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- 摘要
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[IEEE 2019 IEEE International Conference on Systems, Man and Cybernetics (SMC) - Bari, Italy (2019.10.6-2019.10.9)] 2019 IEEE International Conference on Systems, Man and Cybernetics (SMC) - Frequency analysis of entanglement dynamics in coupled quantum oscillators
摘要： We study harmonic oscillators connected by periodic or quasi-periodic couplings in a common heat bath. Driving frequencies of couplings play an important role in sustaining entanglement among the oscillators, even in high temperature. Driving amplitudes and relative driving frequencies determine whether entanglement would occur, while the base frequency determines characteristic parameters of entanglement dynamics. Frequency properties of ripples in logarithmic entropy are investigated by FFT, in cases with multiple coupling terms. Finally, frequency landscape is given for controlling entanglement dynamics.
关键词： quantum entanglement,frequency analysis,quantum parametric oscillators
更新于2025-09-12 10:27:22
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Spin-orbit-coupled quantum memory of a double quantum dot
摘要： The concept of quantum memory plays an incisive role in the quantum information theory. As confirmed by the several recent rigorous mathematical studies, the quantum memory inmate in the bipartite system ρAB can reduce the uncertainty about part B, after measurements done on part A. In the present work, we extend this concept to systems with a spin-orbit coupling and introduce the notion of spin-orbit quantum memory. We self-consistently explore the Uhlmann fidelity, the pre- and the post-measurement entanglement entropy, and the post-measurement conditional quantum entropy of the system with spin-orbit coupling and show that measurement performed on the spin subsystem decreases the uncertainty of the orbital part. The uncovered effect enhances with the strength of the spin-orbit coupling. We study the concept of macroscopic realism introduced by Leggett and Garg [Phys. Rev. Lett. 54, 857 (1985)] and observe that POVM measurements done on the system under the particular protocol are noninvasive. For the extended system, we perform quantum Monte Carlo calculations and consider the reshuffling of the electron densities due to an external electric field.
关键词： quantum Monte Carlo,spin-orbit coupling,entanglement entropy,POVM measurements,conditional quantum entropy,quantum memory,Uhlmann fidelity
更新于2025-09-12 10:27:22
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Enhancing entanglement of entangled coherent states via a f-deformed photon-addition operation
摘要： In this paper, we introduce a new kind of photon-added entangled coherent states (PA-ECSs), by performing repeatedly a f -deformed photon-addition (DPA) operation, A? = f (?n)a?, on each mode of the entangled coherent states (ECSs), |Ψ±(α)(cid:3). By choosing a particular deformation function f (?n), we study how the entanglement properties can be enhanced by DPA operation. As a result, we show that both the single and two-mode DPA operation can be used to improve the entanglement of |Ψ+(α)(cid:3), where the e?ects of improvement by two-mode DPA operation are more prominent than those by single-mode DPA operation, in any amplitude regime. Moreover, our results show there exists a family of coherent amplitudes |α| such that the two-mode DPA operation preserves the maximal entanglement of the odd ECSs |Ψ?(α)(cid:3), where the non-deformed photon-addition operation a? suppresses the entanglement amount. Finally, a theoretical scheme for the physical generation of the introduced states based on a Jaynes-Cummings model with intensity-dependent couplings is proposed.
关键词： entangled coherent states,entanglement enhancement,Jaynes-Cummings model,f-deformed,photon-addition
更新于2025-09-12 10:27:22
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Using quantum entangled photons to measure the absolute photon detection efficiency of a multi-pixel SiPM array
摘要： Spontaneous parametric down-conversion (SPDC) of a visible pump photon is the generation of two less energetic, quantum entangled photons (QEPs), often in the near infrared (NIR), using a non-linear crystal e.g. beta barium borate. Since the detection of one QEP predicates the existence of its entangled twin, QEPs have previously been used to measure the absolute photon detection efficiency (PDE), ??(??), of a detector under test by measuring time-coincident events with an additional trigger detector, allowing evaluation of ?????? ?? (??) without recourse to a calibrated reference detector. In this paper, the QEP absolute PDE measurement technique is outlined, and an extension of this technique is proposed to measure ??(??) for pixels on a multi-pixel array where each pixel provides an individual signal output. By treating all pixels in a multi-pixel array as indistinguishable, Monte Carlo simulations show that the symmetry of the measurement allows ??(??) to be determined for each pixel. A route towards experimental measurements using this technique with a 64-pixel SiPM array combined with a 64-channel waveform digitiser module is outlined.
关键词： Silicon photomultiplier,SiPM,Photon detection efficiency,Quantum entanglement
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Coupling Distant Quantum Dots using a Photonic Crystal Fano Structure
摘要： Building a quantum computer by taking the advantage of quantum entanglement can lead to a significant increase in our ability to solve certain types of problems. Quantum computer has run on various forms in which photon has been recognized as a highly desirable one due to the robustness of photonic states against decoherence. In particular, it is promising to use a semiconductor on-chip nanophotonic system where photons can be manipulated via combinations of cavities and waveguides (WGs) [1] because of its multi-functionalities, robustness and scalability towards highly integrated chips. Photonic nanocavities combined with semiconductor quantum dots (QDs) constitute one of the best candidates [2]. To achieve QD-QD coupling, it is usually proposed to place the nanocavities, embedded with QDs, in close proximity with their physical distance on the order of a few wavelengths because the cavity mode is usually tightly confined in space, resulting in limited penetration depth of the evanescent fields. However, going beyond short-distant coupling to long-distant coupling is essential because of the requirement of producing and maintaining entanglement between spatially separated qubits on-chip, both for measurement purposes and to permit individual control of separated qubits. Here a photonic crystal (PhC) nanocavity coupled WG structure is proposed where two nanocavities, separated by ~20 wavelengths, with each incorporating a semiconductor QD, are side coupled with an open bus WG. If the structure is properly designed, light originally leaking out through the WG will experience destructive interferences at the WG outputs due to the Fano interference effect [3, 4], leading to a high-Q optical mode that is confined only between the two cavities, cf. Fig. 1(a). Such a configuration can promote a strong coupling between the two cavities without causing mode doubling which is the usual case in coupled cavity systems, even if the two cavities are well separated in space, thus facilitating distant QD-QD interactions. A Green function based approach [5, 6] is used to investigate the quantum dynamics of the system so the loss in the open system is taken into account automatically. Numerical simulations show that QD 2 can be well excited even if only QD 1 is driven, cf. Fig. 1(b). In addition, a sound concurrence, a measure of entanglement between the two QDs, and a Mollow triplet in the QD emission can be observed, reflecting a well coupling between the two QDs, thanks to their strong interactions with the optical Fano mode. Future work aims for structure optimizations as well as experimental demonstration of distant QD-QD entanglement, combined with site-controlled semiconductor QDs [7].
关键词： photonic crystal,quantum entanglement,quantum computer,quantum dots,Fano interference
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Hyper-Entanglement in Time and Frequency
摘要： Hyper-entanglement, i.e. entanglement in more than one degree of freedom, enables a multiplicative increase in Hilbert space size. Such systems can be treated as multi-partite even though the number of state particles is not increased, making them highly attractive for applications in high-capacity quantum communications and information processing. Until now, such states have been realized only using combinations of fully independent degrees of freedom, described by commuting operators, such as polarization and optical paths. Time and frequency, in turn, are linked and described by non-commuting operators. Here, using two discrete forms of energy-time entanglement we demonstrate that time and frequency can be used for genuine multi-partite hyper-entangled states. This is achieved by increasing the time-frequency product to far exceed the Heisenberg uncertainty limit, effectively making the time and frequency degrees independent.
关键词： time and frequency,hyper-entanglement,quantum communications,information processing,Heisenberg uncertainty limit
更新于2025-09-12 10:27:22
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Microscale Generation of Entangled Photons without Momentum Conservation
摘要： We report, for the first time, the observation of spontaneous parametric down-conversion (SPDC) free of phase matching (momentum conservation). We alleviate the need to conserve momentum by exploiting the position-momentum uncertainty relation and using a planar geometry source, a 6 μm thick layer of lithium niobate. Nonphase-matched SPDC opens up a new platform on which to investigate fundamental quantum effects but it also has practical applications. The ultrasmall thickness leads to a frequency spectrum an order of magnitude broader than that of phase-matched SPDC. The strong two-photon correlations are still preserved due to energy conservation. This results in ultrashort temporal correlation widths and huge frequency entanglement. The studies we make here can be considered as the initial steps into the emerging field of nonlinear quantum optics on the microscale and nanoscale.
关键词： quantum optics,spontaneous parametric down-conversion,phase matching,lithium niobate,frequency entanglement,momentum conservation
更新于2025-09-12 10:27:22
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Entanglement via entangled-boundary-condition trajectories: Long-time accuracy
摘要： Entanglement is considered as a purely quantum effect. The present paper, however, joins many other works that pursue the idea of describing it using classical quantities. In particular, we are interested in the entanglement dynamics of a pure state composed of two parts, initially prepared in a product of coherent states and governed by a generic Hamiltonian. In this scenario, the linear entropy of the reduced state, our entanglement quanti?er, was shown to be written, in the short-time regime, in terms of a real trajectory of the underlying classical dynamics. We extend this semiclassical result by demonstrating that it is possible to include complex trajectories in the calculation. This strategy contributes to improving the previous approximation, extending its accuracy for longer values of time. We also show, for a particular Hamiltonian, a ?rst application of the achieved formula, attesting to its ef?ciency.
关键词： semiclassical approximation,entanglement,quantum dynamics,linear entropy,complex trajectories
更新于2025-09-11 14:15:04
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One Step Quantum Key Distribution Protocol Based on the Hyperentangled Bell State
摘要： Considering the security and ef?ciency of quantum communication system, one step quantum key distribution protocol based on hyperentangled Bell state is proposed. Every 6 classical bits are divided into a group, which are encoded by single particle and hyperentangled Bell state, the sender Alice sends them to receiver Bob, Bob randomly selects the position of hyperentangled Bell state to measure and detects the existence of eavesdropper Eve by comparing measurement results in his hand and transmitted by Alice. Quantum key distribution protocol based on grouping is proposed to solve the storage problem of quantum information and improve the maneuverability, a security analysis is calculated under the intercept-measure-resend attack which introduce at least an error rate of 46.875%, if Eve wants to get all the information, the probability of detection eavesdropping under the entanglement-measure attack is 93.75%, so it proves that proposed protocol does not need to store the quantum state and asymptotically secure under intercept-measure-resend attack and entanglement-measure attack.
关键词： intercept-measure-resend attack,hyperentangled bell state,single particle,quantum key distribution,Entanglement-measure attack
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Towards Optimized Photon-Pair Sources for Two-Photon Transitions
摘要： Two-photon absorption (TPA) is a nonlinear optical process with wide applications in ?uorescence microscopy and spectroscopy of organic molecules and compounds, as it enables atoms or molecules to transition into states that may otherwise be inaccessible by a single photon, either because of selection rules or energy conservation. Despite its common use, TPA is a rather inef?cient process, often requiring very large photon numbers to produce significant results. It has been demonstrated and analytically described [1,2], that using frequency entangled pairs of photons can in some cases enhance the ef?ciency of TPA. For this to occur, the joint spectral amplitude (JSA) of the photon-pair state, which describes the spectral entanglement between the pair, must be engineered according to the spectral properties of the TPA response-function of the speci?c system in question. In this work, we consider different cases for the spectral functionality of TPA and propose that the control of the group indices of the modes involved in the pair-generation process is a key property in the design of photon-pair sources for optimized TPA.
关键词： joint spectral amplitude,spectral entanglement,group indices,Two-photon absorption,photon-pair sources
更新于2025-09-11 14:15:04