We investigate the dependence of the average parameter estimation precision （APEP）, which is defined by the quantum Fisher information, on the polar angle of the initial coherent spin state ｜θ0,φ0〉 in a one-axis...We investigate the dependence of the average parameter estimation precision （APEP）, which is defined by the quantum Fisher information, on the polar angle of the initial coherent spin state ｜θ0,φ0〉 in a one-axis twisting model. Jin et al. [New J. Phys. 11 （2009） 073049] found that the spin squeezing sensitively depends on the polar angle θ0 of the initial coherent spin state. We show explicitly that the APEP is robust to the initial polar angle θ0 in the vicinity of π/2 and a near- Heisenberg limit 2IN in quantum single-parameter estimation may still be achieved for states created with the nonlinear evolution of the nonideal coherent spin states θ0- π/2. Based on this model, we also consider the effects of the collective dephasing on spin squeezing and the APEE展开更多
We investigate spin squeezing effects of trapped ions in an off-resonance optical potential system using the arbitrary range spin spin interaction and transverse field model. The collective spin noises at any time are...We investigate spin squeezing effects of trapped ions in an off-resonance optical potential system using the arbitrary range spin spin interaction and transverse field model. The collective spin noises at any time are analyzed exactly. The general expression of spin squeezing factor is presented for arbitrary-range spin interaction. For the nearest-neighbor and next-nearest neighbor spin interaction model, the analytic solutions are reduced from the general expressions. It is shown that the maximum spin squeezing is enhanced for the general arbitrary-range spin interaction compared with the nearest-neighbor interaction model as the long-range interaction with arbitrary sites enforces stronger correlation.展开更多
We study thermal spin squeezing (TSS) and thermal global entanglement (TGE) in a general Heisenberg spin chain, in the presence of Dzyaloshinskii-Moriya interaction and an external magnetic field. We derive an inequal...We study thermal spin squeezing (TSS) and thermal global entanglement (TGE) in a general Heisenberg spin chain, in the presence of Dzyaloshinskii-Moriya interaction and an external magnetic field. We derive an inequality associating the squeezing parameter and the global concurrence, which establishes (TSS) as a signature of (TGE). The inequality reduces to equality for particular symmetric chains which also associates TSS with bipartite entanglement in such systems. We also check the results by presenting two numerical examples.展开更多
We study spin squeezing and classical bifurcation in a nonfinear bipartite system. We show that the spin squeezing can be associated with a fixed-point bifurcation in the classical dynamics, namely, it acts as an indi...We study spin squeezing and classical bifurcation in a nonfinear bipartite system. We show that the spin squeezing can be associated with a fixed-point bifurcation in the classical dynamics, namely, it acts as an indicator of the classical bifurcation. For the ground state of a system with coupled giant spins, we find that the spin squeezing achieves its minimum value near the bifurcation point. We also study the dynamics of the spin squeezing, for an initial state corresponding to one of the fixed point, we find that in the stable regime, the spin squeezing exhibits periodic oscillation and always persists except at some fixed times, while in the unstable regime, the periodic oscillation phenomenon disappears and the spin squeezing survives for a short time. Finally, we show that the mean spin squeezing, which is defined to be averaged over time, attains its minimum value near the bifurcation point.展开更多
Multi-mode cavities have now attracted much attention both experimentally and theoretically. In this paper, inspired by recent experiments of cavity-assisted Raman transitions, we realize a two-axis spin Hamiltonian H...Multi-mode cavities have now attracted much attention both experimentally and theoretically. In this paper, inspired by recent experiments of cavity-assisted Raman transitions, we realize a two-axis spin Hamiltonian H = q（J_x^2＋ χJ_y^2） ＋ ω_0J_z in two cavities. This realized Hamiltonian has a distinct property that all parameters can be tuned independently. For proper parameters, the well-studied one- and two-axis twisting Hamiltonians are recovered, and the scaling of N^（-1） of the maximal squeezing factor can occur naturally. On the other hand, in the two-axis twisting Hamiltonian, spin squeezing is usually reduced when increasing the atomic resonant frequency ω_0. Surprisingly, we find that by combining with the dimensionless parameter χ（-1）, this atomic resonant frequency ω_0 can enhance spin squeezing greatly. These results are beneficial for achieving the required spin squeezing in experiments.展开更多
Taking into account the dephasing process in the realistic atomic ensemble,we theoretically study the generation of atomic spin squeezing via atomic coherence induced by the coupling and probe fields.Using the Heisenb...Taking into account the dephasing process in the realistic atomic ensemble,we theoretically study the generation of atomic spin squeezing via atomic coherence induced by the coupling and probe fields.Using the Heisenberg–Langevin approach,we find that the perfect spin squeezing in the X component can be obtained while the coupling and probe fields produce the maximum coherence between the ground state sublevels 1 and 2.Moreover,the degree of atomic spin squeezing in the X component can be strengthened with the increasing atomic density and/or Rabi frequency of the mixing field.The theoretical results provide a proof-of-principle demonstration of generating the atomic spin squeezing via quantum coherence in the realistic atomic ensemble which may find potential applications in quantum information processing and quantum networks.展开更多
The phenomenon that a clock at a higher gravitational potential ticks faster than one at a lower potential,also known as gravitational redshift,is one of the classical tests of Einstein’s theory of general relativity...The phenomenon that a clock at a higher gravitational potential ticks faster than one at a lower potential,also known as gravitational redshift,is one of the classical tests of Einstein’s theory of general relativity.Owing to their ultra-high accuracy and stability,state-of-the-art optical lattice clocks have enabled resolving the gravitational redshift with a millimeter-scale height difference.Further reducing the vertical inter-clock separation down to the sub-millimeter level and especially shortening the required measurement time may be achieved by employing spin squeezing.Here,we theoretically investigate the spin-squeezing-enhanced differential frequency comparison between two optical clocks within a lattice-trapped cloud of^(171)Yb atoms.The numerical results illustrate that for a sample of 10^(4)atoms,the atomic-collision-limited resolution of the vertical separation between two clocks can reach 0.48 mm,corresponding to a fractional gravitational redshift at the 10^(-20)level.In addition,the required averaging time may be reduced to less than one hundredth of that of conventional clocks with independent atoms.Our work opens a door to the future spin-squeezing-enhanced test of general relativity.展开更多
Exploring the quantum advantages of various non-classical quantum states in noisy environments is a central subject in quantum sensing.Here we provide a complete picture for the frequency estimation precision of three...Exploring the quantum advantages of various non-classical quantum states in noisy environments is a central subject in quantum sensing.Here we provide a complete picture for the frequency estimation precision of three important states(the Greenberger-Horne-Zeilinger(GHZ)state,the maximal spin squeezed state,and the spin coherent state)of a spin-S under both individual dephasing and collective dephasing by general Gaussian noise,ranging from the Markovian limit to the extreme non-Markovian limit.Whether or not the noise is Markovian,the spin coherent state is always worse than the classical scheme under collective dephasing although it is equivalent to the classical scheme under individual dephasing.Moreover,the maximal spin squeezed state always give the best sensing precision(and outperforms the widely studied GHZ state)in all cases.This establishes the general advantage of the spin squeezed state for noisy frequency estimation in many quantum sensing platforms.展开更多
We propose a Rydberg molecule dressing scheme to create strong and long-ranged interactions at selective distances. This is achieved through laser coupling ground-state atoms off-resonantly to an attractive molecular ...We propose a Rydberg molecule dressing scheme to create strong and long-ranged interactions at selective distances. This is achieved through laser coupling ground-state atoms off-resonantly to an attractive molecular curve of two interacting Rydberg atoms. Although dephasing due to Rydberg state decay occurs in all dressing schemes, an advantage of the molecule dressing is that a large ratio of dressed interaction to dephasing rate can be realized at large atomic separations. In an optical lattice or tweezer setting, we show that the strong interaction permits the fast generation of spin squeezing for several tens of dressed atoms.The proposed setting offers a new route to study complex many-body dynamics and to realize quantum information processing with non-convex long-range interactions.展开更多
Atomic nonlinear interferometry has wide applications in quantum metrology and quantum information science.Here we propose a nonlinear time-reversal interferometry scheme with high robustness and metrological gain bas...Atomic nonlinear interferometry has wide applications in quantum metrology and quantum information science.Here we propose a nonlinear time-reversal interferometry scheme with high robustness and metrological gain based on the spin squeezing generated by arbitrary quadratic collective-spin interaction,which could be described by the Lipkin–Meshkov–Glick(LMG)model.We optimize the squeezing process,encoding process,and anti-squeezing process,finding that the two particular cases of the LMG model,one-axis twisting and two-axis twisting outperform in robustness and precision,respectively.Moreover,we propose a Floquet driving method to realize equivalent time reverse in the atomic system,which leads to high performance in precision,robustness,and operability.Our study sets a benchmark for achieving high precision and high robustness in atomic nonlinear interferometry.展开更多
Spin squeezing is a fascinating manifestation of many-particle entanglement and one of the most promising quantum resources.In this paper,we propose a novel realization of a solid-state quantum spin squeezing by apply...Spin squeezing is a fascinating manifestation of many-particle entanglement and one of the most promising quantum resources.In this paper,we propose a novel realization of a solid-state quantum spin squeezing by applying SiV centers embedded in a diamond waveguide with the help of a microwave field.The phenomena about the generation of spin squeezing are analyzed numerically in Markovian environments.Our analysis shows that spin squeezing can be generated with the microwave field’s help under some realistic conditions,despite the presence of dephasing and mechanical damping.This solid-state spin squeezing based on SiV centers in diamonds might be applied to magnetometers,interferometry,and other precise measurements.展开更多
We study squeezed properties of magnon squeezed thermal spin states by using the distribution of Q function in the ferromagnet. It is found that the distribution of Q function strongly depends on the temperature T and...We study squeezed properties of magnon squeezed thermal spin states by using the distribution of Q function in the ferromagnet. It is found that the distribution of Q function strongly depends on the temperature T and coupling parameter γ. Below the transition temperature Tc, the distribution Q function in the squeezed thermal spin state presents a richer structure than in the normal state. Non-classical effects have been observed. In the transition from the normal to the squeezed thermal spin state, the phase symmetry of the magnon system is spontaneously broken.展开更多
We calculate the concurrence and spin squeezing parameter of three atoms induced by a coherent field. It shows that when the mean numbers of photon of the field is very small, concurrence exhibits a certain kind of ap...We calculate the concurrence and spin squeezing parameter of three atoms induced by a coherent field. It shows that when the mean numbers of photon of the field is very small, concurrence exhibits a certain kind of approximative periodic vibration. With the increase of the mean numbers of photon, its periodicity will be interrupted. As for the relationship between the concurrence and spin squeezing, numeric result shows that under Dick model, spin squeezing serves as a sufficient but not necessary condition for concurrence.展开更多
We study the spin squeezing property of weighted graph states,which can be used to improve sensitivity in interferometry.We study the time evolution of spin squeezing under local decoherence acting independently on ea...We study the spin squeezing property of weighted graph states,which can be used to improve sensitivity in interferometry.We study the time evolution of spin squeezing under local decoherence acting independently on each qubit.Based on the analysis,the spin squeezing of the weighted graph states is somehow robust in the presence of decoherence and the decoherence limit in the improvement of the interferometric sensitivity is still achievable.Furthermore,one can obtain the optimal improvement of sensitivity by tuning the weighted of each edges of the weighted graph state.展开更多
基金supported by the National Basic Research Program of China(Grant No.2012CB921602)the National Natural Science Foundation of China(Grant Nos.11025527 and 10935010)
文摘We investigate the dependence of the average parameter estimation precision （APEP）, which is defined by the quantum Fisher information, on the polar angle of the initial coherent spin state ｜θ0,φ0〉 in a one-axis twisting model. Jin et al. [New J. Phys. 11 （2009） 073049] found that the spin squeezing sensitively depends on the polar angle θ0 of the initial coherent spin state. We show explicitly that the APEP is robust to the initial polar angle θ0 in the vicinity of π/2 and a near- Heisenberg limit 2IN in quantum single-parameter estimation may still be achieved for states created with the nonlinear evolution of the nonideal coherent spin states θ0- π/2. Based on this model, we also consider the effects of the collective dephasing on spin squeezing and the APEE
基金Supported by the National Natural Science Foundation of China under Grant No 51427801
文摘We investigate spin squeezing effects of trapped ions in an off-resonance optical potential system using the arbitrary range spin spin interaction and transverse field model. The collective spin noises at any time are analyzed exactly. The general expression of spin squeezing factor is presented for arbitrary-range spin interaction. For the nearest-neighbor and next-nearest neighbor spin interaction model, the analytic solutions are reduced from the general expressions. It is shown that the maximum spin squeezing is enhanced for the general arbitrary-range spin interaction compared with the nearest-neighbor interaction model as the long-range interaction with arbitrary sites enforces stronger correlation.
文摘We study thermal spin squeezing (TSS) and thermal global entanglement (TGE) in a general Heisenberg spin chain, in the presence of Dzyaloshinskii-Moriya interaction and an external magnetic field. We derive an inequality associating the squeezing parameter and the global concurrence, which establishes (TSS) as a signature of (TGE). The inequality reduces to equality for particular symmetric chains which also associates TSS with bipartite entanglement in such systems. We also check the results by presenting two numerical examples.
基金Supported by the National Foundation Research Program of China under Grant No. 2012CB921602National Natural Science Foundation of China under Grant Nos. 11025527 and 10935010
文摘We study spin squeezing and classical bifurcation in a nonfinear bipartite system. We show that the spin squeezing can be associated with a fixed-point bifurcation in the classical dynamics, namely, it acts as an indicator of the classical bifurcation. For the ground state of a system with coupled giant spins, we find that the spin squeezing achieves its minimum value near the bifurcation point. We also study the dynamics of the spin squeezing, for an initial state corresponding to one of the fixed point, we find that in the stable regime, the spin squeezing exhibits periodic oscillation and always persists except at some fixed times, while in the unstable regime, the periodic oscillation phenomenon disappears and the spin squeezing survives for a short time. Finally, we show that the mean spin squeezing, which is defined to be averaged over time, attains its minimum value near the bifurcation point.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11422433,11447028,61227902,11434007,and 61275211)the Natural Science Foundation of Zhejiang Province,China(Grant No.LY13A040001)the Scientific Research Foundation of the Education Department of Zhejiang Province,China(Grant No.Y201122352)
文摘Multi-mode cavities have now attracted much attention both experimentally and theoretically. In this paper, inspired by recent experiments of cavity-assisted Raman transitions, we realize a two-axis spin Hamiltonian H = q（J_x^2＋ χJ_y^2） ＋ ω_0J_z in two cavities. This realized Hamiltonian has a distinct property that all parameters can be tuned independently. For proper parameters, the well-studied one- and two-axis twisting Hamiltonians are recovered, and the scaling of N^（-1） of the maximal squeezing factor can occur naturally. On the other hand, in the two-axis twisting Hamiltonian, spin squeezing is usually reduced when increasing the atomic resonant frequency ω_0. Surprisingly, we find that by combining with the dimensionless parameter χ（-1）, this atomic resonant frequency ω_0 can enhance spin squeezing greatly. These results are beneficial for achieving the required spin squeezing in experiments.
文摘Taking into account the dephasing process in the realistic atomic ensemble,we theoretically study the generation of atomic spin squeezing via atomic coherence induced by the coupling and probe fields.Using the Heisenberg–Langevin approach,we find that the perfect spin squeezing in the X component can be obtained while the coupling and probe fields produce the maximum coherence between the ground state sublevels 1 and 2.Moreover,the degree of atomic spin squeezing in the X component can be strengthened with the increasing atomic density and/or Rabi frequency of the mixing field.The theoretical results provide a proof-of-principle demonstration of generating the atomic spin squeezing via quantum coherence in the realistic atomic ensemble which may find potential applications in quantum information processing and quantum networks.
基金supported by CAS Project for Young Scientists in Basic Research(Grant No.YSBR-085)the National Time Service Center(Grant No.E239SC1101)+1 种基金Innovation Program for Quantum Science and Technology(Grant No.2021ZD0303200)China Postdoctoral Science Foundation(Grant No.BX2021020).
文摘The phenomenon that a clock at a higher gravitational potential ticks faster than one at a lower potential,also known as gravitational redshift,is one of the classical tests of Einstein’s theory of general relativity.Owing to their ultra-high accuracy and stability,state-of-the-art optical lattice clocks have enabled resolving the gravitational redshift with a millimeter-scale height difference.Further reducing the vertical inter-clock separation down to the sub-millimeter level and especially shortening the required measurement time may be achieved by employing spin squeezing.Here,we theoretically investigate the spin-squeezing-enhanced differential frequency comparison between two optical clocks within a lattice-trapped cloud of^(171)Yb atoms.The numerical results illustrate that for a sample of 10^(4)atoms,the atomic-collision-limited resolution of the vertical separation between two clocks can reach 0.48 mm,corresponding to a fractional gravitational redshift at the 10^(-20)level.In addition,the required averaging time may be reduced to less than one hundredth of that of conventional clocks with independent atoms.Our work opens a door to the future spin-squeezing-enhanced test of general relativity.
基金supported by the National Natural Science Foundation of China(NSFC)Grant No.12274019the NSAF grant in NSFC with Grant No.U2230402。
文摘Exploring the quantum advantages of various non-classical quantum states in noisy environments is a central subject in quantum sensing.Here we provide a complete picture for the frequency estimation precision of three important states(the Greenberger-Horne-Zeilinger(GHZ)state,the maximal spin squeezed state,and the spin coherent state)of a spin-S under both individual dephasing and collective dephasing by general Gaussian noise,ranging from the Markovian limit to the extreme non-Markovian limit.Whether or not the noise is Markovian,the spin coherent state is always worse than the classical scheme under collective dephasing although it is equivalent to the classical scheme under individual dephasing.Moreover,the maximal spin squeezed state always give the best sensing precision(and outperforms the widely studied GHZ state)in all cases.This establishes the general advantage of the spin squeezed state for noisy frequency estimation in many quantum sensing platforms.
基金support from the Baden-Württemberg Foundation(Grant No.BWST ISF2019-23)(“Internationale Spitzenforschung”)the Deutsche Forschungsgemeinschaft through SPP 1929 GiRyd(Grant No.428276754)+2 种基金support from the EPSRC(Grant Nos.EP/R04340X/1,and EP/W015641/1)the Royal Society through the International Exchanges Cost Share Award(Grant No.IEC181078)support from the National Natural Science Foundation of China(Grant Nos.11774058,11874114,and 12174058)。
文摘We propose a Rydberg molecule dressing scheme to create strong and long-ranged interactions at selective distances. This is achieved through laser coupling ground-state atoms off-resonantly to an attractive molecular curve of two interacting Rydberg atoms. Although dephasing due to Rydberg state decay occurs in all dressing schemes, an advantage of the molecule dressing is that a large ratio of dressed interaction to dephasing rate can be realized at large atomic separations. In an optical lattice or tweezer setting, we show that the strong interaction permits the fast generation of spin squeezing for several tens of dressed atoms.The proposed setting offers a new route to study complex many-body dynamics and to realize quantum information processing with non-convex long-range interactions.
基金Project supported by the National Key R&D Program of China (Grant No.2023YFA1407600)the National Natural Science Foundation of China (Grant Nos.12275145,92050110,91736106,11674390,and 91836302)。
文摘Atomic nonlinear interferometry has wide applications in quantum metrology and quantum information science.Here we propose a nonlinear time-reversal interferometry scheme with high robustness and metrological gain based on the spin squeezing generated by arbitrary quadratic collective-spin interaction,which could be described by the Lipkin–Meshkov–Glick(LMG)model.We optimize the squeezing process,encoding process,and anti-squeezing process,finding that the two particular cases of the LMG model,one-axis twisting and two-axis twisting outperform in robustness and precision,respectively.Moreover,we propose a Floquet driving method to realize equivalent time reverse in the atomic system,which leads to high performance in precision,robustness,and operability.Our study sets a benchmark for achieving high precision and high robustness in atomic nonlinear interferometry.
基金supported by the National Natural Science Foundation of China(Grant No.11664029)the Inner Mongolia Natural Science Foundation,China(Grant No.2021MS01012).
文摘Spin squeezing is a fascinating manifestation of many-particle entanglement and one of the most promising quantum resources.In this paper,we propose a novel realization of a solid-state quantum spin squeezing by applying SiV centers embedded in a diamond waveguide with the help of a microwave field.The phenomena about the generation of spin squeezing are analyzed numerically in Markovian environments.Our analysis shows that spin squeezing can be generated with the microwave field’s help under some realistic conditions,despite the presence of dephasing and mechanical damping.This solid-state spin squeezing based on SiV centers in diamonds might be applied to magnetometers,interferometry,and other precise measurements.
基金supported by National Natural Science Foundation of China under Grant Nos.10174024 and 10474025
文摘We study squeezed properties of magnon squeezed thermal spin states by using the distribution of Q function in the ferromagnet. It is found that the distribution of Q function strongly depends on the temperature T and coupling parameter γ. Below the transition temperature Tc, the distribution Q function in the squeezed thermal spin state presents a richer structure than in the normal state. Non-classical effects have been observed. In the transition from the normal to the squeezed thermal spin state, the phase symmetry of the magnon system is spontaneously broken.
文摘We calculate the concurrence and spin squeezing parameter of three atoms induced by a coherent field. It shows that when the mean numbers of photon of the field is very small, concurrence exhibits a certain kind of approximative periodic vibration. With the increase of the mean numbers of photon, its periodicity will be interrupted. As for the relationship between the concurrence and spin squeezing, numeric result shows that under Dick model, spin squeezing serves as a sufficient but not necessary condition for concurrence.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11004029 and 11174052)the Natural Science Foundation of Jiangsu Province of China (Grant No. BK2010422)+2 种基金the Ph. D. Program of the Ministry of Education of Chinathe Excellent Young Teachers Program of Southeast Universitythe National Basic Research Development Program of China(Grant No. 2011CB921203)
文摘We study the spin squeezing property of weighted graph states,which can be used to improve sensitivity in interferometry.We study the time evolution of spin squeezing under local decoherence acting independently on each qubit.Based on the analysis,the spin squeezing of the weighted graph states is somehow robust in the presence of decoherence and the decoherence limit in the improvement of the interferometric sensitivity is still achievable.Furthermore,one can obtain the optimal improvement of sensitivity by tuning the weighted of each edges of the weighted graph state.
