INSPIRE: Exploring living system responses to quantum states of light

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

This project is jointly funded by the following programs in the Divisions of Physics (PHY) and Chemistry (CHE) of the Directorate for Mathematics and Physical Sciences (MPS), and the Division of Behavioral and Cognitive Sciences (BCS) of the Directorate for Social and Behavioral and Economic Sciences (SBE), with co-funding from the Office of Integrative Activities: MPS/PHY/Atomic, Molecular, and Optical Physics--Experiment, MPS/PHY/Physics of Living Systems, MPS/CHE/Chemistry of Life Processes, SBE/BCS/Program on Perception, Action, and Cognition and the SBE Office of Multidisciplinary Activities. This project will test the limits of how living things detect light and study how the laws of quantum mechanics apply to biological systems. Single photons (individual particles of light) will be used to study both the human visual system and light-sensitive bacteria. In the human visual system, this project will determine whether humans can see a single photon (a longstanding question in psychology) by using a method of creating one photon at a time to test the vision of human observers. This project will also investigate what human observers see when they detect a photon in a superposition - a state of being in two places at the same time - which is allowed by quantum mechanics. Light-sensitive bacteria will also be studied using single photons, to understand the limits of light detection and the possible effects of quantum laws in a different biological system. In addition to advancing our knowledge of how living things detect and use light, this research might help us understand why particles such as photons show strange quantum behavior such as superposition, while the familiar world around us behaves differently. Making quantum effects available to human perception would also have broad popular appeal, and could be a gateway for students and the public to learn about quantum physics. To produce single photons, this project will use a well-known heralded single-photon source design based on spontaneous parametric downconversion. Single photons at 505 nm and 440 nm will be used for experiments with humans and E. coli, respectively. To determine whether humans can see single photons, observers will complete a series of trials in which they must choose whether the stimulus photon appeared on the left or the right side of their visual field. If observers are able to choose left or right with accuracy statistically greater than 50%, this is strong evidence that they can see single photons. An EEG-contingent stimulus delivery method will also be developed to improve the likelihood of detection. If single-photon vision is confirmed, a subsequent experiment will attempt a test of quantum nonlocality with a human observer replacing one single-photon detector. Finally, to test perception of superposition states, observers will be presented with both a classical mixture of photons at the left and right spots, and photons in a superposition of left and right. The observer's frequency of choosing left and right will be compared between the two cases, with any unexpected difference suggesting a deviation from standard quantum mechanics. To study phototactic bacteria (which move in response to light), individual E. coli cells will be immobilized in an IR optical trap and stimulated with single photons. In an established technique, the response of the cells can be measured by tracking their swimming and tumbling behavior with the trapping beam. Other species will be studied in following experiments, including photosynthetic Rhodobacter sphaeroides.