Celestino Creatore

Efficient biologically inspired photocell enhanced by delocalized quantum states.

Artificially implementing the biological light reactions responsible for the remarkably efficient photon-to-charge conversion in photosynthetic complexes represents a new direction for the future development of photovoltaic devices. Here, we develop such a paradigm and present a model photocell based on the nanoscale architecture and molecular elements of photosynthetic reaction centers. Quantum interference of photon absorption and emission induced by the dipole-dipole interaction between molecular excited states guarantees an enhanced light-to-current conversion and power generation for a wide range of electronic, thermal, and optical parameters for optimized dipolar geometries. This result opens a promising new route for designing artificial light-harvesting devices inspired by biological photosynthesis and quantum technologies.

Programming light-harvesting efficiency using DNA origami

The remarkable performance and quantum efficiency of biological light-harvesting complexes has prompted a multidisciplinary interest in engineering biologically inspired antenna systems as a possible route to novel solar cell technologies. Key to the effectiveness of biological “nanomachines” in light capture and energy transport is their highly ordered nanoscale architecture of photoactive molecules. Recently, DNA origami has emerged as a powerful tool for organizing multiple chromophores with base-pair accuracy and full geometric freedom. Here, we present a programmable antenna array on a DNA origami platform that enables the implementation of rationally designed antenna structures. We systematically analyze the light-harvesting efficiency with respect to number of donors and interdye distances of a ring-like antenna using ensemble and single-molecule fluorescence spectroscopy and detailed Förster modeling. This comprehensive study demonstrates exquisite and reliable structural control over multichromophoric geometries and points to DNA origami as highly versatile platform for testing design concepts in artificial light-harvesting networks.

Creation of entangled states in coupled quantum dots via adiabatic rapid passage

Quantum state preparation through external control is fundamental to established methods in quantum information processing and in studies of dynamics. In this respect, excitons in semiconductor quantum dots are of particular interest, since their coupling to light allows them to be driven into a specified state using the coherent interaction with a tuned optical field, such as an external laser pulse. We propose a protocol, based on adiabatic rapid passage, for the creation of entangled states in an ensemble of pairwise coupled two-level systems, such as an ensemble of coupled quantum dots. We show by quantitative analysis using realistic parameters for semiconductor quantum dots that this method is feasible where other approaches are unavailable. Furthermore, this scheme can be generically transferred to some other physical systems, including circuit QED, nuclear and electron spins in solid-state environments, and photonic coupled cavities.

Adiabatic state preparation of interacting two-level systems

We consider performing adiabatic rapid passage (ARP) using frequency-swept driving pulses to excite a collection of interacting two-level systems. Such a model arises in a wide range of many-body quantum systems, such as cavity QED or quantum dots, where a nonlinear component couples to light. We analyze the one-dimensional case using the Jordan-Wigner transformation, as well as the mean-field limit where the system is described by a Lipkin-Meshkov-Glick Hamiltonian. These limits provide complementary insights into the behavior of many-body systems under ARP, suggesting our results are generally applicable. We demonstrate that ARP can be used for state preparation in the presence of interactions, and identify the dependence of the required pulse shapes on the interaction strength. In general, interactions increase the pulse bandwidth required for successful state transfer, introducing new restrictions on the pulse forms required.

Quench dynamics of a disordered array of dissipative coupled cavities

We investigate the mean-field dynamics of a system of interacting photons in an array of coupled cavities in the presence of dissipation and disorder. We follow the evolution of an initially prepared Fock state, and show how the interplay between dissipation and disorder affects the coherence properties of the cavity emission, and show that these properties can be used as signatures of the many-body phase of the whole array.

Emergent Models for Artificial Light-Harvesting

INTRODUCTION AND BACKGROUND Photovoltaic (PV) solar energy conversion is one of the most promising emerging renewable energy technologies and is likely to play an ever-increasing role in the future of electricity generation. The potential of photovoltaics is considered to be much larger than the current energy demand, which is equivalent to ≈13,000 millions tons of oil (BP, 2014). Together with other renewable energy sources, photovoltaics could thus considerably aid the decarbonization of the energy sector in the near future, an objective, which is (should be) seriously sought after to meet the IPCC 2°C target1. Indeed, PV energy conversion is an ever-increasing research field having an impact on other sectors: technological (e.g., dealing with energy storage and distribution issues) and economical (e.g., evaluating the costs of PV devices compared to conventional energy technologies). The typical working principle of a photovoltaic cell is quite simple, and well understood in terms of doped inorganic semiconductors (Wurfel, 2009). Photovoltaic technology has significantly moved forward since the first silicon (Si) solar cell having an efficiency of ≈4% was invented in 1950s in Bell Laboratories, following the breakthrough of the p–n junction developed by Shockley, Brattain, and Bardeen (Chapin et al., 1954). Since then, research on PV has led to singlejunction and multi-junction solar cells with record efficiencies in controlled (laboratory) environments of ≈29% (Green et al., 2014) and 46% (Fraunhofer-ISE, 2014), respectively. However, the efficiency of the most popular technologies in the commercial market – which belong to the so called first generation of solar cells, mainly based on crystalline Si – is in the 10–18% range and around 25% in laboratory. A second generation of cells, mainly aimed at reducing the fabrication costs, is based on thin film architectures, where light is absorbed and charge generated in a solid thin layer of semiconductor (e.g., CdTe, CIGS), with efficiencies restrained to around 22%. Beyond these technologies, a variety of other PV designs has emerged, mainly driven by the progress on materials research and the need of low-cost manufacture devices, organic photovoltaic (OPV) being one of the most interesting solutions. The latest scientific developments in this field have taken various directions (using different concepts, materials, and geometries), all having the potential to result in high-efficiency PV devices. Most current approaches, which have been termed third generation PV [see e.g., Green (2003)], explore schemes beyond the guidelines given by Shockley and Queisser (1961), which are based on the assumption that each photon absorbed above the band gap of the semiconductor photovoltaic material generates a single electron-hole pair. These methods include solar cells exploiting multiple-exciton generation in both inorganic and organic materials, hot carriers collection, upand down-conversions. Reviewing the extensive literature about the past and present PV schemes is beyond the scope of this Opinion, many excellent reviews having already succeeded in this (challenging) task. Here, we will illustrate and highlight our point of view on an emergent strategy for PV and artificial light-harvesting in general. This strategy holds onto an interdisciplinary framework encompassing biology and quantum mechanics. Ideas, which have been developed within this nascent trend, are inspired by the recent discovery of quantum effects in biological systems (Mohseni et al., 2014), and aim to model and reproduce the highly efficient reactions often exhibited by these systems using the tools of quantum mechanics and nanotechnology platforms. Novel theoretical proposals, for instance (Scully, 2010; Blankenship et al., 2011; Scully et al., 2011; Creatore et al., 2013; Zhang et al., 2015), have underlined the relevance of effects of quantum coherence to enhance the performance of photocells whose working principle is inspired by the architecture of biological light-harvesting complexes (LHCs).

Corrigendum: Observation and coherent control of interface-induced electronic resonances in a field-effect transistor

Nature Materials 16, 208–213 (2017); published online 19 September 2016; corrected after print 30 June 2017 In this work we reported the development of a rigorous mathematical and physical framework in order to model the detailed time-resolved behaviour of over 800 resonances that we studied, through continuous-wave and single-pulse microwave spectroscopy measurements in a field-effect transistor.

Coherent control of trapped-charge induced resonances in a field-effect transistor

Trapped charges at oxide interfaces in field effect transistors are well known sources of noise and generally degrade the device performance. At low temperatures, operating in the sub-threshold regime, conduction electrons can be confined to percolation pathways [1]. The scattering potential produced by trapped charge can then have a dramatic effect on the conductance, normally observed as random telegraph noise [2]. Here we show that it is possible to coherently excite the trapped electrons with microwave fields, which induce polarization fields that interact with the percolating electrons, measured as high-quality resonances (Q ~ 104 - 105) in the transistor current. Implementing single-shot measurements gives the possibility to study the dynamics of the trapped electrons, and using a standard Ramsey protocol, coherent control is achieved. Given the long coherence times observed (T2 ~ 10 μs) and since each resonance can be addressed independently in frequency space, the possibility to use such systems as quantum memories or quantum bits is discussed.