Ti/Au TESs as photon number resolving detectors

Transcription

1 Ti/Au TESs as photon number resolving detectors LAPO LOLLI, E. MONTICONE, C. PORTESI, M. RAJTERI, E. TARALLI SIF XCVI National Congress, Bologna September

2 Introduction: What are TES? TESs are Transition Edge Sensors, microcalorimeters that measure the energy of incident single-photons. SINGLE PHOTON SOURCE TES 2

3 Introduction: What is TES? TESs are superconducting multilayer films: f. e. our devices are made by layers of Ti (10 nm), Au (45 nm) and Ti (30 nm), deposited by electron-gun on SiN substrate. Au Si (500 µm) Ti SiN (0.5 µm) We deposit up to 4 aligned TESs, at fixed distance, on a single substrate chip, typically with an effective area of: 20 µm x 20 µm or 10 µm x 10 µm. 3

4 Introduction: What is TES? 4

5 How TESs operate: TESs are maintained in the superconductive phase by a dilution refrigerator, typically critical temperatures of these devices are about 130 mk. NORMAL PHASE Then we bias devices within the superconducting to normal transition. T c 128 mk SUPERCONDUCTING PHASE 5

6 How TESs operate: R The TES temperature is increased by the energy of photon absorbed. hυ ΔT= ε E ν / C e The TES electrical resistance moves from the bias working point to a higher value proportionally to the incident photon energy, (E ν ), with a sudden time constant (τ el ). T c T After photon absorption, resistance value relaxes to the bias working point, with an effective time constant (τ etf ) proportional to the natural thermal time constant. 6

7 TES as single photon detector: τ el τ etf The resistance variation, proportional to energy absorbed by the TES, is read out like a voltage variation. The pulse amplitude is the device response due to the number or to the energy of the incident photons: f. i. knowing the wavelength of incident photons, we discriminate the number of absorbed photon per incident pulse. 7

8 Our best results: Building the histogram from the detected events and fitting data with the function y 2 N i Aexp( µ ) ( x x 0) σ µ ( x xi ) = exp + 2 exp 2 2 2πσ 2σ 0 σ 0 i= 1 i! 2σ 2 we obtain the average number of photons per pulse µ and, more important, the ENERGY RESOLUTION ΔE=0.38 ev E = 2 2ln 2σ x x 2 1 E γ µ=1.99 Result obtained with a pulse laser at 1310 nm (= o.95 ev), on a 20 µm x 20 µm area TES: 7 photons discriminated. 8

9 Our best results: 14 photons Source: attenuated pulsed laser λ = 1310 nm (0.95 ev) Discriminated photons: up to 14 µ = 4.7 ΔE = 0.5 ev TES areas : 20 µm x 20 µm Source: attenuated pulsed laser λ = 1310 nm (0.95 ev) Discriminated photons: up to 2 µ = 0.55 ΔE = 0.22 ev TES areas : 10 µm x 10 µm 1 photon 2 photons ΔE=0.22 ev 9

10 Pulse analysis: Noisy: ΔE = 0.46 ev histogram noisy fit SavGol: ΔE = 0.39 ev histogram SavGol fit occurrences occurrences amplitude [mv] 4 5 (a) amplitude [mv] 4 5 (b) 3000 Wiener: ΔE = 0.22 ev histogram Wiener fit Amplitude histogram values and interpolation for (a) noisy signal carrying one or more photons, (b) the same sub-set after Savitzky-Golay and (c) after Wiener filters. occurrences [D. Alberto et all., IEEE Trans. Appl. Sup., accepted to] amplitude [mv] (c) 10

11 Our best results: Computed energy from the measured pulses vs theoretical energy for 1 to 7 photons detected at 1310 nm: the slope of the linear fit is We observe a very good linear trend of the points. In the inset the averaged pulses used for the energy estimation are reported. 11

12 Preliminary results: Source: PDC heralded single photon source λ = 812 nm (1.53 ev) Discriminated photons: up to 2 ΔE = 0.47 ev TES areas : 20 µm x 20 µm Preliminary measurement obtained by using a parametric down conversion (PDC) heralded single photon source, at 812 nm: we can clearly observe the single photon peak together with the vacuum component. Vacuum components peak high: 2.8 x photon peak high: 2.4 x 10 4 [L. Lolli et all., Int. Jour. Quant. Inf., accepted to] 12

13 Conclusion: We are able to detect, by Ti/Au TESs, single photon in the NIR wavelength range, with a best energy resolution of 0.2 ev. We have a recovery time of pulse photon about 1.67 µs. We can resolve up to 14 incident photons at the same time with an excellent linearity in the measured energy by the pulse response for the first seven photons. We started preliminary test on a heralded single photon source. 13

14 To develop: Single layer film and shorter dimension Improving fiber-tes coupling depositing directly on top of the fiber Antireflection coating or optical cavity Impedance measurement (now at work) 14

15 THANKS FOR THE ATTENTION 15