Quantum teleportation with entanglement channels and a series of two-qubit SWAP gates between the nearestneighbor qubits are usually utilized to achieve the transfers of unknown quantum state from the sender to the di...Quantum teleportation with entanglement channels and a series of two-qubit SWAP gates between the nearestneighbor qubits are usually utilized to achieve the transfers of unknown quantum state from the sender to the distant receiver. In this paper, by simplifying the usual SWAP gates we propose an approach to speed up the transmissions of unknown quantum information, specifically including the single-qubit unknown state and two-qubit unknown entangled ones,by a series of entangling and disentangling operations between the remote qubits with distant interactions. The generic proposal is demonstrated specifically with experimentally-existing Ising-type quantum channels without transverse interaction; liquid NMR-molecules driven by global radio frequency electromagnetic pulses and capacitively-coupled Josephson circuits driven by local microwave pulses. The proposal should be particularly useful to set up the connections between the distant qubits in a chip of quantum computing.展开更多
Stark-chirped rapid adiabatic passage(SCRAP) is an important technique used for coherent quantum controls. In this paper we investigate how the practically-existing dissipation of the system influences on the efficien...Stark-chirped rapid adiabatic passage(SCRAP) is an important technique used for coherent quantum controls. In this paper we investigate how the practically-existing dissipation of the system influences on the efficiency of the passage, and thus the fidelities of the SCRAP-based quantum gates. With flux-biased Josephson qubits as a specifical example, our results show clearly that the efficiency of the logic gates implemented by SCRAP are robust against the weak dissipation. The influence due to the non-adiabtic transitions between the adiabatic passages is comparatively significantly small. Therefore, the SCRAP-based logic gates should be feasible for the realistic physical systems with noises.展开更多
An approach is proposed to implement the universal quantum gates between the ions confined individually in the separated traps.Instead of the typical adiabatic operations,performed for manipulating the ion-ion couplin...An approach is proposed to implement the universal quantum gates between the ions confined individually in the separated traps.Instead of the typical adiabatic operations,performed for manipulating the ion-ion coupling,here the switchable couplings between ions are implemented non-adiabatically by using the fast laser pulses.Consequently,the desirable quantum gates between the ions could be implemented by using only a series of laser pulses.The proposal may be conveniently generalized to the quantum computation with the scalable ion-traps.展开更多
Nonsequential double ionization （NSDI） processes of nonaligned diatomic molecules N2 and O2 are studied using the S-matrix theory. Our results show that the NSDI process significantly depends on the molecular symmet...Nonsequential double ionization （NSDI） processes of nonaligned diatomic molecules N2 and O2 are studied using the S-matrix theory. Our results show that the NSDI process significantly depends on the molecular symmetry and structure. The ratio of NSDI rate to single ionization rate as a function of the field intensity is obtained. It is found that N2 behaves closely with its companion atom Ar in the ratios over the entire intensity range, while O2 exhibits an obvious suppression effect, which is qualitatively consistent with the experiment.展开更多
Hardy＇s theorem on nonlocality has been verified by a series of experiments with two-qubit entangled pure states.However,in this paper we demonstrate the experimental test of the theorem by using the two-photon entan...Hardy＇s theorem on nonlocality has been verified by a series of experiments with two-qubit entangled pure states.However,in this paper we demonstrate the experimental test of the theorem by using the two-photon entangled mixed states.We first investigate the generic logic in Hardy＇s proof of nonlocality,which can be applied for arbitrary two-qubit mixed polarization entangled states and can be reduced naturally to the well-known logic tested successfully by the previous pure state experiments.Then,the optimized violations of locality for various experimental parameters are delivered by the numerical method.Finally,the logic argued above for testing Hardy＇s theorem on nonlocality is demonstrated experimentally by using the mixed entangled-photon pairs generated via pumping two type-I BBO crystals.Our experimental results shows that Hardy＇s proof of nonlocality can also be verified with two-qubit polarization entangled mixed states,with a violation of about 3.4 standard deviations.展开更多
The system of electrons on liquid helium is an interesting candidate to implement quantum computation, due to the long coherence times of the qubits encoded by the electronic spins. In order to implement the quantum l...The system of electrons on liquid helium is an interesting candidate to implement quantum computation, due to the long coherence times of the qubits encoded by the electronic spins. In order to implement the quantum logic operations between the spins, we propose here a configuration, similarly to the cooled ions in a trap, to couple the distant electrons via manipulating their center of mass （CM） vibrations. First, we show that the electrons could be confined in a common harmonic oscillator potential by using an electrostatic field. Then, with a single current pulse （applied on the micro-electrode below the liquid helium） the distant electronic spins can be coupled simultaneously to the CM mode. Finally, by adiabatically eliminating the CM mode, effective interaction between the distant spins is induced for implementing the desired quantum computing.展开更多
We investigate the self-trapping of a Bose Josephson junction, which is dispersively coupled to a driven optical cavity. The cavity-induced nonlinearity is presented analytically, and its effect results in the appeara...We investigate the self-trapping of a Bose Josephson junction, which is dispersively coupled to a driven optical cavity. The cavity-induced nonlinearity is presented analytically, and its effect results in the appearance of the self-trapping for the Bose-Einstein condensates in the Josephson oscillation regime. In addition, there exists competition between the nonlinearities induced by the interatomic interaction and by the driven cavity for the emergences of self-trapping. Our results show that the driven cavity can be utilized as a possible tool to produce the self-trapping for the condensates with weak interatomic interaction.展开更多
We investigate the dynamics of measurement-induced disturbance(MID) for a qubit-qutrit system in noninertial frames under various multi-local decoherence channels(i.e.,dephasing,phase-flip,bit-(trit-) flip,bit-(trit-)...We investigate the dynamics of measurement-induced disturbance(MID) for a qubit-qutrit system in noninertial frames under various multi-local decoherence channels(i.e.,dephasing,phase-flip,bit-(trit-) flip,bit-(trit-) phase-flip,and depolarizing channels).We find that,for any acceleration,the MID can decay in a monotonic way to zero or to a nonzero steady value(i.e.,residual MID exists).Consequently,no sudden death of the MID occurs,which is different from entanglement.展开更多
We present the measurements of the temperature dependence of the internal quality factor （O,i） of a microwave resonator, well below the superconducting transition temperature. The device is a quarter-wavelength niob...We present the measurements of the temperature dependence of the internal quality factor （O,i） of a microwave resonator, well below the superconducting transition temperature. The device is a quarter-wavelength niobium （Tc = 9.2 K） coplanar waveguide resonator. The measured ｜S21｜ parameter shows typically the skewed Lorentzian distributions, from which the fitted quality factor monotonically decreases with the temperature increasing from 30ink to 900mK. It is observed that for the lower temperature range （i.e., at T 〈 700 mK） the temperature dependence of the fitted Qi deviates significantly from the predictions of the usual Mattis-Bardeen theory. The measured 3 dB internal quality factor Qi also verifies such an anomalous temperature dependence. Physically, this phenomenon could be attributed dominantly to the effects of the two-level systems in the device, rather than the usual temperature-dependent complex conductance.展开更多
Bell’s theorem states that quantum mechanics cannot be accounted for by any local theory. One of the examples is the existence of quantum non-locality is essentially violated by the local Bell’s inequality. Therefor...Bell’s theorem states that quantum mechanics cannot be accounted for by any local theory. One of the examples is the existence of quantum non-locality is essentially violated by the local Bell’s inequality. Therefore, the violation of Bell’s inequality(BI) has been regarded as one of the robust evidences of quantum mechanics. Until now, BI has been tested by many experiments, but the maximal violation(i.e., Cirel’son limit) has never been achieved. By improving the design of entangled sources and optimizing the measurement settings, in this work we report the stronger violations of the Clauser–Horne–Shimony–Holt(CHSH)-type Bell’s inequality. The biggest value of Bell’s function in our experiment reaches √to a significant one: S = 2.772 ± 0.063, approaching to the so-called Cirel’son limit in which the Bell function value is S = 22.Further improvement is possible by optimizing the entangled-photon sources.展开更多
We investigate the Hawking radiation of a Kaluza-Klein black hole by using one-dimensional(1D),nonequilibrium,Landauer transport model.The derived Hawking radiation temperature is in consistence with that obtained by ...We investigate the Hawking radiation of a Kaluza-Klein black hole by using one-dimensional(1D),nonequilibrium,Landauer transport model.The derived Hawking radiation temperature is in consistence with that obtained by using the usual anomaly method.With the Landauer transport model,we calculate the entropy flow out of the Kaluza-Klein black hole and the relevant entropy production rate.How these quantities depending on the physical parameters of the black hole is also discussed.展开更多
Entangling multiple qubits is one of the central tasks of quantum information processing.We propose an approach to entangle a number of cold ions(individually trapped in a string of microtraps)by a moved cavity.The ca...Entangling multiple qubits is one of the central tasks of quantum information processing.We propose an approach to entangle a number of cold ions(individually trapped in a string of microtraps)by a moved cavity.The cavity is pushed to include the ions one by one with a uniform velocity and thus the information stored in former ions could be transferred to the latter ones by such a moving cavity bus.Since the positions of the trapped ions are precisely located,the strengths and durations of the ion-cavity interactions can be exactly controlled.As a consequence,by properly setting the relevant parameters,typical multi-ion entangled states,e.g.,W state for 10 ions,could be deterministically generated.The feasibility of the proposal is also discussed.展开更多
The original formula of Bell inequality（BI） in terms of two-spin singlet has to be modified for the entangled-state with parallel spin polarization. Based on classical statistics of the particle-number correlation, ...The original formula of Bell inequality（BI） in terms of two-spin singlet has to be modified for the entangled-state with parallel spin polarization. Based on classical statistics of the particle-number correlation, we prove in this paper an extended BI, which is valid for two-spin entangled states with both parallel and antiparallel polarizations. The BI and its violation can be formulated in a unified formalism based on the spin coherent-state quantum probability statistics with the statedensity operator, which is separated to the local and non-local parts. The local part gives rise to the BI, while the violation is a direct result of the non-local quantum interference between two components of entangled state. The Bell measuring outcome correlation denoted by PB is always less than or at most equal to one for the local realistic model（PB^lc≤ 1）regardless of the specific superposition coefficients of entangled state. Including the non-local quantum interference the maximum violation of BI is found as PB^max =2, which, however depends on state parameters and three measuring directions as well. Our result is suitable for entangled photon pairs.展开更多
We propose an approach to detect an unknown quantum state of the atom(s) by measuring the phase shifts of the transmitted photons through a dispersively-coupled cavity. In the framework of the input-output theory, we ...We propose an approach to detect an unknown quantum state of the atom(s) by measuring the phase shifts of the transmitted photons through a dispersively-coupled cavity. In the framework of the input-output theory, we derive the relations between the phase shifts of the transmitted photons and the states of the atom(s) in the cavity. It is shown that due to the dispersive interaction between the cavity and the atom(s), information about the atomic state can then be extracted by measuring the phase shifts of the transmitted photons through the cavity. The feasibility of the proposal is also discussed with the experimental parameters by numerical method.展开更多
We propose an efficient scheme to generate multiqubit Greenberger-ttorne--Zeilinger （GHZ） states by one- step quantum operation in a driven circuit quantum electrodyna.mics （QED） system. Our proposal is based on a...We propose an efficient scheme to generate multiqubit Greenberger-ttorne--Zeilinger （GHZ） states by one- step quantum operation in a driven circuit quantum electrodyna.mics （QED） system. Our proposal is based on a unitary evolution exp[-iλSx^2], with Sx being the collective spin operator in x direction and A a controllable parameter, induced by driving the resonator. The quantum operation avoids resonator-field decay and may achieve the GHZ states with ideal success probability. The feasibility with the experimentally-demonstrated circuit QED system is also discussed.展开更多
We design and fabricate two types of superconducting niobium coplanar waveguide microwave resonators with different coupling capacitors on high purity Si substrates.Their microwave transmissions are measured at 20 mK....We design and fabricate two types of superconducting niobium coplanar waveguide microwave resonators with different coupling capacitors on high purity Si substrates.Their microwave transmissions are measured at 20 mK.It is found that these two types of resonators possess significantly different loaded quality factors;one is 5.6×10^(3) and the other is 4.0×10^(4).The measured data are fitted well by classical ABCD matrix approach and consequently the coupling capacitances are determined.It is found that the transmission peak deviates from the standard Lorentizian with a frequency broadening.展开更多
Quantum computation requires coherently controlling the evolutions of qubits.Usually,these manipulations are implemented by precisely designing the durations(such as theπ-pulses)of the Rabi oscillations and tunable i...Quantum computation requires coherently controlling the evolutions of qubits.Usually,these manipulations are implemented by precisely designing the durations(such as theπ-pulses)of the Rabi oscillations and tunable interbit coupling.Relaxing this requirement,herein we show that the desired population transfers between the logic states can be deterministically realized(and thus quantum computation could be implemented)both adiabatically and non-adiabatically,by performing the duration-insensitive quantum manipulations.Our proposal is specifically demonstrated with the surface-state of electrons floating on the liquid helium,but could also be applied to the other artificially controllable systems for quantum computing.展开更多
We successfully designed and fabricated an absorption-type of superconducting coplanar waveguide (CPW) resonators. The resonators are made from a niobium film (about 160 nm thick) on a high-resistance Si substrate, an...We successfully designed and fabricated an absorption-type of superconducting coplanar waveguide (CPW) resonators. The resonators are made from a niobium film (about 160 nm thick) on a high-resistance Si substrate, and each resonator is fabricated as a meandered quarter-wavelength transmission line (one end is short to the ground and another end is capacitively coupled to a through feedline). With a vector network analyzer we measured the transmissions of the applied microwave through the resonators at ultra-low temperature. The obtained loaded quality factors are significantly high, i.e. up to ～10 6 . When the temperature increases slowly from the base temperature (20 mK), the resonance frequencies of the resonators are blue shifted and the quality factors are lowered slightly. In principle, this type of device can integrate a series of CPW resonators with a common feedline, making it a promising candidate as the data bus for coupling distant solid-state qubits and the sensitive detector of single photons.展开更多
We study optomechanically induced amplification and perfect transparency in a double-cavity op- tomechanical system. We find that if two control lasers with appropriate amplitudes and detunings are applied to drive th...We study optomechanically induced amplification and perfect transparency in a double-cavity op- tomechanical system. We find that if two control lasers with appropriate amplitudes and detunings are applied to drive the system, optomechanically induced amplification of a probe laser can occur. In addition, perfect optomechanieally induced transparency, which is robust to mechanical dissipation, can be realized by the same type of driving. These results indicate important progress toward signal amplification, light storage, fast light, and slow light in quantum information processes.展开更多
Bell＇s theorem argues the existence of quantum nonlocality which goes basically against the hidden variable theory （HVT）. Many experiments have been done via testing the violations of Bell＇s inequalities to statis...Bell＇s theorem argues the existence of quantum nonlocality which goes basically against the hidden variable theory （HVT）. Many experiments have been done via testing the violations of Bell＇s inequalities to statistically verify the Bell＇s theorem. Alternatively, by testing the Hardy＇s ladder proofs we experimentally demonstrate the deterministic violation of HVT and thus confirm the quantum nonlocality. Our tests are implemented with non-maximal entangled photon pairs generated by spontaneous parametric down conversions （SPDCs）. We show that the degree freedom of photon entanglement could be significantly enhanced by using interference filters. As a consequence, the Hardy＇s ladder proofs could be tested and Bell＇s theorem is verified robustly. The probability of violating the locality reach to 41.9%, which is close to the expectably ideal value 46.4% for the photon pairs with degree of entanglement e = 0.93. The higher violating probability is possible by further optimizing the experimental parameters.展开更多
基金partly supported by the National Natural Science Foundation of China(Grant No.U1330201)
文摘Quantum teleportation with entanglement channels and a series of two-qubit SWAP gates between the nearestneighbor qubits are usually utilized to achieve the transfers of unknown quantum state from the sender to the distant receiver. In this paper, by simplifying the usual SWAP gates we propose an approach to speed up the transmissions of unknown quantum information, specifically including the single-qubit unknown state and two-qubit unknown entangled ones,by a series of entangling and disentangling operations between the remote qubits with distant interactions. The generic proposal is demonstrated specifically with experimentally-existing Ising-type quantum channels without transverse interaction; liquid NMR-molecules driven by global radio frequency electromagnetic pulses and capacitively-coupled Josephson circuits driven by local microwave pulses. The proposal should be particularly useful to set up the connections between the distant qubits in a chip of quantum computing.
基金Supported by the National Science Foundation under Grant Nos.90921010,11174373the National Fundamental Research Program of China under Grant No.2010CB923104+2 种基金National Research Foundation and Ministry of Education,Singapore under Grant No.WBS:R-710-000-008-271the 2013 Doctoral Innovation funds of Southwest Jiaotong Universitythe Fundamental Research Funds for the Central Universities
文摘Stark-chirped rapid adiabatic passage(SCRAP) is an important technique used for coherent quantum controls. In this paper we investigate how the practically-existing dissipation of the system influences on the efficiency of the passage, and thus the fidelities of the SCRAP-based quantum gates. With flux-biased Josephson qubits as a specifical example, our results show clearly that the efficiency of the logic gates implemented by SCRAP are robust against the weak dissipation. The influence due to the non-adiabtic transitions between the adiabatic passages is comparatively significantly small. Therefore, the SCRAP-based logic gates should be feasible for the realistic physical systems with noises.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11147116,10874142 and 90921010the National Basic Research Program of China under Grant No 2010CB923104the Open Project of State Key Laboratory of Functional Materials for Informatics.
文摘An approach is proposed to implement the universal quantum gates between the ions confined individually in the separated traps.Instead of the typical adiabatic operations,performed for manipulating the ion-ion coupling,here the switchable couplings between ions are implemented non-adiabatically by using the fast laser pulses.Consequently,the desirable quantum gates between the ions could be implemented by using only a series of laser pulses.The proposal may be conveniently generalized to the quantum computation with the scalable ion-traps.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11074026, 11074155, and 11104225)the Program for New Century Excellent Talents in University of the Ministry of Education of China (Grant No. NCET-08-0883)the National Basic Research Program of China (Grant No. 2011CB808100)
文摘Nonsequential double ionization （NSDI） processes of nonaligned diatomic molecules N2 and O2 are studied using the S-matrix theory. Our results show that the NSDI process significantly depends on the molecular symmetry and structure. The ratio of NSDI rate to single ionization rate as a function of the field intensity is obtained. It is found that N2 behaves closely with its companion atom Ar in the ratios over the entire intensity range, while O2 exhibits an obvious suppression effect, which is qualitatively consistent with the experiment.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61308008 and U1330201)
文摘Hardy＇s theorem on nonlocality has been verified by a series of experiments with two-qubit entangled pure states.However,in this paper we demonstrate the experimental test of the theorem by using the two-photon entangled mixed states.We first investigate the generic logic in Hardy＇s proof of nonlocality,which can be applied for arbitrary two-qubit mixed polarization entangled states and can be reduced naturally to the well-known logic tested successfully by the previous pure state experiments.Then,the optimized violations of locality for various experimental parameters are delivered by the numerical method.Finally,the logic argued above for testing Hardy＇s theorem on nonlocality is demonstrated experimentally by using the mixed entangled-photon pairs generated via pumping two type-I BBO crystals.Our experimental results shows that Hardy＇s proof of nonlocality can also be verified with two-qubit polarization entangled mixed states,with a violation of about 3.4 standard deviations.
基金Supported by the National Natural Science Foundation of China under Grant Nos.11204249,11174373the National Fundamental Research Program of China under Grant No.2010CB923104
文摘The system of electrons on liquid helium is an interesting candidate to implement quantum computation, due to the long coherence times of the qubits encoded by the electronic spins. In order to implement the quantum logic operations between the spins, we propose here a configuration, similarly to the cooled ions in a trap, to couple the distant electrons via manipulating their center of mass （CM） vibrations. First, we show that the electrons could be confined in a common harmonic oscillator potential by using an electrostatic field. Then, with a single current pulse （applied on the micro-electrode below the liquid helium） the distant electronic spins can be coupled simultaneously to the CM mode. Finally, by adiabatically eliminating the CM mode, effective interaction between the distant spins is induced for implementing the desired quantum computing.
基金Supported by the National Natural Science Foundation of China under Grant Nos.10847006 and 10874142
文摘We investigate the self-trapping of a Bose Josephson junction, which is dispersively coupled to a driven optical cavity. The cavity-induced nonlinearity is presented analytically, and its effect results in the appearance of the self-trapping for the Bose-Einstein condensates in the Josephson oscillation regime. In addition, there exists competition between the nonlinearities induced by the interatomic interaction and by the driven cavity for the emergences of self-trapping. Our results show that the driven cavity can be utilized as a possible tool to produce the self-trapping for the condensates with weak interatomic interaction.
基金Supported by the Natural Science Foundation of China under Grant Nos. 90921010,and 11174373the Fundamental Research Program of China under Grant No. 2010CB923104the Fundamental Research Funds for the Central Universities under Grant Nos. SWJTU09CX078 and 2010XS47
文摘We investigate the dynamics of measurement-induced disturbance(MID) for a qubit-qutrit system in noninertial frames under various multi-local decoherence channels(i.e.,dephasing,phase-flip,bit-(trit-) flip,bit-(trit-) phase-flip,and depolarizing channels).We find that,for any acceleration,the MID can decay in a monotonic way to zero or to a nonzero steady value(i.e.,residual MID exists).Consequently,no sudden death of the MID occurs,which is different from entanglement.
基金Supported by the State Key Development Program for Basic Research of China under Grant No 2011CB923104, the National Natural Science Foundation of China under Grant Nos 61301031, 11174373 and U1330201.
文摘We present the measurements of the temperature dependence of the internal quality factor （O,i） of a microwave resonator, well below the superconducting transition temperature. The device is a quarter-wavelength niobium （Tc = 9.2 K） coplanar waveguide resonator. The measured ｜S21｜ parameter shows typically the skewed Lorentzian distributions, from which the fitted quality factor monotonically decreases with the temperature increasing from 30ink to 900mK. It is observed that for the lower temperature range （i.e., at T 〈 700 mK） the temperature dependence of the fitted Qi deviates significantly from the predictions of the usual Mattis-Bardeen theory. The measured 3 dB internal quality factor Qi also verifies such an anomalous temperature dependence. Physically, this phenomenon could be attributed dominantly to the effects of the two-level systems in the device, rather than the usual temperature-dependent complex conductance.
基金supported by the National Natural Science Foundation of China(Grant Nos.61308008,91321104,U1330201,and 11174373)the Fundamental Research Funds for the Central Universities(Grant No.2682014CX081)
文摘Bell’s theorem states that quantum mechanics cannot be accounted for by any local theory. One of the examples is the existence of quantum non-locality is essentially violated by the local Bell’s inequality. Therefore, the violation of Bell’s inequality(BI) has been regarded as one of the robust evidences of quantum mechanics. Until now, BI has been tested by many experiments, but the maximal violation(i.e., Cirel’son limit) has never been achieved. By improving the design of entangled sources and optimizing the measurement settings, in this work we report the stronger violations of the Clauser–Horne–Shimony–Holt(CHSH)-type Bell’s inequality. The biggest value of Bell’s function in our experiment reaches √to a significant one: S = 2.772 ± 0.063, approaching to the so-called Cirel’son limit in which the Bell function value is S = 22.Further improvement is possible by optimizing the entangled-photon sources.
基金Supported by the National Natural Science Foundation of China under Grant Nos.90921010,11174373,11005086,11205125, 2010CB923104the Youth Foundation of Education Department of Sichuan Province under Grant No.11ZB032the Sichuan Youth Science and Technology Foundation under Grant No.2011JQ0019
文摘We investigate the Hawking radiation of a Kaluza-Klein black hole by using one-dimensional(1D),nonequilibrium,Landauer transport model.The derived Hawking radiation temperature is in consistence with that obtained by using the usual anomaly method.With the Landauer transport model,we calculate the entropy flow out of the Kaluza-Klein black hole and the relevant entropy production rate.How these quantities depending on the physical parameters of the black hole is also discussed.
基金by the National Natural Science Foundation of China under Grant Nos 10874142 and 90921010the National Basic Research Program of China under Grant No 2010CB923104.
文摘Entangling multiple qubits is one of the central tasks of quantum information processing.We propose an approach to entangle a number of cold ions(individually trapped in a string of microtraps)by a moved cavity.The cavity is pushed to include the ions one by one with a uniform velocity and thus the information stored in former ions could be transferred to the latter ones by such a moving cavity bus.Since the positions of the trapped ions are precisely located,the strengths and durations of the ion-cavity interactions can be exactly controlled.As a consequence,by properly setting the relevant parameters,typical multi-ion entangled states,e.g.,W state for 10 ions,could be deterministically generated.The feasibility of the proposal is also discussed.
基金Project supported in part by the National Natural Science Foundation of China(Grant Nos.11275118 and U1330201)
文摘The original formula of Bell inequality（BI） in terms of two-spin singlet has to be modified for the entangled-state with parallel spin polarization. Based on classical statistics of the particle-number correlation, we prove in this paper an extended BI, which is valid for two-spin entangled states with both parallel and antiparallel polarizations. The BI and its violation can be formulated in a unified formalism based on the spin coherent-state quantum probability statistics with the statedensity operator, which is separated to the local and non-local parts. The local part gives rise to the BI, while the violation is a direct result of the non-local quantum interference between two components of entangled state. The Bell measuring outcome correlation denoted by PB is always less than or at most equal to one for the local realistic model（PB^lc≤ 1）regardless of the specific superposition coefficients of entangled state. Including the non-local quantum interference the maximum violation of BI is found as PB^max =2, which, however depends on state parameters and three measuring directions as well. Our result is suitable for entangled photon pairs.
基金Supported by the Special Funds of the National Natural Science Foundation of China under Grant Nos.11247032 and 11247207the National Fundamental Research Program of China under Grant No.2010CB923104
文摘We propose an approach to detect an unknown quantum state of the atom(s) by measuring the phase shifts of the transmitted photons through a dispersively-coupled cavity. In the framework of the input-output theory, we derive the relations between the phase shifts of the transmitted photons and the states of the atom(s) in the cavity. It is shown that due to the dispersive interaction between the cavity and the atom(s), information about the atomic state can then be extracted by measuring the phase shifts of the transmitted photons through the cavity. The feasibility of the proposal is also discussed with the experimental parameters by numerical method.
基金Supported by the National Natural Science Foundation of China under Grant Nos.10874142 and 90921010
文摘We propose an efficient scheme to generate multiqubit Greenberger-ttorne--Zeilinger （GHZ） states by one- step quantum operation in a driven circuit quantum electrodyna.mics （QED） system. Our proposal is based on a unitary evolution exp[-iλSx^2], with Sx being the collective spin operator in x direction and A a controllable parameter, induced by driving the resonator. The quantum operation avoids resonator-field decay and may achieve the GHZ states with ideal success probability. The feasibility with the experimentally-demonstrated circuit QED system is also discussed.
基金Supported by the National Natural Science Foundation of China under Grant No 11174373the National Basic Research Program of China under Grant No 2010CB923104.
文摘We design and fabricate two types of superconducting niobium coplanar waveguide microwave resonators with different coupling capacitors on high purity Si substrates.Their microwave transmissions are measured at 20 mK.It is found that these two types of resonators possess significantly different loaded quality factors;one is 5.6×10^(3) and the other is 4.0×10^(4).The measured data are fitted well by classical ABCD matrix approach and consequently the coupling capacitances are determined.It is found that the transmission peak deviates from the standard Lorentizian with a frequency broadening.
基金supported by the National Natural Science Foundation of China(Grant Nos.90921010 and 11174373)the National FundamentalResearch Program of China(Grant No.2010CB-923104)+1 种基金the National Research Foundation and Ministry of Education,Singapore(Grant No.WBS:R-710-000-008-271)the 2013 Doctoral Innovation funds of Southwes tJiaotong University and the Fundamental Research Funds for the Central Universities
文摘Quantum computation requires coherently controlling the evolutions of qubits.Usually,these manipulations are implemented by precisely designing the durations(such as theπ-pulses)of the Rabi oscillations and tunable interbit coupling.Relaxing this requirement,herein we show that the desired population transfers between the logic states can be deterministically realized(and thus quantum computation could be implemented)both adiabatically and non-adiabatically,by performing the duration-insensitive quantum manipulations.Our proposal is specifically demonstrated with the surface-state of electrons floating on the liquid helium,but could also be applied to the other artificially controllable systems for quantum computing.
基金supported by the National Natural Science Foundation of China (90921010, 11174373)National Basic Research Program of China (2010CB923104)
文摘We successfully designed and fabricated an absorption-type of superconducting coplanar waveguide (CPW) resonators. The resonators are made from a niobium film (about 160 nm thick) on a high-resistance Si substrate, and each resonator is fabricated as a meandered quarter-wavelength transmission line (one end is short to the ground and another end is capacitively coupled to a through feedline). With a vector network analyzer we measured the transmissions of the applied microwave through the resonators at ultra-low temperature. The obtained loaded quality factors are significantly high, i.e. up to ～10 6 . When the temperature increases slowly from the base temperature (20 mK), the resonance frequencies of the resonators are blue shifted and the quality factors are lowered slightly. In principle, this type of device can integrate a series of CPW resonators with a common feedline, making it a promising candidate as the data bus for coupling distant solid-state qubits and the sensitive detector of single photons.
基金Acknowledgements This work was supported by the National Natural Science Foundation of China （Grant Nos. 61378094 and 11174027） and the Natural Science Foundation of Heilongjiang Province, China （No. A201402）. W. Z. Jia was supported by the National Natural Science Foundation of China under Grants Nos. 11347001 and 11404269, the Fundamental Research Funds for the Central Universities （Grant No. 2682014RC21）.
文摘We study optomechanically induced amplification and perfect transparency in a double-cavity op- tomechanical system. We find that if two control lasers with appropriate amplitudes and detunings are applied to drive the system, optomechanically induced amplification of a probe laser can occur. In addition, perfect optomechanieally induced transparency, which is robust to mechanical dissipation, can be realized by the same type of driving. These results indicate important progress toward signal amplification, light storage, fast light, and slow light in quantum information processes.
基金supported by the National Natural Science Foundation of China(Grant Nos.61308008,91321104,U1330201 and 11174373)the National Fundamental Research Program of China(Grant No.2010CB923104)
文摘Bell＇s theorem argues the existence of quantum nonlocality which goes basically against the hidden variable theory （HVT）. Many experiments have been done via testing the violations of Bell＇s inequalities to statistically verify the Bell＇s theorem. Alternatively, by testing the Hardy＇s ladder proofs we experimentally demonstrate the deterministic violation of HVT and thus confirm the quantum nonlocality. Our tests are implemented with non-maximal entangled photon pairs generated by spontaneous parametric down conversions （SPDCs）. We show that the degree freedom of photon entanglement could be significantly enhanced by using interference filters. As a consequence, the Hardy＇s ladder proofs could be tested and Bell＇s theorem is verified robustly. The probability of violating the locality reach to 41.9%, which is close to the expectably ideal value 46.4% for the photon pairs with degree of entanglement e = 0.93. The higher violating probability is possible by further optimizing the experimental parameters.
