Ultrafast fs coherent excitonic dynamics in CdSe quantum dots assemblies addressed and probed by 2D electronic spectroscopy

E. Collini, H. Gattuso, R.D. Levine, F. Remacle

The Journal of Chemical Physics 154 (2021) 014301.



We show in a joint experimental and theoretical study that ultrafast femto-second (fs) electronic coherences can be characterized in semi-conducting colloidal quantum dot (QD) assemblies at room temperature. The dynamics of the electronic response of ensembles of CdSe QDs in the solution and of QD dimers in the solid state is probed by a sequence of 3 fs laser pulses as in two-dimensional (2D) electronic spectroscopy. The quantum dynamics is computed using an excitonic model Hamiltonian based on the effective mass approximation. The Hamiltonian includes the Coulomb, spin-orbit, and crystal field interactions that give rise to the fine structure splittings. In the dimers studied, the interdot distance is sufficiently small to allow for an efficient interdot coupling and delocalization of the excitons over the two QDs of the dimer. To account for the inherent few percent size dispersion of colloidal QDs, the optical response is modeled by averaging over an ensemble of 2000 dimers. The size dispersion is responsible for an inhomogeneous broadening that limits the lifetimes of the excitonic coherences that can be probed to about 150 fs-200 fs. Simulations and experimental measurements in the solid state and in the solution demonstrate that during that time scale, a very rich electronic coherent dynamics takes place that involves several types of intradot and interdot (in the case of dimers) coherences. These electronic coherences exhibit a wide range of beating periods and provide a versatile basis for a quantum information processing device on a fs time scale at room temperature.


Quantum Device Emulates the Dynamics of Two Coupled Oscillators

Ksenia Komarova, Hugo Gattuso, R. D. Levine, and F. Remacle*

J. Phys. Chem. Lett. 2020, 11, 6990-6995



Our quantum device is a solid-state array of semiconducting quantum dots that is addressed and read by 2D electronic spectroscopy. The experimental ultrafast dynamics of the device is well simulated by solving the time-dependent Schro?dinger equation for a Hamiltonian that describes the lower electronically excited states of the dots and three laser pulses. The time evolution induced in the electronic states of the quantum device is used to emulate the quite different nonequilibrium vibrational dynamics of a linear triatomic molecule. We simulate the energy transfer between the two local oscillators and, in a more elaborate application, the expectation values of the quantum mechanical creation and annihilation operators of each local oscillator. The simulation uses the electronic coherences engineered in the device upon interaction with a specific sequence of ultrafast pulses. The algorithm uses the algebraic description of the dynamics of the physical problem and of the hardware.


Room-Temperature Inter-Dot Coherent Dynamics in Multilayer Quantum Dot Materials

Elisabetta Collini,* Hugo Gattuso, Yuval Kolodny, Luca Bolzonello, Andrea Volpato, Hanna T. Fridman, Shira Yochelis, Morin Mor, Johanna Dehnel, Efrat Lifshitz, Yossi Paltiel, Raphael D. Levine, and Francoise Remacle

J. Phys. Chem. C 2020, 124, 16222-16231

Tuning Quantum Dots Coupling Using Organic Linkers with Different Vibrational Modes

Yuval Kolodny,Stav Fererra,Veniamin Borin, Shira Yochelis, Carlo Nazareno Dibenedetto, Morin Mor, Joanna Dehnel, Sergei Remmenik, Elisabetta Fanizza, Marinella Striccoli, Igor Schapiro, Efrat Lifshitz and Yossi Paltiel*

J. Phys. Chem. C 2020, 124, 29, 16159-16165



Signatures of long-lived quantum coherence in light-harvesting complexes invoked a hypothesis that the protein-scaffold vibrations assist energy transfer by bridging energy gaps. To address this hypothesis experimentally in a model system, we compare the coupling strength of donor-acceptor quantum dots (QDs) linked by different organic linkers. The linkers are of the same length, with the same headgroups, but differ in one atom at the center of the chain (carbon, sulfur, or oxygen), which changes the vibrational modes of the molecule. We have studied the energy transfer using these linkers both in dimers of QDs, suspended in solution, and in solid multilayered films. Strongest coupling is achieved when a linker vibration (asymmetric stretch around the central atom in this case) matches the energy gap. The results provide experimental support for the theoretical idea of vibration-assisted transport and noise-assisted quantum transport (NEQT) and have important implications for the artificial design of many-particle nanodevices in which interparticle coupling tuning is required.


Coupling effects in QD dimers at sub-nanometer interparticle distance

Carlo Nazareno Dibenedetto, Elisabetta Fanizza, Rosaria Brescia, Yuval Kolodny, Segei Remennik, Annamaria Panniello, Nicletta Depaio, Shira Yochelis, Roberto Comparelli,Angela Agostiano, Maria Lucia Curri, Yossi Paltiel, Marinella Striccoli

Nano Research volume 13, pages1071-1080(2020)



Currently, intensive research efforts focus on the fabrication of meso-structures of assembled colloidal quantum dots (QDs) with original optical and electronic properties. Such collective features originate from the QDs coupling, depending on the number of connected units and their distance. However, the development of general methodologies to assemble colloidal QD with precise stoichiometry and particle-particle spacing remains a key challenge. Here, we demonstrate that dimers of CdSe QDs, stable in solution, can be obtained by engineering QD surface chemistry, reducing the surface steric hindrance and favoring the link between two QDs. The connection is made by using alkyl dithiols as bifunctional linkers and different chain lengths are used to tune the interparticle distance from few nm down to 0.5 nm. The spectroscopic investigation highlights that coupling phenomena between the QDs in dimers are strongly dependent on the interparticle distance and QD size, ultimately affecting the exciton dissociation efficiency.


Spectral shift, electronic coupling and exciton delocalization in nanocrystal dimers: insights from all-atom electronic structure computations

Maurizio Coden,a Pietro De Checchia and Barbara Fresch

Nanoscale, 2020,12, 18124-18136!divAbstract



Delocalization of excitons promoted by electronic coupling between clusters or quantum dots (QD) changes the dynamical processes in nanostructured aggregates enhancing energy transport. A spectroscopic shift of the absorption spectrum upon QD aggregation is commonly observed and ascribed to quantum mechanical coupling between neighbouring dots but also to exciton delocalization over the sulphur-based ligand shell or to other mechanisms as a change in the dielectric constant of the surrounding medium. We address the question of electronic coupling and exciton delocalization in nanocrystal aggregates by performing all-atom electronic structure calculations in models of colloidal QD dimers. The relation between spectral shift, interdot coupling and exciton delocalization is investigated in atomistic detail in models of dimers formed by CdSe clusters kept together by bridging organic ligands. Our results support the possibility of obtaining exciton delocalization over the dimer and point out the crucial role of the bridging ligand in enhancing interdot electronic coupling.


Surprisal of a quantum state: dynamics, compact representation and coherence effects

K. Komarova, F. Remacle, and R.D. Levine

J. Chem. Phys. 153, 214105 (2020)



Progress towards quantum technologies continues to provide essential new insights on the microscopic dynamics of systems in phase space. This highlights coherence effects whether these are due to ultrafast lasers whose energy width spans several states all the way to the output of quantum computing. Surprisal analysis has provided seminal insights on the probability distributions of quantum systems from elementary particle and also nuclear physics, through molecular reaction dynamics to system biology. It is therefore necessary to extend surprisal analysis to the full quantum regime where it characterizes not only the probabilities of states but also their coherence. In principle this can be done by the maximal entropy formalism but in the full quantum regime its application is far from trivial [E.g., S. Dagan and Y. Dothan, Phys Rev D 26, 248 1982] because an exponential function of not commuting operators is not easily accommodated. Starting from an exact dynamical approach we develop a description of the dynamics where the quantum mechanical surprisal, a linear combination of operators, plays a central role. We provide an explicit route to the Lagrange multipliers of the system and identify those operators that act as the dominant constraints.


Fabrication of QDs Dimers with Sub-Nanometer Interparticle Distance

Carlo Nazareno Dibenedetto, Elisabetta Fanizza, Annamaria Panniello, Angela Agostiano, Maria Lucia Curri, Marinella Striccoli

Toxic Chemical and Biological Agents pp 229-230, 2020.


Colloidal semiconductor quatum dots (QDs) are promosing material for the fabrication of optoelectronic photonic and sensing application. This study presents the fabrication and characterization of naostructures composed of a low number of quatum dots.


Parallel Quantum Computation of Vibrational Dynamics

Ksenia Komarova, Hugo Gattuso, R. D. Levine and F. Remacle

Frontiers in Physics 8 (2020) 486.



The vibrational dynamics in a linear triatomic molecule is emulated by a quantum information processing device operating in parallel. The quantum device is an ensemble of semiconducting quantum dot dimers addressed and probed by ultrafast laser pulses in the visible frequency range at room temperature. A realistic assessment of the inherent noise due to the inevitable size dispersion of colloidal quantum dots is taken into account and limits the time available for computation. At the short times considered only the electronic states of the quantum dots respond to the excitation. A model for the electronic states quantum dot (QD) dimers is used which retains the eight lowest bands of excitonic dimer states build on the lowest and first excited states of a single QD. We show how up to 82 = 64 quantum logic variables can be realistically measured and used to process information for this QD dimer electronic level structure. This is achieved by addressing the lowest and second excited electronic states of the QD's. With a narrower laser bandwidth (= longer pulse) only the lower band of excited states can be coherently addressed enabling 42= 16 logic variables. Already this is sufficient to emulate both energy transfer between the two oscillators and coherent motions in the vibrating molecule.


Massively parallel classical logic via coherent dynamics of an ensemble of quantum systems with dispersion in size

Hugo Gattuso, R. D. Levine and F. Remacle

Proceedings of the National Academy of Sciences 117 (2020) 21022,



There is a worldwide effort toward quantum technology. Information processing, sensing, communication, and related areas are getting much of the attention. The advantages offered by the quantum domain are well recognized and acclaimed. Proposed implementations rely on systems operating at rather low temperatures and on the need to isolate the system from outside sources of noise. We discuss a theoretical scheme that suggests operating with a classical collection of quantum systems. An experimental demonstration of the principle is available. The ensemble is an array of size-disordered quantum dots addressed and probed by laser pulses. The algebraic approach encodes information in the coherences between quantum levels of the dots and demonstrates resilience to size disorder.


Chirality of the Rhodamine Heterodimer Linked to DNA Scaffold: An Experimental and Computational Study

P.S. Rukin, K. Komarova, B. Fresch, E. Collini, F. Remacle

Physical Chemistry Chemical Physics 22 (2020) 7516-7523.



Chiroptical properties of multi-chromophoric systems are governed by the intermolecular arrangement of the monomeric units. We report on a computational and experimental study of the linear optical properties and supramolecular structure of a rhodamine heterodimer assembled on a DNA scaffold. The experimental absorption and circular dichroism (CD) profiles confirm the dimer formation. Computationally, starting from low-cost DFT/TDDFT simulations of the bare dimer we attribute the measured -/+ CD sign sequence of the S1/S2 bands to a specific chiral conformation of the heterodimer. In the monomers, as typical to rhodamine dyes, the electric transition dipole of the lowest ?-?* transition is parallel to the long axis of the xanthene planes. We show that in the heterodimer the sign sequence of the two CD bands is related to the orientation of these long axes. To account explicitly for environment effects, we use molecular dynamics (MD) simulations for characterizing the supramolecular structure of the two optical isomers tethered on DNA. Average absorption and CD-profiles were modeled using ab initio TDDFT calculations at the geometries sampled along the few nanosecond MD run. The absorption profiles computed for both optical isomers are in good agreement with the experimental absorption spectrum and do not allow to discriminate between them. The computed averaged CD profiles provide the orientation of monomers in the enantiomer that is dominant under the experimental conditions.


Effect of Different Conformational Distributions on the Ultrafast Coherence Dynamics in Porphyrin-Based Polymers

Andrea Volpato,Mirco Zerbetto, Luca Bolzonello, Elena Meneghin, Barbara Fresch, Tiziana Benelli, Loris Giorgini, and Elisabetta Collini

J. Phys. Chem. C 2019, 123, 10212-10224

Green open access; UniPD repository:



The optical and transport properties of biological and artificial multichromophoric functional materialsare strongly affected by the disorder and electron−vibrationcouplings. The conformational disorder in multichromophoresbecomes critical especially in the control of coherentdynamics. Indeed, microscopic details of the dephasingprocesses promoted by the disorder are not yet fully clarified.Here we applied 2D electronic spectroscopy to study thedynamics of vibrational coherences in porphyrin-functionalized polymer samples characterized by different conformational disorder. Distinct coherent dephasing behaviors have been found for low-frequency vibrational modes in the studied samples. The experimental results have beeninterpreted on the basis of molecular dynamics and quantum mechanical calculations, whichallowed correlation of the trend in the dephasing times with different conformational distributions in the two polymers.


Characterization of the coherent dynamics of bacteriochlorophyll a in solution

Elena Meneghin, Danilo Pedron, Elisabetta Collini

Chemical Physics 519 (2019) 8591

Gold open access; available at:



Disclosing the physical origin of quantum beatings in the early dynamics of biological light-harvesting pigment- protein complexes is one of the major challenges in the ultrafast spectroscopy community. 2D electronic spec- troscopy (2DES) is a powerful tool for this purpose, but the complexity of the beating behavior in multi- chromophoric systems complicates the interpretation. For this reason, the availability of control datasets pro- viding a full characterization of the response of isolated chromophores is highly desirable to untangle the features of intermolecular interactions from the properties of individual pigments. Here, a thorough 2DES characterization of the frequencies and dephasing times of intramolecular vibrational coherences of bacterio- chlorophyll a in solution is provided. Several beating modes in the ground and excited state have been found and their dephasing times have been determined. The obtained results represent an essential interpretation key of the beating dynamics of pigment-protein complexes binding bacteriochlorophyll a.


Spectroscopy data for the time and frequency characterization of vibrational coherences in bacteriochlorophyll a (Data Article)

Elena Meneghin, Danilo Pedron, Elisabetta Collini

Data in brief 23 (2019) 103707

Gold open access; available at:



Bacteriochlorophyll is the primary pigment in the light-harvesting pigment-protein complexes (PPCs) of the bacterial photosynthetic apparatus. 2D electronic spectroscopy (2DES) represents one of the most exploited and powerful techniques to characterize the ultrafast relaxation dynamics in PPCs, in particular, to assess the presence of coherent mechanisms during energy transport.
The data reported in this work and the associated research article, “Characterization of the coherent dynamics of bacteriochlorophyll a in solution” [Meneghin et al., 2019] are an important contribu- tion to the literature on coherent dynamics of light-harvesting complexes and can be useful in the interpretation of coherent motion in more complex systems with bacteriochlorophyll a (BChla) as a basic unit. The analysis of the provided data allows the identification of vibrational coherences associated with several Franck-Condon active modes and the characterization of their frequencies and dephasing times.
Here we report additional data analysis and additional measures that complement the associated research article [Meneghin et al., 2019] and support its main conclusions. In particular, we compare vibrational coherences extracted from 2DES response with Raman modes detected for BChla powders at cryogenic temperature in resonant and non-resonant conditions. Finally, we show the time- resolved fluorescence decay of the chromophore to support the interpretation of non-coherent dynamics discussed in Ref. [Meneghin et al., 2019].


Optimization and selection of time-frequency transforms for wave-packet analysis in ultrafast spectroscopy

Andrea Volpato, Elisabetta Collini

Optics Express 27 (2019) 2975-2987

Gold open access; available at:



The analysis of quantum beats in time-resolved spectroscopic signals is becoming a task of primary importance because it is now clear that they bring crucial information about chemical reactivity, transport, and relaxation processes. Here we describe how to exploit the wide family of time-frequency transform methodologies to obtain information not only about the frequency but also about the dynamics of the oscillating components contributing to the overall beating signal. Several linear and bilinear transforms have been considered, and a general and easy procedure to judge in a non-arbitrary way the performances of different transforms has been outlined.

Computing using quantum dynamics of nanostructured arrays"
Authors: Noam Gross and Ariela Donval
Paper link:
Open access link:
Conference presentation link:

Abstract: “Quantum field is back at the headlines with several research areas such as: quantum sensing, quantum communication, quantum cryptography and quantum computing. A novel concept of a computer exploiting quantum confinement and nonlinear optics is the basis of an EC H2020 consortium named COPAC [1,2,3]. We joined this consortium which uses the dynamic response of assembled nanostructures in solid arrays short laser pulses and implement a novel paradigm for parallel information processing. Within current paper we will discuss the nanostructures materials and configurations as designed for the project, especially the interaction of the nanostructures with the addressing laser beam unit.”

An n-bit adder realized via coherent optical parallel computing.
Authors: Bogdan Reznychenko, Emmanuel Mazer, Maurizio Coden, Elisabetta Collini, Carlo Nazareno DiBenedetto, Ariela Donval, Barbara Fresch, Hugo Gattuso, Noam Gross, Yossi Paltiel, Francoise Remacle, Marinella Striccoli
Link to the open access version: (pages 146-152)
Abstract: The quantum properties of nanosystems present a new opportunity to enhance the power of classical computers, both for the parallelism of the computation and the speed of the optical operations. In this paper we present the COPAC project aiming at development of a ground-breaking nonlinear coherent spectroscopy combining optical addressing and spatially macroscopically resolved optical readout. The discrete structure of transitions between quantum levels provides a basis for implementation of logic functions even at room temperature. Exploiting the superposition of quantum states gives rise to the possibility of parallel computation by encoding different input values into transition frequencies.
As an example of parallel single instruction multiple data calculation by a device developed during the COPAC project, we present a n-bit adder, showing that due to the properties of the system, the delay of this fundamental circuit can be reduced.


Marcello RighettoaLuca BolzonelloaAndrea VolpatoaGiordano AmorusoaAnnamaria PanniellobElisabetta FanizzabcMarinella Striccolib  and  Elisabetta Collini*a 

a Department of Chemical Sciences, University of Padova, Via Marzolo 1, I-35131 Padova, Italy

b CNR-IPCF SS Bari, c/o Chemistry Department, University of Bari Aldo Moro, Via Orabona 4, I-70126 Bari, Italy

c Chemistry Department, University of Bari Aldo Moro, Via Orabona 4, I-70126 Bari, Italy


Although the harnessing of multiple and hot excitons is a prerequisite for many of the groundbreaking applications of semiconductor quantum dots (QDs), the characterization of their dynamics through conventional spectroscopic techniques is cumbersome. Here, we show how a careful analysis of 2DES maps acquired in different configurations (BOXCARS and pump–probe geometry) allows the tracking and visualization of intraband Auger relaxation mechanisms, driving the hot carrier cooling, and interband bi- and tri-exciton recombination dynamics. The results obtained on archetypal core–shell CdSe/ZnS QDs suggest that, given the global analysis of the resulting datasets, 2D electronic spectroscopy techniques can successfully and efficiently dispel the intertwined dynamics of fast and ultrafast recombination processes in nanomaterials. Hence, we propose this analysis scheme to be used in future research on novel quantum confined systems.

Physical Chemistry Chemical Physics 2018, 20, 18176-18183.


Lasers pumped quantum dynamics in nanostructured arrays for computing.

A. Donval, N. Gross, and M. Oron KiloLambda Technologies, Ltd., 22a Raoul Wallenberg St., Tel Aviv 6971918, Israel.

Tel: +972-3-6497662,



Quantum computation uses qubit in superposition and entanglement states providing more sophisticated computation ability regarding today’s computers. For that purpose of developing a novel computer concept exploiting quantum dynamics at the nanoscale, we joined an EC H2020 program consortium named COPAC [1]. We propose to analyze the nonlinear 2 dimensional optical response of assembled nanostructures in solid arrays to a sequence of short laser pulses. Based on 2D maps of the stimulated emission we implement a novel paradigm for parallel information processing. Within the COPAC project, we, in KiloLambda, will develop the device nanostructure and engineering design.

KEYWORDS: Quantum computer, nanostructure, nanophotonics, parallel information processing

Proceedings Volume 10660, Quantum Information Science, Sensing, and Computation X; 1066005 (2018),,

Event: SPIE Commercial + Scientific Sensing and Imaging, 2018, Orlando, Florida, United States


Fast Energy Transfer in CdSe Quantum Dot Layered Structures: Controlling Coupling with Covalent-Bond Organic Linkers

Eyal Cohen1, Pavel Komm1, Noa Rosenthal-Strauss1, Joanna Dehnel2, Efrat Lifshitz2, Shira Yochelis1, R. D. Levine3, Francoise Remacle4, Barbara Fresch5, Gilad Marcus1, Yossi Paltiel1,6.

1Department of Applied Physics, 6Center for Nano-Science and Nano-Technology, 3The Fritz Haber Center for Molecular Dynamics and Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel; 2Schulich Faculty of Chemistry, Solid State Institute and Rusell Berrie Nanotechnology Institute, Technion, Haifa 3200003, Israel; 4Theoretical Physical Chemistry, UR MolSys, University of Liege, B4000 Liege, Belgium; 5Department of Chemical Science, University of Padova, Via Marzolo 1, 35131 Padova, Italy
The Journal of Physical Chemistry C, 2018, published on line.

KEYWORDS: Semiconductor nanocrystals, excitonic energy transfer, organic linkers, transient absorption.


Quantum dots (QDs) solids and arrays hold a great potential for novel applications, aiming at exploiting of quantum properties in room temperature devices. Careful tailoring of the QDs energy levels and coupling between dots could lead to efficient energy harvesting devices. Here we used a self-assembly method to create a disordered layered structure of QDs, coupled by covalently binding organic molecules. Energy transfer rates from small (donor) to large (acceptor) QDs are measured. Best tailoring of the QDs energy levels and the linking molecules length, result in an energy transfer rate as fast as (30ps)-1. Such rates approach energy transfer rates of the highly efficient photosynthesis complexes, and are compatible with a coherent mechanism of energy transfer. These results may pave the way for new controllable building blocks for future technologies.