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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) - Nonlinear Quantum Spectroscopy Enhanced by Parity-Time Symmetry
摘要： Quantum spectroscopy based on nonlinear interferometers attracts increasing attention due to its unique practical advantages. By tailoring spontaneous parametric down conversion (SPDC) for generation of frequency-correlated photons and their nonlocal quantum interference, it becomes possible to perform sensing and imaging across broad spectral ranges through simple detection of paired photons in the visible. It was recently demonstrated that nonlinear integrated waveguides can improve the performance of quantum spectroscopy. However, while fabrication of integrated circuits with multiple waveguides is well established, their applications for quantum spectroscopy remain largely undeveloped. Here, we formulate a new principle of enhancing spectroscopy in a nonlinear quantum interferometer by drawing on the concept of parity-time (PT) symmetry, which enabled recent breakthroughs in classical optical sensing. The considered measurement geometry is sketched in Fig. 1(a). A pump beam coupled to waveguide 1 (bottom) drives the generation of signal-idler photon pairs through SPDC in the two yellow-shaded regions of length l, where periodic poling can be introduced to achieve phase-matching. We consider the practically important regime of mid-infrared spectroscopy, when the idler wavelength is λi > 2μm, while the pump and signal are in the visible (λp,s < 1μm). The central waveguide section of lenght L has no poling and all waves propagate in the effectively linear regime. Our key suggestion is to introduce a second waveguide 2 (top), which interacts with a sample under test to measure its absorption rate. We consider a waveguide separation such that only the longer-wavelength idler photons can tunnel between the waveguides with the coupling rate Ci. Although signal photons never propagate through waveguide 2, due to nonlocal quantum interference of signal-idler pairs the absorption strength in waveguide 2 can be determined by counting just the signal photons at the output of the ?rst waveguide. Fig. 1(b) shows calculated count rates in dependence on the phase mismatch Δβ in the generation regions and the normalized loss in waveguide 2 (γi/Ci), induced by the analyte. Δβ can be controlled by tuning the pump wavelength. Remarkably, we ?nd that the positions of maximal signal counts along the vertical axis exhibit a sharp shift by a half-period at a critical value of γi/Ci = γcr, see Fig. 1(c). The sensitivity to small absorption changes in the vicinity of the critical value is strongly enhanced. Note that the critical absorption can be ?exibly selected by the waveguide coupling Ci, and thereby the device operation can be optimized for maximum sensitivity at the desired level of absorption, to accurately resolve the sample properties.
关键词： integrated waveguides,Quantum spectroscopy,parity-time symmetry,SPDC,nonlinear interferometers
更新于2025-09-11 14:15:04
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-symmetric Fibonacci aperiodic optical networks of waveguide rings
摘要： In parity-time-symmetric (PT -symmetric) Fibonacci ordered-aperiodic optical networks of waveguide rings, the beat-like pattern of the frequencies corresponding to maximum extraordinary transmission and reflection is investigated. It is found that, resembling acoustic resonance and optical beat, when these frequencies between two contiguous Fibonacci generations are sufficiently close and within a certain limit, the transmission and reflection of the following generation become stronger than those of the previous two; otherwise, they are weakened. These properties are the combined results of the optical PT symmetry and the inherent self-repeating pattern of the Fibonacci ordering, which might deepen the understandings and provide a fresh perspective on the PT -symmetric ordered-aperiodic and disordered systems.
关键词： Aperiodic optical systems,Parity-time symmetry,Optical waveguide networks
更新于2025-09-11 14:15:04
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Surface Nonlinear Optics on Centrosymmetric Dirac Nodal‐Line Semimetal ZrSiS
摘要： Gapless surface states (SSs) are features of topological semimetals and are extensively observed. Nowadays, the emerging question is whether the SSs possess exotic and applicable properties. Here, associated with the symmetrical selection rule for nonlinear optical materials, the surface nonlinear optics on a centrosymmetric Dirac nodal-line semimetal ZrSiS crystal is studied and it is found that the SSs bring record nonlinear susceptibilities. The unprecedented conversion efficiencies for second and third harmonic generations are 0.11‰ and 0.43‰, respectively, more than ten orders of magnitude larger than the typical surface second harmonic generation. This work discovers a new route toward studying the SSs for applications in nonlinear photonics.
关键词： density functional theory calculations,ZrSiS,surface states,nonlinear optics,symmetry breaking
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) - The Role of Trap Symmetry in an Atom-Chip Interferometer above the Bose-Einstein Condensation Threshold
摘要： Cold atom interferometers have demonstrated excellent performance and hold great prospects for time, gravity, acceleration and rotation measurements. Trapped interferometers, for example using atom chips, can potentially enable portable applications of theses sensors. Atom chip interferometers have been successfully demonstrated using Bose-Einstein condensates but are subject to the effect of atom-atom interactions which cause phase decoherence. In this study, we proposed an atom chip interferometer using a gas just above the condensation threshold to reduce the interaction effects. This proposal is similar to white light interferometry in the sense that the difference between the optical paths of the two arms must be close to zero to observe fringes. In a trapped interferometer this condition is analogous to maximizing the degree of symmetry between the two trapping potentials. We demonstrated that if the two trapping potentials are harmonic with slightly different curvatures inhomogeneous dephasing arises. This leads to a typical contrast decay time. Here we use 87Rb in the two states |a>=|F=1,mF=-1> and |b>=|F=2,mF=2>. Both states are trapped by the same magnetic field created by an atom chip. As described by the Breit-Rabi formula, the energies of the two levels |a> and |b> have a slightly different magnetic field dependence. We can use this difference to fine tune the curvature difference between the two trapping potentials. We perform Ramsey sequences and record the fringes as a function of the Ramsey time for several temperatures and values of curvature difference. We find a good agreement with the above formula. Coherence times of order 1s have been observed. We will describe the experiment, the model used to extract the contrast decay time and the limitations of this model due to atom interactions. The results open the way for experimental demonstration of atom chip accelerometers and gyroscopes.
关键词： trap symmetry,Ramsey sequences,atom-chip interferometer,Bose-Einstein condensation,coherence times
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) - All-Optical Background-Free Detection of Ring Currents by Dynamical Symmetry Breaking High Harmonic Spectroscopy
摘要： Excited atoms and molecules can carry long-lived currents that circulate in the microscopic media. From a quantum mechanical perspective, these currents can be understood as a coherent wave-packet comprising a superposition of bound- states that oscillates in time [1–3]. When the wave-packet has a non-zero angular momentum expectation value, ring-currents circulate in the medium. For instance, a hydrogen atom excited to a 2p-state with non-zero magnetic quantum number m (e.g. by interaction with circularly polarized light) carries a steady-state ring current [2]. More complex systems can also carry persistent ring currents, e.g. spin-orbit wave-packets in Xenon [4], or multi-electron wave-packets in larger molecules [1]. This phenomenon is general to any quantum system and is especially interesting because it occurs on the natural time-scale of electronic motion – attoseconds to femtoseconds. Understanding ring currents is thus fundamentally important for manipulating and controlling ultrafast processes on the nanoscale, including chemical bond formation and topologically protected surface currents [5], as well as for the generation of intense attosecond-duration magnetic fields [1,6]. However, ring currents are very difficult to detect, particularly in a time-resolved manner. Only very recently were ring currents directly experimentally resolved in Argon through pump-probe angularly-resolved incidence photoelectron spectrum measurements [3]. Here we propose and theoretically explore an all-optical technique for ultrafast time-resolved detection of ring currents in atoms, molecules and solids, based on high harmonic generation (HHG). In this technique a microscopic medium interacts with a bi-chromatic (ω-2ω) bi-elliptical laser pulse, generating high harmonic photons. We show that the harmonic spectra emitted from current-carrying media differs from that of current-free media. We use dynamical symmetry (DS) considerations [7] to derive conditions for a maximal (background-free) signal in the harmonic ellipticity, which occurs when the pump beams are cross-linearly polarized [8]. In this configuration the bi-chromatic laser field exhibits a dynamical reflection symmetry that leads to linearly polarized harmonic selection rules [7]; however, this selection rule is broken when the medium carries a current, because ring-currents are not reflection-symmetric (similar to chiral systems [9], but where the current can be described in 2D). Thus, current-carrying media emit elliptically polarized harmonics, where the harmonic ellipticity is correlated to the intensity and sign of the current in the system. We numerically demonstrate the approach by pump-probe HHG calculations from Neon noble gas atoms, and from both aligned and un-oriented aromatic molecules (benzene and furan), using a non-interacting electron quantum model, and time-dependent density functional theory calculations. The presented work could be useful for ultrafast spectroscopy of current-carrying processes (chemical reactions, topological currents, etc.), as well as for manipulation and control of ring currents, paving the way for their table-top all- optical detection.
关键词： high harmonic generation,ultrafast spectroscopy,ring currents,dynamical symmetry breaking
更新于2025-09-11 14:15:04
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Fine tunable PT-symmetric optoelectronic oscillator based on laser wavelength tuning
摘要： A fine tunable parity-time symmetric optoelectronic oscillator (PT-OEO) based on laser wavelength tuning is proposed and experimentally demonstrated. In the PT-OEO, an intensity modulator (IM) and a dispersion compensating fiber (DCF) are merged into the loop. Tuning the laser wavelength leads to a reconfigurable dispersion-induced power fading, serving as rough tunable oscillation mode selection. Meanwhile, to implement a fine-mode selection, parity-time symmetry breaking is introduced. Consequently, a fine tunable PT-OEO is achieved without using a high quality-factor (Q-factor) electrical filter. Experiment shows that the frequency of the generated signal can be tuned from 20.34 to 19.49 GHz with a step of 203 MHz, when the laser wavelength is manipulated from 1545 to 1565 nm. The phase noise is evaluated as -116.1 dBc/Hz @ 10-kHz offset frequency.
关键词： optoelectronic oscillator,Dispersion-induced power fading,parity-time symmetry
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) - Multi-Scale Symmetries and Selection Rules in High Harmonic Generation
摘要： Symmetry-based analysis is very useful in many fields of science. In the case of time-dependent systems, the symmetries of interest are dynamical, and are maintained during the system’s evolution in time. Interestingly, such symmetries may manifest over several length scales, e.g. both microscopically and macroscopically. For example, in high harmonic generation (HHG), micro-scale dynamical symmetries (DSs) yield selection rules that forbid some harmonic orders and determine the polarizations of the allowed harmonics [1], as was formulated recently in a consistent group theory [2]. Macroscopically, DSs of the wave equation may induce selection rules with respect to phase-matching conditions and conservation of angular or linear momentum [3]. However, the DSs of these different length scales are generally thought to be non-interacting, and have so far only been described separately. Here we formulate and explore plethora of multi-scale dynamical symmetries (MSDS), where the symmetry operations involve both microscopic and macroscopic length scales. We derive all possible MSDS operations and their resulting selection rules in HHG, and experimentally demonstrate non-trivial selection rules of the new theory.
关键词： selection rules,dynamical symmetries,high harmonic generation,multi-scale dynamical symmetries,symmetry-based analysis
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) - Experimental Realisation of PT-Symmetric Flat Bands
摘要： Non-Hermitian physics, and in particular its well-known representative of PT-symmetry, is a field of great interest in current research. Photonics allows for the implementation of its associated complex potentials by means of judiciously distributed refractive index, gain and loss. In this vein, femtosecond laser-written waveguide systems are a versatile platform to explore non-Hermitian physics in discrete settings. In light of the widespread use of light for rapid long-distance transmission, the capability to temporarily halt its propagation is desirable for a wide range of applications. In this vein, flat band structures are of particular importance. This work shows how flat bands can be synthesized by judiciously applying loss to the system. We experimentally investigate the emergence of a flat band at the systems exceptional point and observe the associated compact localised eigenmodes that can be excited at arbitrary locations of the periodic lattice.
关键词： flat bands,photonics,Non-Hermitian physics,compact localised eigenmodes,PT-symmetry
更新于2025-09-11 14:15:04
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Novel Fluorescent C2-Symmetric Sequential On-Off-On Switch for Cu2+ and Pyrophosphate and Its Application in Monitoring of Endogenous Alkaline Phosphatase Activity
摘要： A doubly armed hydrazone-based FLRHYDDFP probe selectively detects Cu2+ and pyrophosphate (PPi) ions through an colorimetric response-“colorless → yellow → colorless”- as well as “on-off-on” photonic switching response under physiological conditions in a sequential manner. The binding stoichiometries of the analytes Cu2+ and PPi were 1:2 and 2:4 for FLRHYDDFP-Cu2+ and Cu2+/PPi, respectively. The sequential sensing ability of FLRHYDDFP toward Cu2+ and PPi, attributed to effective complexation-aided d→π* electron transfer (ET) from Cu2+ to FLRHYDDFP and intramolecular charge/electron transfer from FLRHYDDFP to FLRHYDDFP+, resulted in the formation of a non-symmetric Cu2+ chelate that provided a yellow-colored solution with a significant bathochromic shift from 376 to 446 nm in the UV-Vis spectrum and quenching in the emission spectrum. Upon addition of PPi, Cu2+ was extruded from the complex, resulting in a revival of the fluorescence centered at 572 nm. Thus, sequential addition of Cu2+ and PPi yielded a colorless–yellow–colorless transition under visible light and on-off-on switching under 365-nm light (fluorescence). The lowest detection limits for Cu2+ and PPi, when using colorimetric and fluorimetric methods, were in the sub-micromolar and nanomolar levels, respectively. By exploiting this PPi sensing strategy, invitro as well as endogenous alkaline phosphatase activity could be monitored effectively, as demonstrated by exploiting the intracellular production or residual PPi in human salivary glands (normal) and cancer cell lines.
关键词： Endogenous Alkaline Phosphatase,C2v Symmetry,d→π* Electron Transfer,Intramolecular Charge/Electron Transfer,Human Salivary Gland Cells and Cancer Cells,Hydrazone
更新于2025-09-11 14:15:04
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Spectral Methods in Transition Metal Complexes || Electronic Spectroscopy
摘要： The electronic spectrum covers the range from 200 to 800 nm of the electromagnetic spectrum: 200–400 nm is the ultraviolet region and 400–800 nm is the visible region. Hence, the electronic spectrum is also known as the UV-Vis spectrum. The major application of this spectrum to metal complexes is the determination of the geometry of the complex. In order to arrive at this application, we must understand Term Symbols ?rst. If we want to understand these concepts, selection rules, and transitions, we must have a clear understanding of the concepts of the symmetry of molecules, the symmetry elements, symmetry operations, point groups of molecules, character tables, direct product concepts, and so on. Hence, we will discuss these concepts before the term symbols.
关键词： UV-Vis spectrum,symmetry elements,electronic spectrum,character tables,direct product,Term Symbols,symmetry,metal complexes,point groups,geometry,symmetry operations
更新于2025-09-10 09:29:36