Photon correlation spectroscopy as a witness for quantum coherence

The development of spectroscopic techniques able to detect and verify quantum coherence is a goal of increasing importance given the rapid progress of new quantum technologies, the advances in the field of quantum thermodynamics, and the emergence of new questions in chemistry and biology regarding the possible relevance of quantum coherence in biochemical processes. Ideally, these tools should be able to detect and verify the presence of quantum coherence in both the transient dynamics and the steady state of driven-dissipative systems, such as light-harvesting complexes driven by thermal photons in natural conditions. This requirement poses a challenge for standard laser spectroscopy methods. Here, we propose photon correlation measurements as a new tool to analyse quantum dynamics in molecular aggregates in driven-dissipative situations. We show that the photon correlation statistics on the light emitted by a molecular dimer model can signal the presence of coherent dynamics. Deviations from the counting statistics of independent emitters constitute a direct fingerprint of quantum coherence in the steady state. Furthermore, the analysis of frequency resolved photon correlations can signal the presence of coherent dynamics even in the absence of steady state coherence, providing direct spectroscopic access to the much sought-after site energies in molecular aggregates

Bunching and anti-bunching of localised particles in disordered media

We consider pairs of non-interacting quantum particles transmitted through a disordered medium, with emphasis on the role of their quantum statistics. It is shown that particle-number correlations measured in transmission are strikingly sensitive to the quantum nature of the particles when they undergo Anderson localisation, due to bosonic bunching and fermionic anti-bunching in the scattering channels of the medium. The case of distinguishable particles is also discussed.Comment: 5 pages, 3 figure

Cavity-mediated electron-photon superconductivity

We investigate electron paring in a two-dimensional electron system mediated by vacuum fluctuations inside a nanoplasmonic terahertz cavity. We show that the structured cavity vacuum can induce long-range attractive interactions between current fluctuations which lead to pairing in generic materials with critical temperatures in the low-Kelvin regime for realistic parameters. The induced state is a pair density wave superconductor which can show a transition from a fully gapped to a partially gapped phase - akin to the pseudogap phase in high-$T_c$ superconductors. Our findings provide a promising tool for engineering intrinsic electron interactions in two-dimensional materials.Comment: 11 page

Nonlinear optical signals and spectroscopy with quantum light

Conventional nonlinear spectroscopy uses classical light to detect matter properties through the variation of its response with frequencies or time delays. Quantum light opens up new avenues for spectroscopy by utilizing parameters of the quantum state of light as novel control knobs and through the variation of photon statistics by coupling to matter. We present an intuitive diagrammatic approach for calculating ultrafast spectroscopy signals induced by quantum light, focusing on applications involving entangled photons with nonclassical bandwidth properties - known as "time-energy entanglement". Nonlinear optical signals induced by quantized light fields are expressed using time ordered multipoint correlation functions of superoperators. These are different from Glauber's g- functions for photon counting which use normally ordered products of ordinary operators. Entangled photon pairs are not subjected to the classical Fourier limitations on the joint temporal and spectral resolution. After a brief survey of properties of entangled photon pairs relevant to their spectroscopic applications, different optical signals, and photon counting setups are discussed and illustrated for simple multi-level model systems

Optical control of the current-voltage relation in stacked superconductors

We simulate the current-voltage relation of short layered superconductors, which we model as stacks of capacitively coupled Josephson junctions. The system is driven by external laser fields, in order to optically control the voltage drop across the junction. We identify parameter regimes in which supercurrents can be stabilised against thermally induced phase slips, thus reducing the effective voltage across the superconductor. Furthermore, single driven Josephson junctions are known to exhibit phase-locked states, where the superconducting phase is locked to the driving field. We numerically observe their persistence in the presence of thermal fluctuations and capacitive coupling between adjacent Josephson junctions. Our results indicate how macroscopic material properties can be manipulated by exploiting the large optical nonlinearities of Josephson plasmons.Comment: 7 pages, 7 figure

Radiative Transfer Models of the Galactic Center

This thesis discusses research being done to understand the inner parts of the Milky Way Galaxy. We already know that there are dense star clouds, a supermassive black hole, and a large bar structure, but much of the inner galaxy is shrouded in mystery. Dust absorption, for one thing, prevents us from seeing the galactic center directly with our eyes. To help understand the elusive inner Milky Way, we examine radio telescope data taken in Antarctica by Oberlin College Professor Chris Martin. His gigahertz radio observations were already analyzed to help understand how gas funnels into the Milky Way\u27s supermassive black hole. We study this data further to characterize turbulence and predict how hot or cold the gas is. The analysis of this data will also help prepare for the next thing: Herschel Space Observatory. This European telescope is scheduled to be launched in late April and will begin taking data in the fall of 2009. Chris Martin was granted 125 hours of observation time on the telescope to study the Inner Milky Way

Radiative Transfer Models of the Galactic Center

This thesis discusses research being done to understand the inner parts of the Milky Way Galaxy. We already know that there are dense star clouds, a supermassive black hole, and a large bar structure, but much of the inner galaxy is shrouded in mystery. Dust absorption, for one thing, prevents us from seeing the galactic center directly with our eyes. To help understand the elusive inner Milky Way, we examine radio telescope data taken in Antarctica by Oberlin College Professor Chris Martin. His gigahertz radio observations were already analyzed to help understand how gas funnels into the Milky Way\u27s supermassive black hole. We study this data further to characterize turbulence and predict how hot or cold the gas is. The analysis of this data will also help prepare for the next thing: Herschel Space Observatory. This European telescope is scheduled to be launched in late April and will begin taking data in the fall of 2009. Chris Martin was granted 125 hours of observation time on the telescope to study the Inner Milky Way

Polarization-Entangled Two-Photon Absorption in Inhomogeneously Broadened Ensembles

Entangled photons are promising candidates for a variety of novel spectroscopic applications. In this paper, we simulate two-photon absorption (TPA) of entangled photons in a molecular ensemble with inhomogeneous broadening. We compare our results with a homogeneously broadened case and comment on the consequences for the possible quantum enhancement of TPA cross sections. We find that, while there are differences in the TPA cross section, this difference always remains small and of the order unity. We further consider the impact of the polarization degrees of freedom and carry out the orientational average of a model system Hamiltonian. We find that certain molecular geometries can give rise to a substantial polarization dependence of the entangled TPA rate. This effect can increase the TPA cross section by up to a factor of five