High-precision Quantum Research Articles

A Comparative Study of CH and mCH Mechanisms in Hydrosilylation Reactions

The cyclic process of Si-H oxidation addition, olefin insertion, and reductive elimination was discussed by density functional theory (DFT) and high-precision quantum chemical calculations. All the calculations were performed at the B3LYP-D3/def2-TZVP level. Two fundamental mechanisms of Chalk-Harrod (CH) and modified Chalk-Harrod (mCH) were explored, in the perspective of computational chemistry. Pt(PH3)2 was used as model for the renowned Speier's catalyst, while HSiR (R=(CH3)3 and CH3(OSi(CH3)3)2 and CH2=CHR’ (R’=H, CH2OH and CH2OCH2CH2OH) were used as the reactant models. Significant findings include the identification of the olefin insertion as the rate-determining step in both mechanisms.The energy barrier of rate-determining step was 27.6 kcal/mol and 41.0 kcal/mol, respectively, according to the CH mechanism and the mCH mechanism, when HSi(CH3)3 and CH2=CH2 were used as the reactant models. But the barrier of rate-determining step become to 27.2 kcal/mol and 28.4 kcal/mol, when HSiCH3(OSi(CH3)3)2 and CH2=CHCH2OCH2CH2OH were used as the reactant models. The difference in energy barriers betweeen the CH and mCH mechanisms become closer as the reactant models increase. The reaction between polyhydrosiloxane and allyl polyether may very potentially follow the mCH mechanism rather than CH mechanism.

High-precision chemical quantum sensing in flowing monodisperse microdroplets.

A method is presented for high-precision chemical detection that integrates quantum sensing with droplet microfluidics. Using nanodiamonds (ND) with fluorescent nitrogen-vacancy (NV) centers as quantum sensors, rapidly flowing microdroplets containing analyte molecules are analyzed. A noise-suppressed mode of optically detected magnetic resonance is enabled by pairing controllable flow with microwave control of NV electronic spins, to detect analyte-induced signals of a few hundredths of a percent of the ND fluorescence. Using this method, paramagnetic ions in droplets are detected with low limit-of-detection using small analyte volumes, with exceptional measurement stability over >103 s. In addition, these droplets are used as microconfinement chambers by co-encapsulating ND quantum sensors with various analytes such as single cells, suggesting wide-ranging applications including single-cell metabolomics and real-time intracellular measurements from bioreactors. Important advances are enabled by this work, including portable chemical testing devices, amplification-free chemical assays, and chemical imaging tools for probing reactions within microenvironments.

Theoretical kinetics study of hydrogen abstraction reactions of O2(X3Σg/a1Δg) + CnH2n+2 (n ≤ 4)

The chain-initial reactions of small-molecule alkane (CnH2n+2(n ≤ 4)) oxidation participated by electronically excited oxygen O2(a1Δg) are crucial for understanding the role of O2(a1Δg) in plasma-assisted combustion and fuel reforming. Accordingly, in the present work, the energy barriers for the reactions O2(X3Σg/a1Δg) + alkane (n ≤ 4) → products were investigated by using high-precision quantum calculations. Rate constants for each reaction channel within the temperature range of 300–1500 K were predicted based on transition state theory (TST), supplementing plasma kinetics parameters. The energy barriers and rate constants for methane and ethane oxidation dehydrogenation reactions showed good agreement with literature data, validating the accuracy of the computational method employed in this work. The calculations revealed that the dehydrogenation sites have vital impacts on the reaction system. The energy barriers of the reaction channels involved in O2(a1Δg) were reduced at different dehydrogenation sites. Specifically, the change rate of each reaction energy barrier at primary, secondary and tertiary site was about 40 %, 65 % and 65 %, respectively. The reactions involving O2(a1Δg) significantly increased the reaction rate coefficient, especially for single hydrogen abstraction at the secondary and tertiary sites. The effect of O2(a1Δg) on ignition promotion and its regularity were further studied through kinetic simulations. The results suggested that adding O2(a1Δg) reduces the ignition delay time (IDT) of small molecular alkanes by approximately one order of magnitude, attributed to variations in energy barrier and branching ratios of different reaction channels. Notably, the H-atom abstraction reaction on primary site showed the largest sensitivity in IDT at 800 K, particularly for propane and isobutane, with IDT change rates of 98.0 % and 96.3 %, respectively. This study provided reasonable rate coefficients for kinetic modeling of plasma-assisted alkane ignition.

The aromatic amino acid phenylalanine: a versatile tool for binding transition metal ions.

The human body contains many different types of transition metal ions, such as Zn2+, Cu2+, which are involved in many physiological processes. An excess or deficiency of these ions can cause diseases, such as Alzheimer's disease, which is closely related to the levels of these ions in the body. In-depth understanding of various physiological and pathological mechanisms related to metal ions requires understanding the interaction between metal ions and nearby amino acids at the atomic level. This article selected four transition metal ions: Zn2+, Cu2+, Fe2+, and Mn2+ and the aromatic amino acid Phe, known for its strong coordination capability, as study subjects, comprehensively examining their binding situations. The results show that there are multiple binding modes between them and Phe, and most of the binding modes involve benzene ring coordination. The coordination strength order of the four metal ions with benzene ring, carbonyl O, hydroxyl O and amino N is different. For the lowest energy structure formed by each ion with Phe, all four ions are bound to N, carbonyl O, and benzene ring. Zn2+ is combined with two C's of the benzene ring, Cu2+ with four C's of the benzene ring, and Fe2+ and Mn2+ with the benzene ring as a whole. Part of the reason for this phenomenon may be derived from the tendency of transition metal ions to reach 18e stable structures when bound to ligands. There is a strong binding force between the four ions and Phe, and the binding trend is Cu2+(-294.9kcal/mol) > Zn2+(-261.3kcal/mol) > Fe2+(-247.5kcal/mol) > Mn2+(-220.2kcal/mol). Mayer bond order analysis and molecular orbital localization analysis found that there are very strong chemical interactions between transition metal ions and surrounding atoms, especially with N and carbonyl O. Several initial structures with different coordination modes to Phe were created according to chemical intuition for each divalent cation. Then semiempirical MD simulations at GFN2 level were run on these structures. The numerous generated structures were classified according to some criteria, then representative geometries were preliminarily optimized by TPSSh/6-31G*/LanL2DZ. To get more accurate electronic energies, high-precision quantum chemistry calculations at the level of TPSSh/def2TZVPP//TPSSh/def2QZVPP were carried out on the selected low-lying structures. All the optimized structures were confirmed to be minima without imaginary frequency by performing frequency analyses. Further electronic structure analyses such as IRI, Mayer bond order, IBSI etc. were performed to get more insights into the binding between the transition metal ions and Phe.

A Review of Ground State Hanle Effect on Paraffin Coated Alkali Atoms under EIT and EIA

IntroductionThis review is specifically aimed at providing deeper understanding of the ground state Hanle effect through novel methods of atomic vapor interaction with resonant light. Electromagnetically Induced Transparency (EIT) and absorption (EIA) are the primary phenomena in this context. EIT is a process in which destructive interference at absorption frequencies within a medium is caused by a control laser and makes the medium clear to the probe laser light. It should be noted that this transparency is crucial for turning on/off the light pulses, slowing down or stopping in several cases, thus enhancing the effectiveness of atomic magnetometers. However, constructive interference that occurs in EIA raises the density of the medium, which is advantageous for achieveing precise measurements. Thus, studying Hanle effect contribute in development of commercially valuable applications and the improvement of atomic clocks. ObjectiveThe objective of this study is to review the fundamental principles of the Hanle effect, EIT, EIA, and coating methods for alkali atoms. These principles and techniques are essential for improving the sensitivity and functionality of atomic magnetometers and other quantum devices. By understanding and applying these phenomena, significant progress has been made in the development of high-precision measurement tools and quantum technologies. ResultsAdvancements in atomic magnetometer sensitivity represent a rapidly growing area of interest that has made the significant progress in the development of quantum devices. This review consolidates the state of art research and development of fundamental principles and practical applications of the Hanle effect, EIT, EIA, and coating methods for alkali atoms. It highlights how advancements in EIT and EIA have contributed to the sensitivity improvements of atomic magnetometers, and show the importance of coating methods for maintaining system integrity and performance. These developments are essential in revolutioning of modern quantum technologies and precision measurement devices.

Experimental enhancement of six-beam quantum squeezing by phase-sensitive cascaded four-wave mixing processes.

We experimentally realize the enhancement of six-beam quantum squeezing by utilizing a six-beam phase-sensitive amplifier (PSA) based on cascaded four-wave mixing processes. Compared to the intensity-difference squeezing (IDS) of about 5.03 or 5.09 dB generated by a six-beam phase-insensitive amplifier (PIA), the six-beam IDS generated by the six-beam PSA is enhanced to about 6.64 dB. The intrinsic interference of six-beam PSA induces this enhancement. In addition, we investigate the dependence of IDS generated by the six-beam PSA and PIAs on the powers of two pump beams. The results show that the IDS of six-beam PSA is always better than that of six-beam PIAs. Our scheme may find potential applications in high-precision multi-parameter quantum metrology.

Efficient simulation of potential energy operators on quantum hardware: a study on sodium iodide (NaI)

This study introduces a conceptually novel polynomial encoding algorithm for simulating potential energy operators encoded in diagonal unitary forms in a quantum computing machine. The current trend in quantum computational chemistry is effective experimentation to achieve high-precision quantum computational advantage. However, high computational gate complexity and fidelity loss are some of the impediments to the realization of this advantage in a real quantum hardware. In this study, we address the challenges of building a diagonal Hamiltonian operator having exponential functional form, and its implementation in the context of the time evolution problem (Hamiltonian simulation and encoding). Potential energy operators when represented in the first quantization form is an example of such types of operators. Through systematic decomposition and construction, we demonstrate the efficacy of the proposed polynomial encoding method in reducing gate complexity from O(2n)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathcal {O}(2^n)$$\\end{document} to O∑i=1rnCr\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathcal {O}\\left( \\sum _{i=1}^{r} {} ^nC_r \\right)$$\\end{document} (for some r≪n\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$r\\ll n$$\\end{document}). This offers a solution with lower complexity in comparison to the conventional Hadamard basis encoding approach. The effectiveness of the proposed algorithm was validated with its implementation in the IBM quantum simulator and IBM quantum hardware. This study demonstrates the proposed approach by taking the example of the potential energy operator of the sodium iodide molecule (NaI) in the first quantization form. The numerical results demonstrate the potential applicability of the proposed method in quantum chemistry problems, while the analytical bound for error analysis and computational gate complexity discussed, throw light on issues regarding its implementation.

Remote cross-resonance gate between superconducting fixed-frequency qubits

High-fidelity quantum state transfer and remote entanglement between superconducting fixed-frequency qubits have not yet been realized. In this study, we propose an alternative remote cross-resonance gate. Considering multiple modes of a superconducting coaxial cable connecting qubits, we must find conditions under which the cross-resonance gate operates with a certain accuracy even in the presence of qubit frequency shifts due to manufacturing errors. For 0.25- and 0.5 m cables, remote cross-resonance gates with a concurrence of >99.9% in entanglement generation are obtained even with ±10 MHz frequency shifts. For a 1 m cable with a narrow mode spacing, a concurrence of 99.5% is achieved by reducing the coupling between the qubits and cable. The optimized echoed raised-cosine pulse duration is 150–400 ns, which is similar to the operation time of cross-resonance gates between neighboring qubits on a chip. The dissipation through the cable modes does not considerably affect the obtained results. Such high-precision quantum interconnects pave the way not only for scaling up quantum computer systems but also for nonlocal connections on a chip.

Effective information bounds in modified quantum mechanics

A common feature of collapse models and an expected signature of the quantization of gravity at energies well below the Planck scale is the deviation from ordinary quantum-mechanical behavior. Here, we analyze the general consequences of such modifications from the point of view of quantum information theory and we anticipate applications to different quantum systems. We show that quantum systems undergo corrections to the quantum speed limit which, in turn, imply the modification of the Heisenberg limit for parameter estimation. Our results hold for a wide class of scenarios beyond ordinary quantum mechanics. For some nonlocal models inspired by quantum gravity, the bounds are found to oscillate in time, an effect that could be tested in future high-precision quantum experiments.

Auxiliary-cavity-enhanced quantum estimation of optorotational-coupling strength.

A scheme is proposed to achieve significantly enhanced quantum estimation of optorotational-coupling (ORC) strength by coupling a driven auxiliary cavity to a Laguerre-Gaussian (L-G) rotational cavity, where the ORC originates from the exchange of orbital angular momentum between a L-G light and rotational mirror. The results indicate that, by appropriately designing the auxiliary-cavity mechanism, the estimation error of the ORC parameter is significantly reduced, and revealing the estimation precision has a much stronger thermal noise and dissipation robustness in comparison with the unassisted case. Our study paves the way toward achieving high-precision quantum sensors.

A physical organic strategy to predict and interpret stabilities of chemical bonds in energetic compounds for the discovery of thermal-resistant properties.

The in-depth understanding about the stability of chemical bonds in energetic compounds plays a central role for molecular design and safety-related evaluations. Most energetic compounds contain nitro as explosophores, and nitro cleavage is fundamental for thermal and mechanical stability. However, the quantum chemistry approach to accurately predict energy and temperature properties related to bond stability is challenging, due to the tradeoff between computational costs and deviations. Herein, the bond orders are proposed as accurate and computational-cost efficient descriptors for predicting the chemical bond stability and thermal-resistant properties. The intrinsic bond strength index (IBSI) demonstrates the best prediction for experimental homolytic bond dissociation energies (R2 > 0.996), which is on par with the results from high-precision quantum chemistry methods. The effects from bond connectivity and steric hindrance hierarchy were analyzed to reveal underlying mechanisms. Additionally, the IBSI descriptors are successfully applied to predict the thermal decomposition temperatures of 24 heat-resistant energetic compounds (R2 = 0.995), thus validating the effectiveness for the prediction and interpretation of chemical bond stability in energetic compounds via a physical organic approach. All DFT calculations were performed with Gaussian 09 software. To investigate the dependence of the method on functionals and basis sets, 9 DFT methods were considered (B3LYP/6-31G(d,p), B3LYP/6-311G(d,p), B3LYP/def2-TZVP, M062X/6-31G(d,p), M062X/6-311G(d,p), M062X/def2-TZVP, ωB97XD/6-31G(d,p), ωB97XD/6-311G(d,p), and ωB97XD/def2-TZVP). The bond order descriptors LBO and IBSI are obtained through the bond order analysis module in the Multiwfn software.

Predicting Two-Photon Absorption Spectra of Octupolar Molecules: A Deep-Learning Approach Based Exclusively on Molecular Structures.

Octupolar molecules possessing a strong two-photon response are vital for numerous advanced applications. However, accurately predicting their two-photon absorption (TPA) spectra requires high-precision quantum chemical calculations, which are computationally expensive due to repeated simulations of molecular excited-state properties. To address this challenge, we introduce a deep learning approach capable of rapidly and accurately forecasting TPA spectra for octupolar molecules. By leveraging the geometric structure as an initial descriptor, we employ a graph neural network to predict the maximum two-photon transition wavelength and cross-section. Our model demonstrates a mean absolute percentage error of less than 4% compared to time-dependent density-functional theory calculations, effectively reproducing experimental observations. Notably, this deep learning technique is nearly 100 000 times faster than comparable quantum calculations, making it an efficient and cost-effective tool for simulating TPA properties of octupolar molecules. Furthermore, this method holds great promise for the high-throughput screening of exceptional TPA materials.

Hybrid quantum algorithms for flow problems.

For quantum computing (QC) to emerge as a practically indispensable computational tool, there is a need for quantum protocols with end-to-end practical applications-in this instance, fluid dynamics. We debut here a high-performance quantum simulator which we term QFlowS (Quantum Flow Simulator), designed for fluid flow simulations using QC. Solving nonlinear flows by QC generally proceeds by solving an equivalent infinite dimensional linear system as a result of linear embedding. Thus, we first choose to simulate two well-known flows using QFlowS and demonstrate a previously unseen, full gate-level implementation of a hybrid and high precision Quantum Linear Systems Algorithms (QLSA) for simulating such flows at low Reynolds numbers. The utility of this simulator is demonstrated by extracting error estimates and power law scaling that relates [Formula: see text] (a parameter crucial to Hamiltonian simulations) to the condition number [Formula: see text] of the simulation matrix and allows the prediction of an optimal scaling parameter for accurate eigenvalue estimation. Further, we include two speedup preserving algorithms for a) the functional form or sparse quantum state preparation and b) in situ quantum postprocessing tool for computing nonlinear functions of the velocity field. We choose the viscous dissipation rate as an example, for which the end-to-end complexity is shown to be [Formula: see text], where [Formula: see text] is the size of the linear system of equations, [Formula: see text] is the solution error, and [Formula: see text] is the error in postprocessing. This work suggests a path toward quantum simulation of fluid flows and highlights the special considerations needed at the gate-level implementation of QC.

High-Precision Quantum Measurements of Qudits Taking into Account the Influence of Amplitude and Phase Relaxation

High-Precision Quantum Measurements of Qudits Taking into Account the Influence of Amplitude and Phase Relaxation

Topolectrical Circuit Correspondence Design of Polyacetylene

In cis and trans geometrical configurations of the polyacetylene molecule, one-dimensional chain is constructed by attaching a number of identical –HC=CH– units one-by-one. We attach as many units as required to obtain the chain of the desired length. In case of a very long polyacetylene chain, which is practically considered infinite in length, a periodic unit is defined, so that its band structure would be calculable. Then, the electronic properties and topological properties of the chain can be predicted. Since experimental synthesis of single-layer polyacetylene chain has lots of limitations, in an alternative approach, emulation of a tight-binding model is used to describe the electron transfer in polyacetylene polymer chain. In case of either synthesis or testing the polyacetylene molecule, it is necessary to improvise a one-to-one correspondence between polyacetylene polymer and topological circuit, which is introduced for the first time in the present study. To this aim, the outputs of density functional theory calculations alongside with the calculations based on the physical chemistry formalisms are used. Here, we observed that the electronic response of the circuit is topologically sustained at frequencies where the coupling was pre-determined via high precision quantum system equivalent topolectrical circuit, as an alternative classical system, to study electron transfer of trans-polyacetylene polymer quantum chain by the precision of one-electron.

Quantum Fisher information of an [formula omitted]-qubit maximal sliced state in decoherence channels and Ising-type interacting model

Various quantum states have been suggested to realize high-precision measurement and quantum Fisher information (QFI) is one of the most important indicators to evaluate the performance. Here, we systematically investigate the QFI of an N-qubit maximal sliced (MS) state in different environments. In the ideal situation, we present the analytical QFI and it decays from N2 to (N−1)2 as the probability amplitude α changed from 0 to 1, which denotes the decreased metrological ability. In the amplitude damping channel, the variation trends of QFI with respect to the damping probability p are similar and it decreases to the number of qubits N at p=1, meaning the vanished entanglement superiority. However, it is different in the phase damping channel where with the increase of the number of qubits a turning point of QFI equal to N is found at p closing to 0.1. In the Ising-type interacting model, with the increasing interaction strength γ, the QFI with respect to α shows a crossover from decreasing to increasing. Particularly, at the critical point γ=1, the QFI of an N-qubit MS state is found analytically equal to N2 and regardless of α. This indicates a great potential in achieving the Heisenberg-limited metrology and may shed some new light on quantum information science.

Hückel Molecular Orbital Analysis for Stability and Instability of Stacked Aromatic and Stacked Antiaromatic Systems.

Face-to-face stacking of aromatic compounds leads to stacked antiaromaticity, while that of antiaromatic compounds leads to stacked aromaticity. This is a prediction with a long history; in the late 2000s, the prediction was confirmed by high-precision quantum chemical calculations, and finally, in 2016, a π-conjugated system with stacked aromaticity was synthesized. Several variations have since been reported, but essentially, they are all the same molecule. To realize stacked aromaticity in a completely new and different molecular system and to trigger an extension of the concept of stacked aromaticity, it is important to understand the origin of stacked aromaticity. The Hückel method, which has been successful in giving qualitatively correct results for π-conjugated systems despite its bold assumptions, is well suited for the analysis of stacked aromaticity. We use this method to model the face-to-face stacking systems of benzene and cyclobutadiene molecules and discuss their stacked antiaromaticity and stacked aromaticity on the basis of their π-electron energies. By further developing the discussion, we search for clues to realize stacked aromaticity in synthesizable molecular systems.

Current Status and Prospects on High-Precision Quantum Tests of the Weak Equivalence Principle with Cold Atom Interferometry

For a hundred years, general relativity has been the best theory to describe gravity and space–time and has successfully explained many physical phenomena. At the same time, quantum mechanics provides the most accurate description of the microscopic world, and quantum science technology has evoked a wide range of developments today. Merging these two very successful theories to form a grand unified theory is one of the most elusive challenges in physics. All the candidate theories that wish to unify gravity and quantum mechanics predict the breaking of the weak equivalence principle, which lies at the heart of general relativity. It is therefore imperative to experimentally verify the equivalence principle in the presence of significant quantum effects of matter. Cold atoms provide well-defined properties and potentially nonlocal correlations as the test masses and will also improve the limits reached by classical tests with macroscopic bodies. The results of rigorous tests using cold atoms may tell us whether and how the equivalence principle can be reformulated into a quantum version. In this paper, we review the principles and developments of the test of the equivalence principle with cold atoms. The status of the experiments and the key techniques involved are discussed in detail. Finally, we give an outlook on new questions and opportunities for further exploration of this topic.

Contrasting Transport Performance of Electron- and Hole-Doped Epitaxial Graphene for Quantum Resistance Metrology

Epitaxial graphene grown on silicon carbide (SiC/graphene) is a promising solution for achieving a high-precision quantum Hall resistance standard. Previous research mainly focused on the quantum resistance metrology of n-type SiC/graphene, while a comprehensive understanding of the quantum resistance metrology behavior of graphene with different doping types is lacking. Here, we fabricated both n- and p-type SiC/graphene devices via polymer-assisted molecular adsorption and conducted systematic magneto-transport measurements in a wide parameter space of carrier density and temperature. It is demonstrated that n-type devices show greater potential for development of quantum resistance metrology compared with p-type devices, as evidenced by their higher carrier mobility, lower critical magnetic field for entering quantized Hall plateaus, and higher robustness of the quantum Hall effect against thermal degeneration. These discrepancies can be reasonably attributed to the weaker scattering from molecular dopants for n-type devices, which is further supported by the analyses on the quantum interference effect in multiple devices. These results enrich our understanding of the charged impurity on electronic transport performance of graphene and, more importantly, provide a useful reference for future development of graphene-based quantum resistance metrology.

Quantum properties of nitrogen-vacancy center in diamond coupled to mechanical resonators

The optical absorption spectrum of the hybrid system composed of the nitrogen-vacancy (NV) center coupled to the mechanical resonators is. investigated. Based on the pump-probe technology, the electronically induced transparency (EIT) is observed and the reasonable explanation for this transparency is given. We demonstrate that the position of the transparency is equal to the detuning difference. In addition, a completely new scheme to measure the coupling between the NV center and current carrying carbon nanotube mechanical resonator is obtained. Furthermore, an optical approach to measure the frequency of the vibrating graphene mechanical resonator is proposed. This work can provide some help for the application in the field of high-precision measurement and quantum information processing.