As superconducting quantum computing continues to advance at an unprecedented pace,there is a compelling demand for the innovation of specialized electronic instruments that act as crucial conduits between quantum pro...As superconducting quantum computing continues to advance at an unprecedented pace,there is a compelling demand for the innovation of specialized electronic instruments that act as crucial conduits between quantum processors and host computers.Here,we introduce a microwave measurement and control system(M^(2)CS)dedicated to large-scale superconducting quantum processors.M^(2)CS features a compact modular design that balances overall performance,scalability and flexibility.Electronic tests of M^(2)CS show key metrics comparable to commercial instruments.Benchmark tests on transmon superconducting qubits further show qubit coherence and gate fidelities comparable to state-of-the-art results,confirming M^(2)CS's capability to meet the stringent requirements of quantum experiments running on intermediate-scale quantum processors.The compact and scalable nature of our design holds the potential to support over 1000 qubits after upgrade in stability and integration.The M^(2)CS architecture may also be adopted to a wider range of scenarios,including other quantum computing platforms such as trapped ions and silicon quantum dots,as well as more traditional applications like microwave kinetic inductance detectors and phased array radar systems.展开更多
Superconducting circuit quantum electrodynamics(QED)architecture composed of superconducting qubit and resonator is a powerful platform for exploring quantum physics and quantum information processing.By employing tec...Superconducting circuit quantum electrodynamics(QED)architecture composed of superconducting qubit and resonator is a powerful platform for exploring quantum physics and quantum information processing.By employing techniques developed for superconducting quantum computing,we experimentally investigate phase-sensitive Landau-Zener-Stückelberg(LZS)interference phenomena in a circuit QED.Our experiments cover an extensive range of LZS transition parameters and demonstrate the LZS induced Rabi-like oscillation as well as phase-dependent steady-state population.展开更多
Chiral anomaly is a distinct quantum anomaly associated with chiral fermions in Dirac or Weyl semimetals.The use of negative magnetoresistance(negative MR)as a signature for this anomaly remains contentious,as trivial...Chiral anomaly is a distinct quantum anomaly associated with chiral fermions in Dirac or Weyl semimetals.The use of negative magnetoresistance(negative MR)as a signature for this anomaly remains contentious,as trivial mechanisms such as current jetting and weak localization can also induce negative MR.In this study,we report a novel nonlinear behavior of the chiral anomaly in the longitudinal direction,which we observed by applying parallel current and magnetic field to the Dirac semimetal Cd_(3)A_(s_(2)).This nonlinear characteristic peaks at an intermediate magnetic field of approximately5 T,displaying a resistance-increasing property concomitant with strengthening of the current source.Through angledependence experiments,we were able to rule out trivial factors,such as thermal effects,geometric artifacts,and anisotropy.Furthermore,additional electric quantum oscillations were observed when the direct current(DC)was applied as high as300μA.Such an unusual phenomenon is ascribed to the formation of quantized levels due to Bloch oscillation in the high DC regime,suggesting that an oscillatory density distribution may arise as the electric field increases.The non-Ohmic electric quantum oscillations open a new avenue for exploring chiral anomaly and other nontrivial topological properties,which is also one of the salient features of nonequilibrium steady states in condensed matter physics.展开更多
We report a metrology scheme which measures the magnetic susceptibility of an atomic spin ensemble along the x and z directions and produces parameter estimation with precision beating the standard quantum limit.The a...We report a metrology scheme which measures the magnetic susceptibility of an atomic spin ensemble along the x and z directions and produces parameter estimation with precision beating the standard quantum limit.The atomic ensemble is initialized via one-axis spin squeezing with optimized squeezing time and parameterΦ(to be estimated)assumed as uniformly distributed between 0 and 2πwhile fixed in each estimation.One estimation ofΦcan be produced with every two magnetic susceptibility data measured along the two axes respectively,which has an imprecision scaling(1.43±0.02)/N^(0.687±0.003)with respect to the number N of the atomic spins.The measurement scheme is easy to implement and is robust against the measurement fluctuation caused by environment noise and measurement defects.展开更多
Spin–momentum locking is a key feature of the topological surface state, which plays an important role in spintronics.The electrical detection of current-induced spin polarization protected by the spin–momentum lock...Spin–momentum locking is a key feature of the topological surface state, which plays an important role in spintronics.The electrical detection of current-induced spin polarization protected by the spin–momentum locking in nonmagnetic systems provides a new platform for developing spintronics, while previous studies were mostly based on magnetic materials.In this study, the spin transport measurement of Dirac semimetal Cd_(3)As_(2) was studied by three-terminal geometry, and a hysteresis loop signal with high resistance and low resistance state was observed. The hysteresis was reversed by reversing the current direction, which illustrates the spin–momentum locking feature of Cd_(3)As_(2). Furthermore, we realized the on–off states of the spin signals through electric modulation of the Fermi arc via the three-terminal configuration, which enables the great potential of Cd_(3)As_(2) in spin field-effect transistors.展开更多
Quantum enhanced metrology has the potential to go beyond the standard quantum limit and eventually to the ultimate Heisenberg bound.In particular,quantum probes prepared in nonclassical coherent states have recently ...Quantum enhanced metrology has the potential to go beyond the standard quantum limit and eventually to the ultimate Heisenberg bound.In particular,quantum probes prepared in nonclassical coherent states have recently been recognized as a useful resource for metrology.Hence,there has been considerable interest in constructing magnetic quantum sensors that combine high resolution and high sensitivity.Here,we explore a nanoscale magnetometer with quantum-enhanced sensitivity,based on 123Sb(I=7/2)nuclear spin doped in silicon,that takes advantage of techniques of spin-squeezing and coherent control.With the optimal squeezed initial state,the magnetic field sensitivity may be expected to approach 6 aT·Hz^(−1/2)·cm^(−3/2) and 603 nT·Hz^(−1/2) at the single-spin level.This magnetic sensor may provide a novel sensitive and high-resolution route to microscopic mapping of magnetic fields as well as other applications.展开更多
Quantum teleportation is of both fundamental interest and great practical importance in quantum information science.To date,quantum teleportation has been implemented in various physical systems,among which supercondu...Quantum teleportation is of both fundamental interest and great practical importance in quantum information science.To date,quantum teleportation has been implemented in various physical systems,among which superconducting qubits are of particular practical significance as they emerge as a leading system to realize large-scale quantum computation.Nevertheless,scaling up the number of superconducting qubits on a single chip becomes increasing challenging because of some emergent technical difficulties.Realization of quantum teleportation and remote computation over qubits on distant superconducting chips is a key quantum communication technology to scaling up the system through a distributed quantum computational network.However,this goal has not been realized yet in experiments due to the technical challenges including making a quantum interconnect between distant superconducting chips and the inefficient transfer of flying microwave photons over the lossy interconnects.Here we demonstrate deterministic teleportation of quantum states and entangling gates between distant superconducting chips connected by a 64-m-long cable bus featuring an ultralow loss of 0.32 dB/km at cryogenic temperatures,where high fidelity remote entanglement is generated via flying microwave photons.Our work demonstrates a prime building block for distributed quantum computation with superconducting qubits,and opens up a new avenue for waveguide quantum electrodynamics and quantum photonics at microwave frequencies.展开更多
The nature of the Cooper pairing in the paradigmatic unconventional superconductor Sr_(2)RuO_(4) is an outstanding puzzle in condensed matter physics.Despite the tremendous efforts made in the past twenty-seven years,...The nature of the Cooper pairing in the paradigmatic unconventional superconductor Sr_(2)RuO_(4) is an outstanding puzzle in condensed matter physics.Despite the tremendous efforts made in the past twenty-seven years,neither the pairing symmetry nor the underlying pairing mechanism in this material has been understood with clear consensus.This is largely due to the lack of a superconducting order that is capable of interpreting in a coherent manner the numerous essential experimental observations.At this stage,it may be desirable to reexamine our existing theoretical descriptions of superconducting Sr_(2)RuO_(4).This review focuses on several recent developments that may provide some clues for future study.We highlight three separate aspects:1)any pairing in the Eu symmetry channel,with which the widely discussed chiral p-wave is associated,shall acquire a 3D structure due to spin-orbit entanglement;2)if the reported Kerr effect is a superconductivity-induced intrinsic bulk response,the superconductivity must either exhibit a chiral character,or be complex mixtures of certain set of helical p-wave pairings;3)when expressed in a multiorbital basis,the Cooper pairing could acquire numerous exotic forms that are inaccessible in single-orbital descriptions.The implications of each of these new perspectives are briefly discussed in connection with selected experimental phenomena.展开更多
Thanks to the quantum simulation,more and more problems in quantum mechanics which were previously inaccessible are now open to us.Capitalizing on the state-of-the-art techniques on quantum coherent control developed ...Thanks to the quantum simulation,more and more problems in quantum mechanics which were previously inaccessible are now open to us.Capitalizing on the state-of-the-art techniques on quantum coherent control developed in past few decades,e.g.,the high-precision quantum gate manipulating,the time-reversal harnessing,the high-fidelity state preparation and tomography,the nuclear magnetic resonance(NMR) system offers a unique platform for quantum simulation of many-body physics and high-energy physics.Here,we review the recent experimental progress and discuss the prospects for quantum simulation realized on NMR systems.展开更多
Quantum entanglement, a key resource in quantum information processing, is reduced by interaction between the quantum system concerned and its unavoidable noisy environment. Therefore it is of particular importance to...Quantum entanglement, a key resource in quantum information processing, is reduced by interaction between the quantum system concerned and its unavoidable noisy environment. Therefore it is of particular importance to study the dynamical properties of entanglement in open quantum systems. In this work, we mainly focus on two qubits coupled to an adjustable environment, namely a semi-infinite transmission line. The two qubits' relaxations, through individual channels or collective channel or both, can be adjusted by the qubits' transition frequencies. We examine entanglement dynamics in this model system with initial Werner state, and show that the phenomena of entanglement sudden death and revival can be observed. Due to the hardness of preparing the Werner state experimentally, we introduce a new type of entangled state called pseudo-Werner state, which preserves as much entangling property as the Werner state, and more importantly,it is experiment friendly. Furthermore, we provide detailed procedures for generating pseudo-Werner state and studying entanglement dynamics with it, which can be straightforwardly implemented in a superconducting waveguide quantum electrodynamics system.展开更多
While the common practice of decomposing general quantum algorithms into a collection of single-and two-qubit gates is conceptually simple,in many cases it is possible to have more efficient solutions where quantum ga...While the common practice of decomposing general quantum algorithms into a collection of single-and two-qubit gates is conceptually simple,in many cases it is possible to have more efficient solutions where quantum gates engaging multiple qubits are used.In the noisy intermediate-scale quantum(NISQ)era where a universal error correction is still unavailable,this strategy is particularly appealing since it can significantly reduce the computational resources required for executing quantum algorithms.In this work,we experimentally investigate a three-qubit ControlledCPHASE-SWAP(CCZS)gate on superconducting quantum circuits.By exploiting the higher energy levels of superconducting qubits,we are able to realize a Fredkin-like CCZS gate with a duration of 40 ns,which is comparable to typical single-and two-qubit gates realized on the same platform.By performing quantum process tomography for the two target qubits,we obtain a process fidelity of86.0%and 81.1%for the control qubit being prepared in|0>and|1>,respectively.We also show that our scheme can be readily extended to realize a general CCZS gate with an arbitrary swap angle.The results reported here provide valuable additions to the toolbox for achieving large-scale hardware-efficient quantum circuits.展开更多
The chiral 2×2 charge order has been reported and confirmed in the kagome superconductor RbV_(3)Sb_(5),while its interplay with superconductivity remains elusive owing to its lowest superconducting transition tem...The chiral 2×2 charge order has been reported and confirmed in the kagome superconductor RbV_(3)Sb_(5),while its interplay with superconductivity remains elusive owing to its lowest superconducting transition temperature Tc of about 0.85K in the AV_(3)Sb_(5) family(A=K,Rb,Cs)that severely challenges electronic spectroscopic probes.Here,utilizing dilution-refrigerator-based scanning tunneling microscopy down to 30 mK,we observe chiral 2×2 pair density waves with residual Fermi arcs in RbV_(3)Sb_(5).We find a superconducting gap of 150 μeV with substantial residual in-gap states.The spatial distribution of this gap exhibits chiral 2×2 modulations,signaling a chiral pair density wave(PDW).Our quasi-particle interference imaging of the zero-energy residual states further reveals arc-like patterns.We discuss the relation of the gap modulations with the residual Fermi arcs under the space-momentum correspondence between PDW and Bogoliubov Fermi states.展开更多
Higher-order topological phases give rise to new bulk and boundary physics,as well as new classes of topological phase transitions.While the realization of higher-order topological phases has been confirmed in many pl...Higher-order topological phases give rise to new bulk and boundary physics,as well as new classes of topological phase transitions.While the realization of higher-order topological phases has been confirmed in many platforms by detecting the existence of gapless boundary modes,a direct determination of the higher-order topology and related topological phase transitions through the bulk in experiments has still been lacking.To bridge the gap,in this work we carry out the simulation of a twodimensional second-order topological phase in a superconducting qubit.Owing to the great flexibility and controllability of the quantum simulator,we observe the realization of higher-order topology directly through the measurement of the pseudo-spin texture in momentum space of the bulk for the first time,in sharp contrast to previous experiments based on the detection of gapless boundary modes in real space.Also through the measurement of the evolution of pseudo-spin texture with parameters,we further observe novel topological phase transitions from the second-order topological phase to the trivial phase,as well as to the first-order topological phase with nonzero Chern number.Our work sheds new light on the study of higher-order topological phases and topological phase transitions.展开更多
Among existing approaches to holonomic quantum computing,the adiabatic holonomic quantum gates(HQGs)suffer errors due to decoherence,while the non-adiabatic HQGs either require additional Hilbert spaces or are difficu...Among existing approaches to holonomic quantum computing,the adiabatic holonomic quantum gates(HQGs)suffer errors due to decoherence,while the non-adiabatic HQGs either require additional Hilbert spaces or are difficult to scale.Here,we report a systematic,scalable approach based on dynamical invariants to realize HQGs without using additional Hilbert spaces.While presenting the theoretical framework of our approach,we design and experimentally evaluate single-qubit and two-qubits HQGs for the nuclear magnetic resonance system.The single-qubit gates acquire average fidelity 0.9972 by randomized benchmarking,and the controlled-NOT gate acquires fidelity 0.9782 by quantum process tomography.Our approach is also platform-independent,and thus may open a way to large-scale holonomic quantum computation.展开更多
Entanglement in quantum systems plays a crucial role in various quantum information tasks. Measuring entanglement has been an important issue in both experiments and theories. In this work, we use parameterized quantu...Entanglement in quantum systems plays a crucial role in various quantum information tasks. Measuring entanglement has been an important issue in both experiments and theories. In this work, we use parameterized quantum circuits(PQCs) to diagonalize density matrices of quantum states and obtain entanglement by only measuring the diagonal elements. With this method, full quantum state tomography can be bypassed, greatly reducing the number of measurements. A comprehensive characterization of entanglement was performed by using Rényi entropy and partially transposed moments. Mutual information, calculated from entropy is also used to characterize dynamical quantum phase transitions. We experimentally demonstrated the method on a four-qubit nuclear magnetic resonance quantum simulator. Our results agree with the theoretical descriptions. The measurement complexity of our PQC-based method grows linearly with the number of diagonal elements in the density matrix, a square root reduction over the full quantum tomography. The proposed method can have great potential in quantum systems with a large number of particles.展开更多
Bloch electrons in multiorbital systems carry quantum geometric information characteristic of their wavevector-dependent interorbital mixing.The geometric nature impacts electromagnetic responses,and this effect carri...Bloch electrons in multiorbital systems carry quantum geometric information characteristic of their wavevector-dependent interorbital mixing.The geometric nature impacts electromagnetic responses,and this effect carries over to the superconducting state,which receives a geometric contribution to the superfluid weight.In this paper,we show that this contribution could become negative under certain appropriate circumstances.This may facilitate the stabilization of Cooper pairings with real space phase modulation,i.e.,the pair density wave order,as we demonstrate through two-orbital model Bogoliubov de-Gennes mean-field calculations.The quantum geometric effect therefore constitutes an intrinsic mechanism for the formation of such a novel phase of matter in the absence of external magnetic field.展开更多
Majorana fermions have been predicted to exist at the edge states of a two-dimensional topological superconductor.We fabricated single quintuple layer(QL)Bi2Te3/FeTe heterostructure with the step-flow epitaxy method a...Majorana fermions have been predicted to exist at the edge states of a two-dimensional topological superconductor.We fabricated single quintuple layer(QL)Bi2Te3/FeTe heterostructure with the step-flow epitaxy method and studied the topological properties of this system by using angle-resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy.We observed the coexistence of robust superconductivity and edge states on the single QL Bi2Te3 islands which can be potential evidence for topological superconductor.展开更多
Topological insulators and semimetals have exotic surface and bulk states with massless Dirac or Weyl fermions,demonstrating microscopic transport phenomenon based on relativistic theory.Chiral anomaly induced negativ...Topological insulators and semimetals have exotic surface and bulk states with massless Dirac or Weyl fermions,demonstrating microscopic transport phenomenon based on relativistic theory.Chiral anomaly induced negative magnetoresistance(negative MR)under parallel magnetic field and current has been used as a probable evidence ofWeyl fermions in recent years.Here we report a novel negative MR result with mutually perpendicular in-plane magnetic field and current in Cd_(3)As_(2)nanowires.The negative MR has a considerable value of-16%around 1.5 K and could persist to room temperature of 300 K with value of-1%.The gate tuning and angle dependence of the negative MR demonstrate the mechanism of the observed negative MR is different from the chiral anomaly.Percolating current paths induced by charge puddles and disorder might be involved to produce such considerable negative MR.Our results indicate the negative MR effect in topological semimetals involves synergistic effects of many mechanisms besides chiral anomaly.展开更多
In classical machine learning,a set of weak classifiers can be adaptively combined for improving the overall performance,a technique called adaptive boosting(or AdaBoost).However,constructing a combined classifier for...In classical machine learning,a set of weak classifiers can be adaptively combined for improving the overall performance,a technique called adaptive boosting(or AdaBoost).However,constructing a combined classifier for a large data set is typically resource consuming.Here we propose a quantum extension of AdaBoost,demonstrating a quantum algorithm that can output the optimal strong classifier with a quadratic speedup in the number of queries of the weak classifiers.Our results also include a generalization of the standard AdaBoost to the cases where the output of each classifier may be probabilistic.We prove that the query complexity of the non-deterministic classifiers is the same as those of deterministic classifiers,which may be of independent interest to the classical machine-learning community.Additionally,once the optimal classifier is determined by our quantum algorithm,no quantum resources are further required.This fact may lead to applications on near term quantum devices.展开更多
Quantum systems are exceedingly difficult to engineer because they are sensitive to various types of noises.In particular,timedependent noises are frequently encountered in experiments but how to overcome them remains...Quantum systems are exceedingly difficult to engineer because they are sensitive to various types of noises.In particular,timedependent noises are frequently encountered in experiments but how to overcome them remains a challenging problem.In this work,we propose a flexible robust control technique to resist time-dependent noises based on inverse geometric optimization working in the filter-function formalism.The basic idea is to parameterize the control filter function geometrically and minimize its overlap with the noise spectral density.This then effectively reduces the noise susceptibility of the controlled system evolution.We show that the proposed method can produce high-quality robust pulses for realizing desired quantum evolutions under realistic noise models.Also,we demonstrate this method in examples including dynamical decoupling and quantum sensing protocols to enhance their performances.展开更多
基金supported by the Science,Technology and Innovation Commission of Shenzhen Municipality(Grant Nos.KQTD20210811090049034,RCBS20231211090824040,and RCBS20231211090815032)the National Natural Science Foundation of China(Grant Nos.12174178,12204228,12374474,and 123b2071)+2 种基金the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0301703)the Shenzhen-Hong Kong Cooperation Zone for Technology and Innovation(Grant No.HZQB-KCZYB-2020050)Guangdong Basic and Applied Basic Research Foundation(Grant Nos.2024A1515011714 and 2022A1515110615)。
文摘As superconducting quantum computing continues to advance at an unprecedented pace,there is a compelling demand for the innovation of specialized electronic instruments that act as crucial conduits between quantum processors and host computers.Here,we introduce a microwave measurement and control system(M^(2)CS)dedicated to large-scale superconducting quantum processors.M^(2)CS features a compact modular design that balances overall performance,scalability and flexibility.Electronic tests of M^(2)CS show key metrics comparable to commercial instruments.Benchmark tests on transmon superconducting qubits further show qubit coherence and gate fidelities comparable to state-of-the-art results,confirming M^(2)CS's capability to meet the stringent requirements of quantum experiments running on intermediate-scale quantum processors.The compact and scalable nature of our design holds the potential to support over 1000 qubits after upgrade in stability and integration.The M^(2)CS architecture may also be adopted to a wider range of scenarios,including other quantum computing platforms such as trapped ions and silicon quantum dots,as well as more traditional applications like microwave kinetic inductance detectors and phased array radar systems.
基金Project supported by the Key-Area Research and Development Program of Guangdong Province,China(Grant No.2018B030326001)the National Natural Science Foundation of China(Grant Nos.U1801661,11874065,and Youth Project No.11904158)+2 种基金the Guangdong Provincial Key Laboratory(Grant No.2019B121203002)the Natural Science Foundation of Hunan Province,China(Grant No.2018JJ1031)the Science,Technology and Innovation Commission of Shenzhen Municipality(Grant Nos.JCYJ20170412152620376 and YTDPT20181011104202253)。
文摘Superconducting circuit quantum electrodynamics(QED)architecture composed of superconducting qubit and resonator is a powerful platform for exploring quantum physics and quantum information processing.By employing techniques developed for superconducting quantum computing,we experimentally investigate phase-sensitive Landau-Zener-Stückelberg(LZS)interference phenomena in a circuit QED.Our experiments cover an extensive range of LZS transition parameters and demonstrate the LZS induced Rabi-like oscillation as well as phase-dependent steady-state population.
基金supported by the National Natural Science Foundation of China(Grant Nos.12074162,12004158,and 91964201)the National Key Research and Development Program of China(Grant Nos.2022YFA1403700 and 2020YFA0309300)+2 种基金the Key-Area Research and Development Program of Guangdong Province(Grant No.2018B030327001)Guangdong Provincial Key Laboratory(Grant No.2019B121203002)Guangdong Basic and Applied Basic Research Foundation(Grant No.2022B1515130005)。
文摘Chiral anomaly is a distinct quantum anomaly associated with chiral fermions in Dirac or Weyl semimetals.The use of negative magnetoresistance(negative MR)as a signature for this anomaly remains contentious,as trivial mechanisms such as current jetting and weak localization can also induce negative MR.In this study,we report a novel nonlinear behavior of the chiral anomaly in the longitudinal direction,which we observed by applying parallel current and magnetic field to the Dirac semimetal Cd_(3)A_(s_(2)).This nonlinear characteristic peaks at an intermediate magnetic field of approximately5 T,displaying a resistance-increasing property concomitant with strengthening of the current source.Through angledependence experiments,we were able to rule out trivial factors,such as thermal effects,geometric artifacts,and anisotropy.Furthermore,additional electric quantum oscillations were observed when the direct current(DC)was applied as high as300μA.Such an unusual phenomenon is ascribed to the formation of quantized levels due to Bloch oscillation in the high DC regime,suggesting that an oscillatory density distribution may arise as the electric field increases.The non-Ohmic electric quantum oscillations open a new avenue for exploring chiral anomaly and other nontrivial topological properties,which is also one of the salient features of nonequilibrium steady states in condensed matter physics.
基金supported by the National Natural Science Foundation of China(Grant Nos.T2121001,11934018,and U1801661)Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB28000000)+2 种基金the Key-Area Research and Development Program of GuangDong Province,China(Grant No.2018B030326001)Guangdong Provincial Key Laboratory(Grant No.2019B121203002)the Science,Technology and Innovation Commission of Shenzhen Municipality(Grant Nos.KYTDPT20181011104202253 and 2016ZT06D348)。
文摘We report a metrology scheme which measures the magnetic susceptibility of an atomic spin ensemble along the x and z directions and produces parameter estimation with precision beating the standard quantum limit.The atomic ensemble is initialized via one-axis spin squeezing with optimized squeezing time and parameterΦ(to be estimated)assumed as uniformly distributed between 0 and 2πwhile fixed in each estimation.One estimation ofΦcan be produced with every two magnetic susceptibility data measured along the two axes respectively,which has an imprecision scaling(1.43±0.02)/N^(0.687±0.003)with respect to the number N of the atomic spins.The measurement scheme is easy to implement and is robust against the measurement fluctuation caused by environment noise and measurement defects.
基金Project supported by the National Key Research and Development Program of China (Grant Nos.2020YFA0309300 and 2022YFA1403700)the National Natural Science Foundation of China (Grant Nos.12004158,12074162,and 91964201)+2 种基金the Key-Area Research and Development Program of Guangdong Province (Grant No.2018B030327001)Guangdong Provincial Key Laboratory (Grant No.2019B121203002)Guangdong Basic and Applied Basic Research Foundation (Grant No.2022B1515130005)。
文摘Spin–momentum locking is a key feature of the topological surface state, which plays an important role in spintronics.The electrical detection of current-induced spin polarization protected by the spin–momentum locking in nonmagnetic systems provides a new platform for developing spintronics, while previous studies were mostly based on magnetic materials.In this study, the spin transport measurement of Dirac semimetal Cd_(3)As_(2) was studied by three-terminal geometry, and a hysteresis loop signal with high resistance and low resistance state was observed. The hysteresis was reversed by reversing the current direction, which illustrates the spin–momentum locking feature of Cd_(3)As_(2). Furthermore, we realized the on–off states of the spin signals through electric modulation of the Fermi arc via the three-terminal configuration, which enables the great potential of Cd_(3)As_(2) in spin field-effect transistors.
基金the National Natural Science Foundation of China(Grant Nos.1212200199,12122506,12004165,12275117,and 12204230)Guangdong Basic and Applied Basic Research Foundation(Grant Nos.2021B1515020070 and 2022B1515020074)+1 种基金Guangdong Provincial Key Laboratory(Grant No.2019B121203002)Shen-zhen Science and Technology Program(Grant Nos.KQTD20200820113010023,RCBS20200714114820298,and RCYX20200714114522109).
文摘Quantum enhanced metrology has the potential to go beyond the standard quantum limit and eventually to the ultimate Heisenberg bound.In particular,quantum probes prepared in nonclassical coherent states have recently been recognized as a useful resource for metrology.Hence,there has been considerable interest in constructing magnetic quantum sensors that combine high resolution and high sensitivity.Here,we explore a nanoscale magnetometer with quantum-enhanced sensitivity,based on 123Sb(I=7/2)nuclear spin doped in silicon,that takes advantage of techniques of spin-squeezing and coherent control.With the optimal squeezed initial state,the magnetic field sensitivity may be expected to approach 6 aT·Hz^(−1/2)·cm^(−3/2) and 603 nT·Hz^(−1/2) at the single-spin level.This magnetic sensor may provide a novel sensitive and high-resolution route to microscopic mapping of magnetic fields as well as other applications.
基金supported by the Key-Area Research and Development Program of Guangdong Province(2018B030326001)the National Natural Science Foundation of China(U1801661,12174178,12374471,12204228)+6 种基金the Guangdong Innovative and Entrepreneurial Research Team Program(2016ZT06D348)the Guangdong Provincial Key Laboratory(2019B121203002)the Science,Technology and Innovation Commission of Shenzhen Municipality(KYTDPT20181011104202253,KQTD20210811090049034,K21547502)the Shenzhen Science and Technology Program(RCYX20221008092907026)the Shenzhen-Hong Kong Cooperation Zone for Technology and Innovation(HZQB-KCZYB-2020050)the Natural Science Foundation of Beijing(Z190012)support from the Tsinghua University Initiative Scientific Research Program and the Ministry of Education of China.
文摘Quantum teleportation is of both fundamental interest and great practical importance in quantum information science.To date,quantum teleportation has been implemented in various physical systems,among which superconducting qubits are of particular practical significance as they emerge as a leading system to realize large-scale quantum computation.Nevertheless,scaling up the number of superconducting qubits on a single chip becomes increasing challenging because of some emergent technical difficulties.Realization of quantum teleportation and remote computation over qubits on distant superconducting chips is a key quantum communication technology to scaling up the system through a distributed quantum computational network.However,this goal has not been realized yet in experiments due to the technical challenges including making a quantum interconnect between distant superconducting chips and the inefficient transfer of flying microwave photons over the lossy interconnects.Here we demonstrate deterministic teleportation of quantum states and entangling gates between distant superconducting chips connected by a 64-m-long cable bus featuring an ultralow loss of 0.32 dB/km at cryogenic temperatures,where high fidelity remote entanglement is generated via flying microwave photons.Our work demonstrates a prime building block for distributed quantum computation with superconducting qubits,and opens up a new avenue for waveguide quantum electrodynamics and quantum photonics at microwave frequencies.
基金supported by the National Natural Science Foundation of China(Grant No.11904155)the Guangdong Provincial Key Laboratory(Grant No.2019B121203002)a Shenzhen Science and Technology Program(Grant No.KQTD20200820113010023).
文摘The nature of the Cooper pairing in the paradigmatic unconventional superconductor Sr_(2)RuO_(4) is an outstanding puzzle in condensed matter physics.Despite the tremendous efforts made in the past twenty-seven years,neither the pairing symmetry nor the underlying pairing mechanism in this material has been understood with clear consensus.This is largely due to the lack of a superconducting order that is capable of interpreting in a coherent manner the numerous essential experimental observations.At this stage,it may be desirable to reexamine our existing theoretical descriptions of superconducting Sr_(2)RuO_(4).This review focuses on several recent developments that may provide some clues for future study.We highlight three separate aspects:1)any pairing in the Eu symmetry channel,with which the widely discussed chiral p-wave is associated,shall acquire a 3D structure due to spin-orbit entanglement;2)if the reported Kerr effect is a superconductivity-induced intrinsic bulk response,the superconductivity must either exhibit a chiral character,or be complex mixtures of certain set of helical p-wave pairings;3)when expressed in a multiorbital basis,the Cooper pairing could acquire numerous exotic forms that are inaccessible in single-orbital descriptions.The implications of each of these new perspectives are briefly discussed in connection with selected experimental phenomena.
基金Project supported by the National Key Research and Development Program of China(Grant No.2019YFA0308100)the National Natural Science Foundation of China(Grant Nos.12075110,11905099,11605005,11875159,and U1801661)+2 种基金Guangdong Basic and Applied Basic Research Foundation,China(Grant No.2019A1515011383)Science,Technology and Innovation Commission of Shenzhen Municipality(Grant Nos.ZDSYS20170303165926217,JCYJ20170412152620376,and JCYJ20180302174036418)Guangdong Innovative and Entrepreneurial Research Team Program,China(Grant No.2016ZT06D348)。
文摘Thanks to the quantum simulation,more and more problems in quantum mechanics which were previously inaccessible are now open to us.Capitalizing on the state-of-the-art techniques on quantum coherent control developed in past few decades,e.g.,the high-precision quantum gate manipulating,the time-reversal harnessing,the high-fidelity state preparation and tomography,the nuclear magnetic resonance(NMR) system offers a unique platform for quantum simulation of many-body physics and high-energy physics.Here,we review the recent experimental progress and discuss the prospects for quantum simulation realized on NMR systems.
基金Project supported by the Key-Area Research and Development Program of Guangdong Province of China (Grant No. 2018B030326001)the National Natural Science Foundation of China (Grant No. 11874065)+2 种基金the Guangdong Provincial Key Laboratory (Grant No. 2019B121203002)the Science, Technology and Innovation Commission of Shenzhen Municipality (Grant No. KYTDPT20181011104202253)the Shenzhen Hong Kong Cooperation Zone for Technology and Innovation of China (Grant No. HZQB-KCZYB2020050)。
文摘Quantum entanglement, a key resource in quantum information processing, is reduced by interaction between the quantum system concerned and its unavoidable noisy environment. Therefore it is of particular importance to study the dynamical properties of entanglement in open quantum systems. In this work, we mainly focus on two qubits coupled to an adjustable environment, namely a semi-infinite transmission line. The two qubits' relaxations, through individual channels or collective channel or both, can be adjusted by the qubits' transition frequencies. We examine entanglement dynamics in this model system with initial Werner state, and show that the phenomena of entanglement sudden death and revival can be observed. Due to the hardness of preparing the Werner state experimentally, we introduce a new type of entangled state called pseudo-Werner state, which preserves as much entangling property as the Werner state, and more importantly,it is experiment friendly. Furthermore, we provide detailed procedures for generating pseudo-Werner state and studying entanglement dynamics with it, which can be straightforwardly implemented in a superconducting waveguide quantum electrodynamics system.
基金supported by the Key-Area Research and Development Program of Guangdong Province(No.2018B030326001)the National Natural Science Foundation of China(Nos.12074166 and 12004162)the Guangdong Provincial Key Laboratory(No.2019B121203002).
文摘While the common practice of decomposing general quantum algorithms into a collection of single-and two-qubit gates is conceptually simple,in many cases it is possible to have more efficient solutions where quantum gates engaging multiple qubits are used.In the noisy intermediate-scale quantum(NISQ)era where a universal error correction is still unavailable,this strategy is particularly appealing since it can significantly reduce the computational resources required for executing quantum algorithms.In this work,we experimentally investigate a three-qubit ControlledCPHASE-SWAP(CCZS)gate on superconducting quantum circuits.By exploiting the higher energy levels of superconducting qubits,we are able to realize a Fredkin-like CCZS gate with a duration of 40 ns,which is comparable to typical single-and two-qubit gates realized on the same platform.By performing quantum process tomography for the two target qubits,we obtain a process fidelity of86.0%and 81.1%for the control qubit being prepared in|0>and|1>,respectively.We also show that our scheme can be readily extended to realize a general CCZS gate with an arbitrary swap angle.The results reported here provide valuable additions to the toolbox for achieving large-scale hardware-efficient quantum circuits.
基金supported by the National Key R&D Program of China(Grant Nos.2023YFA1407300,2023YFA1406500,2022YFA1403800,and 2023YFF0718403)the National Natural Science Foundation of China(Grant Nos.12374060,12274459,and 12074162)+2 种基金Guangdong Provincial Quantum Science Strategic Initiative(Grant No.GDZX2201001)the Beijing Natural Science Foundation(Grant No.Z200005)Guangdong Basic and Applied Basic Research Foundation(Grant No.2022B1515130005)。
文摘The chiral 2×2 charge order has been reported and confirmed in the kagome superconductor RbV_(3)Sb_(5),while its interplay with superconductivity remains elusive owing to its lowest superconducting transition temperature Tc of about 0.85K in the AV_(3)Sb_(5) family(A=K,Rb,Cs)that severely challenges electronic spectroscopic probes.Here,utilizing dilution-refrigerator-based scanning tunneling microscopy down to 30 mK,we observe chiral 2×2 pair density waves with residual Fermi arcs in RbV_(3)Sb_(5).We find a superconducting gap of 150 μeV with substantial residual in-gap states.The spatial distribution of this gap exhibits chiral 2×2 modulations,signaling a chiral pair density wave(PDW).Our quasi-particle interference imaging of the zero-energy residual states further reveals arc-like patterns.We discuss the relation of the gap modulations with the residual Fermi arcs under the space-momentum correspondence between PDW and Bogoliubov Fermi states.
基金supported by the Key-Area Research and Development Program of Guangdong Province(2018B030326001)the National Natural Science Foundation of China(U1801661 and 11904417)+4 种基金the Guangdong Innovative and Entrepreneurial Research Team Program(2016ZT06D348)the Guangdong Provincial Key Laboratory(2019B121203002)the Natural Science Foundation of Guangdong Province(2017B030308003)the Science,Technology and Innovation Commission of Shenzhen Municipality(JCYJ20170412152620376,and KYTDPT20181011104202253)the NSF of Beijing(Z190012)。
文摘Higher-order topological phases give rise to new bulk and boundary physics,as well as new classes of topological phase transitions.While the realization of higher-order topological phases has been confirmed in many platforms by detecting the existence of gapless boundary modes,a direct determination of the higher-order topology and related topological phase transitions through the bulk in experiments has still been lacking.To bridge the gap,in this work we carry out the simulation of a twodimensional second-order topological phase in a superconducting qubit.Owing to the great flexibility and controllability of the quantum simulator,we observe the realization of higher-order topology directly through the measurement of the pseudo-spin texture in momentum space of the bulk for the first time,in sharp contrast to previous experiments based on the detection of gapless boundary modes in real space.Also through the measurement of the evolution of pseudo-spin texture with parameters,we further observe novel topological phase transitions from the second-order topological phase to the trivial phase,as well as to the first-order topological phase with nonzero Chern number.Our work sheds new light on the study of higher-order topological phases and topological phase transitions.
文摘Among existing approaches to holonomic quantum computing,the adiabatic holonomic quantum gates(HQGs)suffer errors due to decoherence,while the non-adiabatic HQGs either require additional Hilbert spaces or are difficult to scale.Here,we report a systematic,scalable approach based on dynamical invariants to realize HQGs without using additional Hilbert spaces.While presenting the theoretical framework of our approach,we design and experimentally evaluate single-qubit and two-qubits HQGs for the nuclear magnetic resonance system.The single-qubit gates acquire average fidelity 0.9972 by randomized benchmarking,and the controlled-NOT gate acquires fidelity 0.9782 by quantum process tomography.Our approach is also platform-independent,and thus may open a way to large-scale holonomic quantum computation.
基金supported by the National Key Research and Development Program of China(Grant Nos.2017YFA0303700,and2019YFA0308100)National Natural Science Foundation of China(Grant Nos.12075110,11975117,11905099,11875159,U1801661+9 种基金11774197)Key R&D Program of Guangdong Province(Grant No.2018B030325002)Guangdong Basic and Applied Basic Research Foundation(Grant No.2019A1515011383)Guangdong International Collaboration Program(Grant No.2020A0505100001)Guangdong Provincial Key Laboratory(Grant No.2019B121203002)Science,Technology and Innovation Commission of Shenzhen Municipality(Grant Nos.ZDSYS20170303165926217,KQTD20190929173815000,JCYJ20200109140803865,JCYJ20170412152620376,and JCYJ201803021-74036418)Tsinghua University Initiative Scientific Research ProgramBeijing Advanced Innovation Center for Future Chip(ICFC)Pengcheng ScholarsGuangdong Innovative and Entrepreneurial Research Team Program(Grant No.2019ZT08C044)。
文摘Entanglement in quantum systems plays a crucial role in various quantum information tasks. Measuring entanglement has been an important issue in both experiments and theories. In this work, we use parameterized quantum circuits(PQCs) to diagonalize density matrices of quantum states and obtain entanglement by only measuring the diagonal elements. With this method, full quantum state tomography can be bypassed, greatly reducing the number of measurements. A comprehensive characterization of entanglement was performed by using Rényi entropy and partially transposed moments. Mutual information, calculated from entropy is also used to characterize dynamical quantum phase transitions. We experimentally demonstrated the method on a four-qubit nuclear magnetic resonance quantum simulator. Our results agree with the theoretical descriptions. The measurement complexity of our PQC-based method grows linearly with the number of diagonal elements in the density matrix, a square root reduction over the full quantum tomography. The proposed method can have great potential in quantum systems with a large number of particles.
基金supported by the National Natural Science Foundation of China(Grant No.11904155)the Guangdong Provincial Key Laboratory(Grant No.2019B121203002)+1 种基金the Guangdong Science and Technology Department(Grant No.2022A1515011948)the Shenzhen Science and Technology Program(Grant No.KQTD20200820113010023)。
文摘Bloch electrons in multiorbital systems carry quantum geometric information characteristic of their wavevector-dependent interorbital mixing.The geometric nature impacts electromagnetic responses,and this effect carries over to the superconducting state,which receives a geometric contribution to the superfluid weight.In this paper,we show that this contribution could become negative under certain appropriate circumstances.This may facilitate the stabilization of Cooper pairings with real space phase modulation,i.e.,the pair density wave order,as we demonstrate through two-orbital model Bogoliubov de-Gennes mean-field calculations.The quantum geometric effect therefore constitutes an intrinsic mechanism for the formation of such a novel phase of matter in the absence of external magnetic field.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61734008 and 11774143)the National Key Research and Development Program of China(Grant Nos.2018YFA0307100,2016YFA0301703,and 2016YFA0300300)+4 种基金the Natural Science Foundation of Guangdong Province,China(Grant Nos.2015A030313840 and 2017A030313033)the State Key Laboratory of Low-Dimensional Quantum Physics(Grant No.KF201602)Technology and Innovation Commission of Shenzhen Municipality,China(Grant Nos.ZDSYS20170303165926217 and JCYJ20170412152334605)Guangdong Provincial Key Laboratory,China(Grant No.2019B121203002)J.-W.M.was partially supported by the Program for Guangdong Introducing Innovative and Entrepreneurial Teams,China(Grant No.2017ZT07C062).
文摘Majorana fermions have been predicted to exist at the edge states of a two-dimensional topological superconductor.We fabricated single quintuple layer(QL)Bi2Te3/FeTe heterostructure with the step-flow epitaxy method and studied the topological properties of this system by using angle-resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy.We observed the coexistence of robust superconductivity and edge states on the single QL Bi2Te3 islands which can be potential evidence for topological superconductor.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.12004158,12074162,and 91964201)the National Key Research and Development Program of China(Grant Nos.2022YFA1403700 and 2020YFA0309300)+2 种基金the Key-Area Research and Development Program of Guangdong Province,China(Grant No.2018B030327001)Guangdong Provincial Key Laboratory(Grant No.2019B121203002)Guangdong Basic and Applied Basic Research Foundation(Grant No.2022B1515130005).
文摘Topological insulators and semimetals have exotic surface and bulk states with massless Dirac or Weyl fermions,demonstrating microscopic transport phenomenon based on relativistic theory.Chiral anomaly induced negative magnetoresistance(negative MR)under parallel magnetic field and current has been used as a probable evidence ofWeyl fermions in recent years.Here we report a novel negative MR result with mutually perpendicular in-plane magnetic field and current in Cd_(3)As_(2)nanowires.The negative MR has a considerable value of-16%around 1.5 K and could persist to room temperature of 300 K with value of-1%.The gate tuning and angle dependence of the negative MR demonstrate the mechanism of the observed negative MR is different from the chiral anomaly.Percolating current paths induced by charge puddles and disorder might be involved to produce such considerable negative MR.Our results indicate the negative MR effect in topological semimetals involves synergistic effects of many mechanisms besides chiral anomaly.
基金supported by the Natural Science Foundation of Guangdong Province(Grant No.2017B030308003)the Key R&D Program of Guangdong Province(Grant No.2018B030326001)+3 种基金the Science,Technology and Innovation Commission of Shenzhen Municipality(Grant Nos.JCYJ20170412152620376,JCYJ20170817105046702,and KYTDPT20181011104202253)the National Natural Science Foundation of China(Grant Nos.11875160,and U1801661)the Economy,Trade and Information Commission of Shenzhen Municipality(Grant No.201901161512)Guangdong Provincial Key Laboratory(Grant No.2019B121203002)。
文摘In classical machine learning,a set of weak classifiers can be adaptively combined for improving the overall performance,a technique called adaptive boosting(or AdaBoost).However,constructing a combined classifier for a large data set is typically resource consuming.Here we propose a quantum extension of AdaBoost,demonstrating a quantum algorithm that can output the optimal strong classifier with a quadratic speedup in the number of queries of the weak classifiers.Our results also include a generalization of the standard AdaBoost to the cases where the output of each classifier may be probabilistic.We prove that the query complexity of the non-deterministic classifiers is the same as those of deterministic classifiers,which may be of independent interest to the classical machine-learning community.Additionally,once the optimal classifier is determined by our quantum algorithm,no quantum resources are further required.This fact may lead to applications on near term quantum devices.
基金supported by the National Natural Science Foundation of China(Grant Nos.12204230,12275117,1212200199,11975117,92065111,12075110,11905099,11875159,11905111,and U1801661)the National Key Research and Development Program of China(Grant No.2019YFA0308100)+6 种基金Guangdong Basic and Applied Basic Research Foundation(Grant Nos.2022B1515020074,2019A1515011383,and 2021B1515020070)Guangdong Provincial Key Laboratory(Grant No.2019B121203002)Guangdong International Collaboration Program(Grant No.2020A0505100001)Shenzhen Science and Technology Program(Grant Nos.RCYX20200714114522109,and KQTD20200820113010023)the Science,Technology and Innovation Commission of Shenzhen Municipality(Grant Nos.ZDSYS20190902092905285,KQTD20190929173815000,and JCYJ20200109140803865)the Pengcheng Scholars,Guangdong Innovative and Entrepreneurial Research Team Program(Grant No.2019ZT08C044)the Pearl River Talent Recruitment Program(Grant No.2019QN01X298)。
文摘Quantum systems are exceedingly difficult to engineer because they are sensitive to various types of noises.In particular,timedependent noises are frequently encountered in experiments but how to overcome them remains a challenging problem.In this work,we propose a flexible robust control technique to resist time-dependent noises based on inverse geometric optimization working in the filter-function formalism.The basic idea is to parameterize the control filter function geometrically and minimize its overlap with the noise spectral density.This then effectively reduces the noise susceptibility of the controlled system evolution.We show that the proposed method can produce high-quality robust pulses for realizing desired quantum evolutions under realistic noise models.Also,we demonstrate this method in examples including dynamical decoupling and quantum sensing protocols to enhance their performances.
