1. An Electronic Primary Thermometer Based on Thermal Shot Noise Lafe Spietz K.W. Lehnert, R.J. Schoelkopf Department Of Applied Physics, Yale University Thanks to: Michel Devoret, Dan Prober, Irfan Siddiqi, Ryan Held

2. 0-0.50.5 300 mK 400 mK 500 mK 600 mK Coulomb Staircase T>T* Motivation: Unfilled Need in Milikelvin Thermometry Mystery kelvins!

3. Outline I. Motivation, overview of thermometry - Limitations of cryogenic thermometry and temperature metrology II. Thermal-shot noise of tunnel junctions - How it makes a thermometer III. Fabrication of devices: - Dolan bridge junction fab at Yale IV. Demonstration of the thermometer from 0.01K to 300 K V. Future work, possible limitations

4. Overview of low temperature thermometry Johnson noise: Primary, slow, difficult, very wide range Resistors: Secondary,can drift, can be field dependent, not good at very low temperatures, cheap and fast Nuclear orientation: Primary, expensive, very limited range, doesn’t work in B field 3He-4He vapor pressure: Primary, difficult, limited range diodes: Secondary, not good below 1K Capacitance: secondary, no B dependence, recalibrate on cycling Paramagnetic salts: primary, limited range, B dependence Primary vs. secondary

5. ITS 90: The Modern Kelvin Plank radiation law Platinum resistance thermometer He gas thermometer 3He 4He vapor pressure ?.6K 961.78K25K5K3K Below.6K undefined! T 90 : triple point of water = 273.16 K(T 90 ) 273.16K

6. Fundamental Noise Sources Johnson-Nyquist Noise Frequency-independent Temperature-dependent Used for thermometry Frequency-independent Temperature independent Shot Noise

7. Johnson Noise Thermometry Limited by calibration of gain and bandwidth--very hard, limits bandwidth, and hence speed. P = GB(S I amp + 4kT/R) G BP R

8. Conduction in Tunnel Junctions Assume: Tunneling amplitudes and D.O.S. independent of Energy Difference gives current:

9. Thermal-Shot Noise of a Tunnel Junction* Sum gives noise: *D. Rogovin and D.J. Scalpino, Ann Phys. 86,1 (1974)

10. Thermal-Shot Noise of a Tunnel Junction

11. Self-Calibration Technique For  = 1 second For eV>>kT Hence can remove GB.

12. Thermometer Demonstration T is measured without reference to unknown system parameters

13. Silicon Substrate PMMA PMGI LOR 40 KeV Electrons.7  m 1  m E-Beam Lithography on Bilayer

14. Silicon Substrate PMMA PMGI LOR Independent Developers Create Undercut

15. SEM of Undercut

16. Silicon Substrate PMMA PMGI LOR Create Suspended Bridges!

17. Device With Bridge

24. Silicon Substrate PMMA PMGI LOR Aluminum Double Angle: 1st Evaporation

25. Silicon Substrate PMMA PMGI LOR Aluminum + Aluminum Oxide Aluminum + Aluminum Oxide Oxidize to Create Barrier

26. Silicon Substrate PMMA PMGI LOR Aluminum Double Angle:2nd Evaporation

27. Completed Junction Profile

28. The Finished Product(AFM)

29. The Measurement

30. Linear I-V

31. Good fit to theory:

32. Calibrate off of shotnoise P shot = GB(S amp +2eI)

33. Comparison of normalized data to functional form

34. Comparison of normalized data to functional form over wide range

35. Fit to extract temperature

36. Preliminary Results: Comparison to Oxford Thermometer

37. Improvements, future work Improve thermal contact to comparison thermometers Compare against better thermometers Investigate self-heating Investigate precision limits—is this the new Kelvin? 4 wire measurement Engineer for commercial distribution

38. Advantages and Disadvantages *R. J. Schoelkopf et al., Phys Rev. Lett. 80, 2437 (1998) Advantages Fast and self-calibrating Primary Wide T range No B-dependence Measures electron temperature Possibility to relate T to frequency!* Disadvantages Lead heating Frequency dependence* I(V) nonlinearities from: Density of states Barrier shape Weak localization, etc

39. Summary Fundamental voltage and temperature dependent noise of a tunnel junction (thermal-shot noise.) Makes fast, accurate thermometer which works over a wide temperature range Relates T to V using only e and k b implications for metrology