All photons count in silicon detector
A breakthrough has been made at KIT in building an efficient single-photon detector
Ultrafast, efficient, and reliable single-photon detectors are one the most sought-after components in photonics and quantum communication, which have not yet reached maturity for practical applications.
Wolfram Pernice of the Karlsruhe Institute of Technology (KIT), in cooperation with colleagues at Yale, Boston and Moscow State Pedagogical Universities have now integrated a single-photon detector with nanophotonic chips.
The researchers say the detector combines near-unity detection efficiency with high timing resolution and has a very low error rate.
The single-photon detector pictured on top of this story is characterised by five factors: 91 percent detection efficiency; direct integration on chip; counting rates on a Gigahertz scale; high timing resolution and negligible dark counting rates.
Without reliable detection of single photons, it is impossible to make real use of the latest advances in optical data transmission or quantum computation; it is like having no analogue-digital converter in a conventional computer to determine whether the applied voltage stands for 0 or 1.
Although a number of different single-photon detector models have been developed over the past few years, thus far, none have provided satisfactory performance.
Several new ideas and advanced developments went into the prototype developed within the "Integrated Quantum Photonics" project at the DFG Centre of Functional Nanostructures (CFN). The new single-photon detector, tested in the telecommunications wavelength range, achieves a previously unattained detection efficiency of 91 percent.
The detector was realised by fabricating superconducting nanowires directly on top of a nanophotonic waveguide. This geometry can be compared to a tube that conducts light, around which a wire in a superconducting state is wound and, as such, has no electric resistivity.
The nanometre-sized wire made of niobium nitride absorbs photons that propagate along the waveguide. When a photon is absorbed, superconductivity is lost, which is detected as an electric signal. The longer the tube, the higher is the detection probability. The lengths involved are in the micron range.
A special feature of the detector is its direct installation on the chip, which allows for it to be replicated at random. The single-photon detectors built thus far were stand-alone units, which were connected to chips with optical fibres. Arrangements of that type suffer from photons being lost in the fibre connection or being absorbed in other ways.
These loss channels do not exist in the detector that is now fully embedded in a silicon photonic circuit. In addition to high detection efficiency, this gives rise to a remarkably low dark count rate. Dark counts arise when a photon is detected erroneously.
For instance, because of a spontaneous emission, an alpha particle, or a spurious field. The new design also provides short timing jitter of 18 picoseconds, which is 18 times 10-12 seconds.
The novel solution also makes it possible to integrate several hundreds of these detectors on a single chip. This is a basic precondition for future use in optical quantum computers.
The detector demonstrated in this study was designed to work at wavelengths in the Telekom bandwidth. The same detector architecture can also be used for wavelengths in the range of visible light. This would allow the principle to be employed in analyses of all structures that emit little light, i.e., photons, such as single molecules or bacteria.
At the beginning of the year, he also won a Helmholtz International Research Group grant, which he wants to use to fund another post-graduate student in his Karlsruhe team.
These results have been published in the paper, " High-speed and high-efficiency travelling wave single-photon detectors embedded in nanophotonic circuits," by W.H.P. Pernice et al in Nature Communications. DOI:10.1038/ncomms2307
