Quantum Stimulated Raman Spectroscopy and Sensing

University Of Denver, Denver CO

Investigators

Abstract

The goal of this proposal is to demonstrate a new sensing technique called “Quantum stimulated Raman spectroscopy” (QSRS) that is extremely sensitive to vibrational resonances in materials, providing a unique “fingerprint” that can distinguish materials. The key innovation behind QSRS is the use of entangled photons (single light particles) as the probing source; calculations suggest that the correlations from entanglement makes QSRS more than a trillion times more sensitive than classical measurements. In addition to this unprecedented enhancement, QSRS measurements are sensitive to quantum excitations, like a single vibrational mode or excited electron. In the proposed work, the team will build the first QSRS setup, test and optimize it with a variety of materials, and then use QSRS to excite, measure, and sense single vibrations and electrons. This new quantum sensitivity enables non-destructive compositional sensing that has potential to be applied in exciting ways, including biological imaging for cancer screening, chemical and weapons detection, and computer chip validation and testing. QSRS is inspired by the orders-of-magnitude cross-section advantage achieved from entangled photon correlations in entangled two photon absorption; but rather than adding two entangled photons to excite a higher-energy level, in QSRS the excitation photons mix such that the difference in their energies is much smaller. This provides direct access to Terahertz energy resonances. THz spectroscopy will be performed by sweeping the energy difference between the excitation photons by selecting the desired energies of the two entangled photons generated by spontaneous parametric downconversion. THz sensing and heralded single THz carrier generation can be performed by setting the energy difference between the photons in the entangled pair to a particular resonance and looking for the unique photon correlation signal of the QSRS process. After characterizing the signal enhancement from entanglement and optimizing the QSRS measurement technique, the team will implement perturbative (few-photon) THz spectroscopy and sensing of a variety of quantum (single carrier) systems to address current research questions, including measurements of the following: phonon density of states in quantum materials, phonon populations during a metal-insulator transition, band splitting in highly correlated electron states in 2D material heterostructures, plasmonic enhancement of QSRS near nanostructures, heralded single magnon generation, and lipid sensing in tissue. These diverse measurements will establish QSRS as a flexible tool for sensitive and non-destructive sensing that can be used for diverse applications such as quantum information technology, cancer diagnostics, non-destructive testing in the semiconductor industry, and chemical sensing. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.