A Quantum Leap in Imaging

Single-photon cameras have emerged as powerful tools with unique capabilities and advantages over traditional cameras. These cameras are designed to detect and count individual photons, offering unprecedented sensitivity and enabling imaging in low-light conditions where conventional cameras struggle.

One of the most significant advantages of single-photon cameras is their exceptional sensitivity. By detecting individual photons, they can capture extremely weak signals and operate in near-darkness. This sensitivity is particularly useful in applications such as astrophotography, night vision, and microscopy, where capturing fine details in low-light environments is crucial. Single-photon cameras can reveal hidden information and provide high-quality images even in challenging lighting conditions.

In addition to sensitivity, single-photon cameras offer high temporal resolution. By accurately measuring the arrival time of each photon, these cameras can capture fast events with remarkable precision. This capability is valuable in applications like fluorescence lifetime imaging and time-correlated single-photon counting, which require precise timing measurements. Single-photon cameras enable researchers to study dynamic processes and capture ultrafast phenomena that would otherwise be challenging to observe.

This imaging technology is not new, in fact, it has existed for a few decades, however the resolution of these devices has remained very low. With pixel counts in the neighborhood of 1,000, the resolution is a far cry from the dozens of megapixels available in commercial devices with traditional digital cameras today. The main reason for this limitation is that single-photon cameras must be supercooled to operate, and getting all of the wiring needed for a high-resolution camera into a cryostat has proven to be unworkable to date.

Present single-photon cameras are constructed of a grid of superconducting nanowires. When sufficient current is piped through these nanowires, their superconductivity is broken. So, a current just slightly below that threshold is supplied. In this way when the energy from even a single photon comes into contact with a wire, it moves above the threshold temporarily, losing its superconductivity. The resultant resistance across the wire can be measured to detect the amount of energy (i.e. photons) striking it.

A team led by researchers at the National Institute of Standards and Technology have developed a technique capable of producing much larger arrays of pixels. They have already demonstrated a 0.4 megapixel single-photon camera, which has a 400 times greater pixel density than the previous state of the art devices.

To achieve this feat, they needed to drastically cut down on the number of wires that the system would require. They were able to do exactly that by creating a shared data bus architecture, in which measurements are read from entire rows and columns of pixels at one time. But this alone was not sufficient to solve the problem, because, of course, data can go in either direction along the bus. And this caused interference between pixels and destroyed the camera’s sensitivity.

So to ensure that signals could be sent to the bus, but not the other way around, a sort of gate was introduced. Next to each pixel element, the researchers wired in a tiny heating element. When a photon struck the detector, the current would flow into the heating element and cause it to heat up. That had the effect of breaking the superconductivity on the bus, but without disturbing any nearby pixels or heating elements. This technique allowed the researchers to use a bus-based readout mechanism without interference.

The present 400,000 pixel milestone is just another step along the way — the technology has rapidly scaled up from a few thousand to a few tens of thousands of pixels and beyond. There is no reason to think that this trend is going to stop any time soon, and that could mean that great things are in store for many applications. Fields ranging from biomedical imaging to particle and quantum physics research can put such cameras to work in important ways.