Since the first laser was invented,the pursuit of high-energy lasers(HELs)has always been enthusiastic.The first revolution of HELs was pushed by the fusion of laser and aerospace in the 1960s,with the chemical rocket...Since the first laser was invented,the pursuit of high-energy lasers(HELs)has always been enthusiastic.The first revolution of HELs was pushed by the fusion of laser and aerospace in the 1960s,with the chemical rocket engines giving fresh impetus to the birth of gas flow and chemical lasers,which finally turned megawatt lasers from dream into reality.Nowadays,the development of HELs has entered the age of electricity as well as the rocket engines.The properties of current electric rocket engines are highly consistent with HELs’goals,including electrical driving,effective heat dissipation,little medium consumption and extremely light weight and size,which inspired a second fusion of laser and aerospace and motivated the exploration for potential HELs.As an exploratory attempt,a new configuration of diode pumped metastable rare gas laser was demonstrated,with the gain generator resembling an electric rocket-engine for improved power scaling ability.展开更多
We demonstrate a simple and fast way to produce 87Rb Bose–Einstein condensates. A digital optical phase lock loop(OPLL) board is introduced to lock and adjust the frequency of the trap laser, which simplifies the opt...We demonstrate a simple and fast way to produce 87Rb Bose–Einstein condensates. A digital optical phase lock loop(OPLL) board is introduced to lock and adjust the frequency of the trap laser, which simplifies the optical design and improves the experimental efficiency. We collect atoms in a magneto-optical trap, then compress the cloud and cut off hot atoms by rf knife in a magnetic quadrupole trap. The atom clouds are then transferred into a spatially mode-matched optical dipole trap by lowering the quadrupole field gradient. Our system reliably produces a condensate with 2 × 106 atoms every7.5 s. The compact optical design and rapid preparation speed of our system will open the gate for mobile quantum sensing.展开更多
To explore the influence of quantum information on the common social problem of honesty and trickery,we propose a Bayesian model for the quantum prisoners’dilemma game.In this model,the players’strategy formation is...To explore the influence of quantum information on the common social problem of honesty and trickery,we propose a Bayesian model for the quantum prisoners’dilemma game.In this model,the players’strategy formation is regarded as a negotiation of their move contract based on their types of decision policies,honesty or trickery.Although the implementation of quantum information cannot eliminate tricky players,players in our model can always end up with higher payoffs than in the classical game.For a good proportion of a credibility parameter value,a rational player will take an honest action,which is in remarkable contrast to the observation that players tend to defect in the classical prisoners’dilemma game.This research suggests that honesty will be promoted to enhance cooperation with the assistance of quantum information resources.展开更多
The dynamical decoupling(DD) method is widely adopted to preserve coherence in different quantum systems. In the case of ideal pulses, its effects on the suppression of noise can be analytically described by the mathe...The dynamical decoupling(DD) method is widely adopted to preserve coherence in different quantum systems. In the case of ideal pulses, its effects on the suppression of noise can be analytically described by the mathematical form of filter function. However, in practical experiments, the unavoidable pulse errors limit the efficiency of DD. In this paper,we study the effects of imperfect pulses on DD efficiency based on quantum trajectories. By directly generating a pseudo noise sequence correlated in time, we can explore the performance of DD with different pulse errors in the typical noise environment. It shows that, for the typical 1/f noise environment, the phase error of operational pulses severely affects the performance of noise suppression, while the detuning and intensity errors have less influence. Also, we get the thresholds of these errors for efficient DD under the given experimental conditions. Our method can be widely applied to guide practical DD experimental implementation.展开更多
Alkali-metal atomic magnetometers employing longitudinal carrier magnetic field have ultrahigh sensitivity to measure transverse magnetic fields and have been applied in a variety of precise-measurement science and te...Alkali-metal atomic magnetometers employing longitudinal carrier magnetic field have ultrahigh sensitivity to measure transverse magnetic fields and have been applied in a variety of precise-measurement science and technologies.In practice,the magnetometer response is not rigorously proportional to the measured transverse magnetic fields and the existing fundamental analytical model of this magnetometer is effective only when the amplitudes of the measured fields are very small.In this paper,we present a modified analytical model to characterize the practical performance of the magnetometer more definitely.We find out how the longitudinal magnetization of the alkali metal atoms vary with larger transverse fields.The linear-response capacity of the magnetometer is determined by these factors:the amplitude and frequency of the longitudinal carrier field,longitudinal and transverse spin relaxation time of the alkali spins and rotation frequency of the transverse fields.We give a detailed and rigorous theoretical derivation by using the perturbation-iteration method and simulation experiments are conducted to verify the validity and correctness of the proposed modified model.This model can be helpful for measuring larger fields more accurately and configuring a desirable magnetometer with proper linear range.展开更多
A typical magnetic-resonance scheme employs a static bias magnetic field and an orthogonal driving magnetic field oscillating at the Larmor frequency, at which the atomic polarization precesses around the static magne...A typical magnetic-resonance scheme employs a static bias magnetic field and an orthogonal driving magnetic field oscillating at the Larmor frequency, at which the atomic polarization precesses around the static magnetic field. Here we demonstrate both theoretically and experimentally the variations of the resonance condition and the spin precession dynamics resulting from the parametric modulation of the bias field. We show that the driving magnetic field with the frequency detuned by different harmonics of the parametric modulation frequency can lead to resonance as well. Also, a series of frequency sidebands centered at the driving frequency and spaced by the parametric modulation frequency can be observed in the precession of the atomic polarization. We further show that the resonant amplitudes of the sidebands can be controlled by varying the ratio between the amplitude and the frequency of the parametric modulation. These effects could be used in different atomic magnetometry applications.展开更多
Calculating the spatial structures of ion crystals is important in ion-trapped quantum computation. Here we demon- strate that the simulated annealing method is a powerful tool to evaluate the structures of ion crysta...Calculating the spatial structures of ion crystals is important in ion-trapped quantum computation. Here we demon- strate that the simulated annealing method is a powerful tool to evaluate the structures of ion crystals. By calculating equilibrium positions of 10 ions under harmonic potential and those of 120 ions under anharmonic potential, both with the standard procedure and simulated annealing method, we find that the standard procedure to evaluate spatial structures is complicated and may be inefficient in some cases, and that the simulated annealing method is more favorable.展开更多
In this paper,we explore how to estimate the phase damping parameter γ and the tunneling amplitude parameter ?from a spin-boson dephasing quantum model by periodical projective measurements.The preparation of initia...In this paper,we explore how to estimate the phase damping parameter γ and the tunneling amplitude parameter ?from a spin-boson dephasing quantum model by periodical projective measurements.The preparation of initial states is accomplished by performing the period measurements in our scheme.The parameter γ can be always estimated when projective measurement bases are chosen as θ = π/2 and φ = 0.Based on the estimated value of γ and the interval information of ?,we can select another measurement bases(θ = π/4 and φ = π/2) to obtain the estimated value of ?.A coherent control is indispensable to estimate ? if γ is in the interval of ?;whereas the control is not necessary if γ is out of the known interval of ?.We establish the relation between the optimal period time and the parameter γ or ? in terms of Fisher information.Although the optimal measurement period cannot be selected beforehand,the aforementioned relation can be utilized to adjust the measurement period to approach the optimal one.展开更多
The properties of the system near the instability boundary are very sensitive to external disturbances, which is important for amplifying some physical effects or improving the sensing accuracy. In this paper, the qua...The properties of the system near the instability boundary are very sensitive to external disturbances, which is important for amplifying some physical effects or improving the sensing accuracy. In this paper, the quantum properties near the instability boundary in a simple optomechanical system have been studied by numerical simulation. Calculations show that the transitional region connecting the Gaussian states and the ring states when crossing the boundary is sometimes different from the region centered on the boundary line, but it is more essential. The change of the mechanical Wigner function in the transitional region directly reflects its bifurcation behavior in classical dynamics. Besides, quantum properties, such as mechanical second-order coherence function and optomechanical entanglement, can be used to judge the corresponding bifurcation types and estimate the parameter width and position of the transitional region. The non-Gaussian transitional states exhibit strong entanglement robustness, and the transitional region as a boundary ribbon can be expected to replace the original classical instability boundary line in future applications.展开更多
We develop a simple and practical scheme to apply sideband cooling to a cloud of rubidium atoms. A sample containing 4 × 10^(70) ^(87)Rb is trapped in a far red detuned optical lattice. Through optimizing the...We develop a simple and practical scheme to apply sideband cooling to a cloud of rubidium atoms. A sample containing 4 × 10^(70) ^(87)Rb is trapped in a far red detuned optical lattice. Through optimizing the relevant parameters, i.e., laser detuning, magnetic field, polarization, and duration time, a temperature around 1.5 μK and phase space density close to 1/500 are achieved. Compared with polarization gradient cooling, the temperature decreases by around one order of magnitude. This technique could be used in high precision measurement such as atomic clocks and atom interferometer. It could also serve as a precooling means before evaporation cooling in a dipole trap, and may be a promising method of achieving quantum degeneracy with purely optical means.展开更多
In quantum mechanics, the expectation value of an operator can be measured by using the projective measurement, ifthe coupling between the measured system and pointer is strong enough. However in the weak coupling reg...In quantum mechanics, the expectation value of an operator can be measured by using the projective measurement, ifthe coupling between the measured system and pointer is strong enough. However in the weak coupling regime, the pointercan not show all the eigenvalue of the physical quantity directly due to the overlapping among the pointer states, whichmakes the measurement of the expectation value difficult. In this paper, we propose an expectation value measurementmethod in the weak coupling regime inspired by the weak measurement scheme. Compared to the projective measurement,our scheme has two obvious advantages. Experimentally we use the internal state and motional state of a single trapped40Ca+ to establish the measurement scheme and realize the proof of principle demonstration of the scheme.展开更多
A dip of the transverse component of the magnetic moment as a function of resonance frequency-detuning will emerge when the intensity of oscillating magnetic field exceeds a specific value, which is demonstrated theor...A dip of the transverse component of the magnetic moment as a function of resonance frequency-detuning will emerge when the intensity of oscillating magnetic field exceeds a specific value, which is demonstrated theoretically and experimentally. The linewidth of magnetic-resonance signal can be much smaller than when the Mx–MR magnetometer operates on condition that the intensity of oscillating magnetic field is smaller than this specific value, and the Mx–MR magnetometer can possess a much higher signal-to-noise ratio. The experimental result shows that the sensitivity of Mx–MR magnetometer can be improved by an order of magnitude under this condition.展开更多
We explore the impact of distributional fairness degree and entanglement degree on the cooperation between different players by investigating a modified prisoner's dilemma game. We not only introduce a new concept of...We explore the impact of distributional fairness degree and entanglement degree on the cooperation between different players by investigating a modified prisoner's dilemma game. We not only introduce a new concept of distributional fairness degree, but also obtain the cooperation conditions for overcoming dilemma in terms of fairness and entanglement inequalities. It is demonstrated that distributional fairness can be of fundamental importance to promote cooperation with the help of quantum entanglement.展开更多
We present a compact and practical scheme of building a ~780 nm external cavity diode laser(ECDL) whose wavelength is mainly determined by an interference filter. The Lorentzian linewidth measured by the heterodyne be...We present a compact and practical scheme of building a ~780 nm external cavity diode laser(ECDL) whose wavelength is mainly determined by an interference filter. The Lorentzian linewidth measured by the heterodyne beating between two identical lasers is 60 k Hz, and the geometry size of the laser is only 71.5 mm×65 mm×40 mm. The linear cavity design is less sensitive to misalignment induced by mechanical and thermal disturbances, and in comparison to a common grating-based design, the sensitivity to vibration is substantially reduced. Due to its excellent performance, the laser design has already been applied to cold atom trapping experiments. This interference filter ECDL method can also be extended to other wavelengths and widen the application range of diode laser.展开更多
The recent advances of atom interferometer and its application in precision inertial measurement are review ed. The principle,characteristics and implementation of atom interferometer are introduced and it can be used...The recent advances of atom interferometer and its application in precision inertial measurement are review ed. The principle,characteristics and implementation of atom interferometer are introduced and it can be used to measure gravitational acceleration,gravity gradient and rotation for its high sensitivity. We also present the principle,structure and new progress of gravimeter,gravity gradiometer and gyroscope based on atom interferometer.展开更多
Symmetry,including the parity-time(PT)-symmetry,is a striking topic,widely discussed and employed in many fields.It is well-known that quantum measurement can destroy or disturb quantum systems.However,can and how doe...Symmetry,including the parity-time(PT)-symmetry,is a striking topic,widely discussed and employed in many fields.It is well-known that quantum measurement can destroy or disturb quantum systems.However,can and how does quantum measurement destroy the symmetry of the measured system?To answer the pertinent question,we establish the correlation between the quan-tum measurement and Floquet PT-symmetry and investigate for the first time how the measurement frequency and measurement strength affect the PT-symmetry of the measured system using the 40Ca+ion.It is already shown that the measurement at high frequencies would break the PT symmetry.Notably,even for an inadequately fast measurement frequency,if the measurement strength is sufficiently strong,the PT symmetry breaking can occur.The current work can enhance our knowledge of quantum measurement and symmetry and may inspire further research on the effect of quantum measurement on symmetry.展开更多
In order to understand our previous numerical finding that steady-state entanglement along the instability boundary remains unchanged in a three-mode optomechanical system[Phys.Rev.A 101023838(2020)],we investigate in...In order to understand our previous numerical finding that steady-state entanglement along the instability boundary remains unchanged in a three-mode optomechanical system[Phys.Rev.A 101023838(2020)],we investigate in detail the boundary entanglement in a simpler two-mode optomechanical system.Studies show that both the mechanism to generate entanglement and the parameter dependence of boundary entanglement are quite similar in these two models.Therefore,the two-mode system has captured the main features in the three-mode system.With the help of analytical calculations and discussing in a much bigger parameter interval,we find that the unchanging behavior previously discovered is actually an extremely slow changing behavior of the boundary entanglement function,and most importantly,this nearly invariant boundary entanglement is a general phenomenon via parametric down conversion process in the weak dissipation regime.This is by itself interesting as threshold quantum signatures in optomechanical phonon lasers,or may have potential value in related applications based on boundary quantum properties.展开更多
This paper presents a new type of cold atom interferometry gravimeter based on Bragg diffraction,w hich is able to increase the gravity m easurem ent sensitivity and stability of com m on Ram an atom gravim eters sign...This paper presents a new type of cold atom interferometry gravimeter based on Bragg diffraction,w hich is able to increase the gravity m easurem ent sensitivity and stability of com m on Ram an atom gravim eters significantly. By com paring w ith Ram an transition,the principles and advantages of Bragg diffraction-based atom gravim eters have been introduced. The theoretical m odel for a tim e-dom ain Bragg atom gravim eter has been constructed. Som e key technical requirem ents for an n-order Bragg diffraction-based atom gravim eter have been deduced,including the tem perature of atom cloud,the diam eter,curvature radius,frequency,intensity,and tim ing sequence of Bragg lasers,etc. The analysis results are verified by the existing experim ental data in discussion. The present study provides a good reference for the understanding and construction of a Bragg atom gravim eter.展开更多
We present a compact, low-noise, and inexpensive optical phase-lock loop (OPLL) system to synchronize the frequency and the phase between two external cavity diode lasers. Based on a direct digital synthesizer tech-...We present a compact, low-noise, and inexpensive optical phase-lock loop (OPLL) system to synchronize the frequency and the phase between two external cavity diode lasers. Based on a direct digital synthesizer tech- nique, a programmable radio-frequency generator is implemented as the reference signal source. The OPLL has a narrow beat note linewidth below 1 Hz and a residual mean-square phase error of 0.06 rad2 in a 10 MHz integration bandwidth. The experimental test results prove the competent performance of the system, which is promising as a low-budget choice in atomic physics applications.展开更多
In this paper we report the optimal design and fabrication of a gold-on-silica linear segmented surface-electrode ion trap. By optimizing the thickness and width of the electrodes, we improved the trapping ability and...In this paper we report the optimal design and fabrication of a gold-on-silica linear segmented surface-electrode ion trap. By optimizing the thickness and width of the electrodes, we improved the trapping ability and trap scalability. By using some practical experimental operation methods, we successfully minimized the trap heating rate. Consequently, we could trap a string of up to 38 ions, and a zigzag structure with 24 ions, and transport two trapped ions to different zones. We also studied the influences of the ion chip surface on the ion lifetime. The excellent trapping ability and flexibility of operation of the planar ion trap shows that it has high feasibility for application in the development a practical quantum information processor or quantum simulator.展开更多
文摘Since the first laser was invented,the pursuit of high-energy lasers(HELs)has always been enthusiastic.The first revolution of HELs was pushed by the fusion of laser and aerospace in the 1960s,with the chemical rocket engines giving fresh impetus to the birth of gas flow and chemical lasers,which finally turned megawatt lasers from dream into reality.Nowadays,the development of HELs has entered the age of electricity as well as the rocket engines.The properties of current electric rocket engines are highly consistent with HELs’goals,including electrical driving,effective heat dissipation,little medium consumption and extremely light weight and size,which inspired a second fusion of laser and aerospace and motivated the exploration for potential HELs.As an exploratory attempt,a new configuration of diode pumped metastable rare gas laser was demonstrated,with the gain generator resembling an electric rocket-engine for improved power scaling ability.
基金National Natural Science Foundation of China(Grant No.51275523)and the State Key Laboratory of Aerodynamics Research Fund,China(Grant No.SKLA2019040302).
文摘We demonstrate a simple and fast way to produce 87Rb Bose–Einstein condensates. A digital optical phase lock loop(OPLL) board is introduced to lock and adjust the frequency of the trap laser, which simplifies the optical design and improves the experimental efficiency. We collect atoms in a magneto-optical trap, then compress the cloud and cut off hot atoms by rf knife in a magnetic quadrupole trap. The atom clouds are then transferred into a spatially mode-matched optical dipole trap by lowering the quadrupole field gradient. Our system reliably produces a condensate with 2 × 106 atoms every7.5 s. The compact optical design and rapid preparation speed of our system will open the gate for mobile quantum sensing.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61773399,61673389,and 61273202)the Special Funded Project of China Postdoctoral Science Foundation(Grant No.2017T100792).
文摘To explore the influence of quantum information on the common social problem of honesty and trickery,we propose a Bayesian model for the quantum prisoners’dilemma game.In this model,the players’strategy formation is regarded as a negotiation of their move contract based on their types of decision policies,honesty or trickery.Although the implementation of quantum information cannot eliminate tricky players,players in our model can always end up with higher payoffs than in the classical game.For a good proportion of a credibility parameter value,a rational player will take an honest action,which is in remarkable contrast to the observation that players tend to defect in the classical prisoners’dilemma game.This research suggests that honesty will be promoted to enhance cooperation with the assistance of quantum information resources.
基金Project supported by the National Basic Research Program of China(Grant No.2016YFA0301903)the National Natural Science Foundation of China(Grant Nos.11174370,11304387,61632021,11305262,and 61205108)the Research Plan Project of the National University of Defense Technology(Grant No.ZK16-03-04)
文摘The dynamical decoupling(DD) method is widely adopted to preserve coherence in different quantum systems. In the case of ideal pulses, its effects on the suppression of noise can be analytically described by the mathematical form of filter function. However, in practical experiments, the unavoidable pulse errors limit the efficiency of DD. In this paper,we study the effects of imperfect pulses on DD efficiency based on quantum trajectories. By directly generating a pseudo noise sequence correlated in time, we can explore the performance of DD with different pulse errors in the typical noise environment. It shows that, for the typical 1/f noise environment, the phase error of operational pulses severely affects the performance of noise suppression, while the detuning and intensity errors have less influence. Also, we get the thresholds of these errors for efficient DD under the given experimental conditions. Our method can be widely applied to guide practical DD experimental implementation.
基金the Hunan Graduate Research and Innovation Project(Grant No.CX2018B009)the Natural Science Foundation of Hunan(Grant No.2018JJ3608)+1 种基金the Research Project of National University of Defense Technology(Grant Nos.ZK170204 and ZZKY-YX-07-02)the National Natural Science Foundation of China(Grant Nos.61671458 and 61701515).
文摘Alkali-metal atomic magnetometers employing longitudinal carrier magnetic field have ultrahigh sensitivity to measure transverse magnetic fields and have been applied in a variety of precise-measurement science and technologies.In practice,the magnetometer response is not rigorously proportional to the measured transverse magnetic fields and the existing fundamental analytical model of this magnetometer is effective only when the amplitudes of the measured fields are very small.In this paper,we present a modified analytical model to characterize the practical performance of the magnetometer more definitely.We find out how the longitudinal magnetization of the alkali metal atoms vary with larger transverse fields.The linear-response capacity of the magnetometer is determined by these factors:the amplitude and frequency of the longitudinal carrier field,longitudinal and transverse spin relaxation time of the alkali spins and rotation frequency of the transverse fields.We give a detailed and rigorous theoretical derivation by using the perturbation-iteration method and simulation experiments are conducted to verify the validity and correctness of the proposed modified model.This model can be helpful for measuring larger fields more accurately and configuring a desirable magnetometer with proper linear range.
基金Project supported by the National Science Fund for Distinguished Young Scholars of China(Grant No.61225003)the National Natural Science Foundation of China(Grant Nos.61531003 and 61571018)the National High Technology Research and Development Program of China
文摘A typical magnetic-resonance scheme employs a static bias magnetic field and an orthogonal driving magnetic field oscillating at the Larmor frequency, at which the atomic polarization precesses around the static magnetic field. Here we demonstrate both theoretically and experimentally the variations of the resonance condition and the spin precession dynamics resulting from the parametric modulation of the bias field. We show that the driving magnetic field with the frequency detuned by different harmonics of the parametric modulation frequency can lead to resonance as well. Also, a series of frequency sidebands centered at the driving frequency and spaced by the parametric modulation frequency can be observed in the precession of the atomic polarization. We further show that the resonant amplitudes of the sidebands can be controlled by varying the ratio between the amplitude and the frequency of the parametric modulation. These effects could be used in different atomic magnetometry applications.
基金supported by the National Basic Research Program of China(Grant No.2016YFA0301903)the National Natural Science Foundation of China(Grant Nos.11304387,11174370,61632021,61205108,and 11305262)the Research Plan Project of National University of Defense Technology(Grant No.ZK16-03-04)
文摘Calculating the spatial structures of ion crystals is important in ion-trapped quantum computation. Here we demon- strate that the simulated annealing method is a powerful tool to evaluate the structures of ion crystals. By calculating equilibrium positions of 10 ions under harmonic potential and those of 120 ions under anharmonic potential, both with the standard procedure and simulated annealing method, we find that the standard procedure to evaluate spatial structures is complicated and may be inefficient in some cases, and that the simulated annealing method is more favorable.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61673389,61273202,and 61134008)
文摘In this paper,we explore how to estimate the phase damping parameter γ and the tunneling amplitude parameter ?from a spin-boson dephasing quantum model by periodical projective measurements.The preparation of initial states is accomplished by performing the period measurements in our scheme.The parameter γ can be always estimated when projective measurement bases are chosen as θ = π/2 and φ = 0.Based on the estimated value of γ and the interval information of ?,we can select another measurement bases(θ = π/4 and φ = π/2) to obtain the estimated value of ?.A coherent control is indispensable to estimate ? if γ is in the interval of ?;whereas the control is not necessary if γ is out of the known interval of ?.We establish the relation between the optimal period time and the parameter γ or ? in terms of Fisher information.Although the optimal measurement period cannot be selected beforehand,the aforementioned relation can be utilized to adjust the measurement period to approach the optimal one.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11574398, 12174448, 12174447, 11904402, 12074433, 11871472, and 12004430)。
文摘The properties of the system near the instability boundary are very sensitive to external disturbances, which is important for amplifying some physical effects or improving the sensing accuracy. In this paper, the quantum properties near the instability boundary in a simple optomechanical system have been studied by numerical simulation. Calculations show that the transitional region connecting the Gaussian states and the ring states when crossing the boundary is sometimes different from the region centered on the boundary line, but it is more essential. The change of the mechanical Wigner function in the transitional region directly reflects its bifurcation behavior in classical dynamics. Besides, quantum properties, such as mechanical second-order coherence function and optomechanical entanglement, can be used to judge the corresponding bifurcation types and estimate the parameter width and position of the transitional region. The non-Gaussian transitional states exhibit strong entanglement robustness, and the transitional region as a boundary ribbon can be expected to replace the original classical instability boundary line in future applications.
基金supported by the National Natural Science Foundation of China(Grant No.51275523)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20134307110009)+1 种基金the Graduate Innovative Research Fund of Hunan Province,China(Grant No.CX20158015)the Excellent Graduate Innovative Fund of National University of Defense Technology(NUDT)(Grant No.B150305)
文摘We develop a simple and practical scheme to apply sideband cooling to a cloud of rubidium atoms. A sample containing 4 × 10^(70) ^(87)Rb is trapped in a far red detuned optical lattice. Through optimizing the relevant parameters, i.e., laser detuning, magnetic field, polarization, and duration time, a temperature around 1.5 μK and phase space density close to 1/500 are achieved. Compared with polarization gradient cooling, the temperature decreases by around one order of magnitude. This technique could be used in high precision measurement such as atomic clocks and atom interferometer. It could also serve as a precooling means before evaporation cooling in a dipole trap, and may be a promising method of achieving quantum degeneracy with purely optical means.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12004430 and 61632021)the National Basic Research Program of China(Grant No.2016YFA0301903).
文摘In quantum mechanics, the expectation value of an operator can be measured by using the projective measurement, ifthe coupling between the measured system and pointer is strong enough. However in the weak coupling regime, the pointercan not show all the eigenvalue of the physical quantity directly due to the overlapping among the pointer states, whichmakes the measurement of the expectation value difficult. In this paper, we propose an expectation value measurementmethod in the weak coupling regime inspired by the weak measurement scheme. Compared to the projective measurement,our scheme has two obvious advantages. Experimentally we use the internal state and motional state of a single trapped40Ca+ to establish the measurement scheme and realize the proof of principle demonstration of the scheme.
基金supported by the National Natural Science Foundation of China(Grant No.61475192)the Science Research Program of National University of Defense Technology,China(Grant No.JC140702)
文摘A dip of the transverse component of the magnetic moment as a function of resonance frequency-detuning will emerge when the intensity of oscillating magnetic field exceeds a specific value, which is demonstrated theoretically and experimentally. The linewidth of magnetic-resonance signal can be much smaller than when the Mx–MR magnetometer operates on condition that the intensity of oscillating magnetic field is smaller than this specific value, and the Mx–MR magnetometer can possess a much higher signal-to-noise ratio. The experimental result shows that the sensitivity of Mx–MR magnetometer can be improved by an order of magnitude under this condition.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61673389,61273202 and 61134008
文摘We explore the impact of distributional fairness degree and entanglement degree on the cooperation between different players by investigating a modified prisoner's dilemma game. We not only introduce a new concept of distributional fairness degree, but also obtain the cooperation conditions for overcoming dilemma in terms of fairness and entanglement inequalities. It is demonstrated that distributional fairness can be of fundamental importance to promote cooperation with the help of quantum entanglement.
基金supported by the National Natural Science Foundation of China (No.51275523)the State Key Laboratory of Aerodynamics Research Fund (No.SKLA2019040302)。
文摘We present a compact and practical scheme of building a ~780 nm external cavity diode laser(ECDL) whose wavelength is mainly determined by an interference filter. The Lorentzian linewidth measured by the heterodyne beating between two identical lasers is 60 k Hz, and the geometry size of the laser is only 71.5 mm×65 mm×40 mm. The linear cavity design is less sensitive to misalignment induced by mechanical and thermal disturbances, and in comparison to a common grating-based design, the sensitivity to vibration is substantially reduced. Due to its excellent performance, the laser design has already been applied to cold atom trapping experiments. This interference filter ECDL method can also be extended to other wavelengths and widen the application range of diode laser.
基金supported by the National Natural Science Foundation of China(No.51275523)Special Research Found for the Doctoral Program of Higher Education(No.20134307110009)
文摘The recent advances of atom interferometer and its application in precision inertial measurement are review ed. The principle,characteristics and implementation of atom interferometer are introduced and it can be used to measure gravitational acceleration,gravity gradient and rotation for its high sensitivity. We also present the principle,structure and new progress of gravimeter,gravity gradiometer and gyroscope based on atom interferometer.
基金This work was supported by the National Basic Research Program of China(Grant No.2016YFA0301903)the National Natural Science Foundation of China(Grant Nos.12074433,12004430,12174447,12174448,and 11904402).
文摘Symmetry,including the parity-time(PT)-symmetry,is a striking topic,widely discussed and employed in many fields.It is well-known that quantum measurement can destroy or disturb quantum systems.However,can and how does quantum measurement destroy the symmetry of the measured system?To answer the pertinent question,we establish the correlation between the quan-tum measurement and Floquet PT-symmetry and investigate for the first time how the measurement frequency and measurement strength affect the PT-symmetry of the measured system using the 40Ca+ion.It is already shown that the measurement at high frequencies would break the PT symmetry.Notably,even for an inadequately fast measurement frequency,if the measurement strength is sufficiently strong,the PT symmetry breaking can occur.The current work can enhance our knowledge of quantum measurement and symmetry and may inspire further research on the effect of quantum measurement on symmetry.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11574398,11904402,12074433,and 12004430)the National Basic Research Program of China(Grant No.2016YFA0301903).
文摘In order to understand our previous numerical finding that steady-state entanglement along the instability boundary remains unchanged in a three-mode optomechanical system[Phys.Rev.A 101023838(2020)],we investigate in detail the boundary entanglement in a simpler two-mode optomechanical system.Studies show that both the mechanism to generate entanglement and the parameter dependence of boundary entanglement are quite similar in these two models.Therefore,the two-mode system has captured the main features in the three-mode system.With the help of analytical calculations and discussing in a much bigger parameter interval,we find that the unchanging behavior previously discovered is actually an extremely slow changing behavior of the boundary entanglement function,and most importantly,this nearly invariant boundary entanglement is a general phenomenon via parametric down conversion process in the weak dissipation regime.This is by itself interesting as threshold quantum signatures in optomechanical phonon lasers,or may have potential value in related applications based on boundary quantum properties.
基金supported by the National Natural Science Foundation of China(No.51275523)the Specialized Research Fund for the Doctoral Program of Higher Education of China(No.20134307110009)the Graduate Innovative Research Fund of Hunan Province(No.CX2014A002)
文摘This paper presents a new type of cold atom interferometry gravimeter based on Bragg diffraction,w hich is able to increase the gravity m easurem ent sensitivity and stability of com m on Ram an atom gravim eters significantly. By com paring w ith Ram an transition,the principles and advantages of Bragg diffraction-based atom gravim eters have been introduced. The theoretical m odel for a tim e-dom ain Bragg atom gravim eter has been constructed. Som e key technical requirem ents for an n-order Bragg diffraction-based atom gravim eter have been deduced,including the tem perature of atom cloud,the diam eter,curvature radius,frequency,intensity,and tim ing sequence of Bragg lasers,etc. The analysis results are verified by the existing experim ental data in discussion. The present study provides a good reference for the understanding and construction of a Bragg atom gravim eter.
基金supported by the National Natural Science Foundation(No.51275523)the Specialized Research Fund for the Doctoral Program of Higher Education(No.20134307110009) of China
文摘We present a compact, low-noise, and inexpensive optical phase-lock loop (OPLL) system to synchronize the frequency and the phase between two external cavity diode lasers. Based on a direct digital synthesizer tech- nique, a programmable radio-frequency generator is implemented as the reference signal source. The OPLL has a narrow beat note linewidth below 1 Hz and a residual mean-square phase error of 0.06 rad2 in a 10 MHz integration bandwidth. The experimental test results prove the competent performance of the system, which is promising as a low-budget choice in atomic physics applications.
基金supported by the National Basic Research Program of China(Grant No.2016YFA0301903)the National Natural Science Foundation of China(Grant Nos.11174370,11304387 and 61205108)the Research Plan Project of National University of Defense Technology(Grant No.ZK16-03-04)
文摘In this paper we report the optimal design and fabrication of a gold-on-silica linear segmented surface-electrode ion trap. By optimizing the thickness and width of the electrodes, we improved the trapping ability and trap scalability. By using some practical experimental operation methods, we successfully minimized the trap heating rate. Consequently, we could trap a string of up to 38 ions, and a zigzag structure with 24 ions, and transport two trapped ions to different zones. We also studied the influences of the ion chip surface on the ion lifetime. The excellent trapping ability and flexibility of operation of the planar ion trap shows that it has high feasibility for application in the development a practical quantum information processor or quantum simulator.