ORCID Profile
0000-0002-8376-0819
Current Organisation
University of Sydney
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Transport Properties and Non-Equilibrium Processes | Quantum information computation and communication | Macromolecular and Materials Chemistry | Radiation and Matter | Theoretical quantum chemistry | Physical Chemistry (Incl. Structural) | Theory and Design of Materials | Quantum physics | Condensed Matter Modelling and Density Functional Theory | Quantum Physics not elsewhere classified |
Solar-Photovoltaic Energy | Expanding Knowledge in the Chemical Sciences | Expanding Knowledge in the Physical Sciences |
Publisher: American Chemical Society (ACS)
Date: 28-06-2021
Publisher: American Chemical Society (ACS)
Date: 02-03-2020
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6CP00104A
Abstract: The contributions of energy funnelling and excitonic delocalization to the performance of photosynthetic complexes can be disentangled by comparing the performance of the natural complexes with models in which both the energy landscape and the delocalization are altered.
Publisher: Springer Science and Business Media LLC
Date: 28-08-2023
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D0SC04116E
Abstract: The first three-dimensional model of transport in moderately disordered materials shows that a little delocalisation can dramatically enhance mobilities.
Publisher: Springer Science and Business Media LLC
Date: 21-06-2016
DOI: 10.1038/NCOMMS11944
Abstract: Blends of electron-donating and -accepting organic semiconductors are widely used as photoactive materials in next-generation solar cells and photodetectors. The yield of free charges in these systems is often determined by the separation of interfacial electron–hole pairs, which is expected to depend on the ability of the faster carrier to escape the Coulomb potential. Here we show, by measuring geminate and non-geminate losses and key transport parameters in a series of bulk-heterojunction solar cells, that the charge-generation yield increases with increasing slower carrier mobility. This is in direct contrast with the well-established Braun model where the dissociation rate is proportional to the mobility sum, and recent models that underscore the importance of fullerene aggregation for coherent electron propagation. The behaviour is attributed to the restriction of opposite charges to different phases, and to an entropic contribution that favours the joint separation of both charge carriers.
Publisher: American Chemical Society (ACS)
Date: 03-2018
DOI: 10.1021/ACS.JPCLETT.8B00292
Abstract: Because of the low dielectric constant, charges in organic solar cells must overcome a strong Coulomb attraction in order to separate. It has been widely argued that intermolecular delocalization would assist charge separation by increasing the effective initial electron-hole separation in a charge-transfer state, thus decreasing their barrier to separation. Here we show that this is not the case: including more than a small amount of delocalization in models of organic solar cells leads to an increase in the free-energy barrier to charge separation. Therefore, if delocalization were to improve the charge separation efficiency, it would have to do so through nonequilibrium kinetic effects that are not captured by a thermodynamic treatment of the barrier height.
Publisher: Springer Science and Business Media LLC
Date: 06-06-2012
DOI: 10.1038/NCOMMS1872
Abstract: Topological phases exhibit some of the most striking phenomena in modern physics. Much of the rich behaviour of quantum Hall systems, topological insulators, and topological superconductors can be traced to the existence of robust bound states at interfaces between different topological phases. This robustness has applications in metrology and holds promise for future uses in quantum computing. Engineered quantum systems--notably in photonics, where wavefunctions can be observed directly--provide versatile platforms for creating and probing a variety of topological phases. Here we use photonic quantum walks to observe bound states between systems with different bulk topological properties and demonstrate their robustness to perturbations--a signature of topological protection. Although such bound states are usually discussed for static (time-independent) systems, here we demonstrate their existence in an explicitly time-dependent situation. Moreover, we discover a new phenomenon: a topologically protected pair of bound states unique to periodically driven systems.
Publisher: Springer Science and Business Media LLC
Date: 10-01-2010
DOI: 10.1038/NCHEM.483
Abstract: Exact first-principles calculations of molecular properties are currently intractable because their computational cost grows exponentially with both the number of atoms and basis set size. A solution is to move to a radically different model of computing by building a quantum computer, which is a device that uses quantum systems themselves to store and process data. Here we report the application of the latest photonic quantum computer technology to calculate properties of the smallest molecular system: the hydrogen molecule in a minimal basis. We calculate the complete energy spectrum to 20 bits of precision and discuss how the technique can be expanded to solve large-scale chemical problems that lie beyond the reach of modern supercomputers. These results represent an early practical step toward a powerful tool with a broad range of quantum-chemical applications.
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8SC00053K
Abstract: Transfer of charges delocalised over multiple molecules can be described using the properties of the component molecules.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 12-08-2022
Abstract: In organic photovoltaics, charges can separate efficiently even if their Coulomb attraction is an order of magnitude greater than the available thermal energy. Delocalization has been suggested to explain this fact, because it could increase the initial separation of charges in the charge-transfer (CT) state, reducing their attraction. However, understanding the mechanism requires a kinetic model of delocalized charge separation, which has proven difficult because it involves tracking the correlated quantum-mechanical motion of the electron and the hole in large simulation boxes required for disordered materials. Here, we report the first three-dimensional simulations of charge-separation dynamics in the presence of disorder, delocalization, and polaron formation, finding that even slight delocalization, across less than two molecules, can substantially enhance the charge-separation efficiency, even starting with thermalized CT states. Delocalization does not enhance efficiency by reducing the Coulomb attraction instead, the enhancement is a kinetic effect produced by the increased overlap of electronic states.
Publisher: IOP Publishing
Date: 03-03-2009
Publisher: American Physical Society (APS)
Date: 21-10-2019
Publisher: American Chemical Society (ACS)
Date: 04-08-2014
DOI: 10.1021/JA505330X
Abstract: The conventional picture of photocurrent generation in organic solar cells involves photoexcitation of the electron donor, followed by electron transfer to the acceptor via an interfacial charge-transfer state (Channel I). It has been shown that the mirror-image process of acceptor photoexcitation leading to hole transfer to the donor is also an efficient means to generate photocurrent (Channel II). The donor and acceptor components may have overlapping or distinct absorption characteristics. Hence, different excitation wavelengths may preferentially activate one channel or the other, or indeed both. As such, the internal quantum efficiency (IQE) of the solar cell may likewise depend on the excitation wavelength. We show that several model high-efficiency organic solar cell blends, notably PCDTBT:PC70BM and PCPDTBT:PC60/70BM, exhibit flat IQEs across the visible spectrum, suggesting that charge generation is occurring either via a dominant single channel or via both channels but with comparable efficiencies. In contrast, blends of the narrow optical gap copolymer DPP-DTT with PC70BM show two distinct spectrally flat regions in their IQEs, consistent with the two channels operating at different efficiencies. The observed energy dependence of the IQE can be successfully modeled as two parallel photodiodes, each with its own energetics and exciton dynamics but both having the same extraction efficiency. Hence, an excitation-energy dependence of the IQE in this case can be explained as the interplay between two photocurrent-generating channels, without recourse to hot excitons or other exotic processes.
Publisher: American Chemical Society (ACS)
Date: 31-12-2016
Abstract: Excitonic couplings between (bacterio)chlorophyll molecules are necessary for simulating energy transport in photosynthetic complexes. Many techniques for calculating the couplings are in use, from the simple (but inaccurate) point-dipole approximation to fully quantum-chemical methods. We compared several approximations to determine their range of applicability, noting that the propagation of experimental uncertainties poses a fundamental limit on the achievable accuracy. In particular, the uncertainty in crystallographic coordinates yields an uncertainty of about 20% in the calculated couplings. Because quantum-chemical corrections are smaller than 20% in most biologically relevant cases, their considerable computational cost is rarely justified. We therefore recommend the electrostatic TrEsp method across the entire range of molecular separations and orientations because its cost is minimal and it generally agrees with quantum-chemical calculations to better than the geometric uncertainty. Understanding these uncertainties can guard against striving for unrealistic precision at the same time, detailed benchmarks can allow important qualitative questions-which do not depend on the precise values of the simulation parameters-to be addressed with greater confidence about the conclusions.
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D1SC02142G
Abstract: Dynamics governing ultrafast chemical reactions can be efficiently simulated using analog quantum simulators composed of a coupled system of qudits and bosonic modes.
Publisher: AIP Publishing
Date: 18-05-2009
DOI: 10.1063/1.3115177
Abstract: While quantum computers are capable of simulating many quantum systems efficiently, the simulation algorithms must begin with the preparation of an appropriate initial state. We present a method for generating physically relevant quantum states on a lattice in real space. In particular, the present algorithm is able to prepare general pure and mixed many-particle states of any number of particles. It relies on a procedure for converting from a second-quantized state to its first-quantized counterpart. The algorithm is efficient in that it operates in time that is polynomial in all the essential descriptors of the system, the number of particles, the resolution of the lattice, and the inverse of the maximum final error. This scaling holds under the assumption that the wave function to be prepared is bounded or its indefinite integral is known and that the Fock operator of the system is efficiently simulatable.
Publisher: Proceedings of the National Academy of Sciences
Date: 02-12-2008
Abstract: The computational cost of exact methods for quantum simulation using classical computers grows exponentially with system size. As a consequence, these techniques can be applied only to small systems. By contrast, we demonstrate that quantum computers could exactly simulate chemical reactions in polynomial time. Our algorithm uses the split-operator approach and explicitly simulates all electron-nuclear and interelectronic interactions in quadratic time. Surprisingly, this treatment is not only more accurate than the Born–Oppenheimer approximation but faster and more efficient as well, for all reactions with more than about four atoms. This is the case even though the entire electronic wave function is propagated on a grid with appropriately short time steps. Although the preparation and measurement of arbitrary states on a quantum computer is inefficient, here we demonstrate how to prepare states of chemical interest efficiently. We also show how to efficiently obtain chemically relevant observables, such as state-to-state transition probabilities and thermal reaction rates. Quantum computers using these techniques could outperform current classical computers with 100 qubits.
Publisher: Wiley
Date: 27-05-2008
DOI: 10.1002/JRS.1985
Publisher: American Chemical Society (ACS)
Date: 05-10-2018
DOI: 10.1021/ACS.JPCLETT.8B02484
Abstract: The dynamics of exciton quenching are critical to the operational performance of organic optoelectronic devices, but their measurement and elucidation remain ongoing challenges. Here, we present a method for quantifying small photoluminescence quenching efficiencies of organic semiconductors under steady-state conditions. Exciton quenching efficiencies of three different organic semiconductors, PC70BM, P3HT, and PCDTBT, are measured at different bulk quencher densities under continuous low-irradiance illumination. By implementing a steady-state bulk-quenching model, we determine exciton diffusion lengths for the studied materials. At low quencher densities we find that a secondary quenching mechanism is in effect, which is responsible for approximately 20% of the total quenched excitons. This quenching mechanism is observed in all three studied materials and exhibits quenching volumes on the order of several thousand cubic nanometers. The exact origin of this quenching process is not clear, but it may be indicative of delocalized excitons being quenched prior to thermalization.
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9SC03712H
Abstract: The dimerisation of photosynthetic reaction centres enhanced their efficiency by improving exciton transfer from an antenna.
Publisher: IOP Publishing
Date: 29-05-2012
Publisher: American Physical Society (APS)
Date: 16-04-2010
Publisher: American Chemical Society (ACS)
Date: 16-08-2017
DOI: 10.1021/ACS.JPCLETT.7B01571
Abstract: In this Letter, we study the role of the donor:acceptor interface nanostructure upon charge separation and recombination in organic photovoltaic devices and blend films, using mixtures of PBTTT and two different fullerene derivatives (PC
Publisher: Wiley
Date: 07-11-2017
Publisher: Annual Reviews
Date: 05-05-2011
DOI: 10.1146/ANNUREV-PHYSCHEM-032210-103512
Abstract: The difficulty of simulating quantum systems, well known to quantum chemists, prompted the idea of quantum computation. One can avoid the steep scaling associated with the exact simulation of increasingly large quantum systems on conventional computers, by mapping the quantum system to another, more controllable one. In this review, we discuss to what extent the ideas in quantum computation, now a well-established field, have been applied to chemical problems. We describe algorithms that achieve significant advantages for the electronic-structure problem, the simulation of chemical dynamics, protein folding, and other tasks. Although theory is still ahead of experiment, we outline recent advances that have led to the first chemical calculations on small quantum information processors.
Publisher: IOP Publishing
Date: 09-2014
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D3SC02453A
Abstract: Analog quantum computers can calculate molecular vibronic spectra using time-domain simulation, with exponentially greater scalability than previous, frequency-domain approaches. An accurate, trapped-ion simulation of SO 2 validates the approach.
Publisher: American Chemical Society (ACS)
Date: 12-04-2023
Publisher: AIP Publishing
Date: 08-12-2009
DOI: 10.1063/1.3266959
Abstract: Quantum computers, if available, could substantially accelerate quantum simulations. We extend this result to show that the computation of molecular properties (energy derivatives) could also be sped up using quantum computers. We provide a quantum algorithm for the numerical evaluation of molecular properties, whose time cost is a constant multiple of the time needed to compute the molecular energy, regardless of the size of the system. Molecular properties computed with the proposed approach could also be used for the optimization of molecular geometries or other properties. For that purpose, we discuss the benefits of quantum techniques for Newton’s method and Householder methods. Finally, global minima for the proposed optimizations can be found using the quantum basin hopper algorithm, which offers an additional quadratic reduction in cost over classical multi-start techniques.
Publisher: American Chemical Society (ACS)
Date: 11-01-2013
DOI: 10.1021/JZ301872B
Abstract: Recent observations of coherence in photosynthetic complexes have led to the question of whether quantum effects can occur in vivo, not under femtosecond laser pulses but in incoherent sunlight and at steady state, and, if so, whether the coherence explains the high exciton transfer efficiency. We introduce the distinction between state coherence and process coherence and show that although some photosynthetic pathways are partially coherent processes, photosynthesis in nature proceeds through stationary states. This distinction allows us to rule out several mechanisms of transport enhancement in sunlight. In particular, although they are crucial for understanding exciton transport, neither wavelike motion nor microscopic coherence, on their own, enhance the efficiency. By contrast, two partially coherent mechanisms-ENAQT and supertransfer-can enhance transport even in sunlight and thus constitute motifs for the optimization of artificial sunlight harvesting. Finally, we clarify the importance of ultrafast spectroscopy in understanding incoherent processes.
Publisher: American Chemical Society (ACS)
Date: 29-08-2014
DOI: 10.1021/JP505179H
Abstract: It has been argued that excitonic energy transport in photosynthetic complexes is efficient because of a balance between coherent evolution and decoherence, a phenomenon called environment-assisted quantum transport (ENAQT). Studies of ENAQT have usually assumed that the excitation is initially localized on a particular chromophore, and that it is transferred to a reaction center through a similarly localized trap. However, these assumptions are not physically accurate. We show that more realistic models of excitation and trapping can lead to very different predictions about the importance of ENAQT. In particular, although ENAQT is a robust effect if one assumes a localized trap, its effect can be negligible if the trapping is more accurately modeled as Förster transfer to a reaction center. Our results call into question the suggested role of ENAQT in the photosynthetic process of green sulfur bacteria and highlight the subtleties associated with drawing lessons for designing biomimetic light-harvesting complexes.
Publisher: arXiv
Date: 2022
Publisher: Springer Science and Business Media LLC
Date: 15-04-2016
DOI: 10.1038/NCOMMS11282
Abstract: Transport phenomena on a quantum scale appear in a variety of systems, ranging from photosynthetic complexes to engineered quantum devices. It has been predicted that the efficiency of coherent transport can be enhanced through dynamic interaction between the system and a noisy environment. We report an experimental simulation of environment-assisted coherent transport, using an engineered network of laser-written waveguides, with relative energies and inter-waveguide couplings tailored to yield the desired Hamiltonian. Controllable-strength decoherence is simulated by broadening the bandwidth of the input illumination, yielding a significant increase in transport efficiency relative to the narrowband case. We show integrated optics to be suitable for simulating specific target Hamiltonians as well as open quantum systems with controllable loss and decoherence.
Publisher: American Chemical Society (ACS)
Date: 21-06-2019
DOI: 10.1021/ACS.JPCLETT.9B01304
Abstract: Quantifying energetic disorder in organic semiconductors continues to attract attention because of its significant impact on the transport physics of these technologically important materials. Here, we show that the energetic disorder of organic semiconductors can be determined from the relationship between the internal quantum efficiency of charge generation and the frequency of the incident light. Our results for a number of materials suggest that energetic disorder in organic semiconductors could be greater than previously reported, and we advance ideas as to why this may be the case.
Publisher: Springer Science and Business Media LLC
Date: 19-08-2014
DOI: 10.1038/SREP06115
Abstract: Large-scale quantum computers will require the ability to apply long sequences of entangling gates to many qubits. In a photonic architecture, where single-qubit gates can be performed easily and precisely, the application of consecutive two-qubit entangling gates has been a significant obstacle. Here, we demonstrate a two-qubit photonic quantum processor that implements two consecutive CNOT gates on the same pair of polarisation-encoded qubits. To demonstrate the flexibility of our system, we implement various instances of the quantum algorithm for solving of systems of linear equations.
Publisher: American Chemical Society (ACS)
Date: 20-02-2023
Start Date: 2022
End Date: 12-2024
Amount: $381,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2024
End Date: 12-2027
Amount: $1,114,292.00
Funder: Australian Research Council
View Funded ActivityStart Date: 05-2014
End Date: 01-2017
Amount: $395,220.00
Funder: Australian Research Council
View Funded Activity