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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) - Experimental Demonstration of Entropic Steering
摘要： Quantum entanglement is a key resource for foundational quantum information and communication tasks, such as teleportation, entanglement swapping and quantum key distribution [1]. Quantum steering is a quantum correlation that is distinct from other nonclassical correlations such as Bell nonlocality [2] and entanglement. Steering describes the effect of measuring one system, let’s say Alice, and affecting the measurement results on the other system, let’s say Bob. Moving through the hierarchy of nonlocal classes, from Bell nonlocality towards nonseparability, requires an increasing number of parties and apparatus that need to be trusted but gives access to protocols which are more robust to noise for projective measurements [3,4]. In a quantum steering task [5] the correlations of Alice and Bob’s measurement outcomes are tested against a classical probability bound which can be only violated if the state shared between the parties is quantum steerable. Establishing such steering criteria via semidefinite programming [6-8] requires assumptions about Alice’s measurements and is restricted to small dimensions. Entropic uncertainty relations [9,10] were recently identified as a fundamental tool to develop steering criteria. It has been shown that using the so-called Tsallis entropy allows for generalising recent entropic steering criteria [11,12] which were restricted to the case of Shannon entropy. Here, we experimentally test the recently derived inequality by Costa et al. [13] for m = 2 measurement directions for Alice and Bob. For that, we consider a shared polarisation encoded Werner state which is defined as ρ = μ|Ψs??Ψs| + (1?μ) I4, where μ ∈ [0; 1], I4 is the 4 × 4 identity matrix and |Ψs? = (|01? ? |10?)/√2 between our observers Alice and Bob [14]. We used data from Wollmann et al. [15] to test if S (q) = C ? ∑k [Sq(Bk|Ak) + (1 ? q)C(Ak, Bk)] violates S (q) ≤ 0 [13]. Violation of this inequality demonstrates steering of Bob’s state. We successfully show quantum steering and found our inequality (Fig.1 (red curve))to be more robust to measurement deviations than comparable inequalities (Fig.1 (blue curve)).
关键词： Tsallis entropy,Quantum steering,Shannon entropy,Quantum entanglement
更新于2025-09-16 10:30:52
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Quantum Coherence Preservation in Extremely Dispersive Plasmonic Media
摘要： Quantum plasmonics experiments have on multiple occasions resulted in the observation of quantum coherence of discrete plasmons, which exhibit remarkable preservation of quantum interference visibility, a seemingly surprising feature for systems mixing light and matter with high Ohmic losses during propagation. However, most experiments to date used essentially weakly confined plasmons, which experience limited light-matter hybridization, thus limiting the potential for decoherence. In this paper, we investigate experimentally the robustness of coherence preservation in a plasmonic system: our setup is based on a hole-array chip supporting plasmons near the surface plasma frequency, where plasmonic dispersion and confinement are much stronger than in previous experiments, making the plasmons much more susceptible for decoherence processes. We, however, report preservation of quantum coherence even in these extreme conditions. We generate polarization-entangled pairs of photons using type-I spontaneous parametric down-conversion and transmit one of the photons through a plasmonic hole array that is numerically designed to convert incident single photons into highly dispersive single surface-plasmon polaritons. Our results show that the quality of photon entanglement after the plasmonic channel is unperturbed by the introduction of a highly dispersive plasmonic element. Our findings provide a lower bound of 100 fs for the pure dephasing time for dispersive plasmons in gold, and show that even in a highly dispersive regime surface plasmons preserve quantum mechanical correlations, making possible harnessing of the power of extreme light confinement for integrated quantum photonics.
关键词： quantum entanglement,Quantum plasmonics,quantum coherence,surface-plasmon polaritons,decoherence
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 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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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 21st International Conference on Transparent Optical Networks (ICTON) - Angers, France (2019.7.9-2019.7.13)] 2019 21st International Conference on Transparent Optical Networks (ICTON) - Silicon Photonics for Quantum Communication
摘要： Silicon quantum photonics, capable to integrate large numbers of optical components with CMOS-compatible fabrication technology and reliable control of quantum states, is expected to play a critical role in future quantum communication. In this talk, we will introduce our recent results of silicon photonics for quantum communication, including high-dimensional silicon chip-to-chip quantum key distribution, chip-to-chip quantum teleportation, on-chip generation of high-dimensional quantum entanglement, and Hong–Ou–Mandel interference between two different III-V/silicon hybrid lasers towards future measurement device independent quantum communication.
关键词： quantum entanglement,high-dimensional quantum photonics,Hong-Ou-Mandel interference,silicon photonics,quantum communication,quantum key distribution
更新于2025-09-11 14:15:04
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Biphoton shaping with cascaded entangled-photon sources
摘要： Quantum entanglement is an integral part of quantum optics and has been exploited in areas such as computation, cryptography and metrology. The entanglement between photons can be present in various degrees of freedom (DOFs), and even the simplest bi-partite systems can occupy a large Hilbert space. Therefore, it is desirable to exploit this multi-dimensional space for various quantum applications by fully controlling the properties of the entangled photons in multiple DOFs. While current entangled-photon sources are capable of generating entanglement in one or more DOFs, there is currently a lack of practical techniques that can shape and control the entanglement properties in multiple DOFs. Here we show that cascading two or more entangled-photon sources with tunable linear media in between allows us to generate photon-pairs whose entanglement properties can be tailored and shaped in the frequency and polarisation domains. We first develop a quantum mechanical model to study the quantum state generated from the cascade structure with special considerations paid to the effects of pump temporal coherence, linear dispersion, and in-structure polarisation transformation applied between the entangled-photon sources. We then experimentally generate photon-pairs with tunable entanglement properties by manipulating the dispersion and birefringence properties of the linear medium placed in between two entangled-photon sources. This is done in an all-fibre, phase stable, and alignment-free configuration. Our results show that the cascade structure offers a great deal of flexibility in tuning the properties of entangled photons in multiple DOFs, opening up a new avenue in engineering quantum light sources.
关键词： nonlinear interferometer,photon-pairs,frequency and polarisation domains,cascade structure,Quantum entanglement
更新于2025-09-11 14:15:04
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Counterpropagating continuous-variable entangled states in lossy coupled-cavity optical waveguides
摘要： We present an integrated source of counterpropagating entangled states based on a coupled resonator optical waveguide that is pumped by a classical pulsed source incident from above the waveguide. We investigate theoretically the generation and propagation of continuous-variable entangled states in this coupled-cavity system in the presence of intrinsic loss. Using a tight-binding approximation, we derive analytic time-dependent expressions for the number of photons in each cavity, as well as for the correlation variance between the photons in different pairs of cavities, to evaluate the degree of quantum entanglement. We also derive simple approximate expressions for these quantities that can be used to guide the design of such systems, and discuss how pumping configurations and physical properties of the system affect the photon statistics and the degree of quantum correlation.
关键词： quantum entanglement,lossy coupled-cavity optical waveguides,continuous-variable entangled states,counterpropagating,tight-binding approximation
更新于2025-09-11 14:15:04
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Generation of entangled states by a linear coupling coupler pumped in two modes induced by broadband laser
摘要： We research on a Kerr nonlinear coupler comprising two nonlinear oscillations linearly couple with each other. This coupler is pumped by external classical fields, which are supposed to be decomposed into two parts: a coherent part and a randomly fluctuating chaotic component (white noise). We can see that the quantum evolution of the pumped couplers is closed in a Hilbert space of two-qubit spanned by single-photon and vacuum states only. Hence, the pumped couplers can treat as a system of two-qubit. Analysis of time evolution of the quantum entanglement shows that maximally entangled states can be generated in the system and compare these results with that obtained previously by other authors.
关键词： quantum entanglement,Generation of entangled states,Bell-like states,white noise,Kerr nonlinear coupler
更新于2025-09-11 14:15:04
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Effect of polarization dependent loss on the quality of transmitted polarization entanglement
摘要： Quantum networking brings together several diverse research areas, such as fiber-optic communication, quantum optics, and quantum information, to achieve capabilities in security, secret sharing, and authentication which are unavailable classically. The development of practical fiber-based quantum networks requires an understanding of the reach, rates, and quality of the entanglement of distributed quantum states. Here, we present a theoretical model describing how the magnitude and orientation of polarization dependent loss (PDL), a common impairment in fiber-optic networks, affects the entanglement quality of distributed quantum states. Furthermore, we theoretically characterize how PDL in one fiber channel can be optimally applied in order to nonlocally compensate for the PDL present in another channel. We present experimental results which verify our theoretical model.
关键词： Optical fiber communication,quantum entanglement
更新于2025-09-10 09:29:36