Ultimate Cold-Electron Bolometer with Strong Electrothermal Feedback Leonid Kuzmin Chalmers University of Technology Bolometer Group Björkliden Through the thorns to the stars! Igenom törnen mot stjärnorna! Через тернии к звездам!

Outline Cold-Electron Bolometer (CEB) Comparison with TES NEP with background load General Ultimate NEP formula Experiments Possible developments Conclusions

Noise Equivalent power less than W/Hz 1/2 !? Wavelengths: submillimeter/infrared bands:  m. 100x100 pixel detector arrays !? Readout electronics with multiplexing (SQUID?) Ideal detector: counting individual photons and providing some energy discrimination !? Detector requrements for future space telescopes SPIRIT, SPECS, …

Cold-Electron Bolometer (CEB) with Capacitive Coupling and Thermal Isolation by Tunnel Junctions

Current responsivity: CEB with Electrothermal Feedback (ETF) - effective time constant ( ~10 ns) - ETF gain - e-ph time constant (~ 10  s at 100 mK)

CEB. Cooling Thermal Conductance

Output Power

TES and CEB. Operating Temperature

Turning Point from ”Heating” to ”Cooling

Electron-Phonon Noise Equilibrium case: NEP e-ph 2 = 4 k B T 2 G e-ph = 20 k B  V T 6 V- volume Nonequilibrium case: (Jochum et al. – 1998) NEP e-ph 2 = 10 k B  V (T ph 6 + T e 6 ) Direct electron cooling 

SIN junction noise For strong electron cooling: P cool >> P e-ph NEP shot = ( 2 P 0 k B T e ) 1/2 P 0 – background power load For P 0 = 0.1 pW, T e = 50 mK, NEP shot = 4*10 –19 W/Hz 1/2 Shot noiseCorrelation termHeat flow noise

General Ultimate NEP Formula NEP shot = ( 2 P 0 E quant ) 1/2 P 0 – background power load E quant – energy level of P 0 quantization E quant = k B T e - normal metal absorber E quant =  - superconducting absorber Kuzmin, Madrid General NEP shot - dominates

NEP e-ph. Normal metal and Superconducting absorbers

Limit NEP for different bolometers NEP shot = ( 2 P 0 E quant ) 1/2 CEB: P 0 = 10 fW, T e = 50 mK, NEP shot = 1*10 –19 W/Hz 1/2 TES: P 0 = 10 fW, T e = 500 mK, NEP shot = 4*10 –19 W/Hz 1/2 Kinetic Ind. Det : P 0 = 10 fW,   = 2 K ( Al,  eV) NEP shot = 7*10 –19 W/Hz 1/2

General Limit NEP formula Systems with linear on T thermal conductance - Spider-web TES with conductance through the legs - CEB with cooling through SIN tunnel junctions (weak dependence on T: G ~T 1/2 ), … NEP shot = 2 P 0 E quant Systems with dominant e-ph thermal conductance (strong nonlinearity on T: G e-ph ~T 4 ) - all bolometers on plane substrates with e-ph conductance - antenna-coupled TES on chip, - NHEB with Andreev mirrors … NEP shot e-ph = 10 P 0 E quant

Electron Cooling and NEP measurements I. Agulo, L. Kuzmin and M. Tarasov Strip width  m

Attowatt NEP in dc experiments

Both, Quasiparticle multiplier, 1987 Both et al., Quasiparticle transistor, 1999

Cascade Quasiparticle Amplifier and CEB A

Conclusions: We propose the -- simplest -- smallest (< 2  m) -- coldest (Te < Tph) -- fastest( ~ 10 ns) - -- most sensitive (under real background Po) -- not saturated (up to Tc of electrodes, > 100 pW) -- ideal ”0-detector” (could not be better!) -- easy multiplied on plane substrate (for large arrays) -- easy amplified by Cascade Quasiparticle Amplifier -- easy multiplexed by SQUIDs -- easy fit in any experiment (from submm to near-IR) Cold-Electron Bolometer with Strong Electrothermal Feedback