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Matthew Eisaman is an assistant professor in the Electrical & Computer Engineering Department at Stony Brook University. From 2008 to 2011, Eisaman was an applied physicist at Xerox PARC. He received an AB in physics from Princeton in 2000 and a PhD in physics from Harvard in 2006, and he was an NRC postdoc at NIST from 2006 to 2008. He holds 17 patents and has coauthored 29 papers with over 3,700 citations. Eisaman invented indirect ocean capture in 2010–2011 while at PARC. From 2014 to 2016, Eisaman led Project Foghorn at X (formerly Google X), which used IOC to make carbon-neutral fuel from seawater.

Energy transfer (ET) from nanocrystals (NCs) has shown potential to enhance the optoelectronic performance of ultrathin semiconductor devices such as ultrathin Si solar cells, but the experimental identification of optimal device geometries for maximizing the performance enhancement is highly challenging due to a large parameter space. Here, we have demonstrated a general theoretical framework combining transfer matrix method (TMM) simulations and energy transfer (ET) calculations to reveal critical device design guidelines for developing an efficient, NC-based ET sensitization of ultrathin Si solar cells, which are otherwise infeasible to identify experimentally. The results uncover that the ET-driven NC sensitization is highly effective in enhancing the short circuit current (JSC) in sub-100 nm-thick Si layers, where, for example, the ET contribution can account for over 60% of the maximum achievable JSC in 10 nm-thick ultrathin Si. The study also reveals the limitation of the ET approach, which becomes ineffective for Si active layers thicker than 5 μm, being dominated by conventional optical coupling. The demonstrated simulation approach not only enables the development of efficient ultrathin Si solar cells but also should be applicable to precisely assessing and analyzing diverse experimental device geometries and configurations for developing new efficient ET-based ultrathin semiconductor optoelectronic devices.

We present the design, construction, characterization, and analysis of a prototype process for a novel electrochemical platform of candidate negative emissions technologies (NETs), termed indirect ocean capture. The IOC technologies remove carbon dioxide gas from the atmosphere by leveraging both air-ocean gas exchange and the pH sensitivity of the ocean’s carbonate buffer system. The system characterized in this paper enables two configurations that capture CO2 either as a pure gas or as a solid mineral. Both configurations use the acid and base produced by the membrane electrodialysis of ocean water. The first configuration, termed the ‘acid process’, acidifies ocean water or brine to shift the carbonate buffer system towards dissolved CO2 gas, which is vacuum stripped from the acidified brine. The second configuration, termed the ‘base process’, adds base to the brine to shift the carbonate buffer system towards carbonate ions, which precipitates as CaCO3. A closed loop cycle is achieved by returning this decarbonized and alkalinized brine to the ocean for additional CO2 absorption from the air. Our evaluation of this prototype scale system focused on the parameters that have the most influence on the ultimate cost of the extracted CO2. In a concurrent techno-economic study, the most cost-sensitive parameters were shown to be the efficiencies of the anion and cation exchange membranes, the number and orientation of CO2 extraction membranes, and the volume of base required for CaCO3 precipitation. The measured parameters provide target values for commercial deployment. The experiments in this study were used to inform the concurrent techno-economic study that quantifies in detail the projected cost of avoided CO2 achievable with this process.

Negative emissions technologies (NETs), which result in the removal of CO2 from the atmosphere, will be necessary to limit global warming to 2 °C. Unlike point-source CO2 capture, NETs are agnostic to the emission source, and reduce the existing atmospheric CO2 concentration. This enables NETs to address distributed emissions from transportation and past emissions that have led to existing atmospheric CO2 concentrations. Despite their critical necessity, there are relatively few NETs that have been developed, and existing technologies do not have sufficiently detailed techno-economic analyses to allow comparison for the purpose of strategic investment and policy decisions. An analysis was performed of the economic feasibility of a novel platform of candidate NETs – indirect ocean capture (IOC) – through industry-validated economic and chemical process modeling supported by inputs from a prototype system. This manuscript details the development of a high-fidelity estimate of the cost of avoided CO2 emissions from this NET by coupling scaled experiments to economic analyses. For the lowest-cost scenario of co-location with a desalination plant, a likely cost of $604 per metric ton of avoided CO2 (tCO2) was found, and a best-case cost of $373/tCO2. Through improvements to unit processes, creative process optimization, and reduced carbon-neutral electricity prices, the cost of IOC negative emissions may be reduced in the future. Although NETs won’t likely require deployment for several years in order to limit warming to 2 °C, an objective techno-economic assessment of the options on the table will ensure that the best technology is developed and ready when deployment is required.

Cu(In 1−x ,Ga x )Se 2 (CIGS) absorber layers were deposited on molybdenum (Mo) coated soda-lime glass substrates with varying Ga content (described as Ga/(In + Ga) ratios) with respect to depth. As the responsible mechanisms for the limitation of the performance of the CIGS solar cells with high Ga contents are not well understood, the goal of this work was to investigate different properties of CIGS absorber films with Ga/(In + Ga) ratios varied between 0.29 and 0.41 (as determined by X-ray florescence spectroscopy (XRF)) in order to better understand the role that the Ga content has on film quality. The Ga grading in the CIGS layer has the effect causing a higher band gap toward the surface and Mo contact while the band gap in the middle of the CIGS layer is lower. Also, a wider and larger Ga/(In + Ga) grading dip located deeper in the CIGS absorber layers tend to produce larger grains in the regions of the films that have lower Ga/(In + Ga) ratios. Moreover, it was found that surface roughness decreases from 51.2 nm to 41.0 nm with increasing Ga/(In + Ga) ratios. However, the surface roughness generally decreases if the Ga grading occurs deeper in the absorber layer.

We investigate the effect of confinement on the crystalline microstructure of the polymer component of polymer : fullerene bulk heterojunction thin films using grazing incidence wide angle X-ray scattering. We find that the polymer crystallite size decreases and the alignment of the molecules along the surface normal increases, as the thin-film thickness is reduced from 920 nm to

Scalable and low-cost doping of graphene could improve technologies in a wide range of fields such as microelectronics, optoelectronics, and energy storage. While achieving strong p-doping is relatively straightforward, non-electrostatic approaches to n-dope graphene, such as chemical doping, have yielded electron densities of 9.5 × 1012e/cm2 or below. Furthermore, chemical doping is susceptible to degradation and can adversely affect intrinsic graphene’s properties. Here we demonstrate strong (1.33 × 1013e/cm2), robust, and spontaneous graphene n-doping on a soda-lime-glass substrate via surface-transfer doping from Na without any external chemical, high-temperature, or vacuum processes. Remarkably, the n-doping reaches 2.11 × 1013e/cm2 when graphene is transferred onto a p-type copper indium gallium diselenide (CIGS) semiconductor that itself has been deposited onto soda-lime-glass, via surface-transfer doping from Na atoms that diffuse to the CIGS surface. Using this effect, we demonstrate an n-graphene/p-semiconductor Schottky junction with ideality factor of 1.21 and strong photo-response. The ability to achieve strong and persistent graphene n-doping on low-cost, industry-standard materials paves the way toward an entirely new class of graphene-based devices such as photodetectors, photovoltaics, sensors, batteries, and supercapacitors.

Fossil fuels are renewable only over geological time scales. The oxidation, via combustion, of considerable amounts of carbonaceous fuels since the dawn of the industrial revolution has led to a rapid accumulation of CO 2 in the atmosphere leading to an anthropogenic influence on the Earth's climate. We highlight here that a versatile energy carrier can be produced by recycling CO 2 and combining it chemically with a substance of high chemical bond energy created from renewable energy. If CO 2 is taken from the atmosphere, a closed-loop production process for carbon-neutral fuels is possible providing an energy-dense and easily distributed storage medium for renewable energy. The rationale for reduced carbon or carbon-neutral energy carriers made from recycled CO $ 2 is described, focusing on, for transport applications, their manifestation as energy-dense carbonaceous liquid fuels. Techniques for the separation of CO 2 directly from the atmosphere are reviewed, and the challenges and advantages relative to flue-gas capture are discussed. Pathways for the production of carbonaceous fuels from CO 2 are discussed. An integrated system is proposed where renewable energy is stored in the form of synthetic methane in the gas grid for supply to the power generation and heat sectors while methanol and drop-in hydrocarbon fuels are supplied to the transport sector. The use of atmospheric CO 2 and water as feed stocks for renewable energy carriers raises the important prospect of alleviating a dependency on imported fossil energy with the associated large financial transfers. Their application in the transport sector yields a high-value end product. The synthesis and storage of carbon-neutral liquid fuels offers the possibility of decarbonizing transport without the paradigm shifts required by either electrification of the vehicle fleet or conversion to a hydrogen economy.They can be supplied either as drop-in hydrocarbon fuels for existing reciprocating and turbine-powered combustion engines or, at lower energetic cost and using simpler chemical plant, in the form of low-carbon-number alcohols which can be burned at high efficiency levels in optimized internal combustion engines. The suitability of these fuels for conventional engines enables the continued provision of globally compatible, affordable vehicles. © 2006 IEEE.

Caustic solvents such as sodium or potassium hydroxides, converted viaCO2 capture to aqueous carbonates or bicarbonates, are a likely candidate for atmospheric CO2 separation. We have performed a comprehensive experimental investigation of CO2 gas regeneration from aqueous potassium carbonate and bicarbonate solutions using bipolar membrane electrodialysis (BPMED). This system allows the regeneration of pure CO2 gas, suitable for subsequent sequestration or reaction to synthetic hydrocarbons and their products, from aqueous carbonate/bicarbonate solutions. Our results indicate that the energy consumption required to regenerate CO2 gas from aqueous bicarbonate (carbonate) solutions using this method can be as low as 100 kJ (200 kJ) per mol of CO2 in the small-current-density limit.

Excitonic energy transfer (ET) offers exciting opportunities for advances in optoelectronic devices such as solar cells. While recent experimental attempts have demonstrated its potential in both organic and inorganic photovoltaics (PVs), what remains to be addressed is quantitative understanding of how different ET modes contribute to PV performance and how ET contribution is differentiated from the classical optical coupling (OC) effects. In this study, we implement an ET scheme using a PV device platform, comprising CdSe/ZnS nanocrystal energy donor and 500 nm-thick ultrathin Si acceptor layers, and present the quantitative mechanistic description of how different ET modes, distinguished from the OC effects, increase the light absorption and PV efficiency. We find that nanocrystal sensitization enhances the short circuit current of ultrathin Si solar cells by up to 35%, of which the efficient ET, primarily driven by a long-range radiative mode, contributes to 38% of the total current enhancement. These results not only confirm the positive impact of ET but also provide a guideline for rationally combining the ET and OC effects for improved light harvesting in PV and other optoelectronic devices.

We introduce a novel hyperspectral laser beam induced current (LBIC) system that uses a supercontinuum laser that can be tuned from 400nm – 1200nm with diffracted limited spot size. The solar cell is light biased while simultaneously being illuminated by a chopped laser beam at a given wavelength. Current-voltage measurements performed by measuring the current perturbation due to the laser using a lock-in amplifier allow us to extract performance metrics at a specific lateral position and depth (by tuning the wavelength of the laser) while the device is at operating conditions. These parameters are simultaneously compared to material deformations as determined from the doping density, and the built-in voltage. Concurrently we also probe lateral recombination variation by measuring the activation energy thereby providing a comprehensive and unique analysis.

We introduce a new nondestructive and parameter-independent optoelectronic method to analyze the internal quantum efficiency (IQE) data that are obtained on a copper indium gallium diselenide (CIGS) solar cells. This method directly reconstructs the distribution of the charge collection probability in the device by inverting the integral transform that connects charge collection probability to the measured IQE. This inversion is generally an ill-posed problem, but we obtain a stable solution using the Truncated Singular Value Decomposition (TSVD) regularization method. This procedure is used to analyze simulated and measured IQE data on CIGS solar cells.

Techniques to facilitate controlled interactions between single photons and atoms are now being actively explored. These techniques are important for the practical realization of quantum networks, in which multiple memory nodes that utilize atoms for generation, storage and processing of quantum states are connected by single-photon transmission in optical fibres. One promising avenue for the realization of quantum networks involves the manipulation of quantum pulses of light in optically dense atomic ensembles using electromagnetically induced transparency (EIT, refs 8, 9). EIT is a coherent control technique that is widely used for controlling the propagation of classical, multi-photon light pulses in applications such as efficient nonlinear optics. Here we demonstrate the use of EIT for the controllable generation, transmission and storage of single photons with tunable frequency, timing and bandwidth. We study the interaction of single photons produced in a 'source' ensemble of 87Rb atoms at room temperature with another 'target' ensemble. This allows us to simultaneously probe the spectral and quantum statistical properties of narrow-bandwidth single-photon pulses, revealing that their quantum nature is preserved under EIT propagation and storage. We measure the time delay associated with the reduced group velocity of the single-photon pulses and report observations of their storage and retrieval.

We present an overview of recent theoretical and experimental work on the control of the propagation and quantum properties of light using electromagnetically induced transparency in atomic ensembles. Specifically, we discuss techniques for the generation and storage of few-photon quantum-mechanical states of light as well as novel approaches to manipulate weak pulses of light via enhanced nonlinear optical processes.

We derive a correction to the phase contribution for the reconstruction of refractive index profiles within thin-film photovoltaics using the Index Matched Inverse Wentzel-Kramers-Brillouin (IM-IWKB) Method. We quantify the improvement of the refractive-index reconstruction due to this modification for structures typical of organic photovoltaics. Near the low-index surface of the photoactive layer, this modification reduces the fractional error in the reconstructed profile by a factor of ten, resulting in a highly accurate refractive index reconstruction throughout the entire film thickness. This technique is applicable to the reconstruction of the refractive index profiles within any thin-film photovoltaic material.

We present a methodology for probing light-matter interactions in prototype photovoltaic devices consisting of an organic semiconductor active layer with a semitransparent metal electrical contact exhibiting surface plasmon-based enhanced optical transmission. We achieve high-spectral irradiance in a spot size of less than 100 μm using a high-brightness laser-driven light source and appropriate coupling optics. Spatially resolved Fourier transform photocurrent spectroscopy in the visible and near-infrared spectral regions allows us to measure external quantum efficiency with high sensitivity in small-area devices (

The effects of thin-film confinement on the material properties of ultrathin polymer (electron donor):fullerene (electron acceptor) bulk heterojunction films can be important for both fundamental understanding and device applications such as thin-film photovoltaics. We use variable angle spectroscopic ellipsometry and near edge X-ray absorption fine structure spectroscopy to measure the optical constants, donor-acceptor volume fraction profile, and the degree of interchain order as a function of the thickness of a poly(3-hexythiophene-2,5-diyl) and phenyl-C61-butyric acid methyl ester bulk heterojunction film. We find that as the thickness of the bulk heterojunction film is decreased from 200 nm to the thickness confinement regime (less than 20 nm), the vertical phase segregation gradient of the donor and acceptor phases becomes less pronounced. In addition, observing the change in exciton bandwidth and the shift of absorption resonances (0-0 and 0-1) relative to neat donor and acceptor films, we find that the conjugation length and disorder in ultrathin films (20 nm) are less affected than thicker (200 nm) films by the addition of fullerene into the polymer. We believe that these findings could be important for discovering methods of precisely controlling the properties of bulk heterojunction films with crucial implications for designing more efficient organic-based photovoltaics.

We present a novel and comprehensive technique to measure the internal quantum efficiency of light absorbed as a guided-mode in a thin-film photovoltaic (TPV) over a broad range of wavelengths. Evanescent prism coupling is utilized to selectively excite individual guided-modes at a given wavelength and polarization across a broad spectrum. The Guided-Mode Quantum Efficiency (GIQE) provides a direct quantitative method to design TPVs which can optimize light trapping through guided-modes for higher power conversion efficiency. Furthermore, using theoretical photocarrier generation profile and GIQE of a specific guided-mode, we can probe the spatially dependent charge extraction in the active layer in a direction normal to the substrate. Therefore this technique enables the identification of regions of poor performance due to recombination and trapping within the active layer in a TPV device.

A single-step doping method to fabricate n- and p-type multilayer graphene (MG) top-gate field effect transistors (GFETs) is demonstrated. The transistors are fabricated on soda-lime glass substrates, with the n-type doping of MG caused by the sodium in the substrate without the addition of external chemicals. Placing a hydrogen silsesquioxane (HSQ) barrier layer between the MG and the substrate blocks the n-doping, resulting in p-type doping of the MG above regions patterned with HSQ. The HSQ is deposited in a single fabrication step using electron beam lithography, allowing the patterning of arbitrary sub-micron spatial patterns of n- and p-type doping. When a MG channel is deposited partially on the barrier and partially on the glass substrate, a p-type and n-type doping profile is created, which is used for fabricating complementary transistors pairs. Unlike chemically doped GFETs in which the external dopants are typically introduced from the top, these substrate doped GFETs allow for a top gate whic...

We demonstrate a novel, multi-purpose optoelectronic characterization technique to quantify light trapping and photoinduced charge generation and extraction in photovoltaics and other multilayer thin-film optoelectronic devices. The technique measures the photogenerated current created via the selective evanescent coupling of incident light into each of the guided modes of an optoelectronic device. In analogy to the internal quantum efficiency commonly used to characterize photovoltaics (the ratio of photogenerated electrons extracted from the device to photons absorbed by the device for normally incident light), we define the guided-mode internal quantum efficiency (GIQE) as the ratio of photogenerated electrons extracted from the device to the photons absorbed by the device for a specific guided mode. We complement the measurement of GIQE with computational modeling to calculate the electromagnetic field distribution within the various layers of the device, enabling us to separate the contribution to the GIQE of the absorption in the photoactive layer from parasitic absorption in other layers. By separately quantifying the quantum efficiency of each guided mode, this technique enables improved optimization and design of optoelectronic devices, including photovoltaics that utilize waveguiding and light-trapping. Additionally, since the electromagnetic field of each guided mode has a unique spatial distribution within the photoactive layer, this technique also provides insight into the spatial distributions of charge-carrier extraction, regions of disorder, trap states, and defects within the photoactive layer.

We introduce a novel organic photovoltaic (OPV) design, termed a “slot OPV”, that applies the principles of slot waveguides to confine light within the ultrathin (< 50 nm) active layer of an OPV. Our calculations demonstrate that a “slot OPV” can be designed with guided-mode absorption for a 10 nm thick active layer equal to the absorption of normal incidence on an OPV with a 100 nm thick active layer. These results, together with the expected improvement in charge extraction for ultrathin layers, suggest that “slot OPVs” can be designed with greater power conversion efficiency than today's state-of-the-art OPV architectures.

We review the current status of single-photon-source and single-photon-detector technologies operating at wavelengths from the ultraviolet to the infrared. We discuss applications of these technologies to quantum communication, a field currently driving much of the development of single-photon sources and detectors.

The paper critiques proposals for de-carbonizing transport and offers a potential solution which may be attained by the gradual evolution of the current fleet of predominantly low-cost vehicles via the development of carbon-neutral liquid fuels. The closed-carbon cycles which are possible using such fuels offer the prospect of maintaining current levels of mobility with affordable transport whilst neutralizing the threat posed by the high predicted growth of greenhouse gas emissions from this sector. Approaches to de-carbonizing transport include electrification and the adoption of molecular hydrogen as an energy carrier. These two solutions result in very expensive vehicles for personal transport which mostly lie idle for 95% of their life time and are purchased with high-cost capital. The total cost of ownership of such vehicles is high and the impact of such vehicles in reducing greenhouse gas emissions from transport is therefore likely to be low due to their unaffordability for a large number of customers. Conversely, powertrains and fuel systems capable of using renewable alcohols in high concentrations have minimal additional cost over existing models as they are made from abundant materials with low embedded energy levels. The use of ethanol and methanol in internal combustion engines is reviewed and it is found that the efficiency and performance of engines using these fuels exceeds that of their fossil fuel counterparts. Low-carbon-number alcohols and, where necessary, more energy-dense hydrocarbons can be supplied using feed stocks from the biosphere up to the biomass limit from biofuels and, beyond the biomass limit, from the atmosphere and oceans using captured CO 2 and hydrogen electrolysed from water. Using the hydrogen in a synthesized fuel rather than as an independent energy carrier can be thought of as a pragmatic implementation of the hydrogen economy. This avoids the extremely high infrastructure and distribution costs which accompany the use of molecular hydrogen. The production of liquid fuels from CO2 and water are reviewed in which fully-closed carbon cycles are theoretically possible with the development of large-scale renewable energy generation and CO2 capture from the atmosphere. An approach to the latter problem where CO 2 concentration and release based on bipolar membrane electrodialysis, developed by the co-authors from PARC, is described in detail and initial results from a laboratory scale device are reported. The development of a Tri-Flex-Fuel vehicle, capable of operating on any combination of gasoline, ethanol, and methanol, using a single fuel system is also described. The low additional technology and materials costs of such vehicles demonstrates that compatible, affordable transport can be developed which provides a feasible means of vehicle evolution towards decarbonized transport without the consequences of huge stranded assets which would be imposed on the automotive industry by the revolution which would be required to mass-produce hydrogen fuel cell vehicles and battery-electric vehicles.

We present an experimental characterization of a heralded single-photon source based on spontaneous four-wave mixing in a single-mode microstructure fiber. We measure the second-order correlation function ${g}^{(2)}(0)$ to be far below the classical, Poissonian limit of 1 over a broad spectral range. With single-spatial-mode output, such a spectrally bright and broad fiber-based heralded single-photon source is suitable for a variety of quantum-information applications.

We demonstrate generation of hyperentangled (time-bin and polarization) photon pairs via four-wave mixing in a microstructure-fiber Sagnac interferometer. The two-photon interference visibility in the time-bin (polarization) degree of freedom is $88%\ifmmode\pm\else\textpm\fi{}2%$ $(84%\ifmmode\pm\else\textpm\fi{}1%)$ without subtraction of accidental coincidences, and Bell's inequality is violated by 27 standard deviations at a $1\phantom{\rule{0.3em}{0ex}}\mathrm{kHz}$ coincidence rate.

We describe an experimental test of local realistic and nonlocal realistic theories using polarization-entangled two-photon singlet states created using a fiber-based polarization Sagnac interferometer. We show a violation of Bell's inequality in the Clauser-Horne-Shimony-Holt form by 15 standard deviations, thus excluding local hidden-variable theories, and a violation of a Leggett-type nonlocal hidden-variable inequality by more than three standard deviations, thus excluding a class of nonlocal hidden-variable theories.

We test local realistic and non-local realistic theories using a fiber-based source of polarization-entangled photons. Our measurements violate local (certain non-local) hidden-variable theories by 15 (Leggett, A.) standard deviations.

We report the development of a spectrally bright and broad heralded single-photon source based on spontaneous four-wave-mixing in a single-mode fiber, measuring the second-order correlation function, g(2)(0), far below unity over a broad spectral range.

We describe an achromatic, phase-stable, broadband source of polarization-entangled photon pairs with high spectral brightness that uses four-wave mixing in a fiber Sagnac interferometer. We achieved a polarization-entangled two-photon coincidence rate of $7\phantom{\rule{0.3em}{0ex}}\mathrm{kHz}$ per $0.5\phantom{\rule{0.3em}{0ex}}\mathrm{THz}$ $(0.9\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$ of bandwidth per $300\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}\mathrm{W}$ of average pump power. At this rate, we observed two-photon fringe interference visibilities greater than 97%, over a $10\phantom{\rule{0.3em}{0ex}}\mathrm{THz}$ $(\ensuremath{\approx}21\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$ spectral range. We measured violations of Bell's inequality by more than 22 standard deviations for each of the four Bell states in less than $3\phantom{\rule{0.3em}{0ex}}\text{minutes}$ per state. The high spectral brightness $(26\phantom{\rule{0.3em}{0ex}}\mathrm{kHz}\phantom{\rule{0.2em}{0ex}}{\mathrm{nm}}^{\ensuremath{-}1}\phantom{\rule{0.2em}{0ex}}{\mathrm{mW}}^{\ensuremath{-}1})$, large tunable wavelength range, single spatial mode, and phase stability make this source a promising candidate for a wide range of quantum-information applications.

We theoretically investigate the feasibility of using spectral hole burning in Pr 3+ :Y 2 SiO 5 to prepare an ensemble of Pr 3+ ions with a spectral distribution optimized for use as a quantum memory for single-photon states. We introduce figures of merit for the spectral distribution of the Pr 3+ ions when used as a quantum-memory node in a Duan-Lukin-Cirac-Zoller-type quantum-repeater scheme. Finally, we describe progress toward optimizing the hole-burning sequence by using a computational model of the hole-burning process to calculate these figures of merit over a wide range of parameters.

We describe the preparation of a high spectral brightness, broad wavelength coverage, single-spatial mode source of polarization-entangled photon pairs operated at room temperature. The source takes advantage of single-mode fiber optics, highly nonlinear microstructure fiber, judicious phase-matching, and the inherent stability provided by a Sagnac interferometer. With a modest average pump power (300 μW), we create all four Bell states with a detected two-photon coincidence rate of 7 kHz per bandwidth of 0.9 nm, in a spectral range of more than 20 nm.

In the emerging field of quantum information technology the two basic subfields are quantum communication and quantum computation. Photonic qubits are considered as most promising information carriers for this new technology due to the immense advantage of suffering negligible decoherence. Additionally, the very small photon-photon interactions can be replaced by inducing effective nonlinearities via measurements which allow for the implementation of crucial two-qubit gate operations. Although the spontaneous parametric down-conversion gives access to the generation of highly entangled few-photon states, such as four-qubit cluster states which allow to demonstrate the new concept of the one-way quantum computer, its applicability is highly limited due to the poor scaling of the simultaneous emission of more than one-entangled photon pair. Therefore of particular interest is the reversible mapping of qubits from photon states to atomic states. This might allow the implementation of photonic quantum repeaters for long-distance quantum communication or the generation of arbitrary multi-photon states as required for linear-optics quantum computing. Thus for the realization of such a quantum network several approaches for achieving the required quantum control between matter and photons have been studied during the past few years. Recent experiments demonstrating the generation of narrow-bandwidth single photons using a room-temperature ensemble of 87 Rb atoms and electromagnetically induced transparency should emphasize the progress towards such a quantum network.

We analyze the quantum properties of single-photon sources based on atomic ensembles under realistic experimental conditions. This explains the experimentally observed enhanced photon correlations in the wings of a spectrally resolved g2measurement.

We have demonstrated a bright single-mode-fiber source of polarization-entangled photon pairs with visibility > 97% and fidelity > 95% at a detected coincidence rate of 7 kHz/nm over a 3 dB, 10THz bandwidth.

We generate hyperentangled (time-bin and polarization) photon-pairs using a microstructure-fiber Sagnac interferometer. Two-photon-interference visibilities in both degrees of freedom are >83%, and the Bell’s inequality is violated by 25 σ at a 1-kHz coincidence rate.

We present a charge-extraction technique, micron-scale charge extraction by linearly increasing voltage, which enables simultaneous spatially resolved measurements of charge carrier mobility and photocurrent in thin-film photovoltaic devices with micron-scale resolution. An intensity-modulated laser with beam diameter near the optical diffraction limit is scanned over the device, while a linear voltage ramp in reverse bias is applied at each position of illumination. We calculate the majority carrier mobility, photocurrent, and number of photogenerated charge carriers from the resulting current transient. We demonstrate this technique on an organic photovoltaic device, but it is applicable to a wide range of photovoltaic materials.

We describe a technique for generating pulses of light with controllable, well-defined photon numbers, propagation direction, timing, and pulse shapes. The technique is based on preparation of an atomic ensemble in a state with a desired number of atomic spin excitations, which is later converted into a photon pulse. Spatio-temporal control over the pulses is obtained by exploiting long-lived coherent memory for photon states and electromagnetically induced transparency in an optically dense atomic medium. Using photon counting experiments we observe collective behavior of atomic spins in a room-temperature ensemble, enabling controlled generation and shaping of few-photon sub-Poissonian light pulses. We discuss the prospects for controlled generation of n-photon Fock states.

We describe proof-of principle experiments demonstrating a novel approach for generating pulses of light with controllable photon numbers, propagation direction, timing, and pulse shapes. The approach is based on preparation of an atomic ensemble in a state with a desired number of atomic spin excitations, which is later converted into a photon pulse by exploiting long-lived coherent memory for photon states and electromagnetically induced transparency (EIT). We discuss our progress toward applying these techniques to transmit quantum states between atomic memory nodes connected by a photonic channel.

We describe our recent work using atomic ensembles to store quantum states of light and control light propagation and its quantum properties.

A convenient optical scheme for compressing the bandwidth and tuning the frequency of single photons could allow photon qubits to be used in matter-based quantum memories. This development is also an important step towards arbitrary waveform generation of quantum states of light.