Next generation single-photon detectors are becoming available. Research grade SPAD arrays promise camera-like detectors with dozens to hundreds of thousands of pixels, providing both spatial and temporal information about single photon events. Concurrently, other detector technologies are under development, such as crossed-delay line detectors. We evaluate the application of SPAD arrays and NCam, a crossed-delay line detector, towards quantum ghost imaging applications. We discuss implementation challenges and performance differences in the context of ghost imaging.
Using a novel imaging device—NCam—fluorophore lifetime measurements can be captured simultaneously with wide-field microscopy methods. Because NCam records single-photon events with spatial and temporal information, the localization precision can be improved compared to camera-based imaging or scanning confocal instruments. We demonstrate this new imaging capability by examining the fluorescence behavior of quantum dots.
The near infrared (NIR) and mid-infrared (MIR) spectral regions contain absorption features that can identify specific molecular bonds and chemical species in a sample. For example, lignan and proteins in plants have specific absorption signatures in the NIR. However, because detectors are inefficient in the NIR and MIR, infrared spectroscopy requires high light levels to overcome detector limitations. Cameras in particular do not perform well in this spectral range, and microscopy methods such as Fourier transform infrared spectroscopy (FT-IR) typically rely on scanning confocal arrangements with single-element detectors to spatially map chemical information. To overcome these limitations, we have developed and exploited a new quantum ghost imaging microscope for obtaining absorption measurements in the NIR without the need of scanning or high light intensities. We report on the use of a novel detector–NCam–in quantum ghost imaging using non-degenerate photon pairs generated by spontaneous parametric down conversion (SPDC). NCam records single-photon arrival events with ∼100 ps resolution, enhancing the correlation window of SPDC pairs over previous wide-field ghost imaging by 30-fold. This permits ghost imaging of living and intact plant samples at light levels lower than what the plants would experience from starlight. For photosynthesizing organisms, this low-light imaging method enables the study of plants without disturbing or eliciting responses from the plant due to the measurement itself.
NIR imaging of biological samples can reveal details about the chemical makeup of the sample. To overcome the difficulties of current imaging devices, which are most sensitive in the visible region of the spectrum, we use ghost imaging with quantum entangled photons. A non-degenerate photon pair is used to probe a sample, revealing structures with fewer photons per second than starlight.
Modern instruments for imaging biological samples often use high-power lasers or fluorescent dyes that can disturb sensitive processes within living organisms such as plants. Additionally, many interesting plant processes have absorption bands within the near-infrared (NIR), a spectral region hard to efficiently and cost-effectively detect using current camera technology. We present a quantum ghost imaging (QGI) protocol using a proprietary time and space-resolving photon-counting visible camera, NCam, and a highly nondegenerate source of entangled photon pairs. The combination of these two technologies allows for low-noise, high-resolution non-destructive imaging in the NIR, while using a camera sensitive for visible wavelengths.
The Extremely Low-Resource Optical Identifier (ELROI) beacon is a concept for a milliwatt optical license plate" that can provide unique ID numbers for everything that goes into space. ELROI is designed to help address the problem of space object identification in the crowded space around the Earth, where over 16,000 objects - from active satellites to rocket bodies and debris - are currently tracked and monitored. Using photon counting to enable extreme background rejection in real time, the ID number can be uniquely identified from the ground in a few minutes, even if the ground station detects only a few photons per second. The ELROI concept has been validated in long-range ground tests. A first orbital prototype, integrated into the student CubeSat NMTSat, was launched in December 2018. We discuss our most recent attempts to observe this prototype, including our ground station and an outline of data analysis techniques, as well as the most recent optical signal characteristics for those interested in making observations with their own ground stations.
KEYWORDS: Photons, Single photon, Superposition, Visual system, Polarization, Human vision and color perception, Sensors, Single photon detectors, Switches
The human eye contains millions of rod photoreceptor cells, and each one is a single-photon detector. Whether people can actually see a single photon|which requires the rod signal to propagate through the rest of the noisy visual system and be perceived in the brain|has been the subject of research for nearly 100 years. Early experiments hinted that people could see just a few photons, but classical light sources are poor tools for answering these questions. Single-photon sources have opened up a new area of vision research, providing the best evidence yet that humans can indeed see single photons, and could even be used to test quantum effects through the visual system. We discuss our program to study the lower limits of human vision with a heralded single-photon source based on spontaneous parametric downconversion, and present two proposed experiments to explore quantum effects through the visual system: testing the perception of superposition states, and using a human observer as a detector in a Bell test.
The Extremely Low-Resource Optical Identifier (ELROI) beacon is a concept for a milliwatt optical "license plate" that can provide unique ID numbers for everything that goes into space. Using photon counting to enable extreme background rejection in real time, the ID number can be uniquely identified from the ground in a few minutes, even if the ground station detects only a few photons per second. The ELROI concept has been validated in long-range ground tests, and orbital prototypes are scheduled for launch in 2018 and beyond. We discuss the design and signal characteristics of these prototypes, including a PC-104 form factor unit which was integrated into a CubeSat and is currently scheduled to launch in May 2018, and basic requirements on ground stations for observing them. We encourage others to consider observing our test flights.
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