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System Composed of Three Types of Electronic Angular Momenta: A <b>J</b> – <b>S</b> – <b>L</b> Triad in a Photoexcited π-Radical Bis(phthalocyaninato)terbium Single-Molecule Magnet
摘要： Interactions of three different types of electronic angular momenta, namely, spin, orbital, and total angular momenta from different origins in a photoexcited neutral bis(phthalocyaninato)terbium single-molecule magnet (Pc2Tb, where Pc2? denotes a phthalocyaninato anion) have been studied. We have conducted varied-temperature and varied-magnetic-field magnetic circular dichroism (MCD) measurements on the highest occupied molecular orbital?lowest unoccupied molecular orbital electronic transition in the ligand side of the neutral Pc2Tb to reveal the quantum nature of the system composed of a π-radical with a spin angular momentum S, the 4f system with a total angular momentum J, and the cyclic π conjugate system with a photoinduced orbital angular momentum L. We have constructed a new theoretical model that gives a quantitative agreement to the temperature and magnetic field dependence of MCD. The theoretical analysis revealed that the system takes eight quantum states that can be expressed as |JzSzLz? = |±±±?, where the three angular momenta are quantized along the fourfold symmetry axis. Thus, we have identified the existence of the magnetic interactions among the three angular momenta and quantitatively determined their magnitudes for the first time.
关键词： single-molecule magnet,electronic angular momenta,quantum states,magnetic circular dichroism,magnetic interactions
更新于2025-09-23 15:21:01
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Local distinguishability of orthogonal quantum states with no more than one ebit of entanglement
摘要： In this paper, we study the local distinguishability of mutually orthogonal product quantum states with entanglement as a valuable resource. We present protocols in which entanglement is used more efficiently than in the previous protocols presented by Zhang et al. [Phys. Rev. A 97, 022334 (2018)]. Specifically, the main technical contributions are as follows: First, we present a method to locally distinguish a set of orthogonal product quantum states in d ? d (d is odd) by using only one ancillary two-qubit maximally entangled state. Then we present a similar method to locally distinguish multipartite orthogonal product states by using entanglement efficiently. Moreover, we propose a method to study the local distinguishability of this kind of orthogonal product state with less than one ebit of entanglement, and analyze the relationship between the probability of error and the quantity of entanglement, which reveals the phenomenon of less nonlocality with more entanglement.
关键词： LOCC,orthogonal quantum states,nonlocality,local distinguishability,entanglement
更新于2025-09-19 17:15:36
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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) - Birefringent Cavities: Effects and Applications of a New Paradigm in CQED
摘要： The enhanced interaction of quantum states of light and matter within an optical resonator is a powerful tool for both addressing fundamental questions of nature and pursuing quantum technologies. Here, we discuss the impact of cavity birefringence – a lifting of the degeneracy of polarisation modes within the resonator – on both of these challenges. A novel model for such systems is experimentally veri?ed by the cavity emission of single photons with time-dependent polarisation states that evolve along their wavepacket [1]. This model is then used to demonstrate how a tailored birefringence allows for enhanced photon emission beyond previous limitations [2].
关键词： polarisation states,CQED,optical resonator,quantum states of light and matter,cavity birefringence,single photons,birefringent cavities
更新于2025-09-12 10:27:22
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Tunable Quantum Beat of Single Photons Enabled by Nonlinear Nanophotonics
摘要： We demonstrate the tunable quantum beat of single photons through the co-development of core nonlinear nanophotonic technologies for frequency-domain manipulation of quantum states in a common physical platform. Spontaneous four-wave mixing in a nonlinear resonator is used to produce nondegenerate, quantum-correlated photon pairs. One photon from each pair is then frequency shifted, without degradation of photon statistics, using four-wave-mixing Bragg scattering in a second nonlinear resonator. Fine tuning of the applied frequency shift enables tunable quantum interference of the two photons as they are impinged on a beam splitter, with an oscillating signature that depends on their frequency difference. Our work showcases the potential of nonlinear nanophotonic devices as a valuable resource for photonic quantum-information science.
关键词： four-wave-mixing Bragg scattering,nonlinear nanophotonics,frequency-domain manipulation,quantum interference,quantum states,quantum beat,single photons,photonic quantum-information science,quantum-correlated photon pairs,spontaneous four-wave mixing
更新于2025-09-11 14:15:04
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Spectroscopic evidence of cooperative (entangled) quantum states of Nd3+ ion pairs in Nd3+: LaF3 crystal
摘要： We demonstrated the existence of entangled 4I9/2(1) x 4G5/2(1) quantum state in a pair of Nd3t ions due to strong resonance quadrupole – quadrupole interaction between the ions. In doing so, we used narrow line (0.05 ?) tunable pulsed dye laser excitation of a 1% Nd3t: LaF3 crystal at liquid helium temperatures at the 4I9/2(1) → 4G5/2(1) transition and measured the site-selective near infrared (NIR) fluorescence spectra of different optical centers (OCs) at the 4F3/2(1) → 4I9/2(1) transition of Nd3t with high spectral resolution (0.1 ?); the NIR fluorescence excitation spectra at the 4I9/2(1) → 4G5/2(1) transition (0.05 ?); and by varying the excitation and detection wavelengths we measured the IR fluorescence kinetics of the selected type of OCs. As a result, we observed inhomogeneous splitting within 30 cm?1 for the fluorescence spectra at the 4F3/2(1) → 4I9/2(1) transition, manifested in the presence of numerous narrow inhomogeneously broadened spectral lines of different OCs. We have attributed each spectral line to a different single-site, pair, triple, or quad optical centers via analysis of the 4F3/2(1) metastable level fluorescence kinetics decay times. Each type of OCs demonstrates its own specific IR fluorescence excitation spectrum at the 4I9/2(1) → 4G5/2(1) transition detected in a 1%Nd3t: LaF3 crystal at 1.6 K. One of the spectral lines of the pair centers (with the frequency 17313.3 cm?1) exhibited the fine splitting with the value of 0.2 cm?1. The shape and the value of fine splitting are explained theoretically assuming that this line corresponds to the excitation of the entangled the 4I9/2(1) x 4G5/2(1) quantum state of the pair of Nd3t ions located at short distance, R ~ 4.1 ?.
关键词： Pairs,Resonance exchange interaction,LaF3,Inhomogeneous splitting,Nd3t,Ion clusters,Crystals,Entangled (cooperative) quantum states
更新于2025-09-11 14:15:04
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Unconditional preparation of nonclassical states via linear-and-quadratic optomechanics
摘要： Reservoir engineering enables the robust and unconditional preparation of pure quantum states in noisy environments. We show how a family of nonclassical states of a mechanical oscillator can be stabilized in a cavity that is parametrically coupled to both the mechanical displacement and the displacement squared. The cavity is driven with three tones, on the red sideband, on the cavity resonance, and on the second blue sideband. The states so stabilized are (squeezed and displaced) superpositions of a finite number of phonons. They show the unique feature of encompassing two prototypes of nonclassicality for bosonic systems: by adjusting the strength of the drives, one can in fact move from a single-phonon- to a Schr?dinger-cat-like state. The scheme is deterministic, supersedes the need for measurement-and-feedback loops, and does not require initialization of the oscillator to the ground state.
关键词： mechanical oscillator,quantum states,Reservoir engineering,nonclassical states,optomechanics
更新于2025-09-09 09:28:46
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Uniform continuity bounds for information characteristics of quantum channels depending on input dimension and on input energy
摘要： We obtain continuity bounds for basic information characteristics of quantum channels depending on their input dimension (if it is finite) and on the input energy bound (if the input dimension is infinite). We pay special attention to the case in which a multimode quantum oscillator is an input system. First, we prove continuity bounds for the output conditional mutual information for a single channel and for n copies of a channel. Then we obtain estimates for the variation of the output Holevo quantity with respect to simultaneous variations of a channel and of an input ensemble. As a result, tight and close-to-tight continuity bounds for basic capacities of quantum channels, which depend on the input dimension, are obtained. They complement the Leung–Smith continuity bounds, which depend on the output dimension. Finally, we obtain tight and close-to-tight continuity bounds for basic capacities of infinite-dimensional energy-constrained channels with respect to the energy-constrained Bures distance generating the strong convergence of quantum channels.
关键词： strong convergence of quantum channels,ensemble of quantum states,the Holevo quantity,quantum conditional mutual information,quantum channel capacities,energy-constrained Bures distance,multi-mode quantum oscillator
更新于2025-09-04 15:30:14
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Entanglement certification from theory to experiment
摘要： Entanglement is an important resource for quantum technologies. There are many ways quantum systems can be entangled, ranging from the two-qubit case to entanglement in high dimensions or between many parties. Consequently, many entanglement quantifiers and classifiers exist, corresponding to different operational paradigms and mathematical techniques. However, for most quantum systems, exactly quantifying the amount of entanglement is extremely demanding, if at all possible. Furthermore, it is difficult to experimentally control and measure complex quantum states. Therefore, there are various approaches to experimentally detect and certify entanglement when exact quantification is not an option. The applicability and performance of these methods strongly depend on the assumptions regarding the involved quantum states and measurements, in short, on the available prior information about the quantum system. In this Review, we discuss the most commonly used quantifiers of entanglement and survey the state-of-the-art detection and certification methods, including their respective underlying assumptions, from both a theoretical and an experimental point of view.
关键词： Entanglement classifiers,Quantum technologies,Entanglement quantifiers,Experimental detection,Quantum states,Certification methods,Entanglement
更新于2025-09-04 15:30:14
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Self-testing quantum states and measurements in the prepare-and-measure scenario
摘要： The goal of self-testing is to characterize an a priori unknown quantum system based solely on measurement statistics, i.e., using an uncharacterized measurement device. Here we develop self-testing methods for quantum prepare-and-measure experiments, thus not necessarily relying on entanglement and/or violation of a Bell inequality. We present noise-robust techniques for self-testing sets of quantum states and measurements, assuming an upper bound on the Hilbert space dimension. We discuss in detail the case of a 2 → 1 random access code with qubits, for which we provide analytically optimal self-tests. The simplicity and noise robustness of our methods should make them directly applicable to experiments.
关键词： qubits,random access code,prepare-and-measure scenario,quantum states,self-testing,measurements
更新于2025-09-04 15:30:14