Purdue University Graduate School
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Quantum Probes for Far-field thermal Sensing and Imaging

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posted on 2024-06-25, 14:48 authored by Haechan AnHaechan An

Quantum-enhanced approaches enable high-resolution imaging and sensing with signal-to-noise ratios beyond classical limits. However, operating in the quantum regime is highly susceptible to environmental influences and experimental conditions. Implementing these techniques necessitates highly controlled environments or intricate preparation methods, which can restrict their practical applications. This thesis explores the practical applications of quantum sensing, focusing on thermal sensing with bright quantum sources in biological and electronic contexts. Additionally, I discuss the development of a multimode source for quantum imaging applications and an on-chip atomic interface for scalable light-atom interactions. I built all the experimental setups from the beginning; a microscope setup for nanodiamond-based thermal sensing inside living cells, a four-wave mixing setup using a Rb cell for thermal imaging of microelectronics and multimode source, and a vacuum chamber for on-chip atomic interface.

Quantum sensing can be realized using atomic spins or optical photons possessing quantum information. Among these, color centers inside diamonds stand out as robust quantum spin defects (effective atomic spins), maintaining their quantum properties even in ambient conditions. In this thesis, I studied the role of an ensemble of color centers inside nanodiamonds as a probe of temperature in a living cell. Our approach involves incubating nanodiamonds in endothelial culture cells to achieve sub-kelvin sensitivity in temperature measurement. The results reveal a temperature error of 0.38 K and a sensitivity of 3.46 K/sqrt(Hz) after 83 seconds of measurement. Furthermore, I discuss the constraints of nanodiamond temperature sensing in living cells, propose strategies to surmount these limitations, and explore potential applications arising from such measurements.

Another ubiquitous quantum probe is light with quantum properties. Photons, the particles of light, can carry quantum correlations and have minimal interactions with each other and, to some extent, the environment. This capability theoretically allows for quantum-enhanced imaging or sensing of sample’s properties. In this thesis, I report on the demonstration of quantum-enhanced temperature sensing in microelectronics using bright quantum optical signals. I discuss the first demonstration of quantum thermal imaging used to identify hot spots and analyze heat transport in electronic systems.

To achieve this, we employed lock-in detection of thermoreflectivity, enabling us to measure temperature changes in a micro-wire induced by an electric current with an accuracy better than 0.04 degrees, averaged over 0.1 seconds. Our results demonstrate a nearly 50 % improvement in accuracy compared to using classical light at the same power, marking the first demonstration of below-shot-noise thermoreflectivity sensing. We applied this imaging technique to both aluminum and niobium-based circuits, achieving a thermal resolution of 42 mK during imaging. We scanned a 48 × 48 μm area with 3-4 dB squeezing compared to classical measurements. Based on these results, we infer possibility of generating a 256×256 pixel image with a temperature sensitivity of 42 mK within 10 minutes. This quantum thermoreflective imaging technique offers a more accurate method for detecting electronic hot spots and assessing heat distribution, and it may provide insights into the fundamental properties of electronic materials and superconductors.

In transitioning from single-mode to multimode quantum imaging, I conducted further research on techniques aimed at generating multimode quantum light. This involved an in-depth analysis of the correlation characteristics essential for utilizing quantum light sources in imaging applications. To achieve the desired multimode correlation regime, I developed a system centered on warm Rubidium vapor with nonlinear gain and feedback processes. The dynamics of optical nonlinearity in the presence of gain and feedback can lead to complexity, even chaos, in certain scenarios. Instabilities in temporal, spectral, spatial, or polarization aspects of optical fields may arise from chaotic responses within an optical x(2) or x(3) nonlinear medium positioned between two cavity mirrors or preceding a single feedback mirror. However, the complex mode dynamics, high-order correlations, and transitions to instability in such systems remain insufficiently understood.

In this study, we focused on a x(3) medium featuring an amplified four-wave mixing process, investigating noise and correlations among multiple optical modes. While individual modes displayed intensity fluctuations, we observed a reduction in relative intensity noise approaching the standard quantum limit, constrained by the camera speed. Remarkably, we recorded a relative noise reduction exceeding 20 dB and detected fourth-order intensity correlations among four spatial modes. Moreover, this process demonstrated the capability to generate over 100 distinct correlated quadruple modes.

In addition to conducting multimode analysis to develop a scalable imaging system, I have explored methodologies aimed at miniaturizing light-atom interactions on a chip for the scalable generation of quantum correlations. While warm atomic vapors have been utilized for generating or storing quantum correlations, they are plagued by challenges such as inhomogeneous broadening and low coherence time. Enhancing control over the velocity, location, and density of atomic gases could significantly improve light-atom interaction. Although laser cooling is a common technique for cooling and trapping atoms in a vacuum, its implementation in large-scale systems poses substantial challenges. As an alternative, I focused on developing an on-chip system integrated with atomic vapor controlled by surface acoustic waves (SAWs).

Surface acoustic waves are induced by an RF signal along the surface of a piezoelectric material and have already been proven to be effective for manipulating particles within microfluidic channels. Expanding upon this concept, I investigated the feasibility of employing a similar approach to manipulate atoms near the surface of a photonic circuit. The interaction between SAWs and warm atomic vapor is expected as a mechanism for controlling atomic gases in proximity to photonic chips for quantum applications. Through theoretical analysis spanning molecular dynamics and fluid dynamics regimes, I identified the experimental conditions necessary to observe acoustic wave behavior in atomic vapor. To validate this theory, I constructed an experiment comprising a vacuum chamber housing Rb atoms and a lithium niobate chip featuring interdigital transducers for launching SAWs. However, preliminary experimental results yielded no significant signals from SAW-atom interactions. Subsequent analysis revealed that observing such interactions requires sensitivity and signal-to-noise ratio (SNR) beyond the capabilities of the current setup. Multiple modifications, including increasing buffer gas pressure and mitigating RF cross-talk, are essential for conclusively observing and controlling these interactions.


STTR Program (Contract No. FA864920P0542) awarded by the United States Air Force Research Lab

Kirk Grant awarded by Purdue’s Birck Nanotechnology Center

CAREER: Active Nonlinear Photonics with Applications in Quantum Networks

Directorate for Engineering

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DoD-NDEP Award number HQ0034-21-1-0014


Degree Type

  • Doctor of Philosophy


  • Electrical and Computer Engineering

Campus location

  • West Lafayette

Advisor/Supervisor/Committee Chair

Mahdi Hosseini

Additional Committee Member 2

Ali Shakouri

Additional Committee Member 3

Weng Cho Chew

Additional Committee Member 4

Zubin Jacob