development Plan of Ministry of Science and Technology(No.2016YFB0402303)the National Natural Science Foundation of China(No.61575222)the open project of the State Key Laboratory of Luminescence and Applications,and China Postdoctoral Science Foundation(No.2017M621858).
文摘Quantum cascade(QC)superluminescent light emitters(SLEs)have emerged as desirable broadband mid-infrared(MIR)light sources for growing number of applications in areas like medical imaging,gas sensing and national defense.However,it is challenging to obtain a practical high-power device due to the very low efficiency of spontaneous emission in the intersubband transitions in QC structures.Herein a design of~5μm SLEs is demonstrated with a two-phonon resonancebased QC active structure coupled with a compact combinatorial waveguide structure which comprises a short straight part adjacent to a tilted stripe and to a J-shaped waveguide.The as-fabricated SLEs achieve a high output power of 1.8 mW,exhibiting the potential to be integrated into array devices without taking up too much chip space.These results may facilitate the realization of SLE arrays to attain larger output power and pave the pathway towards the practical applications of broadband MIR light sources.
基金the National Natural Science Foundation of China under Grant No. 11671388CAS Project QYZDJ-SSW-SYS022GF S&T Innovation Special Zone Project.
文摘In recent years,rapid developments of quantum computer are witnessed in both the hardware and the algorithm domains,making it necessary to have an updated review of some major techniques and applications in quantum algorithm design. In this survey as well as tutorial article,the authors first present an overview of the development of quantum algorithms,then investigate five important techniques:Quantum phase estimation,linear combination of unitaries,quantum linear solver,Grover search,and quantum walk,together with their applications in quantum state preparation,quantum machine learning,and quantum search.In the end,the authors collect some open problems influencing the development of future quantum algorithms.
基金the National Natural Science Foundation of China(Grant Nos.61672110,61572081,61671082,61702469,and61771439).
文摘This research aims to review the developments in the field of quantum private query(QPQ), a type of practical quantum cryptographic protocol. The primary protocol, as proposed by Jacobi et al., and the improvements in the protocol are introduced.Then, the advancements made in sability, theoretical security, and practical security are summarized. Additionally, we describe two new results concerning QPQ security. We emphasize that a procedure to detect outside adversaries is necessary for QPQ, as well as for other quantum secure computation protocols, and then briefly propose such a strategy. Furthermore, we show that the shift-and-addition or low-shift-and-addition technique can be used to obtain a secure real-world implementation of QPQ, where a weak coherent source is used instead of an ideal single-photon source.
基金the National Natural Science Foundation of China (11847016, 11425523 and 11661161018)National Key Research and Development Program of China (2018YFA0306600)Anhui Initiative in Quantum Information Technologies (AHY050000).
文摘Quantum state transfer between two distant parties is at the heart of quantum computation and quantum communication.Among the various protocols,the counterdiabatic driving(CD)method,by suppressing the unwanted transitions with an auxiliary Hamiltonian Hcd(t),offers a fast and robust strategy to transfer quantum states.However,Hcd(t)term often takes a complicated form in higherdimensional systems and is difficult to realize in experiment.Recently,the Floquet-engineered method was proposed to emulate the dynamics induced by Hcd(t)without the need for complex interactions in multi-qubit systems,which can accelerate the adiabatic process through the fast-oscillating control in the original Hamiltonian H0(t).Here,we apply this method in the Heisenberg spin chains,with only control of the two marginal couplings,to achieve the fast,high-fidelity,and robust quantum state transfer.Then we report an experimental implementation of our scheme using a nuclear magnetic resonance simulator.The experimental results demonstrate the feasibility of this method in complex many-body system and thus provide a new alternative to realize the high-fidelity quantum state manipulation in practice.
基金the Scientific Research Foundation of Shanxi Institute of Technology(Grant No.201706001)the Fund for Shanxi“1331 Project”Key Subjects Construction+2 种基金the China Postdoctoral Science Foundation(Grant No.2017M612411)the Education Department Foundation of Henan Province,China(Grant No.18A140009)the National Natural Science Foundation of China(Grant Nos.61821280,11604190,and 61465013).
文摘Based on a hybrid system consisting of a quantum dot coupled with a double-sided micropillar cavity, we investigate the implementation of an error-detected photonic quantum routing controlled by the other photon. The computational errors from unexpected experimental imperfections are heralded by single photon detections, resulting in a unit fidelity for the present scheme, so that this scheme is intrinsically robust. We discuss the performance of the scheme with currently achievable experimental parameters. Our results show that the present scheme is efficient. Furthermore, our scheme could provide a promising building block for quantum networks and distributed quantum information processing in the future.
基金Project supported by the National Natural Science Foundation of China(Grant No.11604090).
文摘We studied quantum correlation and quantum entanglement of a quantum system in which a coherent state light field interacts with two qubits that are initially prepared in a separable and mixed state.The influence of mean photon number of the coherent field and distribution probability of the atom on the geometrical quantum discord and the negativity are discussed.Our results show that the mean photon number of light field and distribution function of the atom can regulate and control the quantum correlation and quantum entanglement.
基金the National Natural Science Foundation of China(91836303,11674308,and 11525419)the Chinese Academy of Sciences,the National Fundamental Research Program(2018YFA0306100)the Anhui Initiative in Quantum Information Technologies.
文摘Gaussian Boson sampling(GBS) provides a highly efficient approach to make use of squeezed states from parametric down-conversion to solve a classically hard-to-solve sampling problem. The GBS protocol not only significantly enhances the photon generation probability, compared to standard Boson sampling with single photon Fock states, but also links to potential applications such as dense subgraph problems and molecular vibronic spectra. Here, we report the first experimental demonstration of GBS using squeezed-state sources with simultaneously high photon indistinguishability and collection efficiency.We implement and validate 3-, 4- and 5-photon GBS with high sampling rates of 832, 163 and 23 kHz,respectively, which is more than 4.4, 12.0, and 29.5 times faster than the previous experiments.Further, we observe a quantum speed-up on a NP-hard optimization problem when comparing with simulated thermal sampler and uniform sampler.
基金the National Natural Science Foundation of China (Grant No. 11874156)the Key R&D Program of Guangdong Province (Grant No. 2018B0303326001)and the National Key R&D Program of China (Grant No. 2016 YFA0301803).
文摘Green-Horne-Zeilinger states are a typical type of multipartite entangled states, which plays a central role in quantum information processing. For the generation of multipartite entangled states, the singlestep method is more preferable as the needed time will not increase with the increasing of the qubit number. However, this scenario has a strict requirement that all two-qubit interaction strengths should be the same, or the generated state will be of low quality. Here, we propose a scheme for generating multipartite entangled states of superconducting qubits, from a coupled circuit cavities scenario, where we rigorously achieve the requirement via adding an extra z-direction ac classical field for each qubit, leading the individual qubit-cavity coupling strength to be tun able in a wide range, and t hus can be tuned to the same value. Meanwhile, in order to obtain our wanted multi-qubits interaction, xdirection ac classical field for each qubit is also introduced. By selecting the appropriate parameters, we numerically shown that high-fidelity multi-qubit GHZ states can be generated. In add计ion, we also show that the coupled cavities scenario is better than a single cavity case. Therefore, our proposal represents a promising alternative for multipartite entangled states generation.
基金National Natural Science Foundation of China(Grant Nos.61672007,11647140)ERC Consolidator(Grant No.615307-QPROGRESS).
文摘An unknown unitary gate, which is secretly chosen from several known ones, can always be distinguished perfectly. In this paper, we implement such a task on IBM’s quantum processor. More precisely,we experimentally demonstrate the discrimination of two qubit unitary gates, the identity gate and the 2/3π-phase shift gate, using two discrimination schemes — the parallel scheme and the sequential scheme. We program these two schemes on the ibmqx4, a 5-qubit superconducting quantum processor via IBM cloud,with the help of the QSI modules. We report that both discrimination schemes achieve success probabilities at least 85%.
基金This work was supported by the National Natural Science Foundation of China(Grant No.61671083)the National Key Research and Development Program of China(Grant No.2016YFA0301304)the Fund of State Key Laboratory of Information Photonics and Optical Communications(Beijing University of Posts and Telecommunications),China.
文摘Bell-state analysis(BSA) has great application in the quantum communication. To our best knowledge, the current works are devoted to the physical realization of symmetrical 2×2-dimensional or 2^N× 2^N-dimensional 2-qudit BSA, and there is no work focused on the physical realization of the asymmetrical high-dimensional(for example 3×4-dimensional 2-qudit) Bell-states complete analysis. In this paper, by using the nonlinear interaction between the atoms and photons, we propose a scheme to completely distinguish the asymmetrical 3×4-dimensional 2-qudit Bell states of a hybrid system. We use the quantum information splitting, which is exploited to resolve the degree-mismatch issue in the quantum state sharing schemes, as an example to show the application of the asymmetrical BSA. Finally, we discuss its possible realization with current experimental techniques. Our asymmetrical high-dimensional BSA protocol may pave a new way for high-capacity long-distance quantum communication.
文摘The quantum characters of particles are depicted as w ave-particle duality, state uncertainty, entanglement, etc. Hereby the similarities also apply to the modern human society. Has many countries gradually entered into the club of quantum society? This article attempts to explore some practical thoughts on those critical issues.