With the rapid advancement of quantum computing,hybrid quantum–classical machine learning has shown numerous potential applications at the current stage,with expectations of being achievable in the noisy intermediate...With the rapid advancement of quantum computing,hybrid quantum–classical machine learning has shown numerous potential applications at the current stage,with expectations of being achievable in the noisy intermediate-scale quantum(NISQ)era.Quantum reinforcement learning,as an indispensable study,has recently demonstrated its ability to solve standard benchmark environments with formally provable theoretical advantages over classical counterparts.However,despite the progress of quantum processors and the emergence of quantum computing clouds,implementing quantum reinforcement learning algorithms utilizing parameterized quantum circuits(PQCs)on NISQ devices remains infrequent.In this work,we take the first step towards executing benchmark quantum reinforcement problems on real devices equipped with at most 136 qubits on the BAQIS Quafu quantum computing cloud.The experimental results demonstrate that the policy agents can successfully accomplish objectives under modified conditions in both the training and inference phases.Moreover,we design hardware-efficient PQC architectures in the quantum model using a multi-objective evolutionary algorithm and develop a learning algorithm that is adaptable to quantum devices.We hope that the Quafu-RL can be a guiding example to show how to realize machine learning tasks by taking advantage of quantum computers on the quantum cloud platform.展开更多
Open quantum system simulations are essential for exploring novel quantum phenomena and evaluating noisy quantum circuits.In this Letter,we investigate whether mixed states generated from noisy quantum circuits can be...Open quantum system simulations are essential for exploring novel quantum phenomena and evaluating noisy quantum circuits.In this Letter,we investigate whether mixed states generated from noisy quantum circuits can be efficiently represented by locally purified density operators(LPDOs).We map an LPDO of N qubits to a pure state of size 2×N defined on a ladder and introduce a unified method for managing virtual and Kraus bonds.We numerically simulate noisy random quantum circuits with depths of up to d=40 using fidelity and entanglement entropy as accuracy measures.The LPDO representation is effective in describing mixed states in both the quantum and classical regions;however,it encounters significant challenges at the quantum-classical critical point,restricting its applicability to the quantum region.In contrast,matrix product operators(MPO)successfully characterize the entanglement trend throughout the simulation,while the truncation in MPOs breaks the positivity condition required for a physical density matrix.This work advances our understanding of efficient mixed-state representations in open quantum systems and provides insights into the entanglement structure of noisy quantum circuits.展开更多
For a compact quantum key distribution (QKD) sender for the polarization encoding BB84 protocol, an eavesdropper could take a side-channel attack by measuring the spatial information of photons to infer their polariza...For a compact quantum key distribution (QKD) sender for the polarization encoding BB84 protocol, an eavesdropper could take a side-channel attack by measuring the spatial information of photons to infer their polarizations. The possibility of this attack can be reduced by introducing an aperture in the QKD sender, however, the effect of the aperture on the QKD security lacks of quantitative analysis. In this paper, we analyze the mutual information between the actual keys encoded at this QKD sender and the inferred keys at the eavesdropper (Eve), demonstrating the effect of the aperture to eliminate the spatial side-channel information quantitatively. It shows that Eve’s potential on eavesdropping spatial side-channel information is totally dependent on the optical design of the QKD sender, including the source arrangement and the aperture. The height of compact QKD senders with integrated light-emitting diode (LED) arrays could be controlled under several millimeters, showing great potential on applications in portable equipment.展开更多
Dispersive optics quantum key distribution(DO-QKD)based on energy-time entangled photon pairs is an important QKD scheme.In DO-QKD,the arrival time of photons is used in key generation and security analysis,which woul...Dispersive optics quantum key distribution(DO-QKD)based on energy-time entangled photon pairs is an important QKD scheme.In DO-QKD,the arrival time of photons is used in key generation and security analysis,which would be greatly affected by fiber dispersion.In this work,we establish a theoretical model of the entanglement-based DO-QKD system,considering the protocol,physical processes(such as fiber transmission and single-photon detection),and the analysis of security tests.Based on this theoretical model,we investigate the influence of chromatic dispersion introduced by transmission fibers on the performance of DO-QKD.By analyzing the benefits and costs of dispersion compensation,the system performance under G.652 and G.655 optical fibers are shown,respectively.The results show that dispersion compensation is unnecessary for DO-QKD systems in campus networks and even metro networks.Whereas,it is still required in DO-QKD systems with longer fiber transmission distances.展开更多
We demonstrate the in situ growth of ultra-thin InA s nanowires with an epitaxial Al film by molecular-beam epitaxy.Our InAs nanowire diameter(~30 nm)is much thinner than before(~100 nm).The ultra-thin InAs nanowires ...We demonstrate the in situ growth of ultra-thin InA s nanowires with an epitaxial Al film by molecular-beam epitaxy.Our InAs nanowire diameter(~30 nm)is much thinner than before(~100 nm).The ultra-thin InAs nanowires are pure phase crystals for various different growth directions.Transmission electron microscopy confirms an atomically abrupt and uniform interface between the Al shell and the InAs wire.Quantum transport study on these devices resolves a hard induced superconducting gap and 2 e-periodic Coulomb blockade at zero magnetic field,a necessary step for future Majorana experiments.By reducing wire diameter,our work presents a promising route for reaching fewer sub-band regime in Major ana nanowire devices.展开更多
In this paper,we present a distal-scanning common path probe for optical coherence tomography(OCT)equipped with a hollow ultrasonic motor and a simple and specially designed beam-splitter.This novel probe proves to be...In this paper,we present a distal-scanning common path probe for optical coherence tomography(OCT)equipped with a hollow ultrasonic motor and a simple and specially designed beam-splitter.This novel probe proves to be able to effectively circumvent polarization and dispersion mismatch caused by fiber motion and is more robust to a variety of interfering factors during the imaging process,experimentally compared to a conventional noncommon path probe.Furthermore,our design counteracts the attenuation of backscattering with depth and the fall-off of the signal,resulting in a more balanced signal range and greater imaging depth.Spectral-domain OCT imaging of phantom and biological tissue is also demonstrated with a sensitivity of∼100dB and a lateral resolution of∼3μm.This low-cost probe offers simplified system configuration and excellent robustness,and is therefore particularly suitable for clinical diagnosis as one-off medical apparatus.展开更多
We introduce Quafu-Qcover,an open-source cloud-based software package developed for solving combinatorial optimization problems using quantum simulators and hardware backends.Quafu-Qcover provides a standardized and c...We introduce Quafu-Qcover,an open-source cloud-based software package developed for solving combinatorial optimization problems using quantum simulators and hardware backends.Quafu-Qcover provides a standardized and comprehensive workflow that utilizes the quantum approximate optimization algorithm(QAOA).It facilitates the automatic conversion of the original problem into a quadratic unconstrained binary optimization(QUBO)model and its corresponding Ising model,which can be subsequently transformed into a weight graph.The core of Qcover relies on a graph decomposition-based classical algorithm,which efficiently derives the optimal parameters for the shallow QAOA circuit.Quafu-Qcover incorporates a dedicated compiler capable of translating QAOA circuits into physical quantum circuits that can be executed on Quafu cloud quantum computers.Compared to a general-purpose compiler,our compiler demonstrates the ability to generate shorter circuit depths,while also exhibiting superior speed performance.Additionally,the Qcover compiler has the capability to dynamically create a library of qubits coupling substructures in real-time,utilizing the most recent calibration data from the superconducting quantum devices.This ensures that computational tasks can be assigned to connected physical qubits with the highest fidelity.The Quafu-Qcover allows us to retrieve quantum computing sampling results using a task ID at any time,enabling asynchronous processing.Moreover,it incorporates modules for results preprocessing and visualization,facilitating an intuitive display of solutions for combinatorial optimization problems.We hope that Quafu-Qcover can serve as an instructive illustration for how to explore application problems on the Quafu cloud quantum computers.展开更多
We have developed a low-damage photolithography method for magnetically doped(Bi,Sb)_(2)Te_(3)quantum anomalous Hall(QAH) thin films incorporating an additional resist layer of poly(methyl methacrylate)(PMMA). By perf...We have developed a low-damage photolithography method for magnetically doped(Bi,Sb)_(2)Te_(3)quantum anomalous Hall(QAH) thin films incorporating an additional resist layer of poly(methyl methacrylate)(PMMA). By performing control experiments on the transport properties of five devices at varied gate voltages(V_(g)s), we revealed that the modified photolithography method enables fabricating QAH devices with the transport and magnetic properties unaffected by fabrication process. Our experiment represents a step towards the production of novel micro-structured electronic devices based on the dissipationless QAH chiral edge states.展开更多
Rechargeable magnesium metal batteries need an electrolyte that forms a stable and ionically conductive solid electrolyte interphase(SEI)on the anodes.Here,we used molecular dynamic simulation,density functional theor...Rechargeable magnesium metal batteries need an electrolyte that forms a stable and ionically conductive solid electrolyte interphase(SEI)on the anodes.Here,we used molecular dynamic simulation,density functional theory calculation,and X-ray photoelectron spectroscopy analysis to investigate the solvation structures and SEI compositions in electrolytes consisting of dual-salts,magnesium bis(trifluoromethanesulfonyl)imide(MgTFSI_(2)),and MgCl_(2),with different additives in 1,2-dimethoxyethane(DME)solvent.We found that the formed[Mg_(3)(μ-Cl)_(4)(DME)mTFSI_(2)](m=3,5)inner-shell solvation clusters in MgTFSI_(2)-MgCl_(2)/DME electrolyte could easily decompose and form a MgO-and MgF_(2)-rich SEI.Such electron-rich inorganic species in the SEI,especially MgF_(2),turned out to be detrimental for Mg plating/stripping.To reduce the MgF_(2)and MgO contents in SEI,we introduce an electron-deficient tri(2,2,2-trifluoroethyl)borate(TFEB)additive in the electrolyte.Mg//Mg cells using the MgTFSI_(2)-MgCl_(2)/DME-TFEB electrolyte could cycle stably for over 400 h with a small polarization voltage of~150 mV.Even with the presence of 800 ppm H_(2)O,the electrolyte with TFEB additive could still preserve its good electrochemical performance.The optimized electrolyte also enabled stable cycling and high-rate capability for Mg//Mo6S8 and Mg//CuS full cells,showing great potential for future applications.展开更多
Supersolidity is a counterintuitive quantum phase of matter where the long-range spatial order of a solid coexists with the frictionless flow characteristic of a superfluid.Recently,evidence of supersolidity has been ...Supersolidity is a counterintuitive quantum phase of matter where the long-range spatial order of a solid coexists with the frictionless flow characteristic of a superfluid.Recently,evidence of supersolidity has been demonstrated in polariton condensates in III-V photonic crystal microcavities by condensing into a topological bound state in the continuum,offering a new light-matter hybrid platform for exploring such quantum phase.In this work,we propose a theoretical scheme for realizing room-temperature supersolidity based on halide perovskite exciton polaritons operating in the optical parametric oscillation regime.By employing a waveguide microcavity geometry,we confine polariton scattering direction in reciprocal space,enabling controlled momentum selection.Leveraging the intrinsic nonlinear interactions among polaritons,we theoretically demonstrate the spontaneous breaking of both continuous translational symmetry and global phase symmetry,i.e.,the evidence of supersolidity.Furthermore,we identify a tunable phase transition sequence in our system:from a Bose-Einstein condensate to a supersolid phase,and ultimately to an insulating phase,as the nonlinear interaction strength increases.展开更多
Quantum optimal control(QOC)relies on accurately modeling system dynamics and is often challenged by unknown or inaccessible interactions in real systems.Taking an unknown collective spin system as an example,this wor...Quantum optimal control(QOC)relies on accurately modeling system dynamics and is often challenged by unknown or inaccessible interactions in real systems.Taking an unknown collective spin system as an example,this work introduces a machine-learning-based,data-driven scheme to overcome the challenges encountered,with a trained neural network(NN)assuming the role of a surrogate model that captures the system’s dynamics and subsequently enables QOC to be performed on the NN instead of on the real system.The trained NN surrogate proves effective for practical QOC tasks and is further demonstrated to be adaptable to different experimental conditions,remaining robust across varying system sizes and pulse durations.展开更多
Magnetic skyrmions are recognized as potential information carriers for building the next-generation spintronic memory and logic devices.Towards functional device applications,efficient electrical detection of skyrmio...Magnetic skyrmions are recognized as potential information carriers for building the next-generation spintronic memory and logic devices.Towards functional device applications,efficient electrical detection of skyrmions at room temperature is one of the most important prerequisites.展开更多
Capturing ultrafast dynamics over a large momentum space is critical for revealing the relationship between the electronic and structural modulations in quantum materials.Here,by performing time-and angle-resolved pho...Capturing ultrafast dynamics over a large momentum space is critical for revealing the relationship between the electronic and structural modulations in quantum materials.Here,by performing time-and angle-resolved photoemission spectroscopy measurements at the Synergetic Extreme Condition User Facility(SECUF)equipped with an extreme ultraviolet light source,we reveal the ultrafast dynamics of a charge-density wave(CDW)material,1T-TiSe_(2),upon photoexcitation.Pump-induced CDW melting is revealed from two aspects:gap closing of the CDW at the Brillouin zone(BZ)center and weakening of the CDW folded band at the BZ boundary.By comparing the transient electronic structure and spectral weight over a large momentum space,we further reveal the carrier redistribution involving the excitation of electrons from theГpoint to the M point.This study provides a comprehensive picture of the physics and ultrafast dynamics of a CDW material across the entire BZ.展开更多
Recent experimental evidence of the charge-6e condensed phase in Kagome superconductors has generated significant interest.This study investigates the unconventional superconductivity in the Kagome superconductor CsV_...Recent experimental evidence of the charge-6e condensed phase in Kagome superconductors has generated significant interest.This study investigates the unconventional superconductivity in the Kagome superconductor CsV_(3)Sb_(5),focusing on the emergence of charge-6e superconductivity(SC)at temperatures higher than the conventional charge-2e SC state.By modeling the phase coherence of the SC order parameter using a frustrated antiferromagnetic XY model on an emergent Kagome lattice,the condensation of fractional vortices with 1/3 vorticity stabilizes the phase coherence in exp(i3θ),resulting in a charge-6e SC state.Using a tensor network approach tailored for frustrated spin systems,a Berezinskii-Kosterlitz-Thouless transition is identified at T_(c)/J≃0.075,where the unbinding of 1/3 fractional vortex-antivortex pairs transforms the system from the charge-6e SC phase to the normal phase.Below T_(c),the 1/3 fractional vortex correlations exhibit a power-law decay,whereas the integer vortex correlations decay exponentially,reflecting the dominance of charge-6e SC in the absence of charge-2e SC.The results provide a theoretical understanding of charge-6e SC in two-dimensional Kagome superconductors,emphasizing the interaction between fractional vortices,frustration,and topology in stabilizing the exotic SC phase.展开更多
The electron-doped cuprate superconductor exhibits a unique electronic structure,where both electron and hole Fermi surface(FS)pockets coexist in the optimally doped(OP)region,while in the overdoped(OD)region there ex...The electron-doped cuprate superconductor exhibits a unique electronic structure,where both electron and hole Fermi surface(FS)pockets coexist in the optimally doped(OP)region,while in the overdoped(OD)region there exists only a large hole FS pocket.It is therefore an intriguing question whether or not a p-n junction arises if the OD electron-doped cuprate interfaces with the OP compound.Here,we construct such an in-plane junction by selectively modulating the doping levels in thin films of La_(2-x)Ce_(x)CuO_(4)(LCCO)—a typical electron-doped cuprate.We find that the junction exhibits non-linear,asymmetricⅠ-Ⅴcharacteristics,which are consistent with those of a p-n semiconductor junction,across a wide temperature range from 250 K to 10 K,regardless of the Hall coefficient sign change or the superconducting transition.We attribute these features to a potential barrier formed at the junction,which is set by the band bending in both OD and OP LCCO.展开更多
Quantum information processing based on Rydberg atoms emerged as a promising direction two decades ago.Recent experimental and theoretical progresses have shined exciting light on this avenue.In this concise review,we...Quantum information processing based on Rydberg atoms emerged as a promising direction two decades ago.Recent experimental and theoretical progresses have shined exciting light on this avenue.In this concise review,we will briefly introduce the basics of Rydberg atoms and their recent applications in associated areas of neutral atom quantum computation and simulation.We shall also include related discussions on quantum optics with Rydberg atomic ensembles,which are increasingly used to explore quantum computation and quantum simulation with photons.展开更多
High-T_(c)superconductivity with possible T_(c)≈80 K has been reported in the single crystal of La_(3)Ni_(2)O_(7)under high pressure.Based on the electronic structure given by the density functional theory calculatio...High-T_(c)superconductivity with possible T_(c)≈80 K has been reported in the single crystal of La_(3)Ni_(2)O_(7)under high pressure.Based on the electronic structure given by the density functional theory calculations,we propose an effective bi-layer model Hamiltonian including both 3d_(z)^(2)and 3d_((x)^(2)-(y)^(2))orbital electrons of the nickel cations.The main feature of the model is that the 3d_(z)^(2)electrons form inter-layerσ-bonding and anti-bonding bands via the apical oxygen anions between the two layers,while the 3d_((x)^(2)-(y)^(2))electrons hybridize with the 3d_(z)^(2)electrons within each NiO_(2)plane.The chemical potential difference of these two orbital electrons ensures that the 3d_(z)^(2)orbitals are close to half-filling and the 3d_((x)^(2)-(y)^(2))orbitals are near quarter-filling.The strong on-site Hubbard repulsion of the 3d_(z)^(2)orbital electrons gives rise to an effective inter-layer antiferromagnetic spin super-exchange J.Applying pressure can self dope holes on the 3d_(z)^(2)orbitals with the same amount of electrons doped on the 3d_((x)^(2)-(y)^(2))orbitals.By performing numerical density-matrix renormalization group calculations on a minimum setup and focusing on the limit of large J and small doping of 3d_(z)^(2)orbitals,we find the superconducting instability on both the 3d_(z)^(2)and3d_((x)^(2)-(y)^(2))orbitals by calculating the equal-time spin singlet pair–pair correlation function.Our numerical results may provide useful insights in the high-T_(c)superconductivity in single crystal La_(3)Ni_(2)O_(7)under high pressure.展开更多
The Mott transition is one of the fundamental issues in condensed matter physics,especially in the system with antiferromagnetic long-range order.However,such a transition is rare in quantum spin liquid(QSL)systems wi...The Mott transition is one of the fundamental issues in condensed matter physics,especially in the system with antiferromagnetic long-range order.However,such a transition is rare in quantum spin liquid(QSL)systems without long-range order.Here we report the experimental pressure-induced insulator to metal transition followed by the emergence of superconductivity in the QSL candidate NaYbSe2 with a triangular lattice of 4 f Yb^3+ions.Detail analysis of transport properties in metallic state shows an evolution from non-Fermi liquid to Fermi liquid behavior when approaching the vicinity of superconductivity.An irreversible structure phase transition occurs around 11 GPa,which is revealed by the x-ray diffraction.These results shed light on the Mott transition in the QSL systems.展开更多
The presumption that Hawking radiations are thermally distributed can be considered to result from their entanglement with the internal degrees of freedom for a black hole.This leads to the‘firewall’paradox if unita...The presumption that Hawking radiations are thermally distributed can be considered to result from their entanglement with the internal degrees of freedom for a black hole.This leads to the‘firewall’paradox if unitary evolution continues into Page’s time when a black hole evaporates away half of its initial entropy.However,if the interior of a black hole houses sufficient degrees of freedom to maintain entanglement with the outside at all times,unitarity can be preserved during the complete radiation process and no firewall will be required.This paper proposes a scenario that rescinds the firewall by introducing the concept of volume for a black hole.Based on the operational definition by Christodoulou and Rovelli(Christodoulou and Rovelli 2015 Phys.Rev.D 91064046),we show that the volume and its associated entropy for a collapsed black hole diverges if the final evaporation stage is treated using noncommutative space.This implicates the interior of a black hole possesses adequate space to store information for a black hole of any mass,like the inside of a‘magician’s bag’.展开更多
The inherent fragility and surface/interface-sensitivity of quantum devices demand fabrication techniques under very clean environment.Here,I briefly introduces several techniques based on molecular beam epitaxy growt...The inherent fragility and surface/interface-sensitivity of quantum devices demand fabrication techniques under very clean environment.Here,I briefly introduces several techniques based on molecular beam epitaxy growth on pre-patterned substrates which enable us to directly prepare in-plane nanostructures and heterostructures in ultrahigh vacuum.The molecular beam epitaxy-based fabrication techniques are especially useful in constructing the high-quality devices and circuits for solid-state quantum computing in a scalable way.展开更多
基金supported by the Beijing Academy of Quantum Information Sciencessupported by the National Natural Science Foundation of China(Grant No.92365206)+2 种基金the support of the China Postdoctoral Science Foundation(Certificate Number:2023M740272)supported by the National Natural Science Foundation of China(Grant No.12247168)China Postdoctoral Science Foundation(Certificate Number:2022TQ0036)。
文摘With the rapid advancement of quantum computing,hybrid quantum–classical machine learning has shown numerous potential applications at the current stage,with expectations of being achievable in the noisy intermediate-scale quantum(NISQ)era.Quantum reinforcement learning,as an indispensable study,has recently demonstrated its ability to solve standard benchmark environments with formally provable theoretical advantages over classical counterparts.However,despite the progress of quantum processors and the emergence of quantum computing clouds,implementing quantum reinforcement learning algorithms utilizing parameterized quantum circuits(PQCs)on NISQ devices remains infrequent.In this work,we take the first step towards executing benchmark quantum reinforcement problems on real devices equipped with at most 136 qubits on the BAQIS Quafu quantum computing cloud.The experimental results demonstrate that the policy agents can successfully accomplish objectives under modified conditions in both the training and inference phases.Moreover,we design hardware-efficient PQC architectures in the quantum model using a multi-objective evolutionary algorithm and develop a learning algorithm that is adaptable to quantum devices.We hope that the Quafu-RL can be a guiding example to show how to realize machine learning tasks by taking advantage of quantum computers on the quantum cloud platform.
基金supported by the National Natural Science Foundation of China(Grant Nos.12174214,12475022,and 92065205)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302100).
文摘Open quantum system simulations are essential for exploring novel quantum phenomena and evaluating noisy quantum circuits.In this Letter,we investigate whether mixed states generated from noisy quantum circuits can be efficiently represented by locally purified density operators(LPDOs).We map an LPDO of N qubits to a pure state of size 2×N defined on a ladder and introduce a unified method for managing virtual and Kraus bonds.We numerically simulate noisy random quantum circuits with depths of up to d=40 using fidelity and entanglement entropy as accuracy measures.The LPDO representation is effective in describing mixed states in both the quantum and classical regions;however,it encounters significant challenges at the quantum-classical critical point,restricting its applicability to the quantum region.In contrast,matrix product operators(MPO)successfully characterize the entanglement trend throughout the simulation,while the truncation in MPOs breaks the positivity condition required for a physical density matrix.This work advances our understanding of efficient mixed-state representations in open quantum systems and provides insights into the entanglement structure of noisy quantum circuits.
基金supported by the National Key Research and Development Program of China under Grant No.2017YFA0303704National Natural Science Foundation of China under Grants No.61575102,No.61671438,No.61875101,and No.61621064+1 种基金Beijing Natural Science Foundation under Grant No.Z180012Beijing Academy of Quantum Information Sciences under Grant No.Y18G26
文摘For a compact quantum key distribution (QKD) sender for the polarization encoding BB84 protocol, an eavesdropper could take a side-channel attack by measuring the spatial information of photons to infer their polarizations. The possibility of this attack can be reduced by introducing an aperture in the QKD sender, however, the effect of the aperture on the QKD security lacks of quantitative analysis. In this paper, we analyze the mutual information between the actual keys encoded at this QKD sender and the inferred keys at the eavesdropper (Eve), demonstrating the effect of the aperture to eliminate the spatial side-channel information quantitatively. It shows that Eve’s potential on eavesdropping spatial side-channel information is totally dependent on the optical design of the QKD sender, including the source arrangement and the aperture. The height of compact QKD senders with integrated light-emitting diode (LED) arrays could be controlled under several millimeters, showing great potential on applications in portable equipment.
基金the National Key R&D Program of China under Grants No.2017YFA0303704 and No.2018YFB2200400Natural Science Foundation of Beijing under Grant No.Z180012National Natural Science Foundation of China under Grants No.61875101 and No.91750206.
文摘Dispersive optics quantum key distribution(DO-QKD)based on energy-time entangled photon pairs is an important QKD scheme.In DO-QKD,the arrival time of photons is used in key generation and security analysis,which would be greatly affected by fiber dispersion.In this work,we establish a theoretical model of the entanglement-based DO-QKD system,considering the protocol,physical processes(such as fiber transmission and single-photon detection),and the analysis of security tests.Based on this theoretical model,we investigate the influence of chromatic dispersion introduced by transmission fibers on the performance of DO-QKD.By analyzing the benefits and costs of dispersion compensation,the system performance under G.652 and G.655 optical fibers are shown,respectively.The results show that dispersion compensation is unnecessary for DO-QKD systems in campus networks and even metro networks.Whereas,it is still required in DO-QKD systems with longer fiber transmission distances.
基金supported by the National Natural Science Foundation of China(Grant Nos.92065106,61974138,12104053,and 11704364)the Beijing Natural Science Foundation(Grant No.1192017)+2 种基金Tsinghua University Initiative Scientifc Research Programthe support from Youth Innovation Promotion Association,Chinese Academy of Sciences(Grant No.Y2021043)China Postdoctoral Science Foundation(Grant Nos.2020M670173 and 2020T130058)。
文摘We demonstrate the in situ growth of ultra-thin InA s nanowires with an epitaxial Al film by molecular-beam epitaxy.Our InAs nanowire diameter(~30 nm)is much thinner than before(~100 nm).The ultra-thin InAs nanowires are pure phase crystals for various different growth directions.Transmission electron microscopy confirms an atomically abrupt and uniform interface between the Al shell and the InAs wire.Quantum transport study on these devices resolves a hard induced superconducting gap and 2 e-periodic Coulomb blockade at zero magnetic field,a necessary step for future Majorana experiments.By reducing wire diameter,our work presents a promising route for reaching fewer sub-band regime in Major ana nanowire devices.
基金supported in part by the National Natural Science Foundation of China under Grants 61975091,61905015,61575108,and 61505034by the Tsinghua Precision Medicine Foundation and“Bio-Brain+X”Advanced Imaging Instrument Development Seed Grant.
文摘In this paper,we present a distal-scanning common path probe for optical coherence tomography(OCT)equipped with a hollow ultrasonic motor and a simple and specially designed beam-splitter.This novel probe proves to be able to effectively circumvent polarization and dispersion mismatch caused by fiber motion and is more robust to a variety of interfering factors during the imaging process,experimentally compared to a conventional noncommon path probe.Furthermore,our design counteracts the attenuation of backscattering with depth and the fall-off of the signal,resulting in a more balanced signal range and greater imaging depth.Spectral-domain OCT imaging of phantom and biological tissue is also demonstrated with a sensitivity of∼100dB and a lateral resolution of∼3μm.This low-cost probe offers simplified system configuration and excellent robustness,and is therefore particularly suitable for clinical diagnosis as one-off medical apparatus.
基金supported by the National Natural Science Foundation of China(Grant No.92365206)the support of the China Postdoctoral Science Foundation(Certificate Number:2023M740272)+1 种基金supported by the National Natural Science Foundation of China(Grant No.12247168)China Postdoctoral Science Foundation(Certificate Number:2022TQ0036)。
文摘We introduce Quafu-Qcover,an open-source cloud-based software package developed for solving combinatorial optimization problems using quantum simulators and hardware backends.Quafu-Qcover provides a standardized and comprehensive workflow that utilizes the quantum approximate optimization algorithm(QAOA).It facilitates the automatic conversion of the original problem into a quadratic unconstrained binary optimization(QUBO)model and its corresponding Ising model,which can be subsequently transformed into a weight graph.The core of Qcover relies on a graph decomposition-based classical algorithm,which efficiently derives the optimal parameters for the shallow QAOA circuit.Quafu-Qcover incorporates a dedicated compiler capable of translating QAOA circuits into physical quantum circuits that can be executed on Quafu cloud quantum computers.Compared to a general-purpose compiler,our compiler demonstrates the ability to generate shorter circuit depths,while also exhibiting superior speed performance.Additionally,the Qcover compiler has the capability to dynamically create a library of qubits coupling substructures in real-time,utilizing the most recent calibration data from the superconducting quantum devices.This ensures that computational tasks can be assigned to connected physical qubits with the highest fidelity.The Quafu-Qcover allows us to retrieve quantum computing sampling results using a task ID at any time,enabling asynchronous processing.Moreover,it incorporates modules for results preprocessing and visualization,facilitating an intuitive display of solutions for combinatorial optimization problems.We hope that Quafu-Qcover can serve as an instructive illustration for how to explore application problems on the Quafu cloud quantum computers.
基金supported by the National Key Research and Development Program of China (Grant No. 2018YFA0307100)the Basic Science Center Project of the National Natural Science Foundation of China (Grant No. 52388201)+4 种基金the National Natural Science Foundation of China (Grant Nos. 12274453 and 92065206)the Innovation Program for Quantum Science and Technology (Grant No. 2021ZD0302502)supported by Open Research Fund Program of the State Key Laboratory of Low-Dimensional Quantum Physics (Grant No. KF202204)supported by the New Cornerstone Science Foundation through the New Cornerstone Investigator Programthe XPLORER PRIZE。
文摘We have developed a low-damage photolithography method for magnetically doped(Bi,Sb)_(2)Te_(3)quantum anomalous Hall(QAH) thin films incorporating an additional resist layer of poly(methyl methacrylate)(PMMA). By performing control experiments on the transport properties of five devices at varied gate voltages(V_(g)s), we revealed that the modified photolithography method enables fabricating QAH devices with the transport and magnetic properties unaffected by fabrication process. Our experiment represents a step towards the production of novel micro-structured electronic devices based on the dissipationless QAH chiral edge states.
基金supported by the National Natural Science Foundation of China(22150710516,U1832218).
文摘Rechargeable magnesium metal batteries need an electrolyte that forms a stable and ionically conductive solid electrolyte interphase(SEI)on the anodes.Here,we used molecular dynamic simulation,density functional theory calculation,and X-ray photoelectron spectroscopy analysis to investigate the solvation structures and SEI compositions in electrolytes consisting of dual-salts,magnesium bis(trifluoromethanesulfonyl)imide(MgTFSI_(2)),and MgCl_(2),with different additives in 1,2-dimethoxyethane(DME)solvent.We found that the formed[Mg_(3)(μ-Cl)_(4)(DME)mTFSI_(2)](m=3,5)inner-shell solvation clusters in MgTFSI_(2)-MgCl_(2)/DME electrolyte could easily decompose and form a MgO-and MgF_(2)-rich SEI.Such electron-rich inorganic species in the SEI,especially MgF_(2),turned out to be detrimental for Mg plating/stripping.To reduce the MgF_(2)and MgO contents in SEI,we introduce an electron-deficient tri(2,2,2-trifluoroethyl)borate(TFEB)additive in the electrolyte.Mg//Mg cells using the MgTFSI_(2)-MgCl_(2)/DME-TFEB electrolyte could cycle stably for over 400 h with a small polarization voltage of~150 mV.Even with the presence of 800 ppm H_(2)O,the electrolyte with TFEB additive could still preserve its good electrochemical performance.The optimized electrolyte also enabled stable cycling and high-rate capability for Mg//Mo6S8 and Mg//CuS full cells,showing great potential for future applications.
基金supported by the National Natural Science Foundation of China(Grant No.12434011 obtained by Q X)the China Postdoctoral Science Foundation(Grant No.Y24PJ2425214 obtained by L T).
文摘Supersolidity is a counterintuitive quantum phase of matter where the long-range spatial order of a solid coexists with the frictionless flow characteristic of a superfluid.Recently,evidence of supersolidity has been demonstrated in polariton condensates in III-V photonic crystal microcavities by condensing into a topological bound state in the continuum,offering a new light-matter hybrid platform for exploring such quantum phase.In this work,we propose a theoretical scheme for realizing room-temperature supersolidity based on halide perovskite exciton polaritons operating in the optical parametric oscillation regime.By employing a waveguide microcavity geometry,we confine polariton scattering direction in reciprocal space,enabling controlled momentum selection.Leveraging the intrinsic nonlinear interactions among polaritons,we theoretically demonstrate the spontaneous breaking of both continuous translational symmetry and global phase symmetry,i.e.,the evidence of supersolidity.Furthermore,we identify a tunable phase transition sequence in our system:from a Bose-Einstein condensate to a supersolid phase,and ultimately to an insulating phase,as the nonlinear interaction strength increases.
基金supported by the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302100)the National Natural Science Foundation of China(Grant Nos.12361131576,92265205,and 92476205).
文摘Quantum optimal control(QOC)relies on accurately modeling system dynamics and is often challenged by unknown or inaccessible interactions in real systems.Taking an unknown collective spin system as an example,this work introduces a machine-learning-based,data-driven scheme to overcome the challenges encountered,with a trained neural network(NN)assuming the role of a surrogate model that captures the system’s dynamics and subsequently enables QOC to be performed on the NN instead of on the real system.The trained NN surrogate proves effective for practical QOC tasks and is further demonstrated to be adaptable to different experimental conditions,remaining robust across varying system sizes and pulse durations.
基金supported by the National Key R&D Program of China(Grant No.2022YFA1405100)the NSFC distinguished Young Scholar program(Grant No.12225409)+6 种基金the Basic Science Center Project of National Natural Science Foundation of China(NSFC)(Grant No.52388201)the NSFC general program(Grant Nos.52271181,51831005,and 12421004)the Innovation Program for Quantum Science and Technology(Grant No.2023ZD0300500)Beijing Natural Science Foundation(Grant No.Z240006)supported by the KAUST Office of Sponsored Research(OSR)under Award Nos.ORA-CRG102021-4665 and ORA-CRG11-2022-5031supported by the National Key Research and Development Program of China(No.2024YFA1408503)Sichuan Province Science and Technology Support Program(No.2025YFHZ0147)。
文摘Magnetic skyrmions are recognized as potential information carriers for building the next-generation spintronic memory and logic devices.Towards functional device applications,efficient electrical detection of skyrmions at room temperature is one of the most important prerequisites.
基金supported by the Synergetic Extreme-Condition User Facility(SECUF)the National Key R&D Program of China(Grant Nos.2021YFA1400100,2020YFA0308800,and 2022YFA1604200)+2 种基金the National Natural Science Foundation of China(Grant Nos.12234011,92250305,52388201,11725418,and 11427903)supported by the China Postdoctoral Science Foundation(Grant Nos.2022M721886 and BX20230187)the Shuimu Tsinghua Scholar Program。
文摘Capturing ultrafast dynamics over a large momentum space is critical for revealing the relationship between the electronic and structural modulations in quantum materials.Here,by performing time-and angle-resolved photoemission spectroscopy measurements at the Synergetic Extreme Condition User Facility(SECUF)equipped with an extreme ultraviolet light source,we reveal the ultrafast dynamics of a charge-density wave(CDW)material,1T-TiSe_(2),upon photoexcitation.Pump-induced CDW melting is revealed from two aspects:gap closing of the CDW at the Brillouin zone(BZ)center and weakening of the CDW folded band at the BZ boundary.By comparing the transient electronic structure and spectral weight over a large momentum space,we further reveal the carrier redistribution involving the excitation of electrons from theГpoint to the M point.This study provides a comprehensive picture of the physics and ultrafast dynamics of a CDW material across the entire BZ.
基金supported by the National Key Research and Development Program of China(Grant No.2023YFA1406400)。
文摘Recent experimental evidence of the charge-6e condensed phase in Kagome superconductors has generated significant interest.This study investigates the unconventional superconductivity in the Kagome superconductor CsV_(3)Sb_(5),focusing on the emergence of charge-6e superconductivity(SC)at temperatures higher than the conventional charge-2e SC state.By modeling the phase coherence of the SC order parameter using a frustrated antiferromagnetic XY model on an emergent Kagome lattice,the condensation of fractional vortices with 1/3 vorticity stabilizes the phase coherence in exp(i3θ),resulting in a charge-6e SC state.Using a tensor network approach tailored for frustrated spin systems,a Berezinskii-Kosterlitz-Thouless transition is identified at T_(c)/J≃0.075,where the unbinding of 1/3 fractional vortex-antivortex pairs transforms the system from the charge-6e SC phase to the normal phase.Below T_(c),the 1/3 fractional vortex correlations exhibit a power-law decay,whereas the integer vortex correlations decay exponentially,reflecting the dominance of charge-6e SC in the absence of charge-2e SC.The results provide a theoretical understanding of charge-6e SC in two-dimensional Kagome superconductors,emphasizing the interaction between fractional vortices,frustration,and topology in stabilizing the exotic SC phase.
基金Project supported by the National Key Research and Development Program of China(Grant No.2022YFA1403100)the National Natural Science Foundation of China(Grant Nos.52388201,12361141820,and 12274249)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302400)。
文摘The electron-doped cuprate superconductor exhibits a unique electronic structure,where both electron and hole Fermi surface(FS)pockets coexist in the optimally doped(OP)region,while in the overdoped(OD)region there exists only a large hole FS pocket.It is therefore an intriguing question whether or not a p-n junction arises if the OD electron-doped cuprate interfaces with the OP compound.Here,we construct such an in-plane junction by selectively modulating the doping levels in thin films of La_(2-x)Ce_(x)CuO_(4)(LCCO)—a typical electron-doped cuprate.We find that the junction exhibits non-linear,asymmetricⅠ-Ⅴcharacteristics,which are consistent with those of a p-n semiconductor junction,across a wide temperature range from 250 K to 10 K,regardless of the Hall coefficient sign change or the superconducting transition.We attribute these features to a potential barrier formed at the junction,which is set by the band bending in both OD and OP LCCO.
基金Project supported by the National Key R&D Program of China(Grant Nos.2018YFA0306504 and 2018YFA0306503)the Key-Area Research and Development Program of Guang Dong Province,China(Grant No.2019B030330001)+1 种基金the National Natural Science Foundation of China(Grant Nos.91636213,11654001,91736311,91836302,and U1930201)support from Beijing Academy of Quantum Information Sciences(BAQIS)Research Program(Grant No.Y18G24)。
文摘Quantum information processing based on Rydberg atoms emerged as a promising direction two decades ago.Recent experimental and theoretical progresses have shined exciting light on this avenue.In this concise review,we will briefly introduce the basics of Rydberg atoms and their recent applications in associated areas of neutral atom quantum computation and simulation.We shall also include related discussions on quantum optics with Rydberg atomic ensembles,which are increasingly used to explore quantum computation and quantum simulation with photons.
基金the support from the National Key Research and Development Program of China(Grant No.2017YFA0302902)the support from the National Key Research and Development Program of China(Grant No.2022YFA1405400)+2 种基金the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0301902)the National Natural Science Foundation of China(Grant No.12274290)the Sponsorship from Yangyang Development Fund。
文摘High-T_(c)superconductivity with possible T_(c)≈80 K has been reported in the single crystal of La_(3)Ni_(2)O_(7)under high pressure.Based on the electronic structure given by the density functional theory calculations,we propose an effective bi-layer model Hamiltonian including both 3d_(z)^(2)and 3d_((x)^(2)-(y)^(2))orbital electrons of the nickel cations.The main feature of the model is that the 3d_(z)^(2)electrons form inter-layerσ-bonding and anti-bonding bands via the apical oxygen anions between the two layers,while the 3d_((x)^(2)-(y)^(2))electrons hybridize with the 3d_(z)^(2)electrons within each NiO_(2)plane.The chemical potential difference of these two orbital electrons ensures that the 3d_(z)^(2)orbitals are close to half-filling and the 3d_((x)^(2)-(y)^(2))orbitals are near quarter-filling.The strong on-site Hubbard repulsion of the 3d_(z)^(2)orbital electrons gives rise to an effective inter-layer antiferromagnetic spin super-exchange J.Applying pressure can self dope holes on the 3d_(z)^(2)orbitals with the same amount of electrons doped on the 3d_((x)^(2)-(y)^(2))orbitals.By performing numerical density-matrix renormalization group calculations on a minimum setup and focusing on the limit of large J and small doping of 3d_(z)^(2)orbitals,we find the superconducting instability on both the 3d_(z)^(2)and3d_((x)^(2)-(y)^(2))orbitals by calculating the equal-time spin singlet pair–pair correlation function.Our numerical results may provide useful insights in the high-T_(c)superconductivity in single crystal La_(3)Ni_(2)O_(7)under high pressure.
基金supported by the National Key R&D Program of China(Grant Nos.2016YFA0300504,2018YFE0202600 and2018YFA0305701)the National Natural Science Foundation of China(Grant Nos.11774423,11822412 and 11921004)+1 种基金the Fundamental Research Funds for the Central Universitiesthe Research Funds of Renmin University of China(Grant Nos.18XNLG14and 19XNLG17)。
文摘The Mott transition is one of the fundamental issues in condensed matter physics,especially in the system with antiferromagnetic long-range order.However,such a transition is rare in quantum spin liquid(QSL)systems without long-range order.Here we report the experimental pressure-induced insulator to metal transition followed by the emergence of superconductivity in the QSL candidate NaYbSe2 with a triangular lattice of 4 f Yb^3+ions.Detail analysis of transport properties in metallic state shows an evolution from non-Fermi liquid to Fermi liquid behavior when approaching the vicinity of superconductivity.An irreversible structure phase transition occurs around 11 GPa,which is revealed by the x-ray diffraction.These results shed light on the Mott transition in the QSL systems.
基金supported by the NSFC(grant No.11654001,No.11747605 and No.91636213).
文摘The presumption that Hawking radiations are thermally distributed can be considered to result from their entanglement with the internal degrees of freedom for a black hole.This leads to the‘firewall’paradox if unitary evolution continues into Page’s time when a black hole evaporates away half of its initial entropy.However,if the interior of a black hole houses sufficient degrees of freedom to maintain entanglement with the outside at all times,unitarity can be preserved during the complete radiation process and no firewall will be required.This paper proposes a scenario that rescinds the firewall by introducing the concept of volume for a black hole.Based on the operational definition by Christodoulou and Rovelli(Christodoulou and Rovelli 2015 Phys.Rev.D 91064046),we show that the volume and its associated entropy for a collapsed black hole diverges if the final evaporation stage is treated using noncommutative space.This implicates the interior of a black hole possesses adequate space to store information for a black hole of any mass,like the inside of a‘magician’s bag’.
基金Project supported by the National Natural Science Foundation of China(Grant No.92065206)
文摘The inherent fragility and surface/interface-sensitivity of quantum devices demand fabrication techniques under very clean environment.Here,I briefly introduces several techniques based on molecular beam epitaxy growth on pre-patterned substrates which enable us to directly prepare in-plane nanostructures and heterostructures in ultrahigh vacuum.The molecular beam epitaxy-based fabrication techniques are especially useful in constructing the high-quality devices and circuits for solid-state quantum computing in a scalable way.
