SINGLE PHOTON DETECTION
(approaching 98% efficiency) and made to handle even higher count rates, approaching 10 billion events per second”. The detector is currently around 80% efficient – meaning 20% of photons that hit the detector are not measured.
Highest-resolution single-photon superconducting camera Meanwhile, scientists at the National Institute of Standards and Technology (NIST), together with other JPL researchers and colleagues at the University of Colorado Boulder, have made advances in single-photon detection by building a superconducting camera containing 400,000 pixels – 400 times more than any other device of its type. The first superconducting
cameras capable of detecting single photons were developed over 20 years ago. Since then, the devices have been limited to containing no more than a few thousands pixels. Connecting a large number of superconducting pixels to a readout wire in a superconducting camera has been a challenge, as it becomes all but impossible to connect every single chilled pixel, among many thousands, to its own readout wire. “The solution to this
challenge is using asymmetric coupling through transduction,” says Dr Bakhrom Oripov, PREP Associate and Researcher at NIST Boulder. “The electrical pulse generated by photons incident on the camera pixels is converted into thermal energy. That thermal energy then triggers the readout wire. This trick allowed us to build a one- way communication channel where a photon detection event signal is routed to the readout wire, but no signal from the readout wire comes back to the camera, eliminating any possibility of crosstalk between neighbouring pixels.” To explain the significance
of applying a current just below the maximum critical current to the superconducting sensors in the camera, Oripov says that “this camera is based on superconducting
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“The PEACOQ detector can count a billion events per second while maintaining time resolution below 100ps”
nanowire single-photon detectors (SNSPDs). These operate with a simple principle: when a photon is absorbed on the nanowire, the energy deposited there locally breaks superconductivity, creating a ‘hotspot’. But unless there is current running through the nanowire, that hotspot is too small and too short-lived to be detected. The closer the biassing current to the critical current of the nanowire, the more sensitive (with a caveat of having more noise) your detector gets.” The unique arrangement of
superconducting nanowires in the camera contributes to the reduction in the number of readout wires and the increase in the number of pixels. Oripov says the team “utilised thermal row-column design, which reduced the number of readout lines needed for a NxN camera to 2N lines. Then, those 2N lines are connected to our readout wires, reducing the total number of rf lines that we need to just four. The image can be read out with just four wires and four sets of amplifiers”. The researchers are confident
when looking to the future of quantum technology advances and applications set to expand and advance space exploration. “We have been getting collaboration requests from a few colleagues working in the field of quantum imaging and quantum optics,” says Oripov. “There are several exciting applications for this camera, such as super-resolution imaging techniques that enable the imaging of objects smaller than the diffraction limit, and sub-shot-noise imaging techniques that enable low- noise imaging at extremely low light levels. The high efficiency and low background noise that a superconducting camera provides helps with
FEATURE
At its core, the new 400,000-pixel NIST camera, the highest resolution of its type, contains two overlapping arrays of superconducting wires
the detection of quantum correlations in both time and space, which are typically required in these applications.” With NIST’s new superconducting camera, the researchers expect that future telescopes will be able to search for life beyond the solar system.
Single-photon detectors on a mature silicon photonics platform Two teams of researchers from Grenoble, France, based at CEA-LETI and CEA-IRIG, worked in close collaboration on a project developing NbN SNSPDs integrated on a silicon-based waveguide using CMOS-compatible processing on 200mm wafers. The work was presented at Photonics West earlier this year. The increasing demand
for SNSPDs, which combine high efficiency, low dark counts, and fast response time, play a crucial role in developing strategic application areas, such as photon- based quantum computing. “Waveguide-integrated single- photon detectors based on superconducting nanowires have already been demonstrated in literature, featuring detection efficiency close to 100% with low noise. The innovation presented by the French team at Photonics West consists in developing single-photon detectors on a mature silicon photonics pre-industrial platform on 200mm SOI formats,” says Ségolène Olivier, Quantum Photonics Program Manager, Optics & Photonics Department at CEA-Leti. “This
means that we have developed a reproducible and high-yield CMOS-compatible technology process to integrate those detectors with other silicon photonics components in order to build functional integrated circuits, such as receivers for quantum communications and, in the longer term, processors for photonic quantum computing. We have reached detection efficiency of more than 80% for a dark count rate (noise) limited to 100Hz. We are currently testing various detector geometries to further enhance detection efficiency.” The researchers have
developed the SNSPD process on their 200mm silicon photonics platform at CEA- LETI, using industrial-grade microelectronics fabrication tools. “The crystalline quality of NbN is important for its superconducting properties and in particular its superconducting-to-resistive transition. We have found in a previous work that a thin aluminium nitride (AIN) layer induces the vertical texturation of the NbN layer and thereby increased its critical temperature (the temperature at which the superconducting-to- resistive transition occurs) by a few Kelvin. This is important to slightly relax the cryogenic constraints and operate the detectors above 2K,” she says. According to Olivier, they
have also developed a full CMOS-compatible metallisation based on planar technology and the use of CMOS-compatible AICu metal. “In general, all the materials we have used for the
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NIST
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