Quantum communication networks,such as quantum key distribution(QKD)networks,typically employ the measurement-resend mechanism between two users using quantum communication devices based on different quantum encoding ...Quantum communication networks,such as quantum key distribution(QKD)networks,typically employ the measurement-resend mechanism between two users using quantum communication devices based on different quantum encoding types.To achieve direct communication between the devices with different quantum encoding types,in this paper,we propose encoding conversion schemes between the polarization bases(rectilinear,diagonal and circular bases)and the time-bin phase bases(two phase bases and time-bin basis)and design the quantum encoding converters.The theoretical analysis of the encoding conversion schemes is given in detail,and the basis correspondence of encoding conversion and the property of bit flip are revealed.The conversion relationship between polarization bases and time-bin phase bases can be easily selected by controlling a phase shifter.Since no optical switches are used in our scheme,the converter can be operated with high speed.The converters can also be modularized,which may be utilized to realize miniaturization in the future.展开更多
Multiple access interference (MAI) is the most serious interference in spectral phase encoding optical code division multiple access (SPE OCDMA) systems. This paper focuses on the behavior of MAI in SPE OCDMA systems ...Multiple access interference (MAI) is the most serious interference in spectral phase encoding optical code division multiple access (SPE OCDMA) systems. This paper focuses on the behavior of MAI in SPE OCDMA systems with pseudorandom coding. The statistical expectation of multi access interference (MAI) is derived and plotted. The results confirm that MAI can be suppressed effectively by pseudorandom coding with m sequences.展开更多
We design proposals to generate a remote Greenberger-Horne-Zeilinger（GHZ） state and a W state of nitrogenvacancy（NV） centers coupled to microtoroidal resonators（MTRs） through noisy channels by utilizing time-bin...We design proposals to generate a remote Greenberger-Horne-Zeilinger（GHZ） state and a W state of nitrogenvacancy（NV） centers coupled to microtoroidal resonators（MTRs） through noisy channels by utilizing time-bin encoding processes and fast-optical-switch-based polarization rotation operations.The polarization and phase noise induced by noisy channels generally affect the time of state generation but not its success probability and fidelity.Besides,the above proposals can be generalized to n-qubit between two or among n remote nodes with success probability unity under ideal conditions.Furthennore,the proposals are robust for regular noise-changeable channels for the n-node case.This method is also useful in other remote quantum information processing tasks through noisy channels.展开更多
This study investigated the effect of velocity encoding on measurement of brain blood flow and blood volume of inflow and outflow using phase-contrast magnetic resonance angiography. A single two-dimensional phase-con...This study investigated the effect of velocity encoding on measurement of brain blood flow and blood volume of inflow and outflow using phase-contrast magnetic resonance angiography. A single two-dimensional phase-contrast magnetic resonance angiography slice was applied perpendicular to the internal carotid artery and the vertebral artery at C2 level. For each subject, the velocity encoding was set from 30 to 90 cm/s with an interval of 10 cm/s for a total of seven settings. Various velocity encodings greatly affected blood flow volume, maximal blood flow velocity and mean blood flow velocity in the internal carotid artery, but did not significantly affect vertebral arteries and jugular veins. When velocity encoding was 60-80 cm/s, the inflow blood volume was 655 _＋ 118 mL/min, and the outflow volume was 506 _＋ 186 mL/min. The ratio of outflow/inflow was steady at 0.78-0.83, and there was no aliasing in any of the images. These findings suggest that velocity encodings of 60 80 cm/s should be selected during measurement of cerebral blood flow volume using phase-contrast magnetic resonance angiography.展开更多
Many monographs point out that differential encoding and decoding is necessary for ef- fectual information transmission against phase ambiguity while seldom discuss the reason why phase ambiguity will emerge inevitabl...Many monographs point out that differential encoding and decoding is necessary for ef- fectual information transmission against phase ambiguity while seldom discuss the reason why phase ambiguity will emerge inevitably.Available algorithms are specially designed for certain modulation scheme;these algorithms cannot satisfy the requirement of soft-defined radio,which perhaps demands a uniform algorithm for different modulations.This paper proposes a new opinion on phase ambiguity from the view of probability.This opinion believes that modulating symbol sequence can affect,at optimum sampling epoch,the modulated waveform as oscillating carrier has done,and so the stochastic sequence leads to phase ambiguity.Based on a general signal model,this paper also puts forward a novel universal algorithm,which is suitable for different signals,even some new ones,by configuring several parameters.展开更多
Optical cryptanalysis is essential to the further investigation of more secure optical cryptosystems.Learning-based at-tack of optical encryption eliminates the need for the retrieval of random phase keys of optical e...Optical cryptanalysis is essential to the further investigation of more secure optical cryptosystems.Learning-based at-tack of optical encryption eliminates the need for the retrieval of random phase keys of optical encryption systems but it is limited for practical applications since it requires a large set of plaintext-ciphertext pairs for the cryptosystem to be at-tacked.Here,we propose a two-step deep learning strategy for ciphertext-only attack(COA)on the classical double ran-dom phase encryption(DRPE).Specifically,we construct a virtual DRPE system to gather the training data.Besides,we divide the inverse problem in COA into two more specific inverse problems and employ two deep neural networks(DNNs)to respectively learn the removal of speckle noise in the autocorrelation domain and the de-correlation operation to retrieve the plaintext image.With these two trained DNNs at hand,we show that the plaintext can be predicted in real-time from an unknown ciphertext alone.The proposed learning-based COA method dispenses with not only the retrieval of random phase keys but also the invasive data acquisition of plaintext-ciphertext pairs in the DPRE system.Numerical simulations and optical experiments demonstrate the feasibility and effectiveness of the proposed learning-based COA method.展开更多
A deterministic phase-encoded encryption system is proposed. A lenticular lens array (LLA) sheet with a particular LPI (lenticular per inch) number is chosen as a modulator (key) instead of the random phase molator. T...A deterministic phase-encoded encryption system is proposed. A lenticular lens array (LLA) sheet with a particular LPI (lenticular per inch) number is chosen as a modulator (key) instead of the random phase molator. The suggested encryption scheme is based on arbitrary two-step phase-shift interferometry (PSI), using an unknown phase step. The encryption and decryption principle is based on an LLA in arbitrary unknown two-step PSI. Right key holograms can be used to theoretically show that the object wavefront is the only one left in the hologram plane and that all accompanying undesired terms are eliminated. The encrypted image can therefore be numerically and successfully decrypted with the right key in the image plane. The number of degrees of freedom of the encryption scheme increases with the distance from the object and the LLA to the CCD, and also with the unknown phase-step and the LLA LPI number. Computer simulations are performed to verify the encryption and decryption principles without a key, with the wrong key and with the right key. Optical experiments are also performed to validate them.展开更多
The optimal velocity encoding of phase-contrast magnetic resonance angiography （PC MRA） in measuring cerebral blood flow volume （BFV） ranges from 60 to 80 cm/s. To verify the accuracy of two-dimensional （2D） PC ...The optimal velocity encoding of phase-contrast magnetic resonance angiography （PC MRA） in measuring cerebral blood flow volume （BFV） ranges from 60 to 80 cm/s. To verify the accuracy of two-dimensional （2D） PC MRA, the present study localized the region of interest at blood vessels of the neck using PC MRA based on three-dimensional time-of-flight sequences, and the velocity encoding was set to 80 cm/s. Results of the measurements showed that the error rate was 7.0±6.0% in the estimation of BFV in the internal carotid artery, the external carotid artery and the ipsilateral common carotid artery. There was no significant difference, and a significant correlation in BFV between internal carotid artery ＋ external carotid artery and ipsilateral common carotid artery. In addition, the BFV of the common carotid artery was correlated with that of the ipsilateral internal carotid artery. The main error was attributed to the external carotid artery and its branches. Therefore, after selecting the appropriate scanning parameters and protocols, 2D PC MRA is more accurate in the determination of BFV in the carotid arteries.展开更多
Quantum secret sharing(QSS)is one of the basic communication primitives in future quantum networks which addresses part of the basic cryptographic tasks of multiparty communication and computation.Nevertheless,it is a...Quantum secret sharing(QSS)is one of the basic communication primitives in future quantum networks which addresses part of the basic cryptographic tasks of multiparty communication and computation.Nevertheless,it is a challenge to provide a practical QSS protocol with security against general attacks.A QSS protocol that balances security and practicality is still lacking.Here,we propose a QSS protocol with simple phase encoding of coherent states among three parties.Removing the requirement of impractical entangled resources and the need for phase randomization,our protocol can be implemented with accessible technology.We provide the finite-key analysis against coherent attacks and implement a proof-of-principle experiment to demonstrate our scheme’s feasibility.Our scheme achieves a key rate of 85.3 bps under a 35 d B channel loss.Combined with security against general attacks and accessible technology,our protocol is a promising candidate for practical multiparty quantum communication networks.展开更多
In recent years,metasurfaces that enable the flexible wavefront modulation at sub-wavelength scale have been widely used into holographic display,due to its prominent advantages in polarization degrees of freedom,view...In recent years,metasurfaces that enable the flexible wavefront modulation at sub-wavelength scale have been widely used into holographic display,due to its prominent advantages in polarization degrees of freedom,viewing angle,and achromaticity in comparison with traditional holographic devices.In holography,the computational complexity of hologram,imaging sharpness,energy utilization,reproduction rate,and system indirection are all determined by the encoding method.Here,we propose a visible frequency broadband dielectric metahologram based on the random Fourier phase-only encoding method.Using this simple and convenient method,we design and fabricate a transmission-type geometric phase all-dielectric metahologram,which can realize holographic display with high quality in the visible frequency range.This method encodes the amplitude information into the phase function only once,eliminating the cumbersome iterations,which greatly simplifies the calculation process,and may facilitate the preparation of large area nanoprint-holograms.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.62001440).
文摘Quantum communication networks,such as quantum key distribution(QKD)networks,typically employ the measurement-resend mechanism between two users using quantum communication devices based on different quantum encoding types.To achieve direct communication between the devices with different quantum encoding types,in this paper,we propose encoding conversion schemes between the polarization bases(rectilinear,diagonal and circular bases)and the time-bin phase bases(two phase bases and time-bin basis)and design the quantum encoding converters.The theoretical analysis of the encoding conversion schemes is given in detail,and the basis correspondence of encoding conversion and the property of bit flip are revealed.The conversion relationship between polarization bases and time-bin phase bases can be easily selected by controlling a phase shifter.Since no optical switches are used in our scheme,the converter can be operated with high speed.The converters can also be modularized,which may be utilized to realize miniaturization in the future.
基金Fund of Science and Technology Develop-ment of Shanghai(No.0 0 JC14 0 5 4
文摘Multiple access interference (MAI) is the most serious interference in spectral phase encoding optical code division multiple access (SPE OCDMA) systems. This paper focuses on the behavior of MAI in SPE OCDMA systems with pseudorandom coding. The statistical expectation of multi access interference (MAI) is derived and plotted. The results confirm that MAI can be suppressed effectively by pseudorandom coding with m sequences.
基金supported by the National Natural Science Foundation of China(Grant Nos.11264042,61465013,11465020,and 11165015)the Program for Chun Miao Excellent Talents of Jilin Provincial Department of Education(Grant No.201316)the Talent Program of Yanbian University of China(Grant No.950010001)
文摘We design proposals to generate a remote Greenberger-Horne-Zeilinger（GHZ） state and a W state of nitrogenvacancy（NV） centers coupled to microtoroidal resonators（MTRs） through noisy channels by utilizing time-bin encoding processes and fast-optical-switch-based polarization rotation operations.The polarization and phase noise induced by noisy channels generally affect the time of state generation but not its success probability and fidelity.Besides,the above proposals can be generalized to n-qubit between two or among n remote nodes with success probability unity under ideal conditions.Furthennore,the proposals are robust for regular noise-changeable channels for the n-node case.This method is also useful in other remote quantum information processing tasks through noisy channels.
基金the Medical Program of the Scientific & Technical Foundation in Xiamen(MRI study of chronic cerebrovascular insufficiency) in 2008,No.3502Z20084028
文摘This study investigated the effect of velocity encoding on measurement of brain blood flow and blood volume of inflow and outflow using phase-contrast magnetic resonance angiography. A single two-dimensional phase-contrast magnetic resonance angiography slice was applied perpendicular to the internal carotid artery and the vertebral artery at C2 level. For each subject, the velocity encoding was set from 30 to 90 cm/s with an interval of 10 cm/s for a total of seven settings. Various velocity encodings greatly affected blood flow volume, maximal blood flow velocity and mean blood flow velocity in the internal carotid artery, but did not significantly affect vertebral arteries and jugular veins. When velocity encoding was 60-80 cm/s, the inflow blood volume was 655 _＋ 118 mL/min, and the outflow volume was 506 _＋ 186 mL/min. The ratio of outflow/inflow was steady at 0.78-0.83, and there was no aliasing in any of the images. These findings suggest that velocity encodings of 60 80 cm/s should be selected during measurement of cerebral blood flow volume using phase-contrast magnetic resonance angiography.
基金Supported by Henan Prominent Talents Innovation Foundation (No.0421000100).
文摘Many monographs point out that differential encoding and decoding is necessary for ef- fectual information transmission against phase ambiguity while seldom discuss the reason why phase ambiguity will emerge inevitably.Available algorithms are specially designed for certain modulation scheme;these algorithms cannot satisfy the requirement of soft-defined radio,which perhaps demands a uniform algorithm for different modulations.This paper proposes a new opinion on phase ambiguity from the view of probability.This opinion believes that modulating symbol sequence can affect,at optimum sampling epoch,the modulated waveform as oscillating carrier has done,and so the stochastic sequence leads to phase ambiguity.Based on a general signal model,this paper also puts forward a novel universal algorithm,which is suitable for different signals,even some new ones,by configuring several parameters.
基金financial supports from the National Natural Science Foundation of China(NSFC)(62061136005,61705141,61805152,61875129,61701321)Sino-German Research Collaboration Group(GZ 1391)+2 种基金the Mobility program(M-0044)sponsored by the Sino-German CenterChinese Academy of Sciences(QYZDB-SSW-JSC002)Science and Technology Innovation Commission of Shenzhen(JCYJ20170817095047279)。
文摘Optical cryptanalysis is essential to the further investigation of more secure optical cryptosystems.Learning-based at-tack of optical encryption eliminates the need for the retrieval of random phase keys of optical encryption systems but it is limited for practical applications since it requires a large set of plaintext-ciphertext pairs for the cryptosystem to be at-tacked.Here,we propose a two-step deep learning strategy for ciphertext-only attack(COA)on the classical double ran-dom phase encryption(DRPE).Specifically,we construct a virtual DRPE system to gather the training data.Besides,we divide the inverse problem in COA into two more specific inverse problems and employ two deep neural networks(DNNs)to respectively learn the removal of speckle noise in the autocorrelation domain and the de-correlation operation to retrieve the plaintext image.With these two trained DNNs at hand,we show that the plaintext can be predicted in real-time from an unknown ciphertext alone.The proposed learning-based COA method dispenses with not only the retrieval of random phase keys but also the invasive data acquisition of plaintext-ciphertext pairs in the DPRE system.Numerical simulations and optical experiments demonstrate the feasibility and effectiveness of the proposed learning-based COA method.
文摘A deterministic phase-encoded encryption system is proposed. A lenticular lens array (LLA) sheet with a particular LPI (lenticular per inch) number is chosen as a modulator (key) instead of the random phase molator. The suggested encryption scheme is based on arbitrary two-step phase-shift interferometry (PSI), using an unknown phase step. The encryption and decryption principle is based on an LLA in arbitrary unknown two-step PSI. Right key holograms can be used to theoretically show that the object wavefront is the only one left in the hologram plane and that all accompanying undesired terms are eliminated. The encrypted image can therefore be numerically and successfully decrypted with the right key in the image plane. The number of degrees of freedom of the encryption scheme increases with the distance from the object and the LLA to the CCD, and also with the unknown phase-step and the LLA LPI number. Computer simulations are performed to verify the encryption and decryption principles without a key, with the wrong key and with the right key. Optical experiments are also performed to validate them.
基金the Medical Program of Scientific & Technical Foundation in Xiamen in 2008, No. 3502Z20084028
文摘The optimal velocity encoding of phase-contrast magnetic resonance angiography （PC MRA） in measuring cerebral blood flow volume （BFV） ranges from 60 to 80 cm/s. To verify the accuracy of two-dimensional （2D） PC MRA, the present study localized the region of interest at blood vessels of the neck using PC MRA based on three-dimensional time-of-flight sequences, and the velocity encoding was set to 80 cm/s. Results of the measurements showed that the error rate was 7.0±6.0% in the estimation of BFV in the internal carotid artery, the external carotid artery and the ipsilateral common carotid artery. There was no significant difference, and a significant correlation in BFV between internal carotid artery ＋ external carotid artery and ipsilateral common carotid artery. In addition, the BFV of the common carotid artery was correlated with that of the ipsilateral internal carotid artery. The main error was attributed to the external carotid artery and its branches. Therefore, after selecting the appropriate scanning parameters and protocols, 2D PC MRA is more accurate in the determination of BFV in the carotid arteries.
基金supported by the National Natural Science Foundation of China(Grant No.12274223)the Natural Science Foundation of Jiangsu Province(Grant No.BK20211145)+3 种基金the Fundamental Research Funds for the Central Universities(Grant No.020414380182)the Key Research and Development Program of Nanjing Jiangbei New Aera(Grant No.ZDYD20210101)the Program for Innovative Talents and Entrepreneurs in Jiangsu(Grant No.JSSCRC2021484)the Program of Songshan Laboratory(Included in the management of Major Science and Technology Program of Henan Province)(Grant No.221100210800)。
文摘Quantum secret sharing(QSS)is one of the basic communication primitives in future quantum networks which addresses part of the basic cryptographic tasks of multiparty communication and computation.Nevertheless,it is a challenge to provide a practical QSS protocol with security against general attacks.A QSS protocol that balances security and practicality is still lacking.Here,we propose a QSS protocol with simple phase encoding of coherent states among three parties.Removing the requirement of impractical entangled resources and the need for phase randomization,our protocol can be implemented with accessible technology.We provide the finite-key analysis against coherent attacks and implement a proof-of-principle experiment to demonstrate our scheme’s feasibility.Our scheme achieves a key rate of 85.3 bps under a 35 d B channel loss.Combined with security against general attacks and accessible technology,our protocol is a promising candidate for practical multiparty quantum communication networks.
基金supported by the National Natural Science Foundation of China(Grant Nos.11634010,91850118,11774289,61675168,and 11804277)the National Key Research and Development Program of China(Grant No.2017YFA0303800)the Fundamental Research Funds for the Central Universities(Grant Nos.3102018zy036,3102019JC008,and 310201911cx022)。
文摘In recent years,metasurfaces that enable the flexible wavefront modulation at sub-wavelength scale have been widely used into holographic display,due to its prominent advantages in polarization degrees of freedom,viewing angle,and achromaticity in comparison with traditional holographic devices.In holography,the computational complexity of hologram,imaging sharpness,energy utilization,reproduction rate,and system indirection are all determined by the encoding method.Here,we propose a visible frequency broadband dielectric metahologram based on the random Fourier phase-only encoding method.Using this simple and convenient method,we design and fabricate a transmission-type geometric phase all-dielectric metahologram,which can realize holographic display with high quality in the visible frequency range.This method encodes the amplitude information into the phase function only once,eliminating the cumbersome iterations,which greatly simplifies the calculation process,and may facilitate the preparation of large area nanoprint-holograms.
