Quantum Photodetectors

About This Grant

Recently, the rapid emergence of quantum optics for quantum communications, signal processing, quantum sensing, and next-generation computing has revealed tantalizing images of imminent technological breakthroughs. However, many of the requisite components do not exhibit the necessary levels of performance, or practical implementations do not yet exist. This is particularly true for one of the key components, single-photon detectors, where the high detection efficiencies (approaching 100%) required for these applications have not been achieved. To date, the most widely used single-photon detector types are superconducting nanowire single-photon detectors (SNSPD) and single-photon avalanche diodes (SPADs). SNSPDs have demonstrated excellent performance but must be operated at < 4 K. SPADs have the advantage of working near or at room temperature. Additionally, SPADs are compact, low-cost, and suitable for deployment in arrays, operating over a wide spectral range from ultraviolet to infrared. Due to fundamental material limitations, state-of-the-art SPADs have not achieved single-photon detection efficiencies exceeding 60%. This program will use a new SPAD material, AlInAsSb. It possesses a unique capability to achieve an ultra-high avalanche probability. Combined with a waveguide structure for high collection efficiency, the high detection efficiencies required for quantum optics applications (~ 99%) can be achieved at room temperature. Previously, SPADs have not achieved photon number resolution, a crucial requirement for quantum computing. This program will develop a novel segmented detector consisting of a linear array of nano-SPADs that can achieve number resolution and high efficiency. Technical Description: A primary thrust of this program is to achieve single-photon avalanche diodes (SPADs) with photon detection efficiencies > 90%, ultimately approaching 99%. We will use a new SPAD material, AlInAsSb. The photon detection efficiency is the product of the external quantum efficiency and the avalanche breakdown probability. For normal incidence devices, our AlInAsSb APDs already have the same external quantum efficiencies as the InP/InGaAs APDs that have been widely used as SPADs at 1550 nm. However, to achieve ~ 99% external quantum efficiency, we will develop waveguide structures that enable high efficiencies since they have longer absorption lengths. We have already demonstrated PIN waveguide detectors with an efficiency exceeding 95%. The advantage of AlInAsSb is that its disparate electron and hole impact ionization coefficients enable high avalanche breakdown probabilities; greater than 90% has already been achieved. The state-of-the-art InP/InGaAs SPADs are limited to ~ 65% by their ionization probabilities. In summary, our approach with AlInAsSb is the only means to achieve the ultra-high detection efficiencies required for quantum optics applications. Previously, SPADs have not achieved photon number resolution, a crucial requirement for quantum computing. This program will develop a novel segmented detector consisting of a linear array of nano-SPADs that can achieve number resolution and high detection efficiency. Another key parameter for SPADs is the dark count rate. Current AlInAsSb SPADs exhibit dark current densities approximately 10 times higher than InP/InGaAs SPADs. A variety of approaches, involving three groups of collaborators, is being pursued to reduce the dark current. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.