We focus on the Mach–Zehnder interferometer(MZI) with the input of a coherent beam and one of the bright entangled twin beams with an external power reference beam employed for measurement. The results show that the ...We focus on the Mach–Zehnder interferometer(MZI) with the input of a coherent beam and one of the bright entangled twin beams with an external power reference beam employed for measurement. The results show that the phase sensitivity can reach sub-Heisenberg limit and approach quantum Cramer–Rao bound by changing the squeezing parameters and the photon number of the coherent beam, under the phase-matching condition. The absence of the external power reference beam will degrade the performance of the phase sensitivity. Meanwhile, this scheme shows good robustness against the losses of the photon detectors. We present a detailed discussion about the phase sensitivities when the inputs are two coherent beams, or a coherent beam plus a single-mode squeezed vacuum beam based on the MZI. This scenario can be applied in the field of phase precision measurements and other optical sensors.展开更多
We investigate quantum phase transitions in XY spin models using Dzyaloshinsky-Moriya(DM) interactions. We identify the quantum critical points via quantum Fisher information and quantum coherence, finding that higher...We investigate quantum phase transitions in XY spin models using Dzyaloshinsky-Moriya(DM) interactions. We identify the quantum critical points via quantum Fisher information and quantum coherence, finding that higher DM couplings suppress quantum phase transitions. However, quantum coherence(characterized by the l_1-norm and relative entropy) decreases as the DM coupling increases. Herein, we present both analytical and numerical results.展开更多
We theoretically study the effect of Kerr effect on the second-order nonlinearity induced transparency in a double-resonant optical cavity system.We show that in the presence of the Kerr effect,as the strength of the ...We theoretically study the effect of Kerr effect on the second-order nonlinearity induced transparency in a double-resonant optical cavity system.We show that in the presence of the Kerr effect,as the strength of the Kerr effect increases,the absorption curve exhibits an asymmetric-symmetric-asymmetric transition,and the zero absorption point shifts with the increase of the Kerr effect.Furthermore,by changing the strength of the Kerr effect,we can control the width of the transparent window,and the position of the zero-absorption point and meanwhile change the left and right width of the absorption peak.The asymmetry absorption curve can be employed to improve the quality factor of the cavity when the frequency detuning is tuned to be around the right peak.The simple dependence of the zeroabsorption point on the strength of Kerr effect suggests that the strength of Kerr effect can be measured by measuring the position of the zero-absorption point in a possible application.展开更多
We present a way to transfer maximally-or partially-entangled states of n single-photon-state(SPS)qubits onto ncoherent-state(CS)qubits,by employing 2nmicrowave cavities coupled to a superconducting flux qutrit.The tw...We present a way to transfer maximally-or partially-entangled states of n single-photon-state(SPS)qubits onto ncoherent-state(CS)qubits,by employing 2nmicrowave cavities coupled to a superconducting flux qutrit.The two logic states of a SPS qubit here are represented by the vacuum state and the single-photon state of a cavity,while the two logic states of a CS qubit are encoded with two coherent states of a cavity.Because of using only one superconducting qutrit as the coupler,the circuit architecture is significantly simplified.The operation time for the state transfer does not increase with the increasing of the number of qubits.When the dissipation of the system is negligible,the quantum state can be transferred in a deterministic way since no measurement is required.Furthermore,the higher-energy intermediate level of the coupler qutrit is not excited during the entire operation and thus decoherence from the qutrit is greatly suppressed.As a specific example,we numerically demonstrate that the high-fidelity transfer of a Bell state of two SPS qubits onto two CS qubits is achievable within the present-day circuit QED technology.Finally,it is worthy to note that when the dissipation is negligible,entangled states of n CS qubits can be transferred back onto n SPS qubits by performing reverse operations.This proposal is quite general and can be extended to accomplish the same task,by employing a natural or artificial atom to couple 2nmicrowave or optical cavities.展开更多
We propose an efficient scheme to implement a multiplex-controlled phase gate with multiple photonic qubits simultaneously controlling one target photonic qubit based on circuit quantum electrodynamics(QED).For conven...We propose an efficient scheme to implement a multiplex-controlled phase gate with multiple photonic qubits simultaneously controlling one target photonic qubit based on circuit quantum electrodynamics(QED).For convenience,we denote this multiqubit gate as MCP gate.The gate is realized by using a two-level coupler to couple multiple cavities.The coupler here is a superconducting qubit.This scheme is simple because the gate implementation requires only one step of operation.In addition,this scheme is quite general because the two logic states of each photonic qubit can be encoded with a vacuum state and an arbitrary non-vacuum state|φ>(e.g.,a Fock state,a superposition of Fock states,a cat state,or a coherent state,etc.)which is orthogonal or quasi-orthogonal to the vacuum state.The scheme has some additional advantages:because only two levels of the coupler are used,i.e.,no auxiliary levels are utilized,decoherence from higher energy levels of the coupler is avoided;the gate operation time does not depend on the number of qubits;and the gate is implemented deterministically because no measurement is applied.As an example,we numerically analyze the circuit-QED based experimental feasibility of implementing a three-qubit MCP gate with photonic qubits each encoded via a vacuum state and a cat state.The scheme can be applied to accomplish the same task in a wide range of physical system,which consists of multiple microwave or optical cavities coupled to a two-level coupler such as a natural or artificial atom.展开更多
Transferring entangled states between matter qubits and microwave-field(or optical-field)qubits is of fundamental interest in quantum mechanics and necessary in hybrid quantum information processing and quantum commun...Transferring entangled states between matter qubits and microwave-field(or optical-field)qubits is of fundamental interest in quantum mechanics and necessary in hybrid quantum information processing and quantum communication.We here propose a way for transferring entangled states between superconducting qubits(matter qubits)and microwave-field qubits.This proposal is realized by a system consisting of multiple superconducting qutrits and microwave cavities.Here,“qutrit”refers to a three-level quantum system with the two lowest levels encoding a qubit while the third level acting as an auxiliary state.In contrast,the microwave-field qubits are encoded with coherent states of microwave cavities.Because the third energy level of each qutrit is not populated during the operation,decoherence from the higher energy levels is greatly suppressed.The entangled states can be deterministically transferred because measurement on the states is not needed.The operation time is independent of the number of superconducting qubits or microwave-field qubits.In addition,the architecture of the circuit system is quite simple because only a coupler qutrit and an auxiliary cavity are required.As an example,our numerical simulations show that high-fidelity transfer of entangled states from two superconducting qubits to two microwave-field qubits is feasible with present circuit QED technology.This proposal is quite general and can be extended to transfer entangled states between other matter qubits(e.g.,atoms,quantum dots,and NV centers)and microwave-or optical-field qubits encoded with coherent states.展开更多
Noether’s theorem is one of the fundamental laws in physics,relating the symmetry of a physical system to its constant of motion and conservation law.On the other hand,there exist a variety of non-Hermitian parity-ti...Noether’s theorem is one of the fundamental laws in physics,relating the symmetry of a physical system to its constant of motion and conservation law.On the other hand,there exist a variety of non-Hermitian parity-time(PT)-symmetric systems,which exhibit novel quantum properties and have attracted increasing interest.In this work,we extend Noether’s theorem to a class of significant PT-symmetry systems for which the eigenvalues of the PT-symmetry Hamiltonian HPTchange from purely real numbers to purely imaginary numbers,and introduce a generalized expectation value of an operator based on biorthogonal quantum mechanics.We find that the generalized expectation value of a time-independent operator is a constant of motion when the operator presents a standard symmetry in the PT-symmetry unbroken regime,or a chiral symmetry in the PT-symmetry broken regime.In addition,we experimentally investigate the extended Noether’s theorem in PT-symmetry single-qubit and two-qubit systems using an optical setup.Our experiment demonstrates the existence of the constant of motion and reveals how this constant of motion can be used to judge whether the PT-symmetry of a system is broken.Furthermore,a novel phenomenon of masking quantum information is first observed in a PT-symmetry two-qubit system.This study not only contributes to full understanding of the relation between symmetry and conservation law in PT-symmetry physics,but also has potential applications in quantum information theory and quantum communication protocols.展开更多
We propose a single-step implementation of a muti-target-qubit controlled phase gate with one catstate qubit (cqubit) simultaneously controlling n — 1 target cqubits. The two logic states of a c.qubit are represented...We propose a single-step implementation of a muti-target-qubit controlled phase gate with one catstate qubit (cqubit) simultaneously controlling n — 1 target cqubits. The two logic states of a c.qubit are represented by two orthogonal cat states of a single cavity mode. In this proposal, the gate is implemented with n microwave cavities coupled to a superconducting transnion qutrit. Because the qutrit remains in the ground state during the gate operation, decoherence caused due to the qutrit5s energy relaxation and dephasing is greatly suppressed. The gate implementation is quite simple because only a single-stcp operation is needed and neither classical pulse nor measurement is required. Numerical simulations demonstrate that high-fidelity realization of a controlled phase gate with one cqubit simultaneously con trolling two targe t cqubits is feasible with present circuit QED technology. This proposal can be extended to a wide range of physical systems to realize the proposed gate, such as multiple microwave or optical cavities coupled to a natural or artificial three-level atom.展开更多
We propose a method for transferring quantum entangled states of two photonic cat-state qubits(cqubits)from two microwave cavities to the other two microwave cavities.This proposal is realized by using four microwave ...We propose a method for transferring quantum entangled states of two photonic cat-state qubits(cqubits)from two microwave cavities to the other two microwave cavities.This proposal is realized by using four microwave cavities coupled to a superconducting flux qutrit.Because of using four cavities with different frequencies,the inter-cavity crosstalk is significantly reduced.Since only one coupler qutrit is used,the circuit resource is minimized.The entanglement transfer is completed with a singlestep operation only,thus this proposal is quite simple.The third energy level of the coupler qutrit is not populated during the state transfer,therefore decoherence from the higher energy level is greatly suppressed.Our numerical simulations show that high-fidelity transfer of two-cqubit entangled states from two transmission line resonators to the other two transmission line resonators is feasible with current circuit QED technology.This proposal is universal and can be applied to accomplish the same task in a wide range of physical systems,such as four microwave or optical cavities,which are coupled to a natural or artificial three-level atom.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos.12104190,12104189,and 12204312)the Natural Science Foundation of Jiangsu Province (Grant No.BK20210874)+2 种基金the Jiangsu Provincial Key Research and Development Program (Grant No.BE2022143)the Jiangxi Provincial Natural Science Foundation (Grant Nos.20224BAB211014 and 20232BAB201042)the General Project of Natural Science Research in Colleges and Universities of Jiangsu Province (Grant No.20KJB140008)。
文摘We focus on the Mach–Zehnder interferometer(MZI) with the input of a coherent beam and one of the bright entangled twin beams with an external power reference beam employed for measurement. The results show that the phase sensitivity can reach sub-Heisenberg limit and approach quantum Cramer–Rao bound by changing the squeezing parameters and the photon number of the coherent beam, under the phase-matching condition. The absence of the external power reference beam will degrade the performance of the phase sensitivity. Meanwhile, this scheme shows good robustness against the losses of the photon detectors. We present a detailed discussion about the phase sensitivities when the inputs are two coherent beams, or a coherent beam plus a single-mode squeezed vacuum beam based on the MZI. This scenario can be applied in the field of phase precision measurements and other optical sensors.
基金supported by the National Natural Science Foundation of China(Grant Nos.11675113,and 11765016)the Natural Science Foundation of Beijing(Grant No.KZ201810028042)Jiangxi Education Department Fund(Grant Nos.GJJ161056,and KJLD14088)
文摘We investigate quantum phase transitions in XY spin models using Dzyaloshinsky-Moriya(DM) interactions. We identify the quantum critical points via quantum Fisher information and quantum coherence, finding that higher DM couplings suppress quantum phase transitions. However, quantum coherence(characterized by the l_1-norm and relative entropy) decreases as the DM coupling increases. Herein, we present both analytical and numerical results.
基金Supported by the Key Scientific Research Plan of Colleges and Universities in Henan Province(23B140006)the National Natural Science Foundation of China(11965017)。
文摘We theoretically study the effect of Kerr effect on the second-order nonlinearity induced transparency in a double-resonant optical cavity system.We show that in the presence of the Kerr effect,as the strength of the Kerr effect increases,the absorption curve exhibits an asymmetric-symmetric-asymmetric transition,and the zero absorption point shifts with the increase of the Kerr effect.Furthermore,by changing the strength of the Kerr effect,we can control the width of the transparent window,and the position of the zero-absorption point and meanwhile change the left and right width of the absorption peak.The asymmetry absorption curve can be employed to improve the quality factor of the cavity when the frequency detuning is tuned to be around the right peak.The simple dependence of the zeroabsorption point on the strength of Kerr effect suggests that the strength of Kerr effect can be measured by measuring the position of the zero-absorption point in a possible application.
基金This work was partly supported by the National Natural Science Foundation of China(NSFC)(Grant Nos.11074062,11374083,and 11774076)the Key-Area Research and Development Program of GuangDong province(Grant No.2018B030326001)the NKRDP of China(Grant No.2016YFA0301802).
文摘We present a way to transfer maximally-or partially-entangled states of n single-photon-state(SPS)qubits onto ncoherent-state(CS)qubits,by employing 2nmicrowave cavities coupled to a superconducting flux qutrit.The two logic states of a SPS qubit here are represented by the vacuum state and the single-photon state of a cavity,while the two logic states of a CS qubit are encoded with two coherent states of a cavity.Because of using only one superconducting qutrit as the coupler,the circuit architecture is significantly simplified.The operation time for the state transfer does not increase with the increasing of the number of qubits.When the dissipation of the system is negligible,the quantum state can be transferred in a deterministic way since no measurement is required.Furthermore,the higher-energy intermediate level of the coupler qutrit is not excited during the entire operation and thus decoherence from the qutrit is greatly suppressed.As a specific example,we numerically demonstrate that the high-fidelity transfer of a Bell state of two SPS qubits onto two CS qubits is achievable within the present-day circuit QED technology.Finally,it is worthy to note that when the dissipation is negligible,entangled states of n CS qubits can be transferred back onto n SPS qubits by performing reverse operations.This proposal is quite general and can be extended to accomplish the same task,by employing a natural or artificial atom to couple 2nmicrowave or optical cavities.
基金This work was partly supported by the National Natural Science Foundation of China(NSFC)(Nos.11074062,11374083,11774076,U21A20436)the Key-Area Research and Development Program of GuangDong Province(No.2018B030326001)the Jiangxi Natural Science Foundation(No.20192ACBL20051).
文摘We propose an efficient scheme to implement a multiplex-controlled phase gate with multiple photonic qubits simultaneously controlling one target photonic qubit based on circuit quantum electrodynamics(QED).For convenience,we denote this multiqubit gate as MCP gate.The gate is realized by using a two-level coupler to couple multiple cavities.The coupler here is a superconducting qubit.This scheme is simple because the gate implementation requires only one step of operation.In addition,this scheme is quite general because the two logic states of each photonic qubit can be encoded with a vacuum state and an arbitrary non-vacuum state|φ>(e.g.,a Fock state,a superposition of Fock states,a cat state,or a coherent state,etc.)which is orthogonal or quasi-orthogonal to the vacuum state.The scheme has some additional advantages:because only two levels of the coupler are used,i.e.,no auxiliary levels are utilized,decoherence from higher energy levels of the coupler is avoided;the gate operation time does not depend on the number of qubits;and the gate is implemented deterministically because no measurement is applied.As an example,we numerically analyze the circuit-QED based experimental feasibility of implementing a three-qubit MCP gate with photonic qubits each encoded via a vacuum state and a cat state.The scheme can be applied to accomplish the same task in a wide range of physical system,which consists of multiple microwave or optical cavities coupled to a two-level coupler such as a natural or artificial atom.
基金supported by the Key-Area Research and Development Program of Guang Dong Province(Grant No.2018B030326001)the National Natural Science Foundation of China(NSFC)(Grant Nos.12004253,11074062,11374083,11774076,11804228,11965017,and U21A20436)the Jiangxi Natural Science Foundation(Grant Nos.20192ACBL20051,20212BAB211019,and 20212BAB201025).
文摘Transferring entangled states between matter qubits and microwave-field(or optical-field)qubits is of fundamental interest in quantum mechanics and necessary in hybrid quantum information processing and quantum communication.We here propose a way for transferring entangled states between superconducting qubits(matter qubits)and microwave-field qubits.This proposal is realized by a system consisting of multiple superconducting qutrits and microwave cavities.Here,“qutrit”refers to a three-level quantum system with the two lowest levels encoding a qubit while the third level acting as an auxiliary state.In contrast,the microwave-field qubits are encoded with coherent states of microwave cavities.Because the third energy level of each qutrit is not populated during the operation,decoherence from the higher energy levels is greatly suppressed.The entangled states can be deterministically transferred because measurement on the states is not needed.The operation time is independent of the number of superconducting qubits or microwave-field qubits.In addition,the architecture of the circuit system is quite simple because only a coupler qutrit and an auxiliary cavity are required.As an example,our numerical simulations show that high-fidelity transfer of entangled states from two superconducting qubits to two microwave-field qubits is feasible with present circuit QED technology.This proposal is quite general and can be extended to transfer entangled states between other matter qubits(e.g.,atoms,quantum dots,and NV centers)and microwave-or optical-field qubits encoded with coherent states.
基金supported by the National Natural Science Foundation of China(Grant Nos.12264040,12204311,11804228,11865013,and U21A20436)the Jiangxi Natural Science Foundation(Grant Nos.20212BAB211018,20192ACBL20051)+8 种基金the Project of Jiangxi Province Higher Educational Science and Technology Program(Grant Nos.GJJ190891,and GJJ211735)the Key-Area Research and Development Program of Guangdong Province(Grant No.2018B03-0326001)supported in part by the Nippon Telegraph and Telephone(NTT)Corporation Researchthe Japan Science and Technology(JST)Agency[via the Quantum Leap Flagship Program(Q-LEAP)Moonshot R&D Grant Number JPMJMS2061]the Japan Society for the Promotion of Science(JSPS)[via the Grants-in-Aid for Scientific Research(KAKENHI)Grant No.JP20H00134]the Army Research Office(ARO)(Grant No.W911NF-18-1-0358)the Asian Office of Aerospace Research and Development(AOARD)(Grant No.FA2386-20-1-4069)the Foundational Questions Institute Fund(FQXi)(Grant No.FQXi-IAF19-06)。
文摘Noether’s theorem is one of the fundamental laws in physics,relating the symmetry of a physical system to its constant of motion and conservation law.On the other hand,there exist a variety of non-Hermitian parity-time(PT)-symmetric systems,which exhibit novel quantum properties and have attracted increasing interest.In this work,we extend Noether’s theorem to a class of significant PT-symmetry systems for which the eigenvalues of the PT-symmetry Hamiltonian HPTchange from purely real numbers to purely imaginary numbers,and introduce a generalized expectation value of an operator based on biorthogonal quantum mechanics.We find that the generalized expectation value of a time-independent operator is a constant of motion when the operator presents a standard symmetry in the PT-symmetry unbroken regime,or a chiral symmetry in the PT-symmetry broken regime.In addition,we experimentally investigate the extended Noether’s theorem in PT-symmetry single-qubit and two-qubit systems using an optical setup.Our experiment demonstrates the existence of the constant of motion and reveals how this constant of motion can be used to judge whether the PT-symmetry of a system is broken.Furthermore,a novel phenomenon of masking quantum information is first observed in a PT-symmetry two-qubit system.This study not only contributes to full understanding of the relation between symmetry and conservation law in PT-symmetry physics,but also has potential applications in quantum information theory and quantum communication protocols.
基金the NKRDP of China (Grant No. 2016YFA0301802)the National Natural Science Foundation of China under Grant Nos. 11074062,11374083, and 11774076.
文摘We propose a single-step implementation of a muti-target-qubit controlled phase gate with one catstate qubit (cqubit) simultaneously controlling n — 1 target cqubits. The two logic states of a c.qubit are represented by two orthogonal cat states of a single cavity mode. In this proposal, the gate is implemented with n microwave cavities coupled to a superconducting transnion qutrit. Because the qutrit remains in the ground state during the gate operation, decoherence caused due to the qutrit5s energy relaxation and dephasing is greatly suppressed. The gate implementation is quite simple because only a single-stcp operation is needed and neither classical pulse nor measurement is required. Numerical simulations demonstrate that high-fidelity realization of a controlled phase gate with one cqubit simultaneously con trolling two targe t cqubits is feasible with present circuit QED technology. This proposal can be extended to a wide range of physical systems to realize the proposed gate, such as multiple microwave or optical cavities coupled to a natural or artificial three-level atom.
基金the Key-Area Research and Development Program of GuangDong Province(Grant No.2018B030326001)the National Natural Science Foundation of China(NSFC)(Grant Nos.11074062,11374083,and 11774076)+1 种基金the NKRDP of China(Grant No.2016YFA0301802)the Jiangxi Natural Science Foundation(Grant No.20192ACBL20051).
文摘We propose a method for transferring quantum entangled states of two photonic cat-state qubits(cqubits)from two microwave cavities to the other two microwave cavities.This proposal is realized by using four microwave cavities coupled to a superconducting flux qutrit.Because of using four cavities with different frequencies,the inter-cavity crosstalk is significantly reduced.Since only one coupler qutrit is used,the circuit resource is minimized.The entanglement transfer is completed with a singlestep operation only,thus this proposal is quite simple.The third energy level of the coupler qutrit is not populated during the state transfer,therefore decoherence from the higher energy level is greatly suppressed.Our numerical simulations show that high-fidelity transfer of two-cqubit entangled states from two transmission line resonators to the other two transmission line resonators is feasible with current circuit QED technology.This proposal is universal and can be applied to accomplish the same task in a wide range of physical systems,such as four microwave or optical cavities,which are coupled to a natural or artificial three-level atom.
