Over the past years we have been applying quantum optical techniques to various biological problems such as: The detection of biopathogens, e.g., anthrax [1] and the SARS-CoV-2 virus [2]. On the theoretical front, I will discuss the application of quantum mechanics to other biological problems, such as the possible connection between quantum coherence in brain microtubules [3] and superradiance [4,5].
[1] “FAST CARS: Engineering a laser spectroscopic technique for rapid identification of bacterial spores,” M. Scully, et al., PNAS (2002).
[2] “Laser technique for direct identification of a single virus I: FASTER CARS,” V. Deckert, et al., PNAS (2020).
[3] “Quantum Coherence in (Brain) Microtubules and Efficient Energy and Information Transport”, N. Mavromatos and d. Nanopoulos, J. Phys: Conf. Ser. 329, 012026 (2011).
[4] “On the Existence of Superradiant Excitonic States in Microtubules”, G. Celardo, et al., NJP (2019).
[5] “The Super of Superradiance”, M. Scully and A. Svidzinksy, Science (2009): A. Svidzinsky, et al., “Single photon superradiance and radiation trapping by atomic shells,” PRA (2016).
KEYWORDS: Mid-IR, Vibration, Difference frequency generation, Spectroscopy, Physical coherence, Visible radiation, Ultrafast phenomena, Sum frequency generation, Near infrared, Molecules
We study Four Wave Mixing (FWM) generated based on a mid-infrared pulse and a near infrared pulse. The mid infrared light is near resonant with vibrational modes of molecule, and it can create a coherence between vibrational states. The near infrared light will probe the coherence and result in FWM based on third order nonlinearity through different pathways. One pathway is a third-order Sum Frequency Generation (tSFG) and the other is a third-order Difference Frequency Generation (tDFG). We report experimental investigation of a time resolved tDFG generated from plastic materials such as mixed beads and a thin Low-Density Polyethylene (LDPE) film. We compare results of the tDFG with that of the tSFG in terms of their intensities and phase matching conditions. Our results show that a vibrational spectroscopy combing the tDFG and the tSFG can be versatile tools in studying of physical chemistry, dynamics of complicated molecular system, bioimaging and so on.
We discuss advances in ultrasensitive Raman-spectroscopic probing of various biosamples. Our approach is based on laser spectroscopy aided by plasmonic nanoantennas, as for example in tip-enhanced Raman spectroscopy. An additional enhancement in sensitivity and speed is obtained by employing quantum molecular coherence driven either by pump and Stokes pulse pair or a direct infrared drive field.
We discuss applications of quantum molecular coherence, as well as nonclassical states of light, such as entangled and squeezed light, to improved molecular spectroscopic sensing. We consider scenarios ranging from remote to near-field configurations, where enhanced sensitivity and resolution are further aided by plasmonic nanostructures and antennas.
Stimulated Raman scattering (SRS) microscopy using picosecond near-IR pulses has provided a great penetration depth with reduced fluorescence interference when imaging biological samples for bioenergy applications. These tools have provided insight into 1) tracking the degradation of chemical composites in biomass feedstocks to investigate the recalcitrant factors during the deconstruction processes, 2) monitoring the production of chemicals in photosynthetic plants and wood-digesting microorganisms, and 3) probing plant-bacteria interactions. However, the above processes are usually slow and require continuous imaging for an extended period. This is challenging for classic SRS because the laser power needed to achieve enough sensitivity causes photodamage in the samples during such long experiments. Quantum-squeezed light with reduced noise in the intensity quadrature can improve the sensitivity of classic SRS microscopy beyond the shot noise limit. The successful squeezing of one of the picosecond pulses in the above SRS will improve sensitivity and reduce photodamage, greatly expanding the range of studies available to SRS microscopy.
Detection and sensing of molecules via their interaction with light opens opportunities for studies ranging from nanoscale single-molecule readout to long-range experiments. Plasmonic antennas allow localized electromagnetic enhancement, allowing Raman-spectroscopic sensing with sub-nanometer spatial resolution. Further signal enhancement can be obtained through the use of molecular coherence - produced either through coherent Raman excitation or via direct infrared driving. The next level of improvements in signal-to-noise ratio will come with the use of properly engineered non-classical states of light.
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