Research

Focus Area I. AMO Physics: Macroscopic Quantum Coherence in Atoms, Molecules and Polarons

• One of the fundamental concepts to understanding the principles of quantum technologies is macroscopic quantum coherence (MQC). My primary focus area is MQC in quantum particles such as atoms, molecules, and polarons.

  Macroscopic quantum coherence in atoms:

  Collective behavior of quantum particles is one of the most intriguing phenomena in quantum optics. As such, superradiance (SR) is spontaneous collective emissions from a group of atoms behaving collectively as a giant dipole due to the buildup of MQC. In the long run, this research will help by “resolving” the fundamental failure of all current error correction algorithms in quantum computation caused by unwanted collective phenomenon. Atomic MQC study in time-domain has been my dedicated research topic over the years. My first publication in 1999 and the most recent publications in 2022 studied atomic MQC. My PhD thesis (Texas A&M University - TAMU) topic was mainly focused on atomic collective phenomenon. In collaboration with the TAMU colleagues, I have accomplished: (i) observations of the shortest ever SR emissions from rubidium (Rb) (2010), sodium (Na) (2014), and cesium (Cs) (2022) atomic vapors; (ii) observations of quantum fluctuations for Rb (2012) after the first measurements in early 80s; (iii) for Na, for the first time; (iv) introduction and demonstration of a SR temporal coherent control, for the first time (2012); (v) observations of SR quantum beatings in Rb (2011,2022) and Cs (2022); and (vi) introduction of a new cascade SR model (2022).
  

  Quantum and classical models

  The primary question of interest is whether the atomic macroscopic quantum coherence is initiated by means of a quantum synchronization (i.e., a quantum analog of classical synchronization) or not. The goal of my research on this focus area is to address this question. We are developing a new model as a correspondence of collective phenomenon to synchronization. These results enable to better understand how to create and maintain MQC of polarons in quantum materials under practical conditions.

  Quantum macroscopic coherence in molecules:

  Femtosecond (fs) dynamics of vibrational and rotational wave packets of dissociating molecular fragments in chemical reactions were first studied by Prof. A. Zewail (Nobel Laureate) using the technique where the laser excited molecule is probed by another time-delayed pulse. Historically, it is referred to as a pump-probe technique. In collaboration with TAMU co-workers, I have studied the dynamics of wave packets in cesium dimers using an ultrafast controlled pump-probe technique. The proper choice of time delay between pump and control pulses does alter the temporal characteristics of this superposition. The experimental observations were supported by a theoretical model based on density matrix formalism with the Franck-Condon factors.
  

  A layout for coherent anti-Stokes Raman spectroscopy

  On the other hand, researchers have been using lasers to study nonlinear optical properties of molecular systems. In the spontaneous Raman process, when light irradiates molecules, the faint lower frequency (Stokes) light is emitted. This frequency shift (i.e., Raman vibrational spectrum) is unique for each molecule to provide a “fingerprint” for species identification. Generally, the spontaneous Raman scattering is incoherent process where no molecular coherence is involved. To create coherence, additional pulse excitations are needed. If two fs driving pulses (called pump and Stokes pulses) resonantly excite the ensemble of molecules, then the molecules start vibrating in unison. This is the main principle of the powerful techniques for molecular specific detection, coherent Raman spectroscopy based on Coherent Anti-Stokes Raman Scattering (CARS) and coherent Stokes Raman Scattering (CSRS) processes.
  

  Nonlinear optical responses of resonantly versus non-resonantly excited molecules

  As mentioned above, a similar question is whether the molecular MQC is initiated by means of a quantum synchronization or not. The goal of my research is to address this question. The CARS technique has been extremely well developed since its first demonstration in 1963 and discovering something new is hardly anticipated. However, to date, this question has not been addressed yet. My research focuses on studying molecular MQC associated with CARS/CSRS processes. I have prior research experience for studying molecules: We performed (i) a theoretical prediction (2016, 2017) and experimental demonstration (2020) of an existence of deferred MQC buildup of the ensemble of molecules, for the first time; and (ii) an observation of collective emissions from pyridine-water complex (2021). To reveal molecular MQC, we have developed new analytical tool of one- and two-dimensional correlation analyses (2021).

  Quantum macroscopic coherence in polarons:

  MQC is an extremely fragile state susceptible to rapid environmental disturbances. Surprisingly, these disturbances also help to isolate the quantum system from decoherence in a sense that they heat water and, counterintuitively, turn it to ice. Current quantum technologies have been realized at ultralow temperatures, when the environmental disturbances including dephasing (i.e., decoherence) are rather negligible. In practice, however, dephasing is highly intrinsic and rapidly overwhelms a delicate MQC. Sustaining MQC under ultrafast dephasing at high temperatures is an issue of an utmost importance that incited recent scientific breakthroughs. To interpret these groundbreaking results, a proposal of a universal quantum analog of vibration isolation (QAVI) mechanism was postulated in 2022. The QAVI mechanism is universal in nature and is proposed to both high-temperature superconductivity and room-temperature SR in polarons in solid-state quantum materials. The QAVI mechanism may ‘potentially lead to a transformation of quantum technologies similar to that of electronics technology in the 20th century’, still, it has yet to be conclusively confirmed. Thus, my research is to address the question of QAVI existence in atomic, molecular and polaronic systems. Currently, my group focuses on repeating the above-mentioned high temperature SR experiments with methyl-ammonium lead iodide (MAPbX3) with using a MHz laser system. Dr. Gangishetty (Department of Chemistry, MSU) is collaborating with our group and developing several compositions and geometries of perovskites. For this purpose, we have recently installed cryostat vacuum system capable of operating at liquid nitrogen and helium temperatures.
  The long-term goal of my overall research at MSU in this focus area is to establish a universal quantum synchronization mechanism for macroscopic quantum phase transition phenomena in quantum gases, liquids, and solid-state materials under dephasing.

Focus Area II. Ultrafast Laser Spectroscopy and its Applications

• My group also specializes at applying ultrafast nonlinear optical microscopy and spectroscopy where the femtosecond laser interacts with molecules. Special cases of these techniques are based on CARS, CSRS, sum frequency generation (SFG), second harmonic generation (SHG), two- and three-photon absorption nonlinear optical processes. The group focuses on promoting the implementation of ultrafast nonlinear optical microscopy and spectroscopy in agriculture, healthcare and environmental ecology. Today the advanced nonlinear optical techniques have already been commercialized and may potentially be used in healthcare for label-free chemical imaging which would revolutionize traditional histopathology practices. However, not much effort from the optics and photonics community has been devoted to the global challenges currently encountered in agriculture and environmental ecology. We initiated and co-chaired the OSA incubator meeting “Agri-Photonics Incubator: Advanced Spectroscopy in Precision Agriculture” in May 2019 in Washington, DC, and published featured article on this topic in Optics and Photonics News (2019). This time we intend to use our research expertise to help address these global challenges.

  Coherent Raman Scattering Spectroscopy:

  Raman vibrational spectrum provides a molecular species identification. However, the spontaneous Raman signal is weak and can be enhanced using four wave mixing processes such as CARS/CSRS. However, CARS signature is vastly obscured by non-resonant background contributions from other molecules present in the sample. Scientists have tried a variety of methods to counteract these background vibrations, unfortunately, with only limited success. Femtosecond (one billionth of one millionth of a second) laser systems in which the pulse energy is compressed within such a short time range that becomes extremely high, put forward the potential improvement in CARS diagnostic capabilities. With the TAMU colleagues, I have developed a patented ultrafast CARS technique. This hybrid technique combines the robustness of frequency-resolved CARS with the advantages of time-resolved CARS spectroscopy. Broadband (fs) pump and Stokes pulses excitation of several characteristic molecular vibrations and the subsequent probing of these coherent vibrations by an optimally shaped time-delayed narrowband pulse help to suppress the non-resonant background and retrieve the species-specific signal. This technique can be applied in a wide range of applications, from national security to healthcare, in particular, in cancer cell research. Our new technique has been reported in Science magazine (2007). We demonstrated that spontaneous Raman signal was enhanced by 6-fold by coherent excitations (2007).

  Rapid detection of bio-agents:

  The 2001 anthrax attacks in the United States, also known as Amerithrax from its Federal Bureau of Investigation (FBI) case name, occurred over the course of several weeks beginning on September 18, 2001, only a few days after the September 11 attacks, killing five people and infecting 17 others (Wikipedia). The traditional anthrax test involved a time-consuming process in which suspicious substances must be cultured in the lab. A rapid and reliable identification of bacterial spores, despite of its cumbersomeness, became a matter of national security, especially, in the fight against bioterrorism. In collaboration with the TAMU team, I demonstrated a rapid and highly specific detection of Bacillus subtilis that operates even in the presence of multiple scattering in such rough sample (powder) and extended their hybrid CARS technique to single-shot identification (2007) of a small sample with approximately 10000 Bacillus subtilis endospores. The results convey the utility of the technique and its potential for “on-the-fly” detection of biohazards, such as Bacillus anthracis.

  All Gaussian coherent Raman spectroscopy (MSU-CARS):

  At MSU, we have developed a new spectroscopy technique. It bears the essential ingredients of the pump-probe experiment, in which two broadband pulses simultaneously excite selected vibrating molecules in unison, and this macroscopic coherent vibration is eventually probed leading to signal enhancement by many orders of magnitude. The novelty of the approach is that all input laser pulses treated as Gaussian pulses, where we found analytic solutions using the Faddeeva function (an error function with complex argument). We published an invited review on CARS/CSRS (2015) in addition to multiple papers. This all-Gaussian coherent Raman scattering reproduces the main properties of the nonlinear four wave mixing processes. In addition, we predicted and observed the above mentioned molecular MQC buildup. This buildup is used to distinguish coherently versus incoherently excited multiple species e.g., benzene versus water (2021).

  Ultrafast nonlinear optical imaging platform:

  We have developed an advanced nonlinear optical imaging platform by upgrading the MSU-CARS setup. This MSU-CARS setup has been modified to a nonlinear optical imaging (NOI) technique. The state-of-the-art laser system is currently operating at 1040 nm wavelength with repetition rate of 1 Megahertz. The additional beams with designated colors are produced by a homemade nonlinear optical parametric amplifier (NOPA) designed for the NOI experiment for fixed tissue characterizations. Currently, from about 400 million to a billion FFPE (formalin fixed paraffin embedded) tissue samples have been archived in repository sites and hospitals worldwide and maximizing their scientific value of these existing biospecimen collection is urgent. Unfortunately, FFPE is not a compatible procedure for the micro-spectroscopy imaging community. That is because paraffin contamination removal is an enduring challenge. For example, incomplete paraffin removal from FFPE tissues can increase false positives in diagnostic histology. The NOI platform records CARS, SFG, SHG and optical images nearly simultaneously (2021). We have a single-photon sensitive EMCCD imaging camera. The NOI platform’s sensitivity reaches down to about 600 parts per million (ppm) by capturing images for the nitrogen molecular vibrations against to images of the background noise in the ambient air (in the lab). For FFPE tissues, the CARS and SFG images show almost no difference since the SFG signal is present in the CARS image and overwhelms any actual CARS signal incoming from chemical species, e.g., collagen. However, paraffin shows a dramatic difference in CARS and SFG images. This is because paraffin only has a CARS signal but neither SFG nor SHG signals since paraffin has no structural variety seen in collagen. With this technique, my group has successfully (spectrally) distinguished the differences between collagen and paraffin. This research has been extended to other tissues including bone, tendon, skin and many more stained and unstained FFPE tissues. We introduced a new analytical tool based on spatial q-score statistical image analysis for FFPE tissues (2022). The q-score serves as a spatial heterogeneity measure for FFPE tissue chemical characterizations.
  

  Ultrafast nonlinear optical imaging platform: The laser setup and chemical microscopic images.

  Correlation spectroscopy and analytic tools:

  Two-dimensional correlation spectroscopy (2DCOS) was initially developed in the late 1980-es by Prof. Isao Noda, well-recognized scientist, whose works have been cited more than 30,000 times. Since then 2DCOS has been widely used in many spectroscopic techniques including nuclear magnetic resonance spectroscopy (NMR), infrared spectroscopy and Raman spectroscopy. For the first time, we implemented the traditional 2DCOS to coherent Raman spectroscopy. we introduced a new noise correlation coherent Raman spectroscopy (2019) aided by 2DCOS analytical tool. In this case, the noise correlations of the simultaneously recorded CARS and CSRS spectra were analyzed, where we have proved that the intensity-intensity correlation in spectral domain was identical to the diagonal projection of the traditional 2DCOS map. In the 2020 review on emergent developments in 2DCOS, co-authored by Prof. I. Noda and his colleagues, they devoted a subsection titled “Diagonal projection” for my work only and cited as in quote “Ariunbold introduced a new concept of diagonal projection of generalized 2D spectra to 1D second-order correlation function.” Furthermore, we developed generalized two-dimensional correlation analyses to distinguish MQC from non-MQC states in the mixed molecular complexes (2021). My student S. Nagpal has completed her PhD thesis on this topic.

Focus Area III. Optical Sensors

• The last focus area of my research is developing optical sensors. We intend to develop cost-effective optical sensors with implementations in agriculture, healthcare and environmental ecology. Two of my graduate students completed master’s theses on the development of laser-induced fluorescence remote sensing with drone. I am a co-PI (10% for MSU) for the research project on environmental pollutions funded by US Coastal Research Program (USCSRP) and U.S. Army Corps of Engineers (USACE) where we are tasked to develop a portable Raman microscope for microplastics characterizations. I have co-established and been supervising the second lab for optical materials at MSU. Two (portable and advanced) homemade Raman microscopes and laser-induced breakdown spectroscopy setup using three high-power nanosecond lasers are available in this lab to study plants and microplastics.

  Raman spectroscopy:

  One of the most important challenges in high-throughput phenotyping of plants is the availability of sensing technologies to achieve comprehensive screening of plant physiological, biochemical and morphological characteristics at molecular level. Such characteristics can be integrated to predict plant growth potential, biomass processibility, and abiotic stress responses, all of which are directly relevant to the traits important for advanced biofuel applications. Current high-throughput phenotyping platforms for plants are inherently limited when integrating morphological and fluorescence spectroscopy. In collaboration with the TAMU colleagues, I developed a high-throughput Raman spectroscopic technique to quantitatively follow the levels of multiple stress responses of plants (2017). Plant pigment molecules of anthocyanins and carotenoids are simultaneously detected and quantified in-vivo from single Raman measurements of leaves that are negatively correlated. In addition, my group developed multiple spontaneous Raman spectroscopic techniques that incorporated multivariate statistical analysis and measurements of Raman spectra of blood and its components from inbred mice (BXD model). Using the new techniques, we were able to distinguish the mice ages within less than 5 months’ period (2018).
  

  Simultaneous detection of the plant pigments.

  Standoff microparticle chemical imaging with digital holography:

  Airborne, respirable-sized microparticles in the 1–10 μm in size range containing hazardous bioagents are known to penetrate the lung alveoli presenting substantial human-health concerns. Recent advances make it feasible to characterize atmospheric microparticles and biological samples only either chemically or morphologically. Our group integrated the digital holography techniques with Raman spectroscopy to image microparticles without microscopic objective lens. The key development is that this technique can characterize microparticles both chemically and morphologically in standoff configuration (2017,2018).
  

  Contact-free, lens-free digital holographic imaging of microparticles.

  Laser induced fluorescence chlorophyll remote sensor:

  A low-cost portable sensor module based on laser-induced fluorescence was constructed by my team (2018). The laser induced fluorescence spectra from plant leaves were obtained and analyzed. The micro-sized spectrometer used in the module has spectral response in the visible region and the excitation source is at UV region which allows quick and easy sensing up to 30 m away from the target. Thus, this module system is a good candidate for future remote sensing applications. The results demonstrate the feasibility of the module to unambiguously investigate the presence of aflatoxin in corn, abiotic stress in plant, and fruit ripeness in situ. This module can be further used to identify early defects in vegetation not visible to the naked eye and can eventually help to increase production. The versatility of the module can also be extended to military, medical, and precision measurements through integrating the device into an unmanned aerial vehicle or a quadcopter. Furthermore, my team has built a drone capable of detecting laser-induced fluorescence of crop on-the-fly in the real farm field with minimized cost.
  

  Plant stress mapping using a drone.