Radio frequency(RF)reflectometry is an effective and sensitive technique for detecting charge signal in semiconductor quantum dots,and its measurement bandwidth can reach the MHz level.However,in accumulation mode dev...Radio frequency(RF)reflectometry is an effective and sensitive technique for detecting charge signal in semiconductor quantum dots,and its measurement bandwidth can reach the MHz level.However,in accumulation mode devices,the presence of parasitic capacitance makes RF reflectometry more difficult.The universal approach is relocating the ion implantation region approximately 10μm from the center of the single-electron transistor(SET)and optimizing the design of the accumulation gates.But,this method puts forward more stringent requirements for micro-nano fabrication processing.Here,we propose a split-gate structure that enables RF reflectometry when the ion-implanted region and the ohmic contact are farther from the SET center.In Si-MOS devices,we employ a split-gate structure to achieve RF detection,with the ion-implanted region located 150μm away from the center of the SET.Within an integration time of 140 nanoseconds,we achieved a readout fidelity exceeding 99.8%and a detection bandwidth of over 2 MHz.This is an alternative solution for micro-nano fabrication processing that cannot achieve ion implantation areas closer to the center of the chip,and is applicable to various silicon-based semiconductor systems.展开更多
In this theoretical work,we describe a mechanism for the coupling between a plane structure consisting of four quantum dots and a resonator.We systematically study the dependence of the quadruple coupling strength and...In this theoretical work,we describe a mechanism for the coupling between a plane structure consisting of four quantum dots and a resonator.We systematically study the dependence of the quadruple coupling strength and the qubit decoherence rate and point out the optimized operating position of the hybrid system.According to the transmission given by the input-output theory,the signatures in the resonator spectrum are predicted.Furthermore,based on the parameters already achieved in previous works,we prove that the device described in this paper can achieve the strong coupling limit,i.e.,this approach can be used for system extension under the existing technical conditions.Our results show an effective and promotable approach to couple quantum dot structures in plane with the resonator and propose a meaningful extension method.展开更多
Scaling up spin qubits in silicon-based quantum dots is one of the pivotal challenges in achieving large-scale semiconductor quantum computation.To satisfy the connectivity requirements and reduce the lithographic com...Scaling up spin qubits in silicon-based quantum dots is one of the pivotal challenges in achieving large-scale semiconductor quantum computation.To satisfy the connectivity requirements and reduce the lithographic complexity,utilizing the qubit array structure and the circuit quantum electrodynamics(cQED)architecture together is expected to be a feasible scaling scheme.A triple-quantum dot(TQD)coupled with a superconducting resonator is regarded as a basic cell to demonstrate this extension scheme.In this article,we investigate a system consisting of a silicon TQD and a high-impedance TiN coplanar waveguide(CPW)resonator.The TQD can couple to the resonator via the right double-quantum dot(RDQD),which reaches the strong coupling regime with a charge–photon coupling strength of g0/(2p)=175 MHz.Moreover,we illustrate the high tunability of the TQD through the characterization of stability diagrams,quadruple points(QPs),and the quantum cellular automata(QCA)process.Our results contribute to fostering the exploration of silicon-based qubit integration.展开更多
The performance of Nb superconducting quantum devices is predominantly limited by dielectric loss at the metal–air interface,where Nb2O5 is considered the main loss source.Here,we suppress the formation of native oxi...The performance of Nb superconducting quantum devices is predominantly limited by dielectric loss at the metal–air interface,where Nb2O5 is considered the main loss source.Here,we suppress the formation of native oxides by in-situ deposition of a TiN capping layer on the Nb film.With TiN capping layers,no Nb2O5 forms on the surface of the Nb film.The quality factor Qi of the Nb resonator increases from 5.6×10^(5) to 7.9×10^(5) at low input power and from 6.8×10^(6) to 1.1×10^(7)at high input power.Furthermore,the TiN capping layer also shows good aging resistance in Nb resonator devices,with no significant performance fluctuations after one month of aging.These findings highlight the effectiveness of TiN capping layers in enhancing the performance and longevity of Nb superconducting quantum devices.展开更多
Reducing the control error is vital for high-fidelity digital and analog quantum operations.In superconducting circuits,one disagreeable error arises from the reflection of microwave signals due to impedance mismatch ...Reducing the control error is vital for high-fidelity digital and analog quantum operations.In superconducting circuits,one disagreeable error arises from the reflection of microwave signals due to impedance mismatch in the control chain.Here,we demonstrate a reflection cancelation method when considering that there are two reflection nodes on the control line.We propose to generate the pre-distortion pulse by passing the envelopes of the microwave signal through digital filters,which enables real-time reflection correction when integrated into the field-programmable gate array(FPGA).We achieve a reduction of single-qubit gate infidelity from 0.67%to 0.11%after eliminating microwave reflection.Real-time correction of microwave reflection paves the way for precise control and manipulation of the qubit state and would ultimately enhance the performance of algorithms and simulations executed on quantum processors.展开更多
The presence of anticrossings induced by coupling between two states causes curvature in energy levels, yielding a nonlinearity in the quantum system. When the system is driven back and forth along the bending energy ...The presence of anticrossings induced by coupling between two states causes curvature in energy levels, yielding a nonlinearity in the quantum system. When the system is driven back and forth along the bending energy levels, subharmonic transitions and energy shifts can be observed, which would cause a significant influence as the system is applied to quantum computing. In this paper, we study a longitudinally driven singlet-triplet(ST) system in a double quantum dot(DQD)system, and illustrate the consequences of nonlinearity by driving the system close to the anticrossings. We provide a straightforward theory to quantitatively describe the energy shift and subharmonics caused by nonlinearity, and find good agreement between our theoretical result and the numerical simulation. Our results reveal the existence of nonlinearity in the vicinity of anticrossings and provide a direct way of analytically assessing its impact, which can be applied to other quantum systems without excessive labor.展开更多
The single-shot readout data process is essential for the realization of high-fidelity qubits and fault-tolerant quantum algorithms in semiconductor quantum dots. However, the fidelity and visibility of the readout pr...The single-shot readout data process is essential for the realization of high-fidelity qubits and fault-tolerant quantum algorithms in semiconductor quantum dots. However, the fidelity and visibility of the readout process are sensitive to the choice of the thresholds and limited by the experimental hardware. By demonstrating the linear dependence between the measured spin state probabilities and readout visibilities along with dark counts, we describe an alternative threshold-independent method for the single-shot readout of spin qubits in semiconductor quantum dots. We can obtain the extrapolated spin state probabilities of the prepared probabilities of the excited spin state through the threshold-independent method. We then analyze the corresponding errors of the method, finding that errors of the extrapolated probabilities cannot be neglected with no constraints on the readout time and threshold voltage. Therefore, by limiting the readout time and threshold voltage, we ensure the accuracy of the extrapolated probability. We then prove that the efficiency and robustness of this method are 60 times larger than those of the most commonly used method. Moreover, we discuss the influence of the electron temperature on the effective area with a fixed external magnetic field and provide a preliminary demonstration for a single-shot readout of up to 0.7K/1.5T in the future.展开更多
Valley, the intrinsic feature of silicon, is an inescapable subject in silicon-based quantum computing. At the spin–valley hotspot, both Rabi frequency and state relaxation rate are significantly enhanced. With prote...Valley, the intrinsic feature of silicon, is an inescapable subject in silicon-based quantum computing. At the spin–valley hotspot, both Rabi frequency and state relaxation rate are significantly enhanced. With protection against charge noise, the valley degree of freedom is also conceived to encode a qubit to realize noise-resistant quantum computing.Here, based on the spin qubit composed of one or three electrons, we characterize the intrinsic properties of valley in an isotopically enriched silicon quantum dot(QD) device. For one-electron qubit, we measure two electric-dipole spin resonance(EDSR) signals which are attributed to partial occupation of two valley states. The resonance frequencies of two EDSR signals have opposite electric field dependences. Moreover, we characterize the electric field dependence of the upper valley state based on three-electron qubit experiments. The difference of electric field dependences of the two valleys is 52.02 MHz/V, which is beneficial for tuning qubit frequency to meet different experimental requirements. As an extension of electrical control spin qubits, the opposite electric field dependence is crucial for qubit addressability,individual single-qubit control and two-qubit gate approaches in scalable quantum computing.展开更多
The excellent mechanical properties make graphene promising for realizing nanomechanical resonators with high resonant frequencies,large quality factors,strong nonlinearities,and the capability to efectively interface...The excellent mechanical properties make graphene promising for realizing nanomechanical resonators with high resonant frequencies,large quality factors,strong nonlinearities,and the capability to efectively interface with various physical systems.Equipped with gate electrodes,it has been demonstrated that these exceptional device properties can be electrically manipulated,leading to a variety of nanomechanical/acoustic applications.Here,we review the recent progress of graphene nanomechanical resonators with a focus on their electrical tunability.First,we provide an overview of diferent graphene nanomechanical resonators,including their device structures,fabrication methods,and measurement setups.Then,the key mechanical properties of these devices,for example,resonant frequencies,nonlinearities,dissipations,and mode coupling mechanisms,are discussed,with their behaviors upon electrical gating being highlighted.After that,various potential classical/quantum applications based on these graphene nanomechanical resonators are reviewed.Finally,we briefy discuss challenges and opportunities in this feld to ofer future prospects for the ongoing studies on graphene nanomechanical resonators.展开更多
Applying a perpendicular electric field to bilayer graphene(BLG)induces an electrically tunable bandgap,so that insulating states with resistances exceeding~10^(8)Ωcan be generated.These high-resistance states pinch ...Applying a perpendicular electric field to bilayer graphene(BLG)induces an electrically tunable bandgap,so that insulating states with resistances exceeding~10^(8)Ωcan be generated.These high-resistance states pinch off the conducting channel,thereby enabling high-quality gated devices for classical and quantum electronics.However,it is challenging to precisely quantify these states electrically due to their high resistances,especially when different areas of the device are operated in different high-resistance states.Here,taking advantage of the strong acoustoelectric effect,we demonstrate the detection of these high-resistance states in a multi-gated BLG device using surface acoustic waves.Under different gating configurations,the device is operated in different high-resistance states.Although these states have similar resistances of~10^(8)Ω,we show their acoustoelectric responses exhibit pronounced differences,thereby allowing the acoustic detection.More interestingly,we demonstrate that when the conducting channel is pinched off by one top gate,we are still able to acoustically,but not electrically,detect the gating effect of another top gate.Our results reveal the powerful capability and the promising future of acoustically characterizing BLG and other two-dimensional materials,especially their electronic states with high resistances.展开更多
Geometric phase gates have attracted considerable attention due to their intrinsic robustness against certain types of noise.Significant progress has been achieved in implementing geometric phase gates using microwave...Geometric phase gates have attracted considerable attention due to their intrinsic robustness against certain types of noise.Significant progress has been achieved in implementing geometric phase gates using microwave control in siliconbased electron spin systems.In this work,we propose an alternative geometric phase gate protocol that differs fundamentally from microwave driving approaches by leveraging square-wave control of rapidly switchable micromagnets driven by spin-orbit torque(SOT)to achieve fast and precise magnetic field modulation.By employing square-wave currents to control magnetization switching,our approach relaxes the requirements on waveform precision while significantly suppressing crosstalk.Moreover,our scheme inherently preserves trajectory closure at the end of each operation,effectively mitigating noise-induced path deviation and enhancing gate robustness even under strong noise conditions,thereby offering a promising pathway toward efficient and reliable quantum operations in large-scale qubit arrays.展开更多
Strained germanium hole spin qubits are promising for quantum computing,but the devices hosting these qubits face challenges from high interface trap density,which originates from the naturally oxidized surface of the...Strained germanium hole spin qubits are promising for quantum computing,but the devices hosting these qubits face challenges from high interface trap density,which originates from the naturally oxidized surface of the wafer.These traps can degrade the device stability and cause an excessively high threshold voltage.Surface passivation is regarded as an effective method to mitigate these impacts.In this study,we perform low-thermal-budget chemical passivation using the nitric acid oxidation of silicon method on the surface of strained germanium devices and investigate the impact of passivation on the device stability.The results demonstrate that surface passivation effectively reduces the interface defect density.This not only improves the stability of the device's threshold voltage but also enhances its long-term static stability.Furthermore,we construct a band diagram of hole surface tunneling at the static operating point to gain a deeper understanding of the physical mechanism through which passivation affects the device stability.This study provides valuable insights for future optimization of strained Ge-based quantum devices and advances our understanding of how interface states affect device stability.展开更多
In semiconductor quantum dot systems,pulse distortion is a significant source of coherent errors,which impedes qubit characterization and control.Here,we demonstrate two calibration methods using a two-qubit system as...In semiconductor quantum dot systems,pulse distortion is a significant source of coherent errors,which impedes qubit characterization and control.Here,we demonstrate two calibration methods using a two-qubit system as the detector to correct distortion and calibrate the transfer function of the control line.Both methods are straightforward to implement,robust against noise,and applicable to a wide range of qubit types.The two methods differ in correction accuracy and complexity.The first,coarse predistortion(CPD)method,partially mitigates distortion.The second,all predistortion(APD)method,measures the transfer function and significantly enhances exchange oscillation uniformity.Both methods use exchange oscillation homogeneity as the metric and are suitable for any qubit driven by a diabatic pulse.We believe these methods will enhance qubit characterization accuracy and operation quality in future applications.展开更多
Hybrid qubits enable the hybridization of charge and spin degrees of freedom,which provides a way to realize both a relatively long coherence time and rapid qubit manipulation.Here,we use microwave driving to demonstr...Hybrid qubits enable the hybridization of charge and spin degrees of freedom,which provides a way to realize both a relatively long coherence time and rapid qubit manipulation.Here,we use microwave driving to demonstrate the coherent operation of a tunable hybrid qubit,including X-rotation,Z-rotation,and rotation around an arbitrary axis in the X-Y panel of the Bloch sphere.Moreover,the coherence properties of the qubit and its tunability are studied.The measured coherence time of the X-rotation reaches~14.3 ns.While for the Z-rotation,the maximum decoherence time is~5.8 ns due to the larger sensitivity to noise.By employing the Hahn echo sequence to mitigate the influence of the low-frequency noise,we have improved the qubit coherence time from~5.8 ns to~15.0 ns.Our results contribute to a further understanding of the hybrid qubit and a step towards achieving high-fidelity qubit gates in the hybrid qubit.展开更多
Conerent photon source is an important element that has been widely used in spectroscopy,imaging,detection,and teleportation in quantum optics.However,it is still a challenge to realize micro-scale coherent emitters i...Conerent photon source is an important element that has been widely used in spectroscopy,imaging,detection,and teleportation in quantum optics.However,it is still a challenge to realize micro-scale coherent emitters in semiconductor systems.We report the observation of gain in a cavity-coupled GaAs double quantum dot system with a voltage bias across the device.By characterizing and analyzing the cavity responses to different quantum dot behaviors,we distinguish the microwave photon emission from the signal gain.This study provides a possibility to realize micro-scale amplifiers or coherent microwave photon sources in circuit quantum electrodynamics(cQED) hybrid systems.展开更多
In quantum computation and quantum information processing, the manipulation and engineering of quantum systems to suit certain purposes are an ongoing task. One such example is quantum state transfer(QST), an essentia...In quantum computation and quantum information processing, the manipulation and engineering of quantum systems to suit certain purposes are an ongoing task. One such example is quantum state transfer(QST), an essential requirement for both quantum communication and large-scale quantum computation. Here we engineer a chain of four superconducting qubits with tunable couplers to realize the perfect state transfer(PST) protocol originally proposed in quantum spin networks and successfully demonstrate the efficient transfer of an arbitrary single-qubit state from one end of the chain to the other,achieving a high fidelity of 0.986 in just 25 ns. This demonstrated QST is readily to extend to larger chain and multi-node configurations, thus serving as a desirable tool for scalable quantum information processing.展开更多
Nonlinear partial differential equations(PDEs)are crucial for modeling complex fluid dynamics and are foundational to many computational fluid dynamics(CFD)applications.However,solving these nonlinear PDEs is challeng...Nonlinear partial differential equations(PDEs)are crucial for modeling complex fluid dynamics and are foundational to many computational fluid dynamics(CFD)applications.However,solving these nonlinear PDEs is challenging due to the vast computational resources they demand,highlighting the pressing need for more efficient computational methods.Quantum computing offers a promising but technically challenging approach to solving nonlinear PDEs.Recently,Liao[arXiv:2406.15821]proposed a framework that leverages quantum computing to accelerate the solution of nonlinear PDEs based on the homotopy analysis method(HAM),a semi-analytical technique that transforms nonlinear PDEs into a series of linear PDEs.However,the no-cloning theorem in quantum computing poses a major limitation,where directly applying quantum simulation to each HAM step results in exponential complexity growth with the HAM truncation order.This study introduces a“quantum-compatible linearization”approach that maps the whole HAM process into a system of linear PDEs,allowing for a one-time solution using established quantum PDE solvers.Our method preserves the exponential speedup of quantum linear PDE solvers while ensuring that computational complexity increases only polynomially with the HAM truncation order.We demonstrate the efficacy of our approach by applying it to the Burgers'equation and the Korteweg-de Vries(KdV)equation.Our approach provides a novel pathway for transforming nonlinear PDEs into linear PDEs,with potential applications to fluid dynamics.This work thus lays the foundation for developing quantum algorithms capable of solving the Navier-Stokes equations,ultimately offering a promising route to accelerate their solutions using quantum computing.展开更多
Classical simulations of quantum circuits are limited in both space and time when the qubit count is above 50, the realm where quantum supremacy reigns. However, recently, for the low depth circuit with more than 50 q...Classical simulations of quantum circuits are limited in both space and time when the qubit count is above 50, the realm where quantum supremacy reigns. However, recently, for the low depth circuit with more than 50 qubits, there are several methods of simulation proposed by teams at Google and IBM. Here,we present a scheme of simulation which can extract a large amount of measurement outcomes within a short time, achieving a 64-qubit simulation of a universal random circuit of depth 22 using a 128-node cluster, and 56-and 42-qubit circuits on a single PC. We also estimate that a 72-qubit circuit of depth 23 can be simulated in about 16 h on a supercomputer identical to that used by the IBM team. Moreover, the simulation processes are exceedingly separable, hence parallelizable, involving just a few inter-process communications. Our work enables simulating more qubits with less hardware burden and provides a new perspective for classical simulations.展开更多
The computer advances of the past century can be traced to the increase in their numbers on chips that has accompanied the miniaturization of transistors.However,computers are nearing the fundamental limits of such mi...The computer advances of the past century can be traced to the increase in their numbers on chips that has accompanied the miniaturization of transistors.However,computers are nearing the fundamental limits of such miniaturization[1].Many practical problems require huge amounts of computational resources that exceed the capabilities of today's computers.A 54-qubit quantum computer on the other hand can solve in minutes a problem that would take a classical machine 10,000 years[2].展开更多
In a circuit quantum electrodynamics(circuit QED) architecture, the microwave resonator could be used to couple and probe qubits. The long-range coupling and information transfer between nonlocal qubits can be perform...In a circuit quantum electrodynamics(circuit QED) architecture, the microwave resonator could be used to couple and probe qubits. The long-range coupling and information transfer between nonlocal qubits can be performed via photons trapped in a microwave resonator, promising an effective approach for scaling up solid-state qubits. A series of important advances in the hybrid system composed of a microwave resonator and semiconductor qubits have been achieved in recent years. For instance,with applications of high-impedance microwave resonators, the strong coupling regime between charge/spin qubits and a microwave resonator has been reached. Simultaneously, resonator-based dispersive readout and single-shot readout to probe the qubit state have been further improved due to the increase of the coupling strength. Here, we briefly introduce this hybrid system related to the progress and fruits in achieving the strong coupling between charge/spin qubits in double quantum dots(DQDs)and the resonator, the long-range coupling between qubits, and also the applications of the resonator for qubit state readout.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.92165207,12474490,12034018,and 92265113)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302300)the USTC Tang Scholarship.
文摘Radio frequency(RF)reflectometry is an effective and sensitive technique for detecting charge signal in semiconductor quantum dots,and its measurement bandwidth can reach the MHz level.However,in accumulation mode devices,the presence of parasitic capacitance makes RF reflectometry more difficult.The universal approach is relocating the ion implantation region approximately 10μm from the center of the single-electron transistor(SET)and optimizing the design of the accumulation gates.But,this method puts forward more stringent requirements for micro-nano fabrication processing.Here,we propose a split-gate structure that enables RF reflectometry when the ion-implanted region and the ohmic contact are farther from the SET center.In Si-MOS devices,we employ a split-gate structure to achieve RF detection,with the ion-implanted region located 150μm away from the center of the SET.Within an integration time of 140 nanoseconds,we achieved a readout fidelity exceeding 99.8%and a detection bandwidth of over 2 MHz.This is an alternative solution for micro-nano fabrication processing that cannot achieve ion implantation areas closer to the center of the chip,and is applicable to various silicon-based semiconductor systems.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.92265113,12074368,and 12034018).
文摘In this theoretical work,we describe a mechanism for the coupling between a plane structure consisting of four quantum dots and a resonator.We systematically study the dependence of the quadruple coupling strength and the qubit decoherence rate and point out the optimized operating position of the hybrid system.According to the transmission given by the input-output theory,the signatures in the resonator spectrum are predicted.Furthermore,based on the parameters already achieved in previous works,we prove that the device described in this paper can achieve the strong coupling limit,i.e.,this approach can be used for system extension under the existing technical conditions.Our results show an effective and promotable approach to couple quantum dot structures in plane with the resonator and propose a meaningful extension method.
基金the National Natural Science Foun-dation of China(Grant Nos.92265113,12074368,12304560,and 12034018)China Postdoctoral Science Foundation(Grant Nos.BX20220281 and 2023M733408).
文摘Scaling up spin qubits in silicon-based quantum dots is one of the pivotal challenges in achieving large-scale semiconductor quantum computation.To satisfy the connectivity requirements and reduce the lithographic complexity,utilizing the qubit array structure and the circuit quantum electrodynamics(cQED)architecture together is expected to be a feasible scaling scheme.A triple-quantum dot(TQD)coupled with a superconducting resonator is regarded as a basic cell to demonstrate this extension scheme.In this article,we investigate a system consisting of a silicon TQD and a high-impedance TiN coplanar waveguide(CPW)resonator.The TQD can couple to the resonator via the right double-quantum dot(RDQD),which reaches the strong coupling regime with a charge–photon coupling strength of g0/(2p)=175 MHz.Moreover,we illustrate the high tunability of the TQD through the characterization of stability diagrams,quadruple points(QPs),and the quantum cellular automata(QCA)process.Our results contribute to fostering the exploration of silicon-based qubit integration.
基金the National Natural Science Foun-dation of China(Grant Nos.12034018 and 11625419).
文摘The performance of Nb superconducting quantum devices is predominantly limited by dielectric loss at the metal–air interface,where Nb2O5 is considered the main loss source.Here,we suppress the formation of native oxides by in-situ deposition of a TiN capping layer on the Nb film.With TiN capping layers,no Nb2O5 forms on the surface of the Nb film.The quality factor Qi of the Nb resonator increases from 5.6×10^(5) to 7.9×10^(5) at low input power and from 6.8×10^(6) to 1.1×10^(7)at high input power.Furthermore,the TiN capping layer also shows good aging resistance in Nb resonator devices,with no significant performance fluctuations after one month of aging.These findings highlight the effectiveness of TiN capping layers in enhancing the performance and longevity of Nb superconducting quantum devices.
基金the National Natural Science Foun-dation of China(Grant Nos.12034018 and 11625419).
文摘Reducing the control error is vital for high-fidelity digital and analog quantum operations.In superconducting circuits,one disagreeable error arises from the reflection of microwave signals due to impedance mismatch in the control chain.Here,we demonstrate a reflection cancelation method when considering that there are two reflection nodes on the control line.We propose to generate the pre-distortion pulse by passing the envelopes of the microwave signal through digital filters,which enables real-time reflection correction when integrated into the field-programmable gate array(FPGA).We achieve a reduction of single-qubit gate infidelity from 0.67%to 0.11%after eliminating microwave reflection.Real-time correction of microwave reflection paves the way for precise control and manipulation of the qubit state and would ultimately enhance the performance of algorithms and simulations executed on quantum processors.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 12074368, 92165207, 12034018 and 92265113)the Anhui Province Natural Science Foundation (Grant No. 2108085J03)。
文摘The presence of anticrossings induced by coupling between two states causes curvature in energy levels, yielding a nonlinearity in the quantum system. When the system is driven back and forth along the bending energy levels, subharmonic transitions and energy shifts can be observed, which would cause a significant influence as the system is applied to quantum computing. In this paper, we study a longitudinally driven singlet-triplet(ST) system in a double quantum dot(DQD)system, and illustrate the consequences of nonlinearity by driving the system close to the anticrossings. We provide a straightforward theory to quantitatively describe the energy shift and subharmonics caused by nonlinearity, and find good agreement between our theoretical result and the numerical simulation. Our results reveal the existence of nonlinearity in the vicinity of anticrossings and provide a direct way of analytically assessing its impact, which can be applied to other quantum systems without excessive labor.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.12074368,92165207,12034018,and 62004185)the Anhui Province Natural Science Foundation (Grant No.2108085J03)the USTC Tang Scholarship。
文摘The single-shot readout data process is essential for the realization of high-fidelity qubits and fault-tolerant quantum algorithms in semiconductor quantum dots. However, the fidelity and visibility of the readout process are sensitive to the choice of the thresholds and limited by the experimental hardware. By demonstrating the linear dependence between the measured spin state probabilities and readout visibilities along with dark counts, we describe an alternative threshold-independent method for the single-shot readout of spin qubits in semiconductor quantum dots. We can obtain the extrapolated spin state probabilities of the prepared probabilities of the excited spin state through the threshold-independent method. We then analyze the corresponding errors of the method, finding that errors of the extrapolated probabilities cannot be neglected with no constraints on the readout time and threshold voltage. Therefore, by limiting the readout time and threshold voltage, we ensure the accuracy of the extrapolated probability. We then prove that the efficiency and robustness of this method are 60 times larger than those of the most commonly used method. Moreover, we discuss the influence of the electron temperature on the effective area with a fixed external magnetic field and provide a preliminary demonstration for a single-shot readout of up to 0.7K/1.5T in the future.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 12074368, 92165207, 12034018, and 92265113)the Innovation Program for Quantum Science and Technology (Grant No. 2021ZD0302300)+1 种基金the Anhui Province Natural Science Foundation (Grant No. 2108085J03)the USTC Tang Scholarship。
文摘Valley, the intrinsic feature of silicon, is an inescapable subject in silicon-based quantum computing. At the spin–valley hotspot, both Rabi frequency and state relaxation rate are significantly enhanced. With protection against charge noise, the valley degree of freedom is also conceived to encode a qubit to realize noise-resistant quantum computing.Here, based on the spin qubit composed of one or three electrons, we characterize the intrinsic properties of valley in an isotopically enriched silicon quantum dot(QD) device. For one-electron qubit, we measure two electric-dipole spin resonance(EDSR) signals which are attributed to partial occupation of two valley states. The resonance frequencies of two EDSR signals have opposite electric field dependences. Moreover, we characterize the electric field dependence of the upper valley state based on three-electron qubit experiments. The difference of electric field dependences of the two valleys is 52.02 MHz/V, which is beneficial for tuning qubit frequency to meet different experimental requirements. As an extension of electrical control spin qubits, the opposite electric field dependence is crucial for qubit addressability,individual single-qubit control and two-qubit gate approaches in scalable quantum computing.
基金supported by the Natural Science Foundation of Jiangsu Province(Grant No.BK20240123)the National Key Research and Development Program of China(Grant No.2022YFA1405900)the National Natural Science Foundation of China(Grant Nos.12274397,12274401,and 12034018)。
文摘The excellent mechanical properties make graphene promising for realizing nanomechanical resonators with high resonant frequencies,large quality factors,strong nonlinearities,and the capability to efectively interface with various physical systems.Equipped with gate electrodes,it has been demonstrated that these exceptional device properties can be electrically manipulated,leading to a variety of nanomechanical/acoustic applications.Here,we review the recent progress of graphene nanomechanical resonators with a focus on their electrical tunability.First,we provide an overview of diferent graphene nanomechanical resonators,including their device structures,fabrication methods,and measurement setups.Then,the key mechanical properties of these devices,for example,resonant frequencies,nonlinearities,dissipations,and mode coupling mechanisms,are discussed,with their behaviors upon electrical gating being highlighted.After that,various potential classical/quantum applications based on these graphene nanomechanical resonators are reviewed.Finally,we briefy discuss challenges and opportunities in this feld to ofer future prospects for the ongoing studies on graphene nanomechanical resonators.
基金Project supported by the Natural Science Foundation of Jiangsu Province(Grant No.BK20240123)the National Key Research and Development Program of China(Grant No.2022YFA1405900)the National Natural Science Foundation of China(Grant Nos.12274397,12274401,and 12034018)。
文摘Applying a perpendicular electric field to bilayer graphene(BLG)induces an electrically tunable bandgap,so that insulating states with resistances exceeding~10^(8)Ωcan be generated.These high-resistance states pinch off the conducting channel,thereby enabling high-quality gated devices for classical and quantum electronics.However,it is challenging to precisely quantify these states electrically due to their high resistances,especially when different areas of the device are operated in different high-resistance states.Here,taking advantage of the strong acoustoelectric effect,we demonstrate the detection of these high-resistance states in a multi-gated BLG device using surface acoustic waves.Under different gating configurations,the device is operated in different high-resistance states.Although these states have similar resistances of~10^(8)Ω,we show their acoustoelectric responses exhibit pronounced differences,thereby allowing the acoustic detection.More interestingly,we demonstrate that when the conducting channel is pinched off by one top gate,we are still able to acoustically,but not electrically,detect the gating effect of another top gate.Our results reveal the powerful capability and the promising future of acoustically characterizing BLG and other two-dimensional materials,especially their electronic states with high resistances.
基金supported by the National Natural Science Foundation of China(Grant Nos.12304560,92265113,12074368,and 12034018)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302300)China Postdoctoral Science Foundation(Grant Nos.BX20220281 and 2023M733408).
文摘Geometric phase gates have attracted considerable attention due to their intrinsic robustness against certain types of noise.Significant progress has been achieved in implementing geometric phase gates using microwave control in siliconbased electron spin systems.In this work,we propose an alternative geometric phase gate protocol that differs fundamentally from microwave driving approaches by leveraging square-wave control of rapidly switchable micromagnets driven by spin-orbit torque(SOT)to achieve fast and precise magnetic field modulation.By employing square-wave currents to control magnetization switching,our approach relaxes the requirements on waveform precision while significantly suppressing crosstalk.Moreover,our scheme inherently preserves trajectory closure at the end of each operation,effectively mitigating noise-induced path deviation and enhancing gate robustness even under strong noise conditions,thereby offering a promising pathway toward efficient and reliable quantum operations in large-scale qubit arrays.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.92265113,12034018,12474490,and 62404248)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302300)。
文摘Strained germanium hole spin qubits are promising for quantum computing,but the devices hosting these qubits face challenges from high interface trap density,which originates from the naturally oxidized surface of the wafer.These traps can degrade the device stability and cause an excessively high threshold voltage.Surface passivation is regarded as an effective method to mitigate these impacts.In this study,we perform low-thermal-budget chemical passivation using the nitric acid oxidation of silicon method on the surface of strained germanium devices and investigate the impact of passivation on the device stability.The results demonstrate that surface passivation effectively reduces the interface defect density.This not only improves the stability of the device's threshold voltage but also enhances its long-term static stability.Furthermore,we construct a band diagram of hole surface tunneling at the static operating point to gain a deeper understanding of the physical mechanism through which passivation affects the device stability.This study provides valuable insights for future optimization of strained Ge-based quantum devices and advances our understanding of how interface states affect device stability.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12074368,92165207,12474490,12034018,and 92265113)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302300)+1 种基金the USTC Tang Scholarshippartially carried out at the USTC Center for Micro and Nanoscale Research and Fabrication。
文摘In semiconductor quantum dot systems,pulse distortion is a significant source of coherent errors,which impedes qubit characterization and control.Here,we demonstrate two calibration methods using a two-qubit system as the detector to correct distortion and calibrate the transfer function of the control line.Both methods are straightforward to implement,robust against noise,and applicable to a wide range of qubit types.The two methods differ in correction accuracy and complexity.The first,coarse predistortion(CPD)method,partially mitigates distortion.The second,all predistortion(APD)method,measures the transfer function and significantly enhances exchange oscillation uniformity.Both methods use exchange oscillation homogeneity as the metric and are suitable for any qubit driven by a diabatic pulse.We believe these methods will enhance qubit characterization accuracy and operation quality in future applications.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.92265113,12074368,and 12034018)the USTC Tang Scholarship。
文摘Hybrid qubits enable the hybridization of charge and spin degrees of freedom,which provides a way to realize both a relatively long coherence time and rapid qubit manipulation.Here,we use microwave driving to demonstrate the coherent operation of a tunable hybrid qubit,including X-rotation,Z-rotation,and rotation around an arbitrary axis in the X-Y panel of the Bloch sphere.Moreover,the coherence properties of the qubit and its tunability are studied.The measured coherence time of the X-rotation reaches~14.3 ns.While for the Z-rotation,the maximum decoherence time is~5.8 ns due to the larger sensitivity to noise.By employing the Hahn echo sequence to mitigate the influence of the low-frequency noise,we have improved the qubit coherence time from~5.8 ns to~15.0 ns.Our results contribute to a further understanding of the hybrid qubit and a step towards achieving high-fidelity qubit gates in the hybrid qubit.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFA0301700)the National Natural Science Foundation of China(Grant Nos.61922074,11674300,61674132,11625419,and 11804327)+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB24030601)the Anhui Initiative in Quantum Information Technologies,China(Grant No.AHY080000)。
文摘Conerent photon source is an important element that has been widely used in spectroscopy,imaging,detection,and teleportation in quantum optics.However,it is still a challenge to realize micro-scale coherent emitters in semiconductor systems.We report the observation of gain in a cavity-coupled GaAs double quantum dot system with a voltage bias across the device.By characterizing and analyzing the cavity responses to different quantum dot behaviors,we distinguish the microwave photon emission from the signal gain.This study provides a possibility to realize micro-scale amplifiers or coherent microwave photon sources in circuit quantum electrodynamics(cQED) hybrid systems.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 12034018 and 11625419)。
文摘In quantum computation and quantum information processing, the manipulation and engineering of quantum systems to suit certain purposes are an ongoing task. One such example is quantum state transfer(QST), an essential requirement for both quantum communication and large-scale quantum computation. Here we engineer a chain of four superconducting qubits with tunable couplers to realize the perfect state transfer(PST) protocol originally proposed in quantum spin networks and successfully demonstrate the efficient transfer of an arbitrary single-qubit state from one end of the chain to the other,achieving a high fidelity of 0.986 in just 25 ns. This demonstrated QST is readily to extend to larger chain and multi-node configurations, thus serving as a desirable tool for scalable quantum information processing.
基金supported by the National Key Research and Development Program of China(Grant No.2023YFB4502500)the National Natural Science Foundation of China(Grant No.12404564)Anhui Province Science and Technology Innovation(Grant No.202423s06050001)。
文摘Nonlinear partial differential equations(PDEs)are crucial for modeling complex fluid dynamics and are foundational to many computational fluid dynamics(CFD)applications.However,solving these nonlinear PDEs is challenging due to the vast computational resources they demand,highlighting the pressing need for more efficient computational methods.Quantum computing offers a promising but technically challenging approach to solving nonlinear PDEs.Recently,Liao[arXiv:2406.15821]proposed a framework that leverages quantum computing to accelerate the solution of nonlinear PDEs based on the homotopy analysis method(HAM),a semi-analytical technique that transforms nonlinear PDEs into a series of linear PDEs.However,the no-cloning theorem in quantum computing poses a major limitation,where directly applying quantum simulation to each HAM step results in exponential complexity growth with the HAM truncation order.This study introduces a“quantum-compatible linearization”approach that maps the whole HAM process into a system of linear PDEs,allowing for a one-time solution using established quantum PDE solvers.Our method preserves the exponential speedup of quantum linear PDE solvers while ensuring that computational complexity increases only polynomially with the HAM truncation order.We demonstrate the efficacy of our approach by applying it to the Burgers'equation and the Korteweg-de Vries(KdV)equation.Our approach provides a novel pathway for transforming nonlinear PDEs into linear PDEs,with potential applications to fluid dynamics.This work thus lays the foundation for developing quantum algorithms capable of solving the Navier-Stokes equations,ultimately offering a promising route to accelerate their solutions using quantum computing.
基金supported by the National Key Research and Development Program of China(2016YFA0301700)the National Natural Science Foundation of China(11625419)+1 种基金the Anhui Initiative in Quantum Information Technologies(AHY080000)supported by Yangzi Cloud Computing Data Centre and Gyrotech,Nanjing,China
文摘Classical simulations of quantum circuits are limited in both space and time when the qubit count is above 50, the realm where quantum supremacy reigns. However, recently, for the low depth circuit with more than 50 qubits, there are several methods of simulation proposed by teams at Google and IBM. Here,we present a scheme of simulation which can extract a large amount of measurement outcomes within a short time, achieving a 64-qubit simulation of a universal random circuit of depth 22 using a 128-node cluster, and 56-and 42-qubit circuits on a single PC. We also estimate that a 72-qubit circuit of depth 23 can be simulated in about 16 h on a supercomputer identical to that used by the IBM team. Moreover, the simulation processes are exceedingly separable, hence parallelizable, involving just a few inter-process communications. Our work enables simulating more qubits with less hardware burden and provides a new perspective for classical simulations.
基金supported by the National Natural Science Foundation of China(41930647 and 62001260)the Strategic Priority Research Program(A)of the Chinese Academy of Sciences(XDA20030203)。
文摘The computer advances of the past century can be traced to the increase in their numbers on chips that has accompanied the miniaturization of transistors.However,computers are nearing the fundamental limits of such miniaturization[1].Many practical problems require huge amounts of computational resources that exceed the capabilities of today's computers.A 54-qubit quantum computer on the other hand can solve in minutes a problem that would take a classical machine 10,000 years[2].
基金supported by the National Key Research and Development Program of China(Grant No.2016YFA0301700)the National Natural Science Foundation of China(Grant Nos.61922074,12074368,and12034018)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302300)。
文摘In a circuit quantum electrodynamics(circuit QED) architecture, the microwave resonator could be used to couple and probe qubits. The long-range coupling and information transfer between nonlocal qubits can be performed via photons trapped in a microwave resonator, promising an effective approach for scaling up solid-state qubits. A series of important advances in the hybrid system composed of a microwave resonator and semiconductor qubits have been achieved in recent years. For instance,with applications of high-impedance microwave resonators, the strong coupling regime between charge/spin qubits and a microwave resonator has been reached. Simultaneously, resonator-based dispersive readout and single-shot readout to probe the qubit state have been further improved due to the increase of the coupling strength. Here, we briefly introduce this hybrid system related to the progress and fruits in achieving the strong coupling between charge/spin qubits in double quantum dots(DQDs)and the resonator, the long-range coupling between qubits, and also the applications of the resonator for qubit state readout.
