Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Accounts of Chemical Research

Vibronic Engineering for Quantum Functional Groups

Haowen Zhou, Taras A. Khvorost, Anastassia N. Alexandrova, Justin Ryan Caram

Published Apr 7, 2025• 6 citations
Publisher

Abstract

ConspectusChemists have a firm understanding of the concept of a functional group: a small molecular moiety that confers properties (reactivity, solubility, and chemical recognition) onto a larger scaffold. Analogously, a quantum functional group (QFG) would act as an isolated "quantum handle" that could attach onto an extended molecule and enable quantum state preparation and measurement (SPAM). However, the complexity associated with molecular chemistry is often at odds with the requirements of nonthermal state preparation. The rest of the molecule acts as a local bath that leads to dephasing and loss of quantum information upon excitation and relaxation. Yet, there exists an enormous chemical space of potential chemical bonding motifs to design isolated QFGs. The goal of this Account is to explore the underlying chemical design principles for the optimization of QFG performance.For typical state preparation, an applied field is used to put the qubit into a specific known state (via optical cycling and laser cooling), where it can be manipulated or entangled with other species. That same field (or another) can be used to read out or report on the qubit state at the end of the operation. For example, in trapped ions/neutral atoms, state preparation is accomplished by pumping a specific transition using a narrowband laser. From there, further operations can be performed on the qubit via selective RF or laser excitation, and the state can be read out via fluorescence. However, extending this paradigm to molecular systems is highly challenging: molecules have many more degrees of freedom that can couple to the absorbed or emitted field. Overcoming this requires greatly limiting the number of these "off-diagonal" decay pathways through the judicious selection of the QFG and vibronic engineering of the molecular substrate.Our work has demonstrated that alkaline-earth (I) alkoxides (MOR) may meet the necessary requirements for efficient SPAM. In particular, we capitalize on the -OM (M = Ca, Sr) motif, which acts as a quantum handle that has been attached to a variety of aliphatic and aromatic hydrocarbons. The precise breakdown of the optical cycling property depends on familiar chemical concepts, including conjugation, conformer formation, electron-withdrawing abilities, and symmetry. In this Account, we review the recent efforts in the field to construct QFGs and codesign molecular scaffolds that can host them without destruction of their desired quantum properties. QFGs are explored as attachments to photoswitching scaffolds and mounted in pairs to larger hosts. A variety of physical phenomena relevant to the ability of these QFGs to function as qubits, from Fermi resonances to super radiance, have been explored. We thus began deriving the first set of rules for vibronic engineering toward the QFG functionality. Prospects toward increasing the number densities of these QFGs through molecular and material design are also presented.

DOI
10.1021/acs.accounts.4c00773

Related papers

Franck-Condon Tuning of Optical Cycling Centers by Organic Functionalization

Claire E. Dickerson, Han Jie Guo, Ashley Jiwon Shin +4 more

Laser induced electronic excitations that spontaneously emit photons and decay directly to the initial ground state ("optical cycling transitions") are used in quantum information and precision measurement for state initialization and readout. To extend this primarily atomic technique to large, organic compounds, we theoretically investigate optical cycling of alkaline earth phenoxides and their functionalized derivatives. We find that optical cycle leakage due to wave function mismatch is low in these species, and can be further suppressed by using chemical substitution to boost the electron-withdrawing strength of the aromatic molecular ligand through resonance and induction effects. This provides a straightforward way to use chemical functional groups to construct optical cycling moieties for laser cooling, state preparation, and quantum measurement.

arXiv:2010.04207•Physical Review Letters•Mar 26, 2021•42 citations

Optical Cycling Functionalization of Arenes

Claire E. Dickerson, Han Jie Guo, Guo‐Zhu Zhu +4 more

Closed, laser-induced optical transitions (“optical cycling transitions”) of molecules can be used for state preparation and measurement in quantum information science and quantum sensing. Increasingly complex molecular species supporting optical cycling can provide new capabilities for quantum science, and it is not clear if there is a limit on their size or complexity. We explore Ca–O–L molecular constructs to support the optical cycling center, Ca, with ligands, L, being arenes. We find that L can be as large as coronene (i.e., CaOC 24 H 11 ) without losing the diagonality of the Franck–Condon factor (FCF). Furthermore, L can be substituted with electron-withdrawing groups to improve the FCF. Larger L, beyond ∼7 rings, can disrupt the diagonality of the FCF by closing the HOMO–LUMO ligand electronic state gap and reordering with the local states on the cycling center. Overall, we find that optical cycling can be retained for arenes, and we offer a principle for their design.

The Journal of Physical Chemistry Letters•Apr 20, 2021•29 citations

Surface chemical trapping of optical cycling centers

Han Jie Guo, Claire E. Dickerson, Ashley Jiwon Shin +5 more

Quantum information processors based on trapped atoms utilize laser-induced optical cycling transitions for state preparation and measurement. These transitions consist of an electronic excitation from the ground to an excited state and a decay back to the initial ground state, associated with a photon emission. While this technique has been used primarily with atoms, it has also recently been shown to work for some divalent metal hydroxides (e.g. SrOH) and alkoxides (e.g. SrOCH3). This extension to molecules is possible because these molecules feature nearly isolated, atomic-like ground and first-excited electronic states centered on the radical metal atom. We theoretically investigate the extension of this idea to a larger scale by growing the alkyl group, R, beyond the initial methyl group, CH3, while preserving the isolated and highly vertical character of the electronic excitation on the radical metal atom, M. Theory suggests that in the limit as the size of the ligand carbon chain increases, it can be considered a functionalized diamond (or cubic boron nitride) surface. Several requirements must be observed for the cycling centers to function when bound to the surface. First, the surface must have a significant band gap that fully encapsulates both the ground and excited states of the cycling center. Second, while the surface lattice imposes strict limits on the achievable spacing between the SrO- groups, at high coverage, SrO- centers can interact, and show geometric changes and/or electronic state mixing. We show that the coverage of the diamond surface with SrO- cycling centers needs to be significantly sub-monolayer for the functionality of the cycling center to be preserved. Having the lattice-imposed spatial control of SrO- placements will allow nanometer-scale proximity between qubits and will eliminate the need for atom traps for localized cycling emitters. Our results also imply that a functionalization could be done on a scanning microscope tip for local quantum sensing or on photonic structures for optically-mediated quantum information processing.

Physical Chemistry Chemical Physics•Sep 21, 2020•10 citations

Engineering Quantum Optical Matter: Defects, Entanglement, and Chemical Reactivity

Wang, Derek Schawn

The discovery of quantum theory has led to explanations for nearly all physical phenomena from the smallest to largest length scales. In recent decades, as quantum theories have become better understood, scientists and engineers now seek to apply the unique advantages of quantum systems to solve practical problems. The purpose of this dissertation is to engineer quantum light-matter systems, or quantum optical matter, for practical applications by using theoretical and computational methods at the intersection of quantum chemistry and quantum optics. This dissertation consists of three parts. In the first, we design and control a class of quantum optical matter, defects in solid-state materials, that can be used as a nanoscale interface between quantum light and quantum matter degrees of freedom. In the second part, we click together simple and generic systems of quantum optical matter, where the particular features of specific systems like defects in solid-state materials have been abstracted away, to form more complex composite systems. We then show that certain composite systems can emit entangled photons and perform multi-qubit gates on photons with applications in photonic quantum computing. Finally, in the third part, we study another application of quantum optical matter: chemistry. In particular, we propose an explanation for experiments in the field of vibrational polariton chemistry where it has been observed that molecules packed into a cavity with fundamental modes resonant with molecular vibrational resonances exhibit altered chemical reactivity.

•Jan 1, 2022•0 citations

ANALOG QUANTUM SIMULATION OF MOLECULAR DYNAMICS AND SPECTROSCOPIC OBSERVABLES

Ryan J. MacDonell, Ivan Kassal

Modern computational techniques used to simulate quantum chemistry are on the boundary of tractability due to the exponential growth of the molecular wavefunction, requiring a careful balance between molecule size and simulation accuracy. In recent years, quantum computing has risen in popularity as a potential alternative to conventional (classical) techniques; however, most methods rely on access to "digital" quantum computers composed of qubits and quantum gates, which at present are severely limited by noise. We have developed a real-time, analog approach to simulate vibronic chemical dynamics with existing quantum technology. Our approach uses an intuitive mapping of molecular electronic and vibrational degrees of freedom onto quantum resonators and qudit (d-level system) states, with controllable couplings between degrees of freedom. The measurement output can be mapped onto different time-dependent observables, including the time-domain simulation of vibronic spectra. Our approach can also incorporate controlled sources of noise to simulate system-bath interactions and dissipative dynamics at a minimal cost. We present experimental results using a trapped-ion device, thus showing the potential for near-term simulation of chemical dynamics in complex environments beyond the abilities of classical computers.

International Symposium on Molecular Spectroscopy (ISMS)•Jun 23, 2022•0 citations

Quantum state preparation and control of single molecular ions

D Leibfried

Preparing molecules at rest and in a very pure quantum state is a long-standing aspiration in chemistry and physics, so far achieved only for a select set of molecules in dedicated experimental setups. Here, a quantum-limited combination of mass spectrometry and Raman spectroscopy is proposed that should be applicable to a wide range of molecular ions. Excitation of electrons in the molecule followed by uncontrolled decay and branching into several lower-energy states is avoided. Instead, the molecule is always confined to rotational states within the electronic and vibrational ground-state manifold, while a co-trapped atomic ion provides efficient entropy removal and allows for extraction of information about the molecule. The outlined techniques might enable the preparation, manipulation and measurement of a multitude of molecular ion species with the same instrument, with applications including, but not limited to, precise determination of molecular properties and fundamental tests of physics.

arXiv:1109.0208•New Journal of Physics•Feb 14, 2012•42 citations
ConspectusChemists have a firm understanding of the concept of a functional group: a small molecular moiety that confers properties (reactivity, solubility, and chemical recognition) onto a larger scaffold. Analogously, a quantum functional group (QFG) would act as an isolated "quantum handle" that could attach onto an extended molecule and enable quantum state preparation and measurement (SPAM). However, the complexity associated with molecular chemistry is often at odds with the requirements of nonthermal state preparation. The rest of the molecule acts as a local bath that leads to dephasing and loss of quantum information upon excitation and relaxation. Yet, there exists an enormous chemical space of potential chemical bonding motifs to design isolated QFGs. The goal of this Account is to explore the underlying chemical design principles for the optimization of QFG performance.For typical state preparation, an applied field is used to put the qubit into a specific known state (via optical cycling and laser cooling), where it can be manipulated or entangled with other species. That same field (or another) can be used to read out or report on the qubit state at the end of the operation. For example, in trapped ions/neutral atoms, state preparation is accomplished by pumping a specific transition using a narrowband laser. From there, further operations can be performed on the qubit via selective RF or laser excitation, and the state can be read out via fluorescence. However, extending this paradigm to molecular systems is highly challenging: molecules have many more degrees of freedom that can couple to the absorbed or emitted field. Overcoming this requires greatly limiting the number of these "off-diagonal" decay pathways through the judicious selection of the QFG and vibronic engineering of the molecular substrate.Our work has demonstrated that alkaline-earth (I) alkoxides (MOR) may meet the necessary requirements for efficient SPAM. In particular, we capitalize on the -OM (M = Ca, Sr) motif, which acts as a quantum handle that has been attached to a variety of aliphatic and aromatic hydrocarbons. The precise breakdown of the optical cycling property depends on familiar chemical concepts, including conjugation, conformer formation, electron-withdrawing abilities, and symmetry. In this Account, we review the recent efforts in the field to construct QFGs and codesign molecular scaffolds that can host them without destruction of their desired quantum properties. QFGs are explored as attachments to photoswitching scaffolds and mounted in pairs to larger hosts. A variety of physical phenomena relevant to the ability of these QFGs to function as qubits, from Fermi resonances to super radiance, have been explored. We thus began deriving the first set of rules for vibronic engineering toward the QFG functionality. Prospects toward increasing the number densities of these QFGs through molecular and material design are also presented.
Laser induced electronic excitations that spontaneously emit photons and decay directly to the initial ground state ("optical cycling transitions") are used in quantum information and precision measurement for state initialization and readout. To extend this primarily atomic technique to large, organic compounds, we theoretically investigate optical cycling of alkaline earth phenoxides and their functionalized derivatives. We find that optical cycle leakage due to wave function mismatch is low in these species, and can be further suppressed by using chemical substitution to boost the electron-withdrawing strength of the aromatic molecular ligand through resonance and induction effects. This provides a straightforward way to use chemical functional groups to construct optical cycling moieties for laser cooling, state preparation, and quantum measurement.
Closed, laser-induced optical transitions (“optical cycling transitions”) of molecules can be used for state preparation and measurement in quantum information science and quantum sensing. Increasingly complex molecular species supporting optical cycling can provide new capabilities for quantum science, and it is not clear if there is a limit on their size or complexity. We explore Ca–O–L molecular constructs to support the optical cycling center, Ca, with ligands, L, being arenes. We find that L can be as large as coronene (i.e., CaOC 24 H 11 ) without losing the diagonality of the Franck–Condon factor (FCF). Furthermore, L can be substituted with electron-withdrawing groups to improve the FCF. Larger L, beyond ∼7 rings, can disrupt the diagonality of the FCF by closing the HOMO–LUMO ligand electronic state gap and reordering with the local states on the cycling center. Overall, we find that optical cycling can be retained for arenes, and we offer a principle for their design.
Quantum information processors based on trapped atoms utilize laser-induced optical cycling transitions for state preparation and measurement. These transitions consist of an electronic excitation from the ground to an excited state and a decay back to the initial ground state, associated with a photon emission. While this technique has been used primarily with atoms, it has also recently been shown to work for some divalent metal hydroxides (e.g. SrOH) and alkoxides (e.g. SrOCH3). This extension to molecules is possible because these molecules feature nearly isolated, atomic-like ground and first-excited electronic states centered on the radical metal atom. We theoretically investigate the extension of this idea to a larger scale by growing the alkyl group, R, beyond the initial methyl group, CH3, while preserving the isolated and highly vertical character of the electronic excitation on the radical metal atom, M. Theory suggests that in the limit as the size of the ligand carbon chain increases, it can be considered a functionalized diamond (or cubic boron nitride) surface. Several requirements must be observed for the cycling centers to function when bound to the surface. First, the surface must have a significant band gap that fully encapsulates both the ground and excited states of the cycling center. Second, while the surface lattice imposes strict limits on the achievable spacing between the SrO- groups, at high coverage, SrO- centers can interact, and show geometric changes and/or electronic state mixing. We show that the coverage of the diamond surface with SrO- cycling centers needs to be significantly sub-monolayer for the functionality of the cycling center to be preserved. Having the lattice-imposed spatial control of SrO- placements will allow nanometer-scale proximity between qubits and will eliminate the need for atom traps for localized cycling emitters. Our results also imply that a functionalization could be done on a scanning microscope tip for local quantum sensing or on photonic structures for optically-mediated quantum information processing.
The discovery of quantum theory has led to explanations for nearly all physical phenomena from the smallest to largest length scales. In recent decades, as quantum theories have become better understood, scientists and engineers now seek to apply the unique advantages of quantum systems to solve practical problems. The purpose of this dissertation is to engineer quantum light-matter systems, or quantum optical matter, for practical applications by using theoretical and computational methods at the intersection of quantum chemistry and quantum optics. This dissertation consists of three parts. In the first, we design and control a class of quantum optical matter, defects in solid-state materials, that can be used as a nanoscale interface between quantum light and quantum matter degrees of freedom. In the second part, we click together simple and generic systems of quantum optical matter, where the particular features of specific systems like defects in solid-state materials have been abstracted away, to form more complex composite systems. We then show that certain composite systems can emit entangled photons and perform multi-qubit gates on photons with applications in photonic quantum computing. Finally, in the third part, we study another application of quantum optical matter: chemistry. In particular, we propose an explanation for experiments in the field of vibrational polariton chemistry where it has been observed that molecules packed into a cavity with fundamental modes resonant with molecular vibrational resonances exhibit altered chemical reactivity.
Modern computational techniques used to simulate quantum chemistry are on the boundary of tractability due to the exponential growth of the molecular wavefunction, requiring a careful balance between molecule size and simulation accuracy. In recent years, quantum computing has risen in popularity as a potential alternative to conventional (classical) techniques; however, most methods rely on access to "digital" quantum computers composed of qubits and quantum gates, which at present are severely limited by noise. We have developed a real-time, analog approach to simulate vibronic chemical dynamics with existing quantum technology. Our approach uses an intuitive mapping of molecular electronic and vibrational degrees of freedom onto quantum resonators and qudit (d-level system) states, with controllable couplings between degrees of freedom. The measurement output can be mapped onto different time-dependent observables, including the time-domain simulation of vibronic spectra. Our approach can also incorporate controlled sources of noise to simulate system-bath interactions and dissipative dynamics at a minimal cost. We present experimental results using a trapped-ion device, thus showing the potential for near-term simulation of chemical dynamics in complex environments beyond the abilities of classical computers.
Preparing molecules at rest and in a very pure quantum state is a long-standing aspiration in chemistry and physics, so far achieved only for a select set of molecules in dedicated experimental setups. Here, a quantum-limited combination of mass spectrometry and Raman spectroscopy is proposed that should be applicable to a wide range of molecular ions. Excitation of electrons in the molecule followed by uncontrolled decay and branching into several lower-energy states is avoided. Instead, the molecule is always confined to rotational states within the electronic and vibrational ground-state manifold, while a co-trapped atomic ion provides efficient entropy removal and allows for extraction of information about the molecule. The outlined techniques might enable the preparation, manipulation and measurement of a multitude of molecular ion species with the same instrument, with applications including, but not limited to, precise determination of molecular properties and fundamental tests of physics.