A quantum light source proves that light-sensitive cells in frog eyes can detect single photons
Miniature light detectors in frog eyes known as retinal rod cells are directly and unambiguously shown to detect single photons of light — an astounding sensitivity considering that a humble 60 watt light bulb spews out a staggering 1020 photons per second. Using a specially developed light source that generates single photons, a new A*STAR study finds that a rod cell has an almost one-in-three chance of detecting an incoming photon.
Scientists have known for some time that rod cells are sensitive to single photons. This was inferred based on statistical modeling in studies that used classical light sources such as lamps, lasers and light-emitting diodes that generate a statistical distribution of photons. In contrast, the light source developed by Leonid Krivitsky and co-workers at the A*STAR Data Storage Institute and A*STAR Institute of Medical Biology is a truly single-photon source and hence eliminates the need to statistically analyze measurement results, thus enhancing measurement accuracy1.
“Our method is both direct and universal,” notes Krivitsky, “as it is not based on any particular statistical model of the cell response and thus does not involve any indirect assumptions.”
In the developed light source, a nonlinear optical crystal is irradiated with light from an ultraviolet laser. Most photons pass directly through the crystal, but approximately one in a million is split into two visible-light photons having twice the wavelength (532 nanometers) of the original photon (266 nanometers). One of these two photons is detected by a photodiode and used to trigger an acousto-optical modulator, causing it to divert the second photon to a tapered optical fiber directed at a pipette containing a rod cell from a frog’s eye (see image). Any signal produced by the rod cell is then detected.
Racing against the clock, since rod cells lose their viability after one to two hours, the researchers measured ten rods cells taken from ten different frogs. They found an average quantum efficiency of approximately 30 per cent — very close to that of human rod cells estimated from behavioral experiments. Krivitsky notes that rod-cell efficiency is comparable to the quantum efficiencies of state-of-the-art man-made single-photon detectors such as photomultipliers (40 per cent) and avalanche photodiodes (50 per cent); remarkably, rod cells occupy an area of only 5 by 50 micrometers and contain their own power supply.
The new light source could be further used to investigate how the quantum efficiency varies with wavelength, since it is easy to vary the wavelength of the generated single photons.
The A*STAR-affiliated researchers contributing to this research are from the Data Storage Institute and the Institute of Medical Biology. More information about the group’s research can be found at the Advanced Concepts & Nanotechnology webpage.
 Phan, N. M., Cheng, M. F., Bessarab, D. A. & Krivitsky, L. A. Interaction of fixed number of photons with retinal rod cells. Physics Review Letters 112, 213601 (2014).
A*STAR Research | ResearchSEA
SF State astronomer searches for signs of life on Wolf 1061 exoplanet
20.01.2017 | San Francisco State University
Molecule flash mob
19.01.2017 | Technische Universität Wien
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
19.01.2017 | Event News
10.01.2017 | Event News
09.01.2017 | Event News
20.01.2017 | Awards Funding
20.01.2017 | Materials Sciences
20.01.2017 | Life Sciences