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26 January 2009 Titanium TES based photon number resolving detectors with 1 MHz counting rate and 65% quantum efficiency
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A transition edge sensor (TES) is one of superconducting photon detectors, which has a photon number resolving ability in light pulses. The TES device is a kind of calorimeters operated at an extremely low temperature, and the energy of the photons is measured as a resistance change in a superconducting transition region of the TES. The advantages of the TESs are an excellent energy resolution and a high quantum efficiency. However a response speed is limited due to slow thermal recovery time. To overcome this, we fabricated new TES devices which are based on a titanium superconductor. The critical temperature of our titanium films is around 410 mK, which greatly improves the thermal recovery time. The observed decay time constant of response signals to the light pulses is around several hundreds of ns, that make it possible to operate the devices at a counting rate over 1 MHz. The photon number resolving power is 0.35 eV(FWHM) for a 5 μm size device even at the high operating temperature. The system quantum efficiency is 65 % by embedding the TES films in an optical structure with a high reflection dielectric mirror and an anti-reflection coatings fabricated by an ion beam assisted sputtering method. These features are very promising for high speed photon number resolving applications in the quantum information field.
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Daiji Fukuda, Go Fujii, Takayuki Numata, Akio Yoshizawa, Hidemi Tsuchida, Shuichiro Inoue, and Tatsuya Zama "Titanium TES based photon number resolving detectors with 1 MHz counting rate and 65% quantum efficiency", Proc. SPIE 7236, Quantum Communications Realized II, 72360C (26 January 2009);

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