Karl Michael Ziems
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View article: Cost-effective scalable quantum error mitigation for tiled Ansätze
Cost-effective scalable quantum error mitigation for tiled Ansätze Open
We introduce a cost-effective quantum error mitigation technique that builds on the recent Ansatz-based gate and readout error mitigation method (M0). The technique, tiled M0, leverages the unique structure of tiled Ansätze (e.g., tUPS, QN…
View article: Hyperfine Coupling Constants on Quantum Computers: Performance, Errors, and Future Prospects
Hyperfine Coupling Constants on Quantum Computers: Performance, Errors, and Future Prospects Open
We present the first implementation and computation of electron spin resonance isotropic hyperfine coupling constants (HFCs) on a quantum hardware. As illustrative test cases, we compute the HFCs for the hydroxyl radical (OH•), …
View article: Reduced density matrix and cumulant approximations of quantum linear response
Reduced density matrix and cumulant approximations of quantum linear response Open
Linear response (LR) is an important tool in the computational chemist's toolbox. It is therefore no surprise that the emergence of quantum computers has led to a quantum version, quantum LR (qLR). However, the current quantum era of near-…
View article: Critical Limitations in Quantum-Selected Configuration Interaction Methods
Critical Limitations in Quantum-Selected Configuration Interaction Methods Open
Quantum Selected Configuration Interaction (QSCI) methods (also known as Sample-based Quantum Diagonalization, SQD) have emerged as promising near-term approaches to solving the electronic Schrödinger equation with quantum computers. In th…
View article: Exact closed-form expression for unitary spin-adapted fermionic singlet double excitation operators
Exact closed-form expression for unitary spin-adapted fermionic singlet double excitation operators Open
We derive exact closed-form expressions for the matrix exponential of the anti-Hermitian spin-adapted singlet double excitation fermionic operators. These expressions enable the efficient implementation of such operators within unitary pro…
View article: Understanding and mitigating noise in molecular quantum linear response for spectroscopic properties on quantum computers
Understanding and mitigating noise in molecular quantum linear response for spectroscopic properties on quantum computers Open
Absorption spectra of LiH obtained on a quantum computer using quantum linear response, Pauli saving, QWC, and Ansatz-based read-out and gate error mitigation.
View article: Self-consistent Quantum Linear Response with a Polarizable Embedding environment
Self-consistent Quantum Linear Response with a Polarizable Embedding environment Open
Quantum computing presents a promising avenue for solving complex problems, particularly in quantum chemistry, where it could accelerate the computation of molecular properties and excited states. This work focuses on hybrid quantum-classi…
View article: Divergences in classical and quantum linear response and equation of motion formulations
Divergences in classical and quantum linear response and equation of motion formulations Open
Calculating molecular properties using quantum devices can be performed through the quantum linear response (qLR) or, equivalently, the quantum equation of motion (qEOM) formulations. Different parameterizations of qLR and qEOM are availab…
View article: Understanding and mitigating noise in molecular quantum linear response for spectroscopic properties on quantum computers
Understanding and mitigating noise in molecular quantum linear response for spectroscopic properties on quantum computers Open
The promise of quantum computing to circumvent the exponential scaling of quantum chemistry has sparked a race to develop chemistry algorithms for quantum architecture. However, most works neglect the quantum-inherent shot noise, let alone…
View article: Reduced Density Matrix Formulation of Quantum Linear Response
Reduced Density Matrix Formulation of Quantum Linear Response Open
The prediction of spectral properties via linear response (LR) theory is an important tool in quantum chemistry for understanding photoinduced processes in molecular systems. With the advances of quantum computing, we recently adapted this…
View article: Electric Field Gradient Calculations for Ice VIII and IX Using Polarizable Embedding: A Comparative Study on Classical Computers and Quantum Simulators
Electric Field Gradient Calculations for Ice VIII and IX Using Polarizable Embedding: A Comparative Study on Classical Computers and Quantum Simulators Open
We test the performance of the polarizable embedding variational quantum eigensolver self-consistent field (PE-VQE-SCF) model for computing electric field gradients with comparisons to conventional complete active space self-consistent-fie…
View article: Divergences in classical and quantum linear response and equation of motion formulations
Divergences in classical and quantum linear response and equation of motion formulations Open
Calculating molecular properties using quantum devices can be done through the quantum linear response (qLR) or, equivalently, the quantum equation of motion (qEOM) formulations. Different parameterizations of qLR and qEOM are available, n…
View article: Subspace Methods for the Simulation of Molecular Response Properties on a Quantum Computer
Subspace Methods for the Simulation of Molecular Response Properties on a Quantum Computer Open
We explore Davidson methods for obtaining excitation energies and other linear response properties within the recently developed quantum self-consistent linear response (q-sc-LR) method. Davidson-type methods allow for obtaining only a few…
View article: Attosecond core-level absorption spectroscopy reveals the electronic and nuclear dynamics of molecular ring opening
Attosecond core-level absorption spectroscopy reveals the electronic and nuclear dynamics of molecular ring opening Open
View article: Subspace methods for the simulation of molecular response properties on a quantum computer
Subspace methods for the simulation of molecular response properties on a quantum computer Open
We explore Davidson methods for obtaining excitation energies and other linear response properties within quantum self-consistent linear response (q-sc-LR) theory. Davidson-type methods allow for obtaining only a few selected excitation en…
View article: Theory data for: Attosecond Core-Level Absorption Spectroscopy Reveals the Electronic and Nuclear Dynamics of Molecular Ring-Opening
Theory data for: Attosecond Core-Level Absorption Spectroscopy Reveals the Electronic and Nuclear Dynamics of Molecular Ring-Opening Open
Raw theory data and analysis scripts for the theoretical part of the publication: "Attosecond Core-Level Absorption Spectroscopy Reveals the Electronic and Nuclear Dynamics of Molecular Ring-Opening" https://www.researchsquare.com/article/…
View article: Imaging Ultrafast Dissociation Dynamics: OCS & Roaming in Formaldehyde
Imaging Ultrafast Dissociation Dynamics: OCS & Roaming in Formaldehyde Open
Upon photoexcitation, molecules break apart, following different dissociation reactions. We can image these dissociation pathways using Coulomb explosion imaging (CEI) and sometimes we can control them using asymmetric laser fields. In the…
View article: Which options exist for NISQ-friendly linear response formulations?
Which options exist for NISQ-friendly linear response formulations? Open
Linear response (LR) theory is a powerful tool in classic quantum chemistry crucial to understanding photo-induced processes in chemistry and biology. However, performing simulations for large systems and in the case of strong electron cor…
View article: Quantum Equation of Motion with Orbital Optimization for Computing Molecular Properties in Near-Term Quantum Computing
Quantum Equation of Motion with Orbital Optimization for Computing Molecular Properties in Near-Term Quantum Computing Open
Determining the properties of molecules and materials is one of the premier applications of quantum computing. A major question in the field is how to use imperfect near-term quantum computers to solve problems of practical value. Inspired…
View article: Attosecond Core-Level Absorption Spectroscopy Reveals the Electronic and Nuclear Dynamics of Molecular Ring-Opening
Attosecond Core-Level Absorption Spectroscopy Reveals the Electronic and Nuclear Dynamics of Molecular Ring-Opening Open
We show that attosecond core-level spectroscopy is a powerful tool for investigating molecular dynamics due to its combined attosecond temporal resolution and the broad coherent spectrum that allows deciphering the signatures of nuclear an…
View article: The contribution of Compton ionization to ultrafast x-ray scattering
The contribution of Compton ionization to ultrafast x-ray scattering Open
We investigate the role of Compton ionization in ultrafast non-resonant x-ray scattering using a molecular model system, which includes the ionization continuum via an orthonormalized plane wave ansatz. Elastic and inelastic components of …
View article: Attosecond ionization dynamics of modulated, few-cycle XUV pulses
Attosecond ionization dynamics of modulated, few-cycle XUV pulses Open
Few-cycle, attosecond extreme ultraviolet (XUV) pulses in the strong field regime are becoming experimentally feasible, prompting theoretical investigating of the ionization dynamics induced by such pulses. Here, we provide a systematic st…
View article: Non-Adiabatic Electronic and Vibrational Ring-Opening Dynamics resolved with Attosecond Core-Level Spectroscopy
Non-Adiabatic Electronic and Vibrational Ring-Opening Dynamics resolved with Attosecond Core-Level Spectroscopy Open
Non-adiabatic dynamics and conical intersections play a central role in the chemistry of most polyatomic molecules, ranging from isomerization to heterocyclic ring opening and avoided photo-damage of DNA. Studying the underpinning correlat…
View article: Laser-induced electron diffraction in the over-the-barrier ionization (OBI) regime
Laser-induced electron diffraction in the over-the-barrier ionization (OBI) regime Open
Large polyatomic molecules typically exhibit low ionization potentials, Ip, leading to over-the-barrier ionization (OBI) already at relatively low intensities (~1013 W/cm2). We revisit laser-induced electron diffraction (LIED) in the over-…
View article: CCDC 2110902: Experimental Crystal Structure Determination
CCDC 2110902: Experimental Crystal Structure Determination Open
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available …
View article: CCDC 2110903: Experimental Crystal Structure Determination
CCDC 2110903: Experimental Crystal Structure Determination Open
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available …
View article: Nuclear–Electron Correlation Effects and Their Photoelectron Imprint in Molecular XUV Ionisation
Nuclear–Electron Correlation Effects and Their Photoelectron Imprint in Molecular XUV Ionisation Open
The ionisation of molecules by attosecond XUV pulses is accompanied by complex correlated dynamics, such as the creation of coherent electron wave packets in the parent ion, their interplay with nuclear wave packets, and a correlated photo…
View article: Novel [FeFe]-Hydrogenase Mimics: Unexpected Course of the Reaction of Ferrocenyl α-Thienyl Thioketone with Fe3(CO)12
Novel [FeFe]-Hydrogenase Mimics: Unexpected Course of the Reaction of Ferrocenyl α-Thienyl Thioketone with Fe3(CO)12 Open
The influence of the substitution pattern in ferrocenyl α-thienyl thioketone used as a proligand in complexation reactions with Fe3(CO)12 was investigated. As a result, two new sulfur–iron complexes, considered [FeFe]-hydrogenase mimics, w…
View article: Post-Ionization Dynamics of the Polar Molecule OCS in Asymmetric Laser Fields
Post-Ionization Dynamics of the Polar Molecule OCS in Asymmetric Laser Fields Open
We have investigated the dissociation mechanisms of the prototypical heavy polar molecule OCS into the two break-up channels of the dication, OCS 2+ → O + + CS + and OC + + S + , in phase-locked two-color intense laser fields. The branchin…
View article: Unraveling the Light‐Activated Reaction Mechanism in a Catalytically Competent Key Intermediate of a Multifunctional Molecular Catalyst for Artificial Photosynthesis
Unraveling the Light‐Activated Reaction Mechanism in a Catalytically Competent Key Intermediate of a Multifunctional Molecular Catalyst for Artificial Photosynthesis Open
Understanding photodriven multielectron reaction pathways requires the identification and spectroscopic characterization of intermediates and their excited‐state dynamics, which is very challenging due to their short lifetimes. To the best…