An Electronic Primary Thermometer Based on Thermal Shot Noise

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. Motivation: Unfilled Need in Milikelvin Thermometry Coulomb Staircase T>T* 300 mK 400 mK 500 mK 600 mK -0.5 0 0.5 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 temperaturethermometry • 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 T90 : triple point of water = 273.16 K(T90 ) Below .6K undefined! Plank radiation law He gas thermometer .6K 273.16K ? 3K 5K 25K 961.78K Platinum resistance thermometer 3He 4He vapor pressure

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

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

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

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 eV>>kT Hence can remove GB. For t= 1 second

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

13. 40 KeV Electrons E-Beam Lithography onBilayer PMMA .7 mm PMGI LOR 1 mm Silicon Substrate

14. Independent Developers Create Undercut PMMA PMGI LOR Silicon Substrate

15. SEM of Undercut

16. Create Suspended Bridges! PMMA PMGI LOR Silicon Substrate

17. Device With Bridge

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

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

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

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 Pshot = GB(Samp+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)

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 kb implications for metrology