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[6] Excitation-pulse intensity mediated control of coherent nonlinear optical response of a V-type system, R. Tripathi, K. K. Maurya, and R. Singh, Phys. Rev. A 114, 013113 (2026). DOI.
We demonstrate a simple way to control quantum systems using only the intensity of ultrafast laser pulses. Studying a three-level system common in atoms, molecules, and semiconductor materials, we show that strong light pulses can create complex quantum dynamics that depend on pulse duration and energy spacing between excited states. Specific quantum pathways can be selectively enhanced or suppressed by adjusting the intensity of excitation pulses, allowing individual features in two-dimensional spectra to be isolated and their phase precisely tuned. Unlike earlier methods that require complex pulse shaping or polarization control, this approach relies solely on intensity control and operates in a high-intensity regime. The findings offer a straightforward strategy for manipulating coherent light-matter interactions and could aid future advances in quantum technologies, photonic devices, and ultrafast spectroscopy.
[5] Indirect excitons and many-body interactions in InGaAs double quantum wells, C. L. Smallwood, R. Owen, M. W. Day, T. Suzuki, R. Singh, T. M. Autry, S. Bhalerao, F. Jabeen, and S. T. Cundiff, Phys. Rev. B 112, 035305 (2025). DOI, Editor's suggestion.
[4] Quantitative line shape analysis for arbitrary inhomogeneity in two-dimensional coherent spectroscopy, B. De, P. Kumar, K. K. Maurya, R. Tripathi, and R. Singh, Opt. Lett. 50, 4502 (2025). DOI, Featured on Quantum Zeitgeist.
Two-dimensional coherent spectroscopy (2DCS) is a powerful technique for separating different sources of spectral broadening in materials. Existing analysis methods generally assume that variations in transition energies follow a simple Gaussian distribution, which is often not the case in real systems. In this work, we develop a new framework that can extract both intrinsic linewidths and an arbitrary energy distributions directly from measured 2D spectra. We apply this method to excitons in a semiconductor quantum well demonstrates its ability to reveal complex disorder without relying on system-specific assumptions. This approach extends quantitative 2DCS analysis to a much broader class of materials and nanostructures.
[3] Coherent nonlinear optical response for high-intensity excitation, R. Tripathi, K. K. Maurya, P. Kumar, B. De, and R. Singh, J. Chem. Phys. 162, 114111 (2025). DOI, Special Collection: David Jonas Festschrift.
We have developed a general simulation framework for nonlinear coherent spectroscopy under strong laser excitation, where conventional perturbative theories often fail. Using a phase-cycling approach, the method calculates coherent optical signals exactly, without assuming weak excitation, simplified pulse shapes, or a fixed nonlinear order. It successfully reproduces a range of experimental observations in semiconductor nanostructures, including signal saturation, higher-order wave-mixing effects, coherent switching between nonlinear signals, and modified photon-echo dynamics. The framework provides a practical and flexible tool for interpreting multidimensional spectroscopy experiments in both perturbative and strongly driven regimes. These results are particularly significant for the community of researchers performing spectroscopy with intense light.
[2] Exciton-exciton interaction: A quantitative comparison between complimentary phenomenological models, P. Kumar*, B. De*, R. Tripathi, and R. Singh, Phys. Rev. B 109, 155423 (2024). DOI (*equal contribution)
Exciton-exciton interactions play a key role in determining how semiconductor nanostructures respond to light, but accurately modeling these many-body effects is often challenging. In this work, we compare two widely used phenomenological descriptions of exciton interactions: a modified optical Bloch equation model and an anharmonic oscillator model. The former model treats excitons as excitation of two fermions whereas the latter as weakly interacting spin-one composite bosons. Using two-dimensional coherent spectroscopy simulations and experiments on semiconductor quantum wells, we show that these seemingly different approaches produce equivalent spectral signatures and can be quantitatively mapped onto each other. This provides a simple framework for interpreting many-body effects and comparing interaction strengths across a wide range of excitonic materials, from quantum wells to emerging two-dimensional semiconductors.
[1] Coherent control of a semiconductor quantum dot ensemble, T. Suzuki and R. Singh, In Semiconductors and Semimetals, edited by S. T. Cundiff and M. Kira (Elsevier, 2020), p. 347. DOI
Pre-IISERB
Spectroscopic insights into high defect tolerance of Zn: CuInSe 2 quantum-dot-sensitized solar cells, J. Du, R. Singh, I. Fedin, A. S. Fuhr, and V. I. Klimov, Nat. Energy 5, 409 (2020). DOI, Featured on cover, LANL press release, Physics World
Hot-electron dynamics in quantum dots manipulated by spin-exchange Auger interactions, R. Singh, W. Liu, J. Lim, I. Robel, and V. I. Klimov, Nat. Nanotechnol. 14, 1035 (2019). DOI, LANL press release
Dephasing of InAs quantum dot p-shell excitons using two-dimensional coherent spectroscopy, T. Suzuki, R. Singh, G. Moody, M. Aβmann, M. Bayer, A. Ludwig, A. D. Wieck, and S. T. Cundiff, Phys. Rev. B 98, 1095304 (2018). DOI
Enhanced Multiple Exciton Generation in PbS|CdS Janus-like Heterostructured Nanocrystals, D. M. Kroupa, G. F. Pach, M. Vörös, F. Giberti, B. D. Chernomordik, R. W. Crisp, A. J. Nozik, J. C. Johnson, R. Singh, V. I. Klimov, G. Galli, and M. C. Beard, ACS Nano 12, 10084 (2018). DOI
Micromachining of Polyurethane Membranes for Tissue Engineering Applications, A. Arefin, Q. Mcculloch, R. Martinez, S. A. Martin, R. Singh, O. M. Ishak, E. M. Higgins, K. E. Haffey, J.-H. Huang, S. Iyer, P. Nath, R. Iyer, and J. F. Harris, ACS Biomater. Sci. Eng. 4 3522 (2018). DOI
Deconvolution of Optical Multidimensional Coherent Spectra, M. Richter, R. Singh, M. E. Siemens, and S. T. Cundiff, Sci. Adv. 4, eaar7697 (2018). DOI
Transient Spectroscopy of Glass-Embedded Perovskite Quantum Dots: Novel Structures in an Old Wrapping, O. V. Kozlov, R. Singh, B. Ai, J. Zhang, C. Liu, and V. I. Klimov, Z. Phys. Chem. 232, 1495 (2018). DOI
Detuning Dependence of Rabi Oscillations in an InAs Self-Assembled Quantum Dot Ensemble, T. Suzuki, R. Singh, M. Bayer, A. Ludwig, A. D. Wieck, and S. T. Cundiff, Phys. Rev. B 97, 161301(R) (2018). DOI, Selected as "Editor's suggestion"
Localization dynamics of excitons in disordered semiconductor quantum wells, R. Singh, M. Richter, G. Moody, M. E. Siemens, H. Li, and S. T. Cundiff, Phys. Rev. B 95, 237307 (2017). DOI
Coherent Control of the Exciton-Biexciton System in an InAs Self Assembled Quantum Dot Ensemble, T. Suzuki, R. Singh, M. Bayer, A. Ludwig, A. D. Wieck, and S. T. Cundiff, Phys. Rev. Lett. 117, 157402 (2016). DOI, Synopsis on Physics, Selected as "Editor's suggestion"
Polarization-dependent exciton linewidth in semiconductor quantum wells: A consequence of bosonic nature of excitons, R. Singh, T. Suzuki, T. M. Autry, G. Moody, M. E. Siemens, and S. T. Cundiff, Phys. Rev. B 94, 081304(R) (2016). DOI
Quantifying spectral diffusion by the direct measurement of the correlation function for excitons in semiconductor quantum wells, R. Singh, G. Moody, M. E. Siemens, H. Li, and S. T. Cundiff, J. Opt. Soc. Am. B 33, C137 (2016). DOI
Multi-dimensional coherent optical spectroscopy of semiconductor nanostructures: Collinear and non-collinear approaches, G. Nardin, T. M. Autry, G. Moody, R. Singh, H. Li, and S. T. Cundiff, J. Appl. Phys. 117, 112804 (2015). DOI
Coherent Coupling of Excitons and Trions in a Photoexcited CdTe/CdMgTe Quantum Well, G. Moody, I. A. Akimov, H. Li, R. Singh, D. R. Yakovlev, G. Karczewski, M. Wiater, T. Wojtowicz, M. Bayer, and S. T. Cundiff, Phys. Rev. Lett. 112, 097401 (2014). DOI
Coherent excitonic coupling in an asymmetric double InGaAs quantum well, G. Nardin, G. Moody, R. Singh, T. M. Autry, H. Li, F. Morier-Genoud, and S. T. Cundiff, Phys. Rev. Lett. 112, 046402 (2014). DOI
Biexcitons in semiconductor quantum dot ensembles, G. Moody, R. Singh, H. Li, I. A. Akimov, M. Bayer, D. Reuter, A. D. Wieck, A. S. Bracker, D. Gammon, and S. T. Cundiff, Phys. Status Solidi (b) 250, 1753 (2013). DOI
Anisotropic homogeneous linewidth of the heavy hole exciton in (110)-oriented GaAs quantum wells, R. Singh, T. M. Autry, G. Nardin, G. Moody, H. Li, K. Pierz, M. Bieler, and S. T. Cundiff, Phys. Rev. B 88, 045304 (2013). DOI
Correlation and dephasing effects on the non-radiative coherence between bright excitons in an InAs quantum dot ensemble measured with 2D spectroscopy, G. Moody, R. Singh, H. Li, I. A. Akimov, M. Bayer, D. Reuter, A. D. Wieck, and S. T. Cundiff, Solid State Commun. 163, 65 (2013). DOI
Fifth-order nonlinear optical response of excitonic states in an InAs quantum dot ensemble measured with 2D spectroscopy, G. Moody, R. Singh, H. Li, I. A. Akimov, M. Bayer, D. Reuter, A. D. Wieck, and S. T. Cundiff, Phys. Rev. B 87, 045313 (2013). DOI
Influence of confinement on biexciton binding in semiconductor quantum dot ensembles measured with 2D spectroscopy, G. Moody, R. Singh, H. Li, I. A. Akimov, M. Bayer, D. Reuter, A. D. Wieck, A. S. Bracker, D. Gammon, and S. T. Cundiff, Phys. Rev. B 87, 041304(R) (2013) DOI
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