New Photon Detector Big Step For Quantum Computer

First Posted: Jan 26, 2013 03:58 PM EST

One of the very important elements still missing for photonics and quantum communication are easy to make, ultrafast, efficient, and reliable single-photon detectors. Now a team around physicist Dr. Wolfram Pernice of the Karlsruhe Institute of Technology (KIT), Germany, claims to made a decisive breakthrough by integrating those detectors on nanophotonic chips. The detector boasts a near-unity detection efficiency, combined with high timing resolution and has a very low error rate.

The ability to detect single photons is crucial to make real use of the latest advances in optical data transmission or quantum computation; not having this capability is likened by the researchers to "not having an analog-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 sufficient performance to be widely implemented and used in even small-scale applications.

Several new ideas and advanced developments went into the fascinating prototype developed within the "Integrated Quantum Photonics" project, which is part of the German Research Association's (DFG) Center of Functional Nanostructures (CFN). The new single-photon detector, tested in the telecommunications wavelength range, achieves a previously unattained detection efficiency of 91%, with the results published by Nature Communications (doi:10.1038/ncomms2307):

"The detector was realized 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 nanometer-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 micrometer 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 fibers. Arrangements of that type suffer from photons being lost in the fiber 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 ultrashort timing jitter of 18 picoseconds, which is 18 times 10^-12 seconds."

These attributes will allow the integration of several hundred detectors on a single chip, which is one of the basic preconditions for future use in optical quantum computers.

While the detector demonstrated in the original study was designed to work at wavelengths in the telekom bandwidth, the scientists, including researchers at Yale University, Boston University, and Moscow State Pedagogical University, say that the same architecture will also work for wavelengths in the range of visible light. This would allow for example a high precision analyses of anything that emits very low levels of light, and thus photons, such as single molecules or bacteria.

This is another exciting breakthrough achieved with nanotechnology tools, and at Science World Report we are looking forward to many more discoveries and inventions in this area to report on. According to the DFG Center of Functional Nanostructures (CFN), their network, based in Karlsruhe, Germany currently includes 250 scientists and engineers focusing on the areas of nano-photonics, nano-electronics, molecular nanostructures, nano-biology, and nano-energy.

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