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

arXiv:2610.15743

Molecular Vibronic Complexity as a Quantum Resource for Optimal Control: Nonadiabatic Mixing Creates Protected Coherence Subspaces in Dissipative Environments

Elisa Palacino-González

quant-phphysics.chem-phSubmitted Oct 11, 2026• Announced Oct 13, 2026
arXivHTMLPDF

Abstract

In molecules, electronic coherence typically decays within a few hundred femtoseconds, a timescale usually attributed to the environment. We show that it is set to a large extent by which coherences are excited: the molecule can host coherences that the bath barely sees, and optimal control can find and exploit them. Using gradient-based optimal control (GRAPE) with Redfield dynamics, we maximize the total vibronic coherence between the electronic ground and an optically bright electronic excited state in a three-state model with nonadiabatic features, in two regimes of low and high nonadiabatic mixing and for different system-bath coupling strengths. The Liouvillian spectrum reveals, in both regimes, a well-separated coherence mode with substantial ground-bright character that decays on a picosecond timescale. This mode is protected by mixing with the dark state, which brings the geometry of the optically accessible excited state close to that of the ground state and thus weakens its coupling to the bath. Without prior information, GRAPE finds this mode and keeps the photoexcited wave packet near the Franck-Condon region. At equal fluence, it increases the coherence at 800 fs by more than two orders of magnitude over a Gaussian pulse at the weakest coupling, and by many more at stronger coupling. The Liouvillian predicts the bath dependence of the long-lived coherence to within 1\%, and a Gaussian pulse tuned to the mode frequency comes within 10\% of the best pulse found. Beyond two-level and spin systems, our study puts forward the vibronic structure of molecules as a route to protected coherence subspaces, identifying a dark-state protection mechanism and a design criterion based on molecular parameters. These results lay the groundwork for our goal of using vibronic molecular systems as a resource for long-lived, controllable coherences in molecular quantum information science.

Comments
37 pages main file; 4 pages SI; 10 figures

Related papers

COHERENT CONTROL OF DECOHERENCE

Ian A. Walmsley, Matthijs P. A. Branderhorst, Pablo Londero +3 more

Any real system, no matter how well isolated, unavoidably interacts with the environment. This interaction makes the evolution of a quantum system nonunitary and destroys the coherence of quantum superpositions. This process, known as decoherence, is widely regarded as the most important and fundamental obstacle to the practical realization of quantum information processing. On the other hand, the objectives of quantum control are predicated on the ability to manipulate the system coherently over a period of time. Quantum control has been applied successfully to several experimental systems and coupling such a controlled system to an environment makes the study of coherence loss possible. The standard model of decoherence is formulated in terms of a system, defined by the observables that can be measured, and a reservoir, de¯ned by those degrees of freedom that are not accessed by observation. The vibrational and rotational degree of freedom of diatomic molecules form an experimental model of such a system and bath 1. The nature of the ro-vibrational coupling does not allow a Decoherence Free Subspace, instead we try to identify a Decoherence Resistant Subspace using closed loop control. We set up a learning control loop experiment to monitor the coherence in a vibrational wavepacket, consisting of about 6 vibrational states of the A(1Σ+g ) electronic state, excited by a shaped, ultrashort optical pulse, and then to determine the pulse shape that yielded the longest coherence lifetime. The coherence of the vibrational wavepacket was monitored by measuring the fluorescence quantum beats from the outer turning point of the wave packet's trajectory. The closed loop controller altered the shape of the driving optical pulse to maximize the the depth of modulation of the quantum beats at a prescribed time after excitation, within the constraints of the laser system. The outcome of this closed loop control experiment shows an improvement of the beat decay constant of about 60%, as shown in Fig. (1), a result which occurs for several di®erent pulse shapes. Our experiments show that a number of interesting decoherence-resistant excitations exist. The nature of the dephasing was examined theoretically. Using measured optical pulse shapes, we simulated numerically the molecular wavepacket in the limit of perturbation theory. The experiment and simulations show that there are di®erent mechanisms contributing to the decoherence resistant excitation. The shaped pulse reduces the °uctuations in the wave packet spatial extent, which in turn changes the system reservoir coupling. Other components of the optimal pulse are a sequence of pulses that creates constructive interference of the vibrational wavepacket at the desired time, and chirp which compensates for the anharmonicity of the adiabatic potential. The experimental results show general agreement with numerical simulations. We conclude that wavepackets resistant to dephasing do exist,and that learning algorithms provide an effcient means for finding them.

Frontiers in Optics•Jan 1, 2005•0 citations

Cooling molecular vibrations with shaped laser pulses: optimal control theory exploiting the timescale separation between coherent excitation and spontaneous emission

Daniel M. Reich, Christiane P. Koch

Laser cooling of molecules employing broadband optical pumping involves a timescale separation between laser excitation and spontaneous emission. Here, we optimize the optical pumping step using shaped laser pulses. We derive two optimization functionals to drive population into those excited state levels that have the largest spontaneous emission rates to the target state. We show that, when using optimal control, laser cooling of molecules works even if the Franck–Condon map governing the transitions is preferential to heating rather than cooling. Our optimization functional is also applicable to the laser cooling of other degrees of freedom provided the cooling cycle consists of coherent excitation and dissipative de-excitation steps whose timescales are separated.

arXiv:1308.0803•New Journal of Physics•Dec 20, 2013•28 citations

Quantum Ghost Spectroscopy Reveals Hidden Electronic Coherence in Molecular Aggregates

Mingran Zhang, Yihe Xu, Vladislav V. Yakovlev +1 more

Ultrafast spectroscopy of molecular systems is fundamentally constrained by the Fourier uncertainty principle: high temporal resolution smears out electronic state signatures, while high spectral resolution obscures dynamic information. Here we overcome this limitation using time-resolved quantum ghost spectroscopy (tr-QGS) with entangled photon pairs, which enables independent control of temporal and spectral scales. We apply this approach to perylene bismide (PBI-1) trimers for energy transfer,by combining a quantum description of light-molecule interaction with time-dependent density matrix renormalization group (TD-DMRG) simulations. This explicitly includes five vibrational modes and nonadiabatic coupling between electronic states. Our simulations reveal that tr-QGS uniquely captures electronic coherence oscillating at 0.7 eV for >50 fs, a signature of nonadiabatic coupling that was obscured in conventional time-resolved fluorescence due to Fourier-limited broadening. Moreover, we observe a direct transfer from electronic to vibrational coherence at 200 fs, providing real-time visualization of vibronic relaxation pathways. The entangled photon correlation enables a sensitivity below the shot-noise limit and suppresses photobleaching artifacts that plague classical measurements. These results establish tr-QGS as a transformative tool for interrogating nonadiabatic dynamics in molecular aggregates, light-harvesting complexes, and photocatalysts, offering a route to reveal quantum coherence in chemistry with unprecedented time-energy precision.

quant-pharXiv:2605.23639•May 25, 2026

Vibronic coupling limits the use of high-lying electronic states in complex molecules for laser cooling

Haowen Zhou, Paweł Wójcik, Guo‐Zhu Zhu +7 more

Laser cooling of large, complex molecules is a long-standing goal, instrumental for enabling new quantum technology and precision measurements. A primary consideration for the feasibility of laser cooling, which determines the efficiency and technical requirements of the process, is the number of excited-state decay pathways leading to vibrational excitations. Therefore, the assessment of the laser-cooling potential of a molecule begins with estimate of the vibrational branching ratios of the first few electronic excited states theoretically to find the optimum cooling scheme. Such calculations, typically done within the Born-Oppenheimer and harmonic approximations, have suggested that one leading candidate for large, polyatomic molecule laser cooling, alkaline earth phenoxides, can most efficiently be laser cooled via the third electronically excited ( C ̃ ) state. Here, we report the first detailed spectroscopic characterization of the C ̃ state in CaOPh and SrOPh. We find that nonadiabatic couplings between the A ̃ , B ̃ , and C ̃ states lead to substantial mixing, giving rise to vibronic states that enable additional decay pathways. Based on the intensity ratio of these extra decay channels, we estimate a nonadiabatic coupling strength of ∼ 0.1 cm − 1 . While this coupling strength is small, the large density of vibrational states available at photonic energy scales in a polyatomic molecule leads to significant mixing. Only the lowest excited state A ̃ is exempt from this coupling because it is highly separated from the ground state. Thus, this result is expected to be general for large molecules and implies that only the lowest electronic excited state should be considered when judging the suitability of a molecule for laser cooling.

arXiv:2510.22367•Physical Review Research•Nov 19, 2025•2 citations

Analysis of some intuitive approaches to the coherent control of state-selected ultracold molecules

Benjamin L. Brown, Ian A. Walmsley

Coherent femtosecond optical pulses provide a unique means to manipulate the collision process between a pair of ultracold atoms. The capability to arbitrarily shape strong electric fields gives the possibility of dynamically sculpting the system Hamiltonian on the collisional timescale. In this paper we explore theoretically physically intuitive excitation schemes by which a control field can manipulate the vibronic state populations in an ultracold molecular system, with the goal of bringing atom pairs to short ( R < 10 Å) separations where they may form a tightly bound molecule. The microscopic dynamics of individual pairs of colliding atoms under the influence of an external optical field are explored through explicitly time-dependent numerical simulations. The results provide physical justification for the employment of optimal control techniques for the achievement of state-selective formation of ultracold molecules.

Journal of Physics B Atomic Molecular and Optical Physics•Sep 25, 2006•12 citations

Correlation-Enabled Beatings in Two-Dimensional Electronic Spectroscopy

Sirui Chen, Dragomir Davidović

Long-lived beatings in two-dimensional electronic spectroscopy (2DES) remain difficult to interpret within standard excitonic open-system models, which typically assume factorized initialization and predict rapid coherence decay. We show that persistent beatings can arise from a correlation-driven mechanism that requires both slow bath memory and ultrafast pulse sequences that propagate system-bath correlations across optical interactions. In this regime, the pulse sequence unitarily dresses the bath-memory contribution and activates nonsecular population-coherence transfer during field-free evolution, sustaining coherence signatures far beyond factorized or weak-memory descriptions. Rather than addressing what is oscillating (excitonic versus vibronic) or quantum-versus-classical semantics, this work reframes long-lived beatings as a protocol-level dynamical effect: correlation-mediated retrieval under ultrafast control.

quant-pharXiv:2602.04061•Feb 5, 2026
In molecules, electronic coherence typically decays within a few hundred femtoseconds, a timescale usually attributed to the environment. We show that it is set to a large extent by which coherences are excited: the molecule can host coherences that the bath barely sees, and optimal control can find and exploit them. Using gradient-based optimal control (GRAPE) with Redfield dynamics, we maximize the total vibronic coherence between the electronic ground and an optically bright electronic excited state in a three-state model with nonadiabatic features, in two regimes of low and high nonadiabatic mixing and for different system-bath coupling strengths. The Liouvillian spectrum reveals, in both regimes, a well-separated coherence mode with substantial ground-bright character that decays on a picosecond timescale. This mode is protected by mixing with the dark state, which brings the geometry of the optically accessible excited state close to that of the ground state and thus weakens its coupling to the bath. Without prior information, GRAPE finds this mode and keeps the photoexcited wave packet near the Franck-Condon region. At equal fluence, it increases the coherence at 800 fs by more than two orders of magnitude over a Gaussian pulse at the weakest coupling, and by many more at stronger coupling. The Liouvillian predicts the bath dependence of the long-lived coherence to within 1%, and a Gaussian pulse tuned to the mode frequency comes within 10% of the best pulse found. Beyond two-level and spin systems, our study puts forward the vibronic structure of molecules as a route to protected coherence subspaces, identifying a dark-state protection mechanism and a design criterion based on molecular parameters. These results lay the groundwork for our goal of using vibronic molecular systems as a resource for long-lived, controllable coherences in molecular quantum information science.
Any real system, no matter how well isolated, unavoidably interacts with the environment. This interaction makes the evolution of a quantum system nonunitary and destroys the coherence of quantum superpositions. This process, known as decoherence, is widely regarded as the most important and fundamental obstacle to the practical realization of quantum information processing. On the other hand, the objectives of quantum control are predicated on the ability to manipulate the system coherently over a period of time. Quantum control has been applied successfully to several experimental systems and coupling such a controlled system to an environment makes the study of coherence loss possible. The standard model of decoherence is formulated in terms of a system, defined by the observables that can be measured, and a reservoir, de¯ned by those degrees of freedom that are not accessed by observation. The vibrational and rotational degree of freedom of diatomic molecules form an experimental model of such a system and bath 1. The nature of the ro-vibrational coupling does not allow a Decoherence Free Subspace, instead we try to identify a Decoherence Resistant Subspace using closed loop control. We set up a learning control loop experiment to monitor the coherence in a vibrational wavepacket, consisting of about 6 vibrational states of the A(1Σ+g ) electronic state, excited by a shaped, ultrashort optical pulse, and then to determine the pulse shape that yielded the longest coherence lifetime. The coherence of the vibrational wavepacket was monitored by measuring the fluorescence quantum beats from the outer turning point of the wave packet's trajectory. The closed loop controller altered the shape of the driving optical pulse to maximize the the depth of modulation of the quantum beats at a prescribed time after excitation, within the constraints of the laser system. The outcome of this closed loop control experiment shows an improvement of the beat decay constant of about 60%, as shown in Fig. (1), a result which occurs for several di®erent pulse shapes. Our experiments show that a number of interesting decoherence-resistant excitations exist. The nature of the dephasing was examined theoretically. Using measured optical pulse shapes, we simulated numerically the molecular wavepacket in the limit of perturbation theory. The experiment and simulations show that there are di®erent mechanisms contributing to the decoherence resistant excitation. The shaped pulse reduces the °uctuations in the wave packet spatial extent, which in turn changes the system reservoir coupling. Other components of the optimal pulse are a sequence of pulses that creates constructive interference of the vibrational wavepacket at the desired time, and chirp which compensates for the anharmonicity of the adiabatic potential. The experimental results show general agreement with numerical simulations. We conclude that wavepackets resistant to dephasing do exist,and that learning algorithms provide an effcient means for finding them.
Laser cooling of molecules employing broadband optical pumping involves a timescale separation between laser excitation and spontaneous emission. Here, we optimize the optical pumping step using shaped laser pulses. We derive two optimization functionals to drive population into those excited state levels that have the largest spontaneous emission rates to the target state. We show that, when using optimal control, laser cooling of molecules works even if the Franck–Condon map governing the transitions is preferential to heating rather than cooling. Our optimization functional is also applicable to the laser cooling of other degrees of freedom provided the cooling cycle consists of coherent excitation and dissipative de-excitation steps whose timescales are separated.
Ultrafast spectroscopy of molecular systems is fundamentally constrained by the Fourier uncertainty principle: high temporal resolution smears out electronic state signatures, while high spectral resolution obscures dynamic information. Here we overcome this limitation using time-resolved quantum ghost spectroscopy (tr-QGS) with entangled photon pairs, which enables independent control of temporal and spectral scales. We apply this approach to perylene bismide (PBI-1) trimers for energy transfer,by combining a quantum description of light-molecule interaction with time-dependent density matrix renormalization group (TD-DMRG) simulations. This explicitly includes five vibrational modes and nonadiabatic coupling between electronic states. Our simulations reveal that tr-QGS uniquely captures electronic coherence oscillating at 0.7 eV for >50 fs, a signature of nonadiabatic coupling that was obscured in conventional time-resolved fluorescence due to Fourier-limited broadening. Moreover, we observe a direct transfer from electronic to vibrational coherence at 200 fs, providing real-time visualization of vibronic relaxation pathways. The entangled photon correlation enables a sensitivity below the shot-noise limit and suppresses photobleaching artifacts that plague classical measurements. These results establish tr-QGS as a transformative tool for interrogating nonadiabatic dynamics in molecular aggregates, light-harvesting complexes, and photocatalysts, offering a route to reveal quantum coherence in chemistry with unprecedented time-energy precision.
Laser cooling of large, complex molecules is a long-standing goal, instrumental for enabling new quantum technology and precision measurements. A primary consideration for the feasibility of laser cooling, which determines the efficiency and technical requirements of the process, is the number of excited-state decay pathways leading to vibrational excitations. Therefore, the assessment of the laser-cooling potential of a molecule begins with estimate of the vibrational branching ratios of the first few electronic excited states theoretically to find the optimum cooling scheme. Such calculations, typically done within the Born-Oppenheimer and harmonic approximations, have suggested that one leading candidate for large, polyatomic molecule laser cooling, alkaline earth phenoxides, can most efficiently be laser cooled via the third electronically excited ( C ̃ ) state. Here, we report the first detailed spectroscopic characterization of the C ̃ state in CaOPh and SrOPh. We find that nonadiabatic couplings between the A ̃ , B ̃ , and C ̃ states lead to substantial mixing, giving rise to vibronic states that enable additional decay pathways. Based on the intensity ratio of these extra decay channels, we estimate a nonadiabatic coupling strength of ∼ 0.1 cm − 1 . While this coupling strength is small, the large density of vibrational states available at photonic energy scales in a polyatomic molecule leads to significant mixing. Only the lowest excited state A ̃ is exempt from this coupling because it is highly separated from the ground state. Thus, this result is expected to be general for large molecules and implies that only the lowest electronic excited state should be considered when judging the suitability of a molecule for laser cooling.
Coherent femtosecond optical pulses provide a unique means to manipulate the collision process between a pair of ultracold atoms. The capability to arbitrarily shape strong electric fields gives the possibility of dynamically sculpting the system Hamiltonian on the collisional timescale. In this paper we explore theoretically physically intuitive excitation schemes by which a control field can manipulate the vibronic state populations in an ultracold molecular system, with the goal of bringing atom pairs to short ( R < 10 Å) separations where they may form a tightly bound molecule. The microscopic dynamics of individual pairs of colliding atoms under the influence of an external optical field are explored through explicitly time-dependent numerical simulations. The results provide physical justification for the employment of optimal control techniques for the achievement of state-selective formation of ultracold molecules.
Long-lived beatings in two-dimensional electronic spectroscopy (2DES) remain difficult to interpret within standard excitonic open-system models, which typically assume factorized initialization and predict rapid coherence decay. We show that persistent beatings can arise from a correlation-driven mechanism that requires both slow bath memory and ultrafast pulse sequences that propagate system-bath correlations across optical interactions. In this regime, the pulse sequence unitarily dresses the bath-memory contribution and activates nonsecular population-coherence transfer during field-free evolution, sustaining coherence signatures far beyond factorized or weak-memory descriptions. Rather than addressing what is oscillating (excitonic versus vibronic) or quantum-versus-classical semantics, this work reframes long-lived beatings as a protocol-level dynamical effect: correlation-mediated retrieval under ultrafast control.